Science Tuesday, er, Friday: Unexpected surprises...

Fossil Find Challenges Theories on T. Rex
By HENRY FOUNTAIN, The New York Times, September 18, 2009

Paleontologists said Thursday that they had discovered what amounted to a miniature prototype of Tyrannosaurus rex, complete with the oversize head, powerful jaws, long legs — and, as every schoolchild knows, puny arms — that were hallmarks of the king of the dinosaurs.

But this scaled-down version, which was about nine feet long and weighed only 150 pounds, lived 125 million years ago, about 35 million years before giant Tyrannosaurs roamed the earth. So the discovery calls into question theories about the evolution of T. rex, which was about five times longer and almost 100 times heavier.

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Remarkable Creatures: In a Shark’s Tooth, a New Family Tree
By SEAN B. CARROLL, The New York Times, September 15, 2009

“Like a locomotive with a mouth full of butcher knives.”

That is how a shark expert, Matt Hooper, described Carcharodon megalodon to the police chief in Peter Benchley’s novel “Jaws.” He was referring to the 50-foot-long, 50-ton body and enormous six- to seven-inch-long teeth that made the extinct megalodon shark perhaps the most awesome predator that has ever roamed the seas.

Hooper had just gotten his first glimpse of the massive great white shark that was terrorizing the residents of Amity Island. Hooper explained that the Latin name for the great white was Carcharodon carcharias and that “the closest ancestor we can find for it” was megalodon. So maybe, he speculated, this creature wasn’t merely a great white, but a surviving sea monster from an earlier era.

Hooper was toying with a simple and long-established idea: that the most feared predator in the ocean today, the great white shark, evolved from megalodon, the most fearsome predator of a few million years ago.

That is how the two species had been viewed, until recently, when new ways of looking at shark teeth, and new shark fossils from a Peruvian desert, convinced most experts that great whites are not descended from a megatoothed megashark. Rather, they evolved from a more moderate-size, smooth-toothed relative of mako sharks.

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New Clues to Sex Anomalies in How Y Chromosomes Are Copied
By NICHOLAS WADE, The New York Times, September 15, 2009

The first words ever spoken, so fable holds, were a palindrome and an introduction: “Madam, I’m Adam.”

A few years ago palindromes — phrases that read the same backward as forward — turned out to be an essential protective feature of Adam’s Y, the male-determining chromosome that all living men have inherited from a single individual who lived some 60,000 years ago. Each man carries a Y from his father and an X chromosome from his mother. Women have two X chromosomes, one from each parent.

The new twist in the story is the discovery that the palindrome system has a simple weakness, one that explains a wide range of sex anomalies from feminization to sex reversal similar to Turner’s syndrome, the condition of women who carry only one X chromosome.

The palindromes were discovered in 2003 when the Y chromosome’s sequence of bases, represented by the familiar letters G, C, T and A, was first worked out by David C. Page of the Whitehead Institute in Cambridge, Mass., and colleagues at the DNA sequencing center at Washington University School of Medicine in St. Louis.

They came as a total surprise but one that immediately explained a serious evolutionary puzzle, that of how the genes on the Y chromosome are protected from crippling mutations.

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Observatory: Fibers in a Cave Point to Ancient Craft Work
By HENRY FOUNTAIN, The New York Times, September 15, 2009

Archeologists looking for signs of what the ancient climate was like in the Caucasus Mountains have come across something else: signs of ancient craft work.

They found fibers of wild flax, up to 34,000 years old, in the Dzudzuana Cave in the former Soviet republic of Georgia. Some of the fibers were twisted and some were dyed, which indicates they were used for sewing clothes, weaving baskets or making ropes. That makes the fibers the oldest known to have been used by humans.

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