Predicting body length and assessing the shape of tail-propelled Mesozoic marine reptiles

Body length is a crucial ecological predictor in vertebrates, yet total
body length proxies have seldom been assessed for ancient marine top
predators. Here, we test the strength of phylogenetic imputation and 23
linear measurements, sampling both broad skeletal regions and frequently
fossilised elements (such as vertebral centra), in predicting the body
length of the main clades of tail-propelled Mesozoic marine reptiles
(Ichthyosauria, Mosasauridae, and pelagic thalattosuchians). We embed this
marine reptile sample within a comparative framework with raptorial
cetaceans, and analyse the evolution of body proportions in these clades.
We find that trunk length and centrum dimensions are strong predictors of
body length, opening up the possibility to build vast datasets of body
length estimations for Mesozoic marine reptiles from minimal preserved
remains. We provide body length calculation equations for all traits and
all clades. Proxies fared much better and often had distinct slopes when
applied clade-wide rather than when applied to the global dataset. We also
show that body length in Mesozoic marine reptiles is more labile than
their skeletal architectures, rendering phylogenetic imputation methods
less effective than skeletal proxies for assessing body lengths.