Dimetrodon

Dimetrodon - ancestor of the mammals belonged to the family called Pelycosaurs, which had both mammal and reptile characteristics. Dimetrodon preceded the earliest dinosaurs by more than 40 million years but physically it looked a lot like one. It is often referred to as mammal-like reptile, based on characteristics of the skull and dentition. Dimetrodon was a dominant carnivore, the largest one of the Permian period. It was a predacious reptile that was on the top of the food chain during the early Permian.
This pelycosaur possessed a spectacular sail on its back, supported by long, bony spines, each of which grew out of a separate spinal vertebra. The sail was probably an early experiment in controlling body temperature. It is believed that the sail absorbed the heat of the sun and warmed the blood and body. It warmed up early after sunrise and cooled off more efficiently during the heat of the day. It may have also been used for mating and dominance rituals and making it look much larger than it was to predators. Dimetrodon had a large skull with two types of teeth (sharp canines and shearing teeth). It was probably quite slow because it walked on four side-sprawling legs.
Dimetrodon is one of the more recognized of the early reptiles..
TIME - 280 - 260 MYA, Early Permian period.RANGE - Russia, E. Europe. USA Texas, Oklahoma.DIET - Smaller reptiles and other small vertebrates.SIZE - Up to 6ft (2m) long.

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Best Evidence Yet for Dinosaur Migrations—Teeth Tell Tale

Sauropod dinosaurs may well have been the largest animals to ever walk—and walk and walk and walk—the Earth.

A new fossil-teeth analysis has uncovered the best evidence yet that dinosaurs migrated seasonally like modern-day birds or elephants, according to a new study.

(See pictures of great migrations.)

Chemical signals in prehistoric tooth enamel reveal that roughly bus-lengthCamarasaurus dinosaurs walked hundreds of miles on marathon migrations inlate Jurassic North America.

Responding to shifts in food and water availability, the long-necked plant-eaters likely trudged from floodplain lowlands to distant uplands and back again as the seasons changed across parts of what are now Utah and Wyoming, researchers say. (See a sauropod picture.)

"On the African Serengeti the large mammals do a wet season-dry season migration and that's sort of what we're envisioning here," said Colorado College geochemist Henry Fricke, who led the study, published today in the journalNature.

Fricke and colleagues theorize that the dinosaurs left a basin floodplain area at the onset of the summer dry season, when droughts may have been common and plant supplies limited.

The sauropods moved nearly 200 miles (300 kilometers) to highlands that were presumably cooler and wetter in that season, Fricke said. That's tough to prove, though, because erosion of the areas' ancient rock has deprived scientists of crucial evidence needed to "reconstruct" the long-gone highlands, he said.

The animals likely returned to the lowlands during the wet winters, when food and drink were again plentiful, he added.

(Related: "Huge New Dinosaur Trackway Found in U.S.")

The Telltale Teeth

Scientists have long suggested that some dinosaurs might have migrated, but it's been extremely hard to find any evidence for the behavior.

Fricke and colleagues compared ratios of oxygen isotopes—varying versions of the element—in the fossil Camarasaurus teeth with oxygen isotopes found in prehistoric layers of lowland soil.

(Also see "Biggest Dinosaurs Grew Huge By Not Chewing Their Food.")

Because the dinosaurs' teeth were replaced roughly every five months, each tooth offers a unique record of what the animal drank during the tooth's life span.

The soil and teeth turned out to have distinctly different oxygen-isotope ratios, suggesting the teeth had formed elsewhere, for the most part. The ratios in the teeth, tellingly, were akin to what you'd expect had the teeth grown at high elevations.

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