Cimolopteryx

Cimolopteryx Temporal range: Late Cretaceous, 75–65.5 Ma PreЄ Є O S D C P T J K Pg N
Left coracoid of C. rara
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Charadriiformes
Family:	†Cimolopterygidae Brodkorb, 1963
Genus:	†Cimolopteryx Marsh, 1892
Type species
†Cimolopteryx rara Marsh, 1892
Species[1]
†C. rara Marsh, 1892 †C. maxima Brodkorb, 1963 †C. minima Brodkorb, 1963 †C. petra Hope, 2002

Cimolopteryx (meaning "Cretaceous wing"^[2]) is a prehistoric bird genus from the late Cretaceous Period. Remains attributed to Cimolopteryx have been found in the Frenchman Formation of Saskatchewan, the Lance Formation of Wyoming, and possibly the Hell Creek Formation of Montana. All date to the end of the Maastrichtian age, about 65.5 million years ago.^[1] An additional specimen from the much earlier Dinosaur Park Formation of Alberta (mid Campanian age, about 75 million years ago) may belong to a new species of Cimolopteryx.^[1]

Description and history

Cimolopteryx was a fairly small bird, with a maximum size about equal to that of a small gull.^[1] It is known almost exclusively from a number of coracoids (a bone in the shoulder girdle). These have a distinct enough anatomy, however, to allow it to be distinguished from other birds, and even for distinct species to be recognized. The first such coracoid to be found (specimen number YMP 1845, in the collections of the Peabody Museum of Natural History) was first mentioned and informally named by paleontologist Othniel Charles Marsh in the footnote of an 1889 paper, but it was not validly described by him until 1892. Marsh also described a second species in the same paper, which he named Cimolopteryx retusa, but this has since been recognized as a different kind of bird and reclassified as Palintropus retusus.^[1]

Classification and species

The classification of various species assigned to the genus Cimolopteryx is uncertain. As of a re-evaluation of the fossil remains in 2002 by Sylvia Hope, at most five species were recognized: Cimolopteryx rara, C. petra, C. maxima, C. minima, and one yet-unnamed species. C. rara and C. petra are almost identical, and were found in the same environments (the Lance and Frenchman formations), but differ in size, with C. petra smaller than C. rara. In a 2009 review, Nicholas Longrich synonymized them as the same species, dismissing the size difference as possibly based on gender or growth stage.^[3] However, Longrich reversed his position following a 2011 analysis of Lancian birds, in which he and co-authors considered all four named species to be distinct.^[4] An additional, unnamed species is known from the much earlier Dinosaur Park Formation of Alberta. Also known only from a partial coracoid, its exact identity is uncertain.^[1] C. maxima was about twice the size of C. rara, but not enough of its anatomy is known to determine if it belongs to Cimolopteryx or a different genus.^[1] As its name suggests, C. minima is one of the smallest species in the genus, about the same size as specimens referred to C. petra. It may group together in the same "species group" as several indeterminate fossils possibly belonging to Cimolopteryx.^[1] Several collections of material that is similar to Cimolopteryx were referred to by Hope as undetermined species, which lack enough unique characteristics to be properly identified, and these may or may not belong to Cimolopteryx.^[1]

Hope regarded Cimolopteryx as a likely member of the modern bird group Charadriiformes, which includes a diverse array of shorebirds. However, since all species are known only from parts of the shoulder girdle and wing bone fragments, this classification is tentative.^[1]

References

1. ^ ^{a b c d e f g h i j} Hope, S. (2002). "The Mesozoic radiation of Neornithes." Pp. 339-388 in Chiappe, L.M. and Witmer, L. (eds.), Mesozoic Birds: Above the Heads of Dinosaurs.
2. ^ Holtz, Thomas R. Jr. (2008) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages Winter 2010 Supplementary Information
3. ^ Longrich, N. (2009). "An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada." Cretaceous Research, 30(1): 161-177.
4. ^ Longrich, N.R., Tokaryk, T. and Field, D.J. (2011). "Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary." Proceedings of the National Academy of Sciences, 108(37): 15253-15257. doi:10.1073/pnas.1110395108