User:Abyssal/Fuscinapeda

Cretaceous bird and mammal tracks

Richard T. McCrea and William A. S. Sarjeant published a paper describing new bird and mammal ichnotaxa from the Gates Formation in Alberta, Canada. Numerous bird trackway had recently been discovered associated with non-avian dinosaur footprints in the Smoky River Coal Mine near Grande Cache, Alberta. This paper was the second report of birds tracks from the region but the first for the Gates Formation, specifically. Two avian ichnotaxa are known from the W3 Main site, but only one is common. A third ichnotaxon has been reported from talus blocks at another site, the W3 Bird locale. W3 Extension is another Gates Formation site that has yielded fossil bird footprints. The authors characterize the bird fauna of the Gates Formation as being "diverse" but known only from trace fossils. The authors also reported the discovery of three-toed mammal footprints bearing sharp forward pointing claws. These mammal tracks were found on a single talus block that also contained bird prints. Significantly, these fossil mammal tracks were the first known from the Cretaceous period that were not left by marsupials. The authors amended the definitions of Aquatilavipes, Aquatilavipes swiboldae, and Fuscinapeda.

The W3 Main tracksite is at about 1700 meters of altitude. Common meteorological conditions like fog or overcasts skies inhibit the study of the tracksite. Compounding the problem, the footwall itself is oriented in such a way that the sun only shines on it for part of the day. However, despite these obstacles, McCrea and Sarjeant determined that the bird tracks were very abundant, comprising about 750 of the 1200 or more tracks in the 500 m^2 study area. Not all of the bird tracks were complete, in some prints only one or two toe marks were preserved. The trackmakers seems to have been a long legged bird, probably built like a modern heron. The prints are all wider than they are long and bear short claws. The authors regarded them as a new ichnospecies in the ichnogenus Aquatilavipes, although noted that this referral necessitated an emendation to the genus's diagnosis as well as the diagnosis of a related form, Fuscinapeda.

McCrea and Sarjeant emdended the diagnosis of the ichnogenus Aquatilavipes. Their emendation incorporated another emendation published in 1992 by Martin G. Lockley and others who noted that some Aquatilavipes tracks bear faint impressions of digital pads in certain sedimentary contexts. The authors made this emendation to more clearly distinguish between Aquatilavipes and the similar ichnogenus Fuscinapeda, which they also emended later in the paper. The two taxa differ in that Aquatilavipes has more slender digits. Another ichnotaxa resembling Aquatilavipes is Aviadactyla, although in this ichnogenus the toeprints fuse farther from the body and have a "stick-like" character. Ludicharadripodiscus differs by consistently leaving impressions of the hallux. Other similar ichnotaxa include Avipeda, which has shorter and thicker digit impressions than Aquatilavipes and Ornithotarnocia, which has a thicker digit III and greater asymmetry.

The authors emended the diagnosis for Fuscinapeda in order to clarify the distinction between the two ichnogenera, which was that Fuscinapeda had thicker digits.

Diagnosis for Fuscinapeda:

Small to large size Three toes, moderately thick digits No webbing or hallux Digit III 25% longer than II and IV Digital span > 95 degrees, frequently > 120 Digits II and IV similar length All digits clawed, with claws often flexing inward "Length of digits II and III may be similar, but digit IV is frequently somewhat larger." Better preserved specimens show digital pads, 3 or 4 on digit III, two on digits II and IV

Reference

• 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.