Fossorial

Oryctodromeus is a small bipedal dinosaur known from middle Cretaceous (95-100 My) Wayan Formation of Idaho and the Vaughn Member of the Blackleaf Formation of Montana. This taxon is hypothesized to be a burrowing dinosaur, which cared for its young within these burrows. This dissertation is a broad three-part treatment of this taxon, and excepting the introductory and concluding chapters this dissertation consists of three main chapters. Chapter two describes the osteology and phylogenetic relationships of this animal. Notable features of the Oryctodromeus skeleton described include a network of ossified tendons along the vertebral column that completely ensheath the tail, a long tail that forms more than half the length of the animal, and unusual femoral heads whose morphology may be related to burrowing behavior. The first full skeletal and skull reconstructions of this animal are presented. Chapter three investigates patterns of preservation of Oryctodromeus. Data suggests that preservation of single to multiple individuals of this taxon typically occurred in burrows that may be difficult to impossible to recognize in the fossil record. New examples of burrows from Oryctodromeus from the Vaughn and Wayan, as well as additional evidence for social behavior, are also described. A third chapter details the ontogenetic histology, growth rates and patterns of skeletal fusion based on seven limb elements (femora and tibiae) from different individuals. Based on the data in this dissertation, three growth stages can be recognized in Oryctodromeus based on bone histology. Juveniles are defined by more rapidly growing fibrolamellar tissue, sub-adults are defined by a cortex of inner fibrolamellar tissue and outer zonal parallel fibered tissue, and near-adult individuals have tissue similar to sub adults with dense avascular bone in the outermost cortex that signals a decrease in growth rate. LAG’s suggest a minimum age of six to seven years for more mature individuals. Patterns of neurocentral fusion in Oryctodromeus appear similar to those of crocodylians and some other small ornithischians, while the growth rates of Oryctodromeus appear slower than those of some dinosaurs, but similar to taxa such as Orodromeus and Tenontosaurus.

El rol de la vizcacha (Lagostomus maximus) en los procesos de formación de los sitios arqueológicos de la llanura Interserrana argentina The role of the vizcacha (Lagostomus maximus) in the formation processes of archaeological sites from the Argentinian interhill plains Resumen El movimiento de sedimentos que generan los mamíferos cavadores constituye uno de los principales procesos de formación que sufren los sitios arqueológicos de la región pampeana. En este trabajo se presentan los resultados de un estudio actualista realizado sobre una colonia de vizcachas ubicada en la localidad arqueológica El Trebolar, provincia de Buenos Aires. El objetivo principal fue describir el impacto que estos roedores generan sobre el paisaje, con el fin de identificar su accionar en los sitios arqueológicos de la región. A partir del relevamiento de 21 vizcacheras se pudo establecer que las vizcachas afectan al registro arqueológico de diferentes maneras. Por un lado, su actividad cavadora altera las secuencias estratigráficas y genera asociaciones de materiales de distinta cronología. Por otra parte, las vizcacheras son ocupadas por otros animales, dando lugar a conjuntos faunísticos con alta riqueza taxonómica. Además, estos roedores acarrean a sus madrigueras objetos disponibles localmente. Por último, un alto porcentaje de especímenes óseos presentan surcos que generan las vizcachas para mantener funcionales sus incisivos. En conclusión, las distintas evidencias presentadas permitirían reconocer el accionar de este roedor en el registro fósil, diferenciándolo de otros animales fosoriales que habitan la región pampeana.
The movement of sediments generated by digging animals/burrowing mammals is one of the main formation processes affecting the archaeological sites in the Pampas region. In this article, we present/report the results of an actualistic study conducted on a vizcacha colony, in the archaeological locality El Trebolar, province of Buenos Aires. The main objective was to describe the impact that these rodents generate on the landscape in order to identify their action on the archaeological sites of the region. The analysis of 21 vizcacheras showed that the vizcachas affect the archaeological record in different ways. Firstly, their digging activity alters stratigraphic sequences and generates associations of material of different chronology. Secondly, the vizcacheras are occupied by other animals, producing/giving rise to taxonomically rich faunal assemblages. In addition, these rodents carry locally available objects to their burrows. Finally, a high percentage of bone specimens present/shows grooves generated by vizcachas to keep their incisors functional. In conclusion, evidence would allow recognizing the action of this rodent in the fossil record, distinguishing it from other fossorial animals that inhabit the Pampas region.

Vertebrate assemblages from the mid-Cretaceous (Albian-Cenomanian) Wayan Formation of Idaho and Vaughn
Member of the Blackleaf Formation of Montana are dominated by the small burrowing dinosaur, Oryctodromeus
cubicularis. Specimens can be assigned to three distinct taphofacies dependent on degrees of skeletal articulation
and associated lithofacies. Taphofacies A comprises mostly to fully articulated specimens in bioturbated sandstones.
Taphofacies B comprises partially articulated to associated collections of skeletal elements in pedogenic
mudstones, siltstones, and fine-grained sandstones. Taphofacies C comprises isolated skeletal elements within
the debris-flow deposit of the Robison Bonebed. Except for one associated nodosaur skeleton, Oryctodromeus is
the only vertebrate represented by significant associations of skeletal elements or portions of articulated skeletal
elements within the Wayan Formation/Vaughn Member units, and occurrences represent a paleocommunity
dominated by a small cursorial and fossorial vertebrate. The co-occurrence of multiple individuals, representing
presumed juvenile and adult growth stages, reinforce previous suggestions of parental care in this species. In
addition, newly reported Oryctodromeus burrows compare in overall morphology and size with the burrow
containing the holotype of Oryctodromeus. These data suggest the possibility that evidence for additional fossil
taxa having had a communal and fossorial lifestyle may be discerned through further focused taphonomic investigations.

The Mussentuchit Member of the Cedar Mountain Formation of eastern Utah represents the best source of data on Cenomanian vertebrate assemblages from North America. However, increasing data has
recently been forthcoming from the late Albian to Cenomanian Wayan Formation of Idaho and Vaughn Member of the Blackleaf Formation of Montana, which are both at least partially coeval with the Mussentuchit Member. While the paleontological assemblages of the Wayan Formation and Vaughn Member are fragmentary, numerous vertebrate forms are represented, with the small burrowing neornithischian Oryctodromeus cubicularis dominating these assemblages. The differences between the Wayan Formation and Vaughn Member assemblages, the Mussentuchit and few other mid-Cretaceous assemblages are likely a result of some combination of preservational biases, paleogeography, and paleoenvironmental differences. The chronostratigraphy, fossil content, bracketing facies, and ages of the Wayan Formation and Vaughn Member suggest these sediments represent the same depositional system prior to disruption by subsequent tectonic and volcanic events. This assemblage
from the Wayan Formation and Vaughn Member is here termed the Wayan-Vaughn Assemblage (WVA). Continued work in the WVA, particularly with microvertebrate materials, may reveal additional shared
taxa between the WVA and other coeval units.

ABSTRACT Burrow construction in the subterranean Ctenomys talarum (Rodentia: Ctenomyidae) primarily occurs by scratch-digging. In this study, we compared the limbs of an ontogenetic series of C. talarum to identify variation in bony elements related to fossorial habits using a morphometrical and biomechanical approach.Diameters and functional lengths of long bones were
measured and 10 functional indices were constructed. We
found that limb proportions of C. talarum undergo significant changes throughout postnatal ontogeny, and no significant differences between sexes were observed. Five of six forelimb indices and two of four hindlimb indices showed differences between ages. According to discriminant analysis, the indices that contributed most to discrimination among age groups were robustness of the humerus and ulna, relative epicondylar width, crural and brachial indices, and index of fossorial ability (IFA).
Particularly, pups could be differentiated from juveniles and adults by more robust humeri and ulnae, wider epicondyles, longer middle limb elements, and a proportionally shorter olecranon. Greater robustness indicated a possible compensation for lower bone stiffness while wider epicondyles may be associated to improved effective forces in those muscles that originate onto them, compensating the lower muscular development. The gradual increase in the IFA suggested a gradual enhancement in the scratch-digging performance due to an improvement in the mechanical advantage of forearm extensors. Middle limb indices were higher in pups than in juveniles–adults, reflecting relatively more gracile limbs in their middle segments, which is in accordance with their incipient fossorial ability. In sum, our results show that in C. talarum some scratch-digging adaptations are already present during early postnatal ontogeny, which suggests that they are prenatally shaped, and other traits develop progressively. The role of early digging behavior as a factor influencing on morphology development is discussed.

The genus Hypnomys Bate, 1918 includes some endemic Neogene chronospecies from Mallorca and Menorca, evolved in insularity conditions from the Lower Pliocene to the human arrival at the archipelago. The study of the allometric proportions (functional length and sagittal diameter) of the limbs’ long bones of Hypnomys eliomyoides Agusti, 1980 (Lower Pleistocene of Menorca), Hypnomys sp. (Pleistocene of Menorca), Hypnomys onicensis (Reumer, 1994) (Upper Pliocene-Lower Pleistocene of Mallorca) and Hypnomys morpheus Bate, 1918 (Upper Pleistocene of Mallorca) only indicates small differences with the garden dormouse (Eliomys quercinus Linnaeus, 1776) and other mainland rodents and insectivores. The study about the locomotion type by means of Similarity Matrix of Bou indicates that 1) Hypnomys spp. presents the greater similarities with the arboreal, jumping and gliding species; 2) the jumping and digging life style of Hypnomys spp. are more developed (25%) than in E. quercinus; 3) the walking locomotion of Hypnomys spp. is only a 7% greater than in E. quercinus; and 4) the degree of similarity with the gliding locomotion of Hypnomys sp. is greater (17%) than in E. quercinus. Some of this data indicates that Hypnomys spp. was better adapted to the arboreal life than E. quercinus, due to the relationship between the jumping and gliding capacities with the arboreal locomotion. The greater similarity of Hypnomys spp. with the walking locomotion does not necessarily involve more terrestrial habits. Our interpretation contrasts with earlier conclusions of Hypnomys life style (Hypnomys cf. onicensis and Hypnomys morpheus) where the terrestrial locomotion was overestimated in front of the arboreal locomotion. The locomotion type of Hypnomys would be related with the presence of important forest masses on the Balearic Islands during the Neogene, a different degree of environmental stress from that of the mainland ecosystems and a probable expansion of the ecological niche occupied by these species.

Tadpoles of the monotypic Indian dancing frog family Micrixalidae have remained obscure for over 125 years. Here we report the discovery of the elusive tadpoles of Micrixalus herrei from the sand beds of a forested stream in southern Western Ghats, and confirm their identity through DNA barcoding. These actively burrowing tadpoles lead an entirely fossorial life from eggs to late metamorphic stages. We describe their internal and external morphological characters while highlighting the following features: eel-like appearance, extensively muscularized body and tail, reduced tail fins, skin-covered eyes, delayed development of eye pigmentation in early pre-metamorphic stages (Gosner stages 25-29), prominent tubular sinistral spiracle, large transverse processes on vertebrae II and III, ankylosed ribs on transverse processes of vertebra II, notochord terminating before the atlantal cotyle-occipital condyle junction, absence of keratodonts, serrated well-formed jaw sheaths, and extensiv...

The feedback between organisms and their environment is of great relevance to the understanding of ecosystem functioning. Particularly, subterranean mammals living on desert systems play an important role in ecosystem processes modifying their environment and influencing the life strategies of plants and animals. The mendocino tuco-tuco Ctenomys mendocinus, is a fossorial rodent inhabiting a wide range of soil and climate conditions in the central arid lands of Argentina. The purpose of our study was to quantify the degree of environmental segregation: soil properties and vegetation in four habitat types, their impact on woody vegetation, and diet. The highest activity was recorded in sand dunes and was associated with high habitat heterogeneity and soft soils. Degree of herbivory varied among habitats, with Lycium (Solanaceae) being the most gnawed shrub. Tuco-tucos behave like folivorous grazers, feeding on leaves of grasses, mostly Panicum (Poaceae). This is the first study integrating multiple approaches of tucos' auto-ecology in a heterogeneous desert matrix, suggesting a differential use of its environment, possibly according to food supply and soil hardness. Despite life underground impose general constrains for most subterranean species, our results suggest that both above and under ground habitat features play important roles in the occurrence of fossorial rodents.