Combined paleohistological and isotopic inferences of thermometabolism in extinct Neosuchia, usingGoniopholisandDyrosaurus(Pseudosuchia: Crocodylomorpha) as case studies

Abstract

The evolution of thermometabolism in pseudosuchians (Late Triassic to the present) remains a partly unsolved issue: extant taxa (crocodilians) are ectothermic, but the clade was inferred ancestrally endothermic. Here we inferred the thermometabolic regime of two neosuchian groups, Goniopholididae (Early Jurassic to Late Cretaceous) and Dyrosauridae (middle Cretaceous to late Eocene), close relatives of extant crocodilians, in order to elucidate the evolutionary pattern across Metasuchia (Early Jurassic to the present), a clade comprising Neosuchia (Early Jurassic to the present) and Notosuchia (Middle Jurassic until the late Miocene). We propose a new integrative approach combining geochemical analyses to infer body temperature from the stable oxygen isotope composition of tooth phosphate and paleohistology and phylogenetic comparative methods to infer resting metabolic rates and red blood cell dimensions. †Dyrosaurus and †Goniopholis share with extant crocodilians similar lifestyles, body forms, bone tissue organization, body temperatures, metabolic rates, and red blood cell dimensions. Consistently, we infer ectothermy for †Dyrosaurus and †Goniopholis with the parsimonious implication of neosuchians and metasuchians being primitively ectothermic.

Paleohistological inferences of thermometabolic regimes in Notosuchia (Pseudosuchia: Crocodylomorpha) revisited

“…Thermal paleophysiology is an emergent discipline (Cubo and Huttenlocker 2020). It has great potential resulting from the synergy between physiological studies aimed at deciphering the mechanisms of thermogenesis in extant amniotes (e.g., Bal and Periasamy 2020; Jastroch and Seebacher 2020; Grigg et al 2021) and paleobiological inferences in extinct amniotes using phylogenetic comparative methods (e.g., Cubo et al 2012, 2020, 2022; Legendre et al 2016; Huttenlocker and Farmer 2017; Olivier et al 2017; Fleischle et al 2018; Cubo and Jalil 2019; Faure-Brac et al 2021; Knaus et al 2021). Logistic phylogenetic regressions are the third step in efforts performed during the last decade to carry out reliable inferences of thermometabolic status in extinct amniotes.…”

“…This contribution represented significant methodological progress, because paleobiological inference models included the phylogeny (rather than circumventing its effects, as did the preceding method), assuming an evolutionary model (Molina-Venegas et al 2018). PEMs have been widely used to infer the thermometabolic status of extinct amniotes (Legendre et al 2016; Olivier et al 2017; Fleischle et al 2018; Cubo and Jalil 2019; Cubo et al 2020, 2022; Faure-Brac and Cubo 2020; Faure-Brac et al 2021; Knaus et al 2021). Using logistic phylogenetic regressions is a new step in this sequence.…”

A survey of osteoderm histology and ornamentation among Crocodylomorpha: A new proxy to infer lifestyle?

“…The presence of osteoderm ornamentation may have been selected in semiaquatic crocodylomorphs because the presence of this feature contributes to heat captation, through enhanced vascularization (Clarac et al, 2018 ). Indeed, all the species studied here are inferred to be ectotherms (from histological and geochemical proxies; Cubo et al, 2020 ; Faure‐Brac et al, 2021 ). Because thermal conductivity, heat capacity, and density in water are higher than those in air, body heat loss is higher in water than in air and maintaining a high body temperature is more costly (Schmidt‐Nielsen, 1997 ; Vogel, 2005 ).…”

“…The presence of osteoderm ornamentation may have been selected in semiaquatic crocodylomorphs because the presence of this feature contributes to heat captation, through enhanced vascularization (Clarac et al, 2018). Indeed, all the species studied here are inferred to be ectotherms (from histological and geochemical proxies; Cubo et al, 2020;Faure-Brac et al, 2021).…”

On the origins of endothermy in amniotes

“…Extant birds and mammals, the only extant endothermic amniotes, are crown groups within, respectively, the Sauropsid and Synapsid clades and diverged from a common amniote ancestor over 320 million years ago. For more than two decades, many studies tried to decipher the evolutionary pathways of endothermy within the clade Amniota, using various proxies, including qualitative histology, 9 , 10 , 11 quantitative histology, 12 , 13 , 14 , 15 , 16 , 17 isotopic geochemistry, 18 , 19 , 20 correlation of metabolic rates with body mass, 21 inner ear biomechanics, 22 estimation of blood pressure, 23 , 24 body mass growth curves, 25 or estimation of maximum metabolic rate. 26 These studies provided evidence that endothermy was present in, at least, four different amniote clades: Archosauromorpha, 27 Sauropterygia, 14 , 20 Ichthyosauria, 20 and Therapsida.…”