I am currently a Research Assistant Professor in the Huffington Department of Earth Sciences at Southern Methodist University in Dallas. In addition to my research in vertebrate paleontology, I use stable isotope geochemistry to address questions related to ancient terrestrial ecosystems.
My primary research interests are paleoclimatology and paleoecology. Using sedimentological and geochemical techniques, I reconstruct terrestrial paleoenvironments and provide detailed paleoclimatic information for comparison with faunal data. My current research involves (1) determination of the effect of paleoclimate on primary productivity and faunal richness in Mesozoic terrestrial ecosystems and (2) refinement of geochemical techniques to estimate soil CO2 concentrations in ancient environments. I emphasize the importance of connections between the biosphere, atmosphere, and geosphere in deep-time paleoenvironments, and use the sedimentary and faunal records to reconstruct the details of ecological interactions. Phone: 214-768-2901 Address: Department of Earth Sciences
Southern Methodist University
3225 Daniel Ave
Dallas, TX 75275-0395
Paleosols are an important component of the terrestrial stratigraphic record and are increasingly... more Paleosols are an important component of the terrestrial stratigraphic record and are increasingly utilized in stratigraphic analyses and paleoenvironmental and paleoclimate reconstructions. This chapter is designed to be accessible to students and researchers who are new to the study of paleosols. The topics discussed here are particularly relevant to sedimentologists, stratigraphers, and paleoclimatologists who wish to incorporate paleosol data into their research. We review methods for identifying, describing, and classifying paleosols. Modern soil features are described and related to their paleosol counterparts, and recommendations are made for streamlining field descriptions of paleosols without sacrificing valuable data used in paleoenvironmental and paleoclimate reconstructions. Finally, we discuss soil and paleosol classification systems, assess their applicability to paleosols, and evaluate their potential drawbacks.
A new stem cheloniid turtle, Cabindachelys landanensis, gen. et sp. nov., is represented by a nea... more A new stem cheloniid turtle, Cabindachelys landanensis, gen. et sp. nov., is represented by a nearly complete skull and partial hyoid collected in lower Paleocene shallow marine deposits, equivalent to the offshore Landana Formation, near the town of Landana in Cabinda, Angola. A partial chelonioid carapace previously reported from this locality is referred here to C. landanensis. Cabindachelys landanensis possesses clear synapomorphies of Pan-Cheloniidae, including a rod-like rostrum basisphenoidale, V-shaped basisphenoid crest, and secondary palate, but also retains a reduced foramen palatinum posterius, unlike most other pan-cheloniids. Phylogenetic analysis suggests that C. landanensis forms a weakly-supported clade with Erquelinnesia gosseleti, Euclastes acutirostris, Euclastes wielandi and Terlinguachelys fischbecki, although a close relationship between the protostegid T. fischbecki and these durophagous pan-cheloniids is unlikely. The Paleocene–Eocene strata near Landana have produced a number of turtle fossils, including the holotype specimen of the pleurodire Taphrosphys congolensis. A turtle humerus collected c. 1 m above the holotype skull of C. landanensis differs from humeri of chelonioids and Taphrosphys, indicating that a third turtle taxon is present at Landana. Cheloniid fossil material is rare in the Landana assemblage, in comparison with the abundant remains of Taphrosphys congolensis found throughout the stratigraphic section. This disparity implies that C. landanensis preferred open marine habitats, whereas Taphrosphys congolensis spent more time in nearshore environments. The appearance of new durophagous species such as C. landanensis in the early Paleocene reflects the rapid radiation of pan-cheloniids as they diversified into open niches following the K–Pg extinction.
Carbon isotope analysis of paleosol carbonates is one of the most widely used methods for produci... more Carbon isotope analysis of paleosol carbonates is one of the most widely used methods for producing quantitative estimates of CO2 levels in the ancient atmosphere, and is increasingly used to estimate soil pCO2 as a proxy for primary productivity. Recent efforts to improve the carbonate CO2 paleobarometer by refining input parameters (e.g., soil temperature, soil CO2 production function) have yielded more accurate estimates of ancient atmospheric pCO2. The carbonate CO2 paleobarometer is especially sensitive to input values for the carbon-isotope composition of soil organic matter (OM), which should ideally reflect the d13C value of OM present when pedogenic carbonates were forming. Published soil pCO2 estimates derived from pedogenic carbonate in Upper Jurassic paleosols are re-evaluated here using OM occluded within pedogenic carbonates rather than average values of fossilized plant material collected throughout the sampled stratigraphic sections. The new soil pCO2 estimates calculated using occluded OM range from 4,600 to 20,000 ppmV and are much lower than the previously published estimates, which were often in excess of 60,000 ppmV. In order to determine which OM source provides more accurate results, estimates of atmospheric pCO2 obtained using plant material and occluded OM from a carbonate-bearing modern soil are compared with measured, pre-industrial atmospheric CO2 levels. In the modern soil profile, plant OM d13C is highly variable and slightly more negative than the d13C of occluded OM. The observed ~1% offset between the average d13C values of plant material and occluded OM is much less than the overall range of ~6% in plant OM. Estimates of atmospheric pCO2 from the modern soil that are calculated using occluded OM differ by less than 100 ppmV, on average, from estimates based on plant OM. These results suggest that occluded OM produces reasonably accurate pCO2 estimates when used with the carbonate CO2 paleobarometer. Applying a -1% correction to the d13C of occluded OM also produces accurate pCO2 estimates, but the extreme variability in d13C of plant matter leads to inaccurate pCO2 estimates, even when samples are averaged.
Climate models indicate increased desertification in the continental interior of Pangea during th... more Climate models indicate increased desertification in the continental interior of Pangea during the Permian, which would have affected the composition of the flora and fauna. We present a multi-proxy paleoenvironmental reconstruction of a terrestrial ecosystem in central Pangea of Lopingian age. The reconstruction is based on biological and physical data from the Moradi Formation, located in the Tim Mersoi Basin, northern Niger. Paleosols and sedimentological evidence indicate that the prevailing climate was semi-arid to very arid with marked intervals of high water availability. Carbon stable isotope data from organic matter and paleosols suggest that both the soil productivity and actual evapotranspiration were very low, corresponding to arid conditions. Histological analysis of pareiasaur bones shows evidence of active metabolism and reveals distinct growth marks. These interruptions of bone formation are indicative of growth rhythms, and are considered as markers for contrasting seasonality or episodic climate events. The macrofossil floras have low diversity and represent gymnosperm-dominated woodlands. Most notable are ovuliferous dwarf shoots of voltzian conifers, and a 25-m long tree trunk with irregularly positioned branch scars. The combined biological and physical evidence suggests that the Moradi Formation was deposited under a generally arid climate with recurring periods of water abundance, allowing for a well-established ground water-dependent ecosystem. With respect to its environment, this system is comparable with modern ecosystems such as the southern African Namib Desert and the Lake Eyre Basin in Australia, which are discussed as modern analogues.
Approximately 1000 m of strata in the Upper Paleozoic Lukuga Formation in the Dekese core in the ... more Approximately 1000 m of strata in the Upper Paleozoic Lukuga Formation in the Dekese core in the central Congo Basin provide lithostratigraphic, mineralogical, and isotopic evidence for substantial climatic variation within a long-lived lacustrine basin. Lithostratigraphic indicators of cold climate include polymictic strata (dropstone deposits) and coupled laminations of fine clay-size material and coarse silt (glacial varves). Dropstones are concentrated in three stratigraphic zones in the lower ~ 425 m of the Lukuga Formation, and varved strata occur in two broad stratigraphic zones in the lower ~ 700 m of the formation. These sedimentological indicators suggest that the lower ~ 2/3 of the Lukuga Formation was strongly influenced by frigid conditions and glacial-like processes. The clay-size fraction of 97 samples is dominated by detrital minerals, including quartz, feldspar, chlorite, illite, and poorly ordered expansible 2:1 phyllosilicates. Based on variation in the mineralogy of these samples, the Lukuga Formation is divisible into three Clay Mineral Zones (CMZs), numbered in ascending stratigraphic order. CMZ 1 and CMZ 3 include several horizons of expansible 2:1 phyllosilicates that represent warmer/wetter intervals. Intervening CMZ 2 is a long (~ 500 m) zone of chlorite and illite with no expansible phyllosilicates and is interpreted as a continuous cold/frigid interval. There are numerous calcite-cemented layers, including spar-filled veins that cross depositional bedding and represent postburial alteration, radiaxial fibrous cements that displace detrital grains, and micrite that crystallized near the time of deposition. Eighty-two stable isotope analyses of micrite yield δ13C values that range from –44.6‰ to –4.1‰ and δ18O values that range from –20.0‰ to 5.0‰ (VPDB). The carbon isotope data likely reflect a range of local carbon sources derived from bacterial activity and are unrelated to paleoclimatic conditions. In contrast, stratigraphic patterns in the oxygen isotope data suggest five or six intervals of frigid conditions conducive to glacial processes.
A new pterosaur species, Cimoliopterus dunni, sp. nov., is described based on a partial rostrum f... more A new pterosaur species, Cimoliopterus dunni, sp. nov., is described based on a partial rostrum from the upper Cenomanian Britton Formation in the Eagle Ford Group of north-central Texas. The holotype preserves alveoli for a minimum of 26 upper teeth and bears a thin premaxillary crest that begins above the fourth pair of alveoli. The rostrum, characterized by a slight lateral flare, lacks the pronounced lateral expansion found in ornithocheirids and anhanguerids. The tip of the snout is small and blunt, and the anterior face of the rostrum is oriented posteroventrally, forming an approximately 45 angle with the anterior portion of the palate. The anteroventrally oriented first pair of alveoli is directed more ventrally than anteriorly. Phylogenetic analysis suggests that Cimoliopterus dunni and Cimoliopterus cuvieri, from the Cenomanian Grey Chalk Subgroup in Kent, England, are basal pteranodontoids that are closely related to Aetodactylus halli from the middle Cenomanian Tarrant Formation of north Texas. Cimoliopterus dunni marks only the second known occurrence of Cimoliopterus, extending its geographic range from Europe to North America. In conjunction with Coloborhynchus wadleighi from the upper Albian Pawpaw Formation, Cimoliopterus dunni provides unambiguous evidence of biogeographic linkages between the pterosaur faunas of North America and Europe in the middle Cretaceous.
Paleosols are ancient soils that have been incorporated into the geological record. Soils form in... more Paleosols are ancient soils that have been incorporated into the geological record. Soils form in response to interactions among the lithosphere, hydrosphere, biosphere, and atmosphere, so paleosols potentially record physical, biological, and chemical information about past conditions near Earth’s surface. As a result, paleosols are an important resource for terrestrial environmental and climatic reconstructions. Long-standing paleosol research topics include morphology, classification, and clay mineralogy, all of which provide information about pedogenic processes and local paleoenvironments. Paleosols are also used to infer processes involved in the development of
stratigraphic architecture and basin evolution. Recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight intomajor regional to global changes in temperature, precipitation, and atmospheric pCO2. These
new proxies focus on morphological and chemical transfer functions and stable isotope geochemistry to provide estimates of precipitation, temperature, pCO2, and productivity, as well as chronometric estimates of mineral crystallization in deep-time pedogenic systems. Looking forward, consensus must be reached on terminology that most effectively communicates paleosol characteristics and implies important processes. Proxy development will continue to improve as data sets become available across greater ranges of environments and timescales.
The Bench 19 Bonebed at Bentiaba, Angola, is a unique concentration of marine vertebrates preserv... more The Bench 19 Bonebed at Bentiaba, Angola, is a unique concentration of marine vertebrates preserving six species of mosasaurs in sediments best correlated by magnetostratigraphy to chron C32n.1n between 71.4 and 71.64 Ma. The bonebed formed at a paleolatitude near 24°S, with an Atlantic width at that latitude approximating 2700 km, roughly half that of the current width. The locality lies on an uncharacteristically narrow continental shelf near transform faults that controlled the coastal outline of Africa in the formation of the South Atlantic Ocean. Biostratigraphic change through the Bentiaba section indicates that the accumulation occurred in an ecological time dimension within the 240 ky bin delimited by chron 32n.1n. The fauna occurs in a 10 m sand unit in the Mocuio Formation with bones and partial skeletons concentrated in, but not limited to, the basal 1–2 m. The sediment entombing the fossils is an immature feldspathic sand shown by detrital zircon ages to be derived from nearby granitic shield rocks. Specimens do not appear to have a strong preferred orientation and they are not concentrated in a strand line. Stable oxygen isotope analysis of associated bivalve shells indicates a water temperature of 18.5°C. The bonebed is clearly mixed with scattered dinosaur and pterosaur elements in a marine assemblage. Gut contents, scavenging marks and associated shed shark teeth in the Bench 19 Fauna indicate biological association and attrition due to feeding activities. The ecological diversity of mosasaur species is shown by tooth and body-size disparity and by d13C analysis of tooth enamel, which indicate a variety of foraging areas and dietary niches. The Bench 19 Fauna was formed in arid latitudes along a coastal desert similar to that of modern Namibia on a narrow, tectonically controlled continental shelf, in shallow waters below wave base. The area was used as a foraging ground for diverse species, including molluscivorus Globidens phosphaticus, small species expected near the coast, abundant Prognathodon kianda, which fed on other mosasaurs at Bench 19, and species that may have been transient and opportunistic feeders in the area.
Elemental analyses of paleosol B horizons in the Upper Jurassic Morrison Formation of the western... more Elemental analyses of paleosol B horizons in the Upper Jurassic Morrison Formation of the western United States provide estimates of mean annual precipitation (MAP) and allow determination of humidity regimes. Samples were collected from the lower Morrison Formation in New Mexico and the upper Morrison Formation in Wyoming and Montana. The chemical index of alteration minus potassium (CIA – K) and the calcium and magnesium weathering index (CALMAG) were used to estimate paleorainfall. CIA – K
values calculated for paleosols without shrink-swell (vertic) features correspond to MAP estimates between 800 and 1100 mm yr–1, with an average of 1000 mm yr–1. CALMAG values, calculated for vertic paleosols, correspond to MAP estimates between 50 and 1200 mm yr–1, with an average of 700 mm yr–1. MAP estimates from the older New Mexico strata indicate that early Morrison environments were relatively arid. MAP estimates from the younger Wyoming and Montana deposits reflect wetter conditions in the
northernmost part of the Morrison Formation, but the transition from arid interior environments was abrupt. Humidity provinces inferred from geochemical proxy-based estimates of evapotranspiration and energy influx from precipitation range from semiarid to superhumid, suggesting wetter conditions than the MAP estimates, but supporting the relative differences in moisture among the
three study areas. Paleoprecipitation patterns within the Morrison depositional basin do not match the modern latitudinal distribution of rainfall that arises from zonal atmospheric circulation. Comparison with the Upper Jurassic
Lourinhã Formation in Portugal and the Vega Formation in Spain reveals that MAP in Late Jurassic Portuguese environments was similar to that in the wet northern
part of the Morrison Formation, although more arid conditions prevailed in some areas of Portugal. Inferred humidity regimes for the Lourinhã Formation, which range from semiarid to superhumid, also indicate small scale
geographic variability in climate, although less pronounced than that observed in the Morrison Formation. Paleoenvironments in northern Spain were similar to the drier Morrison environments in the continental interior.
Given the abrupt climatic transitions inferred here for the Morrison Formation, paleoprecipitation estimates derived from a geographically restricted sample may reflect only local conditions and should not necessarily be extrapolated to larger areas.
The state of Texas has one of the greatest records of pterosaurs in the world, surpassing all oth... more The state of Texas has one of the greatest records of pterosaurs in the world, surpassing all other US states and most countries in the number of occurrences. Uniquely, this record extends over the entire 150þ million history of the Pterosauria. A review of this pterosaur record confirms at least 30 pterosaurs known from 13 occurrences, including five valid species. The holotypes of two of these species have been described before and are diagnosed and erected here as the new species Radiodactylus langstoni, gen. et sp. nov., named in honour of Dr. Wann Langston Jr, the father of Texas pterosaurology, and Alamodactylus byrdi, gen. et sp. nov.. Phylogenetic analysis of all Texas pterosaurs that can be coded for more than one character confirms that these species are distinct from others and occupy phylogenetic positions close to their original classifications. Radiodactylus langstoni is recovered as a non-azhdarchid azhdarchoid, Quetzalcoatlus northropi as an azhdarchid, Alamodactylus byrdi as a non-pteranodontoid pteranodontian, Aetodactylus as a pteranodontoid, and Coloborhynchus wadleighi as an ornithocheirid. The presence of eudimorphodontid, dsungaripterid, as well as other azhdarchid and pteranodontoid pterosaurs, is also confirmed in Texas.
Basin. Together with the underlying Comanche Series and overlying younger Gulf Series, this set o... more Basin. Together with the underlying Comanche Series and overlying younger Gulf Series, this set of strata provides a record of the last 50 million years of the Cretaceous. Although both marine and terrestrial vertebrates are known in this interval, the Late Cretaceous record is primarily marine. On this fi eld trip, sites are visited that have yielded sharks, bony fi sh, turtles, dinosaurs, crocodiles, pterosaurs, mammals, long-and short-necked plesiosaurs, and a classic record of mosasaur evolution. *
Fourteen soil profiles from California were collected in order to measure the d13C of coexisting ... more Fourteen soil profiles from California were collected in order to measure the d13C of coexisting soil calcite and organic matter. Thirteen of the profiles contained a measurable amount of calcite ranging from 0.04 to 54.6 wt %. Soil calcite d13CPDB (d13C value vs. the calcite standard Peedee Belemnite) values range from 14.4 to 1.3‰, whereas organic matter d13CPDB values range from 24.0 to 27.7‰. The hydrology of these profiles is divided into two broad groups: (1) soils characterized by gravity-driven, piston-type vertical flow through the profile and (2) soils affected by groundwater within the profile at depths where calcite is present. The difference between soil calcite and organic matter d13CPDB
values, D13Ccc-om, is smaller in profiles affected by groundwater saturation as well as most Vertisols and may be a product of waterlogging. The larger D13Ccc-om values in soils with gravity-driven flow are consistent with open-system mixing of tropospheric CO2 and CO2 derived from in situ oxidation of soil organic matter with mean soil PCO2 values potentially in excess of ~20,000 ppmV at the time of calcite crystallization. There is a correlation between estimates of soil PCO2 and a value termed ‘‘EPPT-U’’ (kJm2/yr) among the soil profiles characterized by gravity-driven flow. EPPT-U is the energy flux through the soil during periods of soil moisture utilization, and it is the product of water mass and temperature in the profile during the growing season. Thus, soils with high water-holding capacity/storage and/or low/high growing season temperature may form soil calcite in the presence of high soil PCO2, and vice versa. The results of this research have important implications for reconstructions of paleoclimate from stable carbon isotopes of
calcareous paleosol profiles.
In this paper we present a method for estimating soil pCO2 in ancient environments using the meas... more In this paper we present a method for estimating soil pCO2 in ancient environments using the measured carbon-isotope values of pedogenic carbonates and plant-derived organic matter. The validity of soil pCO2 estimates proves to be highly dependent on the organic δ13C values used in the calculations. Organic matter should be sourced from the same paleosol profiles as sampled carbonates to yield the most reliable estimates of soil pCO2. In order to demonstrate the potential use of soil pCO2 estimates in paleoecological and paleoenvironmental studies, we compare samples from three Upper Jurassic localities. Soil pCO2 estimates, interpreted as a qualitative indicator of primary paleoproductivity, are used to rank the Late Jurassic terrestrial environments represented by the Morrison Formation in western North America, the informally named Lourinhã formation in Western Europe, and the Stanleyville Group in Central Africa. Because modern terrestrial environments show a positive correlation between primary productivity and faunal richness, a similar relationship is expected in ancient ecosystems. When the relative paleoproductivity levels inferred for each study area are compared with estimates of dinosaur generic richness, a positive correlation emerges. Both the Morrison and Lourinhã formations have high inferred productivity levels and high estimated faunal richness. In contrast, the Stanleyville Group appears to have had low primary productivity and low faunal richness. Paleoclimatic data available for each study area indicate that both productivity and faunal richness are positively linked to water availability, as observed in modern terrestrial ecosystems.
Investigation of the palaeoclimatic conditions associated with Upper Jurassic strata in Portugal ... more Investigation of the palaeoclimatic conditions associated with Upper Jurassic strata in Portugal and comparison with published palaeoclimate reconstructions of the Upper Jurassic Morrison Formation in western North America provide important insights into the conditions that allowed two of the richest terrestrial faunas of this period to flourish. Geochemical analyses and observations of palaeosol morphology in the informally named Upper Jurassic Lourinhã formation of western Portugal indicate warm and wet palaeoclimatic conditions with strongly seasonal precipitation patterns. Palaeosol profiles are dominated by carbonate accumulations and abundant shrink-swell (vertic) features that are both indicative of seasonal variation in moisture availability. The δ18OSMOW and δDSMOW values of phyllosilicates sampled from palaeosol profiles range from +22.4‰ to +22.7‰ and -53.0‰ to -37.3‰, respectively. These isotope values correspond to temperatures of formation between 32°C and 39°C ± 3°, with an average of 36°C, which suggest surface temperatures between 27°C and 34°C (average 31°C). On average, these surface temperature estimates are 1°C higher than the highest summer temperatures modelled for Late Jurassic Iberia using general circulation models. Elemental analysis of matrix material from palaeosol B-horizons provides proxy (chemical index of alteration minus potassium) estimates of mean annual precipitation ranging from 766 to 1394 mm/year, with an average of approximately 1100 mm/year. Palaeoclimatic conditions during deposition of the Lourinhã formation are broadly similar to those inferred for the Morrison Formation, except somewhat wetter. Seasonal variation in moisture availability does not seem to have negatively impacted the ability of these environments to support rich and relatively abundant faunas. The similar climate between these two Late Jurassic terrestrial ecosystems is probably one of the factors which explains the similarity of their vertebrate faunas.
Upper Permian and Lower Triassic palaeosols from northeastern Tethyan localities exposed within t... more Upper Permian and Lower Triassic palaeosols from northeastern Tethyan localities exposed within the Bogda Mountains, NW China, provide a wealth of information regarding long-term palaeoclimatic and palaeoenvironmental variations. Wuchiapingian palaeosols are characterized by intense redoximorphy, accumulation of vascular plant matter, accumulation of clay minerals and Fe-oxides, slickensides, and clastic dikes, suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget. Changsinghian to early Induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter, indicative of sub-humid to sub-arid soil moisture and variable soil moisture regimes. Induan to Olenekian palaeosols contain pedogenic CaCO3 accumulations and gypsum pseudomorphs, indicating a drier environment characterized by net soil moisture deficiency. Elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus Potassium (CIA-K) proxy. Estimates from various Wuchiapingian strata indicate relatively stable palaeoprecipitation. During the late Changsinghian and early Induan, palaeoprecipitation appears to have decreased from 1100 to 230 (±180)mm/year over less than 100 m of vertical stratigraphic section. In the Induan and Olenekian, palaeoprecipitation appears much less stable than in Wuchiapingian, with values vacillating from 290 to 1014 mm/year. The transition to a relatively unstable precipitation state coincides generally with the Permian–Triassic boundary, and may reflect climatic disturbances associated with the end-Permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics, moisture availability, and expansion of the subtropical high pressure belt.
Paleopedology and geochemical analysis of Upper Jurassic deposits in the Stanleyville Group of Ce... more Paleopedology and geochemical analysis of Upper Jurassic deposits in the Stanleyville Group of Central Africa indicate harsh Late Jurassic paleoclimates in the interior of Gondwana. Subsurface samples collected from the Samba borehole near the center of the Congo Basin show only weak morphological evidence of pedogenesis, but are characterized by an abundance of shrink-swell (vertic) features and rare calcium carbonate nodules, indicating seasonal variations in moisture availability and net soil moisture deficiency, respectively. X-ray diffraction analysis of paleosol matrix material reveals the presence of analcime and the clay mineral palygorskite, strong indicators of hot, arid climatic conditions. The δ18O and δD values of clay minerals from paleosol profiles range from +22.3‰ to +25.4‰ and −44.4‰ to −39.6‰ SMOW, respectively, and correspond to crystallization temperatures between 25°C and 40°C. These crystallization temperatures compare favorably with austral summer surface temperature estimates for Central Africa that result from Late Jurassic global circulation models. Calculations of soil CO2 production using the δ13C values of pedogenic carbonates and plant-derived organic matter produce lower CO2 production estimates for the Stanleyville Group relative to the roughly contemporary Morrison Formation of the western U.S. These low soil CO2 production estimates provide further support for arid Late Jurassic climate conditions in the Congo Basin. The paleoclimatic conditions inferred here from the Stanleyville Group are similar to those reconstructed from other Upper Jurassic African continental localities between 5°S and 20°S paleolatitude. However, penecontemporaneous terrestrial coastal sites within this latitudinal belt of Gondwana retain evidence of generally wetter conditions, suggesting that those regions may have received more rainfall than the continental interior. The paleoclimatic setting reconstructed here from geologic indicators and geochemical proxies suggests that general circulation models accurately predict unique paleoenvironmental conditions that lack modern analogs.
Remains of a pteranodontid pterosaur are recorded in the basal Austin Group of North Texas. The s... more Remains of a pteranodontid pterosaur are recorded in the basal Austin Group of North Texas. The specimen described here comprises a partial left wing and strongly resembles Pteranodon although diagnostic features of that genus are lacking. With an estimated early Coniacian age, this specimen represents the earliest occurrence of the Pteranodontidae in North America and the second earliest occurrence worldwide, predated only by Ornithostoma from the Cambridge Greensand of England. Pterosaur material recovered from the Eagle Ford and Austin groups of Texas records an early Late Cretaceous change in the composition of North American pterosaur communities between the late Cenomanian and the early Coniacian. This faunal transition appears to be primarily a decrease in morphological disparity rather than a significant reduction in taxonomic diversity. However, the lack of Early Cretaceous Lagerstatten in North America may produce underestimates of true pterosaur richness during this interval, thereby obscuring a subsequent drop in diversity.
Both body fossil and ichnofossil evidence for gregarious behavior in sauropod dinosaurs is examin... more Both body fossil and ichnofossil evidence for gregarious behavior in sauropod dinosaurs is examined. Some localities suggest that herds were partitioned on the basis of age, whereas other sites reveal groups consisting of both adult and juvenile/subadult individuals. Two skeletal accumulations showing evidence of age segregation are examined in detail. The Mother's Day Quarry in the Upper Jurassic Morrison Formation of Montana contains the remains of several immature diplodocoid sauropods. An assemblage in the Upper Cretaceous Javelina Formation of Big Bend National Park in Texas consists entirely of juvenile Alamosaurus. Both the Mother's Day and Big Bend assemblages are interpreted here as remnants of age-segregated herds. The differences between skeletal accumulations composed entirely of immature animals and mixed-age ichnological assemblages imply that herd composition was variable. When age segregation is recognized, in both fossil and modern taxa, it is thought to minimize the fitness costs related to behavioral synchronization within social groups. Age segregation of herds also contraindicates extended parental care as typical of at least some sauropod taxa.
Paleosols are an important component of the terrestrial stratigraphic record and are increasingly... more Paleosols are an important component of the terrestrial stratigraphic record and are increasingly utilized in stratigraphic analyses and paleoenvironmental and paleoclimate reconstructions. This chapter is designed to be accessible to students and researchers who are new to the study of paleosols. The topics discussed here are particularly relevant to sedimentologists, stratigraphers, and paleoclimatologists who wish to incorporate paleosol data into their research. We review methods for identifying, describing, and classifying paleosols. Modern soil features are described and related to their paleosol counterparts, and recommendations are made for streamlining field descriptions of paleosols without sacrificing valuable data used in paleoenvironmental and paleoclimate reconstructions. Finally, we discuss soil and paleosol classification systems, assess their applicability to paleosols, and evaluate their potential drawbacks.
A new stem cheloniid turtle, Cabindachelys landanensis, gen. et sp. nov., is represented by a nea... more A new stem cheloniid turtle, Cabindachelys landanensis, gen. et sp. nov., is represented by a nearly complete skull and partial hyoid collected in lower Paleocene shallow marine deposits, equivalent to the offshore Landana Formation, near the town of Landana in Cabinda, Angola. A partial chelonioid carapace previously reported from this locality is referred here to C. landanensis. Cabindachelys landanensis possesses clear synapomorphies of Pan-Cheloniidae, including a rod-like rostrum basisphenoidale, V-shaped basisphenoid crest, and secondary palate, but also retains a reduced foramen palatinum posterius, unlike most other pan-cheloniids. Phylogenetic analysis suggests that C. landanensis forms a weakly-supported clade with Erquelinnesia gosseleti, Euclastes acutirostris, Euclastes wielandi and Terlinguachelys fischbecki, although a close relationship between the protostegid T. fischbecki and these durophagous pan-cheloniids is unlikely. The Paleocene–Eocene strata near Landana have produced a number of turtle fossils, including the holotype specimen of the pleurodire Taphrosphys congolensis. A turtle humerus collected c. 1 m above the holotype skull of C. landanensis differs from humeri of chelonioids and Taphrosphys, indicating that a third turtle taxon is present at Landana. Cheloniid fossil material is rare in the Landana assemblage, in comparison with the abundant remains of Taphrosphys congolensis found throughout the stratigraphic section. This disparity implies that C. landanensis preferred open marine habitats, whereas Taphrosphys congolensis spent more time in nearshore environments. The appearance of new durophagous species such as C. landanensis in the early Paleocene reflects the rapid radiation of pan-cheloniids as they diversified into open niches following the K–Pg extinction.
Carbon isotope analysis of paleosol carbonates is one of the most widely used methods for produci... more Carbon isotope analysis of paleosol carbonates is one of the most widely used methods for producing quantitative estimates of CO2 levels in the ancient atmosphere, and is increasingly used to estimate soil pCO2 as a proxy for primary productivity. Recent efforts to improve the carbonate CO2 paleobarometer by refining input parameters (e.g., soil temperature, soil CO2 production function) have yielded more accurate estimates of ancient atmospheric pCO2. The carbonate CO2 paleobarometer is especially sensitive to input values for the carbon-isotope composition of soil organic matter (OM), which should ideally reflect the d13C value of OM present when pedogenic carbonates were forming. Published soil pCO2 estimates derived from pedogenic carbonate in Upper Jurassic paleosols are re-evaluated here using OM occluded within pedogenic carbonates rather than average values of fossilized plant material collected throughout the sampled stratigraphic sections. The new soil pCO2 estimates calculated using occluded OM range from 4,600 to 20,000 ppmV and are much lower than the previously published estimates, which were often in excess of 60,000 ppmV. In order to determine which OM source provides more accurate results, estimates of atmospheric pCO2 obtained using plant material and occluded OM from a carbonate-bearing modern soil are compared with measured, pre-industrial atmospheric CO2 levels. In the modern soil profile, plant OM d13C is highly variable and slightly more negative than the d13C of occluded OM. The observed ~1% offset between the average d13C values of plant material and occluded OM is much less than the overall range of ~6% in plant OM. Estimates of atmospheric pCO2 from the modern soil that are calculated using occluded OM differ by less than 100 ppmV, on average, from estimates based on plant OM. These results suggest that occluded OM produces reasonably accurate pCO2 estimates when used with the carbonate CO2 paleobarometer. Applying a -1% correction to the d13C of occluded OM also produces accurate pCO2 estimates, but the extreme variability in d13C of plant matter leads to inaccurate pCO2 estimates, even when samples are averaged.
Climate models indicate increased desertification in the continental interior of Pangea during th... more Climate models indicate increased desertification in the continental interior of Pangea during the Permian, which would have affected the composition of the flora and fauna. We present a multi-proxy paleoenvironmental reconstruction of a terrestrial ecosystem in central Pangea of Lopingian age. The reconstruction is based on biological and physical data from the Moradi Formation, located in the Tim Mersoi Basin, northern Niger. Paleosols and sedimentological evidence indicate that the prevailing climate was semi-arid to very arid with marked intervals of high water availability. Carbon stable isotope data from organic matter and paleosols suggest that both the soil productivity and actual evapotranspiration were very low, corresponding to arid conditions. Histological analysis of pareiasaur bones shows evidence of active metabolism and reveals distinct growth marks. These interruptions of bone formation are indicative of growth rhythms, and are considered as markers for contrasting seasonality or episodic climate events. The macrofossil floras have low diversity and represent gymnosperm-dominated woodlands. Most notable are ovuliferous dwarf shoots of voltzian conifers, and a 25-m long tree trunk with irregularly positioned branch scars. The combined biological and physical evidence suggests that the Moradi Formation was deposited under a generally arid climate with recurring periods of water abundance, allowing for a well-established ground water-dependent ecosystem. With respect to its environment, this system is comparable with modern ecosystems such as the southern African Namib Desert and the Lake Eyre Basin in Australia, which are discussed as modern analogues.
Approximately 1000 m of strata in the Upper Paleozoic Lukuga Formation in the Dekese core in the ... more Approximately 1000 m of strata in the Upper Paleozoic Lukuga Formation in the Dekese core in the central Congo Basin provide lithostratigraphic, mineralogical, and isotopic evidence for substantial climatic variation within a long-lived lacustrine basin. Lithostratigraphic indicators of cold climate include polymictic strata (dropstone deposits) and coupled laminations of fine clay-size material and coarse silt (glacial varves). Dropstones are concentrated in three stratigraphic zones in the lower ~ 425 m of the Lukuga Formation, and varved strata occur in two broad stratigraphic zones in the lower ~ 700 m of the formation. These sedimentological indicators suggest that the lower ~ 2/3 of the Lukuga Formation was strongly influenced by frigid conditions and glacial-like processes. The clay-size fraction of 97 samples is dominated by detrital minerals, including quartz, feldspar, chlorite, illite, and poorly ordered expansible 2:1 phyllosilicates. Based on variation in the mineralogy of these samples, the Lukuga Formation is divisible into three Clay Mineral Zones (CMZs), numbered in ascending stratigraphic order. CMZ 1 and CMZ 3 include several horizons of expansible 2:1 phyllosilicates that represent warmer/wetter intervals. Intervening CMZ 2 is a long (~ 500 m) zone of chlorite and illite with no expansible phyllosilicates and is interpreted as a continuous cold/frigid interval. There are numerous calcite-cemented layers, including spar-filled veins that cross depositional bedding and represent postburial alteration, radiaxial fibrous cements that displace detrital grains, and micrite that crystallized near the time of deposition. Eighty-two stable isotope analyses of micrite yield δ13C values that range from –44.6‰ to –4.1‰ and δ18O values that range from –20.0‰ to 5.0‰ (VPDB). The carbon isotope data likely reflect a range of local carbon sources derived from bacterial activity and are unrelated to paleoclimatic conditions. In contrast, stratigraphic patterns in the oxygen isotope data suggest five or six intervals of frigid conditions conducive to glacial processes.
A new pterosaur species, Cimoliopterus dunni, sp. nov., is described based on a partial rostrum f... more A new pterosaur species, Cimoliopterus dunni, sp. nov., is described based on a partial rostrum from the upper Cenomanian Britton Formation in the Eagle Ford Group of north-central Texas. The holotype preserves alveoli for a minimum of 26 upper teeth and bears a thin premaxillary crest that begins above the fourth pair of alveoli. The rostrum, characterized by a slight lateral flare, lacks the pronounced lateral expansion found in ornithocheirids and anhanguerids. The tip of the snout is small and blunt, and the anterior face of the rostrum is oriented posteroventrally, forming an approximately 45 angle with the anterior portion of the palate. The anteroventrally oriented first pair of alveoli is directed more ventrally than anteriorly. Phylogenetic analysis suggests that Cimoliopterus dunni and Cimoliopterus cuvieri, from the Cenomanian Grey Chalk Subgroup in Kent, England, are basal pteranodontoids that are closely related to Aetodactylus halli from the middle Cenomanian Tarrant Formation of north Texas. Cimoliopterus dunni marks only the second known occurrence of Cimoliopterus, extending its geographic range from Europe to North America. In conjunction with Coloborhynchus wadleighi from the upper Albian Pawpaw Formation, Cimoliopterus dunni provides unambiguous evidence of biogeographic linkages between the pterosaur faunas of North America and Europe in the middle Cretaceous.
Paleosols are ancient soils that have been incorporated into the geological record. Soils form in... more Paleosols are ancient soils that have been incorporated into the geological record. Soils form in response to interactions among the lithosphere, hydrosphere, biosphere, and atmosphere, so paleosols potentially record physical, biological, and chemical information about past conditions near Earth’s surface. As a result, paleosols are an important resource for terrestrial environmental and climatic reconstructions. Long-standing paleosol research topics include morphology, classification, and clay mineralogy, all of which provide information about pedogenic processes and local paleoenvironments. Paleosols are also used to infer processes involved in the development of
stratigraphic architecture and basin evolution. Recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight intomajor regional to global changes in temperature, precipitation, and atmospheric pCO2. These
new proxies focus on morphological and chemical transfer functions and stable isotope geochemistry to provide estimates of precipitation, temperature, pCO2, and productivity, as well as chronometric estimates of mineral crystallization in deep-time pedogenic systems. Looking forward, consensus must be reached on terminology that most effectively communicates paleosol characteristics and implies important processes. Proxy development will continue to improve as data sets become available across greater ranges of environments and timescales.
The Bench 19 Bonebed at Bentiaba, Angola, is a unique concentration of marine vertebrates preserv... more The Bench 19 Bonebed at Bentiaba, Angola, is a unique concentration of marine vertebrates preserving six species of mosasaurs in sediments best correlated by magnetostratigraphy to chron C32n.1n between 71.4 and 71.64 Ma. The bonebed formed at a paleolatitude near 24°S, with an Atlantic width at that latitude approximating 2700 km, roughly half that of the current width. The locality lies on an uncharacteristically narrow continental shelf near transform faults that controlled the coastal outline of Africa in the formation of the South Atlantic Ocean. Biostratigraphic change through the Bentiaba section indicates that the accumulation occurred in an ecological time dimension within the 240 ky bin delimited by chron 32n.1n. The fauna occurs in a 10 m sand unit in the Mocuio Formation with bones and partial skeletons concentrated in, but not limited to, the basal 1–2 m. The sediment entombing the fossils is an immature feldspathic sand shown by detrital zircon ages to be derived from nearby granitic shield rocks. Specimens do not appear to have a strong preferred orientation and they are not concentrated in a strand line. Stable oxygen isotope analysis of associated bivalve shells indicates a water temperature of 18.5°C. The bonebed is clearly mixed with scattered dinosaur and pterosaur elements in a marine assemblage. Gut contents, scavenging marks and associated shed shark teeth in the Bench 19 Fauna indicate biological association and attrition due to feeding activities. The ecological diversity of mosasaur species is shown by tooth and body-size disparity and by d13C analysis of tooth enamel, which indicate a variety of foraging areas and dietary niches. The Bench 19 Fauna was formed in arid latitudes along a coastal desert similar to that of modern Namibia on a narrow, tectonically controlled continental shelf, in shallow waters below wave base. The area was used as a foraging ground for diverse species, including molluscivorus Globidens phosphaticus, small species expected near the coast, abundant Prognathodon kianda, which fed on other mosasaurs at Bench 19, and species that may have been transient and opportunistic feeders in the area.
Elemental analyses of paleosol B horizons in the Upper Jurassic Morrison Formation of the western... more Elemental analyses of paleosol B horizons in the Upper Jurassic Morrison Formation of the western United States provide estimates of mean annual precipitation (MAP) and allow determination of humidity regimes. Samples were collected from the lower Morrison Formation in New Mexico and the upper Morrison Formation in Wyoming and Montana. The chemical index of alteration minus potassium (CIA – K) and the calcium and magnesium weathering index (CALMAG) were used to estimate paleorainfall. CIA – K
values calculated for paleosols without shrink-swell (vertic) features correspond to MAP estimates between 800 and 1100 mm yr–1, with an average of 1000 mm yr–1. CALMAG values, calculated for vertic paleosols, correspond to MAP estimates between 50 and 1200 mm yr–1, with an average of 700 mm yr–1. MAP estimates from the older New Mexico strata indicate that early Morrison environments were relatively arid. MAP estimates from the younger Wyoming and Montana deposits reflect wetter conditions in the
northernmost part of the Morrison Formation, but the transition from arid interior environments was abrupt. Humidity provinces inferred from geochemical proxy-based estimates of evapotranspiration and energy influx from precipitation range from semiarid to superhumid, suggesting wetter conditions than the MAP estimates, but supporting the relative differences in moisture among the
three study areas. Paleoprecipitation patterns within the Morrison depositional basin do not match the modern latitudinal distribution of rainfall that arises from zonal atmospheric circulation. Comparison with the Upper Jurassic
Lourinhã Formation in Portugal and the Vega Formation in Spain reveals that MAP in Late Jurassic Portuguese environments was similar to that in the wet northern
part of the Morrison Formation, although more arid conditions prevailed in some areas of Portugal. Inferred humidity regimes for the Lourinhã Formation, which range from semiarid to superhumid, also indicate small scale
geographic variability in climate, although less pronounced than that observed in the Morrison Formation. Paleoenvironments in northern Spain were similar to the drier Morrison environments in the continental interior.
Given the abrupt climatic transitions inferred here for the Morrison Formation, paleoprecipitation estimates derived from a geographically restricted sample may reflect only local conditions and should not necessarily be extrapolated to larger areas.
The state of Texas has one of the greatest records of pterosaurs in the world, surpassing all oth... more The state of Texas has one of the greatest records of pterosaurs in the world, surpassing all other US states and most countries in the number of occurrences. Uniquely, this record extends over the entire 150þ million history of the Pterosauria. A review of this pterosaur record confirms at least 30 pterosaurs known from 13 occurrences, including five valid species. The holotypes of two of these species have been described before and are diagnosed and erected here as the new species Radiodactylus langstoni, gen. et sp. nov., named in honour of Dr. Wann Langston Jr, the father of Texas pterosaurology, and Alamodactylus byrdi, gen. et sp. nov.. Phylogenetic analysis of all Texas pterosaurs that can be coded for more than one character confirms that these species are distinct from others and occupy phylogenetic positions close to their original classifications. Radiodactylus langstoni is recovered as a non-azhdarchid azhdarchoid, Quetzalcoatlus northropi as an azhdarchid, Alamodactylus byrdi as a non-pteranodontoid pteranodontian, Aetodactylus as a pteranodontoid, and Coloborhynchus wadleighi as an ornithocheirid. The presence of eudimorphodontid, dsungaripterid, as well as other azhdarchid and pteranodontoid pterosaurs, is also confirmed in Texas.
Basin. Together with the underlying Comanche Series and overlying younger Gulf Series, this set o... more Basin. Together with the underlying Comanche Series and overlying younger Gulf Series, this set of strata provides a record of the last 50 million years of the Cretaceous. Although both marine and terrestrial vertebrates are known in this interval, the Late Cretaceous record is primarily marine. On this fi eld trip, sites are visited that have yielded sharks, bony fi sh, turtles, dinosaurs, crocodiles, pterosaurs, mammals, long-and short-necked plesiosaurs, and a classic record of mosasaur evolution. *
Fourteen soil profiles from California were collected in order to measure the d13C of coexisting ... more Fourteen soil profiles from California were collected in order to measure the d13C of coexisting soil calcite and organic matter. Thirteen of the profiles contained a measurable amount of calcite ranging from 0.04 to 54.6 wt %. Soil calcite d13CPDB (d13C value vs. the calcite standard Peedee Belemnite) values range from 14.4 to 1.3‰, whereas organic matter d13CPDB values range from 24.0 to 27.7‰. The hydrology of these profiles is divided into two broad groups: (1) soils characterized by gravity-driven, piston-type vertical flow through the profile and (2) soils affected by groundwater within the profile at depths where calcite is present. The difference between soil calcite and organic matter d13CPDB
values, D13Ccc-om, is smaller in profiles affected by groundwater saturation as well as most Vertisols and may be a product of waterlogging. The larger D13Ccc-om values in soils with gravity-driven flow are consistent with open-system mixing of tropospheric CO2 and CO2 derived from in situ oxidation of soil organic matter with mean soil PCO2 values potentially in excess of ~20,000 ppmV at the time of calcite crystallization. There is a correlation between estimates of soil PCO2 and a value termed ‘‘EPPT-U’’ (kJm2/yr) among the soil profiles characterized by gravity-driven flow. EPPT-U is the energy flux through the soil during periods of soil moisture utilization, and it is the product of water mass and temperature in the profile during the growing season. Thus, soils with high water-holding capacity/storage and/or low/high growing season temperature may form soil calcite in the presence of high soil PCO2, and vice versa. The results of this research have important implications for reconstructions of paleoclimate from stable carbon isotopes of
calcareous paleosol profiles.
In this paper we present a method for estimating soil pCO2 in ancient environments using the meas... more In this paper we present a method for estimating soil pCO2 in ancient environments using the measured carbon-isotope values of pedogenic carbonates and plant-derived organic matter. The validity of soil pCO2 estimates proves to be highly dependent on the organic δ13C values used in the calculations. Organic matter should be sourced from the same paleosol profiles as sampled carbonates to yield the most reliable estimates of soil pCO2. In order to demonstrate the potential use of soil pCO2 estimates in paleoecological and paleoenvironmental studies, we compare samples from three Upper Jurassic localities. Soil pCO2 estimates, interpreted as a qualitative indicator of primary paleoproductivity, are used to rank the Late Jurassic terrestrial environments represented by the Morrison Formation in western North America, the informally named Lourinhã formation in Western Europe, and the Stanleyville Group in Central Africa. Because modern terrestrial environments show a positive correlation between primary productivity and faunal richness, a similar relationship is expected in ancient ecosystems. When the relative paleoproductivity levels inferred for each study area are compared with estimates of dinosaur generic richness, a positive correlation emerges. Both the Morrison and Lourinhã formations have high inferred productivity levels and high estimated faunal richness. In contrast, the Stanleyville Group appears to have had low primary productivity and low faunal richness. Paleoclimatic data available for each study area indicate that both productivity and faunal richness are positively linked to water availability, as observed in modern terrestrial ecosystems.
Investigation of the palaeoclimatic conditions associated with Upper Jurassic strata in Portugal ... more Investigation of the palaeoclimatic conditions associated with Upper Jurassic strata in Portugal and comparison with published palaeoclimate reconstructions of the Upper Jurassic Morrison Formation in western North America provide important insights into the conditions that allowed two of the richest terrestrial faunas of this period to flourish. Geochemical analyses and observations of palaeosol morphology in the informally named Upper Jurassic Lourinhã formation of western Portugal indicate warm and wet palaeoclimatic conditions with strongly seasonal precipitation patterns. Palaeosol profiles are dominated by carbonate accumulations and abundant shrink-swell (vertic) features that are both indicative of seasonal variation in moisture availability. The δ18OSMOW and δDSMOW values of phyllosilicates sampled from palaeosol profiles range from +22.4‰ to +22.7‰ and -53.0‰ to -37.3‰, respectively. These isotope values correspond to temperatures of formation between 32°C and 39°C ± 3°, with an average of 36°C, which suggest surface temperatures between 27°C and 34°C (average 31°C). On average, these surface temperature estimates are 1°C higher than the highest summer temperatures modelled for Late Jurassic Iberia using general circulation models. Elemental analysis of matrix material from palaeosol B-horizons provides proxy (chemical index of alteration minus potassium) estimates of mean annual precipitation ranging from 766 to 1394 mm/year, with an average of approximately 1100 mm/year. Palaeoclimatic conditions during deposition of the Lourinhã formation are broadly similar to those inferred for the Morrison Formation, except somewhat wetter. Seasonal variation in moisture availability does not seem to have negatively impacted the ability of these environments to support rich and relatively abundant faunas. The similar climate between these two Late Jurassic terrestrial ecosystems is probably one of the factors which explains the similarity of their vertebrate faunas.
Upper Permian and Lower Triassic palaeosols from northeastern Tethyan localities exposed within t... more Upper Permian and Lower Triassic palaeosols from northeastern Tethyan localities exposed within the Bogda Mountains, NW China, provide a wealth of information regarding long-term palaeoclimatic and palaeoenvironmental variations. Wuchiapingian palaeosols are characterized by intense redoximorphy, accumulation of vascular plant matter, accumulation of clay minerals and Fe-oxides, slickensides, and clastic dikes, suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget. Changsinghian to early Induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter, indicative of sub-humid to sub-arid soil moisture and variable soil moisture regimes. Induan to Olenekian palaeosols contain pedogenic CaCO3 accumulations and gypsum pseudomorphs, indicating a drier environment characterized by net soil moisture deficiency. Elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus Potassium (CIA-K) proxy. Estimates from various Wuchiapingian strata indicate relatively stable palaeoprecipitation. During the late Changsinghian and early Induan, palaeoprecipitation appears to have decreased from 1100 to 230 (±180)mm/year over less than 100 m of vertical stratigraphic section. In the Induan and Olenekian, palaeoprecipitation appears much less stable than in Wuchiapingian, with values vacillating from 290 to 1014 mm/year. The transition to a relatively unstable precipitation state coincides generally with the Permian–Triassic boundary, and may reflect climatic disturbances associated with the end-Permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics, moisture availability, and expansion of the subtropical high pressure belt.
Paleopedology and geochemical analysis of Upper Jurassic deposits in the Stanleyville Group of Ce... more Paleopedology and geochemical analysis of Upper Jurassic deposits in the Stanleyville Group of Central Africa indicate harsh Late Jurassic paleoclimates in the interior of Gondwana. Subsurface samples collected from the Samba borehole near the center of the Congo Basin show only weak morphological evidence of pedogenesis, but are characterized by an abundance of shrink-swell (vertic) features and rare calcium carbonate nodules, indicating seasonal variations in moisture availability and net soil moisture deficiency, respectively. X-ray diffraction analysis of paleosol matrix material reveals the presence of analcime and the clay mineral palygorskite, strong indicators of hot, arid climatic conditions. The δ18O and δD values of clay minerals from paleosol profiles range from +22.3‰ to +25.4‰ and −44.4‰ to −39.6‰ SMOW, respectively, and correspond to crystallization temperatures between 25°C and 40°C. These crystallization temperatures compare favorably with austral summer surface temperature estimates for Central Africa that result from Late Jurassic global circulation models. Calculations of soil CO2 production using the δ13C values of pedogenic carbonates and plant-derived organic matter produce lower CO2 production estimates for the Stanleyville Group relative to the roughly contemporary Morrison Formation of the western U.S. These low soil CO2 production estimates provide further support for arid Late Jurassic climate conditions in the Congo Basin. The paleoclimatic conditions inferred here from the Stanleyville Group are similar to those reconstructed from other Upper Jurassic African continental localities between 5°S and 20°S paleolatitude. However, penecontemporaneous terrestrial coastal sites within this latitudinal belt of Gondwana retain evidence of generally wetter conditions, suggesting that those regions may have received more rainfall than the continental interior. The paleoclimatic setting reconstructed here from geologic indicators and geochemical proxies suggests that general circulation models accurately predict unique paleoenvironmental conditions that lack modern analogs.
Remains of a pteranodontid pterosaur are recorded in the basal Austin Group of North Texas. The s... more Remains of a pteranodontid pterosaur are recorded in the basal Austin Group of North Texas. The specimen described here comprises a partial left wing and strongly resembles Pteranodon although diagnostic features of that genus are lacking. With an estimated early Coniacian age, this specimen represents the earliest occurrence of the Pteranodontidae in North America and the second earliest occurrence worldwide, predated only by Ornithostoma from the Cambridge Greensand of England. Pterosaur material recovered from the Eagle Ford and Austin groups of Texas records an early Late Cretaceous change in the composition of North American pterosaur communities between the late Cenomanian and the early Coniacian. This faunal transition appears to be primarily a decrease in morphological disparity rather than a significant reduction in taxonomic diversity. However, the lack of Early Cretaceous Lagerstatten in North America may produce underestimates of true pterosaur richness during this interval, thereby obscuring a subsequent drop in diversity.
Both body fossil and ichnofossil evidence for gregarious behavior in sauropod dinosaurs is examin... more Both body fossil and ichnofossil evidence for gregarious behavior in sauropod dinosaurs is examined. Some localities suggest that herds were partitioned on the basis of age, whereas other sites reveal groups consisting of both adult and juvenile/subadult individuals. Two skeletal accumulations showing evidence of age segregation are examined in detail. The Mother's Day Quarry in the Upper Jurassic Morrison Formation of Montana contains the remains of several immature diplodocoid sauropods. An assemblage in the Upper Cretaceous Javelina Formation of Big Bend National Park in Texas consists entirely of juvenile Alamosaurus. Both the Mother's Day and Big Bend assemblages are interpreted here as remnants of age-segregated herds. The differences between skeletal accumulations composed entirely of immature animals and mixed-age ichnological assemblages imply that herd composition was variable. When age segregation is recognized, in both fossil and modern taxa, it is thought to minimize the fitness costs related to behavioral synchronization within social groups. Age segregation of herds also contraindicates extended parental care as typical of at least some sauropod taxa.
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minimum of 26 upper teeth and bears a thin premaxillary crest that begins above the fourth pair of alveoli. The rostrum,
characterized by a slight lateral flare, lacks the pronounced lateral expansion found in ornithocheirids and anhanguerids. The tip of the snout is small and blunt, and the anterior face of the rostrum is oriented posteroventrally, forming an approximately 45 angle with the anterior portion of the palate. The anteroventrally oriented first pair of alveoli is directed more ventrally than anteriorly. Phylogenetic analysis suggests that Cimoliopterus dunni and Cimoliopterus cuvieri, from the Cenomanian Grey Chalk Subgroup in Kent, England, are basal pteranodontoids that are closely related to Aetodactylus halli from the middle Cenomanian Tarrant Formation of north Texas. Cimoliopterus dunni marks only the second known occurrence of Cimoliopterus, extending its geographic range from Europe to North America. In conjunction with Coloborhynchus wadleighi from the upper Albian Pawpaw Formation, Cimoliopterus dunni provides unambiguous evidence of biogeographic linkages between the pterosaur faunas of North America and Europe in the middle Cretaceous.
stratigraphic architecture and basin evolution. Recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight intomajor regional to global changes in temperature, precipitation, and atmospheric pCO2. These
new proxies focus on morphological and chemical transfer functions and stable isotope geochemistry to provide estimates of precipitation, temperature, pCO2, and productivity, as well as chronometric estimates of mineral crystallization in deep-time pedogenic systems. Looking forward, consensus must be reached on terminology that most effectively communicates paleosol characteristics and implies important processes. Proxy development will continue to improve as data sets become available across greater ranges of environments and timescales.
values calculated for paleosols without shrink-swell (vertic) features correspond to MAP estimates between 800 and 1100 mm yr–1, with an average of 1000 mm yr–1. CALMAG values, calculated for vertic paleosols, correspond to MAP estimates between 50 and 1200 mm yr–1, with an average of 700 mm yr–1. MAP estimates from the older New Mexico strata indicate that early Morrison environments were relatively arid. MAP estimates from the younger Wyoming and Montana deposits reflect wetter conditions in the
northernmost part of the Morrison Formation, but the transition from arid interior environments was abrupt. Humidity provinces inferred from geochemical proxy-based estimates of evapotranspiration and energy influx from precipitation range from semiarid to superhumid, suggesting wetter conditions than the MAP estimates, but supporting the relative differences in moisture among the
three study areas. Paleoprecipitation patterns within the Morrison depositional basin do not match the modern latitudinal distribution of rainfall that arises from zonal atmospheric circulation. Comparison with the Upper Jurassic
Lourinhã Formation in Portugal and the Vega Formation in Spain reveals that MAP in Late Jurassic Portuguese environments was similar to that in the wet northern
part of the Morrison Formation, although more arid conditions prevailed in some areas of Portugal. Inferred humidity regimes for the Lourinhã Formation, which range from semiarid to superhumid, also indicate small scale
geographic variability in climate, although less pronounced than that observed in the Morrison Formation. Paleoenvironments in northern Spain were similar to the drier Morrison environments in the continental interior.
Given the abrupt climatic transitions inferred here for the Morrison Formation, paleoprecipitation estimates derived from a geographically restricted sample may reflect only local conditions and should not necessarily be extrapolated to larger areas.
values, D13Ccc-om, is smaller in profiles affected by groundwater saturation as well as most Vertisols and may be a product of waterlogging. The larger D13Ccc-om values in soils with gravity-driven flow are consistent with open-system mixing of tropospheric CO2 and CO2 derived from in situ oxidation of soil organic matter with mean soil PCO2 values potentially in excess of ~20,000 ppmV at the time of calcite crystallization. There is a correlation between estimates of soil PCO2 and a value termed ‘‘EPPT-U’’ (kJm2/yr) among the soil profiles characterized by gravity-driven flow. EPPT-U is the energy flux through the soil during periods of soil moisture utilization, and it is the product of water mass and temperature in the profile during the growing season. Thus, soils with high water-holding capacity/storage and/or low/high growing season temperature may form soil calcite in the presence of high soil PCO2, and vice versa. The results of this research have important implications for reconstructions of paleoclimate from stable carbon isotopes of
calcareous paleosol profiles.
minimum of 26 upper teeth and bears a thin premaxillary crest that begins above the fourth pair of alveoli. The rostrum,
characterized by a slight lateral flare, lacks the pronounced lateral expansion found in ornithocheirids and anhanguerids. The tip of the snout is small and blunt, and the anterior face of the rostrum is oriented posteroventrally, forming an approximately 45 angle with the anterior portion of the palate. The anteroventrally oriented first pair of alveoli is directed more ventrally than anteriorly. Phylogenetic analysis suggests that Cimoliopterus dunni and Cimoliopterus cuvieri, from the Cenomanian Grey Chalk Subgroup in Kent, England, are basal pteranodontoids that are closely related to Aetodactylus halli from the middle Cenomanian Tarrant Formation of north Texas. Cimoliopterus dunni marks only the second known occurrence of Cimoliopterus, extending its geographic range from Europe to North America. In conjunction with Coloborhynchus wadleighi from the upper Albian Pawpaw Formation, Cimoliopterus dunni provides unambiguous evidence of biogeographic linkages between the pterosaur faunas of North America and Europe in the middle Cretaceous.
stratigraphic architecture and basin evolution. Recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight intomajor regional to global changes in temperature, precipitation, and atmospheric pCO2. These
new proxies focus on morphological and chemical transfer functions and stable isotope geochemistry to provide estimates of precipitation, temperature, pCO2, and productivity, as well as chronometric estimates of mineral crystallization in deep-time pedogenic systems. Looking forward, consensus must be reached on terminology that most effectively communicates paleosol characteristics and implies important processes. Proxy development will continue to improve as data sets become available across greater ranges of environments and timescales.
values calculated for paleosols without shrink-swell (vertic) features correspond to MAP estimates between 800 and 1100 mm yr–1, with an average of 1000 mm yr–1. CALMAG values, calculated for vertic paleosols, correspond to MAP estimates between 50 and 1200 mm yr–1, with an average of 700 mm yr–1. MAP estimates from the older New Mexico strata indicate that early Morrison environments were relatively arid. MAP estimates from the younger Wyoming and Montana deposits reflect wetter conditions in the
northernmost part of the Morrison Formation, but the transition from arid interior environments was abrupt. Humidity provinces inferred from geochemical proxy-based estimates of evapotranspiration and energy influx from precipitation range from semiarid to superhumid, suggesting wetter conditions than the MAP estimates, but supporting the relative differences in moisture among the
three study areas. Paleoprecipitation patterns within the Morrison depositional basin do not match the modern latitudinal distribution of rainfall that arises from zonal atmospheric circulation. Comparison with the Upper Jurassic
Lourinhã Formation in Portugal and the Vega Formation in Spain reveals that MAP in Late Jurassic Portuguese environments was similar to that in the wet northern
part of the Morrison Formation, although more arid conditions prevailed in some areas of Portugal. Inferred humidity regimes for the Lourinhã Formation, which range from semiarid to superhumid, also indicate small scale
geographic variability in climate, although less pronounced than that observed in the Morrison Formation. Paleoenvironments in northern Spain were similar to the drier Morrison environments in the continental interior.
Given the abrupt climatic transitions inferred here for the Morrison Formation, paleoprecipitation estimates derived from a geographically restricted sample may reflect only local conditions and should not necessarily be extrapolated to larger areas.
values, D13Ccc-om, is smaller in profiles affected by groundwater saturation as well as most Vertisols and may be a product of waterlogging. The larger D13Ccc-om values in soils with gravity-driven flow are consistent with open-system mixing of tropospheric CO2 and CO2 derived from in situ oxidation of soil organic matter with mean soil PCO2 values potentially in excess of ~20,000 ppmV at the time of calcite crystallization. There is a correlation between estimates of soil PCO2 and a value termed ‘‘EPPT-U’’ (kJm2/yr) among the soil profiles characterized by gravity-driven flow. EPPT-U is the energy flux through the soil during periods of soil moisture utilization, and it is the product of water mass and temperature in the profile during the growing season. Thus, soils with high water-holding capacity/storage and/or low/high growing season temperature may form soil calcite in the presence of high soil PCO2, and vice versa. The results of this research have important implications for reconstructions of paleoclimate from stable carbon isotopes of
calcareous paleosol profiles.