Reversals produce whale teeth, part 2

Short one today.
You might remember over a year ago a presentation on the evolution of mammal molars from simple to complex and back to simple again in toothed whales (Odontoceti, Fig. 1).

Figure 3. Mammal tooth evolution alongside odontocete tooth evolution, reversing the earlier addition of cusps.

Figure 1. Mammal tooth evolution alongside odontocete tooth evolution, reversing the earlier addition of cusps.

On the same note,
here’s a presentation of three skulls, Pachygenelus (pre-mammal cynodont), Megazostrodon (last common ancestor of all mammals in the large reptile tree (LRT, 1698+ taxa), and Maiacetus, a toothed pre-whale with limbs (Fig. 2).

Figure 1. The pre-mammal, Pachygenelus, the first mammal, Megazostrodon, and a transitional toothed whale, Maiacetus, with teeth highlighted to show the reversal in odontocete molars.

Figure 2. The pre-mammal, Pachygenelus, the first mammal, Megazostrodon, and a transitional toothed whale, Maiacetus, with teeth highlighted to show the reversal in odontocete molars. This may be the first time Megazostrodon was compared to a pre-whale.

Just concentrate on the teeth today,
and note how the simple cones (Fig. 3) of basal therapsids, then the canine led simple triangles of basal cynodonts (Fig. 2) then multicusped teeth of basal mammals (Fig. 2), slowly reversed over time to become, once again, triangles, then simple cones in odontocete whales (Fig. 4).

Figure 3. Basal therapsids, including Cutleria, with simple cones for teeth, as in odontocete whales.

Figure 3. Basal therapsids, including Cutleria, with simple cones for teeth, as in odontocete whales.

Figure 4. The killer whale (Orcinus orca) skeleton and skull with parts colorized.

Figure 4. The killer whale (Orcinus orca) skeleton and skull with parts colorized. Simple conical teeth line the jaws as in pre-cynodont synapsids.

As long-time readers know, baleen whales had their own evolution
as mysticetes arose from mesonychids, hippos, anthracobunids and desmostylians in turn, according to results recovered from the large reptile tree, which minimizes taxon exclusion by testing a wide gamut of nearly 1700 taxa.

Still waiting for a competing analysis
that tests a similar gamut of taxa. Emails to whale experts have not earned replies.


References

https://pterosaurheresies.wordpress.com/2019/01/02/mammal-tooth-evolution-toward-complexity-and-then-simplicity/

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