Vertebral microstructure marks the emergence of pelagic ichthyosaurs soon after the End Permian Mass Extinction.

Ichthyosaurs were the first fully marine tetrapods, and evolved a streamlined body, flippers, live birth, and endothermy-like physiology. However, the transition to these adaptations and how it relates to divergence into ocean environments is ambiguous. Here, we use vertebral bone microstructure to document the first ontogenetic series of two Early Triassic taxa that include the oldest ichthyosaur foetal fossils.

Pseudosuchian thermometabolism: A review of the past two decades.

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.

On the origins of endothermy in amniotes.

A recent study showed evidence that endothermy was ancestral for amniotes using a variety of proxies and a large sample of taxa. However, it did not include numerous crucial taxa. We reevaluated this hypothesis using a large sample of early amniotes and tetrapodomorphs.

Were the synapsids primitively endotherms? A palaeohistological approach using phylogenetic eigenvector maps.

The acquisition of mammalian endothermy is poorly constrained both phylogenetically and temporally. Here, we inferred the resting metabolic rates (RMRs) and the thermometabolic regimes (endothermy or ectothermy) of a sample of eight extinct synapsids using palaeohistology, phylogenetic eigenvector maps (PEMs), and a sample of 17 extant tetrapods of known RMR (quantified using respirometry). We inferred high RMR values and an endothermic metabolism for the anomodonts ( sp.

The influence of plane of section on the identification of bone tissue types in amniotes with implications for paleophysiological inferences.

The proportion of woven bone (WB) to parallel-fibered bone has been extensively used to infer bone growth rates and resting metabolic rates of extinct organisms. The aim of this study is to test in a variety of amniotes how reliably WB content can be measured using transverse sections. For this, we analyzed femoral transverse mid-diaphyseal thin sections of 14 extant and extinct taxa and the corresponding longitudinal sections for comparative purposes.