Journal of Paleontology, 96(5), 2022, p. 1166–1188
Copyright © The Author(s), 2022. Published by Cambridge University Press on behalf of The
Paleontological Society. This is an Open Access article, distributed under the terms of the
Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which
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0022-3360/22/1937-2337
doi: 10.1017/jpa.2022.23
Morphology and paleobiology of the Late Cretaceous large-sized shark
Cretodus crassidens (Dixon, 1850) (Neoselachii; Lamniformes)
Jacopo Amalfitano,1* Fabio Marco Dalla Vecchia,2 Giorgio Carnevale,3 Eliana Fornaciari,1
Guido Roghi,4 and Luca Giusberti1
1
Dipartimento di Geoscienze, Università degli Studi di Padova, Padova I-35131, Veneto, Italy <jacopo.amalfitano@unipd.it>
<eliana.fornaciari@unipd.it> <luca.giuberti@unipd.it>
2
Institut Català de Paleontologia (ICP), Universitat Autònoma de Barcelona, Cerdanyola del Vallès E-08193, Catalunya, Spain
<fabio.dallavecchia@icp.cat>
3
Dipartimento di Scienze della Terra, Università degli Studi di Torino, Torino I-10125, Piemonte, Italy <giorgio.carnevale@unito.it>
4
Istituto di Geoscience e Georisorse, CNR, Padova I-35131, Veneto, Italy <guido.roghi@igg.cnr.it>
Abstract.—The definition of the Cretaceous shark genus Cretodus Sokolov, 1965 is primarily based on isolated teeth.
This genus includes five species. Among these, Cretodus houghtonorum Shimada and Everhart, 2019 is the only species
based on a partially preserved skeleton. Here, the taxonomic attribution of a virtually complete skeleton of Cretodus from
the Turonian of northeastern Italy is discussed, together with a few specimens from the Turonian of England. One of the
latter is investigated through micropaleontological analysis to determine its stratigraphic position. The material is referred
to Cretodus crassidens (Dixon, 1850), the diagnosis of which is emended herein. The dentition is tentatively reconstructed, exhibiting strong similarities with congeneric species, although it differs in having strong vertical folds on
the main cusp labial face, a mesiodistally broad tooth aspect, weak and well-spaced ‘costulae’ at crown base, and a different dental formula in the number of parasymphyseal and lateral rows. Some tooth malformations are interpreted as
feeding-related or senile characters. The Italian specimen suggests that Cretodus crassidens had a wide and laterally
expanded mouth and head, a stout body, and attained a gigantic size. Cretodus crassidens was a moderate-speed swimming shark ecologically like the extant tiger shark Galeocerdo cuvier (Péron and Lesueur in Lesueur, 1822). The age
estimate from vertebral-band counting suggests that the Italian individual was at least 23 years old and the growth
model indicates a longevity of 64 years and a maximum attainable total length of 9–11 m. Cretodus crassidens occurs
both in Boreal and Tethyan domains, implying a broad paleobiogeographic distribution and a preference toward offshore
settings.
Introduction
The extinct shark Cretodus Sokolov, 1965, like many other
extinct chondrichthyans, was defined based on isolated teeth
collected from Upper Cretaceous (Cenomanian–Turonian) marine deposits from all over the world (Cappetta, 2012). However,
this large lamniform is also represented by associated skeletal
remains recently reported from the middle-upper Turonian Scaglia Rossa of Veneto, northeastern Italy (Amalfitano et al.,
2017a) and from the middle Turonian Blue Hill Shale Member
of the Carlile Shale of Kansas, USA (Shimada and Everhart,
2019). The partial skeleton from Kansas was assigned to a
new species, Cretodus houghtonorum Shimada and Everhart,
2019, whereas the Italian specimen has been regarded since its
discovery as close to Cretodus crassidens (Dixon, 1850). Amalfitano et al. (2017a) prudently referred the Italian specimen to
Cretodus sp. in a study focused on a pellet-like accumulation
*Corresponding author.
of turtle bones alongside the vertebral column of the shark,
which was interpreted as its gastric content. Based on dental
characters, Shimada and Everhart (2019) considered the specimen discussed by Amalfitano et al. (2017a) to be conspecific
with, or closely allied to, Cretodus crassidens. The attribution
to Cretodus crassidens is confirmed herein based on a detailed
analysis of the Italian specimen and further supported by additional information and comparison with other material, including the holotype, from the English Chalk Group of southern
England, UK. A tentative reconstruction of the dentition of
this species is also provided here, together with a discussion
on several paleobiological traits of the species.
Geological setting
The geological setting of the ‘Lastame’ lithofacies of the Scaglia
Rossa of the Lessini Mountains (∼30 km N of Verona, Veneto,
Italy; Fig. 1), which yielded the Cretodus remains, has been
thoroughly described in a series of papers dealing with the
remarkable vertebrate assemblage of this Cretaceous Lagerstätte
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https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
Figure 1. (1) Simplified location map and lithostratigraphic context of the
‘Lastame’ localities. The quarries are located on Mt. Loffa (Lessini Mountains,
Verona Province). (2) Lithostratigraphic chart summarizing Cenomanian–Santonian formations of northeastern Italy. ‘Lastame’ spans from Turonian pro parte to
Coniacian pro parte. BL = Belluno; PD = Padova; RO = Rovigo; TV = Treviso;
VE = Venezia; VI = Vicenza; VR = Verona; * = location of the Benedetti quarry
yielding the Italian specimen of Cretodus crassidens; gray = mountain ranges or
hills; white = plains and valleys.
(Amalfitano et al., 2017a, b, 2019; Amadori et al., 2019, 2020a, b;
Palci et al., 2013). The 7 m thick nodular/subnodular interval of
whitish and pinkish-reddish limestones of the Scaglia Rossa
extensively quarried in Verona Province is characterized by
abundant echinoids, inoceramids, ammonoids, and rudists, but
also by vertebrate remains, e.g., lamniform sharks, sclerorhynchiforms, bony fishes, marine turtles, and mosasaurs. The
Lastame spans from Turonian p.p. to Coniacian p.p. (e.g.,
Cigala-Fulgosi et al., 1980; Trevisani and Cestari, 2007; Walliser and Schöne, 2020), but most of the vertebrate skeletons and
partial remains so far investigated comes from the middle-upper
Turonian interval (e.g., Amalfitano et al., 2017a, b, 2019;
Amadori et al., 2020a, b).
The Cretodus remains from southern England (UK) examined herein come from the Upper Cretaceous Chalk of Kent
(especially near the town of Lewes; Fig. 2.1) and surrounding
counties. The associated remains are referred to the classic ‘Middle Chalk Group’ of southern England (Hopson, 2005). This
unit is part of the Chalk Group, specifically the White Chalk
Subgroup, deposited in the northwestern part of the Anglo-Paris
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
1167
Figure. 2. (1) Simplified location map of the English Chalk. Cretaceous rocks
at outcrop (dark gray) and concealed (light gray) in England. (2) Lithostratigraphic chart summarizing the Cenomanian–Turonian formations of the Chalk
Group. BGS = British Geological Survey, Fm. = Formation. Modified after Hopson (2005) and Wilkinson (2011).
Basin and equivalent to the lowest part of the Lewes Nodular
Chalk Formation, the New Pit Chalk Formation, and the Holywell Nodular Chalk Formation (with the exclusion of the Plenus
Marls Member) in the Southern Province (Hopson, 2005; Wilkinson, 2011; Gale, 2019; Fig. 2.2). The ‘Middle Chalk’ spans
from the upper Cenomanian (only the Plenus Marl Member)
to the middle Turonian (Wilkinson, 2011) and yielded remains
of numerous fossil fish taxa, although the number of vertebrates
per volume of rock is very low (Mantell, 1822; Woodward,
1902, 1903, 1907, 1908, 1909, 1911, 1912; Kriwet, 2002; Friedman et al., 2016); the ichthyofauna therein includes a large variety of bony fishes (e.g., Dixon, 1850; Woodward, 1902, 1903,
1907, 1908, 1909, 1911, 1912; Kriwet, 2002) and several cartilaginous fishes (e.g., Cretoxyrhina and Ptychodus; Dixon, 1850;
Woodward, 1902, 1903, 1907, 1908, 1909, 1911, 1912; Longbottom and Patterson, 2002).
Materials and methods
The material studied herein consists of a partial articulated skeleton (101 teeth, two segments of 86 disconnected and coinstacked vertebral centra and fragments of cranial mineralized
cartilage) from the Scaglia Rossa exhibited at the Paleontological and Prehistorical Museum ‘Don Alberto Benedetti’
(Museo Paleontologico e Preistorico) of Sant’Anna d’Alfaedo,
Verona Province, Italy (MPPSA IGVR 91032) and some
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Journal of Paleontology 96(5):1166–1188
specimens from the Chalk Group of southern England (UK).
The English material includes a disturbed tooth set with a single
vertebral centrum housed at the Booth Museum of Natural History of Brighton, England, UK (BMB 007312), and a disarticulated tooth set (NHMUK PV OR 25786) and several isolated
teeth that belong to the collections of The Natural History
Museum of London (NHMUK PV OR 25823 [holotype of Cretodus crassidens], 41704, 49951, 44623, and NHMUK PV P
4577, 5402, 11144, 12368, 12860, 12870).
The specimens were photographed using a Nikon D810
camera with a 60–90 mm lens and a Canon PowerShot SX720
HS. Measurements were retrieved through the image analysis
software ImageJ (https://imagej.nih.gov/ij/, v. 1.6; Schneider
et al., 2012). Images and interpretative drawings of the specimens were produced using the free software packages GIMP
(GNU Image Manipulation Program, https://www.gimp.org/,
v. 2.10.6) and Inkscape (https://inkscape.org/, v. 0.92). The synonymy list follows the standards proposed by Matthews (1973)
and include selected synonyms directly referring to the material
described herein. The growth model was reconstructed using the
software package Past 3.26 (https://past.en.lo4d.com/windows;
Hammer et al., 2001) and plotted with the Desmos graphing
software (https://www.desmos.com/).
The reconstruction of the dentition of Cretodus crassidens
provided herein is based on the disarticulated dentition of the Italian specimen MPPSA IGVR 91032, therefore might be subject to
biases such as taphonomic or preparation loss and interpretation
bias. Specimen MPPSA IGVR 91032, in fact, was discovered
between 1996 and 1997 by quarry owners Giovanni and Gianfranco Benedetti and was prepared by Giovanni Benedetti in
2003 (Amalfitano et al., 2017a). According to the preparator,
the two slabs come from the same layer and were separated by
a karst fissure; thus, the skeletal remains in the two slabs should
belong to the same individual. Nevertheless, the two slabs differ
slightly in color and the different sizes between the last vertebral
centrum on the main slab and the first centrum on the second slab
suggest that several vertebrae are missing between the two segments (Amalfitano et al., 2017a). Furthermore, the vertebrae on
the second slab are all glued. Most of the teeth (∼70%) detached
from slab A when it was exposed by quarry works or remained
attached to the counterslab (now missing); they were glued onto
the slab later and mostly not in their exact original position
(some might be lost). However, the glued teeth undoubtedly
belong to this specimen because their morphological characters
are identical to the in-situ teeth (Amalfitano et al., 2017a). The
teeth are figured only on the labial side or the lingual side because
most of them are still embedded in the sedimentary matrix or were
glued after detaching and are exposed mainly on one side. Chemical or physical preparation to separate the teeth from the matrix
(e.g., Siversson et al., 2007), as well as sectioning the vertebral
centra (e.g., Newbrey et al., 2015; Shimada and Everhart,
2019), was not possible because the specimen is subject to Italian
cultural heritage care laws and cannot be altered without special
permission. Ammonium chlorite coating of the teeth (e.g., Siversson et al., 2007; Amadori et al., 2019) was also not performed
because of technical issues related to the position and size of
the specimen in the Museum exhibition. Teeth in the reconstruction are illustrated from the left side of the jaws and missing
elements were filled with mirrored images of teeth from the
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
right side. Tooth numbering of MPPSA IGVR 91032 in the
text, figures, and tables is consistent with that of Amalfitano
et al. (2017a, fig. 6). Some correction of the tooth measurements
of MPPSA IGVR 91032 and new tooth measurements of BMB
007312 are provided in Appendices 1 and 2.
Except for the uninformative calcified cartilage fragments,
the morphology of each anatomical element is described and figured in detail herein. Terminology and abbreviations follow
usual standards for shark teeth, placoid scales, and vertebral centra (e.g., Ridewood, 1921; Shimada, 1997a, b, c; Siversson, 1999;
Cappetta, 2012; Newbrey et al., 2015; Shimada and Everhart,
2019). Nevertheless, the symphyseal teeth sensu Shimada and
Everhart (2019) are referred herein as parasymphyseal teeth,
and the intermediate teeth from the same paper as third anterior
teeth following Siversson’s (1999) terminology. In the literature
of fossil lamniforms, teeth near the symphysis have been consistently addressed as symphyseal teeth (e.g., Siversson, 1999;
Shimada, 2002). However, Lamniformes all lack symphyseal
teeth (Smith et al., 2013), therefore the erroneous use in dental
nomenclature of symphyseal teeth in Lamniformes should be
replaced by the term parasymphyseal teeth, already used in
other papers (e.g., Cook et al., 2011; Siversson et al., 2013).
The intermediate position sensu Applegate (1967) refers to
teeth arising from the area (intermediate bar) between the hollows (bullae) where the other teeth accommodate in the odontaspidid dentition, but the majority of lamniforms do not exhibit
this condition, having two separate hollows in the upper jaw
without teeth on the intermediate bar and a single hollow in
the lower jaw (e.g., Siversson, 1999).
A least square linear regression method was applied to the
vertebral centrum length data to estimate the original vertebral
count of the shark and to provide a length estimate of MPPSA
IGVR 91032 (modelled in Past 3.26, Supplemental Data 1;
data from Amalfitano et al., 2017a, appendix B). Tooth size is
usually employed as a parameter to infer total length of a fossil
or extant shark, considering both crown or tooth height (e.g.,
Gottfried et al., 1996; Shimada, 2003, 2019) and tooth width.
Tooth width exhibits less variability than crown height (Bass
et al., 1975) and thus has been considered more reliable by several authors (e.g., Newbrey et al., 2015; Perez et al., 2021). In
this paper, we considered both methods, despite that the total
jaw width method is not directly applicable because of poor
preservation of most of the tooth roots in the sample considered
herein. Length estimates are provided using the equation by Shimada and Everhart (2019) that exploits the theoretical linear
relationship of crown height (CH) and total length (TL) for
Cretoxyrhina mantelli (see Shimada, 2008, fig. 5):
TL(cm) = 12.5 × CH(mm)
(1)
However, Shimada et al. (2020) provided a more conservative
estimate based on the linear function:
TL(cm) = 11.784 × CH(mm) - 0.331
(2)
with CH of any anterior tooth in any given non-Alopias macrophagous lamniform taxon, although this possibly underestimated the body total length.
Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
Using the definition of bite circumference sensu Lowry
et al. (2009) to bypass the lack of a reliable total jaw width
and applying the reverse of their formula:
log(bite ‘circumference’[mm])
= 1.007 × log(TL[ mm]) - 0.8
(3)
for the great white shark Carcharodon carcharias (Linnaeus,
1758), it is possible to have a TL estimate of Cretodus crassidens
also from the arch-like arrangement of teeth in specimen MPPSA
IGVR 91032 (geometrical approximation in Supplemental Data 2).
An attempt to assess the growth pattern of the fossil shark
using the von Bertalanffy growth function (VBGF; von Bertalanffy, 1938) is proposed below. The VBGF has been widely
used to describe the growth of fish (Haddon, 2001). This function was specifically used as a quantitative method to describe
the growth of extant elasmobranchs based on growth bands on
calcified structures such as vertebral centra (e.g., Cailliet and
Goldman, 2004; Goldman, 2004). The method has also been
applied to some extinct sharks (e.g., Shimada, 2008; Cook
et al., 2011; Newbrey et al., 2015; Shimada and Everhart,
2019; Jambura and Kriwet, 2020; Shimada et al., 2021). The
VBGF provides the best fit for species with slow growth and
extended longevity (maximum total length >100 cm of total
length and 0.02 < k < 0.25 yr–1, where k is the growth coefficient), such as large pelagic sharks (Liu et al., 2021). It must
be mentioned that conventional VBGF analyses uses independent measurements from a dataset with many random samples
from a population. The VBGF method applied here exploits original and derived measurements (Table 1) from a single but bestpreserved specimen, that would be considered dependent measurements. This exploratory method has been recently applied
in other papers (e.g., Shimada and Everhart, 2019; Shimada
Table 1. Raw measurements (BN, CR) and derived measurements (pCR, TL1,
TL2, and CH) based on a vertebral centrum of Cretodus crassidens (Dixon,
1850) (MPPSA IGVR 91032; Fig. 11). BN = band pair number; CH = crown
height; CR = center radius; pCR = percentage of center radius; TL = total length.
BN
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
CR (mm)
10.7
14.1
16.9
19.4
21.4
23.5
25.5
27.3
29.1
30.8
32.7
34.5
36.5
38.0
39.2
40.7
42.4
44.4
45.3
46.3
47.2
48.0
48.7
49.6
pCR (%)
21.5
28.5
34.0
39.1
43.2
47.3
51.4
55.0
58.6
62.1
65.8
69.5
73.6
76.5
78.9
82.0
85.5
89.4
91.2
93.2
95.1
96.7
98.2
100.0
TL1 (cm)
141.9
187.8
224.3
258.1
285.1
312.1
339.1
362.8
387.1
410.0
434.4
458.7
485.7
504.6
520.8
541.1
564.1
589.8
601.9
615.4
627.6
638.4
647.8
660.0
TL2 (cm)
167.7
221.9
265.1
305.0
336.9
368.9
400.8
428.7
457.5
484.6
513.4
542.1
574.0
596.4
615.5
639.5
666.6
697.0
711.3
727.3
741.7
754.5
765.6
780.0
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
CH (mm)
12.0
15.9
19.0
21.9
24.2
26.5
28.8
30.8
32.8
34.8
36.9
38.9
41.2
42.8
44.2
45.9
47.9
50.0
51.1
52.2
53.2
54.2
55.0
56.0
1169
et al., 2021) and has proven to be a viable approach to attempt
to explore the growth pattern of extinct elasmobranchs, although
with the obvious limits dependent from the restricted sample.
Parameters obtained from the VBGF and other derived measurements are applied with equations from Natanson et al. (2006) for
longevity to discuss and compare the results of the analyses.
Specimen BMB 007312 is still embedded in Chalk soft
matrix. The matrix was hence collected as powdered residual
fallen from the specimen after simple handling. The sample
was prepared as unprocessed material on a smear slide and
examined under a light microscope at 1250X magnification to
establish the stratigraphic position of the specimen. The calcareous nannofossil content of the samples was analyzed with
semiquantitative methods (three vertical traverses corresponding
to 6–7 mm2) following Gardin and Monechi (1998).
Repositories and institutional abbreviations.—Types, figured,
and other specimens examined in this study are deposited in
the following institutions: Booth Museum of Natural History
of Brighton, UK (BMB); Sternberg Museum of Natural
History, Fort Hays State University, Hays, Kansas, USA
(FHSM); Museo Paleontologico e Preistorico di Sant’Anna
d’Alfaedo, Verona, Italy (MPPSA IGVR); and The Natural
History Museum, London, UK (NHMUK).
Systematic paleontology
Class Chondrichthyes Huxley, 1880
Subclass Elasmobranchii Bonaparte, 1838
Cohort Euselachii Hay, 1902
Subcohort Neoselachii Compagno, 1977
Order Lamniformes Berg, 1958
Family Pseudoscapanorhynchidae Herman, 1979 (sensu
Siversson and Machalski, 2017)
Genus Cretodus Sokolov, 1965 (sensu Shimada and
Everhart, 2019)
Type species.—Otodus sulcatus Geinitz, 1843; ‘unterer Pläner
( plenus-marl), upper part of upper Cenomanian, Plauen,
Saxony, Germany.
Cretodus crassidens (Dixon, 1850)
Figures 3–10
Selected synonymy:
†1850
1889
1911
1987
2012
2017a
2019
Oxyrhina crassidens Dixon, p. 367, pl. 31, figs. 13, 13A.
Oxyrhina crassidens; Woodward, p. 382.
Oxyrhina crassidens; Woodward, p. 205, pl. 44, figs. 1, 2.
Cretodus crassidens; Cappetta, p. 98.
Cretodus crassidens, Cappetta, p. 255.
Cretodus sp.; Amalfitano et al., p. 109, figs. 2, 4, 6–9, 15.
Cretodus crassidens; Shimada and Everhart, p. 4, fig.
9A–P.
Holotype.—NHMUK PV OR 25823 (isolated tooth).
Diagnosis (emended).—A Cretodus species that differs from all
other species of the genus by teeth with mesiodistally broad
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Journal of Paleontology 96(5):1166–1188
Figure 3. Partial articulated skeleton of Cretodus crassidens (Dixon, 1850) from the middle Turonian of the Scaglia Rossa Veneta of northeastern Italy, MPPSA
IGVR 91032: (1) Orthophoto of the specimen. The slab embedding the tooth accumulation, the tessellated cartilage elements, the anterior portion of the vertebral
column, and the turtle remains is Slab A. The one embedding the caudalmost vertebral centra is Slab B. (2) Interpretative drawing of (1). (3) Interpretative drawing of
the tooth accumulation. Teeth in situ are indicated (yellow in electronic version), with tesselated cartilage elements (dark gray) and anteriormost vertebral centra (light
gray). Scale bars = 1 m (1, 2), 20 cm (3).
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
aspect (crown width to 82% of crown height even in a2), slightly
ogival to triangular main cusp, with vertical strong folds and
deep grooves on the labial face, weak and well-spaced basal
crown ‘costulae’ (or ‘striae’) on labial and lingual faces,
robust lateral cusplets (lateral cusplet height ∼25–55% of
crown height), sinusoid to parabolic crown base and sinusoid
to parabolic basal concavity. Aberrant lateral cusplets can be
present or replaced by weakly crenulated heels on the
shoulders of the main cusp or rounded papillae.
Occurrence.—The type locality is Houghton, Sussex (England,
UK); the stratigraphic horizon is the ‘Middle Chalk,’ Turonian.
All other English specimens come from localities of the ‘Middle
Chalk’: Lewes, Sussex, and Whyteleafe, in Surrey (England,
UK), although the exact geospatial coordinates are not known.
The Italian specimen comes from the ‘Lastame’ lithofacies of
Scaglia Rossa Veneta (middle-upper Turonian) of Mt. Loffa,
Sant’Anna d’Alfaedo (Lessini Mountains, Veneto, Italy),
specifically from Benedetti Quarry (45.6°N, 10.9°E).
The matrix obtained from BMB 007312 contains abundant
and well-preserved calcareous nannofossils. The assemblage is
well-diversified and contains 13 specimens of Lucianorhabdus
maleformis Reinhardt, 1966, four specimens of Quadrum gartneri Prins and Perch-Nielsen in Manivit et al., 1977 in ∼6 mm2,
that, together with the absence of Eiffellithus eximius s.s. Huber
et al., 2017 (only one uncertain specimen) and Lucianorhabdus
quadrifidus Forchheimer, 1972, are indicative of the Biozone
UC 7 of Burnett (1999). The corresponding interval would be
lower-middle Turonian. Correlation with the foraminiferal
zonation of the Chalk Group allows assignment of the sample
to the Helvetoglobotruncana helvetica Biozone and possibly
the lower part of the Marginotruncana sigali Biozone, corresponding to the British Geological Survey (BGS) Zones 9–10
(Wilkinson, 2011; Huber et al., 2017). Based on biostratigraphic
data, the sample is placed between the middle-upper part of the
Holywell Nodular Chalk Formation and basal part of the New
Pit Chalk Formation.
Description.—The English specimens include mainly isolated
teeth, previously reported by Woodward (1911) under various
names. There are also several associated specimens: the
disarticulated tooth set NHMUK PV 25786 (including seven
disarticulated teeth), the disturbed tooth set BMB 007312 and
the Italian specimen MPPSA IGVR 91032 (Figs. 3, 4, 8–11).
The English specimen BMB 007312 includes 18 teeth, nine
still embedded in matrix, associated with two vertebral
centra, one fragmentary and the other complete and
undeformed, characterized by maximum diameter 95 mm and
thickness ∼40 mm; this specimen was possibly reported as ‘a
small group of associated teeth from Lewes’ by Woodward
(1911, p. 206; Figs. 5, 6). The Italian specimen MPPSA IGVR
91032 is a virtually complete articulated skeleton that includes
120 teeth, 86 vertebral centra, as well as fragments of cranial
mineralized cartilage. This specimen also preserves placoid
scales retrieved from residues processed from matrix samples,
and includes a circular accumulation of bones of a marine turtle
alongside the shark vertebral column, interpreted as a gastric
pellet (Amalfitano et al., 2017a). Dental characters and other
morphological features are described in detail below.
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
1171
Materials.—NHMUK PV OR 25786 (disarticulated tooth set,
sensu Shimada, 2005), 41704, 49951, 44623; NHMUK PV P
4577, 5402, 11144, 12368, 12860, 12870; BMB 007312
(disturbed tooth set, sensu Shimada, 2005); MPPSA IGVR
91032.
Remarks.—The dental characters of the specimens described
above are fully consistent with the diagnosis of Cretodus
proposed by Shimada and Everhart (2019). In this paper, an
emended diagnosis is introduced specifying new details
observed on the materials analyzed.
The anatomy of Cretodus crassidens
Teeth.—Some of the most representative teeth are illustrated in
Figure 4; a reconstruction of the dentition is illustrated in
Figure 7. Here follows a description of general dental
characters and an interpretation of the tooth pattern within the
upper and lower series, considering that the specimen IGVR
91032 preserves a largely disarticulated dentition.
General characters.—Teeth mesiodistally broad (crown
width to 82% of crown height even in anterior teeth, specifically
a2), with main cusp and a pair of large lateral cusplets, the mesial
one divergent and the distal one slightly convergent with respect
to main cusp (can be divergent in some teeth). Main cusp is massive, slightly ogival to triangular, with strong vertical folds and
two to five deep grooves on labial face. Lateral teeth have triangular main cusp. Lateral cusplets are well separated from
main cusp but connected on labial side with basally extended
crown base on both root lobes. Numerous, regularly and wellspaced, well-marked, and very short vertical grooves and ridges
(‘costulae’ or ‘striae’) are present at crown base on both labial
and lingual sides, more marked on labial side. Cutting edges
are usually continuous and sharp, connecting main cusp and
cusplets. Mesial root lobe is usually slightly pointed, whereas
distal lobe is more expanded and rounded. Labial face of root
is flat or slightly recessed at crown base. Lingual face of root
is overall swollen and bulgy, with lingual protuberance (more
evident and protruding in parasymphyseals, anteriors, and
mesialmost laterals). Lateral teeth exhibit more splayed root
lobes than parasymphyseals and anteriors.
Upper dentition.—Upper teeth are labiolingually thick,
massive, and almost straight, with convex labial and lingual
faces and tip slightly turned outward in certain specimens. Cutting edges are straight and continuous. Crown base and basal
root concavity are deeply sinusoid (especially in anterior
teeth). Root-lobes angle is acute in parasymphyseals and anteriors, and is right in laterals. Root lobe apices are directed
basally. The upper dentition includes two parasymphyseal
rows, three anterior rows, and at least 10 lateral rows, but a
large gap is present after L8 (possibly two missing rows). Distinctive characters of tooth rows are:
(1) Upper parasymphyseal teeth (P): Main cusp is rather slender
(PCH-PCW ratio 1.4–1.5). P1 exhibits a mesially curved
main cusp. P2 almost straight and is the smallest among
these teeth. The height of the lateral cusplet represents
32% of crown height.
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Figure 4. Selection of representative teeth of Cretodus crassidens (Dixon, 1850) from the middle Turonian of the Scaglia Rossa Veneta of northeastern Italy,
MPPSA IGVR 91032: (1) first upper parasymphyseal tooth (no. 16), labial view; (2) first lower parasymphyseal tooth (no. 22), labial view; (3) first upper anterior
tooth (no. 37), labial view; (4) second lower anterior tooth (no. 3), labial view; (5) second lower anterior tooth (no. 11), lingual view; (6) second upper anterior tooth
(no. 13), labial view; (7) third upper anterior tooth (no. 53), labial view; (8) third lower anterior tooth (no. 24), labial view; (9) first lower lateral tooth (no. 62), labial
view; (10) third lower lateral tooth (no. 59), labial view; (11) sixth upper lateral tooth (no. 20), lingual view; (12) fourth upper lateral tooth (no. 61), labial view; (13)
seventh lower lateral tooth (no. 103), lingual view; (14) eighth lower lateral tooth (no. 94), labial view; (15) ninth lower later tooth (no. 92), lingual view; (16) commissural upper lateral tooth (no. 104), labial view. Numbers match those used by Amalfitano et al. (2017a, fig. 6). Scale bar = 20 mm.
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Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
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Figure 5. Associated remains of Cretodus crassidens (Dixon, 1850) from the lower Turonian of the Chalk Group of England, BMB 007312: (1, 2) blocks with
embedded teeth; (3, 4) complete vertebral centrum in frontal and dorsal views; (5) two fragments of a partial vertebral centrum in frontal view; (6) isolated teeth
from the same tooth set (second one from left in labial view, all others in lingual view). Scale bars = 50 mm.
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1174
Journal of Paleontology 96(5):1166–1188
(2) Upper anterior teeth (A): A1 is reduced (maximum
observed height 51 mm) and strongly oblique distally (21°
referring to the vertical axis). A2 and A3 have almost
upright and apparently symmetrical main cusps; A2 is
imperceptibly slanted mesially, and A3 distally. These
teeth are rather large (A2 is 61 mm total height, the largest
one of upper anteriors) and slender (TH-TW ratio 1.3–1.4).
The root lobes of A1 are less splayed with respect to those of
the adjacent teeth and U-shaped. The height of the lateral
cusplet is ∼28–33% of crown height.
(3) Upper lateral teeth (L): Main cusp slightly to strongly distally oblique. Their maximum height ranges from 48 to
16 mm. L1-L3 teeth have an almost upright main cusp,
from L4 onward the inclination becomes more evident.
L11?-L12? possibly represent the commissural teeth.
Teeth are generally larger than high except for the first
three, with L2 representing the highest tooth (like in many
other lamniforms; Shimada, 2002); lateral cusplet height
is 35–54% of crown height, with the ratio increasing toward
the commissural rows. Root lobes become generally more
divergent distally.
Lower dentition.—Lower teeth have a sigmoid profile
(labiolingual direction), nearly flat labial face, and convex lingual face; the tip has a reversed curvature, so that although
most of the crown is curved inward toward the mouth cavity,
the tip is turned outward (as also observed in other sharks; Frazzetta, 1988), which confers a more labiolingually compressed
and curved aspect with respect to the upper teeth. Main cusp
of lower teeth is generally mesiodistally broader than those of
upper teeth. Crown base and root concavity are shallow and
more parabolic than those of upper teeth. Cutting edges are sigmoid in profile. Crown base slightly overhangs the upper portion
of the root, creating a shallow recess and conferring a slightly
inflated aspect. Root-lobes angle is almost right in parasymphyseals and anteriors, obtuse in laterals. Root-lobes apices slightly
diverge. Lower dentition includes a single parasymphyseal row,
three anterior rows, and at least eight lateral rows, with a gap in
the posteriormost positions, including commissural teeth. Distinctive characters of tooth rows are:
(1) Lower parasymphyseal teeth (p): These two teeth have a
rather symmetric outline and slender main cusp (PCH-PCW
ratio 1.3). Lateral cusplets are strongly divergent. The lateral
cusplet height is ∼21–26% of crown height.
(2) Lower anterior teeth (a): These are the largest teeth in the
dentition (a1 is 67 mm high, whereas a2 is 69 mm high,
although incompletely mineralized; in this case it could
be higher; 56 mm high in crown height). Tooth a1 is more
symmetrical than a2, which is slightly slanted in distal direction. Main cusp of a2 bears four deep enameloid folds on
the labial face extending for almost its entire height. Tooth
a2 enlarged (crown width to 82% of crown height). Lateral
cusplets height is 25–31% of crown height (similar to upper
anterior ratio). Tooth a3 is rather large (60 mm TH in
functional row), with main cusp slightly bent distally and
divergent cusplets. Tooth as high as wide (TH-TW ratio
1.18–1.02). Lateral cusplet height is ∼29% of crown height.
(3) Lower lateral teeth (l): Main cusp is almost upright to
slightly oblique. The inclination of the cusp increases distally. Total height ranges 32–53 mm, but this range does
not include the distalmost rows (which comprises teeth
with crown height measuring 22 mm, l7, and 17 mm, l8).
Teeth l1–l4 are almost as large as high, with almost upright
cusps. Observing the size of l8 compared with those of the
corresponding upper laterals, it is possible to suggest that
there are at least four missing rows in the commissural
part of the lower dentition. Lateral cusplet height represents
Figure 6. Second lower anterior tooth of Cretodus crassidens (Dixon, 1850), BMB 007312: (1) labial view; (2) mesial view; (3) distal view; (4) lingual view. Arrow
indicates a dental malformation (crenulation on the cutting edge between the distal cusplet and the main cusp). Scale bar = 50 mm.
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Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
1175
Figure 7. Interpretation of the dentition pattern in Cretodus crassidens (Dixon, 1850), based on specimen MPPSA IGVR 91032. Numbers in gray match those used
by Amalfitano et al. (2017a, fig. 6). * = mirrored right teeth; dotted lines = reconstructed portions of the teeth based on other teeth in the sample; ? possibly missing
tooth rows; // = gaps in the reconstruction. Scale bar = 50 mm.
Figure 8. Vertebral centra of Cretodus crassidens (Dixon, 1850), MPPSA IGVR 91032: (1) interpretive drawing of slabs, with glued vertebral centra in dark gray;
(2) exposed articular surface of corpus calcareum; (3) exposed intermedialia showing pattern of calcification of the vertebral centrum, showing radial and concentric
lamellae patterns; (4) lateral side of vertebral centra exhibiting septae. Black and white scale bars in centimeters.
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incremental growth bands. These bands are not easily
discernable on the vertebral centra of BMB 007312, probably
due to erosion. In MPPSA IGVR 91032, a vertebral centrum
deprived of the articular surface of the corpus calcareum due
to biostratinomic processes (Fig. 8.3) presents concentric
lamellae in the intermedialia and radial lamellae that are
moderately thick (∼1 mm). The radial lamellae tend to branch
near the half of the radius length, enlarging and merging into
composite and thick longitudinal septae toward the centrum
periphery. The longitudinal septae, visible in lateral view in
both MPPSA IGVR 91032 and BMB 007312 (Figs. 5.4, 8.4),
are well-spaced with low density along the lateral surface of
the centrum, separated by large fossae (∼20 mm wide), except
for the dorsal and ventral sides of the centrum, which exhibit
a higher density of septae (three or four in an interval of
∼20 mm). Diagonal or transverse septae are absent. Articular
foramina are visible on some centra from MPPSA IGVR
91032 but are better visible on the complete vertebral centrum
of BMB 007312, being more oval and larger than adjacent
fossae (Figs. 5.4, 8.4).
Figure 9. Placoid scales of Cretodus crassidens (Dixon, 1850), MPPSA IGVR
91032: (1) tricuspid placoid scale, in frontal, lateral, and posterior views; (2) single cusp placoid scale, in frontal, lateral, and posterior views; (3) rounded cusp
placoid scale, in frontal, lateral, and posterior views. Scale bar = 500 μm.
∼25–53% of crown height, with the ratio increasing toward
the distalmost rows.
Vertebral column.—MPPSA IGVR 91032 comprises only 86
vertebral centra, 51 on slab A and 35 on slab
B. Measurements were provided by Amalfitano et al. (2017a,
appendix B). Centra on slab A are partially articulated and
represent the anterior part of the vertebral column (Figs. 3.1–
3.2, 8.1). Centra on slab B are artificially aligned and decrease
in size posteriorly (Figs. 3.1–3.2, 8.1). Vertebral centra are
round, with height equal to width (Fig. 8.2). The sizes of the
last centrum on slab A and the first centrum on slab B differ
by ∼20 mm, suggesting that a portion of the vertebral column
between the two segments is missing (Amalfitano et al.,
2017a). This is also indicated by the low vertebral count (86).
The diameter of the centra on slab A ranges from 115 mm
(vertebra 16) to 53 mm (vertebra 1); that on slab B ranges
from 79 mm (first centrum of the slab) to 28 mm (last three
centra) (Amalfitano et al., 2017a, appendix B). The mean
length of the vertebral centra is ∼32.5 ± 6.22 mm (Amalfitano
et al., 2017a, appendix B). The centra are well-calcified and
structurally match the definition of ‘lamnoid vertebrae’ (sensu
Applegate, 1967, p. 62; Fig. 8.2–8.4). Many centra of MPPSA
IGVR 91032 suffer slight taphonomic distortion and some are
incomplete, whereas a single one of BMB 007312 is nearly
intact. The articular surface of the corpus calcareum is devoid
of any kind of ornamentation and generally exhibits ∼20
prominent concentric rings that are interpreted to be annual
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Tessellated cartilage elements.—Seven main fragments of
tessellated calcified cartilage are present on slab A of MPPSA
IGVR 91032. Four occur close to each other at one extremity
of the tooth accumulation and three are glued within the turtle
remains. These tessellated cartilage elements probably split
away from the slab during removal of the counterslab and
have erroneously been glued to the turtle remains (Amalfitano
et al., 2017a). The fragments are flat and range 55–130 mm in
length and 40–85 mm in width. Their exposed surface shows
the striated texture corresponding to the underlying polygonal
prisms (tesserae; Dingerkus et al., 1991; Dean and Summers,
2006), which are well recognizable in the damaged areas.
One of the fragments close to the tooth accumulation still has
a lateral tooth associated (Fig. 3.3). The presence of a
tooth rooted into one of the fragments further indicates that
the fragment is part of the palatoquadrate or Meckel’s
cartilage, possibly a commissural portion considering the
tooth size.
Placoid scales.—Placoid scales (or dermal denticles) that
covered the body of Cretodus crassidens are common in the
reddish calcareous marly limestone embedding MPPSA IGVR
91032. They appear as whitish submillimetric prisms in the
reddish rock. They are usually composed of a base, with a
nutrient foramen at the bottom, and a crown (Fig. 9). The base
is often missing because it is delicate and is easily damaged
by the action of the acid used to dissolve the limestone to
isolate them (Amalfitano et al., 2017a). Placoid scale height
ranges 1–0.3 mm and width 0.6–0.3 mm. It was not possible
to determine how the placoid scales were originally
distributed. All scales are ornamented with strong parallel
basoapical ridges and plications on the convex anterior face of
their crown; ridges and plications do not extend posteriorly
and have different sizes (from broad to slender) and general
shapes (e.g., rhomboid, Fig. 9.1, 9.2; rounded or drop-like,
Fig. 9.3). Except for some tricuspid scales (Fig. 9.1), the cusp
is usually single, varying usually from pointed to rounded in
shape (Fig. 9.2, 9.3).
Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
1177
Figure 10. Variability in cusplet number and tooth malformations within the dentition of Cretodus crassidens (Dixon, 1850), MPPSA IGVR 91032: (1) tooth no.
10: the right shoulder of the central cusp has a crenulated cutting edge, whereas the other (arrows in detail view) bears a cusplet with two additional cuspules (a
tricuspid cusplet); (2) tooth no. 24: the cutting edge between the main cusp and the cusplet has an accessory papilla (arrow in detail view); (3) tooth no. 33: cutting
edge between the main cusp and the left cusplet has an accessory papilla (arrow in detail view); (4) tooth no. 35: smaller accessory cusplet occurs mesial to the mesial
cusplet (arrow in detail view); (5) tooth no. 7: smaller accessory cusplet occurs mesial to the mesial cusplet (arrow in detail view); (6) tooth no. 32: left cusplet (arrow
in detail view) is much smaller than the right cusplet; (7) tooth no. 10: right shoulder of the main cusp has an irregularly crenulated heel (the cusplet is absent; arrows in
detail view), whereas the left shoulder has a cusplet with two additional cuspules (tricuspid cusplet); (8) tooth no. 47: the main cusp is bent lingually and the right
cusplet is enlarged, bulky, and recurved lingually (arrow in main view; detail view is from the side); (9) tooth no. 58: right distal cusplet is enlarged and high; a distal
slice of the main cusp grew independently and has its own apex (arrow in detail view); (10, 11) tooth no. 66 in labial and lateral view: the main cusp is partially twisted;
its upper part is blunt and bears a diminutive and demarcated apex (arrow). Numbers matching those used by Amalfitano et al. (2017a, fig. 6). Scale bars = 10 mm.
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Discussion
Taxonomy.—Genus-level taxonomy was recently commented
upon by Siversson and Machalski (2017, p. 453, 454) and
Shimada and Everhart (2019). The types of the first two
described species of Cretodus—Cretodus semiplicatus
(Münster in Agassiz, 1843) from the Turonian of Germany
and Cretodus crassidens from the Turonian of the UK—are
each based on isolated and poorly preserved teeth (Shimada
and Everhart, 2019). The syntypes of Cretodus semiplicatus
are considered marginally diagnostic for their poor
preservation state and position (lateroposterior tooth, generally
conservative in morphology among lamniforms and thus less
taxonomically informative; Siversson and Machalski, 2017;
Shimada and Everhart, 2019). Furthermore, being almost
coeval, they could be conspecific with the type specimen of
Cretodus crassidens (see Siversson and Machalski, 2017).
Differences in morphology are addressed as dependent on
different tooth position (syntype of Cretodus semiplicatus
interpreted as a lower lateroposterior tooth, thus a more
posterior position) and ontogenetic stage (Siversson and
Machalski, 2017). The type specimen of Cretodus crassidens,
a large, robust tooth with crenulated heels and lateral cusplet
loss, might indicate a senile, female morphotype (Siversson
and Machalski, 2017).
Shimada and Everhart (2019) clearly distinguished five
species of the genus—Cretodus crassidens, Cretodus giganteus
(Case, 2001), Cretodus houghtonorum, Cretodus longiplicatus
Werner, 1989, and Cretodus semiplicatus—and proposed a
phylogenetic hypothesis recognizing three categories based on
similarities between the species (‘longiplicatus/semiplicatusgrade,’ ‘giganteus/houghtonorum-grade,’ and ‘crassidensgrade’). Based on the original illustration of the holotype of Cretodus sulcatus (Geinitz, 1843), it is possible that Cretodus longiplicatus is a junior synonym of Cretodus sulcatus (see
Siversson and Machalski, 2017). Cretodus crassidens is easily
distinguished from its congenerics by its mesiodistally broad
teeth with large main cusp, robust lateral cusplets, and long vertical folds (to two-thirds of CH) and grooves on the labial face,
especially in anteriormost rows. A rather large main cusp is also
present in Cretodus giganteus, but this species seems to be more
related to Cretodus houghtonorum for other characters and displays a thinner mesiodistal aspect (Shimada and Everhart,
2019). Basal crown ‘costulae’ (or ‘striae’; Shimada and Everhart, 2019) are stronger and wider spaced than those of the
‘giganteus/houghtonorum-grade’ (sensu Shimada and Everhart,
2019) but weaker and less dense than those of the ‘semiplicatus/
longiplicatus-grade’ (sensu Shimada and Everhart, 2019) and
less evident in large teeth, but the difference is well recognizable
in lateral teeth. Lateral cusplets of Cretodus crassidens also
Figure 11. Estimated total length range for Cretodus crassidens (Dixon, 1850), MPPSA IGVR 91032. Gray silhouette indicates the lower limit (660 cm); black
silhouette indicates the upper limit (780 cm). Silhouette modified after illustration by O.E. Demuth figured by Cooper et al. (2020, fig. 2D).
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Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
1179
Figure 12. Correlation diagram of mean scale crown width (x axis) and mean ridge distance (y axis). Taxa in the light gray cloud are from the group of fast pelagic
hunting sharks, whereas those in the dark gray cloud are from the group of large nearshore predators/moderate speed pelagic predators. Note that the Cretodus crassidens mean (star) falls within the cloud of correlation of large nearshore predators and moderate pelagic predators. Diagram modified after Reif (1985). Taxa not
otherwise mentioned in the text include: Carcharhinus amblyrhynchos (Bleeker, 1856), Carcharhinus falciformis (Müller and Henle, 1841), Carcharhinus galapagensis (Snodgrass and Heller, 1905), Carcharhinus melanopterus (Quoy and Gaimard, 1824), Carcharhinus plumbeus (Nardo, 1827), Isurus oxyrinchus Rafinesque,
1810, Lamna nasus (Bonnaterre, 1788), Prionace glauca (Linnaeus, 1758), and Sphyrna tudes (Valenciennes, 1822).
differ from those of Cretodus giganteus by having a more robust
aspect and divergent mesial and convergent distal cusplets,
whereas both the cusplets of Cretodus giganteus are divergent
(Shimada and Everhart, 2019).
The reconstruction of the dentition of Cretodus crassidens
differs from that of the congeneric Cretodus houghtonorum in
its mesiodistally broad morphology and strong vertical enameloid folds; the number of parasymphyseal teeth (‘symphyseal’ of
Shimada and Everhart, 2019), three in the upper dentition and
one in the lower one in Cretodus houghtonorum, two in both
dentitions in Cretodus crassidens; and the presence of a reduced
first upper anterior in Cretodus crassidens, although Shimada
and Everhart (2019) interpreted it as an upper ‘intermediate’
(third upper anterior) tooth. The lateral teeth have similarly
upright cusp, becoming more oblique distally, in both Cretodus
crassidens and Cretodus houghtonorum. The number of lateral
tooth rows is different: Cretodus crassidens has at least 10 upper
laterals and eight lower laterals, whereas Cretodus houghtonorum
has 11 upper laterals and eight lower laterals. Therefore, Cretodus
crassidens has the following dental formula:
2P 3A 10(+2?)L
2p 3a 8(+ 4?)l
It must be noted that ontogenetic variation could strongly
affect the taxonomy of Cretodus. Tooth size has been variously
addressed as dependent on ontogenetic stage and dietary shifts
during ontogeny, and care must be taken when using it as
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taxonomic character (Adnet, 2006; Purdy and Francis, 2007;
Belben et al., 2017; Marramà and Kriwet, 2017).
Comparing the dentition pattern presented herein with that
of other Cretaceous lamniform sharks, the lack of specialized
intermediate teeth combined with the presence of at least one
upper parasymphyseal file is commonly found in Cretaceous
taxa other than Cretodus (e.g., Archaeolamna Silversson,
1992, Cardabiodon Siversson, 1999, Cretalamna Glickman,
1958, Cretoxyrhina Glickman, 1958, Haimrichia Vullo, Guinot, and Barbe, 2016; Shimada, 1997c, 2007; Siverson, 1999;
Cook et al., 2011; Dickerson et al., 2013; Siversson et al.,
2013, 2015; Vullo et al., 2016). The presence of a reduced
first upper anterior has been reported in other Cretaceous and
modern lamniforms (e.g., Alopias Rafinesque, 1810, Carcharias Rafinesque, 1810, Cardabiodon, Haimrichia, Odontaspis
Agassiz, 1838; Applegate, 1965; Shimada, 2002; Siversson,
1999; Vullo et al., 2016).
Vertebral centra are considered poor in diagnostic characters in lamniforms, except for a few cases in which their morphology has been observed in detail (e.g., Newbrey et al., 2015).
Comparing vertebral centrum morphology in Cretodus with
that of other neoselachians (Newbrey et al., 2015), Cretodus is
characterized by distinctive radial lamellae branching and organizing in composite and thick septae toward the periphery of the
centrum, divided by large fossae. These structures are different
from those observed in other extant and extinct lamniform
sharks and could represent a genus- or family-level diagnostic
character. However, a family-level taxonomic discussion is
well beyond the scope of this paper and needs further evidence
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Figure 13. Growth band pairs count of Cretodus crassidens (Dixon, 1850),
MPPSA IGVR 91032. Vertebral centrum shows 23 incremental growth band
pairs presumably formed annually (arrow indicates the center of the centrum;
‘0’ indicates vertebral size at birth). Scale bar = 50 mm.
from additional complete or associated remains of closely
related genera.
Teratologic remarks.—A certain variability in the morphological
pattern of the cusplets that could be interpreted as malformations
(Gudger, 1937; Becker et al., 2000) can be observed in MPPSA
IGVR 91032 (Figs. 10, 11; Amalfitano et al., 2017a, fig. 6). In
tooth number 10, one of the shoulders of the central cusp bears
a cusplet with two further cuspules, i.e., a tricuspid cusplet
(Fig. 10.1). The other shoulder has a crenulated cutting edge
(Fig. 10.1). In three teeth (nos. 22, 24, and 33), a papilla is
present on the cutting edge between the central cusp and the
normally developed cusplet. In two cases (nos. 24 and 33;
Fig. 10.2, 10.3), this occurs in the mesial half of the crown. A
small supplementary cusplet is found in three teeth (nos. 2, 7,
and 35; Fig. 10.4, 10.5) mesial to the mesial cusplet. In another
tooth (no. 9), it is unclear whether the small supplementary
cusplet is mesial to the mesial cusplet or distal to the distal
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cusplet. In two cases (nos. 2 and 35), it is triangular in outline
and pointed, whereas in others it is papilla-like. In one tooth
(no. 32; Fig. 10.6), one cusplet (the distal one) is smaller than
the other.
Besides those with additional or smaller cusplets, the sample also contains malformed teeth (Fig. 10.7–10.11). Tooth
number 10 has a weakly and irregularly crenulated heel on the
shoulder of the main cusp instead of a well-formed cusplet
(Fig. 10.7). This kind of malformation also occurs in three
other teeth (nos. 52, 81, and 96). The main cusp of tooth number
47 (Fig. 10.8) is bent lingually and one cusplet is overgrown,
bulky, and also recurved lingually. Tooth number 58
(Fig. 10.9) has the central cusp divided into two parts by a
deep notch; the distal slice grew independently with its own
apex, like a shark tooth figured by Welton and Farish (1993,
fig. 17K). Furthermore, the distal cusplet is overgrown and
tall. Tooth number 66 (Fig. 10.10, 10.11) has a main cusp that
is partially twisted, and its apical part is blunt with a demarcated,
diminutive apex.
Malformed teeth also occur in other Cretodus crassidens
specimens from the Chalk Group of England discussed herein.
The most common malformation is the loss of lateral cusplet
and replacement by a weakly, irregularly crenulated heel on
the shoulder of the main cusp. This kind of malformed tooth
is present in specimens with associated tooth sets, e.g.,
NHMUK PV OR 25786 and BMB 007312, but also in isolated
teeth, namely the holotype NHMUK PV OR 25823, NHMUK
PV OR 49951, and NHMUK PV P 12870.
Malformed teeth have been object of several studies and
reports on both fossil and living sharks. Gudger (1937) provided
the probably first methodic report of malformed teeth in extant
sharks. Later, some authors focused on tooth pattern reversal
(Compagno, 1967; Reif, 1980), which also contributed to the
development of subsequent studies on pattern formation in
development of chondrichthyan dentitions from an evolutionary
perspective (Smith et al., 2013). Other studies focused on
feeding-related malformations in early growth stages (Becker
et al., 2000; Becker and Chamberlain, 2012). Tooth anomalies
in fossil and extant sharks consist mainly of curved or twisted
crowns, punctures or notches, deformed or missing cusps,
fusion of teeth of the same tooth family, excessive growth of
dentine, or abnormal root morphology (Becker et al., 2000;
Witzmann et al., 2021). Because damaged shark teeth cannot
heal, Johnson (1987) and Welton and Farish (1993) regarded
all shark tooth deformities as developmental in origin, i.e., the
result of mutation or damage at an early growth stage (Wiztmann
et al., 2021). Based on comparisons with extant sharks, Becker
et al. (2000) noted that many of the observed tooth anomalies in
extant and fossil sharks were likely from feeding-related injury to
the dental lamina of the jaws, particularly by impaction of chondrichthyan and teleost fin and tail spines. Furthermore, these
authors explicitly stated that at least some malformed teeth could
be caused by disease or mutation. However, the original cause of
any dental anomaly could be virtually impossible to determine
in a fossil shark (Shimada, 1997c; Wiztmann et al., 2021).
Teeth of the sample described above are affected by several
malformations that do not differ from malformations listed
above and reported in other sharks. Fifteen teeth out of 120
total (including those with atypical size or number of cusplets)
Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
exhibit malformations. Despite the incompleteness of the sample, the incidence of malformations in only one specimen is
rather high, if compared with other Cretaceous species numbers
with larger datasets (e.g., from ∼0.015% in Squalicorax kaupi
(Agassiz, 1843) to ∼0.36% in Paranomotodon sp.; Becker
et al., 2000). This difference is certainly due to a sampling
bias, but the high incidence could be due to the peculiar trophic
preferences of Cretodus crassidens, as evidenced by the association with marine turtle remains, or to the ontogenetic stage of
the individual. Thus, the dental malformations could be interpreted as feeding-related injuries to the dental lamina (e.g.,
Becker et al., 2000) or as senile characters (especially the lateral
cusplet loss and replacement with crenulated heel; Siversson and
Machalski, 2017).
Body size and body form: paleoecological remarks.—The
Italian specimen MPPSA IGVR 91032 allows some
suppositions on the overall morphology and size of Cretodus
crassidens. The two segments preserved measure ∼244 cm
and 182 cm (although the latter was completely reworked by
the preparator). The sum is ∼426 cm, but many vertebral
centra are missing and this could be an underestimation of the
TL of the individual. Applying the least square liner
regression method (Supplemental Data 1; r2 = 0.86115), it is
possible to estimate an original vertebral count of 169
vertebral centra, similar to the vertebral count of other extant
and extinct large lamniform sharks (Springer and Garrick,
1964; Shimada et al., 2006; Natanson et al., 2018). The mean
length of the vertebral centra is ∼ 32.5 ± 6.22 mm, therefore
the estimated articulated vertebral column is ∼549 cm long.
Considering the intervertebral disc length (+10%; Newbrey
et al., 2015), taphonomic compression (+20%; Newbrey et al.,
2015), and skull length (+50 cm; approximation based on the
Cretoxyrhina skull length, 60 cm, from Shimada, 1997c and
Newbrey et al., 2015, and presuming a shorter and more
laterally expanded skull in Cretodus), the estimated total
length of the Italian specimen is ∼764 cm. The body size
estimates reported by Amalfitano et al. (2017a) suggested a
TL ranging 661–776 cm based on the size of the vertebral
centra. The new estimate, based on the vertebral centrum
length and approximate vertebral count, falls within the
previous estimated range. This estimate can be compared also
to TL estimates based on tooth size. The largest CH measured
in the Italian specimen is ∼56 mm (Appendix 1) and if the
CH of 56 mm is applied to the equation used by Shimada
(2008), the calculation provides a TL of 700 cm. On the other
hand, the linear function from Shimada et al. (2020) provides
an estimated TL of ∼659.6 cm, which, if applied to the largest
teeth of the Cretodus crassidens dentition, is very close to the
previous value of 661 cm based on vertebral centra diameter.
Shimada and Everhart (2019) also suggested that Cretodus
had a stouter body than Cretoxyrhina, observing the
arrangement of the teeth in a 120 cm wide arch (assuming that
they are not dislodged) and the 156 cm long, 108 cm wide
elliptical accumulation of turtle bones interpreted as gastric
content. These indicate a rather stout body, with an abdominal
width of at least 108 cm, and a wide, gently curved, laterally
expanded mouth aperture, almost semielliptical, more like
Galeocerdo Müller and Henle, 1837 (Randall, 1992) or,
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
1181
compared to any other lamniform shark, Squalicorax Whitley,
1939 (Shimada and Cicimurri, 2005). Accordingly, the head
would also be laterally expanded. The shape of vertebral
centra, almost perfectly circular and rostrocaudally short, is
like many other Cretaceous lamniform sharks (e.g.,
Cretoxyrhina, Shimada, 1997c; Cardabiodon, Newbrey et al.,
2015; Squalicorax, Shimada and Cicimurri, 2005). Thus, it
could be inferred that this shark had a fusiform body with a
circular girth at the trunk region, with a great vertebral column
elasticity that allowed carangiform swimming behavior
(Newbrey et al., 2015). The length of the entire semielliptical
dental arch, calculated with a geometric approximation
(Supplemental Data 2), is ∼137 cm. Using, then, this new value
applied to the relation between ‘bite circumference’ and TL by
Lowry et al. (2009), the estimated TL of the individual is ∼813
cm. All of these estimates are more or less consistent, and it is
reasonable to define an estimated range of TL between ∼660
and ∼ 780 cm (Fig. 11), based on the vertebral centrum
diameter, which is apparently the least biased proxy.
Another parameter useful to infer body form and paleoecology of a shark is the morphology of the placoid scales (Reif,
1982, 1985; Reif and Dinkelacker, 1982), which are preserved
in MPPSA IGVR 91032. Amalfitano et al. (2017a) and Shimada
and Everhart (2019) discussed the morphology of the placoid
scales to infer the swimming behavior of Cretodus. Shimada
and Everhart (2019) observed, contra Amalfitano et al.
(2017a), that the strong ridges and plications ornamenting the
placoid scale crown do not extend posteriorly on the exterior
crown face, unlike those of typical fast-swimming lamniforms,
including fossil taxa interpreted as fast pelagic-hunting sharks,
e.g., Cretoxyrhina (Shimada, 1997b, c; Shimada et al., 2006;
Amalfitano et al., 2019) and Cardabiodon (Dickerson et al.,
2013; Newbrey et al., 2015). This morphological condition is
also present in scales of the holotype of Cretodus houghtonoum
(FHSM VP 17575; Shimada and Everhart, 2019). For this reason, the ridge spacing and the crown width from the original
sample of Amalfitano et al. (2017a) were measured (Appendix
3). The mean scale crown width is 562 ± 103.31 μm, whereas
the mean ridge spacing is 87.32 ± 30.65 μm. Plotting these
values with those of extant sharks and Cretoxyrhina mantelli
Agassiz, 1835 (data retrieved from Reif, 1985, Shimada,
1997a, and Amalfitano et al., 2019; Fig. 12), the Cretodus crassidens value falls close to the group of large nearshore predators
and moderate-speed pelagic predators (sensu Reif, 1985). This
confirms the assumption made by Shimada and Everhart
(2019) that considers Cretodus a more sluggish swimmer with
higher maneuverability (as also evidenced by vertebral centra
morphology) than thunniform fast-cruising swimmers, e.g.,
Cretoxyrhina. This assumption is corroborated by association
with the turtle remains, which suggests a trophic preference of
Cretodus crassidens toward these reptiles, similar to that of
the extant tiger shark, Galeocerdo cuvier (Péron and Lesueur
in Lesueur, 1922), which displays very similar placoid scale
ornamentation combined with the ecological niche of a large
nearshore predator (Reif, 1985). Shimada and Everhart (2019),
in their discussion of the ecology of the genus Cretodus,
reported that during excavation of the holotype of Cretodus
houghtonoum (FHSM VP 17575) that remains of two additional
species of sharks were identified from the same stratigraphic
1182
Journal of Paleontology 96(5):1166–1188
Figure 14. Suggested growth models of Cretodus crassidens (Dixon, 1850) based on MPPSA IGVR 91032 (see text; Table 1): (1) von Bertalanffy growth function
fitted to data points that show the relationship of number of vertebral growth band pairs with estimated total body length of 660 cm (TL1); (2) von Bertalanffy growth
function fitted to data points that show relationship of number of vertebral growth band pairs with estimated total body length of 780 cm (TL2). Gray silhouette indicates the lower limit (660 cm); black silhouette indicates the upper limit (780 cm). Silhouette modified after illustration by O.E. Demuth figured by Cooper et al.
(2020, fig. 2D).
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
Amalfitano et al.—Morphology and paleobiology of the shark Cretodus crassidens
Figure 15. Plot of percentage increment of the vertebral radius of Cretodus
crassidens (Dixon, 1850) (MPPSA IGVR 91032) and Cretodus houghtonorum
Shimada and Everhart, 2019 (FHSM VP 17575). Arrows indicate peaks interpreted as maturity onset for Cretodus crassidens (black) and Cretodus houghtonorum (gray).
horizon in immediate association with FHSM VP 17575,
namely two teeth of Squalicorax cf. S. falcatus (Agassiz,
1843) (FHSM VP 19273 and 19274) and two partial dorsal
fin spines of a hybodontid shark (FHSM VP 19272) comingled
with remains of Cretodus houghtonorum. This fossil association
is interpreted as another case of a ‘vertebrate three-level
trophic chain’ (Kriwet et al., 2008, p. 183), but involving
three species of sharks in this instance (Shimada and Everhart, 2019). The individual of Cretodus houghtonorum must
have died shortly after ingesting the hybodont because of the
absence of acid-etching alteration on the hybodont remains;
the Cretodus houghtonorum carcass was scavenged by S. cf.
S. falcatus before or during the decay, followed by
disarticulation and scattering of the skeletal and dental elements
of Cretodus houghtonorum due to the presence of weak water
currents on the seafloor (Shimada and Everhart, 2019).
Hybodont remains are more common in shallow-nearshore
environments, if not in fresh or brackish water environments
(e.g., Underwood and Rees, 2002; Underwood, 2004; Sweetman and Underwood, 2006), and the presumed predator-prey
relationship between Cretodus houghtonorum and the
hybodontid shark suggests that Cretodus houghtonorum dwelled,
at least sometimes, in shallow-nearshore environments. This
assumption is supported by the fact that although Cretodus
houghtonorum and Cretoxyrhina mantelli lived contemporaneously (Shimada, 2006), the distribution of the two taxa
indicates that they likely practiced resource partitioning within
the North American Western Interior Sea, because Cretodus
houghtonorum teeth are more commonly found in nearshore
deposits whereas those of Cretoxyrhina mantelli are common in
offshore deposits (Shimada and Everhart, 2019). The occurrence
of Cretodus crassidens in the pelagic deposits of the Scaglia
Rossa and Chalk Group, however, implies that this species preferentially dwelled in the offshore setting. It must be remarked,
however, that Cretodus crassidens is represented by a single specimen in the Scaglia Rossa to date, whereas Cretoxyrhina mantelli
and Ptychodus spp. remains are much more common (Amadori
et al., 2019, 2020a, b; Amalfitano et al., 2019).
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
1183
Age estimate and growth model.—One of the vertebral centra of
MPPSA IGVR 91032 exhibits a total of 23 pairs of growth
bands on the articular surface of the corpus calcareum
(Fig. 13, Table 1). Each pair of growth bands is traditionally
interpreted to have been deposited annually (Cailliet, 1990;
Cailliet and Goldman, 2004), with the total band pair number
(BN) indicating the age at death. Such growth band pairs do
not necessarily record age or time but rather are related simply
to growth or vertebral size (Harry, 2018; Natanson et al.,
2018; Natanson and Deacy, 2019). Hence, the relationship of
BN with time or age is loosely correlated (Natanson et al.,
2018) and generally tends to retrieve an underestimation or an
overestimation, because not all growth bands are necessarily
consistent with aging for the entire lifespan (Passerotti et al.,
2014; Harry, 2018, Natanson et al., 2018), especially in older
individuals or when later growth bands are not annual.
However, it is possible to hypothesize that the individual of
Cretodus crassidens MPPSA IGVR 91032 was at least
23 years old at the time of its death if the deposition of each
pair of growth bands is annual. The hypothetical von
Bertalanffy growth function (VBGF) is here reconstructed
based on the individual MPPSA IGVR 91032 and following
the same estimates made by Shimada and Everhart (2019),
with the aim to compare the ontogenetic growth of the two
species Cretodus crassidens and Cretodus houghtonorum
(Figs. 14, 15). The VBGF is applied to the size estimates
discussed above, namely ∼660 cm and ∼780 cm. The VBGF
fitted to the BN-TL (660 cm) (Fig. 14.1) data gives the
following growth parameter estimates: L∞ (maximum TL) =
955.22 cm; L0 (total length at birth) = 141.9 cm; k = 0.045 yr-1;
estimated longevity (after Natanson et al., 2006) = 64.429 yr.
The BN-TL (780 cm) data (Fig. 14.2), on the other hand,
retrieve the following parameters: L∞ = 1128.8 cm; L0 = 167.7 cm.
The longevity estimate of ∼64 yr is consistent with those for
extant large lamniform sharks (Camhi et al., 2008) and that of
Cretodus houghtonorum (∼55 years; Shimada and Everhart,
2019).
The percentage increment of the centrum radius of Cretodus crassidens and Cretodus houghtonorum was also considered to find any significant variation in growth rate and for
further comparison (Fig. 15). The percentage increment of the
two species is almost identical, except for two delayed peaks,
which could correspond to the maturity onset at 12–17 years
and 10–15 years, respectively. The maturity onset is consistent
with those of other large macropredatory lamniform sharks
(Camhi et al., 2008). The delayed growth peaks could alternatively be caused by sexual dimorphism, with females maturing
later than males (Camhi et al., 2008). However, despite the
strong similarities between the two species, there is no evidence
to support Cretodus crassidens and Cretodus houghtonorum
dentitions as gynandric heterodont variants, but rather they
were vicariant species dwelling in different environments (Cretodus crassidens in offshore settings, Cretodus houghtonorum
in nearshore settings) or geographically separated (Cretodus
crassidens in the European Tethys and Boreal seas, Cretodus
houghtonorum in the Western Interior Seaway; see also Guinot
and Cavin, 2016 for vicariances related to the Cenomanian
diversification event). After attaining maturity, the growth rate
1184
Journal of Paleontology 96(5):1166–1188
in the plot generally tends to become asymptotic, as evidenced
after the peaks at 17 and 15 yr, respectively.
The growth model provided herein allows calculation of the
possible TL of other specimens. The growth bands are not well
preserved on the two vertebral centra of BMB 007312. The specimen also includes the lower second anterior tooth, the CH of
which measures 47 mm (Appendix B). If the linear functions
CH-TL extrapolated from MPPSA IGVR 91032 is applied, i.e.,
TL1 (cm) = 11.78 × CH(mm) + 0.24
(4)
TL2 (cm) = 13.92 × CH(mm) + 0.29
(5)
the estimated TL of BMB 007312 results in a range between
∼554 cm and ∼654 cm (versus an estimated TL range of 546–
573 cm when applying the equations used by Amalfitano et al.
[2017a] based on vertebral centrum diameter). The age at
death was ∼16–17 years if the CH is considered, comparing
this specimen to MPPSA IGVR 91032 (Table 1).
Conclusions
The specimen MPPSA IGVR 91032 and others described herein
provide new morphological and paleobiological information
about the Late Cretaceous large-sized shark genus Cretodus.
The specimen is assigned to Cretodus crassidens and reconstruction of its dentition based on the Italian specimen reveals
the peculiarities of this species with respect to other species of
the genus. Cretodus crassidens likely represents a separate lineage within Cretodus (see the phylogenetic hypothesis by Shimada and Everhart, 2019). The body form and size estimates
are indicative of a large-sized macropredatory shark, reaching
a size over the limit that defines gigantic elasmobranch species
(> 6 m; Pimiento et al., 2019). The maximum estimated total
length (9–11 m) and length at birth are comparable to those of
the giant Cenozoic genus Otodus Agassiz, 1838 (Shimada
et al., 2021). Cretodus crassidens was probably characterized
by a moderate-speed swimming behavior, suggested by the
morphology of the vertebral centra and the placoid scales.
This shark was a large predator feeding on, among others,
large protostegid turtles, as evidenced by the gastric content preserved within the individual from the basinal high settings of the
‘Lastame.’ Estimated age at death (23 yr) and longevity (64 yr)
are consistent with those of extant large lamniform shark populations not subject to anthropic pressure. Interestingly, this study
notes that Cretodus crassidens fossils occur both in Boreal and
Tethyan domains at the same interval, implying a broad paleobiogeographic distribution. Moreover, Cretodus crassidens
exhibits a likely preference toward offshore settings, in contrast
with other species of the genus found in nearshore settings, indicating a possible vicariance scenario. Another conceivable
hypothesis could be age- (thus size-) related partitioning with
very large individuals less suited to hunt in nearshore environments; however, further evidence is required to fully resolve
that scenario.
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
Acknowledgments
R. Zorzin (Museo Civico di Storia Naturale di Verona),
E. Bernard (NHMUK), and L. Ismail and J. Cooper (BMB)
are deeply thanked for access to the specimens and to information about the collections under their care. Copyright of
the NHMUK photos is reserved by K. Webb and The Natural
History Museum (NHMUK). S. Castelli (Dipartimento di Geoscienze, Università degli Studi di Padova) is also acknowledged
for their valuable contribution with photos and postproduction
for the Italian material. Funding for this research was provided
by University of Padova (Progetto di Ateneo CPDA159701/
2015, titled ‘Reappraisal of two key Fossil-Lagerstätten in Scaglia deposits of northeastern Italy in the context of Late Cretaceous climatic variability: a multidisciplinary approach,’
assigned to E. Fornaciari and Dotazione Ordinaria Ricerca
(DOR) funds assigned to L. Giusberti). The reviewers
M. Siversson, C. Underwood, and D.J. Ward, and the Editor
H.-D. Sues are deeply thanked for helpful and valuable suggestions on an earlier draft of this paper.
Data availability statement
Data available from the Dryad Digital Repository: https://doi.
org/10.5061/dryad.31zcrjdnk.
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Woodward, A.S., 1909, The fossil fishes of the English Chalk, part 5:
Monographs of the Palaeontographical Society, London, v. 63, no. 308,
p. 153–184.
Woodward, A.S., 1911, The fossil fishes of the English Chalk, part 6: Monographs of the Palaeontographical Society, London, v. 64, p. 185–224.
Woodward, A.S., 1912, The fossil fishes of the English Chalk, part 7:
Monographs of the Palaeontographical Society, London, v. 65, no. 320,
p. 225–264.
Accepted: 13 March 2022
1188
Journal of Paleontology 96(5):1166–1188
Appendix 1. Corrections to tooth measurements of MPPSA IGVR 91032 (in
mm). The numbers of teeth are those reported by Amalfitano et al. (2017a, fig. 6).
CH = crown height; CT = crown thickness (labiolingual); CW = crown width;
DCL = distal cutting-edge length; LCH = cusplet height; MCL = mesial
cutting-edge length; PCH = central cusp height; PCW = central cusp width; TH
= tooth height; TT = tooth thickness (labiolingual); TW = tooth width.
Gray-shaded cells are those corrected.
Appendix 3. Placoid scale measurements of Cretodus crassidens (Dixon, 1850).
Sample
Scale
location
IGVR 91032
unknown
Tooth TH TW TT CH CW CT LCH PCH PCW MCL DCL
3
6
16
69
41
48
52
36
22
21
10
56
33
34
46
25
16
10
6
16
11
39
24
22
27
17
14
42
26
41
24
Appendix 2. Tooth measurements of BMB 007312 (in mm). The table includes
measurements of some of the best-preserved teeth. CH = crown height; CT =
crown thickness (labiolingual); CW = crown width; DCL = distal cutting-edge
length; LCH = cusplet height; MCL = mesial cutting-edge length; PCH = central
cusp height; PCW = central cusp width; TH = tooth height; TT = tooth thickness
(labiolingual); TW = tooth width; * = tooth isolated from the matrix.
Tooth TH TW TT CH CW CT LCH PCH PCW MCL DCL
a2
51 36 20 47
33 11
8
38
22
50
49
l2?*
- 12
29
19
a1
- 11
38
22
L1?
- 26 19+
6
4
18
14
25
L8?
19?
- 16 20?
4
13
10
16
https://doi.org/10.1017/jpa.2022.23 Published online by Cambridge University Press
mean (n = 7)
Ridge spacing (μm)
Scale width
(μm)
88-123-162
433
99-113-92
711
78-83-93-58-60-89
548
82-138-105-137-86-76
694
49-50-46-76-116-88-49-74-65-25
497
115-115-81-59
600
69-130
451
87.32 ± 30.65
562 ± 103.31