Extinct Equus species

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    Bruce MacFadden


    Eric–If you had to guess, how many extinct species of Equus are valid from throughout the world? 50?

    Bruce MacFadden


    Eric–I wonder if you could respond to this inquiry, thanks–Bruce

    From: Christina Picchi
    Sent: Sunday, March 13, 2016 4:30 PM
    To: MacFadden,Bruce J
    Subject: Re: Equus lambei?

    Dear Dr. Bruce MacFadden,

    I was suggested your name by Julie B. Rokor from ResearchGate. My question involves the phylogenetic placement of an Equus species compared to another. There are two papers that I have which suggest they are sister taxa, but I was wondering if you could clarify or weigh in with your expertise.

    Is Equus lambei (Equus alaskae?) conspecific to Equus caballus?

    The papers that I have for reference are
    Vila et. al (2001): Widespread Origins of Domestic Horse Lineages
    Weinstock et. al (2005): Evolution, Systematics, and Phylogeography of Pleistocene Horses in the New World A Molecular Perspective

    These place the Yukon/Alaskan horse in a separate clade from modern horses, but also suggest that they may have influenced domestication. One main reason I pose this question is due to the highly controversial paper written by Jay Kirkpatrick and Patricia Fazio that proposes Equus caballus be treated as a native species, because of Ann Forsten’s work (~1990) that had stated Equus lambei was “genetically identical” to Equus caballus.

    Thank you for your time and for any comments you may have on this matter,
    Christina Picchi

    Eric Scott

    Hi, Christina and Bruce –

    Thanks for your e-mails! The question Christina poses is actually a bit thorny. The short answer is that some North American Pleistocene fossils that have been assigned morphologically to Equus lambei are genetically indistinguishable from E. ferus (that’s the name for the wild horse; E. caballus applies to domestic & feral horses only). Strictly technically, one would need to successfully extract DNA from the holotype of E. lambei itself to confirm or refute whether the species is a junior synonym of E. ferus; even if other specimens referred to that species turn out to be E. ferus, the name lambei would still technically remain valid for the holotype. But if one steps away from technicalities like that, it is nevertheless clear that Pleistocene horses genetically similar if not identical to E. ferus were present in late Pleistocene North America.

    So, if you’re asking whether or not Equus lambei is a junior synonym of E. ferus, the answer in a taxonomic sense would be “probably”. But if you’re asking whether or not E. ferus (again, the wild form of E. caballus) was present in late Pleistocene North America, the answer is “Yes!” Does that help?

    This is not to say, of course, that this means Kirkpatrick & Fazio are necessarily correct about treating living feral Equus caballus as native North American wildlife. But that’s a separate question.


    Eric Scott
    Associate Curator for Paleontology
    Dr. John D. Cooper Archaeological and Paleontological Center
    Santa Ana, California 92701
    (714) 647-2103
    [email protected]


    Bruce MacFadden


    Thanks Eric! And thanks for responding here in the Forum. I will pass your analysis on to Christina!

    Hope all is well in California. –Bruce

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