Deinonychosauria
Encyclopedia
The Deinonychosauria were a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 of coelurosaurian theropod
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...

 dinosaurs from the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...

 and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two further groups — Dromaeosauridae
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...

 and Troodontidae
Troodontidae
Troodontidae is a family of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and scrappy and they have therefore been allied, at various times, with many dinosaurian lineages...

. The largest known of these was Utahraptor
Utahraptor
Utahraptor is a genus of theropod dinosaurs, including the largest known members of the family Dromaeosauridae. Fossil specimens date to the upper Barremian stage of the early Cretaceous period...

(7 m or 23 ft), and Anchiornis
Anchiornis
Anchiornis is a genus of small, feathered, deinonychosaurian dinosaur. The genus Anchiornis contains the type species Anchiornis huxleyi, named in honor of Thomas Henry Huxley, an early proponent of biological evolution, and the first to propose a close evolutionary relationship between birds and...

was the smallest (34 cm
1 E-1 m
To help compare different orders of magnitude this page lists lengths between 10 centimetres and 100 centimetres .Distances shorter than 10 centimetres-Conversions:10 centimetres is equal to...

 or 13 in). By modern classifications, bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s are closely related to this group of dinosaurs, and share a common ancestor with them.

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 enlarged second toe bore an unusually large, curved sickle-shaped claw (held off the ground or 'retracted' when walking), which is thought to have been used in capturing prey and climbing trees. This claw was especially blade-like in the large-bodied predatory eudromaeosaurs
Eudromaeosauria
Eudromaeosauria is a subgroup of terrestrial dromaeosaurid theropod dinosaurs. They were relatively large-bodied, feathered hypercarnivores that flourished in the Cretaceous Period.Eudromaeosaur fossils are known almost exclusively from the northern hemisphere...

. One eudromaeosaur species, Balaur bondoc
Balaur (dinosaur)
Balaur is a uniquely specialized species of carnivorous dinosaur. It lived in what is now Romania during the latter part of the Late Cretaceous. Balaur was described by scientists in August 2010, and was named after the balaur, a dragon of Romanian folklore. It is known from a single partial...

, also possessed a first toe which was highly modified in parallel with the second. Both the first and second toes on each foot of B. bondoc were also held retracted and bore enlarged, sickle-shaped claws.

Dromaeosauridae

The subgroup dromaeosauridae includes such dinosaurs as Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...

and Deinonychus
Deinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...

. They are commonly called "raptors" and were smart, fast, and agile hunters that may have cooperated in groups.

Troodontidae

Much less is known about the dromaeosaurids' sister group, the troodontids, because fossils of them are less common. The best known troodontids are Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...

and Saurornithoides
Saurornithoides
Saurornithoides is a genus of troodontid maniraptoran dinosaur, living during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing...

. Troodontids were generally small and slender, and had long, narrow skulls containing sharp, curved teeth. They may be the most intelligent dinosaurs known, with a remarkably large brain-to-body mass ratio. Like their sister group, they were smart, active and agile hunters who displayed bird-like characteristics.

Taxonomy

  • Infraorder Deinonychosauria
    • Euronychodon
      Euronychodon
      Euronychodon is the name given to a genus of coelurosaur dinosaur from the Late Cretaceous, described by Miguel Telles Antunes and Denise Sigogneau-Russell in 1991. It is similar to another coelurosaur, Paronychodon....

      ?
    • Pamparaptor
      Pamparaptor
      Pamparaptor is an extinct genus of carnivorous deinonychosaur from the late Cretaceous period. It is a basal dromaeosaurid with troodontid-like pes which lived during the late Cretaceous period in what is now Neuquén province, Patagonia, Argentina. It is known from the holotype MUCPv-1163, an...

    • Paronychodon
      Paronychodon
      Paronychodon was a theropod dinosaur genus. It is a tooth taxon, considered dubious because of the fragmentary nature of the fossils, which include "buckets" of teeth but no other remains...

      ?
    • Family Archaeopterygidae
      Archaeopterygidae
      The Archaeopterygidae is a group of maniraptoran dinosaurs that lived during the late Jurassic and period.-Taxonomy:The order Archaeopterygiformes was coined by Max Fürbringer in 1888 to contain the single family Archaeopterygidae and genus Archaeopteryx...

      ?
    • Superfamiliy Dromaeosauroidea
      • Family Dromaeosauridae
        Dromaeosauridae
        Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...

        • Subfamily Microraptorinae
          Microraptorinae
          Microraptorinae is a subfamily of Dromaeosauridae. Microraptorines were among the most primitive dromaeosaurids. They appeared 125 million years ago in China. Many may have been semi-arboreal gliders...

        • Subfamily Unenlagiinae
          Unenlagiinae
          Unenlagiinae is a subfamily of Dromaeosauridae. Unenlagiines are one of the most basal lineages of dromaeosaurids. Unenlagiines are known from South America and Madagascar....

        • Node Eudromaeosauria
          Eudromaeosauria
          Eudromaeosauria is a subgroup of terrestrial dromaeosaurid theropod dinosaurs. They were relatively large-bodied, feathered hypercarnivores that flourished in the Cretaceous Period.Eudromaeosaur fossils are known almost exclusively from the northern hemisphere...

          • Subfamily Dromaeosaurinae
            Dromaeosaurinae
            Dromaeosaurinae is a subfamily of Dromaeosauridae. Most dromaeosaurines lived in what is now the USA and Canada, , as well as Mongolia, , and possibly Denmark, , as well. Isolated teeth that may belong to African dromaeosaurines have also been discovered in Ethiopia...

          • Subfamily Saurornitholestinae
            Saurornitholestinae
            Saurornitholestinae is a subfamily of Dromaeosauridae.-Species:...

          • Subfamily Velociraptorinae
            Velociraptorinae
            Velociraptorinae is a subfamily of the theropod group Dromaeosauridae. Velociraptorine remains are found mostly in northern hemisphere. In Late Cretaceous, they are mostly present in Mongolia, Romania and China,and in early, in USA. The earliest velociraptorines are probably Nuthetes from the...

    • Superfamily Troodontoidea
      • Family Troodontidae
        Troodontidae
        Troodontidae is a family of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and scrappy and they have therefore been allied, at various times, with many dinosaurian lineages...

        • ?Subfamily Elopteryginae
        • Subfamily Troodontinae
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