Introducing “Gonzo” December 20th, 2005 by Mike Keesey :: see related comic

Surprise!

I based my drawing of Darwin on the portrait from a £10 note tacked above my desk. I love that the U.K. has seen fit to put one of the greatest scientists of all time on their money. The closest we Americans have to scientists on money are Benjamin Franklin (an active scientist, he of the famous kite experiment, confirming that lightning is electricity) and Thomas Jefferson (our only paleo-geek president, who hoped Lewis and Clark would find mammoths, etc. in the North American interior), who are of course numismatically commemorated for reasons other than science (i.e., founding our country).

But I’m not going to write about Darwin today; I’m going to write about his revealer!

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Buitreraptor gonzalezorum Makovicky et al. 2005 is a new deinonychosaur (that’s “‘raptor” for you Jurassic Park fans) from the Cenomanian (early Late Cretaceous) of Argentina. It’s pretty cool for several reasons.

Most obviously, it has a really, really, really long snout. It’s almost like a deinonychosaur trying to be a spinosaur—or a heron, as I illustrated here: Three Gonzos Fishing. (The behavior is purely speculative, of course.)

The other cool things about this animal have to do with its phylogenetic relationships. Makovicky et al. found this topology:

Paraves
--<i>Eumaniraptora</i>
   |--<i>Avialae</i> (stem-based sense; including <i>Aves</i>)
–Deinonychosauria
      |–Troodontidae
      --<i>Dromaeosauridae</i> sensu lato
         |--+--<i>Microraptoria</i>
         |–Dromaeosauridae sensu stricto             (Velociraptor, Deinonychus, etc.)
         --<i>Unenlagiinae</i>
            |--<i>Buitreraptor</i>
–+–Unenlagia
               `–Rahonavis

Formerly, Rahonavis, a small flying animal from the Maastrichtian (latest Cretaceous) of Madgascar, and Unenlagia, a larger, birdlike animal from the Turonian–Coniacian (middle Late Cretaceous) of Argentina, had been difficult to pin down, bouncing back and forth in different studies between Avialae (birds) and Deinonychosauria (”‘raptors”). Both are somewhat incomplete, based on postcranial remains. Buitreraptor material overlaps that of Unenlagia and Rahonavis material, enabling better comparison. Interestingly, it seems to form a clade, called Unenlagiinae, with Unenlagia and Rahonavis.

Unenlagiinae is interesting first because of its geography: all of its constituents are Gondwanan (southern hemisphere), and all other deinonychosaurs are Laurasian (north hemisphere). (Indeed, there may be a fourth unenlagiine, Neuquenraptor, from the same locality as Unenlagia, although Makovicky et al. regard it as a synonym of Unenlagia) This would imply that the first deinonychosaurs (and the first avialans) were Laurasian, but somewhere along the way the unenlagiine lineage infiltrated Gondwana.

Perhaps even more interesting is what this means for the origins of bird flight. Avialans (stem-based sense—the most inclusive clade including modern birds but not Deinonychus) are no longer the only flying theropods. There are also at least two genera of flying deinonychosaur: Rahonavis and Microraptor (a Chinese microraptorian). But these are more closely related to flightless deinonychosaurs than to each other: Rahonavis to Buitreraptor and Unenlagia, and Microraptor to Sinornithosaurus and Dromaeosauridae sensu stricto. There is also Pedopenna Xu and Zhang 2005, possibly a basal paravian, which is only known from a leg with remnants of long feathers, similar to those of the strange “leg-wings” of Microraptor.

Did flight evolve several times within Paraves? Or, as some have suggested for a long time (e.g., Paul 1988), are troodontids, dromaeosaurids sensu stricto, etc. secondarily flightless, like modern-day ostriches and kiwis? And was the first form of flight two-winged, as in modern birds, or “four-winged”, as in Microraptor (Xu et al. 2003) and possibly Pedopenna and the basal avialan Archaeopteryx (as suggested by Longrich 2003)? (The condition is currently unknown in Rahonavis.)

Hopefully time will tell.

References:

• Longrich, N. 2003. Archaeopteryx: two wings or four? J. Vert. Paleo. 23(3):72A
• Makovicky, P.J., S. Apesteguía, and F. L. Agnolín. 2005: The earliest dromaeosaurid theropod from South America. Nature 437:1007–1011.
• Paul, G. S. 1988. Predatory dinosaurs of the world. Simon and Schuster. 424pp.
• Xu, X., Z. Zhou, X. Wang, X. Kuang, F. Zhang and X. Du. 2003. Four-winged dinosaurs from China. Nature 421:335–340.
• X. Xu and F. Zhang. 2005 April. A new maniraptoran dinosaur from China with long feathers on the metatarsus. Naturwissenschaften 92(4):173–177.

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