Effigia okeeffeae Nesbitt and Norell, 2006

Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, Bulletin of the American Museum of Natural History 2011 (352), pp. 1-292 : 31-32

Effigia okeeffeae Nesbitt and Norell, 2006

( fig. 8I)

AGE: Late Norian–?Rhaetian, Late Triassic ( Heckert et al., 2008).

OCCURRENCE: Coelophysis Quarry , ‘‘siltstone member’’ of the Chinle Formation, Ghost Ranch, northern New Mexico.

HOLOTYPE: AMNH 30587, nearly complete skull, much of the cervical dorsal, and sacral vertebrae and the first two caudal vertebrae, right pes, left and right femur, left and right tibia, left and right fibula, right and fragments of the left scapula, left and right coracoids, right humerus, right ulna, right radius, right manus, left and right ilium, left and right ischia, right pubis, gastralia, and dorsal ribs.

REFERRED MATERIAL: AMNH FR 30588, femur, ilium, ischium, pubis, sacrum, nearly complete caudal series; AMNH FR 30589, partial skull and cervicals; AMNH FR 30590, proximal part of the femur.

REMARKS: Nesbitt and Norell (2006) named Effigia from an articulated skeleton from the Coelophysis Quarry in northern New Mexico. The combination of a postcranial skeleton like that of ‘‘ Chatterjeea ’’ and an edentulous, highly apomorphic skull similar to Shuvosaurus showed that the skull of Shuvosaurus belongs to the body of ‘‘ Chatterjeea . ’’ Furthermore, the skeleton of Effigia bears an uncanny resemblance to that of theropods and more specifically, ornithomimids, even though it is more closely related to Crocodylia than Aves ( Nesbitt and Norell, 2006). The realization of this convergence led Nesbitt et al. (2007) to critically examine the fossil record of early dinosaurs in North America and to conclude that many of the specimens once thought to be theropods actually belong to close relatives of Effigia .

In a superficial review of the taxonomy of Shuvosaurus, Lucas et al. (2007c) challenged the difference cited by Nesbitt and Norell (2006) and Nesbitt (2007) separating Effigia from Shuvosaurus . The two taxa are obviously closely related given their divergent morphology and numerous apomorphies between the two taxa (Nesbitt, 2007). However, the comments of Lucas et al. (2007) must be addressed.

Of the six characters explicitly used to differentiate Effigia from Shuvosaurus by Nesbitt (2007), Lucas et al. (2007) accepted differences between the maxilla, lacrimal, and squamosal, but stated ‘‘the biological significances’’ of the differences are unknown. It is not clear why Lucas et al. (2007) required an understanding of ‘‘biological significance’’ for a difference to be valid. The absence of a posterior process of the maxilla in Effigia represents a genuine difference between the two taxa and nearly all other archosaurs. Furthermore, the squamosal of Lotosaurus (IVPP V 48013 ) also lacks a posterior squamosal process. The premaxillae of Shuvosaurus (e.g., TTU-P 9280) apparently lack any posterior process whereas that of Effigia has a small tonguelike process. The posterior process of the maxilla of Effigia is rather robust, and this suggests that the premaxillae of Shuvosaurus genuinely lack this process even though the preservation and preparation of the material of Shuvosaurus is poor. The relative sizes of the dentaries cannot be compared at present after the repreparation of the specimen. Prior to the disarticulation of the type skull of Shuvosaurus in 2005, the body of the dentary of Shuvosaurus extended well past the premaxilla-maxilla articulation, whereas in Effigia , the body of the dentary is anterior to and at the premaxilla-maxilla articulation ( Chatterjee, 1993; Rauhut, 1997). However, after repreparation, some of the original bone on the posterior portion of the dentary was lost (S.J.N., personal obs.). Therefore, all six characters discussed by Lucas et al. (2007) represent differences between Effigia and Shuvosaurus .

Furthermore, Lucas et al. (2007) dismissed the differences in the postcrania of the two taxa listed by Nesbitt (2007). These include two characters: the anterior cervical centra have distinct keels ( Long and Murry, 1995: fig. 163 A–D), whereas those of Effigia lack keels (Nesbitt, 2007: fig. 28D), and difference in the size of the coracoid foramen. Additionally, the only ulna of Shuvosaurus (TTU- P unnumbered) is proportionally much more stout than that of Effigia . Unfortunately, limited comparisons can be made at this time because much of the Shuvosaurus postcrania remains unprepared. As a result of the discussion presented above, Effigia and Shuvosaurus are separate terminal taxa here.

Effigia is distinguished from all other suchians except Shuvosaurus by the presence of an edentulous premaxilla, maxilla, and dentary, a posteriorly long anterodorsal process of the premaxilla, a long preacetabular process of the ilium that connects to the posterior process by a large thin flange, and a pubic boot that is 33% the length of the pubic shaft. It is distinguished from Shuvosaurus by the presence of both a dorsal and posterior process of the maxilla, relatively shorter dentary, the absence of posterior process of the squamosal, a small fossa on the posterolateral side of the squamosal, and the presence of a large pit on the posterior side of the lacrimal (from Nesbitt, 2007).

KEY REFERENCES: Nesbitt and Norell, 2006; Nesbitt, 2007.