On Wed, May 6, 2020 at 5:11 AM Ben Creisler <bcreisler@gmail.com> wrote:
Ben CreislerA new paper. It would appear to name a new taxon but I can't check the full text. The thumbnail image caption isn't readable.Fangyuan Mao & Jin Meng (2020)
Making a mammalian ear. Modular decoupling of the mammalian middle ear and jaw discovered in a new species of Cretaceous stem therian mammals.
Zoology, Article 125767 (advance online publication)
doi: https://doi.org/10.1016/j.zool.2020.125767
https://www.sciencedirect.com/science/article/abs/pii/S094420062030026X
Highlights
Fossils of a stem therian mammal from the Early Cretaceous Jehol Biota, China, preserved unprecedented details of the middle ear morphologies.
The surangular bone is one of the ear ossicles, which was probably common in basal mammals and may have persisted in embryologic stage of some extant mammals.
The ear ossicles and jaw have evolved initially as integrated modules but eventually decoupled under natural selection.
The fossils documented the decoupling moment and the phenotype is interpreted as being recapitulated in early development of extant mammals.
The decoupled modules provided the potential for future improvement of hearing and chewing functions and diversities.
Abstract
Evolution of the definitive mammalian middle ear (DMME) as a textbook example in vertebrate evolution has been extensively studied during the last 200 years. Fossils provide the direct evidence on evolutionary stages of the DMME, but because of delicacy of the miniscule ossicles, unequivocal evidence about them has always been rare. Recent work on a stem therian mammal (124 million years old) shows presence of the surangular bone in the basal mammals as a primitive feature and potentially retained in the embryonic stage of some extant mammals. The work also proposed that the DMME and mammalian jaw evolved in a modular fashion. It started as a highly integrated complex in structures and functions, the two modules were regulated by similar developmental genetic mechanisms and eventually decoupled under natural selection so that the physical constraint the two modules imposed on each other was removed, allowing future improvement of each module for better function.