1. Department of Science and Resource Management, Petrified Forest National Park, Petrified Forest, AZ 86028, U.S.A.,
2. Texas Vertebrate Paleontology Collections, Jackson School of Geosciences, Austin, TX 78758, U.S.A.,
3. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A.,
4. University of Michigan Museum of Paleontology, Ann Arbor, MI 48109, U.S.A., .