I've interrupted my series of picture posts from the US trip in order to discuss a new paper that just came out this week on a new and exciting fossil mysticete from Peru. Previously organized programming will return shortly.
One of the strangest aspects of the fossil record of baleen whales is the apparent lack of fossil neobalaenids, or pygmy right whales. There is no shortage of fossil right whales (Balaenidae - e.g.
Balaena ricei,
Balaenula spp.,
Balaenella,
Eubalaena shinshuensis), rorquals ("
Megaptera"
miocaena,
Diunatans, Parabalaenoptera,
Archaebalaenoptera, etc.), gray whales (
Archaeschrichtius,
Eschrichtioides,
Gricetoides), and all manner of extinct groups (Cetotheriidae, Aetiocetidae, Mammalodontidae, Eomysticetidae, stem-balaenopteroids). Up until 2012, the only described pygmy right whale fossil is a single partial
petrosal (earbone) from the latest Miocene of Beaumaris, Australia, recently published by my colleague Erich Fitzgerald. Those of us who are "in the know" are aware of a few tantalizing bits and pieces from here and there - including some Miocene material from Angola recently reported by SMU Ph.D. student John Graf (and colleagues) at the 2011 SVP meeting.
The late Miocene earbone of an indeterminate neobalaenid recently described by Fitzgerald (2012) from Australia.
This new fossil from the late Miocene Pisco Formation of Peru is beautifully preserved, and includes a nearly complete skull with baleen preserved
in situ. Baleen! The baleen racks have been left in place in "articulation" with the palate, and prepared out in three dimensions. The skull is tiny - approximately one meter in length, and 50 centimeters wide (roughly the size of a killer whale skull) - although somewhat wider, it is about the same length as tiny, dainty whales like
Herpetocetus. It's age and similarity to
Caperea, inspired the genus name
Miocaperea, and
pulchra ("beautiful" in latin) for the beautiful preservation of the
specimen.
The holotype skull of Miocaperea pulchra from the late Miocene of Peru (from Bisconti 2012).
It shares numerous hallmark features with modern
Caperea, such as a short and attenuated rostrum that is somewhat arched, an extremely thrusted supraoccipital shield that is transversely arched, a bizarrely constructed squamosal which seems to lack a zygomatic process, and a huge posterior process of the petrosal that is inflated and broadly exposed on the lateral side of the skull.
The earbone region of Miocaperea (from Bisconti 2012).
It includes a number of differences from modern
Caperea, however, such as a substantially more primitive (or should I say, less bizarre) earbone, lack of exposure of the alisphenoid bone on the braincase, and a foramen pseudovale that is located between the squamosal and pterygoid, rather than completely within the pterygoid (a unique feature of
Caperea).
Caperea also has a really unique postcranial skeleton, recently detailed by Buccholz (2010). Unfortunately,
Miocaperea is not known from any postcranial elements.
Side by side comparison of the skulls of Caperea (left) and Miocaperea (right), from Bisconti (2012).
The fossil was collected in 1985 by Swiss private collector Jakob Siber from the Aguado de Lomas locality of the Pisco Formation in Peru, and later donated to the Staatliches Museum für Naturkunde in Stuttgart, Germany, along with the skeleton of
Balaenoptera siberi described by Giorgio Pilleri and Siber several years later. Bisconti (2012:877) gives an interesting discussion of the legal status of the specimen:
"The new specimen is the holotype of Miocaperea pulchra gen. et sp. nov., found from the upper Miocene Pisco Formation at Aguada de Loma, Peru (Fig. 1), and is now permanently housed in the Staatliches Museum für Naturkunde, Stuttgart, Germany, as specimen no. 46978 of the palaeontological collection. The specimen was excavated by Jakob Siber in 1985, and was legally exported by the Siber+Siber Aathal/Zürich company (E.P.J. Heizmann, pers. comm.). Mr Siber confirmed the legal status of the specimen before the Society of Friends of the Natural History Museum Stuttgart bought it (E.P.J. Heizmann, pers. comm.). The legal documentation can be provided by Siber+Siber Aathal/Zürich. The specimen came to the Stuttgart collection as a present from the Society of Friends of the State Museum of Natural History (SMNS), together with further Peruvian material (e.g. the skeleton of Balaenoptera siberi Pilleri, 1989, which is exhibited in the Schloss Rosenstein building of the SMNS)."
I'll confess that I am wholly ignorant of Peruvian fossil/artifact exportation laws, but this section did pique my curiosity. I can't comment on anything specific about this specimen, but there must have been some question from someone to include this statement in the paper in the first place - If fossil exportation is illegal from Peru, then
clearly private fossil dealers have not heeded it at all, given the sheer abundance of Peruvian Pisco Fm. fossils for sale on the internet. Another example of a beautiful South American fossil collected by private fossil collectors and later donated (although under what circumstances I'm unclear) to a museum is the type specimen of
Pelagornis chilensis described by Mayr and Rubilar Rogers (2010) from Bahia Inglesa, Chile. The above listed website maintains that its Peruvian fossils were acquired years ago, and also indicates that Peru currently considers fossil export to be illegal. China and Mongolia have as well, but
it's clear that commercial fossil dealers don't really care either.
Edit: I received a nice email from Dave Bohaska, who informed me that when he started working at the USNM in 1989 fossil export from Peru was still legal - but that sometime after he started, it was outlawed. It indeed appears that the type of
Miocaperea was legally collected, as outlined by Bisconti (2012).
Three-dimensionally preserved baleen in Miocaperea (from Bisconti 2012).
So, what exactly does this tell us about the evolution of the pygmy right whale? Given how derived the fossil is, and how similar it is to
Caperea (aside from some minor earbone characters, I'm hard pressed to point at any one character of the skull that would really preclude it from being included even within
Caperea itself, but I'm a bit conservative, taxonomically speaking) - it doesn't really give us too much information regarding morphological transformations that culminated in the bizarre morphology of
Caperea. It's a fairly advanced cetacean, although it is from the Aguado de Lomas locality, and therefore about 7-8 million years old or so. In the eastern North Pacific, for example, we have species of baleen whales that are beginning to show features that are about as advanced as modern balaenopterids and balaenids, but have different configurations of skull features - indicating they do not belong to modern genera or species, but are essentially modern in terms of architecture (as opposed to the clearly primitive skulls of "kelloggitheres" during earlier parts of the Miocene).
Comparison of the skulls of Balaenoptera (left), Caperea (middle), and Balaena (right), from Churchill et al. (2012).
Bisconti also spent a fair amount of the paper discussing previously published phylogenies with varying positions of
Caperea among the mysticetes. Most studies have agreed upon
Caperea having a sister taxon relationship with right whales - forming a clade called the Balaenoidea. Examples include Demere et al. (2005), Churchill et al. (2012), and Ekdale et al. (2011). One of my labmates - Felix Marx - published a paper in the Journal of Mammalian Evolution regarding the phylogeny of modern and fossil mysticetes, in which he included a large number of species. Instead of the typical Balaenoidea, his analysis resulted in a novel position of
Caperea as the sister taxon of the rorqual-gray whale clade - separated from balaenids by all "Kelloggitheres" and the Cetotheriidae. This topic came up at the Aquatic Tetrapods (SATLW) conference last year in San Diego, and there was an interesting dialogue between Felix, Nick Pyenson, and some of the San Diego researchers. In these analyses, the way characters are defined and coded is of the utmost importance, and the different phylogenetic position of
Caperea in Marx (2010) and other studies is probably due to differences in character selection, definition, and coding. I won't go into the specifics, as the minutiae of phylogenetics and cladistics are perhaps a tad too dull for the general audience. Nevertheless, the phylogenetic analyses of Churchill et al. (2012) and Ekdale et al. (2011) both responded to the novel relationship which Marx (2010) published.
Different phylogenetic hypotheses for neobalaenid and balaenid relationships
(from Churchill et al., 2012).
What implications does this have for understanding the fossil record of cetaceans? Although the fossil baleen whale assemblage of the Pisco Formation is very poorly known, and thus far represented only by a few described species (
Piscobalaena nana,
Piscocetus sacaco,
Balaenoptera siberi, and now
Miocaperea pulchra), it is one of the largest marine mammal fossil assemblages yet amassed by researchers. The large assemblage already includes numerous pinnipeds (
Acrophoca,
Piscophoca,
Hydrarctos), a slew of dolphins (
Brachydelphis, Lomacetus, Australithax, Piscolithax, Belonodelphis, Scaphokogia, Acrophyseter, Livyatan, Messapicetus gregarius, Nazcacetus, Ninoziphius, Atocetus, Odobenocetops, Hemisyntrachelus, Pliopontos, Incacetus), and aquatic sloths (
Thalassocnus). There are abundant balaenopterids known from the Pisco Formation that await description (several undescribed taxa were used in the phylogenetic analysis of another recent paper by Bisconti, and also occur in the supplementary info for the Lambert et al. 2010 paper on
Livyatan). Given what we know of the current fossil record of baleen whales from Peru - published and unpublished - most are balaenopterids, and the cetotheriid
Piscobalaena, and there aren't multiple skeletons of this little neobalaenid. One could certainly make the case that fossils of neobalaenids are rare (N=2 published specimens, worldwide). Both specimens are from the southern hemisphere; likewise, no neobalaenid fossils are yet known from the northern hemisphere, including well-sampled rocks from California, Italy, Japan, and the eastern USA. Assuming this point to be generally accurate, I'll make the case that even in large and "well known" fossil assemblages like the Pisco, there will always be little 'surprises' like this waiting for us. Another example of this is
Livyatan - although in that case, there were previous discoveries of mysterious gigantic physeteroid teeth, and the embarrassingly large rostrum named
Ontocetus oxymycterus by Kellogg (1925) - another topic for a blog post... some day. Comparable examples of weird, rare taxa in fossil assemblages from California would include the "killer" walrus
Pelagiarctos from Sharktooth Hill, and the
Pelagornis fossil I described with N. Adam Smith from the Purisima Formation. Discoveries like this serve to remind us that no matter how well-sampled and heavily collected a productive locality is, there is always going to be something surprising waiting for us.
References-
Bisconti, M. 2012. Comparative osteology and phylogenetic relationships of
Miocaperea pulchra, the first fossil pygmy right whale genus and species (Cetacea, Mysticeti, Neobalaenidae). Zoological Journal of the Linnean Society 166: 876-911.
Buchholtz, E. 2010. Vertebral and rib anatomy in Caperea marginata: Implications for evolutionary patterning of the mammalian vertebral column. Marine Mammal Science 27: 382-397.
Churchill, M., Berta, A., Deméré, T.A. 2012. The systematics of right whales (Mysticeti: Balaenidae). Marine Mammal Science 28: 497-521.
Deméré, T. A., Berta, A., and McGowen, M. R. 2005. The taxonomic and evolutionary history of modern balaenopteroid mysticetes. Journal of Mammalian Evolution 12: 99-143.
Ekdale, E. G., Berta, A., and Deméré, T. A. 2011. The comparative osteology of the petrotympanic complex (ear region) of extant baleen whales (Cetacea: Mysticeti). PLoS ONE 6:1-42.
Fitzgerald, E.M.G. 2012. Possible neobalaenid from the Miocene of
Australia implies a long evolutionary history for the pygmy right whale Caperea marginata (Cetacea, Mysticeti). Journal of Vertebrate Paleontology 32:976-980.
Graf, J., Jacobs, L., Polcyn, M., Mateus, O., Schulp, A. 2011. New fossil whales from Angola. Society of Vertebrate Paleontology 2011 meeting abstracts: 119A.
Marx, F. G. 2011. The more the merrier? A large cladistic analysis of mysticetes, and comments on the transition from teeth to baleen. Journal of Mammalian Evolution 18:77-100.
