PREFACE The Pelyeosauria, or Theromorpha, of the late Paleozoic, reptiles particularly characteristic of the Permo-Carboniferous redbeds of the American Southwest, form a group of major importance in the history of land vertebrates. As first recognized by Cope, they represent an early stage in the beginning of mammal-like forms. They are also the dominant types in the oldest adequately known reptilian fauna and possess many archaic features which illustrate the structure of the primitive reptilian stock. Most of the earlier work on pelycosaurs was done by Cope. He realized the significance of the material, but his brief and often inadequate descriptions and meager illustrations failed to give the group the scientific prominence it deserved. A decade of work on the group by Case culminated in the publication in 1907 of his Revision of the Pelyeosauria of North America. Case figured most of the important material then known, straightened out many taxonomic snarls, and gave the first account of the general structure of a number of the more adequately represented types. Through the influence of this work, the pelycosaurs were at length generally accorded a place of importance among fossil vertebrates. This earlier period of the study of the pelycosaurs occupied essentially 3 decades. Since Case’s 1907 work increases in our knowledge have been slow. The paucity of material of even the most common types necessitated the leaving of lacunae in Case’s descriptions, few of which have since been filled. Many new data have been obtained, but little has . . .

Abstract: Tetrapod footprints are among the most common fossil remains in continental Permian strata and thus are of biostratigraphic interest. Based on the vertical distribution of the 13 best-known Permian tetrapod ichnotaxa, three footprint biochrons are suggested for the period: (1) Dromopus – latest Carboniferous (approximately Gzhelian) to late Early Permian (approximately Artinskian), representing ichnoassemblages dominated by tracks of temnospondyls, reptiliomorphs, pelycosaurs and early diapsids; (2) Erpetopus – late Early Permian (approximately Kungurian) to late Middle Permian (approximately Capitanian), representing ichnoassemblages dominated by tracks of non-diapsid eureptiles; and (3) Paradoxichnium – Late Permian (Wuchiapingian and Changhsingian), representing ichnoassemblages dominated by tracks of medium- and large-sized parareptiles, non-diapsid eureptiles and early saurians. This is the most conservative ichnostratigraphic concept, and it may be possible to refine it to almost stage-level resolution by future comprehensive analysis, especially of Permian captorhinomorph and therapsid footprints. Other major tasks to improve Permian tetrapod footprint ichnostratigraphy include enhanced knowledge of Middle Permian tetrapod footprints, and clarification of the palaeoenvironmental factors that may control the distribution of tetrapod footprints in space and time.