Where are the auditory bullae in desmostylians?

A reader wondered about
tympanic (auditory) bullae (ear container bones) in desmostylians. Then I wondered, too. All whales are famous for having them. Nobody talks about them in desmostylans. So what gives? Here are the data:

Short answer:
apparently bullae are easily knocked off and/or ignored during the process of fossilization and extraction, both in mysticetes and desmostylians. Some examples follow:

Gray whale (Eschrichtius)
Bullae were present, but somehow got knocked off when it came time to draw the diagram (Fig. 1).

Figure 1. Gray whale (genus: Eschrichtius) in which bullae were present, but omitted from a palate diagram.

Cornwallius (a pre-desmostylian cambaythere) — overlooked bulla, called a ‘mass’ in the text.

Figure 3. The pre-desmostylian Cornwallius. Here the tympanic bulla (bright green) was considered “a mass” in the text and otherwise not labeled.

Neoparadoxia (basal desmostylian)
Here you can see the depression that receives the bullae, but the bullae became missing at some stage in the process.

Figure 3. Palate of Neoparadoxia, a basal desmostylian, apparently missing the tympanic bullae (ear bones). Note the ear canal bones extending laterally, as in the hippo (figure 6).

Desmostylus, a derived desmostylian close to right whales
Same here. Bulla not published. Depression for the reception still present.

Figure 4. Desmostylus with missing bullae replaced in the empty spots left behind. Skull is obviously distorted and missing a big part of the cranium.

Caperea, a basal right whale
Here’s an odd one. Not sure what happened to the bulla in ventral view. They seem to appear in occiput view.

Figure 5. Caperea, a basal right whale, apparently missing the bullae in palate view that it had in occipital view. If not, please advise.

Hippopotamus
This goes back somewhat on the tree, but hippos are in the lineage of baleen whales in the LRT and their auditory bones are present.

Figure 6. Hippopotamus with auditory meatus (ear canal) in green, bulla (ear bone container bones) in yellow.

Ear bones compared
Baleen whale bullae greatly resemble toothed whale bullae. It’s true. Based on phylogeny, we’ll have to call this convergence. So is the loss of teeth in the rostrum of the sperm whale and blue whale. Convergence happens, but let’s keep an eye out for those bullae, now that we know what should be there.

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