Dissacus enters the LRT transitonal to mesonychids from oreodonts

Updated October 18, 2021
with a review that nests Dissacus transitional from oreodonts to mesonychids.

According to Wikipedia
“Dissacus (Cope 1881, Fig. 1) is a genus of extinct carnivorous jackal to coyote-sized mammals within the family Mesonychidae, an early group of hoofed mammals that evolved into hunters and omnivores. Their fossils are found in Paleocene to Early Eocene aged strata in France, Asia and southwest North America, from 66–50.3 mya, existing for approximately 15.7 million years.”

Figure 1. Dissacus skull, colors added here.

in the large reptile tree (LRT, 1826+ taxa) Dissacus nested as the base of the Borophagus, Speothos, Tremarctos clade within Carnivora. New scoring of this taxon and related taxa now nests Dissacus between oreodonts and mesonychids.

Figure 2. Subset of the LRT focusing on derived placentals and including Dissacus between oreodonts and mesonychids.

Geisler and McKenna 2007
described the partial remains of Dissacus zanabazari (MAE−BU−97−13786; Fig. 1) from Mongolia. The authors included in their cladogram several taxa not related to mesonychids (e.g. Hapalodectes hatangensis a tree shrew, Diacodexis an artiodactyl, Andrewsarchus an anagalid, Eoconodon an untested mandible and Arctocyon, a marsupial creodont). No oreodonts or basal terrestrial herbivorous placentals, like Phenacodus, were tested.

Cope ED 1881. Notes on Creodonta. American Naturalist 15: 1018–1020.
Geisler JH 2001. New morphological evidence for the phylogeny of Artiodactyla, Cetacea, and Mesonychidae. American Museum Novitates 3344, 1-53.
Geisler J and McKenna MC 2007. A new species of mesonychian mammal from the lower Eocene of Mongolia and its phylogenetic relationships. Acta Palaeontologica Polonica 52, 189-212.
O’Leary MA 1998. Phylogenetic and morphometric reassessment of the dental evidence for a mesonychian and cetacean clade. In Thewissen, J. G. M. (ed) The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea. Plenum Press (New York), pp. 133-161.
O’Leary MA 1999. Parsimony analysis of total evidence from extinct and extant taxa and the cetacean-artiodactyl question (Mammalia, Ungulata). Cladistics 15, 315-330.
O’Leary MA 2001. The phylogenetic position of cetaceans: further combined data analyses, comparisons with the stratigraphic record and a discussion of character optimization. American Zoologist 41, 487-506.
Solé F, Godinot M, Laurent Y, Galoyer A and Smith T 2018. The European Mesonychid Mammals: Phylogeny, Ecology, Biogeography, and Biochronology. Journal of Mammalian Evolution. 25 (3): 339–379.
TetZoo blogpost. Mesonyx and the other mesonychid mesonychians (mesonychians part IV). Although posted by a PhD, what is written here is untested by the poster, so is more journalism than paleo.

5 thoughts on “Dissacus enters the LRT transitonal to mesonychids from oreodonts

  1. “this is what happens when a student or a post-doc teams up with a professor. Even though the young up-and-comer may want to expand the taxon list, if the professor says we don’t need to, it’s too much trouble, we’ll be published anyway…”

    I can tell you straight-up, without equivocation, that this never happens.

    My advisor gave me full freedom to design my ingroup and outgroup sampling protocols. I suppose he might have asked for an explanation had I included a stegosaur in a matrix otherwise dedicated to crown-group crocodylians, but at no time did I ever feel compelled to include or exclude anything.

    I have conveyed this philosophy to my students. They’re free to include or exclude – it’s their thesis project.

    What I describe is universal among vertebrate paleontologists. We’ll certainly advise our students on what taxa might or might not be relevant to their analysis, we would never – NEVER – tell our students to remove a taxon.

    Your allegation is thus simply wrong, and I call on you to retract it so that you don’t mislead your readers about how we work.

    • Thank you for your insight, Chris. You wrote, “What I describe is universal among vertebrate paleontologists.” Unfortunately it only takes one instance anywhere at any time to falsify this statement. And it doesn’t have to be overt. It may rely on tradition and other things left unsaid, but widely recognized based on textbooks, lectures, etc. The above post provides a clear example of taxon and citation exclusion after first promising taxon and citation inclusion (Hone and Benton 2007, 2008). To your point, neither of us have access to conversations at universities and museums around the world. So we are left to wonder why those who are experts in this profession continue to exclude taxa, the number one problem in vertebrate paleontology. Where does taxon exclusion come from? From thinking you know the taxon inclusion list instead of letting the software tell you the taxon list to focus on based on such a wide gamut taxon list that it takes in the spectrum of vertebrates. You wrote, “Your allegation is thus simply wrong.” Please check the cited evidence (above). Let’s also see how many whale papers include tenrecs, how many Vancleavea papers include thalattosaurs, how many turtle papers include Elginia, Sclerosaurus and Bunostegos, how many reptile papers include the amphibian-like reptiles recovered by the LRT, etc. etc.

      • I see no evidence for the sort of advisor pressure you seem to think exists in this case, or in any other case.

        That we sometimes exclude taxa you think should be included doesn’t indicate that an advisor is steering his or her student away from a heterodox path. It’s because we regard the excluded taxa as irrelevant to the questions we ask. We disagree with your methods and do not accept the phylogenetic arrangements you’ve found. There’s no effort to suppress anything here; we just don’t see any compelling reason to frame our research protocols around your results.

        I repeat my call for you to retract your allegation that a student was dissuaded from applying what you believe to be an appropriate taxonomic sampling strategy. It’s baseless and insulting.

      • Chris, you wrote, “It’s because we regard the excluded taxa as irrelevant to the questions we ask. We disagree with your methods and do not accept the phylogenetic arrangements you’ve found.” You’ve answered your own question. That’s the problem. What you and your colleagues see as irrelevant at least needs to be tested to see if they are indeed irrelevant. If someone suggests competing taxa, I add them to the analysis, and I’m just an amateur. It’s time you and your colleagues step up to the plate and take a swing. Hiding in the dugout will not help.

  2. For the sake of clarity – I have, indeed, recommended pruning taxa out of my students’ analyses. In every single case, this involved highly fragmentary taxa whose inclusion did nothing more than cause a loss of resolution.

    My students have gotten results that went completely against what I thought was happening. I didn’t tell them to redo their work because they were finding things that would challenge orthodoxy, nor did I try to prevent them from publishing their results. I don’t know of a single colleague who would do otherwise.

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