Friday mystery object #384 answer


Last week I gave you this unusual looking skull to have a go at identifying:

mystery384

That low and elongated shape, combined with the large number of teeth and absence of a zygomatic arch – all within the context of the relatively large (but still quite small) size – all combine to narrow this down to just a few possible options.

There are a bunch of critters in what used to be called the “Insectivora“, back in the dim and distant days of my undergraduate studies. This wastebasket for things that look like they should be chasing acorns in a cartoon was rightly broken up into more meaningful cladistic groups during the great molecular taxonomic revolution in the dying days of the last century.

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Scrat, a fictional sabre-toothed squirrel that looks like every third member of the old ‘Insectivora’

To be fair, there’s a reason why the “Insectivora” lasted as long as it did and why it took molecular research to finally tease the various groups apart. They don’t have many strong distinguishing anatomical features that are seperate them into clear higher level groupings. Sure, they look a bit different at the family level, but any higher than that and they smoosh into bunch of small toothy critters, many with no cheekbones to speak of.

However, some do have a zygomatic arch, such as the talpid moles and desmans, so it’s not one of them:

mystery330b-e1526623553591

Skull of European mole Talpa europaea Linnaeus, 1758

It also lacks the large orbits of something like a Sengi or Elephant Shrew:

Skull of a North African Sengi Elephantulus rozeti (Duvernoy, 1833).

It also lacks the well-developed sagittal and nuchal crest you’d associate with the Malagasy tenrecs:

Skull of a Tail-less Tenrec Tenrec ecaudatus Lacépède, 1799.

It also lacks the backwards projecting nuchal crest of a solenodon and it’s just too big for one of the true shrews – the largest of which is the Asian House Shrew with a skull length of around 38mm.

So this specimen isn’t as hard to recognise as it could be. The very flat top to the skull with the nostrils up high is a bit of a clue – something often (although not always) associated with aquatic animals. On closer inspection there are two likely suspects – the Web-footed Tenrec or one of the Otter Shrews (which are neither otters nor shrews).

The area around the occipital is a dead give-away here. The Malagasy Web-footed Tenrec Limnogale mergulus (Major, 1896) has an occipital region that’s hard to see in a side view, because the parietals extend down quite low, whereas the Otter Shrews have much higher parietal margin that exposes the occipital region – just like we see in the mystery object.

Finally, the size is give-away. As many of you recognised and hinted at (occasionally with some dodgy puns – I’m looking at you Tony), this is a Giant Otter Shrew Potomogale velox (Du Chaillu, 1860). These semiaquatic relatives of the tenrecs are unusual in how they swim, lacking webbed feet and relying on a laterally flattened tail to swim using a fish-like undulation. So well done to Jane, Tony Irwin, katedmonson, Allen Hazen, Rémi and everyone else who managed to work out this weird mystery.

5 thoughts on “Friday mystery object #384 answer

  1. Thanks for your detailed explanations of distinguishing characteristics–your blog remains a bit of sunshine in a world that is not feeling very sunny at all right now!

  2. And the dentition is weird, though perhaps not quite as weird as Scrat’s! Dental formula (writing upper/lower) is, according to
    https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/giant-otter
    I 2/3 C 1/1 P 3/3 M 3/3
    So the big incisors, I guess, do the work (biting and grabbing prey) that we associate with canines. The tooth immediately behind the upper “caniniform” incisor is the second incisor, followed by the canine, followed by the first premolar, the three of them all looking (in the photos I’ve found) similar in shape and size!

    Just to contribute to the confusion of the old “Insectivora,” I think at least some real shrews have big, stabbing, incisors and reduced canines: one more morphological feature that might have encouraged pre-molecular taxonomists to group otter shrews with shrews.

    Thanks for the explanation and the comparative photos. (The zygomatic arch in Talpa looks delicate: does it get broken off in some preserved specimens? To make identification harder? (Smile))

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