Friday, December 17, 2010

Life Lines 82


Children love dinosaurs. They are extinct relatives and their history was played out long ago so they can’t threaten us. They roamed on earth tens of millions of years ago and most disappeared relatively rapidly some 60 to 70 million years ago, most likely from a collision with a meteor. Most dinosaurs we know from their fossil bones. A few have left imprints of their skin and other remnants behind, including the shells from which they hatched. There is a lot of debate about their physiology, most considering them warm-blooded rather than cold-blooded. There is also debate about their behavior, some arguing they cared for their young after hatching and others arguing for a pattern of dump the eggs and walk away.

The American Museum of Natural History in NY City has recently completed an extensive reorganization of its dinosaur collection and placed them in two of its four connected wings on the origins and variety of the vertebrates. We are vertebrates and belong to the mammals. Our immediate predecessors look more like dinosaurs than mammals. As we enter the first hall of the exhibit we can choose a ten minute film to introduce us to the evolution of vertebrates or a series of paintings that unfold the hundreds of millions of years carved into geological eras. I was immensely pleased by these exhibits. It comes as a shock to see the earliest ancestors of fish, the placoderms, having not teeth but tooth plates, like jagged and irregular chunks of sheet metal that would easily make mince meat of the invertebrate flesh they encountered.

I was surprised to find that sharks came from bony fishes and not the other way around. I marveled at the variety of ways our limbs developed. Some of these early ancestors had up to eight digits to a flipper or foot. The fingers had up to ten phalanges (if you bend your fingers and count, you’ll find three in all except your thumbs). We are surprised that dinosaurs are two or three toed, as if designed by Disney, whose cartoon characters routinely uncrowd their hands with a missing digit.

The exhibits guide us with arrows and mosaic or painted paths, a sort of Yellow Brick Road adventure, as filled with forks and surprises as those Dorothy and her friends took to Oz. I am a passionate museum goer. I don’t develop museum fatigue. I take notes. The students I take with me often wilt and disappear reappearing two hours or so later when we gather to board our bus back to the university. I am used to that and hope a few will read the fine print of the exhibit cards and thrill as I do to see that the curator of the exhibit has demoted reptiles to a cultural term and not of scientific worth. The dinosaurs are part of the saurosids, along with crocodiles, lizards, snakes, turtles, and birds. Birds? Those lovely goldfinches at my feeder? Could they be part and parcel of the saurosids and a bud off the dinosaur branch? It’s controversial, of course, as classifications based on a spotty fossil record often are, but how startling it is to see their two skeletons side by side, reduced to the same size, looking so much like siblings.

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