(Part 2)
BY DR. JOSE PALU-AY DACUDAO
One of the main reasons seems to be that birds have clavicles (collar bones) that fuse to form the well-known furcula, which is the ‘wishbone’ we see in the chicken we eat. Clavicles also exist in more primitive reptiles. But not in dinosaurs. Therefore, birds evolved from primitive reptiles. Dinosaurs also evolved from primitive reptiles. Birds did not evolve from dinosaurs. Or so it was thought.
The problem is that furcula are as fragile as many of our wishes, and almost always never fossilize. But as more fossil discoveries occurred, by 2010 it had become evident that theropod dinosaurs also possess wishbones. So, the wishbone issue has now been definitively resolved.
The popular view that birds are dinosaurs started gaining ground only in the 1960s, with the discovery of Deinonychus. Think of it as the bigger version of its close relative, the Velociraptor, the terrifying intelligent dinosaur pack hunter of Jurassic Park fame. Deinonychus’ skeleton so closely resembles that of Archaeopteryx that with a little imagination, shrinking it and giving it feathers and wings would turn it into Archaeopteryx.
Moreover, in the 1960s, famous American paleontologist, Bakker, showed from analyses of multiple traits that dinosaurs were homeothermic (warm-blooded) and at the very least mesothermic (could partially regulate their body temperature, as in modern mammalian monotremes, the egg-laying platypuses and echidnas). They could raise their body temperature well above that of their environment, just like modern mammals and birds. (Note that feathers are believed to have evolved originally to preserve heat, just like mammalian hair.) Bakker wrote a book that depicts dinosaurs as warm-blooded agile animals. His drawings show bipedal theropods running on two feet as quick as ostriches, with their tails held stiffly above the ground to balance their necks and heads. (I was a great fan of that book. Unfortunately, I lost my copy.)
But perhaps the coelurosaurian Deinonychus really did have feathers, as some features of its bones seem to indicate. In the 1990s, several particularly well-preserved coelurosaurian dinosaurs from Liaoning China definitely show feathers. It now seems that Coelurosauria (the clade maniraptorans belong to) possessed feathers. Although feathers rarely fossilize, they can leave clear anatomical impressions if buried in very fine clay material that later turns to stone, referred to as lagerstätten. The maniraptoran feathered Archaeopteryx was likewise buried in lagerstätten in Germany.
We can go on and on talking about the traits that show that birds are dinosaurs, but this would take at least two pages. In brief, extensive studies have shown that birds are maniraptoran coelurosaurs, one of the clades within the theropods. (To be continued)/PN
