User:Abyssal/Columbosauripus

Columbosauripus tracks are small and were left by a bipedal trackmaker. Only three of its toes supported its body weight. Its toes were naturally spread wide. The bases of the toes were connected by either wide pads or webbing. The second toe mark was not separate from the impression left by the pad cushioning the metatarsals. The toe impressions taper and end in sharp claws of significant length.

McCrea emended the diagnosis original devised by Sternberg in 1932. Columbosauripus footprints are small to medium and left by a semi-digitigrade animal. Some Columbosauripus footprints preserved at W3 Main show impressions left by three toe pads under the third toe. None of the toe impressions are separate from the impression left by the metatarsal pad.

The type ichnospecies of Columbosauripus is Columbosauripus ungulatus, erected by Sternberg in 1932 for fossils from the Aptian-aged Gething Formation of eastern British Columbia. McCrea emended the diagnosis for this ichnotaxon specifically to include information on the phalangeal pads preserved on some Columbosauripus specimens at W3 Main.

Sternberg originally observed that the metatarsals and phalanges at the base of the toes were cushioned by a single large pad rather than discrete smaller ones. The track's heel was quite round, although represented only by a very shallow depression. Digits II and III divaricate at a 38 degree angle. Digits III and IV divaricate at a 39 degree angle.

McCrea emended the diagnosis of Columbosauripus ungulatus. He noted that the ichnotaxon had a low length to width ratio of the footprints with a range from 0.88 to 1.35 but an average of about 1.10. The lengths of the second and fourth toes are roughly equal. The divarication between digits II and III and III and IV are about equal, both being nearly 40 degrees. The far half of the third toe is gently curved.

The holotype of Columbosauripus ungulatus is a natural mold catalogued as NMC 8551 by the Canadian Museum of Nature in Ottawa, Ontario.

McCrea emended the diagnosis of Columbosauripus to add information on the tracks' length to width ratios and the curve in the third toe. Footprints very similar to Columbosauripus ungulatus are found near Grande Cache. They both share the same rounded heel impressions and slightly curved third toe. The tapering width of the toes and the long claw marks they end in are both shared between sites. The Peace River Canyon tracks and the W3 Main Tracks both have second and fourth toes of reoughly equal length. However, the Columbosauripus ungulatus tracks of the Gates Formation are twice as large in terms of both raw footprint size and the length of the paces and strides taken by the trackmaker.

The trackmaker of Columbosauripus may have been a coelurosaur, possibly an ornithomimid. However, so many different kinds of theropods of the Columbosauripus trackmaker's size could be responsible that it is difficult to make a confident identification. In 1990 Thulborn interpreted Irenichnites (which is smaller) as having been left by an ornithomimid. In some of the smaller Irenichnites specimens the second toe impression is disconnected from the rest of the track. Thulborn observed that this corresponds well to a quirk of ornithomimid anatomy. In ornithomimids the second digit diverges higher up on the foot than the others, so its full length may not be recorded in their footprints. Since the impression left by digit II in Columbosauripus is connected to the metatarsal pad it probably was not left by an ornithomimid but rather by some other form of small carnivorous dinosaur. The W2 tracksite and an area over W3 bear Columbosauripus trackways with higher quality preservation than those studied by McCrea. The Cenomanian Dunvegan Formation, located in northeastern British Columbia is another source of Columbosauripus tracks, as is Algeria. (Haubold 1971).

Reference

 * McCrea, Richard T. 2000. Vertebrate palaeoichnology of the lower cretaceous (lower Albian) gates formation of Alberta.
 * http://www.paleofile.com/Ichnolist/Columbosauripus.asp