Climate cooling and clade competition likely drove the decline of lamniform sharks
Résumé
Understanding heterogeneity in species richness between closely
related clades is a key research question in ecology and evolutionary
biology. Multiple hypotheses have been proposed to
interpret such diversity contrasts across the tree of life, with most
studies focusing on speciation rates to explain clades’ evolutionary
radiations, while often neglecting extinction rates. Here we study
a notorious biological model as exemplified by the sister relationships
between mackerel sharks (Lamniformes, 15 extant species)
and ground sharks (Carcharhiniformes, ∼290 extant species). Using
a comprehensive fossil dataset, we found that the diversity dynamics
of lamniforms waxed and waned following repeated cycles of
radiation phases and declining phases. Radiation phases peaked up
to 3 times the current diversity in the early Late Cretaceous. In the
last 20 million years, the group declined to its present-day diversity.
Along with a higher extinction risk for young species, we further
show that this declining pattern is likely attributed to a combination
of abiotic and biotic factors, with a cooling-driven extinction (negative
correlation between temperature and extinction) and clade
competition with some ground sharks. Competition from multiple
clades successively drove the demise and replacement of mackerel
sharks due to a failure to originate facing the rise of ground sharks,
particularly since the Eocene. These effects came from ecologically
similar carcharhiniform species inhibiting diversification of mediumand
large-sized lamniforms. These results imply that the interplay
between abiotic and biotic drivers had a substantial role in extinction
and speciation, respectively, which determines the sequential
rise and decline of marine apex predators.