File:Meckels cartilage - middle ear from the jaw.jpg

Hypothesis of evolutionary middle ear separation from the jaw

We hypothesize that definitive mammalian middle ear (DMME) detachment from the jaw, via Meckel's cartilage (MC) breakdown mediated, in part, by TGF-βR2 upregulation (right panel), occurred independently in four lineages: extant Monotremata (Node 1), multituberculates (Node 2), and likely also in extant marsupials (Node 3) and extant placentals (Node 4) (blue nodes and lines).

In ancestral mammaliaforms, the intact Meckel's element of the cynodont mandibular middle ear or of the partially mandibular middle ear (in Yanoconodon and Maotherium) is attached to Meckel's sulcus (red nodes and lines). Meckel's sulcus is therefore an indicator of MC-mediated connection between the jaw and middle ear. Meckel's sulcus is a prominent feature of zatherians (Peramus), and crown therians through some stem metatherians (Kokopelia) and eutherians (Eomaia, Prokennalestes). Thus, it may be inferred that zatherians and therians ancestrally had an MC-mediated connection between the jaw and middle ear (brown nodes and lines). Assuming that basal eutherians and metatherians had PMMEs, the DMME must have arisen separately in extant placentals (through increased clast activity and autophagy) and in extant marsupials (through increased clast activity and apoptosis).

Reference

Urban DJ, Anthwal N, Luo ZX, Maier JA, Sadier A, Tucker AS & Sears KE. (2017). A new developmental mechanism for the separation of the mammalian middle ear ossicles from the jaw. Proc. Biol. Sci. , 284, . PMID: 28179517 DOI.

Copyright

© 2017 The Author(s) Creative Commons logo Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

Figure 3 text above from figure legend.

Cite this page: Hill, M.A. (2024, April 23) Embryology Meckels cartilage - middle ear from the jaw.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Meckels_cartilage_-_middle_ear_from_the_jaw.jpg

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G