Tetrapod Zoology

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We now move to another mesonychian group: Hapalodectidae. This is yet another of those obscure little groups that sounds really interesting, yet are never the subject of focus or discussion. Virtually all of the literature on them – and that’s still only ten papers or so – mentions the idea that they might have been piscivorous, but I can’t find any elaboration of this and would like to see some. Hapalodectidae was named by Szalay & Gould (1966) as a mesonychid ‘subfamily’ (following Ting & Li (1987) and others, I here refer to the group as Hapalodectidae instead of Hapalodectinae); it’s a small group containing about five genera (or does it? Read on) from North America and eastern Asia, the best known of which is Hapalodectes. Five species of this genus have been named (H. leptognathus and H. anthracinus from North America, and H. serus, H. hetangensis and a new, as yet unnamed species, all from Asia).

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Remains of Hapalodectes had first been reported in 1892 (when they were included within the mesonychid genus Dissacus), and for a long time members of the group were only known from lower jaw fragments. Ting & Li (1987), however, reported good cranial material from the Lower Eocene Lingcha Formation, and a complete skull [shown above] was reported from the Lingcha Formation by Ting et al. (2004). The hapalodectid skull is long and narrow, with a comparatively large, long and laterally expanded braincase. Based on data from the unnamed Upper Eocene Lushi Formation hapalodectid, Szalay (1969) noted indications that the hapalodectid head was proportionally larger than that of most modern mammals. Postcranial remains (partial limb bones) indicate that hapalodectids were terrestrial, but they weren’t cursorial, in contrast to mesonychids (O’Leary 1998).

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Hapalodectids were, mostly, small animals compared to mesonychids and triisodontids, though the largest member of the group, Hapalorestes, did overlap in size with the members of these other groups. Gunnell & Gingerich (1996) estimated their body masses to range from 1 to 8 kg, putting them within the ‘medium-sized’ category for mammals (in contrast, mesonychids are estimated to range from 10 to 250 kg). One of their characteristic features is that the lower third molar is the longest tooth in the tooth row. Another peculiarity is the presence of broad, deep ‘embrasure pits’ on the palate: these would have received the crowns of the lower jaw teeth when the jaws were closed, and they’re peppered with small vascular foramina (Szalay 1969: adjacent reconstruction of palate shown in adjacent image). Similar pits are seen on the palates of stem-whales, and these features, combined with those comments about possible piscivory, have inspired some to imagine hapalodectids as close to whale ancestry: this possibility was depicted in a phylogram-style diagram produced by Szalay (1969). If you watched the TV series The Velvet Claw (or read the accompanying book), you might recall a scene where an otter-like Hapalodectes slips into a river and evolves directly into a humpback whale [a still from that scene is shown at the top of the article: for more on The Velvet Claw see Homage to The Velvet Claw (part I) and Homage to The Velvet Claw (part II)]. It doesn’t seem that hapalodectids did look otter-like, but just what they did look like remains uncertain. Has anyone ever seen (or produced) a life restoration? [lower jaw of Hapalodectes leptognathus below, from Szalay (1969)].

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How are hapalodectids related to other mesonychians? They share a number of detailed dental characters with mesonychids, but differ from them in that their lower cheek teeth are more compressed and blade-like. Szalay (1969) thought that they might have descended from mesonychids like Dissacus. Inspired by efforts to determine cetacean affinities, a larger number of recent studies have included a broad selection of mesonychians, cetaceans, artiodactyls and other placentals (see previous articles in this series!). These have mostly recovered Hapalodectes as the most basal member of a mesonychian clade, the topology of which is poorly resolved.

A number of other mesonychians have been included within Hapalodectidae by some authors, including Lohoodon, Metahapalodectes and Plagiocristodon (McKenna & Bell 1997). However, Zhou & Gingerich (1991) argued that these taxa are mesonychids, not hapalodectids, as they lack ‘a re-entrant groove on the anterior surface of the lower molars’ (p, 219), another characteristic hapalodectid feature.

And – are there more to come? That would be telling.

For previous articles on Paleogene mammals see…

And for other stuff on neat and obscure fossil mammals see…

Refs – –

Gunnell, G. F. & Gingerich, P. D. 1996. New hapalodectid Hapalorestes lowei (Mammalia, Mesonychia) from the early middle Eocene of northwestern Wyoming. Contributions from the Museum of Paleontology, the University of Michigan 29, 413-418.

McKenna, M. C. & Bell, S. K. 1997. Classification of Mammals: Above the Species Level. Columbia University Press (New York).

O’Leary, M. A. 1998. Morphology of the humerus of Hapalodectes (Mammalia, Mesonychia). American Museum Novitates 3242, 1-6.

Szalay, F. S. 1969. The Hapalodectine and a phylogeny of the Mesonychidae (Mammalia, Condylarthra). American Museum Novitates 2361, 1-26.

– . & Gould, S. J. 1966. Asiatic Mesonychidae (Mammalia, Condylarthra). Bulletin of the American Museum of Natural History 132, 127-174.

Ting, S. & Li, C. 1987. The skull of Hapalodectes (?Acreodi, Mammalia), with notes on some Chinese Paleocene mesonychids. Vertebrata PalAsiatica 25, 161-186.

– ., Wang, Y., Schiebout, J. A., Koch, P. L., Clyde, W. C., Bowen, G. J. & Wang, Y. 2004. New Early Eocene mammalian fossils from the Hengyang Basin, Hunan China [sic]. Bulletin of the Carnegie Museum of Natural History 36, 291-301.

Zhou, X. & Gingerich, P. D. 1991. New species of Hapalodectes (Mammalia, Mesonychia) from the Early Wasatchian, Early Eocene, of northwestern Wyoming. Contributions from the Museum of Paleontology, the University of Michigan 28, 215-220.

Comments

  1. #1 Anonymous
    August 17, 2009

    “Has anyone ever seen (or produced) a life restoration?”

    There’s this one:

    http://upload.wikimedia.org/wikipedia/commons/b/b0/Hapalodectes_serus.JPG

    Of course, it is a total peice of crap, but I guess it counts(?).

  2. #2 Brian
    August 17, 2009

    # 1, You’re absolutely right. Everytime I see one of the depictions by that particular ‘artist’, I cringe. Reminds me of the time when, on the Extinction Forums, I ignited a great ‘you’re a meanie and we all come to the rescue of the attacked!” when I criticised one poster’s drawings of extinct macaws. I pointed out that they were quite awful and certainly weren’t doing creatures that had been driven extinct, much justice. Adding insult to injury, rather.

    Oh well..

  3. #3 andy
    August 17, 2009

    Thanks for reminding me of The Velvet Claw… I loved that series, and own the book (alas my copy is currently on a different landmass from where I am). They don’t make programs like that any more. Nature needs POUNDING TRIBAL BEATS over everything these days, so it would seem…

  4. #4 RStretton
    August 17, 2009

    From what you say Darren about carnivorans and associated groups it sounds like they need to remake the classic Velvet Claw as everything seems to have changed! C’mon BBC just one natural history show in place of all the reality tat

  5. #5 Tim Morris
    August 18, 2009

    I’m not sure if the first 2 are being sarcastic or not, or whathaveyou. But it should be noted that the image in question is part of a larger picture, and the artist in question produces art quickly. If you were to look at the picture it came from, that would be different.

    Also, if every paleo-illustrator was to take every piece of “this looks wrong” etc, and immediately jump to fix it, we’d be locked away indefinately.

  6. #6 Brian
    August 18, 2009

    Tim Morris, without trying to make this into a discussion, I would like to point out that any palaeo-artist attempts to produce a lifelike restoration (or so at least it would seem to me!) which means that having inaccuracies pointed out should be part of the course. In fact, a palaeo-artist should be happy people bother to point out where he slipped in his depiction.

    Also, I don’t think that the particular Wikipedia-artist’s work will improve once it’s a small part of a large depiction. Nor do I think his quick working is a virtue or an excuse for subpar depictions. Rather, I think it points out that he puts in too little effort in his work and could potentionally produce much better drawings.

    You appear to know the artist in person, so you could perhaps point out the old adagium of ‘quality over quantity’ to him?

  7. #7 Dartian
    August 18, 2009

    Darren:

    If you watched the TV series The Velvet Claw (or read the accompanying book), you might recall a scene where an otter-like Hapalodectes slips into a river and evolves directly into a humpback whale

    Hmph! They included that silly scene but said almost nothing about pinnipeds (which, even back then, were known to be part of Carnivora) in the entire series/book!

  8. #8 The Anonymous Guy From Comment 1
    August 18, 2009

    “Tim Morris, without trying to make this into a discussion, I would like to point out that any palaeo-artist attempts to produce a lifelike restoration (or so at least it would seem to me!) which means that having inaccuracies pointed out should be part of the course. In fact, a palaeo-artist should be happy people bother to point out where he slipped in his depiction.

    Also, I don’t think that the particular Wikipedia-artist’s work will improve once it’s a small part of a large depiction. Nor do I think his quick working is a virtue or an excuse for subpar depictions. Rather, I think it points out that he puts in too little effort in his work and could potentionally produce much better drawings.

    You appear to know the artist in person, so you could perhaps point out the old adagium of ‘quality over quantity’ to him?”

    Amen. All I will add to that is this: If a peice of work is ugly, it’s ugly. Simple as that. I mean look at it, it looks like soething from a kid’s coloring book that’s been quickly scribbled in with markers. And if it’s part of a larger dipiction, that doesn’t help, it just means even more ugly for the veiwer’s eye to contend with.

  9. #9 Stevo Darkly
    August 20, 2009

    I am fascinated by mesonychids and I greatly enjoyed this series.

  10. #10 Viergacht
    August 22, 2009

    That particular person has been spamming a lot of wikipedia pages with their sub-par art.

  11. #11 Viergacht
    August 22, 2009

    Forgot to add, there’s this restoration: http://www.pbs.org/wgbh/evolution/educators/teachstuds/pdf/whales_inthe_making.pdf

    It’s a blurry pic and the artist is uncredited (looks like it might be Mark Hallett?). Are there any good photos or drawings of the skeleton online?

  12. #12 Owlmirror
    August 23, 2009

    Forgot to add, there’s this restoration: [URL redacted] whales_inthe_making.pdf

    It’s a blurry pic and the artist is uncredited (looks like it might be Mark Hallett?). Are there any good photos or drawings of the skeleton online?

    Those are the illustrations from At the Water’s Edge, by Carl Zimmer, and they are by Carl Buell.

    The one on the right is not Haplodectes as implied by the caption, but is rather Pachyaena (pg 157 in the softcover edition; also viewable on Amazon.com, if you have an account)

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