Stratigraphy, paleontology and age of the Fruitland and Kirtland Formations (upper Cretaceous), San Juan Basin, New Mexico Hunt, A. P. Lucas, S. G. 8V4V3 7742 Gray 1821 [1687,1869,299,331] GBIF Animalia 10 225 Chordata subPhylum Vertebrata    Introduction  Thevertebrate faunasof the Fruitland and Kirtland Formations rep ­ resentthe largest and most diverseLate Cretaceous faunasof the southern WesternInterior and have a long historyof collection and study (  Hunt et al., 1992). Three vertebrate faunascan be discriminated withinthe Fruitland and Kirtland Formations; (1) Fruitland Formation (  Table5); (2) Hunter WashMember, Farmington Memberand De-na-zin members ofthe Kirtland Formation ( Table 6); and (3) Naashoibito Member of theKirtland Formation ( Table 7). These faunasform a sequenceof decreasingdiversity. This is inpart dueto the fact that themajority ofmicrovertebrate sites are in the Fruitland Formation. Microvertebrate localities account for allthe mammalian and amphibianfossils from these strata. It is unfortunate that some recentauthors (e. g.,  Weishampel, 1990) continue tolist the faunaof the Kirtland as a whole  despitethelong realizationthat two faunas ofdemonstrably different ages are present in thisformation (e. g., Lehman, 1981; Lucas, 1981; Lucas et al.. 1987).   Microvertebrates Virtually all fish, amphibian and reptiles, apart from turtlesand dinosaurs, are represented bydisarticulated microvertebrate specimens. The taxonomyof these specimens is, by necessity, largelytypological, but they arecomparable with contemporaneous faunas inthe Western Interior ( e.g., Estes, 1964;  Sahni, 1972; Bryant, 1989).