Fossilized Heart Shakes Up Dinosaur Theories
The discovery of an ancient heart of stone--the first ever found belonging to a dinosaur--reveals that many of these primordial creatures were almost certainly warmblooded, like a modern bird or mammal, researchers announced today.
Detailed, computerized X-ray scans of the 66-million-year-old fossilized heart show that its muscular chambers could have pumped enough richly oxygenated blood for the primitive creature to caper, gambol and leap with all the abandon of an animated special effect.
Considered an unprecedented find, the heart was discovered on a hunch by an Oregon doctor who moonlights as an amateur paleontologist. He scrutinized the rockbound rib cage of the petrified dinosaur specimen with a medical CAT scanner.
The outlines of the heart were preserved in the rib cage of a skeleton belonging to a llama-sized dinosaur called Thescelosaurus that, with teeth like salad tongs, browsed the sandy riverbanks of ancient South Dakota.
Scientists at North Carolina State University and the North Carolina State Museum of Natural Sciences, which owns the specimen, published their analysis of the heart today in Science.
As word of the discovery spread, many experts in the field found themselves caught between caution and astonishment.
“We are all going to approach it with some skepticism, but the prospects are quite exciting,†said dinosaur expert Philip Curie at the Tyrrell Museum of Paleontology in Alberta, Canada.
The four-chambered dinosaur heart is the latest in a series of unusual fossil finds around the world that have transformed scientific ideas about the denizens who dominated the nursery of ancient Earth as completely as they grip the popular imagination today.
Not long ago, many experts believed that most dinosaurs were drab, coldblooded, lumbering mega-lizards effectively mired in the Mesozoic mud. Based on new fossils and sophisticated laboratory studies, more and more experts believe that dinosaurs were fast-growing, warmblooded animals--their tough, pebbled hides covered with layers of soft down or feathers--who mothered their young.
The largest had hollow bones, like birds. Many were surprisingly quick on their feet--often as fast as an antelope or charging rhino.
Traits like feathers and nesting behavior, once thought to belong only to direct ancestors of birds, now are considered likely hallmarks of many dinosaurs, even fierce predators like Tyrannosaurus rex.
“It looks like dinosaurs invented almost everything we attribute to birds,†said Jack Horner, curator of paleontology at the University of Montana’s Museum of The Rockies in Bozeman, Mont.
“The discovery is incredible,†said Horner. “There is certainly no question that it supports the hypothesis that dinosaurs were warmblooded.â€
Most reptiles have hearts with three chambers, two that collect blood from the body and from the lungs, and one that pumps the blood throughout the body. Even in those with four chambers, such as the crocodile, the blood is pumped through double arteries that mix oxygen-rich and depleted blood together.
The result is that reptiles have less oxygen in their blood than do mammals or birds and thus have less energy and less endurance and are less able to sustain their body heat as temperatures fluctuate.
Moreover, the new find strongly suggests that many other avian traits “are a shared characteristic of all the dinosaurs,†Horner said. The Thescelosaurus is not an ancestor of birds, so it must have inherited the avian traits from even more ancient forebears that birds and all dinosaurs had in common.
“This [discovery] challenges some of our most fundamental theories about how and when dinosaurs evolved,†said North Carolina State paleontologist Dale Russell, who was a senior author of the study.
Luis M. Chaippe, an expert on dinosaur evolution at the Los Angeles Museum of Natural History, cautioned that any X-ray scan of a stone may be difficult to interpret. But, if the discovery is confirmed, he said, “it reaffirms the close link between dinosaurs and birds.â€
Paleontologist Robert T. Bakker, an author who has long championed the idea that dinosaurs were warmblooded, said, “It proves that ‘birdness’ is a very old feature of dinosaurs. It strongly suggests that the four-chambered heart goes right to the base of the family tree of dinosaurs.â€
Kevin Padian, an authority on avian and dinosaur evolution at UC Berkeley, said, “If true . . . they all--birds, dinosaurs, flying reptiles--had a common [warmblooded] ancestor.â€
At the American Museum of Natural History in New York, paleontologist Mark A. Norell called the dinosaur specimen “extraordinary†and said, “Our perception that these things are big, overblown lizards really needs to change.â€
The newly analyzed heart belongs to an unusually well-preserved fossil of a 663-pound, 13-foot-long herbivore that thrived near the end of the age of dinosaurs, when herds of duckbill dinosaurs and horned Triceratops grazed on carpets of newly evolved flowers.
It is the only one of its species ever found with a complete skull and with soft tissues intact and not lost to decay. Fossilized tendons are still connected to its spine, and petrified cartilage clings to its ribs.
“We got lucky,†Russell said. The fossil was exposed and, “if it hadn’t been discovered when it was, it could have all been eroded in six months.â€
Fossil hunter Michael Hammer discovered the skeleton in 1993. As he began cleaning the fossil, Hammer showed the specimen to a fellow fossil hunter, Dr. Andrew Kuzmitz, a family practitioner in Ashland, Ore.
Normally, the rust-colored sandstone mold of the heart’s soft tissues would have been chipped away and discarded as part of routine fossil preparation. But Kuzmitz suggested that they examine it with a CAT scanner, a form of medical X-ray that can reveal details of hidden soft tissues and internal organs.
They probed the fossil first with a conventional scanner at Rogue Valley Medical Center in Medford, Ore., and then with a more sophisticated scanner at Ashland Community Hospital that can create three-dimensional X-ray images.
“As soon as the picture came up on the screen, I literally jumped off the ground,†Kuzmitz said. “It was a heart. It was wonderful. This is everybody’s dream. I am still three feet off the ground.â€
They forwarded the computerized X-ray data to Paul Fisher, director of biomedical imaging facility at North Carolina State, who enhanced the CAT scan data into even more detailed three-dimensional images. The presence of a four-chambered heart became obvious, he said. Two cardiologists and two veterinarian experts also studied the images.
“We spent seven to eight months going over the images,†Fisher said.
“Not only does this specimen have a heart,†Fisher said, “but computer-enhanced images of its chest strongly suggest it is a four-chambered, double-pump heart with a single systemic aorta, more like the heart of a bird or a mammal than a reptile.â€
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Chambers of the Heart
Warmblooded animals have hearts with four chambers that separate oxygen-enriched blood from oxygen-depleted blood. Most coldblooded animals, such as reptiles, have three chambers that mix the blood and send less concentrated oxygen to the body. The discovery of a dinosaur fossil with a four-chambered heart suggests that it was warmblooded. Here is a comparison of a human heart and a typical reptilian heart.
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Source: Science Magazine
