Top figure Neofiber alleni

UF 206588, a composite skull belonging to this species

Neofiber alleni

Quick Facts

Common Name: round-tailed muskrat, Florida water rat

This large aquatic rodent is a relative of voles and lemmings.

Although today restricted to Florida and southern Georgia, in the Pleistocene the species lived as far north as South Carolina and possibly West Virginia.

Age Range

Scientific Name and Classification

Neofiber alleni True, 1884

Source of Species Name: This species was named after Professor J. A. Allen, a prominent zoologist and friend of Frederick W. True, curator of mammology at the then U.S. National Museum, who originally named this species.

Classification: Mammalia, Eutheria, Euarchontoglires, Rodentia, Myomorpha, Muroidea, Cricetidae, Avricolinae, Neofibrini

Alternate Scientific Names: none

Figure 1 Neofiber alleni

Figure 1. Map of Florida, with highlights indicating counties where fossils of the species have been found

Overall Geographic Range

Currently, the round-tailed muskrat is found in much of peninsular Florida and in southeastern Georgia (Birkenholz, 1972). Fossils of Neofiber alleni have been identified from many localities in Florida, as well as from the Ladds Cave, northwestern Georgia (Frazier, 1977), the Isle of Hope Site in coastal Georgia (Hulbert and Pratt, 1998), two localities in coastal South Carolina (Saunders, 2002), and possibly Trout Cave in West Virginia (Grady and Garton, 2000). The type locality of this species is Georgiana, Brevard County, Florida (True, 1884b).

Florida Fossil Occurrences

Full list of fossil sites (Click to View)


Rodentia is an order of mammals comprising a large diversity of animals such as rats, mice, squirrels, capybaras, porcupines, and beavers. Neofiber alleni is an extant species of rodent commonly known as the round-tailed muskrat or the Florida water rat. Generally, the Florida water rat is a brown-furred, semi-aquatic inhabitant of wet enivornments rich in vegetation such as swamps and marshes, where it feeds on aquatic grasses. Unlike the muskrat Ondatra zibethicus, which has a flattened tail, the Florida water rat has a tail that is round in cross-section. It is approximately 26 cm (10.2 in) to 38 cm (15.0 in) long from the tip of the nose to the tail, and is intermediate in size between the muskrat and the meadow vole, Microtus pennsylvnicus (Meade, 1952; Birkenholz, 1972; Frazier, 1977). More information about the extant species can be found here.

Neofiber alleni is closely related to Ondatra zibethicus, and the two species are considered to be more closely related to each other than to any other living species. They belong to a subfamily of rodents known as Avricolinae which comprises of some 30 genera and 150 species commonly called voles, lemmings, and muskrats (Robovsky et al., 2007).

Figure 2 Neofiber alleni cranium

Figure 2. UF 206588, a composite skull of Neofiber alleni in A) occlusal, B) dorsal, and C) right lateral views. Abbreviations: I1= lower first incisor; I1= upper first incisor; M1= upper first molar; M2= upper second molar; M3= upper third molar.

Figure 3 Neofiber alleni cranium 2

Figure 3. UF 2139, a partial cranium of Neofiber alleni in A) right lateral and B) occlusal views, and C) a closeup of the dentition in occlusal view. Scale = 5mm. Dental abbreviations as in Figure 2; o.s. = the triangular occluding surfaces of the tooth; r.a. = reentrant angles or folds in the tooth.

The genus Neofiber first appears in the fossil record in the middle Pleistocene of North America in the form of the extinct Leonard’s muskrat, Neofiber leonardi (Hibbard, 1943; Frazier, 1977). Neofiber leonardi is known from fossils in Texas, the Great Plains, Virginia, and Florida (Frazier, 1977; Kasper, 1992). The oldest fossils of Neofiber alleni are from the late Irvingtonian Coleman 2A locality in Sumter County, Florida (Matin, 1974). Based on the similarity and overlapping degrees of variation in the morphology of the teeth through time, it is thought that Neofiber alleni evolved from Neofiber leonardi sometime in the middle Pleistocene (Frazier, 1977; Kasper, 1992). Currently, Neofiber is restricted to Florida and southeastern Georgia, possibly due to their reliance on warm aquatic habitats (Frazier, 1977). But its range was much wider in the Pleistocene.

Like other cricetid rodents, Neofiber alleni does not have any premolar teeth in its upper and lower dentition. Like other avricoline rodents, Neofiber alleni has molar teeth that are characterized by an occlusal surface that looks like a series of triangles (Hulbert, 2001). The skull of Neofiber alleni is similar to that of the common muskrat, Ondatra zibethicus, but is smaller (Frazier, 1977). Neofiber alleni may be differentiated from Neofiber leonardi on the basis of the morphology of their molar teeth. Neofiber leonardi have molars with relatively antero-posteriorly compressed triangular occluding surfaces and antero-posteriorly wider reentrant angles. Furthermore, the anteroexternal column on the lower third molar is better defined in Neofiber leonardi compared to Neofiber alleni.

Figure 4 Neofiber alleni mandible

Figure 4. UF 129196, a left dentary of Neofiber alleni in A) medial, B) left lateral, and C) occlusal views, and D) a closeup of the dentition in occlusal view. Abbreviations: a.e.c= anteroexternal column of the third molar; I1= first incisor; M1= first molar; M2= second molar; M3= third molar. Scale= 5mm.

Figure 5 Neofiber alleni

Figure 5. A right humerus (UF 7675) of Neofiber alleni in A) anterior and B) posterior views and a right femur (UF 7676) B) anterior and D) posterior views.


  • Original Author: Arianna Harrington
  • Original Completion Date: May 15, 2015
  • Editor:  Richard C. Hulbert Jr. and Natali Valdes
  • Last Updated On: May 29, 2015
Scientific References (Click to View)


This material is based upon work supported by the National Science Foundation under Grant Number CSBR 1203222, Jonathan Bloch, Principal Investigator. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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