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THE GIST:

– Dwarf dinosaurs existed on a Late Cretaceous island, a new analysis of bones confirms.

– Dwarf dinosaurs appear to have emerged from a process called progenesis, which shortens the developmental period.

– The dwarf dinosaurs lived fast, reaching sexual maturity at earlier ages than their mainland counterparts, and they likely died young.

A new study not only confirms the existence of dwarf dinosaurs, but also explains how dinosaurs shrank during the Late Cretaceous at a Neverland-like place — Hateg Island, Romania — where dinos never really grew up.

According to the study, which has been accepted for publication in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, the unusual phenomenon appears to have only affected some of the island’s dinosaur residents.

Benton, who directs the Palaeobiology and Biodiversity Research Group at the University of Bristol, and his colleagues conducted one of the most extensive studies yet on the Hateg Island dinosaur remains. They analyzed the dinosaurs’ limb proportions and bone growth patterns, comparing them with those of mainland dinos.

The analysis determined that at least four of the Hateg dinosaurs were dwarves.

The diminutive dinosaurs included the titanosaurian sauropodMagyarosaurus, which had a body length of about 16 to 19 feet. That’s impressive by human standards, but is miniature compared to a sauropod such as Argentinosaurus, which grew to be at least 82 feet long.

Another small dinosaur was the hadrosaurid Telmatosaurus. Its 13-foot-long body contrasted with the average size of other hadrosaurids, which were 23 to 33 feet long, according to Benton.

Two species of Zalmoxes dinosaurs also appear to have been dwarves, with one — Zalmoxes robustus — measuring about 10 feet in length.

“So these forms are all typically half the length of their close relatives on larger land masses, and this equates to a body mass of perhaps one-eighth that of the relatives,” said Benton. “Body mass is what matters most in biological terms, such as physiology and food intake.”

Magnified sections of the dinosaurs’ bones revealed that the animals were adults and not juveniles. The scientists believe the dinosaurs likely shrank due to a process called progenesis, which shortens the developmental period. Sexual maturity happened early, and these dinosaurs may have also died two to five years younger than their “normal”-sized counterparts.

“This in-depth study by Benton and colleagues is both fascinating and provocative,” paleontologist Scott Sampson, a research curator at the Utah Museum of Natural History, told Discovery News, “demonstrating that the largest group of animals ever to walk the earth included dwarfed varieties.”

Sampson added that the study also supports “the more general ‘island rule’– the idea that, when marooned on islands, evolution tends to make large animals smaller, and small animals larger.”

Scientists continue to debate why this happens on islands. Reduced supplies of food, smaller ranges, and few larger predators have all been theorized.

“I think most biologists accept that there is something going on, and that the island rule has validity,” Benton said.

sources: new discovery

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