| Revueltosaurus | |
|---|---|
 | |
| Skull | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | †Aetosauriformes |
| Genus: | †Revueltosaurus Hunt, 1989 |
| Species | |
| Synonyms | |
| |
Revueltosaurus ("Revuelto lizard") is anextinctgenus ofsuchianpseudosuchian[1] fromLate Triassic (lateCarnian to middleNorian stage) deposits ofNew Mexico,Arizona andNorth Carolina, United States. Many specimens, mostly teeth, have been assigned toRevueltosaurus over the years. Currently, three species are included in this genus, all of which were originally thought to represent monospecific genera of basalornithischiandinosaurs.[2][3][4] Revueltosaurus was about 1 meter (3.3 feet) long.
R. callenderi was named by Adrian P. Hunt in1989 and it is thetype species of the genus. Thegeneric name honors its type locality, Revuelto Creek,Quay County of New Mexico. Revuelto is derived from Spanishrevuelta, "revolution", in reference to the importance of the Late Triassic period for terrestrialvertebrate evolution. Thespecific name honours the director of theNew Mexico Museum of Natural HistoryJonathan F. Callender.R. callenderi was originally described as a basal ornithischian on the basis of 32 teeth: theholotypeNMMNH P-4957 a nearly complete premaxillary (incisiform) tooth, theparatypes (NMMNH P-4958-9, a nearly complete maxillary or dentary tooth crown with root and a nearly complete premaxillary tooth crown) and 28 referred specimens. All specimens were collected from the type locality, from theBull Canyon Formation, dating to the Norian stage.[5]
Later, other teeth were described by Padian (1990), Kaye and Padian (1994) and Hunt and Lucas (1994), fromChinle Formation ofArizona. Andrew B. Heckert (2002) redescribed the genus in detail and named a second species,R. hunti on the basis of teeth described by Hunt and Lucas (1994). He referredMNA V3690, an isolated tooth assigned by Kaye and Padian (1994) toR. callenderi from thePlacerias/Downs quarry near St Johns, Arizona, toTecovasaurus. Heckert listed the referred specimens CMNH PR1697-1699 originally described by Padian (1990) and the topotypes NMMNH P-4960, P-16573, P-33783-798. Four teeth were referred to aff.Revueltosaurus callenderi (NMMNH P-17362, P-17382 and P-17187).R. callenderi is known to date only from the Revueltian (early-mid Norian, the type locality dates back to the early Norian) of Bull Canyon Formation (Dockum Group, New Mexico) and the Painted Desert of the Petrified Forest Member (Chinle Formation, Arizona).[6] Parkeret al. (2005) described several partially completeskeletons ofR. callenderi (PEFO 33787-95), including a nearly complete and a partialskulls, from theRevueltosaurus Quarry,Petrified Forest National Park.[7] Other skeletons were discovered from the Painted Desert, including the nearly complete specimen PEFO 34561 which have been fully reconstructed recently.[8] According to Sterling J. Nesbitt (2011), much of theRevueltosauruscranial andpostcranial material originates from a monotypic bonebed. Some specimens occur as isolated bones, while others are completely associated and even fully articulated. Thus, nearly the entire skeleton ofR. callenderi is known and a full description of it is being prepared.[1]
R. hunti was named by Andrew B. Heckert in2002 as a basal ornithischian. Thespecific name honours the paleontologist Adrian P. Hunt for his contributions to the Triassic paleontology. It is known from theholotypeNMMNH P-29357, a nearly complete tooth crown, the paratypes NMMNH P-29358-9 and topotypes P-29347-54 (and aff.R. hunti specimens NMMNH P-29355, P-29359) which were collected in the NMMNH locality 1171,Santa Fe County, New Mexico from the Los Esteros Member of theSanta Rosa Formation, Chinle Group, dating to the latestCarnian stage (Adamanian). Other isolated teeth (which Long and Murry (1995) assigned toR. callenderi) were collected two localities in the Blue Hills, east-central Arizona, from the Blue Mesa Member of the Chinle Formation, dating also to the latest Carnian.UCMP locality V92048 have yielded the topotypes UCMPV 173839-41, and the referred teeth UCMPV 139563-75 are from UCMP locality V7307.[6]
Parkeret al. (2005) confirmed thatR. hunti may be assignable toRevueltosaurus, on the basis of undescribedsquamosal collected from its referred locality that is nearly identical to that seen in the Petrified Forest material ofR. callenderi, thus suggesting thatR. hunti is a pseudosuchian.[7] In response to the report thatR. callenderi was not an ornithischian, Heckert (2005) erected a new genus forR. hunti,Krzyzanowskisaurus. He suggested that the denticulated shelf on the teeth represented acingulum. Irmiset al. (2007) and Nesbittet al. (2007) synonymizedKrzyzanowskisaurus withRevueltosaurus, and argued that this condition of the dentation is anautapomorphy ofR. hunti and is not homologous to the ornithischian asymmetric swelling or a mammalian cingulum.[2][3]
R. olseni was named by Hunt and Lucas in1994 as a basal ornithischian, under the generic namePekinosaurus. Thegeneric name honorsPekin, North Carolina, where its type series was collected. Thespecific name honours the paleontologist Paul E. Olsen. Hunt and Lucas named the genus on the basis of the teeth seriesYPM 7666-9. Note that they designed theholotype to be YPM 8545, but the correct designation is YPM 7666 following Heckertet al. (2012). The type series ofR. olseni was thought to originate from thePekin Formation ofMontgomery County. Heckertet al. (2012) noted that recent field work has shown that strata formerly assigned to that formation, including the type locality ofR. olseni, actually pertain to the overlyingCumnock Formation (located in the Sanford Subbasin, Deep River Basin). Hence, the type locality and the newly discovered Moncure locality are from the same stratigraphic interval. The Cumnock Formation belongs to theChathan Group (of theNewark Supergroup), which is recognized as Late Triassic in age. Most workers have assigned the Cumnock Formation a Carnian age. Most recent work, however, demonstrates that much of it is in fact Norian in age. Therefore, the strata exposed at the Moncure locality are probably early Norian in age. The Moncure locality have yielded many referred specimens ofR. olseni including NCSM 21647, NCSM 23539, 41-46, 48-50, 52-57, NCSM 24722, 58-62 and NCSM 25194-227. NCSM 24728, 25192-3 and 25228 were referred to ?Revueltosaurus. Someosteoderms were referred to it to, as they very similar to those seen in the Petrified Forest material ofR. callenderi.R. olseni is thought to be one of the most common tetrapods from its assemblage.[4]
Irmiset al. (2007) and Nesbittet al. (2007) tentatively synonymizedPekinosaurus (andGaltonia) withRevueltosaurus, and refer its type series toRevueltosaurus sp. They noted that Hunt and Lucas (1994) did not provide any differential diagnosis, autapomorphies, or unique combination of characters forPekinosaurus. Furthermore, they argued that it cannot be differentiated fromR. callenderi.[2][3] Heckertet al. (2012) agreed thatR. olseni is extremely similar toR. callenderi, however they found thatPekinosaurus teeth have slightly different proportions and outline thanR. callenderi. They provided a differential diagnosis for that species and referred it toRevueltosaurus, under the new combinationR. olseni.[4]
All species ofRevueltosaurus were thought to represent monospecific genera of basalornithischiandinosaurs based on theirteeth. New discoveries of skeletal material ofR. callenderi have suggested thatRevueltosaurus is a pseudosuchian. According to William Parker, "we have pretty much erased the record of Triassic ornithischian dinosaurs from North America, Europe and worldwide, except for South America."[9] His co-author Randall Irmis said, "because the teeth look like those we know from herbivorous ornithischians, people assigned them to the dinosaurs. We think we've shown that you can't rely on the dentition to determine what is an early dinosaur, which casts doubt on all the ornithischians from the Triassic of North America".[10] Nearly complete specimens ofR. callenderi were tested in a broad phylogenetic analysis ofbasal archosaurs for the first time when Sterling J. Nesbitt included the specimens PEFO 34561 and PEFO 34269 (a complete and a nearly complete skeleton, respectively) in his 2011 phylogenetic analysis.Revueltosaurus was placed at the base of the cladeSuchia as thesister taxon to the armored and herbivorousaetosaurs. However,Revueltosaurus itself is not an aetosaur, since Aetosauria was redefined to exclude it. The analysis foundGracilisuchus,Turfanosuchus and theRevueltosaurus+Aetosauria clade to nest in a largepolytomy withTicinosuchus+Paracrocodylomorpha. Thecladogram below follows Nesbitt (2011).[1]
