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Osteology of the Reptiles
... Among Archosauria, the number of presacral vertebrae ranges between 21 and 26 (Romer, 1956), with basal Loricata (Nesbitt, 2011) not exceeding 25 presacral vertebrae. In addition to the specimen described in this article, only D. quartacolonia has been interpreted as possessing 25 presacrals, but at present, this remains unclear. ...
... According to the criteria defined by Romer (1956), UFRGS-PV-0629-T possesses 25 presacral vertebrae, divided anteroposteriorly into at least eight cervical, four "transitional" (see below) and 13 dorsal vertebrae ( Figures 5-9). The first six post-axial vertebrae (3-8), characterized by having the parapophysis in the vertebral centrum and the diapophysis in a ventrally directed transverse process, are here considered cervical elements. ...
... Vertebrae 9-12 have the parapophysis still positioned in the centrum (characteristic of a cervical vertebra), while the transverse process assumes a lateral position (characteristic of a truncal vertebra), so that they are at an intermediate stage between the two regions of the spine, being defined here, for description purposes, as the abovementioned "transitional vertebrae." The vertebrae here called "dorsals" (13-25) are defined as those that have the diapophysis and parapophysis positioned in a laterally projected transverse process, according to the definition of Romer (1956). ...
Prestosuchus chiniquensis is the best represented pseudosuchian archosaur from the Pinheiros-Chiniqu a Sequence, Middle-Late Triassic (Ladinian/Carnian) of the Santa Maria Supersequence, Southern Brazil. Several incomplete specimens attributed to this species have been described, but the morphology of the postcranial skeleton of P. chiniquensis is poorly known. In this contribution we present the postcranial material of the UFRGS-PV-0629-T specimen, concluding its description , as its skull and endocast have already been described. Additionally, histologi-cal data provided new information on the poorly known ontogenetic series of P. chiniquensis, and on its growth patterns suggesting a longer period of slow growth when compared to other basal Loricata species. A phylogenetic analysis placed UFRGS-PV-0629-T in a group composed by the lectotype, paralectotype, and other described P. chiniquensis specimens, further corroborating our taxo-nomic hypothesis, that specimens of basal Loricata collected in Brazil are closely related to each other. Due to the association of characters found in the phyloge-netic analysis, the specimen UFRGS-PV-0629-T is attributed as the most complete material ever found for P. chiniquensis. As such, it is clear that the material presented here provides important new information on P. chiniquensis. Based on the results presented here, we revised the diagnosis for P. chiniquensis. However, it also evidences the need for new discoveries and studies of other specimens seeking to understand this and other closely related species, which were important components of worldwide trophic webs of the Triassic biotas.
... It may have originated in the Late Devonian period and it is considered, at least partially, homologous to the sarcopterygian fish fins (Coates, 1994;Shubin et al., 2006;Hall, 2007;Boisvert et al., 2008;Nakamura et al., 2016;Cloutier et al., 2020). The skeleton of the manual autopod is regionalized and includes the carpals, metacarpals, and the series of phalanges that make up each finger (Romer, 1956;Hopson, 1995). The phalangeal formula (PF) has been used to characterize phalangeal organization for at least two centuries. ...
... The phalangeal formula (PF) has been used to characterize phalangeal organization for at least two centuries. This formula is a numerical expression that encodes a manus or foot skeletal configuration by indicating, sequentially from medially to laterally, the number of phalanges of each digit of the manus/pes of a tetrapod taxon (Romer, 1956). There exists a consensus that the Amniota and Lepidosauria manual plesiomorphic phalangeal formula (PPF) is 2-3-4-5-3 (Greer, 1991;Fedak & Hall 2004;Fontanarrosa et al., 2021aFontanarrosa et al., , 2024a. ...
The phalangeal formula (PF) describes the skeletal configuration of the digital regions of the autopodia. The plesiomorphic phalangeal formula (PPF) for the Lepidosauria manus is 2-3-4-5-3. Previous research identified 53 unique PFs in lepidosaurians. Here, we propose a new analytical method treating the PF as a matrix, applying image processing techniques to analyze new organizational patterns including symmetry. We quantified the degree of symmetry of the 53 lepidosaurian PFs through a symmetry score capturing the overlap between the original images and their transformed counterparts after specific geometric operations. We found that the PPF revealed a previously unnoticed diagonal axis of symmetry, a pattern highly improbable compared to thousands of randomly generated PFs. In a PCA of the 53 lepidosaurian PFs symmetry scores, PC1 was significantly correlated with the total number of phalanges whereas PC2 reflected the variability in phalangeal counts among different digits. The PCA effectively summarized the underlying variance of the symmetry scores data, elucidating a reduction trend in phalanx count (PC1) and the degree of diversity of PF arrangements (PC2). This approach is useful for addressing symmetry in meristic characters and systems of articulated pieces which could reveal hidden symmetry patterns in other lineages.
... Ungual phalanx I is the largest among terminal phalanges, characterized by a laterally compressed blade and a concave palmar facet, acquiring a curved appearance, as in extant archosaurs (Romer, 1956). Its lateral and medial surfaces have a longitudinal groove, consistent with the blood supply that fed a keratin covering. ...
... It is necessary to emphasize the level of uncertainty regarding the phalangeal formula not only of T. scutorectangularis but also in other notosuchians, which rarely have well-preserved autopods (Nascimento & Zaher, 2010;Sertich & Groenke, 2010;Turner 2006). Despite their conservative potential in tetrapod lineages, living crocodilians present relevant interspecific discrepancies in their phalangeal formulas, even when closely related, and there is not necessarily a direct relationship between the number of ossification centers during ontogeny and the fixed number of phalanges in maturity (Gregorovicǒvá et al., 2018;Romer, 1956;Vieira et al., 2016). Therefore, caution is needed when extrapolating a fixed number for notosuchians based on complete specimens, as it is not always possible to determine FIGURE 10. 3D segmentation of the right manus elements of Thilastikosuchus scutorectangularis, (FUP-Pv 000019). ...
Notosuchians comprise a clade of mostly terrestrial crocodyliforms generally found in Cretaceous Gondwanan deposits. They evolved into many forms and some species show convergences with mammalian features such as the development of a high degree of heterodonty and multicuspid teeth. South American deposits concentrate the highest number of described notosuchian species, which is more than twice the number of taxa known from strata elsewhere. Here, a novel candidodontid notosuchian, Thilastikosuchus scutorectangularis, gen. et sp. nov., is presented and described, comprising a new monospecific genus and the oldest notosuchian record found in Brazil, and likely from South America. This new taxon lacks the sharp hypertrophied caniniform teeth of closely related forms, such as Malawisuchus and Pakasuchus, but shares the posterior molariform teeth with increasingly wider crowns and denticulated cingula. Additionally, the phylogenetic analysis with the inclusion of the new Brazilian material places Candidodontidae as the earliest notosuchian radiation, shedding new light into its origins.
... Ungual phalanx I is the largest among terminal phalanges, characterized by a laterally compressed blade and a concave palmar facet, acquiring a curved appearance, as in extant archosaurs (Romer, 1956). Its lateral and medial surfaces have a longitudinal groove, consistent with the blood supply that fed a keratin covering. ...
... It is necessary to emphasize the level of uncertainty regarding the phalangeal formula not only of T. scutorectangularis but also in other notosuchians, which rarely have well-preserved autopods (Nascimento & Zaher, 2010;Sertich & Groenke, 2010;Turner 2006). Despite their conservative potential in tetrapod lineages, living crocodilians present relevant interspecific discrepancies in their phalangeal formulas, even when closely related, and there is not necessarily a direct relationship between the number of ossification centers during ontogeny and the fixed number of phalanges in maturity (Gregorovicǒvá et al., 2018;Romer, 1956;Vieira et al., 2016). Therefore, caution is needed when extrapolating a fixed number for notosuchians based on complete specimens, as it is not always possible to determine FIGURE 10. 3D segmentation of the right manus elements of Thilastikosuchus scutorectangularis, (FUP-Pv 000019). ...
... However, Piñeiro et al. (2021) considered the diagnostic features between mesosaur taxa fragile and opted to synonymize the genera into a single taxon: Mesosaurus tenuidens. It is noteworthy that Romer (1966) had previously regarded Stereosternum as synonymous with Mesosaurus. The monospecific hypothesis was most recently supported by Verrière and Fröbisch (2022) who did not find significant morphometric differences to justify separate taxa according to traditional taxonomy. ...
... Within the inner region, resorption cavities, primary osteons, and simple vascular canals predominate 3,4). The centra, rectangular in the parasagittal section, house a long notochordal canal that widens at the ends, resembling the characteristic funnel-shaped centra seen in early amniotes (Romer, 1966;Wintrich et al., 2020;Figure 4d). We did not find open neurocentral sutures, suggesting that specimens are skeletally mature (Griffin et al., 2021). ...
Osteohistological evidence is widely used to infer paleobiological traits of fossil vertebrates, such as ontogeny and growth rates. Mesosaurs, an enigmatic group of aquatic reptiles from the early Permian, are the most well‐known Paleozoic amniotes from Africa and South America. Their fossils are abundant in South America, ranging from the central‐west region of Brazil to the southernmost areas, as well as parts of Paraguay and Uruguay. In this contribution, we examined the bone microstructure of Mesosaurus tenuidens by analyzing thin sections of axial and appendicular elements of several specimens collected from various Brazilian sites. The microstructure of the bones showed minimal histological variability among elements, predominantly composed of parallel‐fibered tissues, indicating slow growth rhythm, along with increased bone density attributed to pachyosteosclerosis. The cortical area consists of poorly vascularized parallel‐fibered bone tissue, which was interrupted by multiple cyclical growth marks, some of them being supernumerary, suggesting a strong influence of seasonality. Moreover, the organization of growth marks suggests distinct life history trajectories among individuals collected from different outcrops, reflecting environmental heterogeneity throughout the basin. Internally, the endosteal domain exhibits greater vascularization compared to the cortices and frequently contained calcified cartilage. In the ontogenetic series, there was a progressive filling of the medullary region from small to large individuals. The presence of the External Fundamental System (a proxy indicating somatic maturity) was observed in femora and ribs, suggesting that determinate growth was already occurring in Permian mesosaurs and may not be an exclusive specialization of crown amniotes.
... As vertebrates transitioned onto land, the relative size of the cleithrum in the pectoral girdle began to decrease and eventually disappeared independently in multiple lineages leading to extant tetrapods 1,4,5 . Consequently, except for some anuran amphibians 6,7 and possibly turtles 8 , no extant tetrapods form the cleithrum, and enlarged endoskeletal elements are instead the dominant component of the pectoral girdle in tetrapods 9 . In contrast to these accumulating anatomical descriptions, the embryonic changes responsible for the evolutionary loss of the cleithrum and expansion of the endoskeleton remain elusive. ...
... Early Synapsida and Sauropsida, such as Edaphosaurus (stem Synapsida) and Procolophonoidea (stem Sauropsida), retained the cleithrum even in their entirely terrestrial habitats 80,81 . However, along with increases in the cervical vertebral number and extension of the neck 82,83 , their crown-groups, including all extant amniotes, completely lost the cleithrum 6,9 . In extant amniotes, the long neck integrates cells from a specialized trunk LPM region, namely the neck LPM 84 , which is located between the head/trunk interface and forelimb bud (Supplementary Fig. 7b, c). ...
The morphological transformation of the pectoral/shoulder girdle is fundamental to the water-to-land transition in vertebrate evolution. Although previous studies have resolved the embryonic origins of tetrapod shoulder girdles, those of fish pectoral girdles remain uncharacterized, creating a gap in the understanding of girdle transformation mechanisms from fish to tetrapods. Here, we identify the embryonic origins of the zebrafish pectoral girdle, including the cleithrum as an ancestral girdle element lost in extant tetrapods. Our combinatorial approach of photoconversion and genetic lineage tracing demonstrates that cleithrum development combines four adjoining embryonic populations. A comparison of these pectoral girdle progenitors with extinct and extant vertebrates highlights that cleithrum loss, indispensable for neck evolution, is associated with the disappearance of its unique developmental environment at the head/trunk interface. Overall, our study establishes an embryological framework for pectoral/shoulder girdle formation and provides evolutionary trajectories from their origin in water to diversification on land.
... The brain (Fig. 16) is housed in the braincase or endocranial cavity of the skull. The outer surface of the brain is rather smooth and covered by external membranes called meninges, while internally the brain has fluid-filled ventricles (Romer 1956). The brain can be divided into three major sections: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). ...
... Numerous nerves are present on the spinal cord that innervate the postcranium, with each spinal nerve branching off into a dorsal and ventral ramus, innervating the epaxial and hypaxial regions, respectively. The complex network of nerves (termed a plexus) that innervate the forelimbs is the brachial plexus, and the network innervating the hind limbs and tail is the lumbosacral plexus (Romer 1956;Chiasson 1962;Richardson et al. 2002). ...
... However, the opposite is observed, with most species under this term being from the Cretaceous, including some from its final stage, the Maastrichtian (Table 1). Historically many of these Cretaceous taxa have been grouped into Hypsilophodontidae (Kuhn, 1964(Kuhn, , 1966Milner & Norman, 1984;Nopcsa, 1901;Romer, 1927Romer, , 1956Sereno, 1986;Sternberg, 1940;Thulborn, 1974;Weishampel & Heinrich, 1992;Zittel & Broili, 1923) which has more recently been considered a paraphyletic assemblage of basal ornithischians (Boyd, 2015;Butler et al., 2008;Han et al., 2018). With some 'hypsilophodontids' surviving until the end of the Mesozoic, it suggests their lineages had a rich and long evolutionary history comparable to members of the major subclades that are considered derived (e.g. ...
... All characters were reworded if necessary to avoid the same anatomical structure being referred to in different terms (e.g. 'antorbital fossa' vs 'external antorbital fenestra' vs 'internal antorbital fenestra' vs 'antorbital fenestra') and to standardize characters to follow Romerian anatomical terms (Romer, 1956;Wilson, 2006). ...
... Lastly, CT was obtained using a LightSpeed VCT scanner (GE Medical Systems) with a slice thickness of 0.6 mm and a dose of 120 kVp. The bone data was recorded from the images available in dedicated manuals (Reese, 1915;Higgins, 1923;Romer, 1976). ...
... Crown-group crocodilians share the same number of precaudal vertebrae: nine cervical, fifteen dorsal, two sacral vertebrae, and a slightly variable number of caudal vertebrae, which should generally be around 37 (Reese, 1915;Higgins, 1923;Romer, 1976;De Cupere et al., 2023). Therefore, Part I of the mummy (head and neck) is missing cervical vertebrae 7-9, and Part II of the crocodile (trunk) lacks thoracic vertebrae 1-4. ...
Remnants of what was believed to be a single baby crocodile, originating from ancient Egypt and curated in the National Museum of Lithuania, have been recently assessed using noninvasive and nondestructive techniques. These had been donated in 1862 to the then Museum of Antiquities by the prominent Polish-Lithuanian collector Count Michał Tyszkiewicz. After careful investigation of the three mummified reptile fragments available, the authors were able to identify at least two individuals based on morpho-anatomical characteristics. This indicates that the two small crocodiles originally described in historic records are still present within the collection and that none of these items was lost during the different lootings perpetrated throughout the museum’s history. Information regarding the post-mortem treatment of these animals was also obtained. This is the first scientific study of animal mummies in the Baltic States, and it should be followed by proper conservation and display of these findings.
... Out of eight cervical vertebrae, only two right side ribs have been preserved, whereas the dorsal series is mostly complete and semi-articulated, excluding the terminal lumbar vertebrae, which lack ribs. The cervical ribs have the recurrent plow-shaped form observed in other archosaurs (Romer, 1956), with an anteroposteriorly stretched shaft orthogonal to bifurcating articular processes. The tuberculum is more dorsally positioned than the capitulum, both being of similar length and roughly aligned. ...
... Anterolaterally, the proximal portion of the shaft bears an undeveloped anterior flange (af), where longitudinal muscle scars for the anterior extension of M. pubioischiofemoralis would attach (pifi 1). Although mostly straight, the diaphysis is also slightly anteriorly curved, generating a concave posterior surface and an anterior convex one, but substantially less so than the more sigmoidal eusuchian condition (Romer, 1956). ...
Baurusuchidae comprises a clade of top‐tier terrestrial predators and are among the most abundant crocodyliforms found in the Adamantina Formation, Bauru Basin, Brazil (Campanian‐Maastrichtian). Here, we provide a detailed description of the cranial and postcranial osteology and myology of the most complete juvenile baurusuchid found to date. Although the preservation of juvenile individuals is somewhat rare, previously reported occurrences of baurusuchid egg clutches, a yearling individual, and larger, but skeletally immature specimens, comprise a unique opportunity to track anatomical changes throughout their ontogenetic series. Its cranial anatomy was resolved with the aid of a three‐dimensional model generated by the acquisition of computed tomography data, and its inferred adductor mandibular musculature was compared to that of mature specimens in order to assess possible ontogenetic shifts. A subsequent phylogenetic analysis included the scoring of Gondwanasuchus scabrosus, the smallest baurusuchid species known to date, to evaluate its phylogenetic relations relative to a known juvenile. We find considerable differences between juveniles and adults concerning skull ornamentation and muscle development, which might indicate ontogenetic niche partitioning, and also anatomical and phylogenetic evidence that G. scabrosus corresponds to a young semaphoront lacking mature cranial features.
... Although the adult eutyrannosaurian endocast tends to lack neuroanatomical detail (Hopson 1979;Witmer and Ridgely 2009), it still approximates the overall shape of the brain (Romer 1956;Jerison 1973;Hopson 1979;Balanoff et al. 2010) and thus allows an ontogenetic assessment of overall brain shape. In Gorgosaurus, both juvenile and adult individuals have a moderately elongate endocast with an anteroposteriorly short hindbrain and steeply angled pontine flexure. ...
Over the past two decades, increased accessibility to computed tomography (CT) scanners has greatly facilitated documentation of the endocranium in numerous extinct theropod taxa. However, most of these studies have focused on the morphology of mature individuals, thus changes or variation through ontogeny of the endocranium in theropods remains largely unknown. The current study sheds light on the endocranial anatomy of the eutyrannosaurian tyrannosauroid, Gorgosaurus libratus , in both an ontogenetic and evolutionary context. Based on CT scans of six Gorgosaurus braincases, including those of two recently discovered juvenile individuals, we virtually reconstruct and describe the endocranial morphology for a growth series of G. libratus . Despite considerable changes in skull architecture, relatively few ontogenetic changes occurred in the endocranium of Gorgosaurus . These changes include a subtle increase in the length of the hindbrain region of the endocast and increased inflation of the tympanic sinus diverticula in adults relative to juveniles. Among the most significant ontogenetic changes is a decrease in the distinctiveness of the brain morphology in endocasts as Gorgosaurus mature. The endocasts of juvenile Gorgosaurus exhibit better defined cerebral hemispheres, optic lobes, and cerebella than those of larger and more mature individuals. This suggests a closer correspondence between the endocast and the brain in juvenile tyrannosaurids, indicating the endocast of juvenile individuals provides a more accurate representation of the structure of the brain and its regions relative to the endocast of more mature individuals. The brain of Gorgosaurus displays a mix of basal archosaurian traits and more derived coelurosaurian traits. More primitive archosaurian features of the Gorgosaurus brain include large olfactory bulbs and tracts, a posteroventrally oriented long axis of the cerebrum, and posteriorly positioned optic lobes, whereas derived features include prominent hindbrain flexure, a somewhat enlarged cerebrum, and a cerebellum that at least partially separates the left and right optic lobes. An understanding of the evolutionary acquisition of such derived features leading to the avian brain may be further elucidated via the study of the endocasts of juvenile individuals (more reflective of the structure/organization of various brain regions) of earlier‐diverging theropods (e.g., Allosauroidea, Megalosauroidea, and Coelophysoidea).
... It is tempting to speculate that the latter decision was based on the earlier referral of D. altus (which is clearly an iguanodontian) to Laosaurus. Romer (1933) listed Nanosaurus and Laosaurus as members of Iguanodontidae, perhaps following Williston (1925), but later referred both to Hypsilophodontidae (Romer 1956(Romer , 1966. Kuhn (1936) listed the three Morrison Formation species of Laosaurus as valid, and in Hypsilophodontidae, but did not include Nanosaurus in his catalog, which might have been an oversight or because he considered it invalid. ...
... The name originated with Karl Alfred von Zittel who coined it to group together Aetosaurus, Typothorax, and Dyoplax. Later authors removed aetosaurs from the group, but made it a suborder of Thecodontia containing animals like Ornithosuchus (e.g., Romer 1956). With the use of phy-logenetics in paleontology, Pseudosuchia became the group containing all archosaurs more closely related to crocodilians than to birds (Gauthier 1986). ...
... The nomenclature of the vertebral laminae follows Wilson (1999) and of the vertebral fossae follows Wilson et al. (2011). We use Romerian terminology (Wilson & Mohabey, 2006), which divides the body into anterior, posterior, ventral, and dorsal portions (Romer, 1956). Nomenclature for internal pneumatic structures follows Britt (1993), Wedel et al. (2000) and O'Connor (2006 ...
Saltasaurines are titanosaur sauropods that lived in South America during the Late Cretaceous. Within this
clade, Neuquensaurus australis is a taxon discovered at Patagonia (Argentina) and has been reported since
the late 19th century. In recent years, new materials (axial and appendicular) have been found, including the
atlas and axis. The aims of this study are to describe the anatomy of the atlas and axis of Neuquensaurus
australis, and compare their anatomy with others titanosaurs in which these elements are known, expanding
the anatomical and palaeobiological knowledge of this taxon. Regarding the anatomy of the atlas, the
intercentrum is U-shaped, similar to Rapetosaurus and Quetecsaurus, and also has a subrectangular process at
the proximal end of the intercentrum, a feature that is absent in the other taxa, so it could be an
autapomorphy of Neuquensaurus. The neurapophyses are ‘D’ shaped, another possible autapomorphy,
since it is only present in Neuquensaurus. Regarding the axis, it presents short vertebral centrum and globose
neural arches. Regarding internal anatomy, the absence of pneumaticity in the atlas, combined with the
presence of a developed pneumatization in the axis, suggests that this is the point where pneumatization of
the axial postcranium begins, at least in Neuquensaurus.
... Apart from mentions in publications about classic general osteology of reptiles, like those from Camp (1923) and Romer (1956), very little attention has been devoted to the osteological variations in the Lacertidae for taxonomic purposes. Most of the classical works on the subject are nearly a century old. ...
A total of 230 cleared and alizarin stained and 136 radiographed specimens of Darevskia belonging to 47 nominal taxa (species, subspecies or singular clades) including the seven parthenogenetic ones and a triploid hybrid were studied.
Sixteen osteological characters in all the tried species were analyzed. These characters by corporal regions were: skull characters: 1.—number of premaxillary teeth; 2.—number of maxillary teeth; 3.—number of dentary teeth; 4.—teeth morphology; 5.—presence of anterolateral process in the postfrontal bone; 6.—presence of anteromedial process in the postorbital bone; 7.—comparative lengths of the postorbital and postfrontal bones; 8.—overlap degree between the postorbital and the squamosal bones. Postcranial characters: 9.—existence of visible (ossified) ribs associated with the third presacral vertebrae; 10.—sternal/xiphisternal costal formula and presence of inscriptional ribs; 11.—number of presacral vertebrae; 12.—number of posterior dorsal vertebrae (short presacral ribs); 13.—presence and form of the sternal fontanelle; 14.—form of the clavicles (emarginated or marginated); 15.—interclavicle form; 16.—morphology of first autotomic vertebrae of the tail.
Our goals were to characterize osteologically the different species of Darevskia, to contrast their relationships traced from osteological traits with the available genetic-derived phylogenies of the group, to compare the osteological characteristics of the parthenogenetic species with their bisexual parental species, and to comment on their parentage and character polarity. Finally, we aimed to search for osteological characteristics of the different groups within Darevskia, diagnosing them for the first time. The results, commented on by characters, are available in the main text, and taxa characteristics are easily consultable and condensed in Table 1.
Osteological characteristics of Darevskia, together with available phylogenetic trees, have permitted us to define some new groups within Darevskia (raddei, chlorogaster, defilippi, and parvula new groups) (Appendix 3), which are reciprocally monophyletic and have diagnostic characteristics. All of them are diagnosed and named as subgenera to be used if necessary, instead of the partial, old and not always comprehensive groups.
... Despite the accumulation of information on snake cranial osteology and all the advancements these data have provided, a significant portion of descriptive studies has focused solely on a few cranial elements (e.g., Stickel 1951;Romer 1956;Underwood 1967aUnderwood , 1967bDowling and Duellman 1978;Cundall 1983;Cundall and Rossman 1984) and/or illustrations, particularly hand-drawn plates, often lacking associated descriptions (e.g., Duméril, Bibron, and Duméril 1854;Jan and Sordelli 1876;Boulenger 1894). In recent years, descriptions have become increasingly detailed, especially with the popularization of computed tomography (CT) scans. ...
Although numerous studies have addressed some aspects of the cranial osteology of Nearctic dipsadid species, only the species within the genera Heterodon and Carphophis have a formal published description of their skull. Similarly, vertebral data on such species are extremely scarce, and most of the available literature is focused on fossils. Such group has a complex phylogenetic history, being recovered as monophyletic or nonmonophyletic depending on the approach. In this paper, we provide detailed and comparative descriptions of the osteology of dipsadid species distributed in the Nearctic region based on 69 specimens of dry material and high-resolution computed tomography (CT) scans. Additionally, we explore the morphological variation of the skull and cervical vertebrae within the context of distinct phylogenetic hypotheses previously proposed. Only two suprageneric groups previously proposed shared exclusive morphological traits: (Carphophis amoenus + Contia tenuis), proposed by three studies, and (Diadophis punctatus (Ca. amoenus + Co. tenuis)), proposed by one study. Large and detailed studies on the skull, mandible, and vertebrae represent an important step toward the understanding of the evolution of species, especially when they also show intraspecific variation.
... There is no suborbital opening (Fig. 12), a feature present in seymouriamorphs (e.g. Seymouria; Klembara et al. 2005), captorhinids (Heaton 1979) and most reptiles (Romer 1956). ...
Recumbirostra is a clade of heavily modified, superficially lizard‐like tetrapods that were originally interpreted as ‘microsaurian lepospondyls’ unrelated to the amniote crown. However, recent work has placed Recumbirostra within Reptilia, based on many similarities between the braincase and postcranium of recumbirostrans with early reptiles. Here, the early Permian hapsidopareiid recumbirostran Hapsidopareion lepton is re‐described using high‐resolution μCT data of three individuals across distinct ontogenetic stages, including the holotype specimen. These data reveal a suite of similarities with the hapsidopareiid Llistrofus pricei , suggesting that the latter is a subjective junior synonym of Hapsidopareion lepton . Furthermore, we highlight derived features present in Recumbirostra and Amniota that are otherwise absent in early reptiliomorphs, including: a single supraoccipital element that contributes to the endosseous labyrinths, the absence of paired endolymphatic fossae, and the presence of a distinct ampullary fossa between the semicircular canals. We also identify plesiomorphies of the braincase and skull roof of Hapsidopareion that are present in recumbirostrans and early stem‐amniotes but lacking in unambiguous crown amniotes. This suggests that features previously uniting recumbirostrans with reptiles are possible symplesiomorphies of Amniota, and a new phylogenetic analysis places Recumbirostra as a crownward group along the amniote stem, more derived than traditionally recognized reptiliomorphs such as Seymouria . Our findings highlight the need for further anatomical and descriptive studies of both stem‐ and crown‐group amniotes, and specifically the need for further revisions to those taxa originally regarded as ‘microsaurs’.
... The limb is covered in scales, each containing small dermal ossicles (osteoderms) beneath them [19,20], which range in color from beige to dark brown. These scales form characteristic keratinized ridges. ...
The Komodo dragon (Varanus komodoensis) is the largest extant lizard and is classified as an endangered species. Despite its rarity, anatomical studies on this species remain limited, hindering a comprehensive understanding of its biology and evolutionary traits. This research presents a detailed anatomical and histological examination of the pelvic limb of a female Komodo dragon, providing valuable insights into the musculoskeletal system of this species. A series of measurements and observations were made on the bones of the pelvic limb, including the femur, tibia, fibula, and pes, all of which are essential for supporting the animal’s large body size and facilitating its predatory behavior. This study also highlights the diverse muscle architecture, where large muscle masses are associated with the femoral retractors and ankle plantarflexors. Histological analysis of the muscle fibers revealed significant variability in fiber diameters, supporting the functional adaptation of the Komodo dragon’s limbs for high-speed ambush predation. This research provides important morphological data that could inform clinical practices, including orthopedic procedures and physiotherapy for Komodo dragons in zoological settings. Additionally, these findings shed light on the evolutionary patterns inherited from the species’ ancestors, which contributed to the development of its distinctive biological adaptations.
... The skin of the Komodo dragon is mostly covered with scales, which often co-occur with ODs, while each OD is almost always accompanied by a scale. Osteoderms, as part of the tetrapod integumentary skeleton (Vickaryous and Sire 2009), are defined as a structural category of mineralized organs embedded in the dermis (Camp 1923;Romer 1956;Francillon-Vieillot et al. 1990). Osteoderms are sometimes described as a type of scute-a term used to describe any keratinized, keratinous or bony element found in the skin (Main et al. 2005). ...
The skin of the Komodo dragon ( Varanus komodoensis ) is covered by a form of armour formed mainly of scales, which often co‐occur with osteoderms. Scales are keratinized, non‐mineralized structures in the uppermost layer of the epidermis that are in contact with each other to form a system in which individual scales are isolated from each other by a softer skin fold zone. In the Varanus , the surface of the scales is flat and smooth (thoracic limb, abdomen, and tail areas), domed and smooth (head area) or domed with conical ornamentation (dorsal surface, pelvic limb—dorsal surface areas). In contrast, osteoderms are mineralized structures that are an integral part of the skin, located below the epidermal surface and positioned parallel (head, tail, thoracic limb‐dorsal surface, thoracic limb‐palmar surface, and tail) or obliquely (pelvic limb‐dorsal surface, groin, abdomen) to the surface. Regardless of the body region, osteoderms are structures that are completely anchored in the dermis, and their surface is smooth and devoid of ornamentation. Tangential sections of the osteoderms demonstrate concentric resting lines. Histological sections of the varanid dermis show the presence of collagen bundles, parallel interlacing or crossing bundles of collagen fibers of varying thickness and degree of compactness, accompanied by muscle fibers. In the area of skin close to the osteoderm, loosely arranged bundles of collagen fibers are present, while in the zone distal to the osteoderm, a compact arrangement of these fibers is present. This study documents the morphological diversity and distribution of osteoderms and scales in selected areas of the body of V. komodoensis . Scales are characterized by a high polymorphism related to body region, while osteoderms show a high morphological similarity independent of the area of occurrence.
... FC-DPV 3622 also preserves a highly deformed pre-orbital area, extending no further anteriorly than the level of the anterior margin of the naris. The morphology and anatomical arrangement of the preserved bones matches the configuration previously described for the mesosaur skull [19,21,25,34,[51][52][53][54][55][56][57] (Figures 1 and 2). ...
Mesosaurs have long been considered to be small to mid-sized aquatic to semiaquatic amniotes that lived in Gondwana during the Early Permian or Late Carboniferous, according to recent research that showed their ghost range extending back to the Pennsylvanian. Previous morphometric analyses based on several hundred mesosaur specimens, including materials from Uruguay, Brazil, South Africa, Namibia, and the Paris National History Museum, provided a comprehensive understanding of mesosaur ontogeny, documented from fetus to adults. As a result, it was possible to determine the approximate size of any individual, measuring just one isolated limb bone, vertebrae, or even cranial elements. Herein, we describe large, poorly preserved and incomplete skulls, as well as axial and appendicular bones, from the Mangrullo Formation Konservat-Lagerstätte of Uruguay that suggest the existence of gigantism in mature mesosaurs reaching more than twice the size of previously described adults and type specimens. The sporadic occurrence of these giant individuals contrasts sharply with the abundant remains of young mesosaurs and, in general, with what is commonly found in the fossil record of vertebrates. The poor preservation of the mature individuals and their presence in coastal areas of the basin is consistent with the hypothesis that older mesosaurs have spent more time near the coast. An alternative hypothesis suggesting pelagic lifestyles is less supported by the available data. Given the preservation of unborn and hatchlings, as well as early juvenile, mature and very mature individuals, the mesosaur record is considered exceptional among early amniotes.
... Carrier (1987) identified five important characteristics involved in an efficient ventilation. Among them, three are possessed by extant crocodilians: they present (1) a diaphragmatic muscle analogous to the mammalian one (Farmer & Carrier, 2000;Gans & Clark, 1976), allowing crocodilians to breathe while running (Carrier, 1987); (2) large vertebral transverse processes (Romer, 1968), supporting epaxial musculature involved in locomotion (Gatesy, 1990) and, therefore, unloading the thorax which can entirely be dedicated to breathe; and (3) are capable of displaying an upright stance, which facilitates breathing during locomotion, but cannot sustain it permanently and can use bounding movement (Carrier, 1987;Seymour et al., 2004). However, they lack the other features identified by Carrier (1987): the lateral stability of the vertebral column and the bipedality. ...
Pseudosuchia, one of the two main clades of Archosauria, is today only represented by some 20 extant species, the crocodilians, representing only a fraction of its extinct diversity. Extant crocodilians are ectotherms but present morphological and anatomical features usually associated with endothermy. In 2004, it was proposed that pseudosuchians were ancestrally endothermic and the features observed in extant crocodilians are the remains of this lost legacy. This contribution has two parts: the first part covers 20 years of studies on this subject, first exploring the evidence for a loss of endothermy in extant crocodilians, before covering the variety of proxies used to infer the thermophymetabolic regime of extinct pseudosuchians. In the second part, the quantitative results of these previous studies are integrated into a comprehensive ancestral state reconstruction to discuss a potential scenario for the evolution of thermometabolism. Pseudosuchian endothermy would then have been lost close to the node Crocodylomorpha. The end‐Triassic mass extinction is proposed to have played the role of a filter, leading to the extinction of endothermic pseudosuchians and the survival of ectothermic ones. This difference in survival in Pseudosuchia is compared to those of dinosaurs, and difference in their metabolism is also considered. Pseudosuchian endothermy might have been of a different level than the dinosaurian one and more studies are expected to clarify this question.
... The phylogenetic dataset is available in Appendices S1 and S2. PARAREPTILIA Olson, 1947sensu Laurin & Reisz (1995 PROCOLOPHONOIDEA Romer, 1956PROCOLOPHONIDAE Seeley, 1888LEPTOPLEURONINAE Ivakhnenko, 1979 Genus Threordatoth nov. ...
Fissure fill deposits from the Late Triassic to Early Jurassic of England and Wales preserve a diverse small tetrapod fauna including procolophonids, an important group of Permian and Triassic parareptiles that radiated across Pangaea following the end‐Permian extinction event. Procolophonids are currently known from two fissure fill sites: incomplete and isolated remains from Ruthin Quarry (Wales) and type and referred material of Hwiccewyrm trispiculum from Cromhall Quarry (southwest England). The age of the Cromhall fissure deposits has been debated but recent radiometric dating suggests a Carnian age for at least some of the fossil assemblages. Here, we present material from several fissure assemblages at Cromhall, which are interpreted as stratigraphically older than the assemblage that yielded Hwiccewyrm . We describe a new species of leptopleuronine procolophonid based on partial remains with unique tooth morphology. Threordatoth chasmatos gen. et sp. nov. is characterized by maxillae with a reduced number of complex tricuspid teeth along with dentaries that bear labiolingually compressed monocuspid teeth and in some cases have a peculiar edentulous tip. These distinct tooth morphologies occlude closely, perhaps facilitated by a flexible dentary symphyseal connection. This unique combination of characters may suggest a high degree of oral food processing of a mode unlike other procolophonids, occurring among the broader leptopleuronine adaptation towards diets of high‐fibre herbivory/omnivory and insectivory. Phylogenetic analysis places the remains of Threordatoth as a derived leptopleuronine, sister taxon to Hwiccewyrm , in a clade with taxa including Soturnia , Hypsognathus , Libognathus and two unnamed leptopleuronines from the southwest USA.
... In addition, the large specimen of the SC-4 site displays some cervical ribs fused to their corresponding vertebrae (Figure 4). Co-ossification between adjacent non-sacral vertebrae and between these vertebrae and their corresponding ribs have been less documented than in the case of the sacral vertebrae for ornithopods and many other reptiles (e.g., [83,[89][90][91][92]). Despite this, costovertebral fusion has been observed in the fully mature holotype of "Delapparentia" (in cervical vertebrae, pers. ...
Styracosternan ornithopods are plenty abundant in the Lower Cretaceous fossil record of Europe. In particular, Iguanodon, the second genus of dinosaurs described worldwide, has been found in UK, Belgium, France, Germany, and Spain, evidencing a wide geographical distribution. Currently, the genus Iguanodon comprises two species, the type species I. bernissartensis from the late Barremian–Aptian of Europe and I. galvensis from the early Barremian of Teruel, Spain. The latter species is well known mainly from perinate and juvenile specimens. Here, axial and appendicular fossils of an adult, large and massively constructed ornithopod from the lower Barremian (Lower Cretaceous) Camarillas Formation of Galve (province of Teruel, Spain) are described. Fossil dimensions and some osteological evidence reveal that the specimen was a large (roughly 10 m long) ornithopod. An autapomorphic feature in the ischium and other characters allow us to ascribe this specimen to I. galvensis. In addition, postcranial co-ossification and fusion of the neurocentral suture indicate that the specimen was skeletally mature. Part of the material studied here was unknown in adults of I. galvensis, providing a better knowledge of the axial and appendicular region of this species.
... Apart from mentions in publications about classic general osteology of reptiles, like those from Camp (1923) and Romer (1956), very little attention has been devoted to the osteological variations in the Lacertidae for taxonomic purposes. Most of the classical works on the subject are nearly a century old. ...
A total of 230 cleared and alizarin stained and 136 radiographed specimens of Darevskia belonging to 47 nominal taxa (species, subspecies or singular clades) including the seven parthenogenetic ones and a triploid hybrid were studied. Sixteen osteological characters in all the tried species were analyzed. These characters by corporal regions were: skull characters: 1.—number of premaxillary teeth; 2.—number of maxillary teeth; 3.—number of dentary teeth; 4.—teeth morphology; 5.—presence of anterolateral process in the postfrontal bone; 6.—presence of anteromedial process in the postorbital bone; 7.—comparative lengths of the postorbital and postfrontal bones; 8.—overlap degree between the postorbital and the squamosal bones. Postcranial characters: 9.—existence of visible (ossified) ribs associated with the third presacral vertebrae; 10.—sternal/xiphisternal costal formula and presence of inscriptional ribs; 11.—number of presacral vertebrae; 12.—number of posterior dorsal vertebrae (short presacral ribs); 13.—presence and form of the sternal fontanelle; 14.—form of the clavicles (emarginated or marginated); 15.—interclavicle form; 16.—morphology of first autotomic vertebrae of the tail. Our goals were to characterize osteologically the different species of Darevskia, to contrast their relationships traced from osteological traits with the available genetic-derived phylogenies of the group, to compare the osteological characteristics of the parthenogenetic species with their bisexual parental species, and to comment on their parentage and character polarity. Finally, we aimed to search for osteological characteristics of the different groups within Darevskia, diagnosing them for the first time. The results, commented on by characters, are available in the main text, and taxa characteristics are easily consultable and condensed in Table 1. Osteological characteristics of Darevskia, together with available phylogenetic trees, have permitted us to define some new groups within Darevskia (raddei, chlorogaster, defilippi, and parvula new groups) (Appendix 3), which are reciprocally monophyletic and have diagnostic characteristics. All of them are diagnosed and named as subgenera to be used if necessary, instead of the partial, old and not always comprehensive groups.
... Historically and more recently, previous authors have described the humerus and femur as extending out laterally and parallel to the ground so that they display dorsal, ventral, anterior, and posterior surfaces (e.g., Haughton, 1929;Boonstra, 1964;Kemp, 1978Kemp, , 1986Fourie & Rubidge, 2007, 2009, following the anatomical conventions used for sprawling animals such as non-therapsid synapsids (e.g., Romer & Price, 1940;Romer, 1956;Hopson, 2012). At least some therapsids are thought to have adopted a dual gait stance, with a sprawled forelimb and a semi-erect or erect hind limb in contrast with the sprawled fore-and hind limbs of the more basal non-therapsid synapsids (Kemp, 1978;Blob, 2001). ...
Therocephalia are an important clade of non-mammalian therapsids that evolved a diverse array of morphotypes and body sizes throughout their evolutionary history. The postcranial anatomy of therocephalians has largely been overlooked, but remains important towards understanding aspects of their palaeobiology and phylogenetic relationships. Here, we provide the first postcranial description of the large akidnognathid eutherocephalian Moschorhinus kitchingi by examining multiple specimens from fossil collections in South Africa. We also compare the postcranial anatomy with previously described therocephalian postcranial material and provide an updated literature review to ensure a reliable foundation of comparison for future descriptive work. Moschorhinus shares all the postcranial features of eutherocephalians that differentiate them from early-diverging therocephalians, but is differentiated from other eutherocephalian taxa by aspects concerning the scapula, interclavicle, sternum, manus, and femur. The novel anatomical data from this contribution shows that Moschorhinus possessed a stocky bauplan with a particularly robust scapula, humerus, and femur. These attributes, coupled with the short and robust skull bearing enlarged conical canines imply that Moschorhinus was well equipped to grapple with and subdue prey items. Additionally, the combination of these attributes differ from those of similarly sized coeval gorgonopsians, which would have occupied a similar niche in late Permian ecosystems. Moreover, Moschorhinus was the only large carnivore known to have survived the Permo-Triassic mass extinction. Thus, the subtle but important postcranial differences may suggest a type of niche partitioning in the predator guild during the Permo-Triassic mass extinction interval.
... This assessment is corroborated by the number of caudal vertebrae present in the fossil. Vertebral columns of the common Early Jurassic genera Ichthyosaurus and Stenopterygius generally have 25 to 35 vertebrae in the region between the pelvis and onset of the tail bend [29]. TV344 has 33 vertebral centra between the inferred pelvic girdle and tail bend, which is consistent with these numbers. ...
A partial ichthyosaur skeleton from the Toarcian (Lower Jurassic) bituminous shales of the ‘Schistes Carton’ unit of southern Luxembourg is described and illustrated. In addition, associated remnant soft tissues are analyzed using a combination of imaging and molecular techniques. The fossil (MNHNL TV344) comprises scattered appendicular elements, together with a consecutive series of semi-articulated vertebrae surrounded by extensive soft-tissue remains. We conclude that TV344 represents a skeletally immature individual (possibly of the genus Stenopterygius) and that the soft parts primarily consist of fossilized skin, including the epidermis (with embedded melanophore pigment cells and melanosome organelles) and dermis. Ground sections of dorsal ribs display cortical microstructures reminiscent of lines of arrested growth (LAGs), providing an opportunity for a tentative age determination of the animal at the time of death (>3 years). It is further inferred that the exceptional preservation of TV344 was facilitated by seafloor dysoxia/anoxia with periodical intervals of oxygenation, which triggered phosphatization and the subsequent formation of a carbonate concretion.
... Subclass Parareptilia Olson (1947) Superfamily Procolophonoidea Romer (1956) Family Procolophonidae Lydekker (1890) Subfamily Leptopleuroninae Ivakhnenko (1979) Genus Cornualbus gen. nov ...
Procolophonidae is the most successful Parareptilia group throughout Pangaea. For almost two decades, the study of the
most derived South American procolophonids only included the description of new specimens belonging to well-known
species, mostly Procolophon trigoniceps. On the basis of a recently collected skull and associated postcranial elements
from the early Carnian (Upper Triassic) of Brazil, we describe a new procolophonid, Cornualbus primus gen. et sp. nov.
A phylogenetic analysis recovers this new procolophonid within the subfamily Leptopleuroninae, forming a clade with the
leptopleuronines Hypsognathus fenneri, Leptopleuron lacertinum, Mandaphon nadra, Hwiccewyrm trispiculum, and
Soturnia caliodon. Cornualbus primus bridges a temporal gap in South American procolophonids, which extended from
the Induan to the Norian, in addition to being the oldest Leptopleuroninae described for South America. Furthermore, the
description of this taxon enriches our knowledge of procolophonid diversity for the South American Triassic period
... This suggests that the deeply notched scapula is autapomorphic for the genus Turfanodon. The large coracoid foramen might house a robust subclavian artery passing through (Romer, 1956). The insertion of the M. supracoracoideus is strongly developed on the humerus (Fig. 2C), indicating that this muscle was well-developed in Turfanodon. ...
Within the dicynodont genus Turfanodon, there are two recognized species, T. bogdaensis and T. jiufengensis. Both species are known by relatively complete cranial materials, but the mandibles and most postcranial bones have been described only for T. jiufengensis. This paper reports new dicynodont specimens from Turpan, Xinjiang, referring them to T. bogdaensis. They can clearly be differentiated from T. jiufengensis by the flatter lateral surface of the snout region, a prominent swelling on the lateral dentary shelf, and the rounded femoral head. The diagnosis of Turfanodon is revised. The combination of a flat circumorbital rim, posterior portion of anterior pterygoid rami with converging ventral ridges, and a possible autapomorphy, a deep notch on scapula forming procoracoid foramen, are confirmed. It also differentiated from all dicynodonts other than Myosaurus, Kembawacela and Lystrosaurus by having accessory ridges lateral to the median palatal ridge.
... Amphicoelous vertebrae have evolved several times in sharks, dipnoans, bony ganoids and teleosts, associating their appearance with improved speed of motion [120]. Amphicoelous vertebrae are also associated with aquatic environments, as transitions from amphicoelous to platycoelous vertebrae has been hypothesized to represent a transition from aquatic to terrestrial environments [123]. ...
Despite making up one of the most ecologically diverse groups of living birds, comprising soaring, diving and giant flightless taxa, the evolutionary relationships and ecological evolution of Anseriformes (waterfowl) remain unresolved. Although Anseriformes have a comparatively rich, global Cretaceous and Paleogene fossil record, morphological datasets for this group that include extinct taxa report conflicting relationships for all known extinct taxa. Correct placement of extinct taxa is necessary to understand whether ancestral anseriform feeding ecology was more terrestrial or one of a set of diverse aquatic ecologies and to better understand avian evolution around the K-T boundary. Here, we present a new morphological dataset for Anseriformes that includes more extant and extinct taxa than any previous anseriform-focused dataset and describe a new anseriform species from the early Eocene Green River Formation of North America. The new taxon has a mediolaterally narrow bill which is rarely found in previously described anseriform fossils. The matrix created to assess the placement of this taxon comprises 41 taxa and 719 discrete morphological characters describing skeletal morphology, musculature, syringeal morphology, ecology, and behavior. We additionally combine the morphological dataset with published sequences using Bayesian methods and perform ancestral state reconstruction for select morphological, ecological and behavioral characters. We recover the new Eocene taxon as the sister taxon to (Anseranatidae+Anatidae) across all analyses, and find that the new taxon represents a novel ecology within known Anseriformes and the Green River taxa. Results provide insight into avian evolution during and following the K-Pg mass extinction and indicate that Anseriformes were likely ancestrally aquatic herbivores with rhamphothecal lamellae..
... As with V. marathonensis, the first vertebra connected to sacral vertebrae is referred to as the cloacal vertebra, which lacks pedestals for the haemal arch, synapophyses, and lymphapophyses [24]. Speculation about the possible relationship between the position of the first haemal arch as a skeletal indicator of sexual dimorphism was previously raised for crocodiles and dinosaurs but ultimately found no confirmation [25,26]. For Komodo dragons, such research is worth considering, In this research, it was concluded that the presence of the haemal arch in Komodo dragons is not gender related. ...
Simple Summary
This study presents morphological research on the tail, with particular emphasis on its skeleton, musculature, and accumulated fat tissue. Additionally, it provides an examination of the spinal cord and anal glands of the Komodo dragon. This project sheds new light on the biological importance of the tail in this lizard, offering insights into conservation implications, which are of utmost importance due to the threat of extinction of this species. As a result of the conducted research is a multifaceted analysis of the tail, with particular emphasis on its numerous biological functions.
Abstract
The Komodo dragon is a unique reptile with an elongated tail that exhibits hitherto unknown adaptations and functions. This tail, composed of 60–86 vertebrae, serves diverse ecological and physiological roles. In juveniles, it is essential for an arboreal lifestyle and balance, while in adults, it functions as a tool for defense and offensive actions. It possesses characteristic haemal arches and a dorsal keel, along with well-developed muscles which enable precise tail control, influencing the Komodo dragon’s maneuverability and directional changes. The tail stores adipose tissue, providing Komodo dragons with the ability to regulate body temperature and independence from other seasonal variations. The tail adipose tissue impacts numerous biochemical processes and may play a crucial role in the animals’ metabolic strategies and reproductive capabilities. Its functions include providing essential mineral compounds for the organism, such as calcium, phosphorus, magnesium, iron, and zinc. Analysing the biochemical composition of tail fat is crucial for understanding the health of Komodo dragons.
... Usually, the cervicals of plesiosaurs bear paired subcentral foramina (Romer, 1956), which are connected to a pair of foramina on the neural canal floor via simple, undivided internal canals . Hypothetically, these canals housed intersegmental arteries, representing vascular canals of vertebral precursors in early ontogenetic stages, which were later incorporated into the vertebrae . ...
Mesozoic vertebrate fossils within glacially transported deposits of Pleistocene
age are rare. Here, we examine five isolated, strongly eroded vertebrae of Mesozoic
marine reptiles, most probably plesiosaurs, from glacigenic sediments of northern Germany. In addition, three consecutive plesiosaur vertebrae, having already been
described in previous publications, are briefly reconsidered. For one heavily eroded
specimen, litho- and biostratigraphical analyses of associated sediment, including thin sectioning and calcareous nannofossil investigations, confirm a mid-Cretaceous age. The internal morphology of the five isolated vertebrae in focus, investigated with the help of microCT, reveals the presence of (neuro)vascular cavities within the respective centra. Unexpectedly, we found diverse internal cavity patterns which have only one feature in common: a medial pair of foramina on the floor of the neural canal that is connected to deep-reaching canals.
... This morphology is in stark contrast to the generally short and immobile ribs, whereby the capitulum and tuberculum remain merged, as seen in non-amniote tetrapods such as lissamphibians [114] and temnospondyls [99]. A bicapitate rib morphology is widely spread among amniotes [115] and likely represents the ancestral condition for this clade [109]. While a web of bone still connects the capitulum and tuberculum, Janis & Keller [107] confirm a bicapitate rib in D. tenuitectus. ...
Among terrestrial tetrapods, the origin of herbivory marked a key evolutionary event that allowed for the evolution of modern terrestrial ecosystems. A 100 Ma gap separates the oldest terrestrial tetrapods and the first undisputed herbivorous tetrapods. While four clades of early tetrapod herbivores are undisputed amniotes, the phylogenetic position of Diadectomorpha with respect to Amniota has long been controversial. Given that the origin of herbivory coincides with the oldest amniotes, and obligate herbivory is unknown within amphibians, this suggests that a key adaptation necessary to evolve obligate herbivory is unique to amniotes. Historically, phylogenetic analyses have found Diadectomorpha as the sister-group to amniotes, but recent analyses recover Diadectomorpha as sister-group to Synapsida, within Amniota. We tested whether diadectomorphs are amniotes by updating the most recent character–taxon matrix. Specifically, we added new characters from the lower jaw and added diadectomorph taxa, resulting in a dataset of 341 characters and 61 operational taxonomic units. We updated the description of five diadectomorph jaws using microcomputed tomography data. Our majority-rule consensus places Diadectomorpha as sister-group to Synapsida; other methods do not recover this relationship. We revise diadectomorph taxonomy, erecting a new species from the early Permian Bromacker locality, Germany, and a new genus to accommodate ‘Diadectes’ sanmiguelensis.
... Anatomical terminology used in this paper is from Zangerl et al. (1988; for scutes), Krahl et al. (2020; for humerus) and Romer (1956; for other postcranials). ...
The article describes a fossil pan-cheloniid Protrachyaspis shorymensis gen. et sp. nov. from the Karakeshi, Kert, Kuyulus, and Monata localities of the Shorym Formation (Bartonian, middle Eocene), as well as unknown localities of the Mangyshlak Peninsula, Kazakhstan. In addition, the shell bones of small pan-cheloniids from the Kuyulus and Tuzbair localities of the Shorym Formation with some traits of P. shorymensis are described, which probably represent remains of juvenile specimens of this species. The new taxon is characterized by a number of features rarely found in pan-cheloniids, including serrated dentaries, distally displaced lateral process of the humerus, and deeply sculptured external carapace surface. These features indicate a likely herbivorous diet and pelagic lifestyle of the new pan-cheloniid. According to the results of the cladistic analysis, P. shorymensis is sister to the Neogene species Trachyaspis lardyi Meyer, 1843, from which it differs in the absence of ridges on the carapace in adult individuals, the configuration of the scutes on the parietal bone, and the structure of the plastron. The stratigraphic gap between the appearance of P. shorymensis and its sister T. lardyi suggests a long ghost lineage of members of this clade throughout the Bartonian – Aquitanian (ca. 20.7 million years) preceding the appearance of T. lardyi. In most trees, the P. shorymensis + T. lardyi clade is located within the Chelonini clade, which, taking into account the middle Eocene age of P. shorymensis, indicates the early divergence of crown cheloniids, previously established based on molecular data. The new taxon is similar to the fragmentary remains of pan-cheloniids with a sculptured external surface of the shell, previously described from four localities of the upper part of the Buchak and lower part of Kiev formations in the south of European Russia and Ukraine, which makes it possible to determine these materials as cf. Protrachyaspis sp., and probably extends the appearance of the P. shorymensis + T. lardyi clade back to the middle Lutetian.
... The reptilian middle ear has been historically understood as more ancestral than that of mammals, but nowadays an independent evolution is widely accepted (Clack et al., 2016;Tucker, 2017). Whereas reptiles possess only one ossicle within the middle ear cavity, mammals are famously differentiated from all other land vertebrates by the presence of three ossicles (Gaupp, 1913;Maier, 1990;Romer, 1956;Starck, 1979Starck, -1982. The mammalian malleus (hammer) is homologous to the articular of non-mammalian tetrapods; the mammalian incus (anvil) corresponds to the original quadrate; and the stapes (stirrup) is homologized to the amphibian and sauropsidian columella (syn. ...
Whereas mammals are characterized by the presence of three middle ear ossicles, reptiles have only one, the columella (stapes). Nevertheless, there is a great diversity of columellar anatomy among sauropsids, especially in the unique and cartilaginous “extracolumella”‐portion. Molecular studies revealed the “columella” of chicken and quails to be formed within the second pharyngeal arch, although conflicting evidence exists for the columellar footplate and distal parts of the columella in these birds. We studied columellar development in four turtles, one lizard, and one caiman species and argue, using early blastematous stages, that, distally, the so‐called “extracolumella” in turtles is mainly of quadrate, that is, first pharyngeal arch origin. Differently, the dorsal aspect of the “extracolumella” of the lizard and a part of the “dorsal columella process” of the caiman are likely quadrate‐derived. This indicates only a partial homology of the distal columellar compartments among reptiles. Moreover, we observed in most species that, at early stages, the footplate differentiates from the otic capsule, which confirms widespread experimental findings of mesodermal cells contributing to the proximal part of the columella. We provide a hypothetical framework for the changes in the columella and quadrate morphology in reptilian evolution. Originally, as evidenced by the fossil record, the columella served as a stabilizing brace between the quadrate and braincase. Associated with changes in the feeding mode of late Permian taxa, the quadrate was integrated along the stress flows from biting, and in early development part of the quadrate differentiated to differently contribute to the distal part of the “columella‐complex,” which now contacts the tympanic membrane. In addition, part of the original otic capsule contributes to the footplate of the mobile columella, providing a connection with the inner ear.
... All cervical vertebrae of plesiosaurs show a pair of large foramina on the ventral surface of the vertebral centrum, called subcentral foramina or subcentralia (Romer, 1956), and are autapomorphy of the clade (Storrs, 1991;o'Keefe, 2001;Benson & Druckenmiller, 2014;Noè et al., 2017;Wintrich et al., 2017b). Storrs (1991) In the middle section of the pectoral vertebra, two ventral foramina and two dorsal foramina are discernible (Fig. 2). ...
Abstract. Elasmosaurids were the most diverse forms of plesiosaurs during the Late Cretaceous and achieved a cosmopolitan distribution. Thus, its fossils have been recorded on all continents, including Antarctica. Knowledge of paleobiological and evolutionary aspects of plesiosaurs has advanced considerably in recent years, including microstructural and paleohistological analyses of bone tissue. However, comparative analyses are still relatively scarce. To analyze how the degree of remodeling varies in the vertebral column of Vegasaurus molyi (MLP 93-I-5-1), from the Upper Cretaceous of Antarctica, histological sections of four vertebrae representing different sections of the column were made. The sections present a high degree of remodeling and an external fundamental system, indicating that the individual has reached skeletal maturity. The caudal vertebra shows the least degree of remodeling and retains the greatest number of lines of arrested growth. The results indicate that the degree of bone remodeling increases from the caudal region to the cervical region. When considering the middle sections of the vertebral elements, there is an increase in the compaction index from the cervical region to the caudal region. These differences in the bone microstructure are perceptible and serve as a criterion for determining which element of the vertebral column and in which part of its thin sections should be created. This will yield more information at the paleohistological level, allowing paleobiological inferences such as ontogenetic stage, differential growth of various parts of the skeleton, and blood supply, among other factors.
... The anatomical terminology follows Romer (1956) as directional (e.g. 'anterior' rather than 'cranial') and anatomical structures are standardized e.g. ...
Titanosaurs were the most diverse sauropod group during the Cretaceous period, with most of its diversity being found during the Late Cretaceous. In this work, Tiamat valdecii, gen. et sp. nov. is described, a new species of basal titanosaur prospected from the Açu Formation (Albian–Cenomanian), Potiguar Basin, Ceará state, north-east Brazil. Te new taxon is composed by an associated sequence of anterior to middle caudal vertebrae, being diagnosed by four diagnostic features: a marked accessory tuberosity dorsoventrally developed, located on the prezygapophyses; deeply medioventral excavated articulation facets of prezygapophysis and post-zygapophyses articular facets; presence of developed hypantrum–hyposphene articulations; and short middle centra with a well-marked articular facet for the haemal arch. Te phylogenetic analysis reveals that Tiamat valdecii was a basal member of Titanosauria. Tiamat is the first species of Early Cretaceous titanosaur known for the Açu Formation. Biomechanical analysis shows that the tuberosity and excavation of the zygapophyses of the middle caudal vertebrae of Tiamat provide greater stability against shear loads in the amphicoelous vertebrae presented; in addition, they allow greater range of lateral movements without afecting the integrity of the joints. These features may have been an evolutionary alternative for the stability of the middle of the caudal vertebral column. The discovery of T. valdecii in the Açu Formation not only increases the known dinosaur diversity for this unit, but also helps us elucidate part of the first titanosaur radiation.
... The temporal roof does not present any opening (also known as fenestra) but is generally emarginated from behind or below or both. Teeth are lost and have been replaced functionally by a horny bill (Romer 1956). ...
... The lack of cranial material from most palaeophiids makes it difficult to elucidate their evolutionary relationships, yet they are commonly regarded as nesting within crown-group Serpentes in an unresolved position within Alethinophidia (Georgalis et al., 2020;McCartney & Seiffert, 2016;Parmley & DeVore, 2005;Rage & Werner, 1999). Some authors have further related Palaeophiidae to the extinct nigerophiids and extant Acrochordus together forming Acrochordoidea (McDowell, 1987;Nessov, 1995;Snetkov, 2011;Zvonok & Snetkov, 2012), whereas others have recognized close affinities with booids and pythonids (Hoffstettter, 1955;Holman, 2000;Parmley & Case, 1988;Rage, 1984), or even as part of Cholophidia along with the extinct marine pachyophiids (Hoffstetter, 1939;Nopsca, 1923a, b;Romer, 1956). Notwithstanding their enigmatic placement among snakes, the taxonomy of Palaeophiidae itself is also problematic, since the fossil taxa that have been considered as members of this family are grouped together and allocated in two different subfamilies, Palaeophiinae and Archaeophiinae, on the sole basis of vertebral features . ...
The Paleocene deposits from the Cerrejón Formation (Colombia, South America) have provided abundant snake remains. All this material has been assigned to the giant snake Titanoboa cerrejonensis. Here, we describe six vertebrae from among the referred materials that do not correspond to Titanoboa. All six vertebrae are morphologically identical, of a similar size, and display a distinct morphology that differs from Titanoboa. This new and unnamed taxon is a large snake estimated to be around eight meters in total length. Anatomical comparisons show that these vertebrae possess certain features typical of the Palaeophiidae, a group of extinct snakes of uncertain relationships known almost exclusively from vertebrae. Among the Palaeophiidae, the new taxon resembles the more generalized forms assigned to the genus Palaeophis, but lacks the extreme aquatic adaptations that define forms assigned to the genus Pterosphenus. We regard the new taxon as an undetermined palaeophiine but do not assign it to Palaeophis as a number of features differ from that described genus. This new record expands the known diversity of aquatic snakes from the Paleogene of South America and provides a substantial new record for the paleogeographic distribution of the Palaeophiidae. The oldest records are from the Cretaceous of Africa, while Paleocene records are poorly known and restricted to Africa, North America, and Europe. The majority of vertebral forms assigned to Palaeophiidae are from the Eocene, principally from the Tethys region, with only one previous South American record coming from the Eocene of Ecuador.
... In this respect, they are perhaps more reminiscent of the cervical vertebrae of Macrocnemus or even Protorosaurus (Gottmann-Quesada and Sander, 2009). Nevertheless, the dorsal margins of the fourth and the fifth cervical neural spines are concave rather than straight, which represents a morphology that is only present in Dinocephalosaurus among known early archosauromorphs, and even rare in reptiles generally (Romer, 1956). ...
Among numerous marine reptiles discovered in the Triassic eastern Tethys, today's Southern China, Dinocephalosaurus is a bizarre animal comparable to European Tanystropheus in developing a prominently long neck. These two taxa are respectively assigned to Dinocephalosauridae and Tanystropheidae, and the two families and other basal members collectively form an early-diverging clade of Archosauromorpha. Here we report a new archosauromorph specimen, IVPP V18579, excavated from the lower Middle Triassic (Anisian), from Luoping, Yunnan in southwestern China. Compared with all the hitherto known dinocephalosaurids and tanystropheids, this skeletally mature individual is exclusively similar to Dinocephalosaurus in a number of characteristics, particularly with the long posterodorsal process of the premaxilla extending posteriorly beyond the level of the external nares, the concave posterior margin of the anteroposteriorly broad quadrate, and the strongly expanded distal end of the chevron in most of the caudal vertebrae. However, this reptile is much smaller than Dinocephalosaurus and different from Dinocephalosaurus and the other dinocephalosaurid, Pectodens, in many aspects, such as an anteriorly tapering long rostrum, the dentition composed of short conical teeth with less heterodonty, relatively but obviously tall neural spines of the axis and the anterior cervical vertebrae. Our phylogenetic analysis suggests that the new archosauromorph is a dinocephalosaurid, and then we erect Austronaga minuta gen. et sp. nov. based on this specimen. Detailed comparisons in osteological anatomy and the discussion about its potential aquatic adaptation of this new taxon are also provided.
Birds are unique among extant tetrapods in exhibiting air-filled cavities that arise from the respiratory system and invade postcranial bones, a phenomenon called postcranial skeletal pneumaticity (PSP). These intraosseous cavities originate from diverticula of the ventilatory air sacs or directly from the gas-exchanging lung. Despite a long history of study, many of the basic characteristics of this system remain poorly understood. In this hybrid review, we synthesize insights from the anatomical, developmental, biomechanical and paleontological literature to review the functional and evolutionary significance of PSP. Leveraging new data, we confirm that the skeletons of pneumatic birds are not less heavy for their mass than those of apneumatic birds. Pneumatic skeletons may nonetheless be lightweight with respect to body volume, but this is a hypothesis that remains to be empirically tested. We also use micro-computed tomography scanning and deep learning-based segmentation to produce a pilot model of the pneumatized spaces in the neck of a Mallard (Anas platyrhynchos). This approach facilitates accurate modelling of bone architecture for quantitative comparative analysis within and between pneumatic taxa. Future work on PSP should focus on the cellular mechanisms and developmental processes that govern the onset and extent of pneumatization, which are essentially unknown.
This article is part of the theme issue ‘The biology of the avian respiratory system’.
Glyphoderma kangi from the Ladinian of the Middle Triassic is the oldest record of cyamodontoid placodonts known in South China, but several aspects of the anatomy of its skull and dorsal shell remained unknown, due to the preservation of the holotype specimen in dorsal view. Two new mostly complete and well-preserved skeletons are described here to reveal new anatomical information on the skull, pectoral girdle, pelvic girdle, transverse processes, ribs, and gastralia. In addition to the unique osteoderms with radiating grooves and ridges that form the carapace, six other types of osteoderms are found covering the skull and the mandible, composing the lateral wall, and forming an incomplete inner layer of the carapace. The inferred inner layer, formed by osteoderms located beneath the surface osteoderms near the peripheral margin of the carapace, probably helped to reinforce the carapace margins together with the dorsal ribs. Features including relative limb length indicate that Glyphoderma kangi has reached the marine adaptation step of at least M4, indicating minimized terrestrial travel and loss of terrestrial feeding. Considering its morphology and ecology, Glyphoderma kangi probably pursued a bottom-dwelling lifestyle where danger mainly came from above.
Thanks to their exceptional diversity, teeth are among the most distinctive features of vertebrates. Parameters such as tooth size, shape, number, identity, and implantation can have substantial implications for the ecology and certain social behaviors of toothed species. Despite decades of research primarily focused on mammalian dentition, particularly using the laboratory mouse model, squamate reptiles (“lizards” and snakes) offer a wide array of tooth types and dentition variations. This diversity, which includes differences in size, shape, function, and replacement capacity, provides invaluable opportunities for investigating these fundamental properties. The central bearded dragon (Pogona vitticeps), a popular pet species with well-established husbandry practices, is of particular interest. It features a broad spectrum of morphs and spontaneous mutants and exhibits a wide range of heterodont phenotypes, including variation in the size, shape, number, implantation, and renewal of teeth at both posterior and anterior positions. These characteristics position the species as a crucial model organism for developmental studies in tooth research and for gaining deeper insights into evolutionary patterns of vertebrate dentitions. In this article, we provide an overview of the current understanding of squamate dentition, its diversity, development, and replacement. Furthermore, we discuss the significant advantages offered by squamate species as model organisms for investigating the evolutionary and developmental aspects of vertebrate dentition.
Among the diverse basal reptile clade Parareptilia, the nycteroleters are among the most poorly understood. The interrelationships of nycteroleters are contentious, being recovered as both monophyletic and paraphyletic in different analyses, yet their anatomy has received little attention. We utilized x-ray computed tomography to investigate the skull of the nycteroleterid Emeroleter levis, revealing aspects of both the external and internal cranial anatomy that were previously unknown or undescribed, especially relating to the palate, braincase, and mandible. Our results reveal a greater diversity in nycteroleter cranial anatomy than was previously recognized, including variation in the contribution of the palatal elements to the orbitonasal ridge among nycteroleters. Of particular note are the unique dentition patterns in Emeroleter, including the presence of dentition on the ectopterygoid, an element which is typically edentulous in most parareptiles. We then incorporate the novel information gained from the computed tomography analysis into an updated phylogenetic analysis of parareptiles, producing a fully resolved Nycteroleteridae and further supporting previous suggestions that the genus ‘Bashkyroleter’ is paraphyletic.
Some of the earliest members of the archosaur-lineage (i.e., non-archosauriform archosauromorphs) are characterised by an extremely elongated neck. Recent fossil discoveries from the Guanling Formation (Middle Triassic) of southern China have revealed a dramatic increase in the known ecomorphological diversity of these extremely long-necked archosauromorphs, including the fully marine and viviparous Dinocephalosaurus orientalis. These recent discoveries merit a reinvestigation of enigmatic Triassic diapsid fossils from contemporaneous European deposits housed in historical collections. Here, we provide a redescription of Trachelosaurus fischeri, represented by a single, disarticulated specimen first described in 1918. Due to its unique morphology, which includes short, bifurcating cervical ribs, and a high presacral vertebral count, this taxon has been referred to either as a “protorosaurian” archosauromorph or a sauropterygian. Our revision clearly shows that Trachelosaurus represents the first unambiguous Dinocephalosaurus- like archosauromorph known from outside the Guanling Formation. Our finding has important systematic implications. Trachelosauridae Abel, 1919 represents the senior synonym for the recently identified Dinocephalosauridae Spiekman, Fraser and Scheyer, 2021. Based on our phylogenetic analyses, which employ two extensive datasets, we also corroborate previous findings that tanystropheids and trachelosaurids represent two families within a larger monophyletic group among non-crocopodan archosauromorphs, which is here named Tanysauria (clade nov.). Trachelosauridae is minimally composed of Trachelosaurus fischeri, Dinocephalosaurus orientalis, Pectodens zhenyuensis, and Austronaga minuta, but one of our analyses also found a probably taxonomically broader clade that may also include Gracilicollum latens and Fuyuansaurus acutirostris. Trachelosaurus fischeri considerably expands the known spatial and temporal range of Trachelosauridae to the earliest Anisian and the Central European Basin. Our findings add to the growing evidence for the presence of a diverse group of fully marine reptiles during the Middle Triassic
The Late Triassic archosauromorph Trilophosaurus buettneri is known from many sites in the Dockum Group and Chinle Formation of Texas and Arizona, spanning nearly 10 Ma from the Otischalkian to the Adamanian estimated holochrons. The holotype specimen, UMMP 2338, was described as a small fragment of a lower jaw in 1928 by E.C. Case. However, at the time no other specimens of the taxon were known. The present availability of several nearly complete skulls, mandibles, and postcranial skeletons referred to T. buettneri allows for reexamination of the anatomical context of the holotype. Here, we provide high-resolution photographs and 3D models of UMMP 2338 to justify our reidentification of the holotypic specimen of T. buettneri as an incomplete maxilla, which may have important implications for future work on trilophosaurid archosauromorphs.
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