rdfs:comment
| - Unlike other deinonychosaurs, hesperonychids (who, despite their name, are unrelated to the cretaceous microraptorine Hesperonychus, a possible renaming of the entire family of deinonychosaurs will take place some time in the future) possess a highly flexible joint on their inner toes, rendering these talons not only hyper-extendable, but also opposable, with the other two toes of the foot (to one degree or another). While some have suggested this trait links the hesperonychids to the arbronychids, other morphological and genetic evidence suggests otherwise, and instead classifies the hesperonychids as basal deinonychosaurs related to the mattiraptors. Perhaps this peculiar pedal anatomy was originally intend for use in the trees, but today only a single hesperonychid genus (Janaata) has m
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abstract
| - Unlike other deinonychosaurs, hesperonychids (who, despite their name, are unrelated to the cretaceous microraptorine Hesperonychus, a possible renaming of the entire family of deinonychosaurs will take place some time in the future) possess a highly flexible joint on their inner toes, rendering these talons not only hyper-extendable, but also opposable, with the other two toes of the foot (to one degree or another). While some have suggested this trait links the hesperonychids to the arbronychids, other morphological and genetic evidence suggests otherwise, and instead classifies the hesperonychids as basal deinonychosaurs related to the mattiraptors. Perhaps this peculiar pedal anatomy was originally intend for use in the trees, but today only a single hesperonychid genus (Janaata) has many arboreal proclivities. In many larger species, this unique toe joint is almost completely atrophied, changing the sickle claw back from a grasping tool to a piton. Recent in-depth studies have shown that their ancestry can be traced back to the likes of Dakotaraptor steini, one of the last of the giant dromaeosaurids of the Maastrichtian. The deinonychosaurs of South America include the apex terrestrial predators on the continent (a land of huge, tyrannosaur-like raptors and tiny to medium raptor-like tyrannosaurs), driving all of the abelisaurs native in the area into the point of extinction during the Pliocene. Although sickle-clawed coelurosaurs have a long history on the continent, the current assemblage of raptorial predators, with the exception of the enigmatic Mergaraptor, are fairly recent additions to the Neotropical fauna derived from North American hesperonychid stock. When these forms first arrived here in the Pliocene, they quickly consolidated their position with some forms attaining enormous sizes. (Ironically, the hesperonychids have since been displaced throughout much of their northern range by the invading Eurasian boreonychid draks.)
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