A monotreme-like auditory apparatus in a Middle Jurassic haramiyidan
Authors: Sarah L Shelley
Junyou Wang
Han Hu
Shundong Bi
John R Wible
Bin Guo
Journal: Nature (2021)
Discipline: Multidisciplinary
Keywords: mammals; auditory ossicles; Mesozoic; evolution; Vilevolodon diplomylos
Affiliations: Centre for Vertebrate Evolutionary Biology, Institute of Palaeontology, Yunnan University, Kunming, China., Inner Mongolia Museum of Natural History, Hohhot, China., Centre for Vertebrate Evolutionary Biology, Institute of Palaeontology, Yunnan University, Kunming, China. ., Section of Mammals, Carnegie Museum of Natural History, Pittsburgh, PA, USA. ., Section of Mammals, Carnegie Museum of Natural History, Pittsburgh, PA, USA., School of Geosciences, University of Edinburgh, Edinburgh, UK., Zoology Division, School of Environmental and Rural Sciences, University of New England, Armidale, New South Wales, Australia., Department of Biology, Indiana University of Pennsylvania, Indiana, PA, USA. .

Abstract:  Among extant vertebrates, mammals are distinguished by having a chain of three auditory ossicles (the malleus, incus and stapes) that transduce sound waves and promote an increased range of audible-especially high-frequencies1. By contrast, the homologous bones in early fossil mammals and relatives also functioned in chewing through their bony attachments to the lower jaw2. Recent discoveries of well-preserved Mesozoic mammals have provided glimpses into the transition from the dual (masticatory and auditory) to the single auditory function for the ossicles, which is now widely accepted to have occurred at least three times in mammal evolution3-6. Here we report a skull and postcranium that we refer to the haramiyidan Vilevolodon diplomylos (dating to the Middle Jurassic epoch (160 million years ago)) and that shows excellent preservation of the malleus, incus and ectotympanic (which supports the tympanic membrane). After comparing this fossil with other Mesozoic and extant mammals, we propose that the overlapping incudomallear articulation found in this and other Mesozoic fossils, in extant monotremes and in early ontogeny in extant marsupials and placentals is a morphology that evolved in several groups of mammals in the transition from the dual to the single function for the ossicles. 

Retracted: No

PubPeer comments:
 Readers should become aware of a recent preprint posted on bioRxiv entitled Monotreme middle ear is not primitive for Mammalia, which calls into question the conclusions by Wang et al., 2021 study. https: www.biorxiv.org content 10.1101 2021.05.03.442467v1 From the abstract: The study on evolution of the mammalian middle ear has been fueled by continuous discoveries of Mesozoic fossils in the last two decades. Wang et al. recently reported a specimen of Vilevolodon diplomylos (IMMNH-PV01699) that adds to the increasing knowledge about the auditory apparatus of  haramiyidans , an extinct Mesozoic group of mammaliaforms. The authors hypothesized that a middle ear with a monotreme-like incus and malleus and incudomallear articulation was primitive for mammals, which challenges the convention that the monotreme middle ear is specialized or autapomorphic in mammals. **We raise concerns about terminology and identification of the incus presented by Wang et al. and show that their analysis does not support their hypothesis; instead, it supports the one by Mao et al.** ,