Eudromaeosauria

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**Eudromaeosauria** ("true dromaeosaurs") is a subgroup of terrestrial dromaeosaurid theropod dinosaurs. They were relatively large-bodied, feathered hypercarnivores (with diets consisting almost entirely of other terrestrial vertebrates) that flourished in the Cretaceous Period.

Eudromaeosaur fossils are known almost exclusively from the northern hemisphere. They first appeared in the early Cretaceous Period (early Aptian stage, about 124 million years ago) and survived until the end of the Cretaceous (Maastrichtian stage, 66 Ma). The earliest known definitive eudromaeosaur is the dromaeosaurine *Utahraptor ostrommaysorum*, from the Cedar Mountain Formation, dated to 124 million years ago. However, the earlier (143-million-year-old) fossils such as those of *Nuthetes destructor* and several indeterminate teeth dating to the Kimmeridgian stage may represent eudromaeosaurs.

## Description

While other dromaeosaurids filled a variety of specialized ecological niches, mainly those of small predators or larger fish-eating forms, eudromaeosaurs functioned as large-bodied predators of often medium to large-sized prey. Aside from their generally larger size, eudromaeosaurs are characterized by several features of the foot. First, there were differences in the positions of the grooves which anchored blood vessels and keratin sheathes of the toe claws. In primitive dromaeosaurids like *Hesperonychus*, these grooves ran parallel to each other on either side of the claw along its length. In eudromaeosaurs, the grooves were asymmetrical, with the inner one split into two distinct grooves and elevated toward the top of the claw, while the single outer groove remained positioned at the midline.

The second distinguishing characteristic of eudromaeosaurs is an expanded and enlarged "heel" on the last bone in the second toe (phalange), which bore the enlarged, sickle-like toe claw. Finally, the first bone of the second toe also possessed an enlarged expansion at the joint, another adaptation relating to the unusually enlarged claw, and which helped the animal hold the claw high off the ground. Also unlike their more basal relatives, the sickle-claw of eudromaeosaurs was sharper and more blade-like. In unenlagiines and microraptorines, the claw is broader at its base.

## Classification

Eudromaeosauria was first defined as a node-based clade by Nick Longrich and Philip J. Currie in 2009, as the most inclusive natural group containing *Dromaeosaurus*, *Velociraptor*, *Deinonychus*, and *Saurornitholestes*, their most recent common ancestor and all of its other descendants. The various "subfamilies" have also been re-defined as clades, usually defined as all species closer to the groups namesake than to *Dromaeosaurus* or any namesakes of other sub-clades.

The subgroups of Eudromaeosauria frequently shift in content based on new analysis, but typically consist of the following groups. For example, the subfamily Velociraptorinae has traditionally included *Velociraptor*, *Deinonychus*, and *Saurornitholestes*, and while the discovery of *Tsaagan* lent support to this grouping, the inclusion of *Saurornitholestes* is still uncertain. The Dromaeosaurinae is usually found to consist of medium to giant-sized species, with generally box-shaped skulls (the other subfamilies generally have narrower snouts). A number of eudromaeosaurs have not been assigned to any particular subfamily, because they are too poorly preserved to be placed confidently in phylogenetic analysis (see section *Phylogeny* below).

The following classification of the various genera of eudromaeosaurs follows the table provided in Holtz, 2010 unless otherwise noted.

* **Eudromaeosauria**
	+ *Atrociraptor*
	+ *Bambiraptor*
	+ *Deinonychus*
	+ *Saurornitholestes*
	+ **Subfamily Dromaeosaurinae**
		- *Achillobator*
		- *Balaur*?
		- *Dakotaraptor*
		- *Dromaeosaurus*
		- *Utahraptor*
		- *Yurgovuchia*
	+ **Subfamily Velociraptorinae**
		- *Acheroraptor* (Evans *et al*, 2013)
		- *Adasaurus*
		- *Itemirus*?
		- *Linheraptor*
		- *Tsaagan*
		- *Velociraptor*

### Phylogeny

The cladogram below follows a 2009 analysis by Longrich and Currie.

The below cladogram follows the clading present in the paper describing *Acheroraptor*:

## References

1. ↑ McDonald AT, Kirkland JI, DeBlieux DD, Madsen SK, Cavin J; et al. (2010). "New Basal Iguanodonts from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs.". *PLoS ONE* **5** (11): e14075. PMC 2989904. PMID 21124919. doi:10.1371/journal.pone.0014075.
2. ↑ Sweetman S.C. (2004). "The first record of velociraptorine dinosaurs (Saurischia, Theropoda) from the Wealden (Early Cretaceous, Barremian) of southern England". *Cretaceous Research* **25** (3): 353–364. doi:10.1016/j.cretres.2004.01.004.
3. ↑ van der Lubbe, T., Richter, U. and Knotschke, N. (2009). "Velociraptorine dromaeosaurid teeth from the Kimmeridgian (Late Jurassic) of Germany." *Acta Palaeontologica Polonica*, **54**(3): 401-408.
4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Longrich, N.R.; Currie, P.J. (2009). "A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America". *PNAS* **106** (13): 5002–7. PMC 2664043. PMID 19289829. doi:10.1073/pnas.0811664106.
5. ↑ Turner, A.S.; Hwang, S.H.; Norell, M.A. (2007). "A small derived theropod from Öösh, Early Cretaceous, Baykhangor Mongolia" (PDF). *American Museum Novitates* **3557**: 1–27. doi:10.1206/0003-0082(2007)3557[1:ASDTFS]2.0.CO;2. Retrieved 2007-03-29.
6. ↑ Holtz, Thomas R. Jr. (2010) *Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,* Winter 2010 Appendix.
7. ↑ Matthew, W. D.; Brown, B. (1922). "The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta". *Bulletin of the American Museum of Natural History* **46**: 367–385. Template:Hdl.
8. ↑ 8.0 8.1 Senter, P.; Kirkland, J. I.; Deblieux, D. D.; Madsen, S.; Toth, N. (2012). Dodson, Peter, ed. "New Dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the Evolution of the Dromaeosaurid Tail". *PLoS ONE* **7** (5): e36790. PMC 3352940. PMID 22615813. doi:10.1371/journal.pone.0036790.
9. ↑ Barsbold, R. (1983). "O ptich'ikh chertakh v stroyenii khishchnykh dinozavrov. ["Avian" features in the morphology of predatory dinosaurs]." *Transactions of the Joint Soviet Mongolian Paleontological Expedition* **24**: 96–103. [Original article in Russian.] Translated by W. Robert Welsh, copy provided by Kenneth Carpenter and converted by Matthew Carrano. PDF fulltext

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