Morphology of the sacral region and reproductive strategies of Metriorhynchidae: a counter-inductive approach

HERRERA Y.; MARTA SUSANA FERNÁNDEZ; LAMAS S.; LISANDRO CAMPOS; GASPARINI Z.

EARTH AND ENVIRONMENTAL SCIENCE TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH

ROYAL SOC EDINBURGH

Lugar: Edinburgo; Año: 2017

1755-6910

Morphological and physiological features indicate Metriorhynchidae as the only group of crocodylomorphs with a pelagic lifestyle. Some of these features have evolved convergently in several clades of tetrapods secondarily adapted to aquatic life. One striking feature of metriorhynchids among crocodylomorphs is the morphology of the pelvic region (i.e. ventrally deflected sacral ribs and reduced pelvic girdle) which increases significantly the depth of this region. This morphology as a whole resembles those of other viviparous Mesozoic marine reptiles not phylogenetically related to metriorhynchids. We tested two alternative hypotheses of reproductive strategies in this clade: oviparity vs viviparity. Giventhe lack of direct evidence supporting one or the other, we explored the use of evidence that may disconfirm either of these hypotheses. Using this counter- inductive approach we found no cases contradicting viviparity in metriorhynchids except for their phylogenetic position as archosaurs. A survey of reproductive modes among amniotes depicts the evolutionary plasticity of the transition to viviparity and a widespread occurrence among tetrapods secondarily adaptedto a marine life. Assuming oviparity for metriorhynchids implies egg-laying out of the water. However, their postcranial morphology (i.e. features of fore and hind limbs, pelvic girdle, and tail) contradicts this possibility. In this context we rejected oviparity for metriorhynchids.