Unfortunately, I didn't get to attend to the annual SVP Meeting in Austin, TX this year, and I can hardly wait to hear about all the interesting talks and papers from those who attended. My curiosity as to the proceedings has been mildly sated, however, by a news report about one of the interesting discoveries announced at the convention; a mid-Triassic (225 Ma) track found near Melbourne, Australia that has been attributed to a theropod dinosaur.
The 14cm-long tracks seem to indicate the presence of a theropod (or, as Zach has pointed out, some as-yet-unknown bipedal crurotarsian) that stood between 4.5 to 5 feet at the hip in what was a polar region of the world at the time, living considerably earlier than the famous Antarctic Early Jurassic theropod Cryolophosaurus ellioti. Indeed, it appears that the claim dinosaurs inhabited every continent except what is now Antarctica has been known to be false for several years now, the presence of this footprint potentially pushing the existence of theropods in the southermost regions of Pangea back even further. Such discoveries often create many more questions than offer up answers, however, although I hope that more is uncovered about early southern dinosaurs in the coming years.
This discovery actually reminds me of another important find in the polar regions, only a bit older and on the opposite pole. In August of 1960 geologists under the auspices of the 21st International Congress of Geology led by Anatol Heintz from the University of Oslo were studying formations on the archipelago of Svalbard, located nearly halfway between the North Pole and Norway. While prospecting along some Early Cretaceous sandstone, Albert F. Lapparent and Robert Laffitte noticed thirteen large, three-toed footprints, the trackmarks of an Ornithopod dinosaur. Unfortunately the scientists were out of time and according to Lapparent "...did not even have a piece of chalk, to show the outlines of the prints." Sketches and measurements were made but the group had to leave for their ship, the schedule not allowing them to stay or return to the site. The scientists would have to wait until 1961 to get back to the tracks (which were fortunately still there, a relief to the researchers as this is not always so) but could not remove or excavate them due to the location, fragility of the fossils, and hardness of the rock the footprints were in. Casts made of latex were the group's answer, although the weather did not cooperate and the latex would not set. The "old fashioned" technique of using plaster of paris was more successful, the team being able to obtain seven track impressions. After the casts were studied in the more amenable conditions of the lab Lapparent concluded that they belonged to Iguanodon*, but the find was certainly a groundbreaking one.
* I have not had the chance to read Lapparent's paper, but it's rare for a track to be attributed, without doubt, to a species or even genus of dinosaur. Tracks and other ichnofossils are often given their own names so that confusion is kept to a minimum, although it is certain that Lapparent's print was made by an Ornithopod dinosaur, the group to which Iguanodon, hadrosaurs, dryosaurs, camptosaurs, and others belong.
Paleontologist Edwin Colbert referred to the discovery as "Closing the Circle" when it came to Iguanodon, and while he was not the first to suggest dinosaur migrations (such hypotheses first being made about Plateosaurus during the first half of the 20th century) it did inspire Colbert to hypothesize about why Iguanodon might be found so far north. In his book Men and Dinosaurs he writes;
Perhaps Iguanodon was a beast of passage, like modern migrating birds, that wandered north into Spitzbergen during the summer months, and then back south, to some point below the Arctic Circle, and therefore a point at which the sun would shine, during the winter months. But to accomplish such a long migration twice each year probably would require at least two months in each direction on the part of such large, ponderous, and slow moving reptile as Iguanodon. Moreover, it would require a great deal of reptilian energy. Such a supposition seems almost beyond the bounds of possibility.
Colbert wrote this words in 1968, a time when the idea of active, dynamic, and possible warm-blooded dinosaurs was still in its infancy, although it should be noted that Colbert ponders the possibility that the track site was once much further south than it is at present and hence would not require such great migrations. Regardless of which answer is right, there has been mounting evidence in the last 50 years that some dinosaurs migrated and did so in large herds, especially ornithischian dinosaurs like the hadrosaur Edmontosaurus and the centrosaur Pachyrhinosaurus, specimens of which have been found in Alaska. Indeed, while reconstructing mass migrations remains difficult it is clear that dinosaurs reached both poles at different times during the Mesozoic, and hopefully further study will help define the ecology of the polar regions during ages past. I would be remiss if I simply suggested that migration was the only way the dinosaurs reached polar regions; some may have lived there year round, and it is that possibility that is one of the most intriguing in modern paleontology.
Bryner, J. (19 October 2007 05:29 pm ET) "Polar Dinosaurs Left Their Tracks." LiveScience.
Colbert, E. (1968) Men and Dinosaurs. E.P. Dutton & Company, pp. 257-263.
I question the theropod diagnosis. As an example, Effigia obtained a bipedal, tripodal posture. Its lineage may extend back as far or farther than theropods. Until some good mid-Triassic dinosaur bones have been found, I remain skeptical.
I question the theropod diagnosis.
More to the point, ostensible Middle Triassic "theropod" tracks have been reported from France for over four decades now...this is hardly news. Though if there's a way to demonstrate that the new track is indeed theropod, I'd be very interested! (Missed the talk, dammit...)
Good points, Zach & Jerry. Regardless of whether this is a theropod track or the footprint of another archosaur that convergently developed bipedalism, I think it's the location that really makes it newsworthy. I would have to wonder what the ecology was like, especially since this is being touted as being in the polar regions. Overall I think that's the more interesting question; when did dinosaurs inhabit these areas, how were the areas different, and how did they impact evolution?
There have been tracks found around (today's) polar regions, have insulative feather imprints been found?
I accept aquatic/marine reptiles near polar areas, but unless terrestrial reptile animals had a thick layer of fat, I can't see them there during the short summers and migrating towards the equator.
Much more likely IMO is that when the tracks were laid, the geoposition/geoclimate was temperate and near a gulf-stream-like current keeping the area moderately warmish, and later the land moved poleward or the poles moved towards the tracks.
Um, yes. Seeing as, in the Triassic and Jurassic, at least, Antarctica was a balmy paradise, I don't think the resident dinosaurs would've been too concerned about cold weather!