User:Abyssal/Iguanodontipus

Ornithopod tracks

The Purbeck Limestone Group preserves a pair of trackways from quadrupedal ornithopods. The Wealden Group at the famous Munchehagen dinosaur tracksite preserves four specimens. Collectively these are some of the oldest and "best-dated" Early Cretaceous quadrupedal ornithopod track sites. However, the English specimen has been the subject diverse interpretations including; two theropod trackways, a theropod and iguanodont walking side-by-side. However, Lockley and Wright interpret the tracks as being made by two quadrupedal ornithopods. The left trackway is poorly preserved and records 26 hindprints, with some associated foreprints. The rear tracks are connected by linear marks in the sediment somewhat prallel to the trackway and may represent dragmarks from toes or the animal's tail. Another possibility is that the linear marks were caused by water erosion after being laid down. The trackway on the right is better preserved but only records a single print left by a forefoot. The trackways from Britain are the longest associated sequence of tracks that preserve prints from the front limb. These foreprints show that iguanodonts sometimes placed their front feet well outside of the width of their back feet while walking. They also show evidence that while walking there was a "slight inward rotation" of the third toe.

Lockley and Wright discussed work by other researchers on similar tracks from "the same general geographic and stratigraphic location." These tracks were possibly left by Iguanodon and assigned to the ichnospecies Iguanodontipus burreyi. Although only hindprints were preserved in the trackway the authors expressed wishes that any subsequent researchers who found I. burreyi manual prints to update the diagnosis for the ichnospecies. Lockley and Wright observe that the specimen they studied with manual prints was not listed by the previous researchers as a synonym of I. burreyi, implying it to be another species. However, since the tracks studied by Lockley and Wright are also iguanodontid tracks they may be of the same genus, although they admit a lack of any compelling reason to either refer them to a known ichnogenus or name them as a new one. Lockley and Wright criticized other authors for not giving "adequate study and attention" to some tracks and erecting new ichnotaxa for them without "adequate reference to existing literature." They singled out Casomiquela and Fasola for erecting an ichnogenus of late Jurassic Sauropod from Chile, Iguanodonichnus, as if it were a Cretaceous ornithopod. They named another trackway Camptosaurichnus ("Camptosaurus track") even though that genus has never been found in South America. A paleontologist named Alonso was also criticized for naming an Argentine trackway Hadrosaurichnus even though their long step length and elongate tracks indicate a theropod as the trackmaker. Criticism aimed at Casanovas-Cladellas for erecting the ichnogenus Hadrosaurichnoides for Early Cretaceous tracks with alleged webbing was slightly more tentative, with Lockley and Wright suggesting that they "may" be theropod tracks due to the narrowness of the trackway and the elongation of the tracks. Despite their criticism of these specific tracks and authors, Lockley and Wright reaffirmed that Iguanodontipus, Amblydactylus, and Caririchnium represent legitmate quadrupedal ornithopod tracks. The authors expressed hope that later researchers would erect ichnotaxa on well-preserved specimens.

Reference

• Lockley, M. G., and Wright, J. L., 2001, Trackways of large quadrapedal ornithopods from the Cretaceous: a review: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 428-442.