SciCombinator

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Concept: Crocodylomorpha

125

Triassic predatory guild evolution reflects a period of ecological flux spurred by the catastrophic end-Permian mass extinction and terminating with the global ecological dominance of dinosaurs in the early Jurassic. In responding to this dynamic ecospace, terrestrial predator diversity attained new levels, prompting unique trophic webs with a seeming overabundance of carnivorous taxa and the evolution of entirely new predatory clades. Key among these was Crocodylomorpha, the largest living reptiles and only one of two archosaurian lineages that survive to the present day. In contrast to their existing role as top, semi-aquatic predators, the earliest crocodylomorphs were generally small-bodied, terrestrial faunivores, occupying subsidiary (meso) predator roles. Here we describe Carnufex carolinensis a new, unexpectedly large-bodied taxon with a slender and ornamented skull from the Carnian Pekin Formation (~231 Ma), representing one of the oldest and earliest diverging crocodylomorphs described to date. Carnufex bridges a problematic gap in the early evolution of pseudosuchians by spanning key transitions in bauplan evolution and body mass near the origin of Crocodylomorpha. With a skull length of >50 cm, the new taxon documents a rare instance of crocodylomorphs ascending to top-tier predator guilds in the equatorial regions of Pangea prior to the dominance of dinosaurs.

Concepts: Predation, Ecology, Extinction, Dinosaur, Triassic, Jurassic, Crocodylomorpha, Crurotarsi

111

The late Campanian-early Maastrichtian site of Lo Hueco (Cuenca, Spain) has provided a set of well-preserved crocodyliform skull and lower jaw remains, which are described here and assigned to a new basal eusuchian taxon, Lohuecosuchus megadontos gen. et sp. nov. The reevaluation of a complete skull from the synchronous site of Fox-Amphoux (Department of Var, France) allows us to define a second species of this new genus. Phylogenetic analysis places Lohuecosuchus in a clade exclusively composed by European Late Cretaceous taxa. This new clade, defined here as Allodaposuchidae, is recognized as the sister group of Hylaeochampsidae, also comprised of European Cretaceous forms. Allodaposuchidae and Hylaeochampsidae are grouped in a clade identified as the sister group of Crocodylia, the only crocodyliform lineage that reaches our days. Allodaposuchidae shows a vicariant distribution pattern in the European Late Cretaceous archipelago, with several Ibero-Armorican forms more closely related to each other than with to Romanian Allodaposuchus precedens.

Concepts: Definition, Extensional definition, Phylogenetic nomenclature, Europe, Cladistics, Spain, Taxon, Crocodylomorpha

39

Crocodyliforms serve as important taphonomic agents, accumulating and modifying vertebrate remains. Previous discussions of Mesozoic crocodyliform feeding in terrestrial and riverine ecosystems have often focused on larger taxa and their interactions with equally large dinosaurian prey. However, recent evidence suggests that the impact of smaller crocodyliforms on their environments should not be discounted. Here we present direct evidence of feeding by a small crocodyliform on juvenile specimens of a ‘hypsilophodontid’ dinosaur from the Upper Cretaceous (Campanian) Kaiparowits Formation of southern Utah. Diagnostic crocodyliform bite marks present on a left scapula and a right femur, as well as a partial probable crocodyliform tooth crown (ovoid in cross-section) preserved within a puncture on the right femur, comprise the bulk of the feeding evidence. Computed tomography scans of the femoral puncture reveal impact damage to the surrounding bone and that the distal tip of the embedded tooth was missing prior to the biting event. This is only the second reported incidence of a fossil crocodyliform tooth being found embedded directly into prey bone. These bite marks provide insight into the trophic interactions of the ecosystem preserved in the Kaiparowits Formation. The high diversity of crocodyliforms within this formation may have led to accentuated niche partitioning, which seems to have included juvenile dinosaurian prey.

Concepts: Ecology, Cretaceous, Fossil, Dinosaur, Cretaceous–Tertiary extinction event, Plesiosaur, Ornithischia, Crocodylomorpha

37

We report a new, small-sized atoposaurid crocodyliform from the Upper Jurassic of Langenberg, Northeastern Germany. Atoposaurids are small-sized Mesozoic crocodyliforms of mainly European distribution, which are considered to be phylogenetically close to the origin of Eusuchia. Knoetschkesuchus langenbergensis gen. nov. sp. nov. is represented by two well-preserved skulls and additional cranial and postcranial remains representing different ontogenetic stages. 3D reconstructions of a juvenile skull based on micro-computed tomography allow the most detailed description of cranial remains of any atoposaurid hitherto presented. Our new analysis contradicts previous preliminary assignment of the Langenberg atoposaurids to Theriosuchus. Knoetschkesuchus gen. nov. is characterized in particular by the presence of two dental morphotypes in the maxilla and dentary, slit-like secondary choanae within a narrow groove on the surface of the pterygoid, absence of lacrimonasal contact, presence of an antorbital foramen and an external mandibular fenestra, and proportional characters of the interorbital and intertemporal region. A similar combination of characters allows attribution of Theriosuchus guimarotae to Knoetschkesuchus, forming the new combination Knoetschkesuchus guimarotae. Our analysis provides an osteological basis for the separation of Theriosuchus and Knoetschkesuchus and helps further delineate generic differences in other closely related crocodylomorphs. Our phylogenetic analysis corroborates inclusion of Knoetschkesuchus into Atoposauridae and supports a position of Atoposauridae within Eusuchia.

Concepts: Mandible, Skull, Computational phylogenetics, Germany, Saxony, Jurassic, Crocodylomorpha, Crocodyliformes

20

The postcranial anatomy of Crocodyliformes has historically been neglected, as most descriptions are based solely on skulls. Yet, the significance of the postcranium in crocodyliforms evolution is reflected in the great lifestyle diversity exhibited by the group, with members ranging from terrestrial animals to semi-aquatic and fully marine forms. Recently, studies have emphasized the importance of the postcranium. Following this trend, here we present a detailed description of the postcranial elements of Pissarrachampsa sera (Mesoeucrocodylia, Baurusuchidae), from the Adamantina Formation (Bauru Group, Late Cretaceous of Brazil). The preserved elements include dorsal vertebrae, partial forelimb, pelvic girdle, and hindlimbs. Comparisons with the postcranial anatomy of baurusuchids and other crocodyliforms, together with body-size and mass estimates, lead to a better understanding of the paleobiology of Pissarrachampsa sera, including its terrestrial lifestyle and its role as a top predator. Furthermore, the complete absence of osteoderms in P. sera, a condition previously known only in marine crocodyliforms, suggests osteoderms very likely played a minor role in locomotion of baurusuchids, unlike other groups of terrestrial crocodyliforms. Finally, a phylogenetic analysis including the newly recognized postcranial features was carried out, and exploratory analyses were performed to investigate the influence of both cranial and postcranial characters in the phylogeny of Crocodyliformes. Our results suggest that crocodyliform relationships are mainly determined by cranial characters. However, this seems to be a consequence of the great number of missing entries in the data set with only postcranial characters and not of the lack of potential (or synapomorphies) for this kind of data to reflect the evolutionary history of Crocodyliformes.

Concepts: Evolution, Biology, Phylogenetics, Cladistics, Computational phylogenetics, Crocodiles, Crocodylomorpha, Crocodyliformes

12

Thalattosuchians were highly specialised aquatic archosaurs of the Jurassic and Early Cretaceous, and represent a peak of aquatic adaptation among crocodylomorphs. Relatively little is known of their endocranial anatomy or its relevance for the evolution of sensory systems, physiology, and other aspects of biology. Nevertheless, such data have significance for two reasons: (1) thalattosuchians represent an important data point regarding adaptation to marine life in tetrapods; and (2) as early-diverging members of the crocodylian stem-lineage, thalattosuchians provide information on the evolutionary assembly of the brain and other endocranial structures in crocodylomorphs. Here we use µCT data to virtually reconstruct the endocranial anatomy of Pelagosaurus typus, an early thalattosuchian with plesiomorphic traits of relevance to the split between the two major subgroups: Teleosauroidea and Metriorhynchoidea. Interpretation of these data in a broad comparative context indicate that several key endocranial features may be unique to thalattosuchians, including: a pyramidal morphology of the semicircular canals, the presence of an elongate endosseous cochlear duct that may indicate enhanced hearing ability, the presence of large, paired canals extending anteriorly from an enlarged pituitary fossa, a relatively straight brain (possibly due to the presence of large, laterally placed orbits), and an enlarged venous sinus projecting dorsally from the endocast that is confluent with the paratympanic sinus system. Notably, we document a large expansion of the nasal cavity anterior to the orbits in Pelagosaurus as an osteological correlate of an enlarged salt gland previously only documented in Late Jurassic metriorhynchoids. This is the first anatomical evidence of this structure in early thalattosuchians. Pelagosaurus also shares the presence of paired olfactory bulbs with metriorhynchoids, and shows an enlarged cerebrum, which may also be present in teleosauroids. Taken together, our findings indicate that physiological and sensory adaptations to marine life occurred early in thalattosuchian evolution, predating the origins of flippers, tail flukes, and hydrodynamic body forms seen later in metriorhynchoids.

Concepts: Biology, Auditory system, Olfactory bulb, Anatomy, Thalattosuchia, Crocodylomorpha, Pelagosaurus, Teleosauridae

11

Crocodylomorphs originated in the Late Triassic and were the only crocodile-line archosaurs to survive the end-Triassic extinction. Recent phylogenetic analyses suggest that the closest relatives of these generally gracile, small-bodied taxa were a group of robust, large-bodied predators known as rauisuchids implying a problematic morphological gap between early crocodylomorphs and their closest relatives. Here we provide a detailed osteological description of the recently named early diverging crocodylomorph Carnufex carolinensis from the Upper Triassic Pekin Formation of North Carolina and assess its phylogenetic position within the Paracrocodylomorpha. Carnufex displays a mosaic of crocodylomorph, rauisuchid, and dinosaurian characters, as well as highly laminar cranial elements and vertebrae, ornamented dermal skull bones, a large, subtriangular antorbital fenestra, and a reduced forelimb. A phylogenetic analysis utilizing a comprehensive dataset of early paracrocodylomorphs and including seven new characters and numerous modifications to characters culled from the literature recovers Carnufex carolinensis as one of the most basal members of Crocodylomorpha, in a polytomy with two other large bodied taxa (CM 73372 and Redondavenator). The analysis also resulted in increased resolution within Crocodylomorpha and a monophyletic clade containing the holotype and two referred specimens of Hesperosuchus as well as Dromicosuchus. Carnufex occupies a key transition at the origin of Crocodylomorpha, indicating that the morphology typifying early crocodylomorphs appeared before the shift to small body size.

Concepts: Bone, Skull, Dinosaur, Triassic, Archosaur, Crocodylomorpha, Crurotarsi, Sphenosuchia

9

The well-known Late Cretaceous Lameta Ghat locality (Jabalpur, India) provides a window of opportunity to study a large stable, near shore sandy beach, which was widely used by sauropod dinosaurs as a hatchery. In this paper, we revisit the eggs and eggshell fragments previously assigned to lizards from this locality and reassign them to crocodylomorphs. Several features point to a crocodilian affinity, including a subspherical to ellipsoidal shape, smooth, uneven external surface, discrete trapezoid shaped shell units with wide top and narrow base, basal knobs and wedge shaped crystallites showing typical inverted triangular extinction under crossed nicols. The crocodylomorph eggshell material presented in this paper adds to the skeletal data of these most probably Cretaceous-Eocene dryosaurid crocodiles.

Concepts: Reptile, Cretaceous, Crocodilia, Sauropoda, Dinosaur, Archosaur, Late Cretaceous, Crocodylomorpha

6

Macelognathus vagans Marsh, 1884 from the Late Jurassic Morrison Fm. of Wyoming was originally described as a dinosaur by Marsh and in 1971 Ostrom suggested crocodilian affinities. In 2005, Göhlich and collaborators identified new material of this species from Colorado as a basal crocodylomorph. However, a partial skull found in association with mandibular and postcranial remains was not described.

Concepts: Reptile, Crocodilia, Dinosaur, Archosaur, Archosauromorpha, Crocodylomorpha, Crurotarsi, Allosaurus

5

Crocodyliforms have a much richer evolutionary history than represented by their extant descendants, including several independent marine and terrestrial radiations during the Mesozoic. However, heterogeneous sampling of their fossil record has obscured their macroevolutionary dynamics, and obfuscated attempts to reconcile external drivers of these patterns. Here, we present a comprehensive analysis of crocodyliform biodiversity through the Jurassic/Cretaceous (J/K) transition using subsampling and phylogenetic approaches and apply maximum-likelihood methods to fit models of extrinsic variables to assess what mediated these patterns. A combination of fluctuations in sea-level and episodic perturbations to the carbon and sulfur cycles was primarily responsible for both a marine and non-marine crocodyliform biodiversity decline through the J/K boundary, primarily documented in Europe. This was tracked by high extinction rates at the boundary and suppressed origination rates throughout the Early Cretaceous. The diversification of Eusuchia and Notosuchia likely emanated from the easing of ecological pressure resulting from the biodiversity decline, which also culminated in the extinction of the marine thalattosuchians in the late Early Cretaceous. Through application of rigorous techniques for estimating biodiversity, our results demonstrate that it is possible to tease apart the complex array of controls on diversification patterns in major archosaur clades.

Concepts: Evolution, Ecology, Phylogenetics, Extinction, Cretaceous, Fossil, Dinosaur, Crocodylomorpha