On Friday I gave you a very nice specimen from the Horniman Museum to identify:
I chose this partly because it’s a great mount and partly because I needed to check the identification, which was out of date.
You all did a great job of breaking down the various options – and there were a few. Jake made the comment:
Is it dippy or a bit ruff ?
This I took as a question about whether the specimen was a Kangaroo Rat (of the genus Dipodomys) or a Rufous Rat-kangaroo (Aepyprymnus rufescens). There was another interpretation that fit with the dippy clue – the correct Family name, which is Dipodidae.
Barbara Powell and Jamie Revell were in the right area and henstridgesj suggested J.j. which was pretty much there, assuming he meant Jaculus jaculus. It is in fact the skeleton of the Greater Egyptian Jerboa, Jaculus orientalis Erxleben, 1777.
The original identification was Dipus aegypticus, which appears to have been a name that was used for both the Lesser and the Greater Egyptian Jerboa, but this specimen is too big to be the Lesser Egyptian Jerboa.
Something I hadn’t noticed before, but which Barbara Powell spotted was the large foramen (hole) in the angle of the mandible, which appears to be diagnostic for Jerboas (I can’t think of anything else with this feature):
For those of you that aren’t familiar with Jerboas here’s a bit of background: they’re rodents, they have an unusual mode of locomotion, with huge hind limbs that the animals use to move at high speed across their desert environment in long leaping bipedal bounds. Unlike Kangaroos they don’t jump with both legs in the same phase, as you can clearly see in the video below:
Jerboas are mainly nocturnal and they spend their days hiding away from the desert heat in underground burrows. As with most rodents their main diet is composed of seeds with the occasional insect as a supplement. They tend to find their food by using their tiny forelimbs to sift through sand grains.
They have plenty of predators and they rely on excellent hearing, eyesight and sense of smell to detect danger, which they then escape from with rapid movement and changes in direction. They’re nimble wee beasties!
Oh, wonderful work, all of you! I admire such sharp observational skills. I’ve been waiting for an explanation for Jake’s encoded question. I’ve never heard of the Jerboa nor seen anything like it on any natural program. How fascinating! Thank you for this Friday mystery object, Paolo.
That’s an interesting observation about the way they jump. This mounted sequence from the Muséum National d’Histoire Naturelle, Paris, seems to have it wrong (assuming both Lesser & Greater jump the same way): http://en.wikipedia.org/wiki/File:Jumping_Jerboa.jpg
It’s not unusual for older taxidermy to get these things wrong – without the high speed cameras of today it would be a struggle to see just how the legs work. My initial guess is that for the Jerboa the staggered landing and launch position of the feet provides a better opportunity for rapid changes in direction. In the Kangaroo the jumping locomotion is more for straight line speed and their greater mass may put constraints on landing on one foot before the other. It’d be interesting to look into this in a bit more detail…
Yes, that’s a good point. I was thinking that the power-to-weight ratio meant they’re not restricted to a two-footed takeoff/landing, but couldn’t see the advantage; greater manoeuvrability would certainly be an advantage. They look more like Skippy than Skippy does!
Funnily enough I was thinking exactly the same thing about Skippy!