Exploring ancestral phenotypes and evolutionary development of the mammalian middle ear based on Early Cretaceous Jehol mammals

Fangyuan Mao; Cunyu Liu; Morgan Hill Chase; Andrew K Smith; Jin Meng

doi:10.1093/nsr/nwaa188

Exploring ancestral phenotypes and evolutionary development of the mammalian middle ear based on Early Cretaceous Jehol mammals

Natl Sci Rev. 2020 Aug 25;8(5):nwaa188. doi: 10.1093/nsr/nwaa188. eCollection 2021 May.

Authors

Fangyuan Mao¹, Cunyu Liu², Morgan Hill Chase³, Andrew K Smith³, Jin Meng⁴

Affiliations

¹ Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
² Beipiao Pterosaur Museum of China, Beipiao 122100, China.
³ Microscopy and Imaging Facility, American Museum of Natural History, New York, NY 10024, USA.
⁴ Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA.

Abstract

We report a new Cretaceous multituberculate mammal with 3D auditory bones preserved. Along with other fossil and extant mammals, the unequivocal auditory bones display features potentially representing ancestral phenotypes of the mammalian middle ear. These phenotypes show that the ectotympanic and the malleus-incus complex changed notably during their retreating from the dentary at various evolutionary stages and suggest convergent evolution of some features to extant mammals. In contrast, the incudomalleolar joint was conservative in having a braced hinge configuration, which narrows the morphological gap between the quadroarticular jaw joint of non-mammalian cynodonts and the incudomalleolar articulations of extant mammals. The saddle-shaped and abutting malleus-incus complexes in therians and monotremes, respectively, could have evolved from the braced hinge joint independently. The evolutionary changes recorded in the Mesozoic mammals are largely consistent with the middle ear morphogenesis during the ontogeny of extant mammals, supporting the relation between evolution and development.

Keywords: Cretaceous; Jehol Biota; ectotympanic; malleus-incus; mammal evolution.