Dromaeosaurus

''Dromaeosaurus'' (, "running lizard") is a genus of dromaeosaurid theropod dinosaur which lived during the Late Cretaceous period (middle late Campanian and Maastrichtian), sometime between 80 and 69 million years ago, in Alberta, Canada and the western United States. The type species is ''Dromaeosaurus albertensis'', which was described by William Diller Matthew and Barnum Brown in 1922. Its fossils were unearthed in the Dinosaur Park Formation. Teeth attributed to this genus have been found in the Prince Creek Formation. ''Dromaeosaurus'' is the type genus of both Dromaeosauridae and Dromaeosaurinae, which include many genera with similar characteristics to ''Dromaeosaurus'' such as possibly its closest relative '' Dakotaraptor''. ''Dromaeosaurus'' was heavily built, more so than other dromaeosaurs that are similar in size, like ''Velociraptor''.

Discovery and naming

Despite receiving widespread attention in popular books on dinosaurs, and the usage of a complete mounted skeleton cast in museums throughout the world, ''Dromaeosaurus'' is poorly known from actual fossils. The preparation of the popular cast by the Tyrrell Museum was only made possible by knowledge gained from other dromaeosaurids that have been discovered more recently.

The first known ''Dromaeosaurus'' remains were discovered by paleontologist Barnum Brown during a 1914 expedition to Red Deer River on behalf of the American Museum of Natural History. The area where these bones were collected is now part of Dinosaur Provincial Park in Alberta, Canada. The find, holotype AMNH 5356, consisted of a partial skull in length, a mandible, two hyoids, a first metacarpal and some foot bones. The skull lacked most of the top of the snout. Several other skull fragments, and about thirty isolated teeth, are known from subsequent discoveries in Alberta and Montana.

In 1922 William Diller Matthew and Brown named and described the type species of ''Dromaeosaurus'': ''Dromaeosaurus albertensis''. The generic name is derived from the Greek (') meaning 'runner' and (') meaning 'lizard'. The specific name, ''"albertensis"'', refers to Alberta.

Another seven species of ''Dromaeosaurus'' were named: ''Dromaeosaurus laevifrons'' (Cope 1876) Matthew & Brown 1922; '' Dromaeosaurus cristatus'' (Cope 1876) Matthew & Brown 1922 (''Troodon''); ''Dromaeosaurus? gracilis'' (Marsh 1888) Matthew & Brown 1922; ''Dromaeosaurus explanatus'' (Cope 1876) Kuhn 1939; '' Dromaeosaurus minutus'' (Marsh 1892) Russell 1972 (an alvarezsaurid); ''Dromaeosaurus falculus'' (Cope 1876) Olshevsky 1979 and '' Dromaeosaurus mongoliensis'' (Barsbold 1983) Paul 1988 ('' Adasaurus''). Most of them were based on fragmentary material, some belonging to other genera, and far less complete than that of ''Dromaeosaurus albertensis'', and those that haven't been reclassified are considered '' nomina dubia'' today. Nevertheless, it has grown apparent that ''Dromaeosaurus albertensis'' is even rarer in its habitat than other small theropods, although it was the first dromaeosaurid of which reasonably good cranial material was described.
The genus ''Chirostenotes'' was once considered to be synonymous with ''Dromaeosaurus'' at one point in time.

Description

''Dromaeosaurus'' was a medium-sized carnivore, about in length and in body mass. Its mouth was full of sharp teeth, and it probably would have had a sharply curved "sickle claw" on each foot. It lived during the Campanian stage of the Late Cretaceous. However, some fragmentary remains such as teeth which may belong to this genus have been found from the late Maastrichtian age Hell Creek and Lance Formations, dating to 66 million years ago. Teeth have also been found in the Aguja Formation.

''Dromaeosaurus'' had a relatively robust skull with a deep snout. Its teeth were rather large and were shaped like a curved cone with a coat of enamel covering the crown. It had only nine teeth in each maxilla. ''Dromaeosaurus'' also had a vein at the back of the head, the ''vena capitis dorsalis'', that drained the front neck muscles through two long canals running to the posterior surface of the brain.
The Meckelian groove of Dromaeosaurus is rather shallow and does not have much depth.

Classification

Matthew and Brown originally placed ''Dromaeosaurus'' to its own subfamily, the Dromaeosaurinae, within the "Deinodontidae" (now known as Tyrannosauridae) based on some similarities in the general proportions of the skull. In 1969, John H. Ostrom recognized that ''Dromaeosaurus'' shared many features with ''Velociraptor'' and the newly discovered ''Deinonychus'', and assigned these forms to a new family: Dromaeosauridae. Since then, many new relatives of ''Dromaeosaurus'' have been found.

The exact relationships of ''Dromaeosaurus'' are somewhat unclear. Although its rugged build gives it a primitive appearance, it was actually a very specialized animal. In an analysis of the clade Dromaeosaurinae, species such as ''Utahraptor'', ''Achillobator'' and '' Yurgovuchia'' have been recovered. The genus ''Dakotaraptor'' has been classified as the sister taxon to ''Dromaeosaurus'', but more recent analysis do not recover such a close relationship.

Below is a cladogram by Senter ''et al.'' in 2012. ''Dromaeosaurus'' is recovered as the sister taxon to ''Yurgovuchia'', ''Utahraptor'' and ''Achillobator''.

The cladogram below follows a 2015 analysis by paleontologists Robert DePalma, David Burnham, Larry Martin, Peter Larson, and Robert Bakker, using updated data from the Theropod Working Group. In this analysis, ''Dromaeosaurus'' is classified as the sister taxon of ''Dakotaraptor''.

Paleobiology

''Dromaeosaurus'' differs from most of its relatives in having a short, massive skull, a deep mandible, and robust teeth. The teeth tend to be more heavily worn than those of its relative '' Saurornitholestes'', suggesting that its jaws were used for crushing and tearing rather than simply slicing through flesh. Therrien ''et al.'' (2005) estimated that ''Dromaeosaurus'' had a bite nearly three times as powerful as that of ''Velociraptor'' and suggested it relied more on its jaws than on the sickle claw to kill its prey. In a study predominantly centered around '' Shuvuuia'', ''Dromaeosaurus'' was compared to the former and also to ''Tyrannosaurus'', in which both ''Dromaeosaurus'' and ''Tyrannosaurus'' were discovered to be diurnal predators.

Feeding behavior

''Dromaeosaurus feeding habits were also discovered to be typical of coelurosaurian theropods, with a characteristic "puncture and pull" feeding method. Studies of wear patterns on the teeth of this animal by Angelica Torices ''et al.'' in a study regarding theropod feeding habits indicate that dromaeosaurid teeth share similar wear patterns to those seen in the tyrannosauridae and troodontidae, respectively. However, micro-wear on the teeth indicated that ''Dromaeosaurus'' likely preferred larger prey items than the troodontids it shared their environment with. Such differentiations in its diet likely allowed the theropod to inhabit the same environment as its more distant maniraptoran relatives. The same study also indicated that both ''Dromaeosaurus'' and ''Saurornitholestes'' (also analyzed in the study) likely included bone in their diet and were better adapted to handle the stresses associated with attacking struggling prey while troodontids, equipped with weaker jaws, preyed on softer animals and prey items such as invertebrates and carrion. This feeding strategy and ability to handle struggling prey was also a feature that the theropod also shared with tyrannosaurids such as ''Gorgosaurus'', which was also analyzed in said study alongside these smaller theropods.

See also

* Timeline of dromaeosaurid research

Footnotes

References

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* Larsson, H.C.E. 2001. Endocranial anatomy of ''Carcharodontosaurus saharicus'' (Theropoda: Allosauroidea) and its implications for theropod brain evolution. pp. 19–33. In: ''Mesozoic Vertebrate Life''. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press.
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* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): ''The Dinosauria'', 2nd, Berkeley: University of California Press. 861 pp. .

{{Taxonbar, from=Q131082

Late Cretaceous dinosaurs of North America
Eudromaeosaurs
Fossil taxa described in 1922
Taxa named by William Diller Matthew
Taxa named by Barnum Brown
Paleontology in Alberta
Campanian genus first appearances
Campanian genus extinctions