[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Metriorhynchid crocodylomorph origin and diversification

Ben Creisler

A new open access PeerJ preprint article:

Mark T. Young, Lorna Steel, Davide Foffa, Stephen L Brusatte, James J.
N .Kitson, Conrad P. D. T. Gillett, Mark A. Bell, Ronan Allain & Yves
Lepage (2015)
An early origin and diversification of macrophagous metriorhynchid
crocodylomorphs, with evidence for multiple instances of parallel
PeerJ PrePrints 3:e1661
doi: https://dx.doi.org/10.7287/peerj.preprints.1345v1

Metriorhynchids were a widely distributed group of marine
crocodylomorphs that thrived during the Middle Jurassic–Early
Cretaceous. Within this group there is a subclade, Geosaurini, that
evolved craniodential characteristics indicative of macrophagy
(feeding on large-bodied prey items). When this subclade evolved and
began to diversify into the myriad of morphologically distinct
lineages is still unclear. Previous phylogenetic analyses suggest this
clade evolved during the Late Jurassic, and rapidly diversified into
numerous different ecomorphotypes. It was hypothesized that this was
in response to the absence of small and medium-sized pliosaurs after
the Middle-Late Jurassic Boundary. However, re-examination of poorly
preserved fossils from the Callovian of England and France casts doubt
on this. Based on our comparative study of these fossils, and new
phylogenetic analyses, we conclude that Geosaurini had evolved and
diversified by the mid Callovian. Although comparatively rare in the
Middle Jurassic, at least four morphofunctionally distinct lineages of
macrophages had evolved. Moreover, based on maximum likelihood
modelling analyses, numerous macrophagy-linked characters (e.g.
contiguous tooth serrations, low tooth count) evolved independently in
these different lineages. Thus, the characteristics that previously
suggested a Late Jurassic origin of Geosaurini was due to long-branch
attraction and incomplete sampling. That these different macrophagous
lineages evolved distinct morphofunctional complexes and began niche
partitioning early in their evolution, suggests that their
diversification was driven by foraging specialisation. We hypothesise
that this may be a common driver of rapid diversification in marine
tetrapod evolution.