Rise of the Cetacea: Part III – The Remingtonocetids


In the previous post of this series we looked at the ambulocetids (if you haven’t read it then check it out here). This time we’re going to continue our exploration of cetacean evolution by looking at another primitive group: the remingtonocetids. The odd title of the family comes from the genus Remingtonocetus, which was itself named in honour of one of the founding fathers of modern palaeocetology (the study of fossil whales), Remington Kellogg.

This very simplified cladogram shows the position of the remingtonocetids relative to other cetaceans.

This very simplified cladogram shows the position of the remingtonocetids relative to other cetaceans.

In addition to Remingtonocetus, there are another four genera in the family: Andrewsiphius; AttockicetusDalanistes; and Kutchicetus (Uhen 2010). The five genera are all known from the middle Eocene of India and Pakistan.

I mentioned in the last post that ambulocetids resembled furry crocodiles more than whales. The remingtonocetids however took this likeness even further. They possessed very elongate rostra and mandibles that had a remarkably long symphysis, in some taxa stretching as far back as their cheek teeth. The crocodilian analogy was further complimented by their low, low body shape. To make these animals even more fearsome some taxa also had mediolaterally flattened teeth, making them look like sharks teeth (Gingerich et al 2001)! The group still were able to move around on land, with isotopic evidence suggesting that these animals remained in a nearshore habitat and had a marine diet (Clementz et al 2006).

This is a reconstruction of Remingtonocetus by the fantastic palaeoartist Carl Buell, Image from Gatesy et al 2013.

This is a reconstruction of Remingtonocetus by the fantastic palaeoartist Carl Buell, Image from Gatesy et al 2013.

Remingtonocetids, like ambulocetids, possessed large mandibular foramina, but the lateral wall of the mandible is thinner than that seen in ambulocetids, meaning that the sensitivity of their underwater hearing had increased. The land mammal hearing mechanism is still present, indicating that these animals could also still hear in air, albeit poorly. The contact between the tympanic and periotic is also further reduced and the morphology of the middle ear ossicles are beginning to approach that of modern cetaceans (Nummela et al 2007).

This is the skeleton of Kutchicetus minimus on exhibit in the National Museum of Nature and Science, Tokyo, Japan. Image by Momotarou2012 from Wikimedia Commons.

This is the skeleton of Kutchicetus minimus on exhibit in the National Museum of Nature and Science, Tokyo, Japan. You can clearly see how long the skull is and just how crocodylian these animals may have appeared! Image by Momotarou2012 from Wikimedia Commons.

Despite becoming increasingly well adapted to an aquatic lifestyle, the early cetacean groups we have looked at so far all spent their time in the water near to the shore. This restricted their ability to disperse and spread out across the globe. The next group we encounter in this series however will change this and we’ll see the beginning of the cetacean’s conquest of the world’s oceans.

 

Other posts in the Rise of the Cetacea series:

Part I - The Pakicetids

Part II -  The Ambulocetids

References

Clementz MT, Goswami A, Gingerich PD, Koch PL. 2006. Isotopic records from early whales and sea cows: contrasting patterns of ecological transition. J. Vertebr. Paleontol. 26:355–70.

Gatesy, J., Geisler, J.H., Chang, J., Buell, C., Berta, A., Meredith, R.W., Springer, M.S. & McGowen, M.R., 2013. A phylogenetic blueprint for a modern whale. Molecular Phylogenetics and Evolution 66, 479–506.

Gingerich PD, Ul-HaqM, Khan IH, Zalmout IS. 2001b. Eocene stratigraphy and archaeocete whales (Mammalia, Cetacea) of Drug Lahar in the eastern Sulaiman Range, Balochistan (Pakistan). Contrib. Mus. Paleontol. Univ. Mich. 30(11):269–319.

Nummela, S., Thewissen, J.G.M., Bajpai, S., Hussain, T., Kumar, K., 2007. Sound transmission in archaic and modern whales: anatomical adaptations for underwater hearing. Anatomical Record 290, 716–733.

Uhen, M.D., 2010. The origin(s) of whales. Annual Review of Earth and Planetary Sciences 38, 189–219.

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