Acaenasuchus geoffreyi (Archosauria:Aetosauria) from the Upper Triassic Chinle Group: Juvenile of Desmatosuchus haplocerus

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Andrew B. Heckert Ph.D., Professor (Creator)
Appalachian State University (ASU )
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Abstract: Aetosaur scutes assigned to Acaenasuchus geoffreyi Long and Murry, 1995, are juvenile scutes of Desmatosuchus haplocerus (Cope, 1892), so A. geoffreyi is a junior subjective synonym of D. haplocerus. Scutes previously assigned to Acaenasuchus lack anterior bars and a strong radial pattern of elongate pits and ridges, but do possess an anterior lamina and a raised boss emanating from the mid-dorsal surface of the scute. Desmatosuchus is the only aetosaur with this combination of features, and the replacement of the anterior bar with a lamina is an autapomorphy of Desmatosuchus. Other characters used by previous workers to distinguish Acaenasuchus from Desmatosuchus include deeply incised pitting on the dorsal scutes and the division of the raised boss posteriorly into two lateral flanges in Acaenasuchus. We interpret the deeply incised pitting as an artifact of ontogenetic variation. The more exaggerated pits and thin grooves on the scutes of "Acaenasuchus" represent a juvenile stage of development, an ontogenetic feature we have observed on other aetosaurs, notably Aetosaurus. The divided boss is the most unique characteristic of "Acaenasuchus/' but even this feature could also represent immature development. Further, of the four localities (the Blue Hills, the Placerias quarry and the Downs' quarry-all near St. John's, AZ, and another locality near Winslow, AZ) that have produced scutes assigned to Acaenasuchus, two (the Placerias and Downs' quarries) also produce abundant adult specimens of Desmatosuchus, and all four localities are in strata of equivalent (latest Carnian) age. Thus, in all critical details of morphology, except size, scutes assigned to Acaenasuchus appear to represent scutes of Desmatosuchus. The apparent rarity and limited geographic and stratigraphic range of Acaenasuchus relative to Desmatosuchus are artifacts of preservational and collecting biases.

Additional Information

Heckert, A.B., and Lucas, S.G. (2002) Acaenasuchus geoffreyi (Archosauria:Aetosauria) from the Upper Triassic Chinle Group: Juvenile of Desmatosuchus haplocerus. New Mexico Museum of Natural History and Science Bulletin 21, p. 205-214. (ISSN 1524-4156) Archived in NC DOCKS with permission of the editor. The version of record is available at:
Language: English
Date: 2002

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