The choanal anatomy of the Sebecus icaeorhinus Simpson, 1937 and the variation of the palatine shape in notosuchians (Crocodyliformes, Mesoeucrocodylia)

Sebecidae is a clade of large carnivorous crocodyliforms that thrived in
the Cenozoic and is the only lineage of the diverse and terrestrial group
Notosuchia that survived the end-Cretaceous mass extinction event. Sebecus
icaeorhinus is the best-known taxon from this clade, both in terms of its
cranial and postcranial anatomy (known primarily from the holotype and the
specimen MPEF-PV 1776 respectively). An additional material represented by
a partial skull (MMP 235) is the only specimen that has preserved a
complete choanal region. Here we describe new information from this
specimen based on an X-ray computed tomography and identify through
comparisons with other taxa a large degree of variability in the palatal
anatomy within Sebecidae, in particular in the shape and extension of the
palatine (the bone that defines the anterior position and shape of the
secondary choana). We quantify here the variation in the shape of the
palatine bone of sebecids through a 2D morphogeometric analysis within the
context of notosuchian crocodyliforms. Although traditional accounts of
palatal evolution in crocodyliforms linked variation of this structure to
the adaptation to the aquatic environment, our analysis allows the
recognition of eight palatine morphotypes among terrestrial crocodyliforms
with very distinct paleoecological traits, including carnivorous,
omnivorous, and possibly herbivorous taxa. Furthermore, we show that
sebecids had a higher morphological disparity in the choanal region than
other terrestrial groups of Notosuchia, underscoring the importance of
this region for comparative, morphofunctional, and phylogenetic studies.