Identification:
                                        I.  Avimimus portentosus
                                       II. Kakuru kujani (based on Avimimus portentosus)
                                       III.  Sinornithoides youngi
                                       IV.   Borogovia gracilicrus (based on other Troodontidae)
                                       V.    Byronosaurus jaffei
                                       VI.   Troodon formosus
                                       VII.  Tochisaurus nemegtensis (based on other Troodontidae)
                                       VIII. Saurornithoides mongoliensis
                                       IX.   Saurornithoides asiamericanus (based on Saurornithoides mongoliensis)
                                       X.    Saurornithoides isfarensis (based on Saurornithoides mongoliensis)
                                       XI.   Saurornithoides junior (based on Saurornithoides mongoliensis)

(Gilmore, 1924 sensu Varricchio, 1997)

    The clades Avimimidae (which consists of two described species) and Troodontidae (which consists of nine) are both primitive maniraptors, or dinosaurs that hunt with their hands.  These dinosaurs (although they all lived in the Cretaceous) are all rather similar to the early coelurosaurs that gave rise to birds, and are, themselves, quite birdlike.

    The avimimids are perhaps the most birdlike of these two groups, but that similarity may be superficial.  Since so few avimimid specimens are known of, it is difficult to place them in relation to any other group, but they share characteristics with the oviraptors and it is safe to say that they are maniraptoriformes.  These dinosaurs are lithe and long-legged, with small heads and long necks, suitable for eating a variety of food.  These dinosaurs live in Asia and Australia.

    The troodontids are clearly specialized predators.  They share the basic body-plan of the avimimids, but have proportionally shorted legs and necks and larger snouts, which are filled with tiny, nastily pointed teeth (a trait from which this clade derives its name).  The troodontids have large, forward-facing eyes and large brains, but the troodontids' major distinguishing features are their toes.  The inner toes of a troodontid's feet are hyper-extendable, able to raise themselves above the ground.  While the claws of weight-bearing toes become bunt against the ground, the claws on the raised inner toes grow into sharp, curved talons.   These talons are similar in shape to the claws of noasaurs, deinonychosaurs, and the mammalian cats, indicating a useful adaptation among predators that had been arrived at this adaptation through convergent evolution.  The troodonids hunt in Asia and North America.
 

Thanks for T. Michael Keesey for his co-authorship of this painting.

Other websites pertinent to this article:

The Dinosauricon's

Coelurosauria cladogram

Troodontidae cladogram

© Daniel Bensen 2000
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This image modified by Adobe Photoshop.