I apologize for the lack of posts over the past month - the last few weeks I have been working furiously in order to complete a long list of manuscript revisions for a long manuscript for the journal Geodiversitas. Additionally, I've been trying to complete a laundry list of collaborations, which are slowly being completed. Now that I have breathing room again, welcome to the 200th post on Coastal Paleo (down under)!
Last week I was pleased to see the publication of not one, not two, but three different papers on cetaceans in the most recent JVP issue. I was also amused by the lamentation by some of my former fellow students from MSU that there weren’t enough dinosaur papers in JVP (one only!). It’s a welcome change, from my perspective – to be honest, roughly half of JVP issues have no marine mammal articles, and the majority have multiple (boooring…) dinosaur papers. To be fair, there are a hell of a lot more dinosaur researchers than there are marine mammal paleontologists, so it’s to be expected. On the other hand, despite the disappointment that comes with scrolling through brand new but marine mammal-less issues of journals, it does come with the upside that we often don’t have to add citations for numerous articles coming out while your manuscript is in review (unless it’s a long article that takes a while for review and revisions; I had a revised article I recently resubmitted which had taken about eight months from submission to completion of revisions, and I had to add citations for about a dozen new articles).
Comparison of Brachydelphis mazeasi (above) and Brachydelphis jahuayensis (below).
From Lambert and Muizon (2013).
The holotype (top) and paratype (bottom) of Brachydelphis jahuayensis from the
Pisco Formation of Peru. From Lambert and Muizon (2013).
Up until the description of Brachydelphis, all fossil “river dolphins” also shared an elongate rostrum (or, if not complete, the indication of an elongate rostrum) – Pontistes, Pliopontos, Ischyorhynchus, Parapontoporia, Zarhachis, Pomatodelphis, the list goes on and on. Brachydelphis on the other hand bore a tiny little rostrum, to the point where it must have resembled something like a true porpoise with weird flippers. A subsequent study reinterpreted the fragmentary Protophocoena minima from the Miocene of Belgium as a brachydelphinine (Lambert and Post 2005). The new study by Lambert and Muizon (2013) focuses on the description of a new species of Brachydelphis with a less stunted rostrum, and in a way is a bit more normal-looking. The rostrum of Brachydelphis jahuayensis, however, is still quite short relative to other “river dolphins”, and perhaps in that aspect still evocative of the name Brachydelphis. They reported on numerous new skulls which are preserved beautifully. The most fascinating aspect of the paper is the age of Brachydelphis jahuayensis – it’s from the El Jahuay vertebrate level of the Pisco Formation, which is younger than Cerro La Bruja, and thus younger than the shorter-snouted Brachydelphis mazeasi. Assuming an ancestor-descendant relationship (which I consider to be reasonable) between the two, it implies that Brachydelphis first evolved a short rostrum, and was then reversed during the late Miocene. It may not be surprising, as we already know that the cetacean rostrum is a fairly plastic feature that is readily adjusted to changes to feeding ecology (presumably, anyway). I actually was one of the reviewers for this paper, and I’m pleased to see it published. Interestingly, this younger, longer-snouted taxon was preliminarily recognized by Gutstein et al. (2009) from similarly aged strata from the Bahia Inglesa locality in Chile, which Lambert and Muizon (2013) referred to Brachydelphis jahuayensis.
Yet another skull of Brachydelphis jahuayensis. From Lambert and Muizon (2013).
The holotype cranium of Septidelphis. From Bianucci (2013).
The fossil platanistine periotic (left), compared to a modern Platanista gangetica periotic (right). From Bianucci et al. (2013).
Bianucci, G. 2013. Septidelphis morii, n. gen. et. sp., from the Pliocene of Italy: new evidence of the explosive radiation of true dolphins (Odontoceti, Delphinidae). Journal of Vertebrate Paleontology 33: 722-740.
Bianucci, G., Lambert, O., Salas-Gismondi, R., Tejada, J., Pujos, F., Urbina, M., and Antoine P.O. 2013. A Miocene relative of the Ganges River dolphin (Odontoceti, Platanistidae) from the Amazonian Basin. Journal of Vertebrate Paleontology 33:741-745.
Cozzuol, M. A. 2010. Fossil record and the evolutionary history of Inioidea; pp. 193–217 in M. Ruiz-García and J. Shostell (eds.), Biology, Evolution and Conservation of River Dolphins within South America and Asia. Nova Science Publishers, New York.
Fordyce, R.E. 1983. Rhabdosteid dolphins (Mammalia: Cetacea) from the middle Miocene, Lake Frome, South Australia. Alcheringa 7: 27-40.
Geisler, J. H., S. J. Godfrey, and O. Lambert. 2012. A new genus and species of late Miocene Inioid (Cetacea, Odontoceti) from the Meherrin River, North Carolina, U.S.A. Journal of Vertebrate Paleontology 32:198–211.
Gutstein, C. S., M. A. Cozzuol, A. O. Vargas,M. E. Su´ arez, C. L. Schultz, and D. Rubilar-Rogers. 2009. Patterns of skull variation of Brachydelphis (Cetacea, Odontoceti) from the Neogene of the southeastern Pacific. Journal of Mammalogy 90:504–519.
Lambert, O., and Muizon, C. de. 2013. A new long-snouted species of the Miocene pontoporiid dolphin Brachydephis and a review of the Mio-Pliocene marine mammal levels in the Sacaco Basin, Peru. Journal of Vertebrate Paleontology 33:709-721.
Muizon C. de 1988. Les vertébrés fossiles de la Formation Pisco (Perou). Troisieme partie: Les odontocètes (Cetacea, Mammalia) du Miocène. Editions Recherche sur les Civilisations 78: 1-244.