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Monotreme ears (Science)
My apologies if this has already been forwarded to the list...
Thomas H. Rich, James A. Hopson, Anne M. Musser, Timothy F. Flannery,
Patricia Vickers-Rich (2005). Independent Origins of Middle Ear Bones in
Monotremes and Therians. Science 307: 910-914.
ABSTRACT: A dentary of the oldest known monotreme, the Early Cretaceous
_Teinolophos trusleri_, has an internal mandibular trough, which in
outgroups to mammals houses accessory jaw bones, and probable contact facets
for angular, coronoid, and splenial bones. Certain of these accessory bones
were detached from the mandible to become middle ear bones in mammals.
Evidence that the angular (homologous with the mammalian ectotympanic) and
the articular and prearticular (homologous with the mammalian malleus) bones
retained attachment to the lower jaw in a basal monotreme indicates that the
definitive mammalian middle ear evolved independently in living monotremes
and therians (marsupials and placentals).