Periotic Bone?

[RickNC]

Found this in gmr which has Cretaceous to Pleistocene fossils.

Looks like an incomplete periotic ear bone but wanted to confirm:

[Boesse]

Based on the configuration of the foramina in the third photo, it's a partial petrosal - and just the pars cochlearis at that - of a balaenopterid whale, probably Balaenoptera sp.

[RickNC]

Based on the configuration of the foramina in the third photo, it's a partial petrosal - and just the pars cochlearis at that - of a balaenopterid whale, probably Balaenoptera sp.

Thanks. Is that different than the periotic?

[Metopocetus]

Thanks. Is that different than the periotic?

It is the same thing.

Bobby, could you explain why you use petrosal vs periotic? I honestly don't know if one is more proper to use or not.

[Boesse]

Excellent question (by the way, you have an awesome screen name). So in terrestrial mammals, the temporal bone is composed of three portions: the squamous portion, petrous portion, and the tympanic bulla. In terrestrial mammals (including pinnipeds, so I really mean non-cetaceans) they are all fused together (to varying degrees). The petrous portion is usually relegated to human anatomy, so in paleo it's called the petrosal, and this term applies to most mammals.

However, at some point anatomists noted that in dolphins the petrosal is effectively isolated from the skull by a series of sinuses, and connected only by small non-fused butt joints and ligaments - and this influenced the adoption of a new term, the periotic; I suspect that some of the middle ear ossicles, or perhaps the tympanic, were referred to as the otic and this became the peri-otic by association.

Anyway, there is a bit of a divide in the paleo-cetacean world; some researchers who work on larger scale cetacean relationships prefer the term petrosal - as it is the same bone, and since cetaceans are mammals, they don't really deserve special status; my undergraduate mentor, Jonathan Geisler, prefers the term petrosal. I'm also of this opinion. Some folks use petrosal for baleen whales, since the petrosal is still somewhat articulated with the skull, rather like a land mammal (although some of this is a secondary reversal, as some archaeocetes possess a less extreme version of the odontocete condition). My Ph.D. advisor - R. E. Fordyce - prefers the term periotic, and my colleague in Australia, Erich Fitzgerald, prefers it as well in order to stress cetacean monophyly. It doesn't really matter, and it effectively boils down entirely into semantics.

[RickNC]

Thanks Bobby for that information. I find very few of these but hundreds of bullas per year.