The extensive dorsotemporal fenestrae in Thalattosuchus superciliosus (Metriorhynchidae, Thalattosuchia): an adaptation for offshore heliothermy?
Abstract
Metriorhynchids are pelagic crocodylomorphs that thrived in the seas from the Middle Jurassic to the end of the Early Cretaceous. They evolved a diversity of aquatic adaptations such as limbs modified in swimming paddles, a hypocercal caudal fin, and preorbital openings associated with their enlarged salt glands. Previous studies, based on both isotopic analyses and bone histology, concluded that the metriorhynchid Thalattosuchus superciliosus was ectothermic with a low maximal metabolic rate. Thus, this taxon is more similar to extant crocodylians than to contemporary marine reptiles (ichthyosaurs and plesiosaurs) who are estimated to be active endotherms. Taking a phylogenetic comparative approach, here we show that the frontoparietal fossae (a cranial site of heat transfer in living alligators) are extensively developed in Thalattosuchus superciliosus compared to fossil terrestrial crocodylomorphs, and a wide sampling of semi-aquatic species (spanning the Early Jurassic to Recent). Since previous studies on living crocodylians have shown that the dorsotemporal fossae are excavated by the temporo-orbital arteries and veins that pass along the circumference of the dorsotemporal fenestrae (while being a site to heat transfer between the skull and the external environment), we assess that the extension of the frontoparietal fossa contributes to the general hypertrophy of metriorhynchid cephalic vasculature thus increasing blood flow and volume toward their neurosensory tissues in order to maintain them at the closer to the optimal temperature. These new results therefore corroborate the previous investigations on metriorhynchid skull microanatomical features which suggested that they were heliothermic epipelagic marine ectotherms that used cranial vasculature to perform heat transfer by exposing the skull roof over the sea water surface.
BibTeX
@article{pellarin2026extensive,
title = {{The extensive dorsotemporal fenestrae in Thalattosuchus superciliosus (Metriorhynchidae, Thalattosuchia): an adaptation for offshore heliothermy?}},
author = {Romain Pellarin and Jorge Cubo and Mark T Young and François Clarac},
journal = {Lethaia},
year = {2026},
month = oct,
doi = {10.18261/let.60.2.8},
url = {https://hal.science/hal-05828645v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The extensive dorsotemporal fenestrae in Thalattosuchus superciliosus (Metriorhynchidae, Thalattosuchia): an adaptation for offshore heliothermy?
AU - Romain Pellarin
AU - Jorge Cubo
AU - Mark T Young
AU - François Clarac
PY - 2026
DA - 2026/10/21
JO - Lethaia
DO - 10.18261/let.60.2.8
UR - https://hal.science/hal-05828645v1
AB - Metriorhynchids are pelagic crocodylomorphs that thrived in the seas from the Middle Jurassic to the end of the Early Cretaceous. They evolved a diversity of aquatic adaptations such as limbs modified in swimming paddles, a hypocercal caudal fin, and preorbital openings associated with their enlarged salt glands. Previous studies, based on both isotopic analyses and bone histology, concluded that the metriorhynchid Thalattosuchus superciliosus was ectothermic with a low maximal metabolic rate. Thus, this taxon is more similar to extant crocodylians than to contemporary marine reptiles (ichthyosaurs and plesiosaurs) who are estimated to be active endotherms. Taking a phylogenetic comparative approach, here we show that the frontoparietal fossae (a cranial site of heat transfer in living alligators) are extensively developed in Thalattosuchus superciliosus compared to fossil terrestrial crocodylomorphs, and a wide sampling of semi-aquatic species (spanning the Early Jurassic to Recent). Since previous studies on living crocodylians have shown that the dorsotemporal fossae are excavated by the temporo-orbital arteries and veins that pass along the circumference of the dorsotemporal fenestrae (while being a site to heat transfer between the skull and the external environment), we assess that the extension of the frontoparietal fossa contributes to the general hypertrophy of metriorhynchid cephalic vasculature thus increasing blood flow and volume toward their neurosensory tissues in order to maintain them at the closer to the optimal temperature. These new results therefore corroborate the previous investigations on metriorhynchid skull microanatomical features which suggested that they were heliothermic epipelagic marine ectotherms that used cranial vasculature to perform heat transfer by exposing the skull roof over the sea water surface.
SN - 0024-1164
ER -