Postcranial Anatomy Research Articles

Cranial ecomorphology of turtles and neck retraction as a possible trigger of ecological diversification.

Turtles have a highly modified body plan, including a rigid shell that constrains postcranial anatomy. Skull morphology and neck mobility may therefore be key to ecological specialization in turtles. However, the ecological signal of turtle skull morphologies has not been rigorously evaluated, leaving uncertainties about the roles of ecological adaptation and convergence. We evaluate turtle cranial ecomorphology using three-dimensional geometric morphometrics and phylogenetic comparative methods. Skull shape correlates with allometry, neck retraction capability, and different aquatic feeding ecologies. We find that ecological variables influence skull shape only, whereas a key functional variable (the capacity for neck retraction) influences both shape and size. Ecology and functional predictions from three-dimensional shape are validated by high success rates for extant species, outperforming previous two-dimensional approaches. We use this to infer ecological and functional traits of extinct species. Neck retraction evolved among crownward stem-turtles by the Late Jurassic, signaling functional decoupling of the skull and neck from the shell, possibly linked to a major episode of ecomorphological diversification. We also find strong evidence for convergent ecological adaptations among marine groups. This includes parallel loss of neck retraction, evidence for active hunting, possible grazing, and suction feeding in extinct marine groups. Our large-scale assessment of dietary and functional adaptation throughout turtle evolution reveals the timing and origin of their distinct ecomorphologies, and highlights the potential for ecology and function to have distinct effects on skull form.

New well-preserved materials of Glossotherium chapadmalense (Xenarthra, Mylodontidae) from the Pliocene of Argentina shed light on the origin and evolution of the genus

ABSTRACT Fossil remains of extinct mylodontine sloths have been discovered in numerous localities throughout the American supercontinent, but knowledge of them is still mainly centered on the Pleistocene forms rather than their Neogene relatives. In this contribution, previously unpublished cranial and postcranial materials herein ascribed to Glossotherium chapadmalense (Kraglievich), coming from the Pliocene Chapadmalal Formation (Province of Buenos Aires, Argentina), are presented. These remains are described and compared with those of other mylodontine species from South and North America, providing an exhaustive characterization of cranial morphology in G. chapadmalense and some preliminary insights into its postcranial anatomy. The results have revealed a unique combination of differences and similarities of this enigmatic species with the larger-sized representatives of Glossotherium. In addition, these materials allowed shedding light on the long-standing uncertainties regarding its taxonomic status, as this form has been alternately considered to belong to the genera Glossotherium or Glossotheridium over the last century. As a result, the genus Glossotherium was present, at least, at the Early–Late Pliocene transition in the Pampean region of Argentina, and is recorded by the Upper Pleistocene throughout the entire South American continent. The radiation of the Pleistocene species is associated with a consistent body mass increase that was probably a response to the cooling temperatures and higher predation pressure in South America during the Late Pliocene–Early Pleistocene. These phenomena were probably driven by the stable emergence of the Panamanian Isthmus around 3 Ma and the successive faunal turnover pulses of the Great American Biotic Interchange.

The choanal anatomy of theSebecus icaeorhinusSimpson, 1937 and the variation of the palatine shape in notosuchians (Crocodyliformes, Mesoeucrocodylia)

AbstractSebecidae is a clade of large carnivorous crocodyliforms that thrived in the Cenozoic and is the only lineage of the diverse and terrestrial group Notosuchia that survived the end-Cretaceous mass extinction event.Sebecus icaeorhinusis the best-known taxon from this clade, both in terms of its cranial and postcranial anatomy (known primarily from the holotype and specimen MPEF-PV 1776, respectively). Additional material represented by a partial skull (MMP 235) is the only specimen that has preserved a complete choanal region. We describe new information from this specimen based on an X-ray computed tomography and identify through comparisons with other taxa a large degree of variability in the palatal anatomy within Sebecidae, in particular in the shape and extension of the palatine (the bone that defines the anterior position and shape of the secondary choana). We quantify variation in the shape of the palatine bone of sebecids through a 2D morphogeometric analysis within the context of notosuchian crocodyliforms. Although traditional accounts of palatal evolution in crocodyliforms linked variation of this structure to the adaptation to the aquatic environment, our analysis allows recognition of eight palatine morphotypes among terrestrial crocodyliforms with very distinct paleoecological traits, including carnivorous, omnivorous, and possibly herbivorous taxa. Furthermore, we show that sebecids had a higher morphological disparity in the choanal region than other terrestrial groups of Notosuchia, underscoring the importance of this region for comparative, morphofunctional, and phylogenetic studies.

Shape variation in the talus and medial cuneiform of chimpanzees and bonobos

AbstractObjectivesBonobos and chimpanzees do not differ from one another in overall frequencies of arboreality versus terrestriality as much as once thought. Thus, at a broad level, one would predict that there is little difference in foot morphology among Pan taxa. However, behavioral data suggest that bonobos more often use smaller diameter substrates (<10 cm) when climbing whereas western chimpanzees frequently climb larger diameter (>15 cm) substrates. This study tests the hypothesis that if Pan medial cuneiform and talus morphology reflects these substrate preferences, then the morphology of these bones should favor hallucial grasping in bonobos and an inverted foot set in western chimpanzees.Materials and MethodsThree‐dimensional geometric morphometric (3DGM) methods were used to explore shape variation in 126 talus and 127 medial cuneiform 3D surface models acquired from 108 chimpanzees (24 western, four Nigeria‐Cameroon, 33 central, 32 eastern, and 15 captive unknowns) and 22 bonobosResultsThe shapes of the talus and medial cuneiform in Pan covary as a functional unit emphasizing hallucial grasping with a less inverted foot set in bonobos and a more inverted foot set with a less abducted hallucial set in western chimpanzees. Other chimpanzee subspecies fall between these two extremes.DiscussionBonobo and western chimpanzee medial cuneiform and talus shapes are consistent with their differing preferences for using smaller and larger diameter substrates, respectively, when vertically climbing. These results suggest that even among closely related taxa, foot, hand, and other postcranial anatomy may be fine‐tuned for specific locomotor behaviors or preferences.

Postcrania of Borealestes (Mammaliformes, Docodonta) and the emergence of ecomorphological diversity in early mammals

AbstractThe Middle Jurassic witnessed the early diversification of mammal groups, including the stem‐mammalian clade, Docodonta. Recent discoveries in China indicate docodontans exhibited ecomorphological diversity akin to small‐bodied mammals living >100 million years later, in the Cenozoic. Our understanding of the emergence of this ecological diversity is hindered by a lack of Middle Jurassic fossil material from other parts of the world. The two partial postcranial skeletons of Borealestes described here come from the Kilmaluag Formation, Scotland. These are the most complete Mesozoic mammaliaform skeletons currently known from the UK, and among the best preserved in Europe. As an early member of Docodonta, Borealestes provides key anatomical information for understanding the clade’s evolution, and the emergence of mammaliaform ecomorphological diversity. Using digital reconstructions from micro‐CT and synchrotron scans, we describe the postcranial anatomy of Borealestes and provide an updated phylogenetic analysis incorporating cranial and postcranial characters. We find Borealestes species form a sister group to a clade comprising Agilodocodon and Microdocodon. To complement observational analyses of the skeleton, we carry out principal components analyses using 3D landmarks on a comparative dataset of 42 extant mammal taxa. Our results indicate Borealestes lacked specializations for derived locomotor behaviour. We detect some similarity in the humerus between Borealestes and Ornithorhynchus. Borealestes is morphologically intermediate between the robust morphology of fossorial and semi‐fossorial/semi‐aquatic Haldanodon and Docofossor, and the gracile morphology for scansorial Agilodocodon and Microdocodon. We suggest ecological diversity in Docodonta may arise from an unspecialized basal bauplan, of which Borealestes may be representative.

The earliest Asian bats (Mammalia: Chiroptera) address major gaps in bat evolution.

Bats dispersed widely after evolving the capacity for powered flight, and fossil bats are known from the early Eocene of most continents. Until now, however, bats have been conspicuously absent from the early Eocene of mainland Asia. Here, we report two teeth from the Junggar Basin of northern Xinjiang, China belonging to the first known early Eocene bats from Asia, representing arguably the most plesiomorphic bat molars currently recognized. These teeth combine certain bat synapomorphies with primitive traits found in other placental mammals, thereby potentially illuminating dental evolution among stem bats. The Junggar Basin teeth suggest that the dentition of the stem chiropteran family Onychonycteridae is surprisingly derived, although their postcranial anatomy is more primitive than that of any other Eocene bats. Additional comparisons with stem bat families Icaronycteridae and Archaeonycteridae fail to identify unambiguous synapomorphies for the latter taxa, raising the possibility that neither is monophyletic as currently recognized. The presence of highly plesiomorphic bats in the early Eocene of central Asia suggests that this region was an important locus for the earliest, transitional phases of bat evolution, as has been demonstrated for other placental mammal orders including Lagomorpha and Rodentia.

The postcranial skeleton of Cerrejonisuchus improcerus (Crocodyliformes: Dyrosauridae) and the unusual anatomy of dyrosaurids.

Dyrosauridae is a clade of neosuchian crocodyliforms that diversified in terrestrial and aquatic environments across the Cretaceous-Paleogene transition. The postcranial anatomy of dyrosaurids has long been overlooked, obscuring both their disparity and their locomotive adaptations. Here we thoroughly describe of the postcranial remains of an unusually small dyrosaurid, Cerrejonisuchus improcerus, from the middle-late Paleocene Cerrejón Formation of Colombia, and we provide a wealth of new data concerning the postcranial anatomy of the key dyrosaurids: Congosaurus bequaerti and Hyposaurus rogersii. We identify a series of postcranial autapomorphies in Cerrejonisuchus improcerus (an elliptic-shaped odontoid laterally wide, a ulna possessing a double concavity, a fibula bearing a widely flattened proximal end, a pubis showing a large non-triangular distal surface) as well as functionally-important traits such as a relatively long ulna (85% of the humerus’ length), short forelimb (83% of hindlimb’s length), or thoracic vertebra bearing comparatively large lateral process (with widened parapophysis and diapophysis) along with strongly arched thoracic ribs allowing a more sturdy and cylindrical rib cage. These indicate a more terrestrial lifestyle for Cerrejonisuchus compared to the derived members of the clade. We also built a dataset of 187 traits on 27 taxa, that extensively samples the cranial and postcranial architectures of exemplar crocodyliforms. We analyze these data in via Principal Coordinate Analysis (PCoA) to visualize the postcranial morphospace occupation of Dyrosauridae, Thalattosuchia, and Crocodylia. Our data reveal the existence of a distinctive postcranial anatomy for Dyrosauridae that is markedly distinct from that of crocodylians. As a result, modern crocodylians are probably not good functional analog for extinct crocodyliformes. Postcranial data should also be more widely used in phylogenetic and disparity analyses of Crocodyliformes.

The postcranial anatomy ofWhatcheeria deltaeand its implications for the family Whatcheeriidae

AbstractHere we describe the postcranial skeleton and present the first full-body reconstruction of the early tetrapod Whatcheeria deltae from the Viséan of Iowa. The skeletal proportions, including an elongate neck and large limbs, are unlike those of other Devonian and Mississippian tetrapods. The robust limbs of Whatcheeria appear adapted for a walking gait, but the lateral lines of the cranium are fundamentally unsuited for sustained subaerial exposure. Thus, although Whatcheeria bears a general resemblance to certain terrestrially adapted Permian and Triassic members of crown tetrapod lineages, its unusual form signals a broader range of early amphibious morphologies and habits than previously considered. From the exceptionally rich collection it is evident that most Whatcheeria specimens represent immature individuals. Rare specimens suggest an adult body size of at least 2 m, over twice that of the holotype. Further comparison suggests that the Pederpes holotype might also be a juvenile and reveals a combination of hindlimb characters unique to Whatcheeria and Pederpes. These new data contribute to a revised diagnosis of the family Whatcheeriidae and a re-evaluation of fragmentary Devonian–Carboniferous fossils reported as ‘whatcheeriid’ but sharing no synapomorphies with the more precisely defined clade.

The myth of the hippo-like anthracothere: The eternal problem of homology and convergence

The notion that anthracotheres had hippo-like body proportions, locomotion and lifestyles has been in the literature for so long, and has been repeated so many times, that it has taken on the aura of unquestionable truth. However, right from the beginning of studies into hippo-anthracothere relationships over a century and a half ago, observations were made that revealed the existence of fundamental differences in dental, cranial and postcranial anatomy in the two groups. The aim of this paper is to review the possible role of anthracotheres in the evolution of hippopotamids. It is concluded that they played no part in it, whereas palaeochoerids could well represent the ghost lineage that has evaded scientists for more than a century.

Postcranial anatomy of the extinct terrestrial slothSimomylodon uccasamamensis(Xenarthra, Mylodontidae) from the Pliocene of the Bolivian Altiplano, and its evolutionary implications

AbstractExtinct terrestrial sloths are common elements of the late Cenozoic South American fossil record. Among them, Mylodontinae species were particularly abundant in the Americas throughout the Pleistocene epoch, and their anatomy is relatively well known. In contrast, less information is available from the Neogene record and particularly from localities at low latitudes, with an additional and considerable bias in favour of craniodental rather than postcranial remains. In this contribution, we provide comparative descriptions of several postcranial bony elements ascribed toSimomylodon uccasamamensis, a moderate‐sized extinct mylodontine from the Andean Altiplano. This species was particularly abundant during latest Miocene – late Pliocene times in the high altitudes of the Andean Cordillera, and so far represents the best known mylodontine from the Neogene of South America. Its anatomy is compared with that of several extinct terrestrial sloths, with the aim of using the observed morphologies to elucidate taxonomy, phylogeny, and locomotion. From a morphofunctional perspective, the postcranium ofS. uccasamamensis is consistent with that of a terrestrial graviportal quadruped, with moderate climbing and digging capabilities.

A Basal Nonmammaliaform Cynodont from the Permian of Zambia and the Origins of Mammalian Endocranial and Postcranial Anatomy

ABSTRACT Nonmammaliaform cynodonts were a diverse group of Permo-Triassic synapsids whose morphological evolution documented the beginning of many classic mammalian traits. Here, we describe a new basal cynodont from the upper Permian Madumabisa Mudstone Formation of Zambia’s Luangwa Basin as Nshimbodon muchingaensis gen. et sp. nov. The holotype, a relatively complete and undistorted cranium and articulated mandible with associated postcranial elements, is interpreted as the most complete and well-preserved example of a charassognathid cynodont, and preserves hitherto unknown details of charassognathid endocranial and postcranial anatomy. A phylogenetic analysis of 111 morphological characters from 25 therapsid taxa (including 15 Permo-Triassic cynodonts) supports a sister-taxon relationship between Nshimbodon and Abdalodon, including them with Charassognathus in a monophyletic Charassognathidae, and placing the family near the base of Cynodontia. In addition to its phylogenetic importance, Nshimbodon provides evidence of correlated transformations in the feeding system, neck, and shoulder, which are consistent with novel mammal-like locomotor and feeding mechanics in the earliest cynodonts. Lastly, given previous reports of charassognathids in the Karoo Basin of South Africa, the occurrence of Nshimbodon indicates that charassognathids, like the basal cynodont Procynosuchus, were geographically widespread in southern Pangea by Lopingian times. Continued collecting in the Madumabisa Mudstone Formation will lead to a better understanding of the formation’s Permian cynodont diversity and biostratigraphy, as well as the biogeographic structure of southern Pangean vertebrate assemblages prior to the Permo-Triassic mass extinction. http://zoobank.org/urn:lsid:zoobank.org:pub:143CE9D3-5742-4E92-B48F-164685F0907C

Postcranial elements of small mammals as indicators of locomotion and habitat.

Many studies have shown a correlation between postcranial anatomy and locomotor behavior in mammals, but the postcrania of small mammals (<5 kg) is often considered to be uninformative of their mode of locomotion due to their more generalized overall anatomy. Such small body size was true of all mammals during the Mesozoic. Anatomical correlates of locomotor behavior are easier to determine in larger mammals, but useful information can be obtained from the smaller ones. Limb bone proportions (e.g., brachial index) can be useful locomotor indicators; but complete skeletons, or even complete long bones, are rare for Mesozoic mammals, although isolated articular surfaces are often preserved. Here we examine the correlation of the morphology of long bone joint anatomy (specifically articular surfaces) and locomotor behavior in extant small mammals and demonstrate that such anatomy may be useful for determining the locomotor mode of Mesozoic mammals, at least for the therian mammals.

Sexual dimorphism in skeletal shape in voles (Arvicolinae): disparate selection on male bodies and female heads

AbstractSexual dimorphism evolves as a response to different selective pressures on males and females. In mammals, sexual selection on traits that improve a male’s ability to compete for access to mates is a common cause of sexual dimorphism. In addition to body mass, adaptations in specific components of the musculoskeletal system that increase strength, stability, and agility, may improve male fighting performance. Here we test the hypotheses that males, when compared to females, are more specialized for physical competition in their skeletal anatomy and that the degree of this sexual dimorphism increases with the intensity of male–male competition. In three species of voles (Cricetidae: Arvicolinae: Microtus), we found partial support for these hypotheses. Male-biased sexual dimorphism in a set of functional indices associated with improved fighting performance was identified in the postcranial anatomy. This dimorphism was greatest in the polygynous Microtus californicus, absent in the monogamous M. ochrogaster, and intermediate in the promiscuous or socially flexible M. oeconomus. However, in the skull, we found results opposite to our predictions. Females had larger skulls relative to overall skeletal size than did males. This may be associated with selection for increased food processing efficiency, which should be highly important because of the compounding effects of increased caloric requirements during gestation and lactation, and the generally low-quality diet of voles. In addition, larger heads in females may be associated with selection for greater digging ability or for defending offspring. These results suggest disparate selective pressures on the postcranial skeletons and skulls of male and female voles.

Postcranial anatomy and histology of Seymouria, and the terrestriality of seymouriamorphs.

Seymouria is the best known of the seymouriamorphs, a group of Permo-Carboniferous reptiliomorphs with both terrestrial and aquatic taxa. The majority of research on Seymouria has focused on cranial anatomy, with few detailed descriptions or illustrations of the postcrania. We utilized neutron computed tomography (nCT) and histological sampling to provide updated, detailed figures that clarify details of the postcranial anatomy and to assess the development and histology of Seymouria through specimens from the early Permian Richards Spur locality. The correlation of morphological and histological data indicate rapid metamorphosis in this terrestrially capable stem amniote, with the youngest specimen being postmetamorphic despite being distinctly younger than premetamorphic individuals of Discosauriscus, the only other seymouriamorph to have been histologically sampled. The microanatomical data (e.g., semi-open medullary cavity) also substantiate the hypothesis that Seymouria was terrestrial based on interpretation of external features, although the persistence of a modestly developed medullary spongiosa in comparison to either Discosauriscus or to other co-occurring terrestrial tetrapods suggests additional nuances that require further exploration. In the absence of clearly recognizable postmetamorphic stages in several seymouriamorph taxa, it is difficult to determine the evolutionary trajectory of terrestriality within the clade. Our analysis provides the first histological characterization of the life history of Seymouria and highlights the need for further study of seymouriamorph ontogeny.

The upper limb of Paranthropus boisei from Ileret, Kenya

Paranthropus boisei was first described in 1959 based on fossils from the Olduvai Gorge and now includes many fossils from Ethiopia to Malawi. Knowledge about its postcranial anatomy has remained elusive because, until recently, no postcranial remains could be reliably attributed to this taxon. Here, we report the first associated hand and upper limb skeleton (KNM-ER 47000) of P. boisei from 1.51 to 1.53 Ma sediments at Ileret, Kenya. While the fossils show a combination of primitive and derived traits, the overall anatomy is characterized by primitive traits that resemble those found in Australopithecus, including an oblique scapular spine, relatively long and curved ulna, lack of third metacarpal styloid process, gracile thumb metacarpal, and curved manual phalanges. Very thick cortical bone throughout the upper limb shows that P. boisei had great upper limb strength, supporting hypotheses that this species spent time climbing trees, although probably to a lesser extent than earlier australopiths. Hand anatomy shows that P. boisei, like earlier australopiths, was capable of the manual dexterity needed to create and use stone tools, but lacked the robust thumb of Homo erectus, which arguably reflects adaptations to the intensification of precision grips and tool use. KNM-ER 47000 provides conclusive evidence that early Pleistocene hominins diverged in postcranial and craniodental anatomy, supporting hypotheses of competitive displacement among these contemporaneous hominins.

A redescription of the late Carboniferous trematopid Actiobates peabodyi from Garnett, Kansas.

Dissorophoids are a diverse clade of predominantly Permo-Carboniferous temnospondyls with a wide geographic distribution and broad ecological diversity. Each of the various dissorophoid clades first appears in the late Carboniferous, but their records are relatively sparse and fragmentary compared to those of the early Permian when dissorophoids reach their peak diversity and distribution, particularly in terrestrial environments where they are by far the most taxonomically diverse clade of non-amniote tetrapods. This provides an impetus for further study of the late Carboniferous terrestrial dissorophoids in order to contextualize the early stages in the clade's radiation into terrestrial ecosystems. Here we present a redescription of the late Carboniferous trematopid Actiobates peabodyi from Kansas, USA, which is represented by a nearly complete skeleton and which represents the earliest occurrence of trematopids in North America. Only the skull was previously described, and the taxon has been largely overlooked in the context of early terrestrial dissorophoid evolution. Here, we provide an updated cranial description, the first postcranial description, and a discussion of the position of A. peabodyi in the context of olsoniform evolution. Our most significant finding is the characterization of postcranial anatomy that is highly similar to that of later trematopid taxa. This high degree of conservatism indicates that the earliest trematopids were already well adapted for terrestrial environments, and post-Carboniferous radiations of olsoniforms may be attributed to an expansion of the dryland terrestrial environments in which these taxa already thrived, rather than to novel acquisition of adaptive features later in the clade's evolution.

Skeletal Anatomy of the Basicranium and Auditory Region in the Metacheiromyid Palaeanodont Metacheiromys (Mammalia, Pholidotamorpha) Based on High-Resolution CT Scans

Abstract Cranial skeletal material of the Eocene palaeanodont Metacheiromys marshi was examined using high-resolution CT scans. The present study represents the first time that CT scans have been conducted on skulls of this extinct fossorial mammal. The bony osteology of the auditory region is described in detail, including the ectotympanic and entotympanic, the petrosal in both tympanic and endocranial views, and the middle ear ossicles. The results of this investigation confirm a number of derived resemblances between palaeanodonts and xenarthrans, including a large entotympanic element in the medial wall of the auditory bulla, the presence of an anteroventral process of the tegmen tympani, and a posttemporal canal. However, the present study also provides novel derived auditory features linking palaeanodonts and pangolins, consistent with current understanding of palaeanodont phylogenetic relationships, including the absence of an ectotympanic styliform process, a posterolaterally oriented aperture to the cochlear fossula, and a convex mallear head / concave incudal head. Several autapomorphic features characterizing the auditory osteology of Metacheiromys are also noted. The presence of a large, spherical mallear head, and of a capacious tympanic cavity extended into sinuses in surrounding bones, likely represent adaptations for fossoriality, consistent with palaeobiological inferences drawn from the postcranial anatomy of Metacheiromys.

The postcranial anatomy of Endothiodon bathystoma (Anomodontia, Therapsida)

ABSTRACT Dicynodonts were herbivorous non-mammalian synapsids that were relatively abundant on the landmass of Pangea from the Mid Permian to Late Triassic. The dicynodont genus Endothiodon is well known from late Permian strata of the Karoo Basin of South Africa. It is characterised by replacement waves of internal tooth rows on the premaxilla and dentary; longitudinal ridges from the premaxilla to the pineal crest; and a pineal foramen on a prominent boss. Endothiodon is well-represented by cranial and postcranial material in various South African museum collections. Recently, an almost complete skeleton of Endothiodon (SAM-PK-K011271) was recovered from the uppermost Pristerognathus Assemblage Zone of the Karoo Supergroup. It comprises the skull and most postcranial elements preserved in articulation. The present study identifies SAM-PK-K011271 as E. bathystoma and we show that it is the second largest E. bathystoma specimen known to date. Furthermore, the well-preserved skeletal remains enable us to present the first comprehensive description of its postcranial anatomy. Abbreviations Institutional abbreviations: AM: Albany Museum, Grahamstown, South Africa; CGS: Council for Geosciences, Pretoria, South Africa; ESI: Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; ISI: Indian Statistical Institute, Kolkata, India; SAM: Iziko South African Museum, Cape Town, South Africa.Anatomical abbreviations: ang, angular; art, articular; ast, astragalus; br, M. brachialis; c, centrale; ca, calcaneum; cb, M. coracobrachialis; cbl, M. coracobrachialis longus; Cd, caudal vertebra; d, dentary; del, M. deltoideus; ent, entepidcondyle; ent f, entepicondylar foramen; f, frontal; fti, M. femorotibialis; H, height; ife, M. iliofemoralis; ifi, M. iliofibularis; it, M. incisura tibialis fossa; iti, M. iliotibialis; il, ilium; is, ischium; j, jugal; l, lacrimal; M., metacarpal; mf, mandibular fenestra; Mt., metatarsal; n, nasal; nc, neural canal; ns, neural spine; ol, olecranon; P., phalanx; pb, pineal boss; pec, M. pectoralis; pifi, M. puboischiofemoralis internus; piti, M. puboischiotibialis; pm, premaxilla; po, postorbital; poz, postzygapophyses; prz, prezygapophyses; pp, preparietal; psf, postspinal fossa; pu, pubis; q, quadrate; r con, radial condyle; ref. l, reflected lamina; S, sacral vertebra; sas, M. serratus anterior superficialis; sc, M. subcoracoideus; scs, M. subcoracoscapularis; sha, M. scapulohumeralis anterior; SL, skull length; spc, M. supracoracoideus; sq, squamosal; sup, supinator; SW, skull width; tha, M. triceps humeralis anterior; thm, M. triceps humeralis medialis; tp, transverse process; tri, M. triceps; W, width.

Appendicular skeleton of Protoceratops andrewsi (Dinosauria, Ornithischia): comparative morphology, ontogenetic changes, and the implications for non-ceratopsid ceratopsian locomotion.

Protoceratops andrewsi is a well-known ceratopsian dinosaur from the Djadokhta Formation (Upper Cretaceous, Mongolia). Since the 1920s, numerous skeletons of different ontogenetic stages from hatchlings to adults, including fully articulated specimens, have been discovered, but the postcranial anatomy of Protoceratops has not been studied in detail. A new, mostly articulated subadult individual provides an excellent opportunity for us to comprehensively describe the anatomy of the limb skeleton, to compare to other ceratopsian dinosaurs, and to study the ontogenetic and intraspecific variation in this species. New data provided by the specimen shed light on the lifestyle of P. andrewsi. The young subadult individuals present an array of morphological characters intermediate between the bipedal Psittacosaurus and fully quadrupedal adult P. andrewsi. We compare these observations with a broad range of non-ceratopsid Neoceratopsia (of various locomotor adaptations) and Psittacosauridae (obligate bipeds), which gives us insight into the evolution of the skeletal characters informative for the postural change in ceratopsian dinosaurs.

Reappraisal of the morphology and phylogenetic relationships of the alligatoroid crocodylian Diplocynodon hantoniensis from the late Eocene of the United Kingdom

AbstractDiplocynodon is a genus of basal alligatoroid comprising nine species, which spanned the late Palaeocene to middle Miocene of Europe. Despite recent revisions of most Diplocynodon species, one of the earliest named and most complete, Diplocynodon hantoniensis, has not been re-described for over 150 years. This species is known from the remains of numerous individuals from the Priabonian (late Eocene) Headon Hill Formation, which crops out at Hordle (Hordwell) Cliff in Hampshire, United Kingdom. Here we re-describe and diagnose Diplocynodon hantoniensis, providing the first detailed description of postcranial anatomy in Diplocynodon, and indeed any basal alligatoroid. Diplocynodon hantoniensis is diagnosed by four autapomorphies, including retention of the ectopterygoid–pterygoid flexure through ontogeny and a unique anterior process of the ectopterygoid adjacent to the posteriormost maxillary alveoli. A critical review of previously referred remains from elsewhere in Europe and the USA restricts Diplocynodon hantoniensis to the late Eocene of the UK. Through comparisons with extant crocodylians, the well-preserved postcranial skeleton enables the interpretation of numerous muscle attachments in the forelimbs and hindlimbs, providing a potentially rich source of character data for future phylogenetic analyses. Based on a comparison of humeral morphology between a large sample of crocodylian species, we outline two new morphological characters in the humerus. We include D. hantoniensis in a phylogenetic analysis, including all putative Diplocynodon species (103 taxa scored for 187 characters). We use four different character-weighting schemes: equal weighting, implied weighting (k value = 8) and extended implied weighting with k-values of 4 and 8. In general, these weighted analyses produce congruent results with the equal-weights analysis, and increase the resolution within Diplocynodon. We recover a monophyletic Diplocynodon in three of the four analyses. However, the fourth analysis, with the strongest downweighting of homoplastic characters and missing data (extended implied weighting with k = 4), recovers the Palaeocene Diplocynodon remensis outside Diplocynodon. Our comprehensive revision of one of the most completely known Diplocynodon species facilitates comparisons in the genus, as well as between other basal alligatoroids, and forms the basis for comparing postcranial anatomy in other fossil crocodylians.