Douglas Riff

The world’s largest gharialsGryposuchus: description ofG. croizati n. sp. (Crocodylia, Gavialidae) from the Upper Miocene Urumaco Formation, Venezuela

A new fossil gharialGryposuchus species is described from the Upper Miocene Urumaco Formation, Venezuela.Gryposuchus croizati new species can be distinguished from other gavialoids, includingGryposuchus colombianus andGryposuchus neogaeus by the following combination of diagnostic characters: 1) slenderness of the parietal interfenestral bar; 2) dental formula, mainly the lesser number of maxillary teeth, with four premaxillary, 19 maxillary and 22 mandibular teeth; 3) large width of palatines between the reduced palatine fenestrae; 4) medial hemicondyle of the quadrate smaller but detached and much more posteriorly elongated than the lateral one and projected ventromedially; 5) pterygoid morphology, with two posterior vacuities. The polymorphism in the contour of the external naris inGryposuchus was evaluated for taxonomic significance. The body size ofG. croizati n. sp. was estimated in 10.15 m (9.67–10.67 m) using the dorsal skull length and the estimation of the body mass was 1,745 kg (1,280–2,379 kg) based on the braincase length. These maximal values placeG. croizati n. sp. among the world’s largest gharials and even Crocodyliforms as a whole.KurzfassungEine neue Gavialart vonGryposuchus wird aus der obermiozän Urumaco-Formation von Venezuela beschrieben.Gryposuchus croizati n. sp. kann von anderen Gavialoiden, einschließlichGryposuchus colombianus undGryposuchus neogaeus, anhand der folgenden diagnostischen Merkmale unterschieden werden: 1) Schlankheit des Interfenestralstabs des Parietale; 2) Zahnformel, vor allem die reduzierte Anzahl von Maxillarzähnen, mit vier Prämaxillar-, 19 Maxillar- und 22 Mandibularzähnen; 3) große Breite der Palatinae zwischen reduzierten Gaumenfenstern; 4) medialer Hemicondylus des Quadratums kleiner aber getrennt und sehr viel stärker posterior verlängert und ventromedial ausgerichtet als der laterale Hemicondylus; 5) Morphologie des Pterygoids, mit zwei posterioren Einbuchtungen. Die Polymorphismen in den Umrissen der äußeren Nasenöffnung inGryposuchus werden taxonomisch evaluiert. Die Körperlänge vonG. croizati n. sp. wurde, basierend auf der dorsalen Schädellänge, auf 10.15 m (9.67–10.67 m) geschätzt. Weiterhin wurde die Körpergröße basierend auf der Gehirnkapsellänge auf 1745 kg (1280–2379 kg) geschätzt. Anhand dieser maximalen Werte dürfteG. croizati n. sp. zu den weltweit größten Gavialen und sogar der Crocodyliformes gehört haben, die je existierten.

The oldest plesiosaur (Reptilia, Sauropterygia) from Antarctica

Antarctic plesiosaurs are known from the Upper Cretaceous López de Bertodano and Snow Hill Island formations (Campanian to upper Maastrichtian), which crop out within the James Ross Basin region of the Antarctic Peninsula. Here we describe the first plesiosaur fossils from the Lachman Crags Member of the Santa Marta Formation, north-western James Ross Island. This material constitutes the stratigraphically oldest plesiosaur occurrence presently known from Antarctica, extending the occurrence of plesiosaurians in this continent back to Santonian times (86.3–83.5 Mya). Furthermore, MN 7163-V represents the first plesiosaur from this region not referable to the Elasmosauridae nor Aristonectes, indicating a greater diversity of this group of aquatic reptiles in Antarctica than previously suspected.

A new Mourasuchus (Alligatoroidea, Caimaninae) from the late Miocene of Venezuela, the phylogeny of Caimaninae and considerations on the feeding habits of Mourasuchus

Mourasuchus (Alligatoroidea, Caimaninae) is one of the most peculiar crocodyliforms due to the skull morphology consisting of a long, wide, dorsoventrally flat rostrum with long, slender mandibular rami. Despite these peculiarities, the systematics, phylogeny and feeding habits of this taxon have not been properly studied. In this paper, we describe a new species of the genus, Mourasuchus pattersoni sp. nov., from the late Miocene of the Urumaco Formation of Venezuela. The new species differs from the other Mourasuchus species in having a lateromedially wide, dorsoventrally high jugal bone and a circular incisive foramen, which both represent autapomorphies of the new taxon. Phylogenetically, M. pattersoni sp. nov. is more closely related to M. amazonensis and the specimen UFAC-1424 (formely attributed to M. nativus) than to M. arendsi or M. atopus, whilst Mourasuchus is recovered once more as a monophyletic group. Furthermore, the cladistic analysis performed in this contribution offers a new phylogenetic assessment of Caimaninae, including many taxa described recently for the group. In this study, we also discuss the crocodylian diversity of the Urumaco Formation as well as how paleoenvironment may have contributed toward its evolution. In addition, we provide a discussion of the potential feeding habits of Mourasuchus. In this contribution, Mourasuchus is regarded as a taxon that likely preferred to prey on small animals. The unusual skull morphology of this group may have evolved to cover a large area with the rostrum, allowing for a more efficient prey capture, while the prey may have consisted predominantly of large amounts of small animals.

Morphometry, Bite-Force, and Paleobiology of the Late Miocene Caiman Purussaurus brasiliensis

Purussaurus brasiliensis thrived in the northwestern portion of South America during the Late Miocene. Although substantial material has been recovered since its early discovery, this fossil crocodilian can still be considered as very poorly understood. In the present work, we used regression equations based on modern crocodilians to present novel details about the morphometry, bite-force and paleobiology of this species. According to our results, an adult Purussaurus brasiliensis was estimated to reach around 12.5 m in length, weighing around 8.4 metric tons, with a mean daily food intake of 40.6 kg. It was capable of generating sustained bite forces of 69,000 N (around 7 metric tons-force). The extreme size and strength reached by this animal seems to have allowed it to include a wide range of prey in its diet, making it a top predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates, and, being unmatched by any other carnivore, it avoided competition. The evolution of a large body size granted P. brasiliensis many advantages, but it may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts.

New lower jaw and teeth referred to Maxakalisaurus topai (Titanosauria: Aeolosaurini) and their implications for the phylogeny of titanosaurid sauropods

Sauropod dinosaurs compose a diversified, well known, and worldwide distributed clade, with a stereotyped body plan: deep trunk, elongated neck and tail, columnar limbs and very small skull. In Brazil, the group is represented by ten formally described Cretaceous species, mostly titanosaurs. This is the case of Maxakalisaurus topai, known based on an incomplete and disarticulated skeleton, unearthed from deposits of the Adamantina Formation in Minas Gerais. Here, we report a partial right dentary, including five isolated teeth, collected from the same site as the type-series of M. topai and tentatively referred to that taxon. The bone is gently curved medially, the functional teeth are set on an anterolingual position, and two replacement teeth are seen per alveoli. New morphological data gathered from that specimen was employed to conduct a comprehensive phylogenetic analysis of Titanosauria (with 42 taxa and 253 characters), based on previous studies. The Aeolosaurini clade was recovered, with Gondwanatitan and Aelosaurus as sister taxa, and Maxakalisaurus, Panamericansaurus, and Rinconsaurus forming a basal polytomy.

Revisiting Gryposuchus jessei Gürich, 1912 (Crocodylia: Gavialoidea): specimen description and comments on the genus

Gryposuchus Gürich, 1912 is the most diverse genus within the Gavialoidea. However, the type species G. jessei Gürich, 1912 has been subject of controversy and was regarded conspecific with G. neogaeus (Burmeinster, 1885) or G. colombianus (Langston, 1965). Here we provide a revision of G. jessei to verify the conspecific hypothesis and the implications for the genus Gryposuchus. Our study shows that G. jessei is a valid species, and a new specimen was referred to this taxon. The comparisons with other Gavialoidea species enabled the proposition of three exclusive characters for the genus. We further advocate a sister affinity between G. jessei and G. pachakamue.

Redescription of the holotype of the Miocene crocodylian Mourasuchus arendsi (Alligatoroidea, Caimaninae) and perspectives on the taxonomy of the species

ABSTRACT The Miocene crocodyliform fauna of South America is one of the most diverse of the world, and the late Miocene Urumaco Formation of Venezuela has one of its most important assemblages. Mourasuchus (Caimaninae) is one of the most peculiar crocodyliforms of the South American Miocene due to its unusual morphology, which prompted peculiar feeding habits to be proposed for this taxon. In this paper we present a redescription of the holotype of the species Mourasuchus arendsi (CIAAP-1297) from the Urumaco Formation of Venezuela. The redescription offered a thorough reassessment of the skull, mandibles and postcranium that comprise the holotype of M. arendsi, providing a comprehensive morphological description of this specimen for the first time. The data provided by this description prompted a review of the taxonomic status of M. arendsi, which has enabled the possibility of M. arendsi being a junior synonym of M. atopus to be considered and thoroughly discussed in this paper. An eventual confirmation of the synonymy does not change the phylogeny of the Caimaninae clade. This contribution also offers assessments on the ontogenetic status of the holotype of M. arendsi and on the differences on the closure of the scapulocoracoid synchondroses between Mourasuchus specimens.

Osteohistological study on both fossil and living Caimaninae (Crocodyliformes, Crocodylia) from South America and preliminary comments on growth physiology and ecology

ABSTRACT Caimaninae is a South American lineage of crocodylians widely distributed in Brazil and composed of six species within three genera. Currently, there is insufficient information regarding growth strategies, growth rates, and ecology extracted from the bone microstructure. Here we present the first osteohistological study of both Caiman yacare and an unidentified fossil Caiman. Long bones of one specimen of C. yacare and of one fossil Caiman found at Solimões Formation (Acre Basin), were used to prepare the histological slides. The microstructure of C. yacare shows fibrolamellar complex present in the femur and tibia, while the humerus and radius of both C. yacare and the fossil Caiman revealed a slow-growing bone matrix with gradual decrease and effective stops. According to the results found here, Caimaninae seem to have the capability to adjust their growth rates in response to seasonal changes. The extant Caiman is classified as juvenile, but for the fossilized specimen no ontogenetic stage can be determined. Caiman yacare shows the presence of intraskeletal variability regarding the record of bone growth. We conclude that Caimaninae likely have been experiencing cyclical changes in growth rates in direct correlation to changes in seasons and environmental conditions since the Miocene.