Abstract:
The order Lamniformes contains charismatic species such as the white shark
Carcharodon carcharias and extinct megatooth shark Otodus megalodon, and is
of particular interest given their influence on marine ecosystems, and
because some members exhibit regional endothermy. However, there
remains significant debate surrounding the prevalence and evolutionary
origin of regional endothermy in the order, and therefore the development
of phenomena such as gigantism and filter-feeding in sharks generally.
Here we show a basal lamniform shark, the smalltooth sand tiger shark
Odontaspis ferox, has centralized skeletal red muscle and a thick compactwalled
ventricle; anatomical features generally consistent with regionally
endothermy. This result, together with the recent discovery of probable
red muscle endothermy in filter feeding basking sharks Cetorhinus maximus,
suggests that this thermophysiology is more prevalent in the Lamniformes
than previously thought, which in turn has implications for understanding
the evolution of regional endothermy, gigantism, and extinction risk of
warm-bodied shark species both past and present.
