Environmental drivers of crocodyliform extinction across the Jurassic/Cretaceous transition
Authors:
Tennant et al
Abstract:
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.
pop sci link.
Enigmatic crocodyliforms from the early Miocene of Cuba
Authors:
Brochu et al
Abstract:
Early Miocene deposits from the Domo de Zaza locality, in the south-central Cuban province of Sancti Spiritus, preserve crocodyliform remains, including compressed serrated teeth closely resembling those of South American sebecids. Fragmentary cranial and mandibular material is more difficult to assess. Referral to any other post-Paleogene crocodyliform known from the Western Hemisphere can be ruled out, and phylogenetic analyses are unable to pinpoint its relationships. Similarities can be found with planocraniids, including ventrally oriented and mediolaterally expanded orbital surfaces, but the morphology of the quadrate is inconsistent with a planocraniid affinity. A sebecid in the Miocene of Cuba would be congruent with evidence from other vertebrates suggesting extensive dispersal between the Greater Antilles and South America during the Neogene, and it would be the first Neogene record of the group outside South America. The other crocodyliform may indicate the presence of an endemic West Indian lineage not closely related to any contemporaneous group. It is also consistent with extant Crocodylus arriving in the Neotropics within the past 5–10 million years.
The ancestors of today's crocodiles colonised the seas during warm phases and became extinct during cold phases, according to a new Anglo-French study which establishes a link between marine crocodilian diversity and the evolution of sea temperature over a period of more than 140 million years.
The research, led by Dr Jeremy Martin from the Université de Lyon, France and formerly from the University of Bristol, UK is published this week in Nature Communications.
Today, crocodiles are 'cold-blooded' animals that mainly live in fresh waters but two notable exceptions, Crocodylus porosus and Crocodylus acutus venture occasionally into the sea. Crocodiles occur in tropical climates, and they are frequently used as markers of warm conditions when they are found as fossils.
While only 23 species of crocodiles exist today, there were hundreds of species in the past. On four occasions in the past 200 million years, major crocodile groups entered the seas, and then became extinct. It is a mystery why they made these moves, and equally why they all eventually went extinct. This new study suggests that crocodiles repeatedly colonized the oceans at times of global warming.
Lead author of the report, Dr Jeremy Martin said: "We thought each of these evolutionary events might have had a different cause. However, there seems to be a common pattern."
Gondwanasuchus scabrosus gen. et sp. nov., a new terrestrial predatory crocodyliform (Mesoeucrocodylia: Baurusuchidae) from the Late Cretaceous Bauru Basin of Brazil
Authors:
1. Thiago da Silva Marinho (a)
2. Fabiano Vidoi Iori (b)
3. Ismar de Souza Carvalho (b)
4. Felipe Mesquita de Vasconcellos (b)
Affiliations:
a. Universidade Federal do Triângulo Mineiro, Instituto de Ciências Exatas, Naturais e Educação, Departamento de Ciências Biológicas, Av. Getúlio Guaritá, 159 Bairro Abadia, Uberaba, MG 38025-440, Brazil
b. Universidade Federal do Rio de Janeiro, Centro de Ciências Matemáticas e da Natureza, Instituto de Geociências, Departamento de Geologia, Av. Athos da Silveira Ramos, 274, Bloco F, Ilha do Fundão – Cidade Universitária, Rio de Janeiro, RJ 21949-900, Brazil
Abstract:
Baurusuchids are among the most common and diverse crocodyliform fossils from the Late Cretaceous Bauru Basin of Brazil. This inland continental basin was the habitat of a rich crocodyliform fauna containing five mesoeucrocodylian families, of which the Baurusuchidae represents highly specialized predatory crocodyliforms of terrestrial habits as indicated by their dental, cranial, and postcranial features. The large size they achieved, together with likely predatory adaptations, would suggest they competed and occupied theropod ecological niches in the Bauru Basin. Here we describe Gondwanasuchus scabrosus gen. et sp. nov., a medium-sized baurusuchid with a strongly laterally compressed skull, bearing unique dentition with deep apicobasal sulci and probably well-developed binocular vision. The cranial and dental features in Gondwanasuchus suggest that this active predator would have fed on small vertebrates and took the role of small theropods in terrestrial guild. Gondwanasuchus is the most distinctive baurusuchid known to date and enriches the knowledge on these important Gondwanan terrestrial predatory crocodyliforms.
