I was as surprised to see this develop, as I’m sure you will be.
Adding the land whale Maiacetus inuus (Gingerich et al. 2009, Eocene ~47 mya, 2.6 m in length; Fig. 1) to the large reptile tree (Fig. 3) nested it at the base of the current Afrothere/herbivore clade along with the tenrec, Hemicentetes (Fig. 2). The resemblance is remarkable, despite the difference in size. And this sets the earliest origin of whales on a slightly different tangent with, I’m sure you’ll agree, much better support.
Figure 1. Maiacetus is a basal whale with legs and it is also a giant tenrec. Compare to Hemicentes in figure 2 and remember that another tenrec, Limnogale, has a long tail, webbed feet and a semiaquatic niche.
Tenrecs have been traditionally associated with
a list of mammals of African origin: golden moles, elephant shrews, aardvarks (Orycteropus), hyraxes (Procavia), elephants (Elephas), and sea cows, as they are here (Fig. 3) as well.
Whales have been traditionally associated with
artiodactyls, as they are here (Fig. 2) as well. The hippopotamus is considered their closest living relative based on DNA data. The present data appears to invalidate the hippo connection. We’ll see what happens when the hippo is added to the large reptile tree, but it does not look promising. Not sure if tenrecs were included in the whale DNA analysis study. If not, that was an oversight.
Figure 2. The short-tailed tenrec, Hemicentetes. Other than size and tail length, this taxon shares a long list of traits with the basal whale, Maiacetus in figure 1. This has not been recognized previously. Skeleton image used with permission from Digimorph.org.
The tenrec Hemicentetes
(Fig. 2) shares more traits with Maiacetus than any other taxon listed. And vice versa, of course. They nest as sisters.
Another very rare tenrec,
Limnogale (29-35cm) has a long thick tail, webbed feet and a semiaquatic lifetyle. That probably seals the deal. Limnogale is nocturnal, so it is using senses underwater we can only surmise from the whale relationship. This needs more study, but Limnogale is hard to catch! And it is very rare. Click here for an image and data on Limnogale. I want more data on that tenrec, but it has not been well studied or sent to digimorph.org yet.
Figure 3. The mammals updated with the addition of a basal whale, Maiacetus, and an aardvark Orycteropus.
While Limnogale has the
wet look and aquatic niche we are looking for in a whale ancestor. another Madagascar tenrec, Hemicentetes has skeletal data (Fig. 2) that enables comparison, but has a spiny coat (Fig. 4) like a hedgehog. Sometimes in evolution, you have to play the cards (data) you are dealt,
Not typical of placental mammals, a cloaca remains present, rather than a separate anus and urogenital opening and tenrecs lack a scrotum. That shows how primitive they are. Living whales also lack a scrotum, but have separate anal and genital openings, perhaps by convergence with most other mammals. Tenrecs are omnivorous. Most tenrecs are nocturnal and have poor eyesight, but their whiskers are sensitive. Distinct from whales, tenrecs tend to have 20-32 young. Some species are social.
Figure 4. The spiny tenrec Hemicentetes with a Digimorph skull overprinted. Until skeletal data on Limnogale comes in, this short tail tenrec will have to do. That foramen below the orbit is retained in some basal land whales.
That little foramen
below the orbit of Hemicentetes (Fig. 4) is also found in basal whales like Dorudon (Fig. 5). Not sure what it is or was used for. That’s another paper to be written by some future grad student.
Figure 5. Dorudon skull featuring the foramen below the orbit, similar to the one in the tenrec, Hemicentetes in figure 4.
For whale ancestors
you might like tenrecs (Fig. 6) more than hippos. The snout is long and narrow. The teeth are similar to those of whales both in pattern and size. With that long otter-like tail on Limnogale, and flexible spine on Hemicentetes, at this point we can only imagine that swimming tenrecs swim in a fashion more similar to whales than any sort of hippo could ever manage. The chest cavity is large. The feet are flat and have not developed hooves or lost digits. The tenrec/whale case may be one more instance where DNA has let us down.
Figure 6. Tenrecs now nest as sisters to whales in the large reptile tree. Here are a few other extinct land whales to scale. They are all giant aquatic tenrecs.
This discovery made my day.
Giant aquatic tenrecs add support to this continuing study and the validity of the large reptile tree at www.ReptileEvolution.com.
This is further evidence
that you don’t have to have the fossil in front of you to add to the present body of knowledge in evolution and paleontology, despite the vocal majority that says otherwise. That restrictive paradigm has to change.
Gingerich PD, Ul-Haq M, von Koenigswald W, Sanders WJ, Smith BH, Zalmout IS 2009. New protocetid whale from the middle eocene of pakistan: birth on land, precocial development, and sexual dimorphism. PLoS ONE 4 (2): e4366. doi:10.1371/journal.pone.0004366