and two Squalicorax circling around a dead Claosaurus'' in the
Western Interior Seaway Evidence of its existence was first found in the
Niobrara Formation near the
Smoky Hill River in
Kansas, United States in the form of partial skull fragments and as an articulated postcranial skeleton both found in 1871. Originally named
Hadrosaurus agilis (Marsh, 1872), In 1892, Marsh named a second species,
C. annectens. It was later reassigned to
Anatosaurus and then
Edmontosaurus, where it is currently. G. R. Wieland named third species
C. affinis in 1903, which he compared to
C. annectens.
C. affinis was founded on remains from the
Pierre Shale of
South Dakota, found in association with remains of the giant sea turtle
Archelon. At some point after its description, the fragmentary remains were mixed up with the original remains of
C. agilis, and a toe bone from
C. agilis was accidentally thought to be the only part of the
holotype remains that could be located. This was corrected by Joseph Gregory in 1948, who found three toe bones from the right foot of a large hadrosaur in the Yale collections that had comparable preservation to the Pierre Shale turtle remains and were associated with labels in Wieland's handwriting. Gregory found the toe bones to be very similar in size to the corresponding bones of Marsh's
Claosaurus annectens, but did not reassign the species due to its much older age and fragmentary remains.
C. affinis was considered a
dubious hadrosaur in the 2004 review by Jack Horner and colleagues. They reported its type material as lost, although they also reported the remains as only including a single toe bone, instead of the three toe bones described by Gregory. ==See also==