Another Burrowing Ornithopod

Above: Type specimen of Koreanoaurus (minus referred pelvis and hindlimbs) from Huh et al. 2010.

Though Bob Bakker had been suggesting that small ornithpods dug burrows for years, on the basis of the kind of sediments the basal ornithopods of Montana were usually found in, we didn't get solid confirmation that these were really burrowing creatures until the discovery of Oryctodromeus. Here was an ornithopod with the same, vaguely burrower-like features as its relatives Orodromeus and Zephyrosaurus, but which was found inside an obvious burrow.

The burrow was the key, because aside from some fairly ambiguous skeletal details, these dinosaurs all had fairly standard ornithpod proportions: elongated necks, long (usually) stiffened tails (but see below), long hind limbs and short front limbs. The overall body plan was that of a bipedal runner, not a dinosaurian wombat.

While still far from mole or wombat like, the new dinosaur Koreanosaurus boseongensis (named by Min Huh, Lee Dae-Gil, Kim Jung-Kyun, Lim Jong-Deock and Pascal Godefroi) is even closer than its relatives. It has very robust forelimbs, and while the humerus is still long, the forearm is short and stout, with a massive scapula and coaracoid, and a big keeled breastbone, all of which indicate attachment sites for powerful muscles useful for digging. Interestingly, the hind limbs are also very specialized. They're relatively short compared to the forelimbs, with a low ratio between the femur and tibia lengths, and with short metatarsals. The length indicates that even if this wasn't a fossorial creature, it was probably a quadruped. The hip is especially interesting. The head of the femur, the bit which fits into the hip socket, is at a 135 degree angle to the rest of the bone. This would have given Koreanosaurus a very un-dinosaurian semi-splaying leg posture, similar to burrowing mammals. The authors speculate that it would have used its legs to brace itself inside an incipient burrow while it used its powerful forelimbs to shovel soil.

So, while the team of scientists was unable to locate any nearby fossil burrows big enough to have been made by this (roughly) meter long ornithopod, the skeletal details are more than enough to suggest a digging lifestyle. But it was no dinosaurian mole, as it still had many features in common with terrestrial dinosaurs, like a long neck and (presumably) long, partly stiffened tail. However, we shouldn't be so quick to assign stiffness to the tail just because this is found in other ornithopods. As I reported before, the Australian Leaellynasaura had an unusual, very long, very flexible tail.

Koreanosaurus was found in seaside cliffs of Boseong, on the south coast of Korea. It is the first Korean dinosaur known from good remains. It should be noted that another Korean dinosaur (a theropod) had previously been unofficially named "Koreanosaurus," but as this was a nomen nudum, it's no more a valid scientific name than "Sue," and is rightly ignored.