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early Oligocene, Whitneyan NALMA


The I-75 LF was discovered in 1965 during the construction of Interstate Highway 75 (“I-75”) through Gainesville in Alachua County in northern peninsular Florida. The fossiliferous sediments consist of dark, sandy clays deposited in a small sinkhole about 5 m in diameter and 2 m deep, developed in marine Eocene limestone. The large mammal fauna from I-75 is composed of two carnivores (the amphicyonid Daphoenus and a mustelid), a horse (Miohippus), a tayassuid, an oreodont, and a small ruminant artiodactyl (Leptomeryx). Leptomeryx is the most abundant mammal in the fauna. I-75 also has a rich microvertebrate fauna, including frogs, salamanders, lizards, snakes, and small mammals (Patton 1969; Holman 1999). Small mammals include: a didelphid marsupial (Herpetotherium), a large geolabidid insectivore (Centetodon cf. C. wolffi), seven species of bats, one rabbit (Palaeolagus), and at least four species of rodents (Eutypomys sp., a heteromyid, and two eomyids). The association of these terrestrial vertebrates with sharks, rays, and marine fish suggests that the I-75 site was deposited near the coast.

Most previous workers placed the I-75 LF in the Whitneyan, making it the oldest land vertebrate fauna known from Florida (Patton 1969; Emry et al. 1987). The Whitneyan comprises a short interval of time in the late early Oligocene (30 to 32 Ma; Emry et al. 1987; Woodburne and Swisher 1995; Tedford et al. 1996). Miohippus and Leptomeryx from I-75 occur from the Chadronian through the early Arikareean. The I-75 Centetodon is similar to C. wolffi from the Orellan and Whitneyan (Lillegraven et al. 1981). The small leporid is referred to Palaeolagus, a common rabbit in Orellan and Whitneyan faunas, which has its last appearance in the early Arikareean. The beaver-like rodent Eutypomys is typical of Whitneyan and older Oligocene faunas in the Great Plains, but survived into the early Arikareean (Emry et al. 1987; Tedford et al. 1996). Most of the age-diagnostic mammals from the I-75 LF range from the Orellan through the early Arikareean. The presence of Centetodon, Eutypomys, Palaeolagus, Miohippus, and Leptomeryx establish an age older than early Arikareean (older than 24 Ma; Tedford et al. 1987, Tedford et al. 1996). A post-Orellan age is suggested by the presence of an advanced species of Miohippus. The absence of taxa in the I-75 LF restricted to the Arikareean (e.g., Nanotragulus) indicates a late Whitneyan age (~30 Ma). The similarity of the bat faunas from I-75 and the early Arikareean Brooksville 2 LF indicates that these two faunas are fairly close in age.

I-75 provides the earliest record of the taxonomic diversity and community structure of North American middle Cenozoic chiropteran faunas. Seven species of bats represented by 40 specimens are known from I-75. The fauna includes a new genus and species of Mormoopidae and an undescribed genus and two new species of Emballonuridae. An undescribed new genus and two new species of possible phyllostomids are represented by just a few isolated teeth. A partial radius constitutes the ear liest fossil record of the Natalidae (Morgan and Czaplewski 2003). A large species of Vespertilionidae is represented by two teeth and a partial radius. Species belonging to Neotropical families are the most abundant bats in the I-75 fauna, including a large emballonurid and a small mormoopid.