Fleshing out Andrewsarchus, the giant tenrec

Updated July 22, 2021
note that adding taxa moves Andrewsarchus and Rhynchocyon a node away from tenrecs.

All we know of Andrewsarchus
is its skull — without a mandible. A few days ago the dentary of a sister taxon, Sinonyx, was added to the skull of Andrewsarchus ((Osborn 1924; middle Eocene, 45 mya; AMNH 20135; 83cm skull length; also see Fig. 1) just to see if it would fit.

Before that…
everyone forever has always fleshed out Andrewsarchus like a giant bear/dog, moving the eyeballs to the top and giving it a bear/dog nose. Image googling Andrewsarchus will give you an idea what a widespread and accepted tradition that has been. I even followed that tradition back in 1989 in the book Giants, which you can see here as subset 1 of a larger pdf of the entire book.

Unfortunately,
Andrewsarchus does not nest with bears, dogs or mesonychids. It nests with tenrecs and Rhynchocyon (Fig. 2.), one type of elephant shrew. (The other type of elephant shrew is unrelated, as we learned here, Fig. 2). Tenrecs have a long flexible nose.

So, here, without further adieu
is a first shot at adding tenrec soft tissue to the skull of Andrewsarchus (Fig. 1). Is it close to being correct? I hope so, given the present evidence.

Figure 1. Andrewsarchus restored as giant tenrec alongside, Canis, the wolf to scale. Note the small and low-set eyes on Andrewsarchus. The mandible comes from Sinonyx. Note the natural tilt of the canid skull permitting binocular vision. Andrewsarchus had low-set eyes, rather un-canid-like. We have to give up the bear-dog restoration of Andrewsarchus.

Figure 1. Andrewsarchus restored as giant tenrec alongside, Canis, the wolf to scale. Note the small and low-set eyes on Andrewsarchus. The mandible comes from Sinonyx. Note the natural tilt of the canid skull permitting binocular vision. Andrewsarchus had low-set eyes, rather un-canid-like. We have to give up the bear-dog restoration of Andrewsarchus.

Now, just imagine the post-crania…
and the best clue we have is the living tenrec, Rhynchocyon (Fig. 2) with long legs, robust torso and short tail, only ten times bigger.

Figure 6. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Figure 3. Rhynchocyon (above) and Macroscelides (below) the other type of elephant shrew compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Maybe it’s time to 
give up the bear-dog restoration for Andrewsarchus and give it the giant  tenrec restoration it deserves based on phylogenetic bracketing and phylogenetic analysis.

Figure 3. The skull of Andrewsarchus mated to the body of Leptictis to make a chimaera.

Figure 3. The skull of Andrewsarchus mated to the body of Leptictis to make a chimaera.

References
Osborn HF 1924. Andrewsarchus, giant mesonychid of Mongolia. American Museum Noviattes 146: 1-5.

14 thoughts on “Fleshing out Andrewsarchus, the giant tenrec

  1. While I certainly like the illustration (I’m assuming you did it?), and the “bear-dog” interpretations of Andrewsarchus have been thankfully abandoned, I think mr gus raised a good point. The metabolic rates of tenrecs would be quite a problem for Andrewsarchus.

    Now, while the basal metabolic rate, etc. of some of the taxa I’ll list aren’t available, body temperature should give you some idea.

    Tailless tenrec: 306ºK or 33.0ºC or 91.4ºF
    Gray wolf: 311ºK or 38.3ºC or 100.9ºF
    Eurasian pygmy shrew: 312ºK or 38.5ºC or 101.3ºF
    Hippopotamus: 309ºK or 35.4ºC or 95.7ºF
    Palestine mole rat: 309ºK or 35.6ºC or 96.0ºF

    I tried to include a wide and varied dataset, but as you can see, the only other animals with a near-tenrec metabolism are either herbivores or similarly small. The metabolic rate of a tenrec (there are quite a few listed here: https://genomics.senescence.info/species/query.php?search=tenrec) would be entirely inefficient for a large predator.

    While I get that it could have modified its metabolic rate, this would (from what I understand, which really isn’t much) be quite difficult.

    So, (and I’m sorry this is so long!) this leaves a couple of options. Either Andrewsarchus wasn’t a tenrec at all (which, being kind of a traditionalist, I’m inclined to agree with), or it was doing something else. I’m not sure what, and it’s not really my place to speculate.

    Okay, that’s my lengthy a̶r̶t̶i̶c̶l̶e̶ comment finished. I’d be interested to see if you have any ideas for how these restrictions (if they are restrictions!) could be bypassed.

      • Yeah, I really need to check that more. Normally, I just assume that there’s a post every time the LRT is updated, and that I’ll never miss anything.

    • Adding taxa since this article appeared moves Andrewsarchus closer to Rhynchocyon, among living taxa. Larger taxa do tend to slow down their metabolism, largely due to the cubed volume vs squared surface area rule.

      • I was unaware of the cubed volume-squared surface area rule. I regret to say I don’t have the strongest comprehension of mathematics and scaling, nor how it affects biology.

        The closer nesting to Rhynchocyon, Sinonyx and Harpagolestes macrocephalus (just checked the LRT) is interesting. I suppose this would imply that it was (in a way) mesonychid again?

      • Mesonychids nest elsewhere, between oreodonts and hippos. As animals get larger their weight/volume increases by the cube. Staying warm is easier.

      • When I said that, I was just referring to H. macrocephalus and Sinonyx’s previous assignment to the Mesonychia.

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