''Megalonyx'' (
Greek
Greek may refer to:
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group
*Greek language, a branch of the Indo-European language family
**Proto-Greek language, the assumed last common ancestor of all kno ...
, "great-claw") is an extinct
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
ground sloth
Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. They varied widely in size with the largest, belonging to genera '' Lestodon'', ''Eremotherium'' and ''Megatherium'', being around the size of elephants. ...
s of the
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Megalonychidae, native to North America. It evolved during the
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58[Late Pleistocene
The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...](_blank)
, living from ~5 million to ~13,000 years ago.
The
type species
In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, ''M. jeffersonii'' (also called Jefferson's ground sloth), the youngest and largest known species, measured about in length and weighed up to .
''Megalonyx'' is suggested to have descended from ''
Pliometanastes,'' a genus of ground sloth that had arrived in North America during the Late
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
around 9 million years ago, prior to the main phase of the
Great American Interchange
The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which land ...
. ''Megalonyx'' had the widest distribution of any North American ground sloth, having a range encompassing most of the contiguous United States, extending as far north as Alaska during warm
interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
periods.
''Megalonyx'' is notable for having been originally described by future U.S. President
Thomas Jefferson
Thomas Jefferson (, 1743July 4, 1826) was an American Founding Fathers of the United States, Founding Father and the third president of the United States from 1801 to 1809. He was the primary author of the United States Declaration of Indepe ...
in 1799 based on remains found in West Virginia; the species ''M. jeffersonii'' was described later, named in honor of him.
''Megalonyx'' became extinct as part of the
end-Pleistocene extinction event, simultaneously with all other mainland ground sloths and most other large mammals native to the Americas. These extinctions followed the
arrival of humans in the Americas, and there is evidence that humans interacted with ''Megalonyx'', including butchering its remains shortly prior to its extinction.
Taxonomy

In 1796, Colonel
John Stuart sent
Thomas Jefferson
Thomas Jefferson (, 1743July 4, 1826) was an American Founding Fathers of the United States, Founding Father and the third president of the United States from 1801 to 1809. He was the primary author of the United States Declaration of Indepe ...
, shortly before he took office as
Vice President of the United States
The vice president of the United States (VPOTUS) is the second-highest ranking office in the Executive branch of the United States government, executive branch of the U.S. federal government, after the president of the United States, and ranks f ...
, some fossil bones: a
femur
The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg.
The Femo ...
fragment,
ulna
The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...
,
radius
In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...
, and foot bones including three large claws. The discoveries were made in a cave in
Greenbrier County, Virginia (presently
West Virginia
West Virginia is a mountainous U.S. state, state in the Southern United States, Southern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States.The United States Census Bureau, Census Bureau and the Association of American ...
). Jefferson examined the bones and presented his observations in the paper "A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia" to the
American Philosophical Society
The American Philosophical Society (APS) is an American scholarly organization and learned society founded in 1743 in Philadelphia that promotes knowledge in the humanities and natural sciences through research, professional meetings, publicat ...
in
Philadelphia
Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...
on March 10, 1797.
[Jefferson, Thomas,]
A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia
, Read before the American Philosophical Society, March 10, 1797. The paper was published in 1799, in the same volume as an accompanying paper by his colleague
Caspar Wistar, who provided detailed anatomical information about the bones, and illustrated them. Together these two papers are considered the first North American publications devoted to paleontology.
In the 1799 paper, Jefferson named the then-unknown animal ''Megalonyx'' ("great-claw") and compared each recovered bone to the corresponding bone in a
lion
The lion (''Panthera leo'') is a large Felidae, cat of the genus ''Panthera'', native to Sub-Saharan Africa and India. It has a muscular, broad-chested body (biology), body; a short, rounded head; round ears; and a dark, hairy tuft at the ...
.
In his original draft of the paper, Jefferson thought the animal was a carnivore, one of the large cats, writing “Let us only say then, what we may safely say, that he was more than three times as large as the lion”. In a postscript, composed after learning of Baron Georges Cuvier's description and illustration of the giant ground sloth ''
Megatherium
''Megatherium'' ( ; from Greek () 'great' + () 'beast') is an extinct genus of ground sloths endemic to South America that lived from the Early Pliocene through the end of the Late Pleistocene. It is best known for the elephant-sized type spe ...
,'' discovered in Argentina (mistakenly referred to as Paraguay), Jefferson revised his interpretation and compared ''Megalonyx'' to ''Megatherium''.
Contrary to Baron Cuvier's view that
extinction
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
had played an important role in natural history, an idea that would reach scientific consensus decades later, Jefferson wrote about a "completeness of nature" whose inherent balance did not allow species to go extinct naturally. He asked
Lewis and Clark
Lewis may refer to:
Names
* Lewis (given name), including a list of people with the given name
* Lewis (surname), including a list of people with the surname
Music
* Lewis (musician), Canadian singer
* " Lewis (Mistreated)", a song by Radiohe ...
, as they planned their famous expedition in 1804–1806, to keep an eye out for living specimens of ''Megalonyx'', as this would support his case. His idea made no headway and was later shown to be incorrect. However, Jefferson's notion that humans and ''Megalonyx'' co-existed in North America has been shown to be correct, as some bones of ''Megalonyx'' show marks made by flint tools.
His presentation to the American Philosophical Society in 1797 is often credited as the beginning of
vertebrate paleontology
Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossilized remains, the behavior, reproduction and appearance of extinct vertebrates (animals with vertebrae and their descendants). It also t ...
in
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
. In 1799,
Caspar Wistar correctly identified the remains as those of a giant ground sloth. In 1822, Desmarest named the species ''Megatherium jeffersonii'' in honor of the former statesman and scientist, although he classified it in the genus ''Megatherium'' instead.
Richard Harlan in 1825 revived the genus ''Megalonyx'' with the type species ''M. jeffersonii'', and provided additional taxonomic description''.'' Scientific papers variously give the
authority
Authority is commonly understood as the legitimate power of a person or group of other people.
In a civil state, ''authority'' may be practiced by legislative, executive, and judicial branches of government,''The New Fontana Dictionary of M ...
for the genus as Jefferson 1799 (after Jefferson's original naming of the genus), or Harlan 1825.
Most authors gave Jefferson as the authority on the genus until a 1942 paper by
George Gaylord Simpson
George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...
, who suggested that the attribution of the authority to Jefferson “is certainly erroneous,”, and suggested that Harlan “may have been the first to use the name in a valid Linnaean form”. A 2024 review paper by
Loren E. Babcock found that Simpson's views were mistaken, and clarified that Jefferson was the valid author of the genus, as the description was done in accordance with the rules of taxonomic nomenclature at the time, despite him not assigning a species to it.
Recent research confirms that the sloth bones were discovered in
Haynes Cave in
Monroe County, West Virginia
Monroe County is a County (United States), county in the U.S. state of West Virginia. As of the 2020 United States census, 2020 census, the population was 12,376. Its county seat is Union, West Virginia, Union.
Monroe County was the home of A ...
. For many decades in the twentieth century, the reported origin of Jefferson's "Certain Bones" was
Organ Cave
Organ Cave is a large and historic cave in Greenbrier County, West Virginia, Greenbrier County, West Virginia, USA. The Organ Cave, West Virginia, surrounding community takes its name from the cave.
In 1973, the Organ Cave System—also known ...
in what is now
Greenbrier County, West Virginia
Greenbrier County () is a county in the U.S. state of West Virginia. As of the 2020 census, the population was 32,977. Its county seat is Lewisburg. The county was formed in 1778 from Botetourt and Montgomery Counties in Virginia.
History
P ...
. This story was popularized in the 1920s by a local man, Andrew Price of
Marlinton
Marlinton is a town in and the county seat of Pocahontas County, West Virginia, United States. The population was 998 at the 2020 United States Census, 2020 census. Located along the Greenbrier River, it is known for its scenery.
History
Marlint ...
. The story came under scrutiny when in 1993 two fragments of a ''Megalonyx''
scapula
The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...
were found in Haynes Cave in neighboring Monroe County.
Smithsonian paleontologist
Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
Frederick Grady presented evidence in 1995 confirming Haynes Cave as the original source of Jefferson's fossil.
[Grady, Fred (1995)]
"The Search for the Cave from which Thomas Jefferson Described the Bones of the ''Megalonyx''"
bstract In: "Selected Abstracts from the 1995 National Speleological Society National Convention in Blacksburg, Virginia"; In: '' Journal of Cave and Karst Studies'', April 1997, pg 57.
Jefferson reported that the bones had been found by
saltpeter
Potassium nitrate is a chemical compound with a sharp, salty, bitter taste and the chemical formula . It is a potassium salt of nitric acid. This salt consists of potassium cations and nitrate anions , and is therefore an alkali metal nitrate ...
workers. He gave the cave owner's name as Frederic Crower. Correspondence between Jefferson and Colonel Stuart, who sent him the bones, indicates that the cave was located about five miles from Stuart's home and that it contained
saltpeter
Potassium nitrate is a chemical compound with a sharp, salty, bitter taste and the chemical formula . It is a potassium salt of nitric acid. This salt consists of potassium cations and nitrate anions , and is therefore an alkali metal nitrate ...
vats. An investigation of property ownership records revealed "Frederic Crower" to be an apparent misspelling of the name Frederic Gromer.
Organ Cave was never owned by Gromer, but Haynes Cave was. Two letters written by Tristram Patton, the subsequent owner of Haynes Cave, indicate that this cave was located in Monroe County near
Second Creek. Monroe County had originally been part of Greenbrier County; it became a separate county shortly after the discovery of the bones. In his own letters Patton described the cave and indicated that more fossil bones remained inside.
''M. jeffersonii'' is still the most commonly identified species of ''Megalonyx''. It was designated the
state fossil
Most states in the US have designated a state fossil, many during the 1980s. It is common to designate a fossilized species, rather than a single specimen or a category of fossils. State fossils are distinct from other state emblems like state d ...
of
West Virginia
West Virginia is a mountainous U.S. state, state in the Southern United States, Southern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States.The United States Census Bureau, Census Bureau and the Association of American ...
in 2008.
''M. leptostomus,'' named by Cope (1893), lived from the Blancan to the Irvingtonian. This species lived from Florida to Texas, north to Kansas and Nebraska, and west to New Mexico, Nevada, Oregon, and Washington. It is about half the size of ''M. jeffersonii''. It evolved into ''M. wheatleyi'', the direct ancestor of ''M. jeffersonii''. Species gradually got larger, with different species mostly based on size and geologic age.
Evolution
The first wave of Megalonychids came to North America by island-hopping across the
Central American Seaway
The Central American Seaway (also known as the Panamanic Seaway, Inter-American Seaway and Proto-Caribbean Seaway) was a body of water that once separated North America from South America. It formed during the Jurassic (200–154 year#Abbreviation ...
from
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
, where ground sloths arose, prior to formation of the
Panamanian land bridge. Based on molecular results, its closest living relatives are the
three-toed sloth
The three-toed or three-fingered sloths are arboreal neotropical mammals. They are the only members of the genus ''Bradypus'' (meaning "slow-footed") and the family Bradypodidae. The five living species of three-toed sloths are the brown-throa ...
s (''Bradypus''); earlier morphological investigations came to a different conclusion.
''Megalonyx'' is thought to be descended from ''
Pliometanastes'', a ground sloth that arrived in North America during the late Miocene, around 9 million years ago.
The earliest representatives of ''Megalonyx'' appeared during the Pliocene.
''M. jeffersonii'' lived from the late
Middle Pleistocene
The Chibanian, more widely known as the Middle Pleistocene (its previous informal name), is an Age (geology), age in the international geologic timescale or a Stage (stratigraphy), stage in chronostratigraphy, being a division of the Pleistocen ...
/ late
Irvingtonian
The Irvingtonian North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), spanning from 1.8 million – 250,000 years Before Present, BP. (250–300,000 years ago)
through to the
Rancholabrean of the
Late Pleistocene
The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...
(11,000 BP
). ''M. jeffersonii'' was probably descended from ''M. wheatleyi.'' The ''Megalonyx'' lineage increased in size with time, with the last species ''M. jeffersonii'' being the largest.
Description
''Megalonyx jeffersonii'' was a large, heavily built herbivore about long.
It was comparable in size to a cow, with some specimens estimated to exceed in mass.
The hind limbs were
plantigrade
151px, Portion of a human skeleton, showing plantigrade habit
In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. ...
(flat-footed) and this, along with its stout tail, allowed it to rear up into a semi-erect position to feed.
The hands had three large claws, which were likely used for grasping and defense.
The teeth of ''Megalonyx jeffersonii'' were hypselodont (high crowned).
Paleobiology
During excavations at Tarkio Valley in southwest
Iowa
Iowa ( ) is a U.S. state, state in the upper Midwestern United States, Midwestern region of the United States. It borders the Mississippi River to the east and the Missouri River and Big Sioux River to the west; Wisconsin to the northeast, Ill ...
, an adult (presumably female) ''Megalonyx jeffersonii'' was found in direct association with two juveniles of different ages, the oldest suggested to be around 3-4 years old, suggesting that adults cared for young of different generations.
A 2022 study estimated, based on the ages of the adult and the two juveniles, that the average lifespan was approximately 19 years, sexual maturity occurred at about 6 and a half years, that
gestation time was around 14 months, and the interval between births was approximately 3 years.
''Megalonyx'' is thought to have been a
browser.
Habitat
''Megalonyx jeffersonii'' ranged over much of North America, with its range spanning nearly the whole contiguous United States and parts of southern Canada, with some remains known as far south as central Mexico.
Their remains have been found as far north as
Alaska
Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...
and the
Yukon
Yukon () is a Provinces and territories of Canada, territory of Canada, bordering British Columbia to the south, the Northwest Territories to the east, the Beaufort Sea to the north, and the U.S. state of Alaska to the west. It is Canada’s we ...
during
interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
intervals.
The sloth ranged as far northeast as
New York.
In 2010, a specimen was discovered at the
Ziegler Reservoir site near Snowmass Village, Colorado, in the Rocky Mountains at an elevation of . The habitat of ''Megalonyx jeffersonii'' was highly variable,
but often associated with
spruce
A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...
-dominated, mixed
conifer
Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
-
hardwood forest.
Extinction
''Megalonyx jeffersonii'' became extinct at the end of the Pleistocene, as part of the
Quaternary extinction event
The Late Pleistocene to the beginning of the Holocene saw the extinction of the majority of the world's megafauna, typically defined as animal species having body masses over , which resulted in a collapse in faunal density and diversity acro ...
, in which all other mainland ground sloths and most other large mammals of the Americas became extinct.
The youngest confirmed radiocarbon date is in Ohio, dating to 13,180–13,034
calibrated
In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...
years
Before Present
Before Present (BP) or "years before present (YBP)" is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because ...
.
This timing was co-incident with both the
Younger Dryas
The Younger Dryas (YD, Greenland Stadial GS-1) was a period in Earth's geologic history that occurred circa 12,900 to 11,700 years Before Present (BP). It is primarily known for the sudden or "abrupt" cooling in the Northern Hemisphere, when the ...
and a major growth in population of recently arrived
Paleoindians
Paleo-Indians were the first peoples who entered and subsequently inhabited the Americas towards the end of the Late Pleistocene period. The prefix ''paleo-'' comes from . The term ''Paleo-Indians'' applies specifically to the lithic period in ...
. In Ohio, a specimen of ''Megalonyx jeffersonii'', dubbed the "Firelands Ground Sloth", dating to around 13,738 to 13,435 calibrated years
Before Present
Before Present (BP) or "years before present (YBP)" is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because ...
(~11,788 to 11,485
BCE) was found with cut marks indicative of butchery, suggesting that hunting may have played a role in its extinction.
See also
* ''
Paramylodon'' a mylodontid ground sloth native to North America during the Pliocene and Pleistocene
* ''
Nothrotheriops'' a nothrotheriid ground sloth native to North America during the Pleistocene
References
Citations
Other sources
* (1871) Preliminary report on the vertebrata discovered in the
Port Kennedy Bone Cave. ''American Philosophical Society'', 12:73-102.
* (1893) A preliminary report on the vertebrate paleontology of the Llano Estacado. ''4th Annual Report on the Geological Survey of Texas'': 136pp.
* (1968) Plio-Pleistocene megalonychid sloths of North America. ''Bulletin of the Florida State Museum Biological Sciences'', 12(5):213-296.
External links
''Sloth Central''Smithsonian National Zoological Park: At the Zoo - Slow and Steady Sloths
{{Taxonbar, from=Q134380
Prehistoric sloths
Prehistoric placental genera
Pliocene xenarthrans
Pliocene mammals of North America
Pleistocene xenarthrans
Pleistocene mammals of North America
Blancan
Hemphillian
Irvingtonian
Rancholabrean
Fossils of Canada
Fossils of Guatemala
Fossils of Honduras
Fossils of Mexico
Fossils of the United States
Symbols of West Virginia
Ringold Formation Miocene Fauna
Younger Dryas
Quaternary species extinctions
Thomas Jefferson
Fossil taxa described in 1799