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Robert Gay Mission Heights Preparatory High School, 1376 E Does the early Jurassic Kayenta Formation preserve two species of Scutellosaurus? Robert Gay Mission Heights Preparatory High School, 1376 E. Cottonwood Ln., Casa Grande, Az. 85122 [email protected] ABSTRACT Several authors have found the pitting of the armor of S. lawleri the armor. Colbert (1981) describes the armor of MNA V.175 as be- The early Jurassic Kayenta Formation, exposed across the American to be diagnostic of the taxon (Colbert 1981, Martill, Batten and ing uniform in thickness with a ventral deflection or concavity. This southwest, preserves a wide variety of armored archosaurs. These in- Loydell 2000). Both Colbert (1981) and Martill et al. (2000) concavity is present even on the tallest osteoderms to maintain the clude several crocodylomorphs, as well as the ornithischian dinosaurs noted that unlike Scelidosaurus, Scutellosaurus lawleri oste- uniform thickness seen as diagnostic by Colbert (1981) to the taxon Scelidosaurus and Scutellosaurus. These genera have traditionally oderms have a pitted appearance. This pitted ornamentation is been considered monotypic. Considering that the Kayenta Formation but in fact is now considered a synapomorphy for the thyreophora is usually dated to the Sinemurian-Pliensbachian stages of the Juras- random across the surface of the osteoderms, unlike the patterns (Norman, Witmer and Weishampel 2007). The lack of this character sic, representing approximately three million years of evolutionary seen in aetosaurus (eg. Parker and Martz, 2010) and crocodyla- in Scutellosaurus n. sp. suggests it may be one of the least derived time, it should not be surprising if the monotypic view of the fossil morphs (Sues, et al. 1996). The ornamentation on the oste- thyreophorans. The preliminary phylogenetic analysis seems to sup- record is not reflective of the actual paleobiology of the early Jurassic oderms of MNA V.3133 matches this description with random port this hypothesis. Period in the American southwest. pitting being present on the dorsal surfaces of the osteoderms. An examination of specimens of Scutellosaurus at the Museum of Colbert (1981) describes four basic osteroderm morphologies, Northern Arizona indicates that there may be more than one species with the four types grading into one another; blade-like grading of Scutellosaurus preserved in the Kayenta Formation. The preserved appendicular and axial skeleton of both S. lawleri and S. n. sp. are vir- to flat. The armor of MNA V.3133 exhibits none of the morpho- tually identical. The dermal armor, however, shows marked differ- logical variation seen in S. lawleri. While only ~30% of the der- Scapula of MNA V.3133 (left) and MNA V.175 (holotype of Scutellosaurus lawleri, right) ences. While the specimen does not preserve a full complement of os- Gold Tooth Spring, Navajo Nation, showing the exposure of the Kayenta Formation in the area. This is the approximate location that MNA V.3133 was collected, though no de- mal armor being preserved leaves some room for error, the fact teoderms, the partial and complete osteoderms (n=41) allow a diagno- tailed location or stratigraphic data is on file for locality MNA PXXXX that there is no variation in morphology between any of the 41 ses of differences between the two taxa. In particular, the new species IS MNA V.3133 SCUTELLOSAURUS? has simplified armor morphologies (from between 4-6 in S. lawleri to The axial and appendicular elements preserved in MNA V.3133 only one in S. n. sp.) and a lack of the medial concavity in the oste- Left lateral view of three typical, complete dorsal vertebrae of MNA V.3133 oderms diagnostic of S. lawleri. In addition, the armor of S. n. sp. also do not significantly differ from the elements preserved in MNA has scalloped margins, unlike the rounded edge found on S. lawleri. V.175. Except in terms of preservation, the elements of both IMPLICATIONS FOR THE UTAH SPECIMEN This evidence together indicates that the genus Scutellosaurus is not specimens are virtually indistinguishable. The skeletal remains In October of 2011 the fragmentary remains of an armored archosaur monotypic and that the fauna preserved by the Kayenta Formation of MNA V.3133 preserve synapomorphies placing it within the were recovered from near the base of the Kayenta Formation in changed during the formation's deposition. Further work is also need- thyreophora and autapomorphies that exclude Scelidosaurus and ed to determine if a fragmentary specimen from southwestern Utah is Warner Valley, Utah. The armor fragments preserve a similar profile Dorsal (left) and ventral (right) views of the least-concave scutes from a random (n=150) sample of scutes, MNA V.175 allow placement within the clade Scutellosaurus. However, there also attributable to S. n. sp. If so, this would represent a significant in cross section as MNA V.3133. The vertebrae are fragmentary and are some characters present in the dermal armor of MNA V.3133 expansion of the known range of Scutellosaurus. plesiomorphic. Investigations continue in Warner Valley which will that are markedly different from the osteoderm characters pre- sent in MNA V.175 and indicate that MNA V.3133 does not rep- hopefully yield more information on this fragmentary archosaur. resent another specimen of S. lawleri. IS MNA V.3133 SCUTELLOSAURUS LAWLERI? CONCLUSIONS The dermal armor of V.3133 differs significantly from the armor MNA V.3133 likely represents a new taxon of Scutellosaurus from of both MNA V.175 and paratype. Colbert (1981) described the the early Jurassic Kayenta Formation of northern Arizona. Autapo- morphies of this new species include ventrally unexcavated scutes, highly diagnostic armor of S. lawleri as follows: 30 scutes from MNA V.3133 in dorsal view. scutes with variable thicknesses, and a delicate scalloped margin for Dorsal (left) and ventral (right) views of complete or nearly complete typical scutes from MNA V.3133 “The most numerous scutes are in the form of broad, flat plates, partial or complete scutes with a known or inferred shape is sig- the scutes. Preliminary phylogenetic analyses seem to support the in- References: each with a longitudinal ridge, and each asymmetrical in shape. nificant. Larger complete or nearly complete scutes tend to be clusion of MNA V.3133 within Scutellosaurus but allow for the pos- Colbert, E., 1981. A primitive ornithischian dinosaur from the Kayenta Formation of Arizona. Flag- These scutes vary in size, the largest being approximately equal thicker, while smaller complete or nearly complete scutes are sibility that MNA V.3133 falls outside of the thyreophora. staff (Arizona): Museum of Northern Arizona. in length to the length of a presacral or antero-medial caudal ver- thinner. All scutes complete enough for the shape to be inferred ACKNOWLEDGEMENTS Felsenstein, J., 2000. PHYLIP: Phylogeny Inference Package. 3.6 ed. Washington: University of tebra. From scutes of this dimension they range downward in are ovoid. Given the hypothesized distribution of osteoderms in Washington. size to mere nubbins. The ventral surfaces of these scutes usual- S. lawleri, the preservation of MNA V.3133 should yield multi- Many thank are extended to Dave and Janet Gillette, as well as An- Martill, D., Batten, D. & Loydell, D., 2000. A New Specimen of the Thyreophoran Dinosaur CF ly show a slight longitudinal concavity” ple osteoderm morphologies. This is not what is seen and sug- drew Milner for discussions on Scutellosaurus and access to speci- Scelidosaurus with Soft Tissue Preservation. Palaeontology, 43(3), pp. 549-559. Pedal phlanges including ungula (left) of MNA V.3133 in ventral (top) and left lateral (bottom) view. gests that a single osteoderm morphology was present over the mens under their care. Nesbitt, S., 2011. The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades. Bulletin of the American Museum of Natural History, Volume 352, pp. 1-292. entire body. The other notable difference is in the thickness of Lesotho- S. Sceli- Norman, D., Witmer, L. & Weishampel, D., 2007. Basal Thyreophora. In: D. Weishampel, P. Dodson Outgroup Cerapoda S. n. sp Emausau- Eurypoda saurus lawleri dosaurus rus & H. Osmolska, eds. The Dinosauria. Berkeley/Los Angeles(California): University of California Press, pp. 335-342. Parker, W. G. & Martz, J. W., 2010. Using positional homology in aetosaur (Archosauria: Pseudo- suchia) osteoderms to evaluate the taxonomic status of Lucasuchus hunti.. Journal of Vertebrate Paleontology, Volume 30, pp. 1100-1108. Sues, H.-D., Shubinb, N., Olsen, P. & Amarald, W., 1996. On the cranial structure of a new proto- suchid (Archosauria: Crocodyliformes) from the McCoy Brook Formation (Lower Jurassic) of Nova Scotia, Canada. Journal of Vertebrate Paleontology, 16(1), pp. 34-41. Outline of Scutellosaurus n. sp., showing preserved elements. Scale Left femoral head of MNA V.3133 in anterior view. Cladogram showing the single consensus tree of 58 most parsimonious trees showing the relationships of MNA bar = 10cm. V.3133 to other ornithischians. See poster text for more details on placement. Distal caudal of MNA V.3133 in left lateral view. .
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