Oviraptors

Previously proposed hypothesis that known terrestrial and flightless members of the pennaraptoran clade Oviraptorosauria (Dinosauria: Theropoda) evolved from scansorial and volant ancestors is evaluated by reviewing publications on the phylogenetic position and morphology of the pennaraptoran clade Scansoriopterygidae.  Publications on the phylogenetic relationships of basal members of the pennaraptoran clade Paraves and morphology of recently discovered basal paravians were also reviewed to re-evaluate a previously supported hypothesis that terrestrial and flightless members of the paravian clade Deinonychosauria evolved from scansorial and volant ancestors.  Uncertainty about the phylogenetic position of Scansoriopterygidae among basal pennaraptorans suggests that scansoriopterygid morphology is close to the ancestral morphology of Pennaraptora.    Functional morphology indicates that all known scansoriopterygids were capable of scansorial locomotion and gliding, but not active flight, suggesting that the most recent common ancestor of Pennaraptora was also a scansorial glider and therefore, supports the descent of known terrestrial and flightless Oviraptorosauria from scansorial and volant ancestors.  This evolutionary scenario (supported by phylogenetic analyses and functional morphology) supports the evolution of pennaceous feathers as a flight adaptation and the “from the trees down” hypothesis of bird flight evolution.

A nearly complete pair of pubes is identified as a new caenagnathid oviraptorosaur, Ojoraptorsaurus boerei, n. gen., n. sp., based on having a “spoon-shaped” depression on the anterior dorsal surface of the pubic boot, an elongated anterior process of the pubic boot, a recessed enclosed pubic fossa, the distal end of the pubic shaft convex anteriorly, and a sub-trapezoidal pubic peduncle articulation surface. Ojoraptorsaurus boerei is most similar to ROM 43250 (previously assigned to Chirostenotes pergracilis Gilmore) from the Horseshoe Canyon Formation (upper Campanian-lower Maastrichtian) of Alberta, Canada, but differs from it in having a pubic fossa that is lower on the shaft, a trapezoidal-shaped articulation surface of the pubes, a shorter shaft length and in being more robust. ROM 43250 is placed in a new genus and species, Epichirostenotes curriei, that is much younger than Chirostenotes pergracilis (sensu stricto), which may include the holotype of Macrophalangia canadensis (CMN 8538) and a referred specimen TMP 79.20.1, all of which are from the Dinosaur Park Formation and predate E. curriei by nearly 3 million years. The holotype specimen of Epichirostenotes curriei (ROM 43250) differs morphologically from Chirostenotes pergracilis (sensu stricto), based on TMP 79.20.1, in features of the ischium. We note minor differences in the morphology of the left manus of the holotype of Chirostenotes pergracilis (CMN 2367) compared to TMP 79.20.1, suggesting that these two may not be conspecific. Ojoraptorsaurus boerei is from the Naashoibito Member of the Ojo Alamo Formation, San Juan Basin, New Mexico, and is part of the Alamo Wash local fauna. This fauna is considered to be 69 Ma and thus is early Maastrichtian in age. Ojoraptorsaurus boerei represents the southern-most occurrence of a caenagnathid in North America. It is the first and only known caenagnathid from New Mexico and from the lower Maastrichtian of North America.