Pronunciation: AK-riss-TAH-vuss
Meaning: Crestless Grandfather
Author/s: Gates et al. (2011)
Synonyms: None known
First Discovery: Montana, USA
Discovery Chart Position: #782
Acristavus gagslarsoni
(Gags Larson's crestless grandfather)Etymology
Acristavus is derived from the Latin "A" (non), "crist" (crest) and "avus" (grandfather), in reference to the absence of a nasal crest found on many hadrosaurids, its age relative to other Two Medicine Formation hadrosaurids, and the primitive nature of its skull. The species epithet, gagslarsoni, honors Gags Larson; the nickname of landowner Russell Ellsworth Larson, on whose property the specimen was discovered.
Discovery
The holotype of Acristavus (MOR 1155) was discovered in the Two Medicine Formation (Museum of Rockies locality number TM-281), approximately 14 km southwest of Choteau, Teton County, Montana, USA, by staff and volunteers of the Old Trail Museum of Choteau, including a group of Junior Paleontologists from the University of
Chicago, during a field expedition in 1999. It consists of a nearly complete partially articulated skull and associated skeleton, including 11 tail vertebrae, three fragmentary back vertebrae, one neck vertebra, much of the left arm, leg and foot, and two toe bones from the right foot.
A referred specimen (UMNHVP 16607—a partial articulated skull roof including the entire braincase, plus a single neck vertebra) was discovered in the Middle Mudstone Member of the Wahweap Formation in Grand Staircase-Escalante National Monument, near the junction of Smokey Mountain Road and Right Hand Collet Canyon, Utah, in July 2000 by co-author C.R. Nelson.
A juvenile specimen (MWC 129, including skull and skeletal fossils) from the Mancos Shale in western Colorado may belong to Acristavus. But it's still stuck in bone obscuring matrix so has yet to be properly scrutinised.
