[Photo] A female (left) and male (right) flea from the middle Jurassic in China. CREDIT: D. Huang et al, Nature

The oldest fleas were five to 10 times larger than today's bloodsuckers, new research finds. But at least they couldn't jump.

These ancient bloodsuckers are the oldest fleas ever found, and the oldest example of bloodsucking parasites in the fossil record, study researcher André Nel of the Muséum National d’Histoire Naturelle in Paris told LiveScience.

These early fleas lacked the strong hindlegs of modern fleas, Nel said.

"Their biology and behavior was certainly different, more like that of a louse creeping among the fur and feathers of the hosts," said Nel, who, along with his colleagues, analyzed nine fossil specimens of the fleas discovered in outcrops in China.

The fleas lived in the Mesozoic era, a chunk of geologic time extending from 250 million years ago to 65 million years ago and includes the Jurassic period. They were giant compared with today's fleas, with one female specimen's body longer than 0.8 inches (2 cm), said study researcher Diying Huang, a researcher at the Chinese Academy of Science in Nanjing, China. Modern fleas don't get much larger than 0.1 inches, or 3 mm, in length.

The fleas' size and tough mouthparts would have made it easy for them to feast on large hosts — even dinosaurs.

"Their long siphonate dentate mouthparts may easily penetrate dinosaur skin," Huang told LiveScience.

The fossils, which reside in the collections of the Nanjing Institute of Geology and Palaeontology, fill in some of the gaps of flea evolution, Nel said. The first fleas evolved from ancestors that fed on plant fluids. Some then evolved from plants to animals, becoming bloodsuckers. These parasites lost their wings and developed grasping legs to cling to fur and feathers.

At some point still not pinpointed in the fossil record, Nel said, fleas evolved amazingly strong hind legs, which can catapult them 50 to 100 times their body length.

The Jurassic bloodsuckers are detailed Wednesday (Feb. 29) online in the journal Nature.