Smithsonian.com

Filed under “Hang on a sec”: a new scientific paper has called into question one of the most exciting paleontological finds of the 21st century. Soft tissue discovered deep inside a Tyrannosaurus rex legbone may be a recent “biofilm” (what you might call scunge if you found it on a dishrag), not remnants of the Toothy One after all. That’s the suggestion of a team led by Thomas Kaye, writing in the scientific journal PLOS One.

Avid Smithsoniacs and dino fans may remember bits and pieces of this story. In 2005, paleontologists Mary Schweitzer and Jack Horner were stuffing a T. rex femur inside a too-small helicopter on their way home. They cracked the bone in half to make it fit, and Schweitzer noticed a goopy residue on the 65-million-year-old insides of the bone (see the Smithsonian story). Then this April, Schweitzer and her colleagues isolated a protein called collagen from the sample, analyzed it, and found striking similarities to the collagen of modern birds.

Kaye’s contradictory opinion comes from using an electron microscope to peer at similar residues he found in different fossils. Studying fossils of 17 dinosaur and mammal species, Kaye and his team saw evidence of biofilms, or slime left behind by bacteria that grew on the bone long after the dinosaur’s death.

Where Schweitzer’s group described the remains of red blood cells, Kaye’s team thought they were seeing iron-rich structures routinely built by bacteria. (The iron content and the structures’ characteristic shape might have made them look like red blood cells in some analyses, Kaye suggested.) Kaye found these structures time and again in his samples – even in a fossilized shell, which never would have contained blood at all. Worst of all, carbon dating suggested the biofilm was as recent as 1960.

Of course, there’s still the matter of the collagen’s similarity to chickens and ostriches – a detail Schweitzer was quick to point out to reporters. And Kaye didn’t sample the T. rex in question, leaving open the chance that Schweitzer’s find was the genuine article.

Personally, I’m leaning toward believing in the extraordinary. At least until the collagen results are explained (I mean, can anyone tell me if bacteria even make collagen?) Either way, it’s fascinating to listen to the well-constructed arguments on both sides. That’s what science is all about.

The closest living relatives of Tyrannosaurus rex are birds such as chickens and ostriches, according to research published today in Science (and promptly reported in the New York Times). Paleontologists used material discovered in a chance find in 2003 to pin down the link.

The dinosaur-ness of birds has been suspected for many years based on anatomical similarities, but the new research is the first molecular evidence. For decades, dinosaurs were thought to be reptiles: big ones, to be sure, but basically cold-blooded, slow-moving, and dim-witted. The movie Jurassic Park popularized the idea of dinosaurs as quick, smart and birdlike. (The movie’s ideas had been proposed in the 1970s–a book by paleontologist Robert Bakker, called The Dinosaur Heresies, nicely conveys this change in thinking and the controversy that accompanied it.)

To get molecular evidence about dinosaurs, you need some actual molecules–a tall order for a group of animals that died out 65 million years ago. But in 2003, scientists Jack Horner and Mary Schweitzer discovered some unfossilized material inside a T. rex bone by a combination of luck, desperation, and sharp eyes (see Smithsonian, May 2006). Faced with flying a giant femur out of a remote Montana field site, they broke the bone in half so it would fit inside their helicopter. If they’d had a larger helicopter, we might never have known.

Unlike in Jurassic Park, the real-life researchers couldn’t recover any DNA from the ancient remains. But they did retrieve molecules of collagen, a structural protein that appears in slightly different forms in many animals. They compared the dinosaur version with 21 living animals, including humans, chimps, mice, chickens, ostriches, alligators and salmon. T. rex’s collagen proved to be most similar to chickens and ostriches; its next closest match was to alligators.

Chickens and ostriches are only distantly related to each other, so the research says little about what kind of birds might be the closest relatives of the famous carnivore. The scientists noted that answering that question would require data from more molecules than just collagen. Whether they are currently cracking into any more giant fossils in search of material was not divulged.

(Images courtesy Science)