User:Abyssal/Irenesauripus

Irenesauripus is an ichnogenus of dinosaur footprint. In 2001, McCrea and Sarjeant used the ratio of an Irenesauripus print's length to its width in order to help identify what kind of animal produced it. Previous workers lead by Moratalla have used this method to distinguish tracks left by ornithopods and theropods. Irenesauripus had an average length-to-width ratio of 1.2 among ten prints examined by McCrea and Sargent at the W3 Main tracksite. Their results excluded ornithopods from candidate trackmakers because the length-to-width ratios of their tracks were at least 1.25. Irenesauripus mclearni was probably left by a large theropod. It was close by a bird trackway left by the new ichnospecies Aquatilavipes curriei.

W3 Main
Irenesauripus is known from a fossil site called the W3 Main track site. This site forms part of a footwall in the Smoky River Coal Mine near Grande Cache, Alberta. The fossil footprints at W3 Main were first reported in the early 1990s. These reports were examined by several follow-up expeditions during the summer of 1998. McCrea and Sargent describe W3 Main as difficult to study because the tracksite is at about 1700 meters of altitude and frequently obscured by adverse weather conditions like fog or overcast skies. Compounding the problem, the footwall itself is oriented in such a way that the sun only shines on it for part of the day. Irenesauripus occurs alongside other theropod tracks like Aquatilavipes curriei, Ornithomimipus, Gypsichnites, and Irenichnites. Ankylosaur tracks of the ichnogenus Tetrapodosaurus are also present. McCrea and Sargent have called this association of different dinosaur trackmakers as "a rich late Early Cretaceous fauna." These tracks are preserved in rippled sandstone in the presence of many trace fossils left by both large and small invertebrates. Plant fossils preserved in the same stratigraphic unit as the tracks, the Gates Formation, include ferns, conifers, cycads, ginkgoes, and two species of flowering plant. Larger plant remains include fossil logs and tree stumps that are spaced far apart from one another. The fossils of W3 Main paint a picture of an ancient coastal plain or delta. The lack of mud cracks in the track bearing sediments is evidence that they were never dehydrated fully before preservation, possibly because the tracks were left in water a few centimeters deep or just because the exposed sediment was very wet when stepped on.

Gates
Sternberg diagnosed Irenesauripus as large. Its body weight was supported mostly on its three weight-bearing toes. Its toes are spaced widely apart. The heel of the foot always made full contact with the underlying substrate, but sometimes the impressions it left differed in width. The toes and the pad under the metatarsals all supported the same fraction of the dinosaur's body weight. The pads under the toe bones were not easily distinguishable from one another. "Claws acuminate". None of Sternberg's Irenesauripus tracks were associated with traces from the forepaw or tail.

McCrea updated Sternberg's diagnosis as follows. Large, bipedal, semi-digitigrade, heel varies in width. Irenesauripus is amesaxonic track, meaning the third digit is always the largest. On rare occasions digit I impressions are present. Widely spaced digit impressions. The molds with the best quality preservation show phalangeal pad impressions and claw marks. Digit two had two pad impressions and a claw mark. Digit III had three pad impressions and a claw mark, Digit IV had three to four pad impressions and a claw mark. Claws acuminate. The number and arrangement of the toe pad impressions resembles the foot anatomy of carnosaurs.

Irenesauripus mclearni is the type ichnospecies of Irenesauripus. It was named by Sternberg in 1932. It was discovered in the Aptian Gething Formation of eastern British Columbia. McCrea updated the diagnosis for the ichnogenus because impressions left by toe pads were found in Irenesauripus tracks at a fossil site not far from Grand Cache, Alberta.

Sternberg's original diagnosis for I. mclearni described the tracks as varying from 11 to 16 inches in length. (27.9 to 40.6 cm). Irenesauripus trails generally form an almost perfectly straight line. The length of the trackmaker's stride would vary based on the terrain it was walking over and its own speed, but was generally about 3 times the length of a track.

The type specimen was part of a trackway that included 16 individual footprints. The average stridelength recorded in this trail was 940 mm and the longest was 1,065 mm. The footprints of the type trackway has a short groove that seems to be a drag mark left by the third toe. This drag mark is absent in other trackways left by the same trackmaking species.

The trackmaker's weight was distributed equally across each weight-bearing toe and the pad that cushioned the metatarsals. The impressions left by the metatarsal pad or "heel" of the track is somewhat narrow. The toe marks are separate for a considerable distance back from their tips. There is no evidence for webbing or wide pads near the base of the toes. Toes become gradually more slender towards their tips. The Irenesauripus trackmaker had sharp claws. Digits II and III divaricate at a 37 degree angle. Digits III and IV divaricate at a 33 degree angle.

The holotype is catalogued at the Canadian Museum of Nature, in Ottawa as NMC 8548.

There are large, three toed dinosaur footprints at Grand Cache that closely resemble Irenesauripus mclearni. In 1932 Sternberg had named three Irenesauripus ichnospecies from Gething Formation rocks of the Peace River Canyon. These species were I. mclearni, I. acutus, and I. occidentalis. In 1995 Phil Currie found that the dimensions and angles of divarication Sternberg reported in I. occidentalis were essentially the same as those of the ichnogenus, Amblydactylus, which was produced by an ornithopod. Curries also observed that Sternberg only reported four instances of I. occidentalis, but Amblydactylus tracks were common. He therefore concluded that Irenesauripus occidentalis tracks are just unusual looking Amblydactylus.

The Grand Cache footprints, however, have toe marks with very similar proportions and angles of divarication. However, the original Peace River Canyon tracks described by Sternberg are a bit smaller than the Grand Cache tracks. The Grand Cache footprints are about the same size as Sternberg's I. acutus, but the toe marks left by the second and third digits are deeper than the fourth. In the Grand Cache Irenesauripus, however, all toe marks are of equal depth. In 1932 Sternberg only reported one single I. acutus trackway of the Peace River Canyon Gething Formation. However, in 1995 Currie identified a total of five I. acutus trackways there.

The Grand Cache Ireneauripus most closeley resemble I. mclearni. However, since the distinguishing traits of these ichnospecies might be due to qualities of the sediment the track maker was walking on they might not even be truly distinct ichnospecies. Other theropod dinosaur track sites are known to show a wide variation in a single ichnotaxon. The Triassic-aged Fleming Fjord Formation of Greenland has produced high quality tracks in the ichnogenus Grallator. It has also produced tracks where the toe prints were just tapering "channels" in the sediment. However, since there are a series of intermediates between the two, it is obvious that the less distinct tracks are just unusual forms of Grallator rather than some new ichnotaxon. This variation in a single kind of dinosaur track can be attributed to the "consistency" of the sediment they left their tracks in.

When it comes to Irenesauripus, I. mclearni tracks may have been left on firmer sediment while less viscous sediments may result in footprints with the longer, thinner toe prints characterizing I. acutus. Since the Grand Cache footprints exhibit traits between these extremes, they might have been left on sediment somewhat softer than I. mclearni tracks were left in, but firmer than the substrate imprinted with I. acutus.

With the Grand Cache footprints referred to Irenesauripus mclearni, document variation in the size of this ichnospecies ranges from 27.9 to 49.5. Irenesauripus glenrosensis track from texas have been found up to 66 cm in length. The longest stride length found in two Grand Cache Irenesauripus trackways was 313 cm. The longest pace length was 161.5 cm. Some Grand Cache prints preserve a backward facing groove at the heel that was probably a toe drag mark, although in this instance it was probably rearmost pad on the fourth toe that dragged. Not all of the Peace River Canyon tracks bear this mark. In 1995 Irby hypothesized that track features like this may have resulted from sexual dimorphism in the track makers.

20:10, 16 January 2012 (UTC)20:10, 16 January 2012 (UTC)Fix that third toe bullshit20:10, 16 January 2012 (UTC)20:10, 16 January 2012 (UTC)~

Less than 2% of the tracks at W3 Main can be referred to Irenesauripus. Only two or three other fossil sites near Grande Cache preserve any Irenesauripus at all. Irenesauripus is much more common at the Peace River Canyon. There they comprise a significant percentage of the documented trace fossils and are found at differing heights within the local strata. The presence of claw marks combined with their large size suggested to McCrea that the Irenesauripus trackmaker was one of the more slender carnosaur species. Allosaurids or megalosaurids are possible trackmakers. In 1997 Langston and Jacobs both interpreted these tracks as Acrocanthosaurus atokensis footprints. Previous researchers have referred poorly preserved large theropod fossils from rocks of similar age in the US. However, in 1998 Harris challenged these referrals noting that no specimen sufficiently well-preserved for a confident identification as Acrocanthosaurus had been made outside of the Texan Trinity Group of Aptian to Albian age. Even if Irenesauripus were not left by Acrocanthosaurus, the trackmaker was still likely an allosaurid of similar size and body plan.

Reference

 * McCrea, Richard T. 2000. Vertebrate palaeoichnology of the lower cretaceous (lower Albian) gates formation of Alberta.
 * McCrea, Richard T. 2001. Tourism Opportunity Analysis: Dinosaur Tracks In the Grande Cache Area Tourism opportunity analysis dinosaur tracks in the Grande Cache area. Publisher: Edmonton : Alberta Economic Development. ISBN 0778512622.
 * McCrea, R. T. and W. A S. Sarjeant. 2001. New ichnotaxa of bird and mammal footprints from the Lower Cretaceous (Albian) Gates Formation of Alberta; pp. 453–478 in D. H. Tanke, and K. Carpenter, (eds.), Mesozoic Vertebrate Life. Indiana University Press, Bloomington and Indianapolis.

Hook
... that fossil dinosaur footprints called Irenichnites have been discovered in an Alberta coal mine?