18" Hadrosaur (Hypacrosaur) Ulna and Vertebra in Stone - Montana

This is a breathtaking specimen that features a caudal vertebra and ulna (arm bone) still sitting within the rock they were found in, a presentation that is quite uncommon. Both are from Hypacrosaurus, a hadrosaur of the Two Medicine Formation of Montana, though it's possible they came from two separate hadrosaurs. This is a natural association and the bones have not been repositioned.

The ulna is almost completely exposed from the rock, with the proximal end still partially embedded. There are multiple repaired cracks through the diaphysis, with some significant gap fill restoration within one of the cracks where the bone was fragmented beyond recovery. The distal end, while weathered, did not require any crack repair or restoration.

Just over half of the vertebra has been exposed from the rock. The cortical bone has weathered away, however it hasn't undergone any repair or restoration. A small section of rock adjacent to the vertebra has been glued back in place. The base of the rock has been cut flat, facilitating aesthetic presentation of this incredible hadrosaur bone association.

Measurments:
Ulna - 17.9" long
Vertebra - 2.25" wide
Rock (not including bones) - 12.7 x 6.8 x 6"

Hypacrosaurus is a very large, Lambeosaurini Hadrsosaur that would have been almost as large as the Tyrannosaurs that it lived alongside. Like Corythosaurus, it had a tall, hollow rounded crest, although not as large and straight. It is known from the remains of two species that spanned 75 to 67 million years ago, in the Late Cretaceous of Alberta, Canada, and Montana, United States, and is the latest hollow-crested duckbill known from good remains in North America. It is estimated to have been around 9.1 meters (30 feet) long and to have weighed up to 4-5 tons.

 Hypacrosaurus drawing by wikipedia user debivort. Creative Commons License
Hypacrosaurus drawing by wikipedia user debivort. Creative Commons License

The Two Medicine Formation is a geographical formation in Central Montana and Southern Alberta, Canada. The formation is predominantly sandstone laid down by rivers and deltas during the Campanian Age of the Cretaceous about 80-75 million years ago. Approximately two thousand feet thick on the western edge, it lies on top of the Virgelle Sandstone formation and under the Bearpaw Shale. It is located between the Front Range of the Rocky Mountains and the Sweetgrass Arch, a tectonic fold feature 40-90 miles east of the Front Range.

The Two Medicine is the same age as the Judith River Formation found further east. It was laid down further inland from the Western Interior Seaway, while the Judith River Formation was deposited along the coast. The Two Medicine contains much of the same dinosaur fauna, but fewer reptiles, amphibians and aquatic fossils.

A view of the Two Medicine Formation quarry operated by Northwest Montana Fossils where much of our Two Medicine dinosaur material has been found.
A view of the Two Medicine Formation quarry operated by Northwest Montana Fossils where much of our Two Medicine dinosaur material has been found.

DETAILS
SPECIES
Hypacrosaurus sp.
LOCATION
Pondera County, Montana
FORMATION
Two Medicine Formation
SIZE
Rock: 12.7 x 6.8", Ulna: 18" long, Vertebra: 2.25" wide
CATEGORY
SUB CATEGORY
ITEM
#196687
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