Deinonychosauria
Deinonychosaurs | |
---|---|
Montage of putative deinonychosaurians | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Clade: | Pennaraptora |
Clade: | Paraves |
Clade: | †Deinonychosauria Colbert & Russell, 1969 |
Subclades | |
Deinonychosauria is a clade of paravian dinosaurs which lived from the Late Jurassic to the Late Cretaceous periods. Fossils have been found across the globe in North America, Europe, Africa, Asia, South America, and Antarctica,[2] with fossilized teeth giving credence to the possibility that they inhabited Australia as well.[3] This group of dinosaurs are known for their sickle-shaped toe claws and features in the shoulder bones.[4]
Deinonychosauria is commonly defined as all dinosaurs more closely related to
Systematics
In 1866 Ernst Haeckel created the now-deprecated subclass of birds known as Sauriurae (meaning "lizard tails" in Greek). It was intended to include Archaeopteryx and distinguish it from all other birds then known, which he grouped in the sister-group Ornithurae ("bird tails"). The distinction Haeckel referred to in this name is that Archaeopteryx possesses a long, reptile-like tail, while all other birds known to him had short tails with few vertebrae, fused at the end into a pygostyle.[7] The unit was not much referred to, and when Hans Friedrich Gadow in 1893 erected Archaeornithes for basically the same fossils, this became the common name for the early reptile-like grade of birds. This was followed by Alfred Romer (1933) and subsequent authors through most of the 20th century.[8] According to Romer, the Archaeornithes are characterised by having clawed wings, a reptilian style ribcage without a large carina and the presence of a long, bony tail.[9] The known members of the group by the time of its erection were Archaeopteryx and Archaeornis.[10] The two are now thought to represent a single species, Archaeopteryx lithographica, the Archaeornis being the Berlin specimen of Archaeopteryx.
During the
Many theropods have been united into new groups... but the placement of Archaeopteryx and the sickle-clawed dromaeosaurs in the same family is by far the most radical–yet it is also one of the most necessary... how alike, in detail after detail, dromaeosaurs and Archaeopteryx were.[14]
The name Deinonychosauria was coined by Ned Colbert and Dale Russell in 1969, and defined as a clade (all theropods closer to dromaeosaurids than to birds) by Jacques Gauthier in 1986. Through the early 2000s, the consensus among paleontologists was that dromaeosaurids were most closely related to the troodontids, and with the troodontids, deinonychosaurians were turned into the sister taxon to avialans, and therefore the closest relatives of avialan birds.[15] In 2012, Turner et al. conducted a phylogenetic analysis (using a dataset of 474 characters scored for 111 taxa) which found Deinonychosauria to be monophyletic.[5]
However, several more recent studies have cast doubt on the hypothesis that dromaeosaurids and troodontids were more closely related to each other than either was to birds. A more robust 2013 study by Godefroit et al. (using a dataset of 1,500 characters scored for 358 taxa) found that troodontids were possibly more closely related to birds than to dromaeosaurids; forcing troodontids to remain in a monophyletic Deinonychosauria required four extra steps in the analysis, making this result less likely, but not implausible.[6][16] Because Deinonychosauria was originally defined as all animals closer to dromaeosaurids than to birds without specific reference to troodontids, Deinonychosauria is a synonym of Dromaeosauridae if Troodontidae is closer to birds.[16]
With the description in 2019 of the Late Jurassic genus
Deinonychosauria | |
In a study conducted in 2020, Archaeopteryx was recovered as an avialan.[17]
Description
Like other theropods, deinonychosaurs were bipedal; that is, they walked on their two hind legs. However, whereas most theropods walked with three toes contacting the ground, fossilized footprint tracks confirm that most deinonychosaurs held the second toe off the ground in a hyperextended position, with only the third and fourth toes bearing the weight of the animal. This is called functional didactyly.
The teeth of deinonychosaurs were curved and serrated, but not blade-like except in some advanced species such as
Most deinonychosaurs seem to have been predatory, though some smaller species especially among the troodontids are known to have been at least omnivorous.[21][20]
Claw function
One of the best-known features of deinonychosaurs is the presence of an enlarged and strongly curved "sickle claw" on a hyper-extendible second toe, modified to hold the sickle claw clear of the ground when walking. While this characteristic claw and its associated modifications to the anatomy of the foot (such as a shortened
A larger study of deinonychosaur claw function, published in 2011 by Fowler and colleagues, concluded that the earlier study by Manning and colleagues was correct and that the "sickle claws" of deinonychosaurs would have been ineffective as cutting weapons. They compared the claw and overall foot anatomy of various deinonychosaurs with modern birds to shed light on their actual function. Fowler and colleagues showed that many modern predatory birds also have enlarged claws on the second toes. In modern raptors, these claws are used to help grip and hold prey of sizes smaller than or equal to the predator, while the birds use their body weight to pin their prey to the ground and eat it alive.[20] Fowler and colleagues suggested that this behavior is entirely consistent with the anatomy of advanced deinonychosaurs like Deinonychus, which had slightly opposing first toes and strong tendons in the toes and foot. This makes it likely that advanced dromaeosaurids also used their claws to puncture and grip their prey to aid in pinning it to the ground, while using shallow wing beats and tail movements to stabilize themselves.[20] Other lines of evidence for this behavior include teeth which had large, hooked serrations only on the back edge (useful in pulling flesh upward rather than slicing it) and large claws on the wings (for greater maneuvering of prey while mantling it with the wings).[20]
In more primitive dromaeosaurids and in troodontids, the feet were not as specialized and the claws were not as large or as hooked. Additionally, the toe joints allowed more range of motion than the simple up-down movements of advanced dromaeosaurids. This makes it likely that these species specialized in smaller prey that could be pinned using only the inner toes, not requiring the feet to be as strong or sturdy.[20]
References
- ^ PMID 31333906.
- ^ Case, J.A., Martin, J.E., and Reguero, M. (2007). "A dromaeosaur from the Maastrichtian of James Ross Island and the Late Cretaceous Antarctic dinosaur fauna." Pp. 1–4 in Cooper, A., Raymond, C., and Team, I.E. (eds.), Antarctica: a Keystone in a Changing World – Online Proceedings for the Tenth International Symposium on Antarctic Earth Sciences, U.S. Geological Survey Open-File Report 2007-1047, SRP 083. U.S. Geological Survey, Washington, D.C.
- ^ "Oz dromaeosaurs(Re: Megaraptor)".
- ^ S2CID 85396846.
- ^ S2CID 83572446.
- ^ S2CID 4364892.
- ^ Haeckel, Ernst. (1866) "Generelle Morphologie der Orgnaismen" Berlin: Georg Reimer. 462 pp.
- ^ Vertebrate Paleontology. University of Chicago Press., 3rd ed., 1966.
- ^ a b Romer, A. S. & Parsons, T. S. (1985): The Vertebrate Body. (6th ed.) Saunders, Philadelphia.
- ^ "Archaeornithes". Merriam-Webster online dictionary. www.merriam-webster.com. Retrieved 19 January 2018.
- ^ Archaeopteryx turns out to be singular bird of a feather. New Scientist 2443:17. 17 April 2004. See commentary on article.
- ^ Max Fürbringer (1888). "Untersuchungen zur Morphologie und Systematik der Vögel: zugleich ein Beitrag zur Anatomie der Stütz-und Bewegungsorgane". T. Van Holkema. 15.
- ^ a b Holtz, T. Jr.; Brett-Surman, M.K. (1999). "The Taxonomy and Systematics of the Dinosaurs". In Farlow, J.O; Brett-Surman, M.K. (eds.). The Complete Dinosaur (first ed.). Indiana University Press. pp. 92–106.
- ^ a b Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster.
- ^ Senter, Phil; Barsbold, R.; Britt, Brooks B.; Burnham, David B. (2004). "Systematics and evolution of Dromaeosauridae (Dinosauria, Theropoda)". Bulletin of the Gunma Museum of Natural History. 8: 1–20.
- ^ a b Mortimer, M. (2012) The Theropod Database: Phylogeny of taxa Archived May 16, 2013, at the Wayback Machine. Retrieved 2013-AUG-15.
- PMID 32140312.
- S2CID 16380823.
- PMID 19289829.
- ^ PMID 22194962.
- PMID 21173263.
- PMID 17148340.