Pliocene (Blancan) vertebrates from the Albuquerque Basin, north-central New Mexico
— Gary S. Morgan and Spencer G. Lucas
Ten sites from the Albuquerque basin in north-central New Mexico have produced vertebrate fossils of Blancan (Pliocene) age. Five of these sites were known previously, and five new sites are described. The Loma Colorado de Abajo local fauna (new name) from Rio Rancho in Sandoval County consists of three taxa, a small land tortoise, the ground squirrel Spermophilus sp., and the primitive pocket gopher Geomys (Nerterogeomys) sp. The Loma Colorado Geomys, represented by one complete and one partial skull, is indicative of a Blancan age, but does not permit a more precise placement of this local fauna. The Belen fauna (new name) from near Belen in Valencia County is composed of a colubrid snake and five species of mammals, the talpid Scalopus (Hesperoscalops) sp., the geomyid Geomys (Nerterogeomys) cf. G (N.) paenebursarius, the horse Equus calobatus, an antilocaprid, and the proboscidean Stegomastodon mirificus. G (N.) paenebursarius is known only from late Blancan faunas, E. calobatus occurs in the late Blancan and Irvingtonian, and S. mirificus occurs 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. Camels are the only fossils in the Los Lunas sites, including Hemiauchenia cf. H. blancoensis and a large Camelops or possible giant camelid. The Veguita site has a maxilla with a complete dentition of the large horse Equus scotti, a species typical of late Blancan and early Irvingtonian faunas. Of the five previously known faunas: the Santo Domingo site from the northernmost Albuquerque basin in Sandoval County contains two horses, E. calobatus and E. scotti, that suggest a late Blancan age; the Tijeras Arroyo fauna has the rabbit Hypolagus cf. H. gidleyi and the horse E. cumminsii that indicate a middle or late Blancan age; the Laguna site includes the pocket gopher Geomys (Nerterogeomys) cf. G (N.) paenebursarius found in late Blancan faunas; the Los Lunas site has the giant marmot Paenemarmota cf. P. barbouri, a species ranging in age from the early Blancan through the late Blancan; and the San Acacia site at the southern end of the Albuquerque basin contains Stegomastodon mirificus and an unidentified species of Equus. 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 of these faunas appear to be late Blancan in age (1.8-2.5 Ma) based on the few age-diagnostic species present, although the absence of Neotropical immigrant mammals (the ground sloth Glossotherium, the glyptodont Glyptotherium, the capybara Neochoerus, and the porcupine Erethizon) 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).
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- Morgan, Gary S.; Lucas, Spencer G., 1999, Pliocene (Blancan) vertebrates from the Albuquerque Basin, north-central New Mexico, in: Albuquerque Country, Pazzaglia, Frank J.; Lucas, S. G.; Austin, G. S., New Mexico Geological Society, Guidebook, 50th Field Conference, pp. 363-370.