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Class Mammalia
Order Pilosa
Family Megalonychidae


Megalonyx leptostomus—Narrow-mouthed Sloth //Megalonyx jeffersonii—Jefferson's Ground Sloth //Megalonyx wheatleyi—Wheatley's Ground Sloth

Megalonyx sp.—Megalonyx Ground SlothsRegional Pleistocene distribution of Megalonyx sp.

Kurtén and Anderson (1980) noted that the family is diagnosed as having a pair of self-sharpening cutting caniniform teeth with a greatly reduced pre-dentary spout. Size tended to increase from its appearance in the late Hemphillian through the Pliocene and Rancholabrean. The Rancholabrean species, Megalonyx jeffersonii, occurred as far north as Alaska and the Northwest Territories of Canada (Kurtén and Anderson 1980).

Megalonyx skeleton

Fig. 1. Megalonyx skeleton at the Museum of Comparative Zoology, Harvard. Wikipedia Commons image by Gainett under the Creative Commons Attribution-Share Alike 3.0 license.


Irvingtonian: Bautista Badlands (Frick 1921; (accessed 25 Apr 2014: ?)).

Early Irvingtonian: El Casco, San Timoteo Badlands (Albright 2000).

?Irvingtonian/Rancholabrean: Emery Borrow Pit (Jefferson 1991b).

Irvingtonian/Rancholabrean: Manix Lake (Jefferson 1991b).

Rancholabrean: Campbell Hill (Jefferson 1991b); Centinella Park (Jefferson 1991b); San Pedro Lumber Yard (Jefferson 1991b); Tule Springs 2 (Jefferson et al. 2015); Tule Springs 4 (Jefferson et al. 2015).

Sangamon: Chandler Sand Pit, Rolling Hills Estates (Jefferson 1991b); San Pedro Lumber Co. (Jefferson 1991b).

Mid Wisconsin: McKittrick (Schultz 1937: ?).

Late Wisconsin: La Mirada (Jefferson 1991b); Tule Springs (Mawby 1967: ? gen.).

Literature. Albright 2000; Frick 1921; Jefferson 1991b; Jefferson et al. 2015; Kurtén and Anderson 1980; Mawby 1967; Schultz 1937.


Megalonyx jeffersonii Desmarest 1822—Jefferson's Ground SlothRegional Pleistocene distribution of Megalonyx jeffersonii.

Jefferson's Ground Sloth was the largest of the North American megalonychid ground sloths (Kurtén and Anderson 1980).


Rancholabrean: Coconino Cavern (Mead et al. 2005); Springerville (McDonald et al. 2004); Tule Springs (Springer et al. 2005)

Sangamon: Beacon and Second streets, San Pedro (Jefferson 2014); Newport Bay Mesa (Jefferson 1991b; cf.)

Mid/Late Wisconsin: Diamond Valley (Springer et al. 2009); Rancho La Brea (Stock and Harris

Literature. Kurtén and Anderson 1980; McDonald et al. 2004; Mead et al. 2005; Springer et al. 2005, 2009; Stock and Harris 1992.


Megalonyx leptostomus/wheatleyi—Narrow-mouthed or Wheatley's Ground SlothPleistocene distribution of Megalonyx leptostomus/wheatleyi.


Late Blancan/Early Irvingtonian: Elsinore: Mimomys (Pajak et al. 1996).

Literature. Pajak et al. 1996.


Megalonyx leptostomus Cope 1893—Narrow-mouthed SlothPleistocene distribution of Megalonyx leptostomus.

Kurtén and Anderson (1980) noted that this taxon was widespread by the middle Pliocene and probably was ancestral to the larger and geologically later Megalonyx wheatleyi.


Late Blancan: 111 Ranch (Morgan and White 2005); La Union Fauna (La Union Local Fauna) (McDonald and Morgan 2011); La Union Fauna (Santa Teresa Local Fauna) (McDonald and Morgan 2011).

Literature. Kurtén and Anderson 1980; McDonald and Morgan 2011.


Megalonyx wheatleyi Cope 1871—Wheatley's Ground SlothPleistocene distribution of Megalonyx wheatleyi.

Vanderhill (1986) examined a nearly complete left femur that represents Megalonyx wheatleyi. It is intermediate in size between the Blancan/Early Irvingtonian M. leptostomus and smaller than M. jeffersonii. The specimen lacks stratigraphic data, but likely comes from the upper 45 m of Rio Grande Valley fill (Vanderhill 1986). This is the specimen referenced by Morgan and Lucas (2003, 2005).


Late Blancan/Irvingtonian: Anza-Borrego (Murray 2008).

Irvingtonian: El Golfo (Croxen et al. 2007).

Early Irvingtonian: Adobe Ranch (McDonald and Morgan 2011; Morgan and Lucas 2003, 2005; Vanderhill 1986).

Medial Irvingtonian: Gutierrez Gravel Pit (McDonald and Morgan 2011: cf.).

Literature. Croxen et al. 2007; McDonald and Morgan 2011; Morgan and Lucas 2003, 2005; Murray 2008; Vanderhill 1986.


Last Update: 15 Apr 2015