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La Union

NM: Doña Ana Co.


Synonym: Mesilla Basin Fauna B.

Vanderhill (1986) named three superposed faunas within the Mesilla Basin: Mesilla Basin Fauna A, Mesilla Basin Fauna B, and Mesilla Basin Fauna C. Morgan (2008) pointed out that three faunas differentiated only by a letter produced confusion, and he renamed them respectively: Anapra (Early Late Blancan, 2.2-3.0 Mya), La Union (Latest Blancan, 1.8-2.2 Mya), and Adobe Ranch (Early Irvingtonian, 1.0-1.8 Mya).

Location of the La Union Fauna.Age. Latest Blancan (2.2-1.8 my) (Morgan and Lucas 2003; Morgan 2008).

General Description. Valley fill deposits lying above the Anapra (=Mesilla Basin Fauna A) between Chamberino and Santa Teresa (Morgan and Lucas 2003). McDonald and Morgan (2011) subdivided the La Union Fauna into three local faunas since the La Union Fauna consists of more than 100 sites over a span of more than 25 km. North to south, these are the Chamberino, La Union, and Santa Teresa local faunas.

Discussion. Magnetostratigraphic data (Vanderhill 1986) indicates the fauna lies between the Gauss/Matuyama boundary (2.6 mya) and the Olduvai Subchron (1.8 mya). Morgan and Lucas (2003) further suggest that the faunal makeup places the fauna in the upper half of the interval. Much of the fauna was listed by Vanderhill (1986), with Morgan and Lucas (2003) incorporating Vanderhill's identifications and adding to the faunal list.

Morgan and Lucas (2003) included Paramylodon ? harlani in the faunal list. This is omitted in McDonald and Morgan (2011), replaced by Paramylodon cf. gabanii.


Lepisosteus sp.—Gars (Morgan et al. 2011).

Ambystoma sp.—Ambystomid Salamanders (Morgan and Harris 2015).

Trachemys scripta or T. gaigeae—Slider or Big Bend Slider (Vanderhill 1986)

Pseudemys scripta

Gopherus sp.—Gopher Tortoises (Morgan et al. 2011)
Cuvieronius sp.—Cuvier's Gomphothere (Morgan and Lucas 2003)
Glyptotherium arizonae—Arizona Glyptodont (Morgan and Lucas 2003)
Megalonyx leptostomus—Narrow-mouthed Sloth (Morgan and Lucas 2003)
Paramylodon garbanii—Garban's Ground Sloth (Morgan 2008: cf.)
Spermophilus sp.—Spermophile Ground Squirrel (Morgan and Lucas 2003)
Dipodomys sp.—Kangaroo Rat (Morgan and Lucas 2003)
Geomys (Nerterogeomys) sp.—Geomys Pocket Gopher (Morgan and Lucas 2003)
Onychomys sp.—Grasshopper Mouse (Morgan and Lucas 2003)
Sigmodon sp.—Cotton Rat (Morgan and Lucas 2003)
Aluralagus virginiae—Virginia Rabbit (Morgan and Lucas 2003)
Scalopus (Hesperoscalops) sp.—Mole (Morgan and Lucas 2003)
Lynx rufus—Bobcat (Morgan and Lucas 2003: ?)
Smilodon gracilis—Slender Smilodon (Morgan and Lucas 2003)
Arctodus pristinus—Lesser Short-faced Bear (Morgan and Lucas 2003)
Spilogale sp.—Spotted Skunk (Morgan and Lucas 2003)
Equus calobatus—Stilt-legged Onager (Morgan and Lucas 2003: ?)
Equus scotti—Scott's Horse (Morgan and Lucas 2003)
Tapirus merriami—Merriam's Tapir (Morgan and Lucas 2003)

Tapirus haysii

Blancocamelus meadi—Blanco Camel (Morgan and Lucas 2003)
Camelops large species—Large American Camel (Morgan and Lucas 2003)
Gigantocamelus sp.—Giant Camel (Morgan and Lucas 2003)
Hemiauchenia gracilis—Gracile Llama (Morgan et al 2008)
Palaeolama sp.—Ancient Llama (Morgan and Lucas 2003)
Odocoileus sp.—Deer (Morgan and Lucas 2003)

Literature. Morgan 2008; Morgan and Lucas 2003; Morgan et al. 2008; Morgan et al. 2008; Vanderhill 1986).


Last Update: 5 Feb 2016