October 21, 2009—The tiniest dinosaur in North America weighed less than a teacup Chihuahua, a new study says.
Seen above as an artist's reconstruction in front of a Tyrannosaurus rex skull at the Natural History Museum of Los Angeles County in California, the agile Fruitadens haagarorum was just 28 inches (70 centimeters) long and weighed less than two pounds (one kilogram).
The diminutive dinosaur likely darted among the legs of larger plant-eaters such as Brachiosaurus and predators such as Allosaurus about 150 million years ago, during the late Jurassic period.
Parts of the skulls, vertebrae, arms, and legs from four F. haagarorum specimens were found in the 1970s in Colorado and later stored at the Natural History Museum.
A recent analysis of the fossil leg bones showed not only that the dinosaur is a new species but that the largest of the specimens are full-grown adults.
The discovery knocks Albertonykus borealis, a chicken-size dinosaur identified in 2008, off its pedestal as the tiniest North American dinosaur.
(Related: "Smallest Meat-Eating Dinosaur in N. America Discovered.")
The newfound dinosaur also had an unusual combination of teeth for a reptile: canine-like teeth in the front of its jaws and molar-shaped teeth along its cheeks, according to the October 21 study, which appears in the journal Proceedings of the Royal Society B.
This arrangement and the creature's small stature mean it's likely that F. haagarorum ate plants, eggs, and insects.
The tiny dinosaur was found in Colorado's fossil-rich Fruita Paleontological Area. To find such an unexpected species in a well-studied area suggests it's "still possible to discover completely unique and remarkable [fossil] species," study leader Richard Butler, of the Bavarian State Collection for Paleontology in Munich, Germany, said in a statement.
"If dinosaur ecosystems were that diverse, who knows what astonishing beasts are waiting for us to discover?"