Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology最新文献

Chameleons are a family of lizards distinguished by several unique features related to their arboreal lifestyles, such as a ballistic tongue, skin color changes, independent movement of both eyes, a prehensile tail, and cleft hands and feet. The veiled chameleon (Chamaeleo calyptratus) has been proposed as a promising model species for studying squamate biology. Despite its potential, the developmental biology of this species remains poorly understood, particularly in terms of gonadal development. This study aimed to elucidate the development of the gonads in the veiled chameleon, from the initial appearance of the gonadal ridges through the sexual differentiation into ovaries and testes, to the establishment of the gonadal structures in both sexes. The study showed the accelerated appearance of gonadal primordia compared to the soma in the veiled chameleon, which is unique and possibly influenced by a prolonged in ovo development period due to the slowed rate of embryonic development in this species. The undifferentiated gonads are characterized by a voluminous medulla and a thin cortex. The process of gonadal sexual differentiation mirrors that seen in other vertebrates. Ovarian differentiation involves the development of a cortex containing germ cells and the loss of these cells in the medulla. Differentiated ovaries are characterized by a thin cortex and early induction of meiosis, leading to the formation of ovarian follicles before hatching. In contrast, testis differentiation involves the loss of germ cells from the cortex, its transformation into a thin epithelium, and the development of germ cell-containing testis cords in the medulla. The testis cords originate from invagination and remain without forming a lumen during embryogenesis. This comprehensive examination of gonadal development in the veiled chameleon provides important insights into sexual differentiation processes in this species. Moreover, it may stimulate further, broader studies in vertebrate developmental biology.

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.

Xenodens calminechari is a mosasaurid taxon named by Longrich et al. (2021) based on the holotype MHNM.KH.331, a left maxilla with several teeth. This holotype was obtained nonscientifically (without technical supervision) from an area in Morocco that yields many manipulated or forged specimens. Examination of Longrich et al. (2021) reveals four tooth crowns occupy what appear to be two alveoli in MHNM.KH.331, and there is potential adhesive connecting the tooth crowns to the maxilla on their lateral sides. We argue that the articulated tooth crowns of this taxon were artificially placed in the maxilla, rendering at least two apomorphies of this taxon the product of forgery. Longrich et al. (2021)'s claims of fused tooth 'roots' in MNHM.KH.331 are instead calcified periodontal ligament and alveolar bone that have ankylosed, resembling the typical mosasaurid condition. Differing tooth crown morphology does not preclude the referral of the teeth of this specimen to a younger ontogenetic stage of another mosasaur (possibly Carinodens) because many extant lizard species show drastic ontogenetic changes in the dentition. We argue that Xenodens calminechari represents a nomen dubium. This specimen constitutes a confluence of two persistent problems in vertebrate paleontology: material sourced from commercial excavations that has not been adequately tested for forgery, and taxa named from tooth-based holotypes that ignore the potential for intraspecific dental variation and interspecific convergence in dental characters, as are common in squamates. We suggest that Longrich et al. CT scan MHNM.KH.331, and we supply CT examples for identifying artificially added tooth crowns to Moroccan mosasaur jaws. Finally, we provide recommendations for the designation of mosasaurid holotypes.

In the context of an increasing interest for Pseudosuchia, we have compiled a Special Issue, comprising 14 collaborative studies that deepen our understanding of pseudosuchian evolution. These contributions range from the description of a new taxon to exhaustive reviews of thermometabolism, morphological adaptation, systematics, and detailed investigations into ontogeny, paleoneurology, paleohistology, and paleobiology. Through these papers, we explore the evolutionary history of pseudosuchian archosaurs, spotlighting their rise and diversification following the end-Permian mass extinction.

With nearly 30 living species of relatively similar ecological traits, Crocodylomorpha is represented today by only a small fraction of its past diversity. The well-documented crocodylomorph fossil record has revealed more than 500 taxa, with much higher ecological and morphological diversity than their extant counterparts. An example of such astonishing diversity is the Late Cretaceous rocks of the Bauru Group (southeast Brazil), from which numerous taxa are known, belonging to the clade Notosuchia. These were predominantly terrestrial taxa, some of which exhibited traits associated with omnivorous or even herbivorous feeding behaviors, such as Sphagesauridae, whereas others were adapted to a carnivore diet, such as Baurusuchidae and Peirosauridae. Among these is Barreirosuchus franciscoi, originally described as a neosuchian (Trematochampsidae) but later interpreted as a peirosaurid notosuchian. Even though included in recent morphological and phylogenetic analyses, B. franciscoi still lacked a more detailed description. Here, we provide an in-depth description of the cranial elements of B. franciscoi, using data from computed tomography and a broad sample of comparative material, including living and fossil crocodylomorphs. Also, the neuro-cavities, including the endocast, nasopharyngeal duct, and the olfactory region, were digitally reconstructed. Finally, a new phylogenetic analysis recovered B. franciscoi nested within Peirosauria, forming the Itasuchidae clade with other potentially semiaquatic species: Rukwasuchus yajabalajekundu, Pepesuchus deiseae, and Itasuchus jesuinoi. The morphological and phylogenetic reassessment of B. franciscoi indicates a semiaquatic form, highlighting the ecological diversity of notosuchians from the Bauru Group as well as the capacity of notosuchians to explore a myriad of environments.

Spatial relationships between oropharyngeal structures and their coordinated dynamics ensure proper adaptations in functions such as respiration, chewing, and swallowing. Thus, the aim of this study is to analyze spatial changes in the normal oropharynx during respiration and mastication. For this purpose, eight 7-8 months old Yucatan minipigs, four of each sex were used. X-ray fluoroscopy was recorded with the field of view focused on the oropharyngeal region. The x-ray video clips showing respiratory cycles and masticatory sequences were digitized and traced. Points to be digitized and traced were located on the soft palate, epiglottis, tongue base, and pharyngeal wall. An X-Y coordinate system was established to trace distances and directions of each structure (structural), and between structures (inter-structural) during phases of respiration, chewing stages, and swallowing episodes. During respiration, the soft palate showed the largest X-Y movements with the largest distance change (1.32 ± 0.64 mm). In contrast, distance changes in the tongue base were significantly smaller (0.32 ± 0.21 mm, p < 0.05). Notably, during chewing the tongue base and epiglottis showed major changes in distance and direction. Similarly, during swallowing the tongue base showed the largest changes (2.94 ± 1.28 mm) followed by the pharyngeal wall and epiglottis. Thus, although coordinated, each pharyngeal structure plays specific roles. Understanding of these spatial and specific dynamics in different oropharyngeal structures would provide the baseline to analyze the potential mechanisms of various swallowing and breathing disorders such as dysphagia and obstructive sleep apnea.

Crocodylomorphs constitute a clade of archosaurs that have thrived since the Mesozoic until today and have survived numerous major biological crises. Contrary to historic belief, their semiaquatic extant representatives (crocodylians) are not living fossils, and, during their evolutionary history, crocodylomorphs have evolved to live in a variety of environments. This review aims to summarize the non-semiaquatic adaptations (i.e., either terrestrial or fully aquatic) of different groups from different periods, highlighting how exactly those different lifestyles are inferred for those animals, with regard to their geographic and temporal distribution and phylogenetic relationships. The ancestral condition for Crocodylomorpha seems to have been a terrestrial lifestyle, linked with several morphological adaptations such as an altirostral skull, long limbs allowing a fully erect posture and a specialized dentition for diets based on land. However, some members of this clade, such as thalattosuchians and dyrosaurids display adaptations for an opposite, aquatic lifestyle, interestingly inferred from the same type of morphological observations. Finally, new techniques for inferring the paleobiology of those extinct animals have been put forward in the last decade, appearing as a complementary approach to traditional morphological descriptions and comparisons. Such is the case of paleoneuroanatomical (CT scan data), histological, and geochemical studies.

Crocodylomorphs have colonized various environments from fully terrestrial to fully aquatic, making it an important clade among archosaurs. A remarkable example of the rich past diversity of Crocodylomorpha Hay, 1930 is the marine colonization undergone by several crocodylomorph lineages, particularly Thalattosuchia Fraas, 1901 during the Early Jurassic–Early Cretaceous, and Dyrosauridae de Stefano, 1903 during the Late Cretaceous–Early Eocene. Thalattosuchia represents the most impressive and singular marine radiation among Crocodylomorpha, occupying various ecological niches, before enigmatically disappearing in the Cretaceous. Dyrosauridae, on the other hand, is known for surviving the end-Cretaceous mass extinction in abundance but subsequently vanished. The evolutionary path undertaken by crocodylomorphs into the aquatic environments and the reasons for their disappearance outside marine extinction events during the Mesozoic remains a mystery. Despite a well-preserved fossil record, attention has primarily centered on craniodental adaptations, overlooking the swimming-related adaptations recorded in the postcranial skeleton. This research primarily involves a comprehensive examination of the pectoral girdle of the most representative members of Thalattosuchia and Dyrosauridae, highlighting their evolutionary trajectories over time. Additionally, this work aims to test the phylogenetic signal residing in the postcranial anatomy of Crocodylomorpha. As such, the most recent and complete Crocodylomorpha phylogenetic dataset has been repurposed: 42 new postcranial characters have been added and several others have been revised to address our phylogenetic question. We stress that postcranial anatomy constitutes an important tool supply to better understand the relations of extinct crocodyliforms, but also offers insights on their development, ecology, and biomechanics.

Prestosuchus chiniquensis is an iconic non-crocodylomorph loricatan from the Brazilian Triassic beds and the best-known taxon, represented by several specimens. The completeness and preservation of its skeleton make it a valuable taxon for paleobiological studies. We explore the microstructure of bone tissues of appendicular elements and ribs of three specimens of Prestosuchus to access a variety of aspects of its paleobiology, such as histovariability, ontogeny, and growth patterns. Integrating our data and other osteohistologically studied P. chiniquensis specimens, we proposed for the first time an ontogenetic model for non-crocodylomorph loricatans. The model encompasses six distinct age classes (I–VI) that allow us to infer the growth patterns of P. chiniquensis and possibly expand to other phylogenetically close taxa. During early ontogeny (age classes I–II), sustained fast growth was maintained by a fibrolamellar complex. In mid ontogeny (age classes III–IV), highly vascularized parallel-fibered bone predominates, suggesting intermediary growth rates. A change for a poorly vascularized parallel-fibered/lamellar bone would mark the attainment of sexual (age classes IV–V) and skeletal maturity, comprising the age class VI. An external fundamental system (EFS) present in the outermost cortex is the main histological feature that characterize the age class VI. Major histovariability features are present between appendicular bones and ribs of skeletally immature individuals. The most prominent of them is the presence of fibrolamellar complex and highly vascularized parallel-fibered bone in appendicular bones and poorly vascularized parallel-fibered bone in ribs. In advanced ontogenetic stages, the histovariability between appendicular bones and ribs tends to be minor. Our data also support previous hypothesis of the presence of one new taxon among the specimens assigned to P. chiniquensis, increasing the diversity of non-crocodylomorph loricatans. The new taxon, represented by the specimen UFRGS-PV-0152-T, awaits a formal anatomical description. Our study advances the preliminary understand of the ontogeny and growth patterns of non-crocodylomorphs loricatans and Pseudosuchia as a whole.

A newly referred specimen of Coahomasuchus kahleorum (TMM 31100-437) from the lower part of the Upper Triassic Dockum Group of Texas preserves much of the skeleton including the majority of the skull. Introduced in the literature in the 1980s as the “carnivorous aetosaur”, TMM 31100-437 bears recurved teeth that previously were considered unique among aetosaurs. The small size of the individual led to speculation that it represents a skeletally immature individual that retains a plesiomorphic dentition for Archosauromorpha. We provide a detailed evaluation of the anatomy and phylogenetic relationships of this specimen. Apomorphies of the osteoderms and braincase support the referral of the specimen to C. kahleorum. Histological analysis of the femur demonstrates that TMM 31100-437 does not represent a juvenile form of another known aetosaur. Thus, TMM 31000-437 provides another case demonstrating that aetosaur species spanned a wide range of maximum body sizes, from approximately 1.5 m to over 5 m in length. Reanalysis of the type specimen of C. kahleorum, along with information from TMM 31000-437, demonstrates that the lateral osteoderms are not autapomorphic as previously described and have distinct lateral and medial flanges as well as a dorsal eminence. Overall, this specimen provides key details regarding body size and diet in an early occurring aetosaur.