Pinniped origins complicated after adding the ‘swan seal’ Acrophoca

Question:
Which terrestrial carnivores gave rise to aquatic pinnipeds (= seals and kin)?

From Pinniped Evolution – ScienceDirect.com
“The traditional view, also referred to as diphyly, proposes that pinnipeds originated from two carnivore lineages, an odobenid (walrus) plus otariids (fur seals and sea lions) grouping affiliated with ursids (bears) and phocids (seals) being related to mustelids (weasels, skunks, otters, and kin).“

From Smithsonian Ocean
“One potential ancestor was Puijila, an otter-like creature with a long tail and webbed feet that likely lived by freshwater lakes about 24 million years ago.“

From Wikipedia – Pinniped
“Pinnipeds belong to the suborder Caniformia of the order Carnivora; their closest living relatives are musteloids (weasels, raccoons, skunks and red panda), having diverged about 50 million years ago.”

Meanwhile, in the LRT the clade Carnivora
has been difficult to build and remains fragile. Here pinnipeds (= seals, sea lions and walruses) are derived from an Eocene relative that looked like Mellivora, the extant honey badger that can swim, but is not a good swimmer, as we learned earlier here.

A better swimmer, the weasel, Mustela, is basal to the otters and to the Mellivora clade leading to pinnipeds.

Another poor swimmer, the European badger, Meles, is basal to a clade that includes Cynogale, the swimming otter civet and Neotherium, a fossil aquatic taxon.

Those hypotheses still hold, even with the following taxon addition.

Figure 1. Skeleton of Acrophoca, the ‘swan seal’. ” data-image-caption=”

Figure 1. Skeleton of Acrophoca, the ‘swan seal’.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/acrophoca-piscophoca-skeleton588.jpg?w=100″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/acrophoca-piscophoca-skeleton588.jpg?w=340″ tabindex=”0″ role=”button” class=”size-full wp-image-87713″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/acrophoca-piscophoca-skeleton588.jpg” alt=”Figure 1. Skeleton of Acrophoca, the ‘swan seal’.” width=”584″ height=”1757″ />

Figure 1. Skeleton of Acrophoca, the ‘swan seal’. Pelvis enlarged.

Now there’s a twist.
The Late Miocene ‘swan seal’ Acrophoca (Figs 1,3 ) is different than most seals and sea lions. Here it nests with the extant mongoose, Eupleres (Fig 2), currently restricted to Madagascar along with several other Cretaceous taxa finding this island their refuge. And these taxa nest within the LRT’s pinniped subset with Mellivora at its base.

Figure 4. Eupleres, the near extinct Western falanouc of Madagascar. ” data-image-caption=”

Figure 4. Eupleres, the near extinct Western falanouc of Madagascar.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/08/eupleres_invivo588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/08/eupleres_invivo588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-70613″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/08/eupleres_invivo588.jpg” alt=”Figure 4. Eupleres, the near extinct Western falanouc of Madagascar.” width=”584″ height=”272″ />

Figure 2. Eupleres, the near extinct Western falanouc of Madagascar.

Acrophoca longirostris
(Muizon 1981, Late Miocene. 1.5m) is the ‘swan neck seal’. According to Wikipedia, “It was thought to have been the ancestor of the modern leopard seal; however, it is now thought to be a species of monk seal. Its teeth were built for piercing, implying a diet consisted primarily of fish. However, it also had interdigitated tooth cusps causing the teeth on the upper jaw to fit with the teeth of the lower jaw, which is consistent with filter feeders. Unlike other earless seals, Acrophoca had a long and flexible neck, with an elongated body. The orientation of the pelvis, which in comparison to modern earless seals is everted, as well as adaptations to the hind limbs suggest that swimming was mainly powered by the back flippers.”

Here Acrophoca nests with extant Eupleres (Fig 2) between seals and sea lions. Note the large naris and exceedingly small orbit, making this pinniped different that others.

Figure 2. Skull of Acrophoca to scale with Palaeogale and extant Eupleres. ” data-image-caption=”

Figure 2. Skull of Acrophoca to scale with Palaeogale and extant Eupleres.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/acrophoca-skull588.jpg?w=200″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/acrophoca-skull588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87716″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/acrophoca-skull588.jpg” alt=”Figure 2. Skull of Acrophoca to scale with Palaeogale and extant Eupleres.” width=”584″ height=”875″ />

Figure 3. Skull of Acrophoca to scale with Palaeogale and extant Eupleres.

Eupleres major
(Doyère 1835 snout-rump length up to 65cm + 25cm tail) is the extant (but nearing extinction) Western falanouc, a mongoose from Madagascar. Here it nests with the later, larger ‘swan seal’ Acrophoca (Figs 1, 3). Note the elongate premaxilla, the gracile mandible, the reduced canine and other traits shared with the Miocen seal. Diet of worms, slugs, snails. A single young is born in a burrow and can travel with the mother within two days.

The mammal subset of the LRT is far from finished.
Adding taxa, like Acrophoca, sometimes recover new hypotheses modeling evolutionary events that require further testing.

It’s complicated. Wish someone else was working on their own LRT in parallel with this study. Then we could compare notes and avoid problems.

References
Doyére LMF 1835. Notice sur un mammifére de Madagascar, formant le type d’un nouveau genre de la famille des Carnassiers insectivores de M. Cuvier. Ann. Sci. Nat. Zool. 4: 270–283.
de Muizon C 1981. Les vertébrés fossiles de la formation Pisco (Pérou). Reserche sur les grandes civilisations. Mémoire 6. Institu Francais d’études Andines.

wiki/Pinniped
wiki/Western falanouc
wiki/Eupleres
wiki/Acrophoca