Monday, December 31, 2012

2012 in Review: Advances in Marine Mammal Paleontology

Even though it's already twelve or so hours into 2013 here, since most of my readers are still in 2012 at the moment I thought I'd take some time to do a brief review of new research on fossil marine mammals published during the last year. It's been a good year for the pygmy right whale, and sirenians. Not much has been done with fossil pinnipeds, unfortunately (but stay tuned... especially around mid-January...).

I'm doing this in alphabetical order of the author's last name - so I promise that a taphonomic article coming first does not reflect my own bias. Early in the year Zain Bela├║stegui and colleagues published on a Miocene mysticete skeleton in PPP which was not only articulated, but also had a number of flask-shaped Gastrochoenolites borings in it. Such borings are common in marine mammal bones, particularly those from lag deposits like the Red Crag in eastern England, as well as the Santa Margarita Sandstone in California. But bored remains from those units are all allochthonous, and the fact that the skeleton was still articulated meant that it was autochthonous, which is a pretty surprising find in my opinion. They also did a great job at summarizing previously published biogenic bone modifications (admittedly a better job than I did in my bite marks paper).

I've already covered Michelangelo Bisconti's publication in Zoological Journal of the Linnean Society on the new neobalaenid (or neobalaenine...?) genus Miocaperea from Peru, which you can check out here. Miocaperea is not the first pygmy right whale to be reported from the fossil record (see below), but it is the first non-fragmentary specimen - and at 7-8 million years old, it indicates that the modern Caperea morphology has been around for a long time.

Although technically not published yet, a recent paper in PPP (online early) by Mark Clementz, my adviser Ewan Fordyce, UW student Stephanie Peek, and UM professor David Fox (who during the 2009 MSU geology field camp final mapping project, I ran into out at Frying Pan Gulch - the U. Minnesota field camp was out there at the same time; Dave is a co-supervisor for my good friend and taphonomy cohort Laura Vietti's Ph.D.) focuses on oxygen and carbon isotopes of Oligocene cetaceans from New Zealand and South Carolina. They studied odontocetes, toothed mysticetes, toothless mysticetes, and the enigmatic kekenodontids (the surprisingly dorudontine-like Kekenodon sp. in above photo). Among their findings - kekenodontid isotopes changed from anterior teeth to posterior, probably reflecting ontogenetic changes from nursing to adult feeding. Low O and C isotope levels for toothless mysticetes were similar to modern mysticetes, suggesting that they already were migrating along a latitudinal gradient, and that toothed mysticetes and odontocetes were "resident" rather than transient populations.

Another paper that just recently came out by my colleague Julia Fahlke in Palaeo-Electronica uses 3D digital models to reconstruct feeding by Basilosaurus on Dorudon, based on several skulls of juvenile Dorudon with large bite marks. The mouth of Basilosaurus was opened and the skulls of poor baby Dorudon rotated until possible fits were found. A pretty neat paper with some great graphics.

Another paper on fossil neobalaenids - which I've also already talked about. This is the first reported find of a neobalaenid (pygmy right whale) in the fossil record, published by Erich Fitzgerald in JVP.

Yet another paper about Caperea... which I just posted about last week, and you can check it out here. This paper came out last week in Proceedings of the Royal Society B, published by R.E. Fordyce and Felix Marx, and includes a new phylogenetic analysis and presents the hypothesis that the modern pygmy right whale is the sole surviving member of the (formerly extinct) family Cetotheriidae.

Jonathan Geisler and colleagues published in JVP over the summer a new genus of iniid river dolphin, Meherrinia, from the Meherrin River, North Carolina, represented by numerous (about a dozen) partial skulls. At SVP in Raleigh this year, Jonathan, Brian Beatty, and Carl Mehling visited a local collector who had several more specimens he donated - in addition to some other great stuff. Meherrinia is the first diagnostic iniid fossil reported from marine rocks.

Ukrainian colleague Pavel Gol'Din and coauthor K.A. Vishnyakova published an article in APP (still in the forthcoming articles section) on a high latitude record of the southern hemisphere beaked whale Africanacetus, previously reported by Bianucci et al. (2007) from the South African continental shelf. The fossil is the highest-latitude record of a beaked whale in the fossil record, and is 6000 km from the type locality, suggesting it had a circum-antarctic distribution. Unfortunately, the age of these specimens - like the South African material - is totally unknown, but assumed to be Neogene in age.

A Pleistocene record of a bottlenose dolphin (Tursiops sp.) was reported on by Toshiyuki Kimura and colleages in the Bulletin of the Gunma Museum. Pleistocene records of marine mammals are fairly rare, and such as in this case, are mostly composed of extant genera and species.

The only paper this year (to my knowledge) on fossil pinnipeds was published by Irina Koretsky and colleagues in the journal Deinsea. In it they describe a new species of the early phocid Leptophoca from both sides of the atlantic - Leptophoca amphiatlantica, based on isolated femora. The new species is found in the Calvert Formation and Saint Mary's Formation of Maryland and Virginia, and the Miocene Upper North Sea Group in the Netherlands (from the "Hoojdonk sandpit", a whimsical name to non-dutch speakers like myself). However, it's unclear exactly how much taxonomic utility is preserved in isolated postcrania.

Korean paleontologists Y.M. Lee, D.K. Choi, and former Otago student Hiroto Ichishima published on a middle Miocene platanistid from south Korea in JVP. This new specimen is just a fragmentary (but well preserved) rostrum - at first glance, some folks would be hard pressed to tell whether this was a dolphin or an ichthyosaur. They identified this specimen as a pomatodelphine (including the Floridan fossil dolphin Pomatodelphis) rather than an allodelphinid dolphin based on tooth morphology. This is interesting, as allodelphinids are already known from the early and middle Miocene of California - but pomatodelphines are not yet known from the Pacific, giving this interesting biogeographic implications.

Japanese colleague Mizuki Murakami recently published parts of his dissertation undertaken at Waseda University regarding fossil porpoises (Phocoenidae) from Japan. He described three new genera between two articles published in the same issue of JVP: Archaeophocoena, Miophocoena, and Pterophocoena. In one of these articles, he reconstructs the facial evolution of phocoenids and other delphinoids in painstaking detail, and in the other, conducts a detailed phylogenetic analysis of delphinoids, with interesting phylogenetic results. It's also the first analysis to include fossil monodontids Denebola and Bohaskaia, as well as the bizarre creature Odobenocetops (which plots out as sister to the monodontids).

A paper in the works for a long time came to fruition this year: Yoshihiko Okazaki (Kitakyushu Museum) described a new eomysticetid from Japan which he named Yamatocetus canaliculatus. It is similar in many regards to Eomysticetus - and is more complete, and has a partial postcranial skeleton. I really ought to talk about this one in more detail later. Aside from all the usual weirdness of an eomysticetid, this taxon also appears to retain individual alveoli, which Okazaki interpreted as housing reduced teeth during life.

Silvia Sorbi and colleagues published on new remains of Metaxytherium subapennum, the geochronologically youngest sirenian in the Mediterranean and youngest species of Metaxytherium. Metaxytherium is principally a middle-late Miocene dugongid - but one relict species persisted in the Mediterranean, even after dwarfism triggered by the Messinian Salinity Crisis (for the uninitiated, the Mediterranean nearly dried up at the Mio-Pliocene boundary), and reflooding of the Mediterranean. Responding to reestablishment of the Mediterranean Sea, Metaxytherium subapennum increased in body size from its ancestors. Unlike hydrodamaline dugongids in the North Pacific, Metaxytherium subapennum was unable to adapt to colder climates and went extinct during the middle Pliocene.

Two recent papers by Tarasenko and Lopatin published in the Palaeontological Journal focus on new records of cetotheriid baleen whales from the Northern Caucasus. Two new genera were reported: Kurdalogonus from Adygea, and Vampalus from Chechnya. For the lazy, these regions of the Russian Federation lie between eastern Ukraine/Black Sea and western Kazakhstan/Caspian Sea. Kurdalogonus in some ways is very similar to Cetotherium rathkei, another cetotheriid from the former Paratethys (Ukraine to be exact). Vampalus, on the other hand, is a bit more of a freak, and was identified as a herpetocetine - although no phylogenetic analysis was conducted (although the earbones, I think, are a bit of a selling point for me). It definitely has some weird stuff going on with the braincase, and in some ways looks like a cross between a herpetocetine and an aetiocetid.

Still with me? Almost done. Early on this year, my good friend Jorge Velez-Juarbe and Nick Pyenson published in JVP a new genus of fossil monodontid, which they named after USNM collections manager Dave Bohaska. I had the pleasure of meeting Dave in October - he's very entertaining and quite a character, and goes above and beyond the call of duty to make sure you have a productive/successful USNM visit, tracking down all sorts of obscure fossils, opening storage jackets, etc. The fossil was collected in the 1960's from the Yorktown Formation at Rice's Pit in Virginia, where the type specimen of Balaena ricei was also collected. Since it was not from the Yorktown at Lee Creek, this specimen was not described by Whitmore and Kaltenbach (2008) in the Lee Creek IV volume, where they described all sorts of monodontid earbones and partial skulls/mandibles as Delphinapterus (modern beluga). Now it appears that two monodontids were present (or, alternatively, everything may be referable to Bohaskaia).

Another paper by Jorge and colleagues early in the year, published in PLOS One. This paper discusses feeding ecology in three sympatric sirenian assemblages from the late Oligocene of Florida, early Miocene of India, and early Pliocene of Mexico. Each of these assemblages included three dugongid sea cows, and although body size and certain feeding adaptations did overlap in each assemblage, at least one consistent difference was present in each. Modern sirenians do not geographically overlap, and these assemblages appear to have evolved iteratively during the Cenozoic - in other words, different niches were haphazardly 'filled' by different species of dugongids through time (rather than the small bodied taxa being closely related and vice versa).

And another sirenian study to finish off 2012. German researcher Manja Voss recently published in Palaeontologische Zeitschrift on a new skeleton of Halitherium schinzii from the early Oligocene of western Germany. This specimen suggests that some taxonomic revision for the species is required. Interestingly, some figures in this paper look like there are Osedax pockmarks on the bones of this animal.

Have a productive 2013 - I didn't get anything published in 2012, although as alluded to above, keep your eyes peeled mid-January; I've got three other papers in review at the moment, and a couple more nearing submission, so 2013 is going to be a good year for me, I can tell already. 

Some of these studies I really ought to talk about in further detail, but I'm sick of typing (and if you're a healthy human being, you're probably sick of reading this). In any event, it's New Year's Eve, stop reading the internet and go to a party already!

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