Earth and Environmental Science Transactions of the Royal Society of Edinburgh

Articles

Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas

Axel Hungerbühlera1, Bill Muellera2, Sankar Chatterjeea2 and Douglas P. Cunninghama2

a1 Mesalands Community College, 911 S. Tenth Street, Tucumcari, NM 88401, USA. Email: axelh@mesalands.edu

a2 Division of Paleontology, Museum of Texas Tech University, Box 43191, Lubbock, TX 79409, USA

ABSTRACT

The skull anatomy of a new species of the phytosaur Machaeroprosopus is described for the first time on the basis of two specimens from the Upper Triassic Cooper Canyon Formation of Texas. Additional information is provided by a third specimen referred to Machaeroprosopus sp. A paranasal bone, an additional paired element of the narial region, is identified. Important new data are presented for the braincase, including the morphology of the epipterygoid and presphenoid, an anterior process of the prootic, an anteroventral process of the laterosphenoid, and a parasphenoid process. Machaeroprosopus lottorum n. sp. is characterised by four apomorphies: a supratemporal fenestra closed on the skull roof with bevelled anterior rim, a comparatively short squamosal, a flat and rugose narial rim, and medially extended palatines that come close to form an ossified secondary palate. With respect to the supratemporal fenestra, the supraoccipital–parietal complex and several features of the squamosal, Machaeroprosopus lottorum n. sp. bridges the morphological gap between species previously referred to the genera Pseudopalatus and Redondasaurus. A parsimony analysis of known species of Machaeroprosopus supports the hypothesis that the development of the rostral crest in Machaeroprosopus is a sexually dimorphic feature, and questions the validity of the genus Redondasaurus. Consequently, Redondasaurus is here considered a junior synonym of Machaeroprosopus.

(Received January 26 2012)

(Accepted March 25 2013)

KEY WORDS

  • Dockum;
  • Norian;
  • Pseudopalatus ;
  • Redondasaurus