The tyrannosauroids have a long and illustrious history in Eurasia and North America, where they have dwelt since the beginning of the Cretaceous, but in South America, the clade is quite new.  Fuzzy, diminutive errosaurids migrated into South America only about five million years ago, during the Pliocene, and are the only neotropical representatives of this mightly clade.

   Ironically, these predators did not grow to become the Tyrannosaurus-like monsters as did the smilotyrannines of Asia and North America.  Rather, the neotropical errosaurids competed for the niche and eventually lost to another group of neararctic predators, the deinonychosaurs.  Thus, the deinonychosaurs (specifically, the clade Hesperonychidae) occupy the all of the large predator niches in South America, while the tyrannosaurs are relegated to the small, running-predator niches that are have traditionally belonged to the deionychosaurs.

    South American errosaurines are, in most respects, similar to their North American kin.  Several species are migratory, and may be found in both North and South America in season.

     Soon after the first errosaurids migrated to South America, a new group emerged on the continent. The ealiest notovenator material was recovered from middle Pliocene rock, and at the present time, this group dominates the small predator guild of the neotropics.

    As a rule, notovenators posses less plumage than their northern cousins (indeed, some are almost bald), and most are extremely gracile, with very long legs and a stiffened tail.  However, the most obvious distinguishing feature between the two groups is the notovenators' toes (or lack thereof).  All members of the clade Notovenatorinae posses only the two outer toes of the foot, the inner toe and the halux being atrophied to mere slivers of bone, invisible beneath layers of skin and muscle.  These creatures also tend to run on the very tips of their toes, giving them a distinctive, ostrich-like gait.

(Text by Daniel Bensen)

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