New Mexico Geological Society Annual Spring Meeting — Abstracts

Ten sites from the Albuquerque Basin in north-central New Mexico have produced vertebrate fossils of Blancan (pliocene) age. Five of these are unpublished sites discovered within the past five years, and five of the sites were known previously. Two ofthe new sites, the Lorna Colorado de Abajo fauna from Rio Rancho in Sandoval County and the Belen fauna from near Belen in Valencia County, contain age-diagnostic species of mammals. The Lorna Colorado de Abajo fauna is composed ofthree species. A small land tortoise (cf. Hesperotestudo) is identified from a shell fragment; the ground squirrel Spermophilus sp. is known from a partial skull; and the primitive pocket gopher Geomys (Nerterogeomys) is represented by one complete and one partial skull and a mandible fragment. The Loma Colorado Geomys is indicative of a Blancan age, but does not permit a more precise placement of this fauna within the Blancan. The Belen fauna includes six species: the partial skeleton of a colubrid snake; a partial mandible of the talpid Sealopus (Hesperosealops) sp.; a mandible of the geomyid Geomys (Nerterogeomys) paenebursarius, a metatarsal of the horse Equus ealobatus, a partial metapodial of a small antilocaprid; and a complete set ofmandibles with right and left m2-m3 of the gomphotheriid proboscidean Stegomastodon mirifieus. The Belen mole mandible represents the first record of the family Talpidae from New Mexico in either the fossil or modern fauna, and the westernmost occurrence of the genus. G. (N.) paenebursarius is restricted to late Blancan faunas, E. ealobatus occurs in the late Blancan and Irvingtonian, and S. mirifieus is found in the middle Blancan through the early Irvingtonian. The overlapping range zone for these three species is late Blancan. The three other new sites from the Albuquerque Basin, two in the vicinity of Los Lunas in Valencia County and one near Veguita in northern Socorro County, each consist of only one species of mammal. A tooth of the typical Blancan camel Hemiauehenia blaneoensis occurs in one of the Los Lunas sites, and several postcranial elements of either the large camel Camelops or a giant camelid (Blaneoeamelus or Gigantoeamelus) were identified from the second Los Lunas site. The Veguita site has a maxilla with a complete dentition of the large horse Equus scotti, a species typical ofmiddle Blancan through early Irvingtonian faunas.

The presence in many of the Albuquerque Basin faunas of mammals that occur in middle Blancan and younger faunas excludes an early Blancan (3.7-4.5 Ma) age for most of these sites. Several ofthese faunas appear to be late Blancan in age (1.8-2.5 Ma) based on the few agediagnostic species present, although the absence ofNeotropical immigrant mammals (e.g., ground sloths, glyptodonts, capybaras, and porcupines) from all Albuquerque Basin Blancan faunas may be significant. The arrival of these immigrants from South America at about 2.5 Ma characterizes most late Blancan faunas from the southwestern United States, suggesting that some Albuquerque Basin Blancan faunas may be middle Blancan in age (2.5-3.7 Ma).