EVIDENCE OF GREGARIOUS BEHAVIOR IN DINOSAURS FROM A NEW TRACK-SITE, MESA RICA SANDSTONE (LOWER ), NORTHEASTERN NEW MEXICO

Adrian P. Hunt1 and B. R. Watts1

1Mesalands Museum, Mesa Technical College, 911 South Tenth Street, Tucumcari, NM, New Mexico, 88401

A new tracksite has been located near Mills, Harding County, New Mexico in the Mesa Rica Sandstone (Lower Cretaceous; late Albian). The tracksite is located on the rim of Mills Canyon in the upper portion of the Mesa Rica Sandstone. Isolated and poorly preserved tracks occur in nearby outcrops. The main tracksite preserves portions of about 12 trackways of a large bipedal dinosaur. The pedal tracks are wider than long, have bilobed heels and average 30-40 cm in length; they represent the iguanodontid ichnogenus Caririchnium.

The new tracksite is an extension of the Dakota megatracksite (DM) which extends from Boulder, Colorado to Mosquero, New Mexico. All DM tracksites are in the upper Mesa Rica Sandstone or lower Pajarito Formation, or their nomenclatural equivalents. These tracksites formed on the western margin of an epeiric seaway.

The trackways at the new tracksite exhibit parallel orientation which is suggestive of gregarious behavior. The only other DM site in New Mexico to show this feature is near Mosquero. At Mosquero, the tracks trend North- North-East and roughly paralleI the shoreline trend, but those at the new site trend East.

Late tracksites in eastern New Mexico indicate gregarious behavior in prosauropods (Pseudotetrasauropus; Redonda Formation) and theropods (: Sheep Pen Sandstone). The new tracksite and the one at Mosquero are the only to exhibit gregarious behavior in ornithischian dinosaurs in New Mexico.

Keywords: paleontology, dinosaur, tracks

pp. 67 1996 New Mexico Geological Society Annual Spring Meeting April 12, 1996, Macey Center