Editing Middle ear (section)

=== Mammals ===
Mammals are unique in having [[evolution of mammalian auditory ossicles|evolved a three-ossicle middle-ear]] independently of the various single-ossicle middle ears of other land vertebrates, all during the Triassic period of geological history. Functionally, the mammalian middle ear is very similar to the single-ossicle ear of non-mammals, except that it responds to sounds of higher frequency, because these are better taken up by the inner ear (which also responds to higher frequencies than those of non-mammals). The malleus, or "hammer", evolved from the [[articular]] bone of the lower jaw, and the incus, or "anvil", from the quadrate. In other vertebrates, these bones form the primary jaw joint, but the expansion of the [[mandible|dentary]] bone in mammals led to the evolution of an entirely new jaw joint, freeing up the old joint to become part of the ear. For a period of time, both jaw joints existed together, one medially and one laterally. The evolutionary process leading to a three-ossicle middle ear was thus an "accidental" byproduct of the simultaneous evolution of the new, secondary jaw joint. In many mammals, the middle ear also becomes protected within a cavity, the [[auditory bulla]], not found in other vertebrates. A bulla evolved late in time and independently numerous times in different mammalian clades, and it can be surrounded by membranes, cartilage or bone. The bulla in humans is part of the [[temporal bone]].<ref name="VB" />

Recently found fossils such as [[Morganucodon]] show intermediary steps of middle ear evolution. A new morganucodontan-like species, ''[[Dianoconodon youngi]]'', shows parts of the [[mandible]] (= dentary) that permit an auditory function, although these bones are still attached to the mandible.<ref>{{Cite journal |last1=Mao |first1=Fangyuan |last2=Zhang |first2=Chi |last3=Ren |first3=Jicheng |last4=Wang |first4=Tao |last5=Wang |first5=Guofu |last6=Zhang |first6=Fakui |last7=Rich |first7=Thomas |last8=Vickers-Rich |first8=Patricia |last9=Meng |first9=Jin |date=2024-04-03 |title=Fossils document evolutionary changes of jaw joint to mammalian middle ear |url=https://www.nature.com/articles/s41586-024-07235-0 |journal=Nature |volume=628 |issue=8008 |language=en |pages=576–581 |doi=10.1038/s41586-024-07235-0 |pmid=38570677 |bibcode=2024Natur.628..576M |issn=1476-4687}}</ref>