Wednesday, October 20, 2010

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.

8 comments:

  1. It's a shame they didn't name it as "Koreanodromeus" or something in order to keep with Oryctodromeus and Orodromeus.

    :(

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  2. Would have been good in spirit, but not exactly the best name for a critter with low cursorial ability. Maybe the naming conventions for these things should shift towards emphasizing the oryctos bit, rather than the dromaeos. Koreanoryctos or something.

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  3. I can't wait to see a reconstruction of this thing.

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  4. I'm disappointed that their matrix only includes Orodromeus from the Montana ornithopod clade, would have been nice to see its position relative to the North American taxa.

    It's a shame they didn't name it as "Koreanodromeus" or something in order to keep with Oryctodromeus and Orodromeus.

    In the authors' defense, it doesn't seem to have been much of a 'dromeus:

    Even though it cannot be definitively proved that KDRC-BB2 and 3 do belong to the same individual, the size and robustness of the scapula and the humerus compared to the femur suggest that Koreanosaurus was a quadruped rather than a strictly cursorial biped like other hypsilophodontids.

    Not to mention it's nowhere near as awkward as Panamericansaurus.

    But yeah, quadrupedal, semi-splaying subterranean basal ornithopods. Don't see that every day.

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  5. So basal ornithopods weren't so boring after all. They evolved quadrupedality, too. And dug burrows, which is more than what iguanodontians can say.

    On stiffened tails, I remember reading that Oryctodromeus didn't even have ossified tail tendons.

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  6. @Albertonykus
    Ah, cool, wasn't sure about ossified tendons in other basal ornithopods, which is why I only brought up Leaellynasaura, which may be a more basal ornithischian anyway.

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  7. OK I misread that, the authors didn't even attempt to test its relationships.

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  8. Michael O. EricksonJanuary 14, 2011 at 11:00 PM

    Drinker lacks ossified tendons as well, which was one of the features that initially led Bakker to suggest that it was a burrower.

    I wonder if a lack of ossified tendons might be a character we could use to assess the probability of burrowing in ornithopod taxa? Although we have Organ (2006) showing that ossified tendons would probably not have significantly restricted lateral flexation of the tail in ornithopods, it certainly would have hindered vertical movement, and flexibility of a long tail in all planes might be most beneficial for a burrower.

    It's kind of a shame the authors didn't try to test Koreanosaurus's relationships; I would have liked to see where it would've ended up on a cladogram.

    Like the blog by the way, good stuff.

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