This is a quickie, as the taxon is just a new species based on some teeth.
Ricardoestesia Currie, Rigby and Sloan 1990
R. isosceles Sankey 2001
Etymology- "Richard Estes' isosceles triangle", after the famous paleontologist Richard Estes, who demonstrated the use of theropod teeth in faunal studies.
Late Campanian-Late Maastrichtian, Late Cretaceous
Horseshoe Canyon Formation, Judith River Formation, Scollard Formation, Alberta; Frenchman Formation, Saskatchewan; Canada. Hell Creek Formation, North Dakota; Hell Creek Formation, South Dakota; Aguja Formation, Texas; Lance Formation, Wyoming; US.
Holotype- (LSUMGS 489:6238) tooth
Referred- (A.M. 8113) tooth
(LSUMG 489:6233) tooth
(LSUMG 489:6234) tooth
(LSUMG 489:6235) tooth
(LSUGM 489:6264) tooth
(RTMP 91.170.9) tooth
Diagnosis- teeth straight and shaped like an isoscleles triangle in lateral view.
This species was originally suggested by Currie, Rigby and Sloan to account for the stright Richardoestesia teeth in some collections.
The teeth are similar to Ricardoestesia gilmorei in most respects. They are laterally compressed with serrations present posteriorly and sometimes anteriorly. The serrations are small (7-11 per mm), flattened, uniform in size and have small interdenticle spaces. The only difference is the straight crown with the tip roughly in the center. R. golmorei teeth are recurved, as is usual for theropods.
Ricardoestesia can be diagnosed by- teeth with very small serrations for size; distal half is convex posteriorly on anterior dentary teeth. The phylogenetic relationships of Ricardoestesia are obscure due to the many plesiomorphies, although it can be safely omitted from several groups (Ornithomimosauria, Segnosauria+Oviraptorosauria, Alvarezsauridae, Troodontidae, Eumaniraptora). Perhaps it is related to basal coelurosaurs, tyrannosaurs or Bagaraatan. A proper assessment of Ricardoestesia's relationships would focus on the better known R. gilmorei, so will not be considered further here.
Reference- Sankey, 2001. Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas. Journal of Paleontology 75(1) 208-215.
If anyone wants a scan of the tooth, I can send it to them. Just ask.