Reconstruction of a new mammal species, Xianshou songae. This mouse-sized animal was a tree dweller in the Jurassic forests and belonged to an extinct group of Mesozoic mammals called euharamiyida. – Zhao Chuang/American Museum of Natural History/Reuters
by Peter Spotts.
The fossil remains of squirrel-like mammals with a hefty dose of cute are helping reset the clock for mammalian evolution, according to a new study.
Over the past three years, a team of researchers has uncovered six 160-million-year-old fossils that represent three new species who were living in trees at the time of the dinosaurs.
In placing these creatures along the mammal family tree, the researchers conclude that mammals emerged and exploded in diversity between 235 million and 201 million years ago, during the Triassic period.
If the results hold up to additional scrutiny, they imply a much earlier start for mammals than some previous studies had indicated.
They also dovetail with DNA studies that have pointed to an earlier emergence for mammals.
Combined with other mammal fossils from the early Jurassic, which began about 200 million years ago, the results also reinforce the notion that mammals were more than Lilliputian interlopers timidly eking out a living under the shadow of mighty dinosaurs.
Instead, they were a thriving group.
Some could swim, some could dig, suggesting a land-based habitat. Along come these new specimens whose bodies are well adapted to living in the canopy of Jurassic forests.