Cleaning out the dustbin

The so-called cetotheres have been a thorn in the side of cetacean taxonomists and systematists for the better part of a century. Traditionally the family Cetotheriidae has included almost any extinct baleen whale that can’t be assigned to the Balaenopteridae (rorquals), Eschrichtiidae (gray whales), or Balaenidae (right whales); in other words, it was a “dustbin” taxon where you could sweep away anything that’s inconvenient.

The nature of the cetothere taxa hasn’t helped. They tend to be very generalized in their characteristics, and what specializations they have tend to be limited to a single taxon. Good specimens are also not particularly common (although fragments are); many taxa are known from a single specimen, so variation isn’t well established (one paleontologist quipped that “Any well-preserved cetothere skull is automatically a new genus.)

Dustbin taxa are not particularly useful. They keep your database nice and neat, but they don’t really reveal much about the relationships of different organisms (although they do reveal our lack of knowledge about those organisms).

In recent years, the cetotheres have started to relinquish their secrets. A subgroup has been recognized by various workers, which include a suite of specializations not seen in other primitive baleen whales. Many of these are related to the structure of the ear and the lower jaw joint. Another character is the extension of the rostral bones (the maxilla and premaxilla) onto the top of the skull, posterior to the orbits and essentially reaching the supraoccipital. This is visible in the Peruvian whale Piscobalaena, above (specimen from Museo de Historia Natural). Compare the area between the orbits to the specimen from the USNM shown below, tentatively referred to Parietobalaena:

Also compare it to our Diorocetus, which is more similar to Parietobalaena (don’t let the rostrum shape fool you; the rostrum proportions seem to vary widely across different taxa).

Based on this suite of similarities, Boutel and Muizon (2006) restricted the definition of Cetotheriidae to just 6 genera: Cetotherium, Mixocetus, Nannocetus, Metopocetus, Herpetocetus, and Piscobalaena. These became Cetotheriidae sensu stricto, as opposed to the old definition for the family, Cetotheriidae sensu lato. Taxa like Diorocetus and Parietobalaena became Mysticeti incertae sedis, meaning that we still don’t know where they fit (essentially, incertae sedis is the new, but somewhat emptier, dustbin).

Other workers have followed this same general pattern. Whitmore and Barnes (2008) assigned the following genera to the Cetotheriidae: Cetotherium, Metopocetus, Amphicetus, Heterocetus, Mesocetus, Cephalotropis, Mixocetus, Plesiocetopsis, Herpetocetus, and Nannocetus. They went a step further and divided the Cetotheriidae into two subfamilies, the Herpetocetinae with Herpetocetus and Nannocetus, the Cetotheriinae with everyone else. (Whitmore and Barnes did not address Piscobalaena.)

That still leaves a lot of taxa unaccounted for: Parietobalaena, Diorocetus, Aglaocetus, Pelocetus, Halicetus, Thinocetus, and possibly Eobalaenoptera, just to name the ones known from Virginia. (I’ve argued in the past that Eobalaenoptera is close to the balaenopterids, but my views have have changed somewhat and it may not be as close as I originally believed). Steeman (2007) made an effort at sorting these taxa out, and erected three new families to accommodate some of them. It’s not yet clear how these families will work out, but you have to start somewhere.

As an aside, the redefinition of Cetotheriidae has led to some awkward problems for writing and speaking about these whales. There’s really no question that the redefinition was in order, because Cetotherium, the type genus of the family, still falls within the group. The problem is that the name Cetotheriidae has a nearly century-long history with a different usage. In writing papers, authors now typically refer to Cetotheriidae s. s. or Cetotheriidae s. l. to make clear which definition they’re using, and sometimes refer to the “non-cetothere cetotheres” (!?) by using quotes (Cetotherium is a cetotheriid, while Diorocetus is a “cetothere”). It’s even tougher when speaking, unless we’re all going to make imaginary quotes in the air with our hands.

While I doubt this will ever be adopted, I would suggest the following change. Use the two subfamilies defined by Whitmore and Barnes (2007), Cetotheriinae and Herpetocetinae, (assuming they are valid taxa), and replace Cetotheriidae with Herpetocetidae. This actually has an historical basis, as the original name from 1872 was the subfamily Cetotheriinae; it was not elevated to a family until 1923. Herpetocetidae doesn’t have the historical baggage associated with Cetotheriidae. Even more ideal would be to replace Cetotheriinae as well, and only use the term cetothere in an informal sense. This is similar to what has happened with Reptilia, which as originally defined was paraphyletic. This is a more questionable suggestion, however, as Cetotherium clearly belongs in this taxon.

Make sure to check out the archives at The Coastal Paleontologist, too. Robert Boessenecker has put up a lot of posts with field and preparation photos of Herpetocetus, which is quite common in the Pliocene of California.

References:

Boutel, V. and C. de Muizon, 2006. The anatomy and relationships of Piscobalaena nana (Cetacea, Mysticeti), a Cetotheriidae s. s. from the early Pliocene of Peru. Geodiversitas 28:319-395.
Steeman, M. E., 2007. Cladistic analysis and a revised classification of fossil and recent mysticetes Zoological Journal of the Linnean Society 150:875-894.
Whitmore, F. C. Jr. and L. G. Barnes, 2008. The Herpetocetinae, a new subfamily of extinct baleen whales (Mammalia, Cetacea, Cetotheriidae), in C. E. Ray, D. J. Bohaska, I. A. Koretsky, L. W. Ward, and L. G. Barnes (eds.), Geology and Paleontology of the Lee Creek Mine, North Carolina, IV. Virginia Museum of Natural History Special Publication 14:141-180.
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9 Responses to Cleaning out the dustbin

  1. Boesse says:

    Herpetocetidae! Hmm, interesting – that would certainly be convienent, but I suspect that might require some sort of proposal to the ICZN. Like you said, the problem is that C. rathkei shows up in that group…

    Problem is, I’m pretty convinced by Bouetel and Muizon (2006) and their monophyletic Cetotheriidae sensu stricto – the problem does continue when I hear folks say ‘cetotheres’, but referring to cetotheriidae sensu lato… sorta aggravating, since I work on Cetotheriidae ss., and they are my favorite group of mysticetes. If one is to take Steeman’s (2007) paper at face value, we can now use Diorocetidae, Pelocetidae, etc. for former cetotheriidae s.l. – or, just call them ‘stem chaomysticetes’.

    I’m not sure Cetotheriinae (sensu Whitmore and Barnes) will remain valid for long – the analysis Jonathan Geisler and I did for my 2008 presentation (although very preliminary) suggests that “cetotheriinae” are paraphyletic, leading up to a monophyletic Herpetocetinae (which probably includes Piscobalaena). So, when we finally continue study of Purisima Herpetocetus material, we *could* tackle something like this.

    This all reminds me, I really need to do some more posts on Herpetocetus – that, and there are potentially two partial Herpetocetus skulls waiting to be excavated as we speak (winter break excavation?). Thanks for writing about my favorite, weird group of whales!

  2. Alton Dooley says:

    I’m inclined to (cautiously) use some of Steeman’s families, at least as a starting point for testing, even though I’m uncertain if I agree with all of them. I do have the feeling that there is an identifiable structure in those taxa, but then I guess everyone feels that, but everyone feels that it’s a different structure! So the danger is that if we use Steeman’s names but they end up not holding up, we end up with taxa jumping back and forth between families, and the names don’t help us; we still end up have to say who’s definition we’re using whenever a family is mentioned.

    Family-level names are included in ICZN (taxa above family are not), so it’s quite likely that a name change would require a formal petition to ICZN.

    At the very least, Cetotheriidae s. s. should be referred to as “cetotheriids” rather than as “cetotheres”; that can at least help keep them straight until the other taxa are sorted out.

    I’m looking forward to some more posts on Herpetocetus; especially since we’re starting to get a fair number of specimens from Virginia that look like cetotheriids.

  3. Doug says:

    Reminds me of Megalosaurus, perhaps the greatest wastebasket of all time.

  4. Alton Dooley says:

    Megalosaurus is a good one. There have been lots of them. Rana among frogs, I believe is another one. I think the thecodonts have been used that way. And, of course, to a certain extent Reptilia.

  5. Alton Dooley says:

    Somehow things got screwed up, and my last two blog post were overwritten. I’m going to try to resurrect those posts.

  6. boesse says:

    Is it just me, or does that Parietobalaena have a wider than usual rostrum?

  7. Alton Dooley says:

    I’ve been thinking the same thing; the label says Parietobalaena. The rostrum is very wide at the base. The skull is also very large for Parietobalaena, I think. Parietobalaena needs a closer look in general, since almost any small Calvert mysticete is placed in it (dustbin?).

    I strongly suspect there are at least three unnamed (or at least unrecognized) mysticetes in the Calvert.

    I was able to reconstruct this blog post, and I think the technical issues are worked out.

  8. boesse says:

    Hmm, interesting. I still really don’t know what to make of cetotheres sensu lato; they’re all very generalized, and they all kinda look the same to me (but then again, I’m used to real autapomorphic “freaks” like Herpetocetus. Some day I’ll need to visit USNM et al. and take a look at all these things from the Chesapeake group to really figure them out. I used to get confused about how they play out on a cladogram, but then again – now that I think about it, Cetotheriidae ss. nearly always come out as basal chaomysticeti (but still later than Eomysticetus), while all these cetotheres s.l. appear after (Demere et al. 2005/8, Bouetel and Muizon 2006, Steeman 2007, etc.) – however, I guess the funky position of Balaenidae in Bouetel and Muizon (2006) confused me – but if you ignore that, the relative positions of cetotheriidae and the ‘pelocetidae’ – ‘diorocetidae’ complex still appears just crownward. Anyway, that’s enough cladistics for me today.

  9. Alton Dooley says:

    “Some day I’ll need to visit USNM et al. and take a look at all these things from the Chesapeake group to really figure them out.”

    🙂

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