Meat-eating dinosaur caught turning veggie
Jeff Hecht
Palaeontologists have caught a cousin of
the carnivorous Velociraptor in the process
of turning vegetarian. Named Falcarius
utahensis, it resembled its predatory
meat-eating ancestors, but evolved teeth
shaped for shredding leaves and a paunchy
gut to digest plant material.
Jim Kirkland, state palaeontologist at the
Utah Geological Survey, US, and
colleagues unearthed a mass graveyard
containing some 2000 identifiable bones
in a Utah dig, of which 99% were from
Falcarius of all ages.
The wide range of bones allowed researchers to study their growth patterns and
individual variation - something rarely possible in palaeontology - says Lindsay
Zanno at the University of Utah. Kirkland says the dinosaurs had gathered around a
spring when they died. He suggests they may have been the victims of mass poisoning
by bacteria or bad water.
Crucially, the discovery offers critical insight into one of the most poorly understood
groups of dinosaurs, the plant-eating Therizinosaurs - which evolved from
meat-eaters.
Gobi Desert mystery
The first member of the group, the elephant-sized Therizinosaurus, was discovered in
1954 in the Gobi desert and was initially thought to be a large turtle or lizard. It took
decades to recognise that it belonged to a family of plant-eaters.
Therizinosaurs have been poorly understood because their fossils are scarce and
usually incomplete. They evolved from swift two-legged predators called theropods,
and their closest relatives were raptor dinosaurs, birds, and another odd group of small
plant-eating dinosaurs called oviraptors. Like other plant-eaters, they grew larger than
their predatory ancestors.
But the mystery for palaeontologists was how predators evolved into the slower
vegetarian lifestyle of therizinosaurs and other plant-eating dinosaurs.
Leaf-shaped teeth
Falcarius is the most primitive - or least specialised - therizinosaur known, says
Kirkland. Living about 125 million years ago, it was little over 1 metre high and 4 m
from nose to tail. It had more numerous and smaller teeth than its predatory ancestors,
but had yet to evolve the beak seen in its plant-eating descendants.
The teeth were leaf-shaped, which Kirkland says is "a first step toward plant eating"
from eating meat or insects. He adds that it had long filamentary feathers, like those
of Beipaosaurus, a slightly smaller and more advanced therizinosaur that lived in
China at about the same time.
Later, therizinosaurs grew much more massive as they evolved the larger digestive
system needed to process plant material. Their necks grew long and their heads grew
small compared with their body size. They shortened their tails "and started walking
like Godzilla", more upright than other theropods, Kirkland told New Scientist.
They also retained fearsome claws on their front legs, which in Therizinosaurus could
reach up to a metre in length, says Zanno. Their function remains unknown, though
may have been useful for self-defence.
Journal reference: Nature (vol 435, p 84)