How bigsmall was Aquilops?

December 12, 2014

Handling Aquilops by Brian Engh

Life restoration of Aquilops by Brian Engh (CC-BY).

If you’ve been reading around about Aquilops, you’ve probably seen it compared in size to a raven, a rabbit, or a cat. Where’d those comparisons come from? You’re about to find out.

Back in April I ran some numbers to get a rough idea of the size of Aquilops, both for my own interest and so we’d have some comparisons handy when the paper came out.

Archaeoceratops skeletal reconstruction by Scott Hartman. Copyright Scott Hartman, 2011, used here by permission.

Archaeoceratops skeletal reconstruction by Scott Hartman. Copyright Scott Hartman, 2011, used here by permission.

I started with the much more completely known Archaeoceratops. The measurements of Scott Hartman’s skeletal recon (shown above and on Scott’s website – thanks, Scott!) match the measurements of the Archaeo holotype given by Dodson and You (2003) almost perfectly. The total length of Archaeoceratops, including tail, is almost exactly one meter. Using graphic double integration, I got a volume of 8.88L total for a 1m Archaeoceratops. That would come down to 8.0L if the lungs occupied 10% of body volume, which is pretty standard for non-birds. So that’s about 17-18 lbs.

Archaeoceratops and Aquilops skulls to scale

Aquilops model by Garrett Stowe, photograph by Tom Luczycki, copyright and courtesy of the Sam Noble Oklahoma Museum of Natural History.

Archaeoceratops has a rostrum-jugal length of 145mm, compared to 84mm in Aquilops. Making the conservative assumption that Aquilops = Archaeoceratops*0.58, I got a body length of 60cm (about two feet), and volumes of 1.73 and 1.56 liters with and without lungs, or about 3.5 lbs in life. The internet informed me that the common raven, Corvus corax, has an adult length of 56-78 cm and a body mass of 0.7-2 kg. So, based on this admittedly tall and teetering tower of assumptions, handwaving, and wild guesses, Aquilops (the holotype individual, anyway) was about the size of a raven, in both length and mass. But ravens, although certainly well-known, are maybe a bit remote from the experience of a lot of people, so we wanted a comparison animal that more people would be familiar with. The estimated length and mass of the holotype individual of Aquilops also nicely overlap the species averages (60 cm, 1.4-2.7 kg) for the black-tailed jackrabbit, Lepus californicus, and they’re pretty close to lots of other rabbits as well, hence the comparison to bunnies.

Of course, ontogeny complicates things. Aquilops has some juvenile characters, like the big round orbit, but it doesn’t look like a hatchling. Our best guess is that it is neither a baby nor fully grown, but probably an older juvenile or young subadult. A full-grown Aquilops might have been somewhat larger, but almost certainly no larger than Archaeoceratops, and probably a meter or less in total length. So, about the size of a big housecat. That’s still pretty darned small for a non-avian dinosaur.

Although Aquilops represents everything I normally stand against – ornithischians, microvertebrates, heads – I confess that I have a sneaking affection for our wee beastie. Somebody’s just gotta make a little plush Aquilops, right? When and if that happens, you know where to find me.


9 Responses to “How bigsmall was Aquilops?”

  1. Andrew Thomas Says:

    You mean, “beautiful heads,” and “beautiful ornithischians!” ;)

  2. Matt Wedel Says:

    I may not condone your pro-head, pro-ornithischian lifestyle, but I will defend to the death your right to keep it to yourself, pervert!

  3. Microvertebrates??? Man, you HAVE been working on sauropods for a long time.

  4. Lovely pic, but you know she’s going to regret wearing short sleeves when that thing starts kicking off.

  5. engh Says:

    agreed. 3 of the 4 rough sketches i sent Andy and Mat involved Aquilops escaping, and this one (the best) biting:

    considering the obvious implausibility of ever handling one at all, we figured these more violent versions didn’t serve our purposes as well as a cuddowy bunny wabbit/kitty cat for the interwebs.

  6. Kurt Kohler Says:

    Is the gal holding Aquilops based on anyone in particular? As in a real person?

    I love this drawing, not because it’s cute (even though it is), but because it makes the critter seem so real.

  7. Not really, no. I tried to make her look like a modern Native American girl, mostly because my girlfriend teaches field biology in the summer to Alaskan native highschool kids and I thought they’d like it, but getting her face to look realistic was taking too long (it takes me shamefully long to draw a decent human face) and the image had to be delivered so i just gave up and cropped it. I looked at reference of a number of faces but didn’t base the face or body or outfit on any one lady in particular. Oh and the hand positioning was based on me holding a ruler sorta how I would hold an iguana or monitor.

    Glad you like the image.

  8. also with regards to her short sleeves; after posting yesterday i realized that i’m friends with several ladies who totally wouldn’t regret handling any number of bitey scratchy Aquilops-sized animals with short sleeves, and do so quite regularly. wildlife biologists are a rugged, capable bunch.

  9. Mike from Ottawa Says:

    I agree with Kurt. The undramatic depiction makes the little guy more mundane and thus more real.

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