Eudromaeosauria ("true dromaeosaurs") is a subgroup of terrestrial
dromaeosaurid
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s. They were relatively small to medium-sized, feathered
hypercarnivore
A hypercarnivore is an animal which has a diet that is more than 70% meat, either via active predation or by scavenging. The remaining non-meat diet may consist of non-animal foods such as fungi, fruits or other plant material. Some extant examp ...
s (with diets consisting almost entirely of other terrestrial vertebrates) that flourished in the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
Period
Period may refer to:
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* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
.
Eudromaeosaur fossils are known almost exclusively from the northern hemisphere. They first appeared in the early Cretaceous Period (early
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...
stage, about 124 million years ago) and survived until the end of the Cretaceous (
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
stage, Ma). The earliest known definitive eudromaeosaur is the dromaeosaurine ''
Utahraptor ostrommaysi
''Utahraptor'' (meaning "Utah's thief") is a genus of large dromaeosaurid dinosaur that lived in North America during the Early Cretaceous period. It was a heavy-built, ground-dwelling, bipedal carnivore. It contains a single species, ''Utahr ...
'', from the
Cedar Mountain Formation
The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain (Utah), Cedar Mountain in northern Emery Coun ...
, dated to 124 million years ago.
However, the earlier (143-million-year-old) fossils such as those of ''
Nuthetes destructor
''Nuthetes'' is the name given to a genus of theropod dinosaur, likely a dromaeosaurid, known only from fossil teeth and jaw fragments found in rocks of the middle Berriasian (Early Cretaceous) age in the Cherty Freshwater Member of the Lulworth ...
'' and several indeterminate teeth dating to the
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age in the Late Jurassic Epoch and a stage in the Upper Jurassic Series. It spans the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma (million years ago). The Kimmeridgian follows the Oxfordian ...
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, differences existed in the positions of the grooves that anchored blood vessels and keratin sheathes of the toe claws. In primitive dromaeosaurids like ''
Hesperonychus
''Hesperonychus'' (meaning "western claw") was a small, carnivorous dinosaur. It was a member of the family Dromaeosauridae, along with its larger relatives ''Deinonychus'' and ''Velociraptor''. There is one described species, ''Hesperonychus eli ...
'', 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 (phalanx), 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
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
by Nick Longrich and
Philip J. Currie
Philip John Currie (born March 13, 1949) is a Canadian palaeontologist and museum curator who helped found the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and is now a professor at the University of Alberta in Edmonton. In the ...
in 2009, as the most inclusive natural group containing ''Dromaeosaurus'', ''
Velociraptor
''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in the pa ...
'', ''
Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
'', and ''Saurornitholestes'', their most recent common ancestor and all of its other descendants. The various "subfamilies" have also been redefined as clades, usually defined as all species closer to the group's namesake than to ''Dromaeosaurus'' or any namesakes of other subclades.
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
''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in the pa ...
'', ''
Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
'', and ''
Saurornitholestes
''Saurornitholestes'' ("lizard-bird thief") is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Canada (Alberta) and the United States (Montana, New Mexico, Alabama, North Carolina, and South Carolina).
Two spec ...
'', and while the discovery of ''
Tsaagan
''Tsaagan'' (meaning "white") is a genus of dromaeosaurid dinosaur from the Djadokhta Formation of the Late Cretaceous of Mongolia.
Discovery and naming
The holotype of ''Tsaagan'' was discovered in 1996 and first identified as a specimen of '' ...
'' lent support to this grouping, the inclusion of ''Saurornitholestes'' is still uncertain. The Dromaeosaurinae are 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
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analysis (see section ''Relationships'' below).
Relationships
The below cladogram follows an analysis by Evans ''et al.'' in 2013. Their analysis used an updated version of the dataset originally compiled by Nick Longrich and Phil Currie to study dromaeosaurid relationships, and found a relatively traditional arrangement of eudromaeosaurian relationships.
See also
*
Timeline of dromaeosaurid research
This timeline of dromaeosaurid research is a chronological listing of events in the history of paleontology focused on the dromaeosaurids, a group of sickle-clawed, bird-like theropod dinosaurs including animals like ''Velociraptor''. Since the ...
References
{{Taxonbar, from=Q897132
Dromaeosaurs