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.

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.

Members of the genus Ctenomys (tuco-tuco; Rodentia: Caviomorpha: Octodontidae) are considered scratch diggers. We compared the forelimbs of adult C. azarae with those of 13 species within other genera of caviomorph rodents to identify morphofunctional variation in osseous elements related to fossorial habits. Eight measurements of the humerus and ulna were used to construct five functional indices that were subjected to principal components analysis and simple comparisons among means. Ctenomys has a general morphology similar to that of terrestrial caviomorph rodents but exhibits some features that reflect its specialized fossorial condition, such as its comparatively large epicondyles. These features indicate greater muscular development and capacity for force production in the pronators and supinators of the forelimb and manus and flexors of the manus. The deltoid complex is well developed, indicating a large moment arm for the deltoid and latissimus dorsi muscles, which increases the capacity for force production on humeral flexion. Humeral indices are the best for differentiating fossorial forms from diggers, occasional diggers, generalized, and cursorial forms. Limb bone segments are used differently by highly fossorial and scratch-digging forms. w w w . m a m m a l o g y . o r g Journal of Mammalogy, 92(3):683-689, 2011 683 * Highlights variables with loadings .0.7.

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 generally accepted hypothesis regarding the origin of fossorial mammals proposes adaptive convergence from open environments towards the use of subterranean environments. We evaluated this hypothesis for South American mole-mice using conventional and Bayesian frameworks, with independent evidence. By using a molecular approach based on Cytochrome b and IRBP sequences, we evaluated phylogenetic relationships, time of origin, the ancestral trait of fossoriality, and ancestral distributions of species belonging to the Andean Clade (Rodentia: Sigmodontinae). Our results indicate that the Andean Clade is highly sustained; with one clade grouping all fossorial forms and another grouping all cursorial species. We hypothesized that fossoriality originated in the Miocene/Pliocene transition, in the Temperate Forests of southern South America. We conclude that the origin of fossorial ecomorphological traits did not necessarily occur under a general model of open environments, the origin of these traits depends on the ecological-historical relationship of the taxon with the environment.

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 lungs of the naked mole-rat Heterocephalus glaber were morphologically (qualitatively) and morphometrically (quantitatively) investigated in adult captive in-burrow body-temperature-maintained (CBTMA) and captive cold-exposed animals (CCEA). The observations were compared with those of ®eld (burrow-dwelling) animals (FA) examined in an earlier study. The lungs of the captive animals were morphologically (qualitatively) similar to those of the ®eld mole-rats. Conspicuous paedomorphic features, i.e. a preponderant double pulmonary capillary arrangement, incomplete differentiation of alveolar pneumocytes, and extension of a cuboidal epithelium to the immediate vicinity of the alveoli, were observed. The prevalent pulmonary underdevelopment was attributed to the relatively low metabolic rate of the poikilothermic naked mole-rat, a species that has evolved in a thermally stable environment. Measurable differences and similarities were found between the lungs of the captive naked mole-rats themselves (i.e. the CBTMA and the CCEA) and between the captive and the ®eld ones. Genetic factors may help explain the conserved pulmonary structural features while environmental (gaseous) change from a hypoxic±hypercapneic (an oxygen de®cient±high carbon dioxide concentration) to a normoxic±normocapnic atmosphere and the thermal shift respectively may have enforced pulmonary transformations between the CBTMA and the FA and between the CCEA and the CBTMA. Paradoxically, the CCEA had a signi®cantly lower mass-speci®c total morphometric pulmonary diffusing capacity of 0.024 compared with that of 0.102 mlO 2 .s 71 .mbar 71 .kg 71 in the CBTMA. The observed morphometric differences indicate that the lung of the naked mole-rat, though morphologically unchanged, is intrinsically tractable to environmental shifts in its habitat. Studies on captive naked mole-rats should not be indiscriminately taken to be representative of the species.

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.

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.

Burrow plugging is readily observed among mammals adapted for digging (i.e., fossorial mammals) as they create and maintain their burrows. We investigated the influence of light, burrow openings, and thermal environment as cues of pocket gopher (Thomomys mazama, Thomomys talpoides) behavior. When given free access to light and no light during artificial-burrow preference trials, both Thomomys spp. consistently plugged (i.e., avoided) light treatments. Burrow openings did not notably affect plugging behavior of T. mazama. Gophers (T. talpoides) plugged the artificial burrows within the light and cold (7 degrees C) treatments, but not within the no-light, and 18 or 31 degrees C treatments when light and temperature were varied independently. Whereas the presence of light and low ambient temperatures induce burrow maintenance by pocket gophers, these cues help meliorate adverse conditions within subsurface environs.

The rudimentary characteristic of the eyes of fossorial animals raises some questions regarding its evolution and functionality. Would these eyes result from atrophy or from stagnated development? How would its visual function work? Anatomical investigations of these organs are the fundamental preamble to answer those questions, which are still little explored by the literature. In this article we have studied anatomical aspects of the eyes of three species of fossorial reptiles, within the suborder Amphisbaena (Amphisbaena alba, Amphisbaena mertensi, Leposternon infraorbitale), as well as a species within the ophidian suborder (Typhlops brongersmianus). The minuscule eyes (1-2 mm diameter) were visualized through a scale, a translucent area which corresponds to the spectacle. This spectacle is a thinner and transparent scale, covering a conjunctival sac. The retrobulbar space was filled with the harderian gland. The eyes of Typhlops presented an oval shape, whereas Amphisbaena specimens presented cup-shaped eyes. In Amphisbaenian sclera is comprised of cartilage, while the thin sclera of Typhlops consists of connective tissue and striated muscle fibers. The retina presented all the typical layers found in vertebrates, regardless the species. The characteristics involved in the fossil adaptation of these species include: reduced size of the eyeball, rudimentary cornea, absence of the anterior chamber, presence of a complex iris-ciliary body, and lens with amorphous nucleate cells. The analysis of the eye morphology of these animals suggests that there might be a specific function concerning light perception.

Many animals create soil surface depressions (pits) while foraging for subterranean resources. Foraging pits typically fill with litter, organic debris and seed, retain moisture, and become hotspots for plant germination. This study aimed to examine whether artificial foraging pits, which mimic those created by Greater bilbies (Macrotis lagotis) and Burrowing bettongs (Bettongia lesueur), develop into patches of enhanced plant germination due to accumulation of leaf litter, or whether physical characteristics of the pits such as temperature and soil moisture influence germination, irrespective of the presence of litter. Compared with the soil surface, significantly more plants germinated in artificially-created foraging pits, irrespective of whether they received added litter. Daytime temperatures were 17-31% (7-11 C) cooler in foraging pits than on the adjacent soil surface, and pits retained significantly more moisture up to 5 days after rainfall. Our results suggest that the mesic conditions in foraging pits may be more important in promoting germination of vascular plants than the presence of litter.

The generally accepted hypothesis regarding the origin of fossorial mammals proposes adaptive convergence from open environments towards the use of subterranean environments. We evaluated this hypothesis for South American mole-mice using conventional and Bayesian frameworks, with independent evidence. By using a molecular approach based on Cytochrome b and IRBP sequences, we evaluated phylogenetic relationships, time of origin, the ancestral trait of fossoriality, and ancestral distributions of species belonging to the Andean Clade (Rodentia: Sigmodontinae). Our results indicate that the Andean Clade is highly sustained; with one clade grouping all fossorial forms and another grouping all cursorial species. We hypothesized that fossoriality originated in the Miocene/Pliocene transition, in the Temperate Forests of southern South America. We conclude that the origin of fossorial ecomorphological traits did not necessarily occur under a general model of open environments, the origin of these traits depends on the ecological-historical relationship of the taxon with the environment.

The generally accepted hypothesis regarding the origin of fossorial mammals proposes adaptive convergence from open environments towards the use of subterranean environments. We evaluated this hypothesis for South American mole-mice using conventional and Bayesian frameworks, with independent evidence. By using a molecular approach based on Cytochrome b and IRBP sequences, we evaluated phylogenetic relationships, time of origin, the ancestral trait of fossoriality, and ancestral distributions of species belonging to the Andean Clade (Rodentia: Sigmodontinae). Our results indicate that the Andean Clade is highly sustained; with one clade grouping all fossorial forms and another grouping all cursorial species. We hypothesized that fossoriality originated in the Miocene/Pliocene transition, in the Temperate Forests of southern South America. We conclude that the origin of fossorial ecomorphological traits did not necessarily occur under a general model of open environments, the origin of these traits depends on the ecological-historical relationship of the taxon with the environment.

A new species of tuco-tuco, genus Ctenomys, is described from sandy soils on the western slopes of the state of Rio Grande do Sul in southern Brazil. This species is distinguished from other named members of this South American endemic genus by several characteristics. Diagnostic traits for this proposed species are a diploid number of 50 chromosomes and an autosomal fundamental number of 68 arms, with the 1st pair much longer than in other related species. Qualitative and quantitative (geometric morphometrics) analyses of the skull morphology and phylogenetic analysis of the mitochondrial cytochrome-b gene support species status, especially when compared with phylogenetically related and geographically neighboring species. Populations of this species have a narrow geographic distribution in a small area (~500 km 2) that has been suffering from anthropogenic pressure from soybean, pine, and eucalyptus plantations, as well as desertification. This scenario suggests that this species could be characterized as endangered.

The rudimentary characteristic of the eyes of fossorial animals raises some questions regarding its evolution and functionality. Would these eyes result from atrophy or from stagnated development? How would its visual function work? Anatomical investigations of these organs are the fundamental preamble to answer those questions, which are still little explored by the literature. In this article we have studied anatomical aspects of the eyes of three species of fossorial reptiles, within the suborder Amphisbaena (Amphisbaena alba, Amphisbaena mertensi, Leposternon infraorbitale), as well as a species within the ophidian suborder (Typhlops brongersmianus). The minuscule eyes (1-2 mm diameter) were visualized through a scale, a translucent area which corresponds to the spectacle. This spectacle is a thinner and transparent scale, covering a conjunctival sac. The retrobulbar space was filled with the harderian gland. The eyes of Typhlops presented an oval shape, whereas Amphisbaena specimens presented cup-shaped eyes. In Amphisbaenian sclera is comprised of cartilage, while the thin sclera of Typhlops consists of connective tissue and striated muscle fibers. The retina presented all the typical layers found in vertebrates, regardless the species. The characteristics involved in the fossil adaptation of these species include: reduced size of the eyeball, rudimentary cornea, absence of the anterior chamber, presence of a complex iris-ciliary body, and lens with amorphous nucleate cells. The analysis of the eye morphology of these animals suggests that there might be a specific function concerning light perception.