By Dan Vergano, USA TODAY
High-tech scans reveal a fossil "heart" within a dinosaur skeleton most likely was just hardened sand that had washed down the gullet of the dead beast.
In the Naturwissenschaften journal, paleontologists led by Timothy Cleland of North Carolina State University in Raleigh, report on a Thescelosaurus dinosaur fossil "heart", first described in 2000 within a specimen nicknamed "Willo" on display at the North Carolina Museum of Natural Sciences. Thescelosaurus ("the marvelous lizard") was a medium-sized (13 feet long), plant-eating, two-legged dinosaur that lived about 65.5 million years ago.
"A three-dimensional, iron-cemented structure found in the anterior thoracic cavity of articulated Thescelosaurus skeletal remains was hypothesized to be the fossilized remains of the animal's four-chambered heart," said the study. That mattered because of a continuing debate over whether dinosaurs possessed a four-chambered heart like birds or mammals. "The hypothesis that this Thescelosaurus has a preserved heart was controversial, and therefore, we reexamined it using higher-resolution computed tomography, paleohistological examination, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy."
The result? The dinosaur is left brokenhearted, says the study.
"Neither the more detailed examination of the gross morphology and orientation of the thoracic 'heart' nor the microstructural studies supported the hypothesis that the structure was a heart." Most likely the structure is a sandy "concretion" that formed after the critter died, says the study.
We asked Cleland to comment on his team's findings:
1. How should we describe the origin of this concretion to readers? Just sand that washed down the gullet of the specimen, and hardened there? What accounts for the shape, most likely?
We really don't know exactly how concretions form, but we do know that their shape and chemistry vary quite a lot. For example, the two large concretions in this specimen have very different shapes to them. One being more rounded the other being more flattened. This structure formed when sand grains were hooked together by iron mineral, so it is very hard. As for the shape, there is a lot of evidence that concretions form around decaying organic matter, and even that microbes might be involved in their formation. It could have been sand packing internal spaces of the rotting animal and then cemented in that shape.
2. What sort of hearts did dinosaurs have, irrespective of this one's dubiousness?
We can't be positive what kind of hearts dinosaurs had, but based on their closest living relatives we can make inferences about it. Birds have a four-chambered heart, and oddly for "reptiles" so do alligators and crocodiles. So because crocodiles share a common ancestor with dinosaurs and birds, and birds are the descendants of one group of dinosaurs, it is safe to assume that dinosaurs most likely had four-chambered hearts too.
3. Could you tell our readers whether the results surprised you? Seems like a fun puzzle.
Science is about testing hypotheses, and we should always be willing to re-evaluate our ideas in light of new technologies and new data. When the first paper defining this as a heart came out in 2000, the researchers did a great job putting forth a new idea based on the data at hand. But their ideas were pretty controversial. When NC State University got a new, higher resolution CT scanner, we decided to test this idea again, using criteria set in advance. One thing our lab works on is looking at exceptional preservation in the fossil record, and how it can come about. If this indeed had been a heart, which would certainly qualify. But I was truly surprised to see the small microstructures that look very much like tissue! They aren't mineral for sure, and they sure are intriguing. That was really a surprise.
