Description
Eocene nonmarine and marginal marine formations located in western San Diego County, California, have yielded a diverse lower vertebrate fauna. Fossil lizards made up a significant portion of the fauna at many localities. Dentary fragments of a gekkonid are questionably referred to the family Gekkonidae. Three iguanids have been identified. Parasauromalus olseni is represented by jaw fragments and teeth. It was previously known only from the Wasatchian and Bridgerian of Wyoming. A second iguanid has a well developed coronoid lappet, a large splenial, 30 to 32 tricuspid dentary teeth, and a Meckelian groove that is closed for a space but opens anteriorly. A third iguanid has 25 to 28 tricuspid dentary teeth and Meckel's groove is closed and fused. The agamid Tinosaurus cf. T. stenodon is represented only by teeth. Two new species of the extinct xantusiid Palaeoxantusia are represented, one by a nearly complete skull and associated mandibles, the other by dentary fragments. The new genus Paracontogenys is questionably referred to the Scincidae because of its resemblance to the Cretaceous and Paleocene genus Contogenys. Pancelosaurus sp. and an unidentified form are referred to the anguid subfamily Anguinae. At least one member of the subfamily Glyptosaurinae is present. An extinct varanid, Saniwa brooksi, is known from a few vertebrae and dentary fragments. A generically undetermined member of the amphisbaenian subfamily Rhineuridae is also present. The San Diego mammalian fauna has been considered to suggest an early Uintan North American land mammal age. The San Diego Eocene lizard fauna is somewhat advanced over typical Bridgerian faunas and therefore also suggests an early Uintan age. In the San Diego area gravels of the later Eocene conglomerate lithosome are considered dominantly nonmarine deltaic with fluvial developed sand bars. The coastal region of San Deigo marked the western termination of the later Eocene Ballena Channel. Much of the river load, including the "Poway type" clasts, would have been transported only during flood periods. Crocodilians, trionychid turtles and possibly the frog remains indicate that free water was available throughout the year. The Mission Valley Formation probably represented a complex of nearshore marine, marine embayments, coastal floodplain and occasional minor channel depositional environments. Although the Friars Formation has been considered "lagoonal'' its vertebrate fauna and local channeling indicate fluvial domination of the depositional environment.
