The walrus (genus: Odobenus) joins the LRT

No surprises here.
Odobenus, the walrus (Figs. 1, 2), nests with the seal, Phoca, in the large reptile tree (LRT, 1280 taxa). But I think you’ll see, the division between seals and walruses runs deep, perhaps with some parallel development of the flippers, fat, etc.

Figure 1. Walrus skeletons, swimming and walking, plus a view of the teeth, which barely erupt and cannot be seen in lateral view.

Figure 1. Walrus skeletons, swimming and walking, plus a view of the teeth, which barely erupt and cannot be seen in lateral view. Yes, that extra bone between the legs of the lower specimen resides in the penis.

Odobenus rasmanus (Linneaus 1758) is the extant walrus. The canines are much enlarged here. The other teeth are flat and barely erupt. The naris is elevated. The jaw joint is aligned with the bottom of the jaw and the retroarticular process is much reduced. The scapula is robust.

FIgure 2. Walrus skull with bones colorized.

FIgure 2. Walrus skull with bones colorized.

Walruses eat bivalve mollusk scraped from the sea floor bottom. 
According to Wikipedia, “The walrus’s body shape shares features with both sea lions (eared seals: Otariidae) and seals (true seals: Phocidae). As with otariids, it can turn its rear flippers forward and move on all fours; however, its swimming technique is more like that of true seals, relying less on flippers and more on sinuous whole body movements.[4] Also like phocids, it lacks external ears.” Earlier the LRT recovered separate terrestrial ancestors for seals and sea lions.

Figure 3. Ancestral walrus taxa from Robert Boessenecker. See references below.

Figure 3. Ancestral walrus taxa to scale from Boessenecker. 2014. Compare Neotherium to Puijila in figure 4. Neotherium nests closer to bears.

Neotherium (Fig. 3)
shares a long list of traits with Puijila, which was originally hailed as a last common ancestor for seals, sea lions and walruses (Fig. 4). In the LRT Pujilia is not basal to sea lions. In the LRT Neotherium nests with Ursus, the bear, not with Odobenus, the walrus.

What are the giant canines used for?
According to Wikipedia, “Tusks are slightly longer and thicker among males, which use them for fighting, dominance and display; the strongest males with the largest tusks typically dominate social groups.  Tusks are also used to form and maintain holes in the ice and aid the walrus in climbing out of water onto ice. Analyses of abrasion patterns on the tusks indicate they are dragged through the sediment while the upper edge of the snout is used for digging.”

You can think of walruses
as aquatic bears or aquatic stylinodontids (Fig. 4). Ursus and Neotherium are sisters to the last common ancestor (LCA) of walruses and stylinodontids with Puijila the LCA of bears and walruses.

Figure 4. Ursus maritimus compared to ancestral and related taxa, Mustela, Puijila and Stylinodon. Seeing them together makes comparisons easier.

Figure 4. Ursus maritimus compared to ancestral and related taxa, Mustela, Puijila and Stylinodon. Seeing them together makes comparisons easier.

Figure 5. Puijila nests down the line from the walrus, a trait you can see it its profile and general morphology. Compare to Neotherium in figure 4.

Figure 5. Puijila nests down the line from the walrus, a trait you can see it its profile and general morphology. Compare to Neotherium in figure 4.

References
Boessenecker R 2014. The evolutionary history of walruses, parts1–5:

  1. http://coastalpaleo.blogspot.com/2014/08/the-evolutionary-history-of-walruses.html
  2. http://coastalpaleo.blogspot.com/2014/08/the-evolutionary-history-of-walruses_26.html
  3. http://coastalpaleo.blogspot.com/2014/09/the-evolutionary-history-of-walruses.html
  4. http://coastalpaleo.blogspot.com/2014/09/
  5. http://coastalpaleo.blogspot.com/2014/11/the-evolutionary-history-of-walruses.html

Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Walrus

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