Ichthyornis
Ichthyornis | |
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Cast skeleton, Rocky Mountain Dinosaur Resource Center | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Clade: | Avialae |
Clade: | Ornithurae |
Clade: | †Ichthyornithes |
Genus: | †Ichthyornis Marsh, 1873 |
Species: | †I. dispar
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Binomial name | |
†Ichthyornis dispar (Marsh, 1872)
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Synonyms | |
Angelinornis Kashin 1972 Species synonymy
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Ichthyornis (meaning "fish bird", after its fish-like vertebrae) is an extinct
Ichthyornis has been historically important in shedding light on
Description of the Ichthyornis
It is thought that Ichthyornis was the Cretaceous ecological equivalent of modern seabirds such as
Ichthyornis is notable primarily for its combination of vertebrae which are concave both in front and back (similar to some fish, which is where it gets its name) and several more subtle features of its skeleton which set it apart from its close relatives. Ichthyornis is perhaps most well known for its teeth. The teeth were present only in the middle portion of the upper and lower jaws. The jaw tips had no teeth and were covered in a beak. The beak of Ichthyornis, like the
The wings and breastbone were very modern in appearance, suggesting strong flight ability and placing it with modern birds in the advanced group Carinatae. Unlike earlier avialans such as the enantiornithines, the species appears to have matured to adulthood in a rather short, continuous process.[4]
A study on an Ichthyornis endocast reveals that it had a relatively basal brain compared to modern birds, similar to that of Archaeopteryx and other non-avian theropods. Conversely, it had a palate remarkably convergent with that of modern neognaths.[5]
Timespan and evolution
Ichthyornis fossils have been found in almost all levels of the Niobrara Chalk, from beds dating to the late
History of study
Ichthyornis was one of the first Mesozoic
However, Marsh did not initially recognize the true importance of the fossil. Soon after receiving it, he reported back to Mudge his opinion that the chalk slab contained the bones of two distinct animals: a small bird animal, and the toothed jaws of some unknown reptile. Marsh considered the unusual vertebrae of the bird to resemble those of a fish, so he named it Ichthyornis, or "fish bird."[8] Later in 1872, Marsh described the toothed jaws as a new species of marine reptile, named Colonosaurus mudgei after their discoverer.[9] The similarity of the lower jaw and teeth to those of mosasaurs is so great that as late as 1952, J.T. Gregory argued that it really belonged to a diminutive species or young individual related to the genus Clidastes.[10]
By early in 1873, Marsh had recognized his error. Through further preparation and exposure of skull bones from the rock, he found that the toothed jaws must have come from the bird itself and not a marine reptile. Due to the previously unknown features of Ichthyornis (vertebrae concave on either side and teeth), Marsh chose to classify it in an entirely new sub-class of birds he called the Odontornithes (or "toothed birds"), and in the new order Ichthyornithes (later Ichthyornithiformes). The only other bird Marsh included in these groups was the newly named Apatornis, which he had previously named as a species of Ichthyornis, I. celer.[11] Mudge later noted the rare and unique quality of these toothed birds (including Hesperornis, which was found to also have teeth by 1877), and the irony of their association with the remains of toothless pterosaurs, flying reptiles which were only known to have had teeth in other regions of the world at that time.[12]
Soon after these discoveries, Ichthyornis was recognized for its significance to the theory of evolution recently published by Charles Darwin. Darwin himself told Marsh in an 1880 letter that Ichthyornis and Hesperornis offered "the best support for the theory of evolution" since he had first published On the Origin of Species in 1859.[1] (While Archaeopteryx was the first known Mesozoic avialan and is now known to have also had teeth, the first specimen with a skull was not described until 1884).[13] Others at the time also recognized the implications of a nearly modern bird with reptilian teeth, and feared the controversy it caused. One Yale student described various men and women urging Marsh to conceal Ichthyornis from the public because it lent too much support to evolutionary theory.[1] Many accused Marsh of having tampered with the fossils or intentionally created a hoax by associating reptilian jaws with the body of a bird, accusations that continued to surface even as late as 1967. However, an overwhelming majority of researchers have demonstrated that Marsh's interpretation of the fossils was correct, and he was fully vindicated by later finds.[1]
Mounted specimens
At the turn of the 20th century, the Peabody Museum of Natural History at Yale University, where most Ichthyornis specimens were housed, began placing many of its most interesting or important specimens on display in the museum's Great Hall. Two panel mounts (that is, pieces where the skeleton is arranged and set into a plaster slab) were created for Ichthyornis; one for I. dispar, and one for "I. victor". Both were created by Hugh Gibb, who prepared many of Marsh's fossils for study and display. The I. dispar mount contained only the holotype fossils, while the "I. victor" mount was a composite incorporating a variety of different specimens to make the piece appear more complete (it did not, however, contain any part of the actual "I. victor" holotype specimen).[1]
At some point before 1937, the catalogue number of the actual "I. victor" type specimen was mistakenly reassigned to the panel mount. Later reports of the specimen, even by the Peabody Museum's staff, therefore mistakenly stated that the original "I. victor" specimen comprised most of the skeleton, when it was in fact only three bones.[1] By 1997, the situation had become so confused that Jacques Gauthier, the current curator of the museum's vertebrate paleontology collection, authorized the dismantling of both panel mounts. This allowed the bones to be properly sorted out and studied in three dimensions, which had been impossible previously when they were embedded in plaster.[1] A full re-description of these specimens was published by paleontologist Julia Clarke in 2004.[1]
Classification
Ichthyornis is close to the ancestry of modern birds, the
Of the several described species, only one, Ichthyornis dispar, is currently recognized, following the seminal review by Julia Clarke.
The cladogram below is the result of a 2014 analysis by Michael Lee and colleagues that expanded on data from an earlier study by O’Connor & Zhou in 2012. The clade names are positioned based on their definitions.[15]
Ornithurae |
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References
- ^ S2CID 84035285.
- ^ S2CID 86151155.
- .
- doi:10.1006/cres.1997.0102.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - PMID 34330706.
- ISBN 978-1-4020-1443-7.
- ^ a b Williston, S.W. (1898). "A brief history of fossil collecting in the Niobrara Chalk prior to 1900. Addenda to Part I". The University Geological Survey of Kansas. 4: 28–32.
- .
- ^ Marsh, O.C. (1872). "Notice of a new reptile from the Cretaceous". American Journal of Science. Series 3. 4 (23): 406.
- JSTOR 1364594.
- .
- ^ Mudge, B.F. (1877). "Annual Report of the committee on Geology, for the year ending November 1, 1876." Transactions of the Kansas Academy of Science, Ninth Annual Meeting, pp. 4–5.
- ISBN 1862393117.
- ^ Mortimer, M. (2010). "Ornithuromorpha: Ichthyornis." The Theropod Database. Accessed online 23 April 2016.
- PMID 24449041.
Further reading
- Brands, Sheila (14 August 2008). "Systema Naturae 2000 / Classification – Genus Phoebetria –". Project: The Taxonomicon. Retrieved 12 June 2012.[permanent dead link]
- Chiappe, Luis M.; Lamb, James P. Jr.; Ericson, Per G.P. (2002). "New enantiornithine bird from the marine Upper Cretaceous of Alabama". Journal of Vertebrate Paleontology. 22 (1): 170–174. S2CID 55026727.
- Marsh, Othniel Charles (1880). Odontornithes, a Monograph on the Extinct Birds of North America. Washington: Government Printing Office.
- Asteriornis
External links
- Ichthyornis dispar: A toothed, flying bird from the Late Cretaceous of Kansas by Mike Everhart, Oceans of Kansas website. Retrieved 2006-09-16.