Extinct Giant Ground Sloth
April 2009

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*How Do We Know This? Like living animals, fossil remains of once-living animals are
classified and grouped according to their relationships to each other and to their ancestors.

(Castañeda & Miller 2004) (DeMuizon et al 2004) (Flynn et al 2005) (Gaudin 2004) (McDonald 1996) (McDonald & De Iuliis 2008)
(McKenna & Bell 1997) (McKenna et al 2006) (Steadman et al 2005)

Describer (Date): Paramylodon harlani - Owen 1840
                           Nothrotheriops shastensis - Sinclair 1905
                           Megalonyx jeffersonii - Wistar 1822
Kingdom: Animalia
    Phylum: Chordata
        Class: Mammalia
            Magnorder: Xenarthra (living and extinct armadillos, anteaters, and sloths; extinct glyptodonts)
              Order: Pilosa (anteaters and sloths)
                Suborder: Tardigrada (includes all sloths)
                    Family: Megatheriidae (family is extinct)
                    Family: Mylodontidae (family is extinct)
                           Genus: Paramylodon
                                 Species: Paramylodon harlani
                    Family: Nothrotheriidae (family is extinct)
                            Genus: Nothrotheriops
                                 Species: Nothrotheriops shastensis
                    Family: Megalonychidae (family has extinct and living members)
                             Genus: Megalonyx (extinct)
                                 Species: Megalonyx jeffersoni
                             Genus: Choloepus - Two- toed Sloth (Living)
                    Family: Bradypodidae - Three-toed Sloth
                             Genus: Bradypus - Three- toed Sloth (Living)
                    Family: Myrmecophagidae - includes living Collard and Giant Anteater (family has extinct and living members)
                    Family: Cyclopedidae - includes living Silky Anteater (family has extinct and living members)
Taxonomic History and Nomenclature


*How Do We Know This? Scientists use knowledge of the earth's rocks, global plate tectonic movements,
and the chemical process of fossilization to make sense of fossil distribution patterns and ancient habitats.

(Hoganson & McDonald 2007) (McDonald 1985) (McDonald et al 2004) (Schubert et al 2004)(Spaulding et al 1983)

Prehistoric Distribution:

*How Do We Know This? Careful study of fossil bone or tooth anatomy yields much exact information
about placement and strength of muscles, tendons, ligaments, nerves, and blood vessels.
In rare cases, skin and hair impressions or actual skin or hair is preserved.
Body weight is more difficult to gauge because fat leaves no impression on the skeleton.

(Bargo et al 2000) (Hill 2006) (McDonald 2004, 2006) (Bargo et al 2006) (McNab 1985) (Naples 1989) (Vizcaíno 2008)

Estimated Body Weight: Paramylodon harlani: varied estimates from 1,000 kg (2,205 lb) to 1,089 kg (2,400 lb)
                                      Nothrotheriops shastensis:estimated 250 kg (551 lb) 
                                      Megalonyx jeffersoni: estimated near 1,000 kg (2,205 lb)

Body Length:                Paramylodon harlani: 3 m (9.8 ft.) - bison sized
                                     Nothrotheriops shastensis: - black bear sized
                                    Megalonyx jeffersoni: 3 m (9.8 ft) - bison sized, slightly smaller than Paramylodon

General Description Teeth   Pelage   Sexual Dimorphism Other Physical Characteristics

*How Do We Know This? Since direct observation of a fossil animal's behavior isn't possible, paleontologists
use comparison and contrast with living animals for guidance. Tracks can sometimes reveal further clues.

(Fariña and Blanco 1996)(France et al 2007)(McDonald & DeIuliis 2008)(McDonald & Pelikan 2005) (Vizcaíno et al 2001) (Vizcaíno et al 2008)


Locomotion Interspecies Interaction

*How Do We Know This? Clues to fossil mammals' diets come from teeth,skull shape,
from fossil dung and gut contents, from lab analysis of oxygen isotopes in bone and teeth,
and by looking at diets of similar modern animals.

(Bargo et al 2006) (Coltrain et al 2004)(Fariña and Blanco1996) (France et al 2007) (Hansen 1978) (Martin 1975)(Poinar et al 1998) (Ruez 2005)

*How do We Know This? Isotope studies of elements present fossil bones and tusks
in microscopic quantities give information about timing of reproductive stress, and timing of nursing.
Clues to stages of development come from tooth replacement patterns and closure of sutures
in skull and limb bones.

(Auler & Smart 1999) (Brenzel & Semken 2006)(Hill & Gillette 1985)

Life Stages

*How do We Know This? Abnormalities in fossil bones may show
evidence of arthritis, cancer, nutritional stress, fractures and more.

(McDonald 1989)

Important Web Resources (including where to view fossils in museums):

©2009 San Diego Zoo Global. Disclaimer: Although San Diego Zoo Global makes every attempt to provide accurate information, some of the facts may become outdated or replaced by new research findings. Questions and comments may be addressed to library@sandiegozoo.org.

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