Earliest record of Palaeolama (Mammalia, Camelidae) with comments on “Palaeolama” guanajuatensis

Abstract

Inglis 1C is a recently described late Pliocene sinkhole deposit on the west coast of Florida (Emslie, 1998; Ruez, 2001, 2002). In a partial report of the fauna from this locality, Palaeolama was noted without comment in the mammalian faunal list (Ruez, 2001). The specimen from Inglis 1C identified here as Palaeolama is an anterior mandibular fragment containing a deciduous lower third premolar (dp3). Prior to this record, the earliest known records of Palaeolama in the United States were from the early Pleistocene at Haile 16A and Leisey Shell Pit faunas of Florida (Morgan and Hulbert, 1995; Webb and Stehli, 1995). The specimen described here represents a significant change in the biochronologic range of Palaeolama in the United States. Fossils from Rancho El Ocote, Mexico, that were described as Palaeolama guanajuatensis are older than the specimen from Inglis 1C, but are here shown to instead represent an early form of Hemiauchenia. Emslie (1998) discussed the Inglis 1C avian fauna, which consists of 27 species and includes the holotype of Scolopax hutchensi and specimens of three other extinct species of birds. Over 5000 identified mammalian fossils were also collected from Inglis 1C, representing 33 species, including the holotype of Peromyscus sarmocophinus (Ruez, 2001). There are abundant amphibian and reptilian fossils from this locality as well, but the herpetofauna is not described. Biochronology of Inglis 1C places it temporally between the older Inglis 1A and younger De Soto Shell Pit faunas of Florida (Ruez, 2001). Both Inglis 1A and De Soto Shell Pit were assigned to the earliest Irvingtonian by Morgan and Hulbert (1995), who list this interval as lasting from 2.0 to 1.6 Ma in the text, but from 1.9 to 1.6 Ma in their figure 5. The most likely age of the Inglis 1C was suggested as approximately 1.9 Ma based on a combination of biochronologic data and glacial fluctuations (Ruez, 2001). The previous earliest records of Palaeolama at Haile 16A and Leisey Shell Pit fall within the late early Irvingtonian, which dates from 1.6 to 1.0 Ma (Morgan and Hulbert, 1995). More specifically, Haile 16A was suggested as most likely deriving from the early half of the late early Irvingtonian (1.6 to 1.3 Ma) by the use of mammalian biochronology (Morgan and Hulbert, 1995). Although the most likely range of the Leisey deposit based on a combination of data (1.5 to 1.1 Ma) overlaps with that of Haile 16A, the latter is considered older based on the presence of Trigonictis, Orthogeomys propinetis, and Sylvilagus webbi (Morgan and Hulbert, 1995). The new record of Palaeolama described here marks a range extension from the ‘late early’ to ‘earliest’ subdivisions of the Irvingtonian landmammal age established for Florida faunas (sensu Morgan and Hulbert, 1995). It is unclear how much absolute time this extension represents. Based on the extremes of the age estimates of the faunas involved, the maximum possible age extension is 700 kyr. It is not possible to specify a minimum age extension using the ages for the biochronologic subdivisions of Morgan and Hulbert (1995), because the oldest age for the ‘late early Irvingtonian’ and the youngest age for the ‘earliest Irvingtonian’ are both 1.6 Ma; although the minimum cannot be specified, it can still be said that Inglis 1C is older than Haile 16A. The above discussion uses the older land-mammal-age subdivisions of Morgan and Hulbert (1995) because they are familiar to students of Florida paleontology and because they give a detailed view of the biochronology of Florida Pliocene and Pleistocene vertebrate localities. More recently, a review of the Pliocene and Pleistocene land-mammal ages in North America used the appearance of Mammuthus to define the Blancan–Irvingtonian boundary (Bell et al., 2004). By this definition, Inglis 1A, Inglis 1C, De Soto Shell Pit, and Haile 16A were considered Blancan, while Leisey was retained in the Irvingtonian. Those authors graphically place Leisey Shell Pit at 1.2 Ma, Haile 16A at 1.45 Ma, and Inglis 1C at 1.8 Ma (Bell et al., 2004:fig. 7.1); by these age estimates, the age extension documented for Palaeolama is 350 kyr.