On the homology of crocodylian post-dentary bones and their macroevolution throughout Pseudosuchia

BONA P.; FERNANDEZ BLANCO M. V.; EZCURRA M.D.; VON BACZKO M. B.; DESOJO J.B.; POL, D.

ANATOMICAL RECORD

WILEY-LISS, DIV JOHN WILEY & SONS INC

Lugar: New York; Año: 2022

0003-276X

The lower jaw of early tetrapods is composed of several intramembranousossifications. However, a tendency toward the independent reduction of thenumber of bones has been observed in the mandible of mammals, lepidosaurs,turtles, crocodiles, and birds. Regarding archosaurs, the coronoid andprearticular bones are interpreted to be lost during the evolution of stem-birdsand stem-crocodiles, respectively, but the homology of the post-dentary bonesretained in living pseudosuchians remains unclear. Here, we combine paleontologicaland embryological evidence to explore in detail the homology of thecrocodylian post-dentary bones. We study mandible embryogenesis on a sampleof 71 embryos of Caiman and compare this pattern with the mandibulartransformations observed across pseudosuchian evolution. In the pre-hatchingontogeny of caimans, at least five intramembranous ossification centers areformed along the margins of the internal mandibular fenestra (perifenestralcenters) and, subsequently, merge to form the coronoid (three intramembranouscenters), angular (one intramembranous center), and articular(one intramembranous and one chondral center). In the fossil record, an independentprearticular is lost around the base of Mesoeucrocodylia (optimized asreappearing in Thalattosuchia if they are placed within Neosuchia), and thecoronoid is apomorphically lost in notosuchians. The integration of embryologicaland paleontological data indicates that most perifenestral centers areinvolved in the origin of the prearticular of non-mesoeucrocodylianpseudosuchians. These centers are rearranged during the evolution to contributeto different post-dentary bones in mesoeucrocodylians bolstering the ideathat the coronoid and the articular of Crocodylia are not completely homologousto those of other diapsids.