Therizinosaur: The Mystery of the Sickle Clawed Dinosaur
The Therizinosaur Nothronychus, plesiosaur and shark. Artwork by
Much of North America was under water 93 million years ago. The Cretaceous
Interior Seaway separated today’s North American land mass. Dominant
predators in these ancient seas included gigantic plesiosaurs, fishes and
Mosasaurs were giant marine lizards, distantly related to living monitor
lizards, who roamed the seas in the Cretaceous Period.
Several kinds of pliosaurs swam the seas of what is now southern Utah and
northern Arizona in the time of the sickle clawed dinosaur Nothronychus
about 93 million years ago. Pliosaurs were marine reptiles, not dinosaurs.
The sea turtle Desmatochelys has been excavated from marine beds in
northern Arizona. Desmatochelys belongs to an extinct group of sea
turtles thought to have fed on ammonites, Mesozoic Era relatives of the
Reconstruction of the bone bed where the Therizinosaur fossil was found, in
marine sediments at the bottom of the Cretaceous Interior Seaway. How did
the sickle clawed dinosaur Nothronychus, an animal who lived on land,
wind up in deposits 60 miles out to sea? Visit the museum to explore this
Nothronychus, the sickle clawed dinosaur. This is the most complete
Therizinosaur specimen known.
Zuniceratops, a member of the great ceratopsian lineage that includes
Triceratops, was discovered by an Arizona Museum of Natural History
expedition to the Arizona-New Mexico border. Zuniceratops lived in
the same region and at the same time as Nothronychus.
The Arizona Museum of Natural History discovered the first Nothronychus
known from North America. Casts of the fossil bones placed on the
illustration show which bones of the Therizinosaur were recovered. You may
see real fossil bones from the animal nearby, and put together a
Possibly the Therizinosaur used its long claws to stir up the bottom mud in
swamps to feed on small life forms such as crayfish and amphibians. Artwork
by Victor Leshyk.
Perhaps Nothronychus used mangrove swamps to hide from predators, to
eat mangrove leaves, or to eat crabs. The claws here are raking leaves from
branches towards the mouth. Artwork by Victor Leshyk.
53 N. Macdonald
Mesa, AZ 85201
(One block north of Main Street in downtown Mesa. Take US 60 or 202 to
Country Club Drive, go to Main Street, and proceed one-half mile east to