Wednesday, November 3, 2010

A bizarre new pilot-whale relative from the Pliocene of the North Sea

This morning when I woke up I had a nice message on facebook from a friend of mine - a link to a press release on a new fossil dolphin from the North Sea. To be honest (I had just woken up and was still fairly groggy when I first read it) I first saw this beautiful painting below, and not quite realizing it was a painting, the first thing I thought was "whoa, another extant cetacean???"

I then thought, "whoa, that reconstruction looks really weird."

Reconstruction of Platalearostrum hoekmani from Post and Kompanje (2010) by Remie Bakker.

Fortunately, I was easily able to find a link to the pdf for the article (which came out today in the European journal Deinsea) and see why the beast in the painting looks so strange. Post and Kompanje (2010) report on a fragmentary cranium of a bizarre new odontocete. While very incomplete, the preserved portion of the rostrum (="snout") does exhibit some strange features - a very low tooth count (6 sockets/alveoli), a laterally convex toothrow, and an insanely wide lateral 'wing' of the premaxilla, which makes the rostrum wider towards the anterior tip. The maxilla is also not the lateral most portion of the rostrum towards the front - another weird feature (which is shared in the pilot whales, Globicephala, and the extinct Protoglobicephala). The lateral 'wing' of the premaxilla is also pointed 'upwards' (dorsally) a bit, to make the dorsal rostrum surface concave, like a giant spoon. Although totally weird, the rostrum shares a number of features with the pilot whale Globicephala - anteriorly widening premaxillae, rugose bone surface on the premax, a short laterally convex toothrow, and a rostrum that is pretty short and blunt in general. Globicephala in general is already a very strange critter, and Platalearostrum makes it look sober in comparison.

The holotype fossil of Platalearostrum hoekmani (modified from Post and Kompanje, 2010)

Other features (aside from its close affinity with Globicephala) indicate its inclusion within the clade Globicephalinae. The authors curiously chose to use the clade Orcininae - in the usage of Bianucci (2005). Recent molecular analyses have shown the Globicephalinae paraphyletic in the sense that Orcinus is usually not included - and everything else (Globicephala, Feresa, Grampus, Pseudorca, Orcaella) make a monophyletic group. Without Orcinus, it just isn't the Orcininae anymore. Orcininae may be a valid term if fossil taxa like Hemisyntrachelus and Arimidelphis are shown to be sister taxa of Orcinus orca and the extinct Orcinus citoniensis. That being said, Globicephala is not in that group. Which is all the more interesting, suggesting two different clades of delphinids trending toward (relative) gigantism during the Pliocene.

Comparison of Globicephala macrorhynchus and Platalearostrum hoekmani (from Post and Kompanje, 2010)

This article made me pretty happy because I've worked a little on fossil globicephalines from the Pliocene of California. There aren't that many - bona fide delphinid fossils are generally quite rare in the Mio-Pliocene record in California, as opposed to the obscenely delphinid rich (and diverse!) Pliocene fossil record of Italy. Things like Orcinus, Globicephala, Protoglobicephala, Arimidelphis, and Hemisyntrachelus are all already living (not necessarily coexisting) in the world's oceans in the Pliocene, and now we have another weird one on top of this. Certainly it can be said that during the Pliocene, delphinids were experimenting with new "body plans" (loosely using the term) and rapidly diversifying. The Pliocene was a weird time, and boasted a combination of many strange marine mammals which were more derived than extant relatives often with novel anatomical features and adaptations, relatives of modern taxa with wider geographic distributions, and holdovers of archaic taxa which had not yet kicked the proverbial bucket.

Klaas Post, Erwin J.O. Kompanje, 2010. A new dolphin (Cetacea, Delphinidae) from the Plio-Pleistocene of the North Sea. Deinsea 14:1-14

Bianucci, G., 2005. Armidelphis sorbinii a new small killer whale-like dolphin from the Pliocene of the Marecchia river (central eastern Italy) and a phylogenetic analysis of the Orcininae (Cetacea: Odontoceti) - Rivista Italiana di Paleontologia et Stratigrafia 111: 329-344


Anonymous said...

Thanks for your nice analysis of our article.

Erwin J.O. Kompanje, the Netherlands

Robert Boessenecker said...

Hallo Erwin!

If you couldn't tell from my post, I really enjoyed the paper! I'm working with Jonathan Geisler on some pilot whale fossils from the Pliocene of Central California which probably belong to Globicephala.

Congratulations on getting the article published!