Tuesday, October 29, 2013

Bird tracks and dinosaurs

Figure 2 from the new study, showing the original
rocks with the tracks encircled.
A report of the oldest set of bird footprints from Australia was published online today in the Palaeontology journal, soon to be published in print.  The tracks were found in 2010 at a place called Dinosaur Cove in Victoria, Australia, where numerous dinosaur bones were excavated from 1984 to 1994.

The authors of the study were unable to specifically identify the trackmakers, but they liken the footprints to those of a modern heron.  A drag mark behind track 2 (T2 in the figure) is claimed to be evidence that the bird was landing from flight, so it was apparently a fully flight-capable bird.  Track 3 is actually attributed to a theropod dinosaur rather than a bird, possibly a coelurosaur.  The rocks in which the tracks were found are dated to the middle of the Cretaceous period, roughly 106 million years ago, during the height of dinosaur diversity.

This report comes on the heels of a featured article by Creation Ministries International that criticizes natural history museums for never displaying modern-style birds alongside dinosaurs, despite the abundant bird fossils found along with dinosaurs.  This trend in museums, CMI says, gives visitors the impression that birds were not around until the dinosaurs died out, reinforcing the idea that dinosaurs evolved into birds.  Paleontologists are well aware of these fossils, as the article notes, but such findings are often not publicized.

The coexistence of birds and dinosaurs is not exactly condemning to the evolutionary model, but it may alter the popular view of their relationship.  In the branches of the evolutionary tree, birds are placed within a group of dinosaurs called Eumaniraptora, which also contains troodontids and dromaeosaurids, including the famed Velociraptor.  Now that these dinosaurs are portrayed with feathers, many people have the impression that they evolved into birds.  However, the evolutionary tree does not quite work like that.  Rather, it is believed that birds, troodontids, and dromaeosaurids share a hypothetical common ancestor that branched into each of these groups.  The downside to the evolutionary view is that this would require some very fast and drastic changes to the dinosaur body plan to get them to fly, because the "bird-like" dinosaurs cannot be taken as intermediate steps.  Modern birds (Aves), troodontids, and dromaeosaurids share approximately the same fossil range, being found mostly in the Cretaceous, with a few of each in the Jurassic rocks.  Curiously, I even found a reference to a bird track dated to the Triassic, when dinosaurs are thought to have evolved.  If this is genuine, then it would really throw a wrench into the prevalent view of bird origins.

For more details on the dinosaur-to-bird evolutionary model, see the Wikipedia entry, "Origin of birds."

For creationist rebuttals of the evolutionary view, see the series of articles by Answers in Genesis entitled "Did birds really evolved from dinosaurs?" at the bottom of their dinosaur page.

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