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A biomechanical transformation model for the evolution of semi-spheroidal articulations between adjoining vertebral bodies in crocodilians
... They also emphasize that this characteristic constitutes stability to the vertebral set, resulting in a strengthening of the dorsal column. Salisbury and Frey (2001) also argue that concavo-convex intercentral joints stabilize the vertebral column against shear loads and consequently increase the rotation ratio between the vertebrae giving more flexibility than that present in ancestral forms with amphicoelous vertebrae. ...
... The sauropod Tiamat has a curious set of vertebrae whose anteriors are concavo-convex (procoelous), and as they move away from the sacrum, they lose this characteristic, becoming amphicoelous (Fig. 3). If we consider the observations of Fronimos and Wilson (2017) and Salisbury and Frey (2001), the concavo-convex condition of the anterior vertebrae provided more stability against shear loads and consequently would increase the range of rotation among vertebrae in sequence. However, the middle vertebrae are amphicoelous and would obey the rotation conditions differently from their previous ones, possibly losing stability and flexibility ( Fig. 9.1). ...
... On the other hand, the middle vertebrae have zygapophyses with a unique morphology among sauropods, presenting a heterocoelous articular surface (concavo-convex). Despite the amphicoelous vertebral centre, which, according to Fronimos and Wilson (2017) and Salisbury and Frey (2001), has less stability against shear loads, our analyses indicate that the middle vertebrae of Tiamat supplied this deficiency with strong zygapophysial connections that offered greater stability, not being totally susceptible to translational displacement and maintaining a high degree of flexibility. ...
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.
... Posteromedially on the pterygoids are the secondary choanae. One of the defining features of the Eusuchia, the clade to which all living crocodylians belong to, is secondary choanae that are fully enclosed by the pterygoids, and another feature is the presence of procoelous vertebrae (Salisbury and Frey 2001;Brochu 2003; read below). The ectopterygoids are robust bones that contact the maxillae and jugals dorsally and the pterygoids posteroventrally. ...
... The posterior articular condyle on the first sacral vertebra is weakly developed. The first caudal vertebra is biconvex, by having semi-spheroidal convex condyles both anteriorly and posteriorly (Salisbury and Frey 2001;Fig. 13f). ...
... The neurocentral sutures close, becoming invisible during ontogeny, with the caudal neurocentral sutures being closed upon hatching, and the cervical neurocentral sutures close last, at maturity (Brochu 1996). The neural arch is joined to the centrum via the neural arch peduncles, and the opening between the peduncles is called the neural canal (or vertebral foramen; Salisbury and Frey 2001), through which the spinal cord passes. The tall and mediolaterally thin dorsal projection on the neural arch is the neural spine. ...
... Interestingly, some small isolated centra (RB66; Fig. 6E), (tentatively assigned to caudal vertebrae) were found disarticulated by the opened neurocentral suture. If these vertebrae are confirmed to be caudal, they would indicate the presence of juvenile individuals in addition to adults, since are more informative, since the combination of dorsal osteoderms that are twice as wide as they are long, with peg and groove articulation and a ventrally folded lateral margin, together with the presence of polygonal ventral osteoderms, points to the clade Goniopholididae (e.g., Wu et al., 1996;Salisbury & Frey, 2001;. Furthermore, the presence of generalist conical teeth is also typical of this clade of neosuchian crocodylomorphs, among others (Guillaume et al., 2020). ...
... All turtle specimens so far identified in Ribota correspond to shell elements (Fig. 7). They are represented by isolated plates, both from the carapace (Fig. 7A-C) and from the rows) and a closed paravertebral bracing system (Salisbury & Frey, 2001;Puértolas-Pascual et al., 2015a;. At least two ventral osteoderms (RB62 and RB35) have been identified (Fig. 6H, I). ...
... They are flat, equidimensional (as wide as they are long), polygonal with pentagonal to hexagonal contours, with straight edges, and present the typical ornamentation of big circular pits evenly distributed over their ventral surface. Although they were isolated, their edges present some crenulation, indicating their sutures with adjacent osteoderms, which would form a rather rigid ventral armour (Wu et al., 1996;Salisbury & Frey, 2001). Some small, flat, elliptical to subcircular osteoderms have been interpreted as belonging to the appendicular region. ...
The Ribota site (Ágreda, Soria, Spain) is a new locality in the Matute Formation (Tithonian–Berriasian) composed of several carbonate layers, outstandingly rich in macrovertebrate remains. Fossils show an unusual replacement of the original bioapatite by quartz, and are found as positive reliefs protruding from lacustrine limestone beds. This type of conservation has allowed the identification of around one hundred vertebrate bone accumulations in an outcrop of more than 10 hectares. Osteichthyans (articulated partial skeletons, cranial material, and isolated postcranial bones and scales), crocodylomorphs (disarticulated cranial material, isolated teeth, vertebrae and osteoderms), turtles (partial carapaces and plastra, but also isolated plates) and pterosaurs (cranial and appendicular elements) have been identified. Around 80 specimens have been collected and a preliminary study of part of the collection (35 specimens) has allowed the identification of at least 5 different taxa: Halecomorphi indet., Neoginglymodi indet., Goniopholididae indet., Testudinata indet., and Pterodactyloidea indet. This new site represents one of the few sites from this time interval preserved in a fully lacustrine environment, so these vertebrate assemblages are unique and composed of different animals that presumably lived around and within the lake. They are dominated by aquatic and amphibian vertebrates and was formed by attrition in this lacustrine environment, possibly far from the lake shoreline. These macrovertebrate assemblages provide new data about the diversity in the faunal ecosystems from the Jurassic/Cretaceous transition of the Iberian Basin Rift System.
... The core region of osteoderms exhibits well-vascularized features and contributes to thermoregulation (Seidel, 1979;Farlow et al., 2010;Grigg and Kirshner, 2015;Clarac and Quilhac, 2019). Osteoderms have been suggested to provide evidence of body outline (Keeble and Benton, 2020) or contribute to the understanding of locomotion in crocodyliformes (Salisbury andFrey, 2001, Mueller-Töwe, 2006). Furthermore, paleohistological studies have revealed that the count of lines of arrested growth (LAGs) on osteoderms can be used to estimate the age of individuals (Parker et al., 2008;Cerda and Desojo, 2011;Taborda et al., 2013). ...
... According to Salisbury and Frey, 2001, the dorsal osteoderms of Indosinosuchus are open paravertebral bracing system. The dorsal armour lacked a ventrolateral bend and was not ventrally inclined at the lateral part of each osteoderm. ...
... In contrast, the neural arch in neosuchians occupies entirely the dorsal surface of the centrum (e.g. Salisbury and Frey 2001). The presence of a well-marked serrated neurocentral and costovertebral joints ( Figure 12C), and the diminutive size of the material as well (ca. ...
Supposed dinosaur remains were collected between 1859 and 1906 in the Lower Cretaceous Recôncavo Basin (Northeast Brazil). Since these materials remained undescribed, and most were considered lost. Recently, some of these historical specimens were rediscovered in the Natural History Museum of London, providing an opportunity to revisit them after 160 years. The specimens come from five different sites, corresponding to the Massacará (Berriasian-Barremian) and Ilhas (Valanginian-Barremian) groups. Identified bones comprise mainly isolated vertebral centra from ornithopods, sauropods, and theropods. Appendicular remains include a theropod pedal phalanx, humerus, and distal half of a left femur with elasmarian affinities. Despite their fragmentary nature, these specimens represent the earliest dinosaur bones discovered in South America, enhancing our understanding of the Cretaceous dinosaur faunas in Northeast Brazil. The dinosaur assemblage in the Recôncavo Basin resembles coeval units in Northeast Brazil, such as the Rio do Peixe Basin, where ornithopods coexist with sauropods and theropods. This study confirms the presence of ornithischian dinosaurs in Brazil based on osteological evidence, expanding their biogeographic and temporal range before the continental rifting between South America and Africa. Additionally, these findings reinforce the fossiliferous potential of Cretaceous deposits in Bahia State, which have been underexplored since their initial discoveries.
... Alligatorids have a complete caudal layer of dermal bone, while some extinct taxa, such as the terrestrial notosuchian Simosuchus clarki, possessed osteoderms covering their entire bodies (Hill 2010). In terrestrial crocodyliforms, the dorsal rows of osteoderms are associated with sustained terrestrial locomotion, but the presence of a nuchal shield of osteoderms in Simosuchus clarki is involved in the extension of the neck (Farlow et al. 2010;Salisbury and Frey 2001). ...
Osteoderms are bony plates formed within the dermis of diverse vertebrate groups. They are present in all crocodylomorphs but
Metriorhynchidae. Most of them show typical bone ornamentation consisting of pits and ridges on their outer surface. The most
widely discussed functional hypothesis suggests that the ornamentation of osteoderms infuences heat exchange with the environ‑
ment through the adjacent vascular network, facilitating the absorption of solar radiation. This process allows semiaquatic crocodiles
to compensate for heat loss resulting from the high thermal conductivity of surrounding water. In order to test this assertion, we
conducted a phylogenetic logistic regression analysis to evaluate the relationship between osteoderm relative area of pits (RAP) and
lifestyle (terrestrial versus aquatic) in a sample of crocodyliforms. Our results revealed that lifestyle is signifcantly explained by
RAP: the lower the degree of ornamentation (RAP), the higher the probability of a terrestrial lifestyle. We used this model to infer
the lifestyle of two extinct taxa, Peirosaurus torminni and Microsuchus schilleri. We concluded that terrestrial notosuchians may
have lost osteoderm ornamentation due to the lower thermal conductivity of air and reduced heat loss in a terrestrial environment
compared to what happens in water. Among these notosuchians, we hypothesize that large terrestrial baurusuchids maintained a
stable body temperature due to thermal inertia, whereas small notosuchians took advantage of the early morning sun exposure to
warm up and stayed in terrestrial burrows during periods of intense solar radiation. Finally, unlike the almost motionless behavior
of freshwater crocodiles, fully marine Metriorhynchidae probably lost osteoderms because they constantly swim, generating heat
by muscular contraction, so osteoderms with a thermoregulatory function for heat absorption were no longer positively selected.
The lack of any pterosaur living descendants creates gaps in the knowledge of the biology of this group, including its cervical biomechanics, which makes it difficult to understand their posture and life habits. To mitigate part of this issue, we reconstructed the cervical osteology and arthrology of three pterosaurs, allowing us to make inferences about the position of the neck of these animals at rest. We used scans of three-dimensionally preserved cervical series of Anhanguera piscator , Azhdarcho lancicollis and Rhamphorhynchus muensteri for the reconstructions, thus representing different lineages. For the recognition of ligaments, joint cartilages, and levels of overlapping of the zygapophyses, we applied the Extant Phylogenetic Bracket method, based on various extant birds and on Caiman latirostris . We inferred that pterosaur intervertebral joints were probably covered by a thin layer of synovial cartilage whose thickness varied along the neck, being thicker in the posterior region. Ignoring this cartilage can affect reconstructions. According to the vertebral angulation, their neck was slightly sinuous when in rest position. Our analyses also indicate that pterosaurs had segmented and supra-segmented articular cervical ligaments, which could confer stabilization, execute passive forces on the neck and store elastic energy.
The origin of modern crocodylians is rooted in the Cretaceous, but their evolutionary history is obscure because the relationships of outgroups and transitional forms are poorly resolved. Here, we describe a new form, Varanosuchus sakonnakhonensis gen. nov., sp. nov., from the Early Cretaceous of Thailand that fills an evolutionary gap between Paralligatoridae and Atoposauridae, two derived neosuchian lineages with previously unsettled phylogenetic relationships. Three individuals, including a complete skull and associated postcranial remains, allow for a detailed description and phylogenetic analysis. The new taxon is distinguished from all other crocodylomorphs by an association of features, including a narrow altirostral morphology, a dorsal part of the postorbital with an anterolaterally facing edge, a depression on the posterolateral surface of the maxilla, and fully pterygoid-bound choanae. A phylogenetic analysis confirms the monophyly and taxonomic content of Atoposauridae and Paralligatoridae, and we underline the difficulty in reaching a robust definition of Eusuchia. Furthermore, we put forward further arguments related to the putative terrestrial ecology with semi-aquatic affinities of atoposaurids based on their altirostral snout morphology and osteoderm ornamentation.
Unlike the majority of sauropsids, which breathe primarily through costal and abdominal muscle contractions, extant crocodilians have evolved the hepatic piston pump, a unique additional ventilatory mechanism powered by the diaphragmaticus muscle. This muscle originates from the bony pelvis, wrapping around the abdominal viscera, extending cranially to the liver. The liver then attaches to the caudal margin of the lungs, resulting in a sub-fusiform morphology for the entire “pulmo-hepatic-diaphragmatic” structure. When the diaphragmaticus muscle contracts during inspiration, the liver is pulled caudally, lowering pressure in the thoracolumbar cavity, and inflating the lungs. It has been established that the hepatic piston pump requires the liver to be displaced to ventilate the lungs, but it has not been determined if the lungs are freely mobile or if the pleural tissues stretch ventrally. It has been hypothesized that the lungs are able to slide craniocaudally with the liver due to the smooth internal ceiling of the thoracolumbar cavity. We assess this through ultrasound video and demonstrate quantitatively and qualitatively that the pulmonary tissues are sliding craniocaudally across the interior thoracolumbar ceiling in actively ventilating live juvenile, sub-adult, and adult individuals ( n = 7) of the American alligator ( Alligator mississippiensis ) during both natural and induced ventilation. The hepatic piston is a novel ventilatory mechanism with a relatively unknown evolutionary history. Questions related to when and under what conditions the hepatic piston first evolved have previously been left unanswered due to a lack fossilized evidence for its presence or absence. By functionally correlating specific characters in the axial skeleton to the hepatic piston, these osteological correlates can be applied to fossil taxa to reconstruct the evolution of the hepatic piston in extinct crocodylomorph archosaurs.
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