PLIOCENE (BLANCAN) VERTEBRATES FROM THE PALOMAS FORMATION, ARROYO DE LA PARIDA, SOCORRO BASIN, CENTRAL NEW MEXICO
CONNELL, S.D. and LOVE, D.W., New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM 87801
Vertebrate fossils were first reported in 1936 from Arroyo de la Parida,
about 6 km northeast of Socorro, Socorro County, central New Mexico. The
Arroyo de la Parida Local Fauna is derived from a 70-m-thick sequence
of sands and gravels that constitute the axial river (ancestral Rio Grande)
facies of the Palomas Formation of Gordon (1910, USGS Prof. Paper 68).
The strata in the vicinity of Arroyo de la Parida are located at the northern
end of the Socorro Basin, representing one of the northernmost occurrences
of the Palomas Formation, which has its type area about 100 km farther
south in Palomas Creek near Truth or Consequences in Sierra County.
The Arroyo de la Parida Local Faula is composed of ten species of vertebrates,
including the land tortoise Hesperotestudo; the ground sloth Megalonyx
cf. M. leptostomus; three species of horses, Equus cf.
E. cumminsii, E. scotti, and E. simplicidens; two camels, a large
species of Camelops and a small species of Hemiauchenia; the small
pronghorn antipocaprid Capromeryx; and two proboscideans, Rhynchotherium
falconeri and Stegomastodon sp. This is a fairly typical faunal assemblage
found in New Mexico Blancan sites, mostly consisting of large grazing
ungulates and dominated by horses of the genus Equus. Five of these species
are restricted to Blancan faunas, including Megalonyx leptostomus,
Equus cumminsii, E. simplicidens, the large Camelops,
and Rhynchotherium falconeri. The most biostratigraphically diagnostic
of these taxa is Rhynchotherium falconeri, a proboscidean characterized
by a strongly downturned mandibular symphysis and the presence of lower
tusks. Rhynchotherium became extinct in the late Pliocene at about
2.2 Ma, together with several other characteristic genera of Blancan mammals.
The lower jaws of R. falconeri from this site were collected near
the top of the local section of the Palomas Formation on the south side
of Arroyo de la Parida, suggesting that the entire fauna, most of which
occurs some 40 m lower in the section, is older than 2.2 Ma. An early
Blancan age for the Arroyo del la Parida Local Fauna is excluded by the
presence of E. scotti, Camelops sp., and the small Hemiauchenia,
all of which first appear in New Mexico faunas during the medial Blancan
(2.6-3.7 Ma). The absence of South American immigrants that arrived following
the Great American Interchange suggests that the Arroyo de la Parida Local
Fauna is older than 2.7 Ma. Megalonyx is the only mammal of South
American origin in southwestern Blancan faunas that was not a participant
in the Great American Interchange. Megalonyx or its progenitor
arrived from South America in the late Miocene, and M. leptostomus
is fairly widespread in early through late Blancan faunas. The Arroyo
de la Parida Local Fauna is thus interpreted to be medial Blancan (2.7-3.7
Ma) and is similar in age to the Belen Fauna from the "Sierra Ladrones
Formation" in the southern Albuquerque Basin and the Cuchillo Negro
Creek Local Fauna from the Palomas Formation in the Engle Basin near Truth
or Consequences.
Morgan, G.S., Lucas, S.G., Sealey, P.L., Connell, S.D., Love, D.W., 2000, Pliocene (Blancan) vertebrates from the Palomas Formation, Arroyo de la Parida, Socorro basin, central New Mexico [abstract]: New Mexico Geology, v. 22, n. 2, p. 47.
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New Mexico Institute of Mining & Technology
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