''Hapalops'' is an extinct genus of ground sloth from the Early to Late Miocene of

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

(

Solimões Formation The Pebas Formation is a lithostratigraphic unit of Miocene age, found in western Amazonia. The formation extends over , including parts of Brazil, Peru, Ecuador and Colombia.Wesselingh et al., 2006 It is interpreted as representing the deposit ...

), Bolivia ( Honda Group), Colombia ( Honda Group),Croft, 2007, p.300 and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

(

Santa Cruz Formation The Santa Cruz Formation is a geological formation in the Magallanes/Austral Basin in southern Patagonia in Argentina and in adjacent areas of Chile. It dates to the late Early Miocene epoch, and is contemporaneous with eponymous Santacrucian ...

) in South America.''Hapalops''
at Fossilworks.org

History

''Hapalops'' was first described by notable Argentine paleontologist and zoologist

Florentino Ameghino Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especially ...

in 1887, with his description of ''H. rectangularis'' as the type species. It was erected based on the posterior part of a left dentary that had been collected from the

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 ...

aged deposits of Santa Cruz, Argentina, though Ameghino also described a second partial mandible from the same deposits as part of the species, making it a paratype. All of these of these fossils have been lost and their fragmentary status puts the validity of the genus as a whole in jeopardy.

Description

Sloths in this genus had a long, robust body with more than 19 thoracic vertebrae, a short

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

, and long limbs with large, curved

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...

s. They were small sloths, measuring about in length. On the ground, they probably walked on the knuckles of the forelimbs, like a

gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...

. ''Hapalops'' had very few teeth with no

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s; the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

included only four pairs of teeth.

Paleobiology

In the Santa Cruz, ''Hapalops'' fed on vegetation in intertropical wooded savannahs. It shared its environment with both herbivorous and predatory

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

s, sheep-sized glyptodonts, armadillos, anteaters,

toxodonts Toxodontia. Retrieved April 2013. is a suborder of the meridiungulate order Notoungulata. Most of the members of the five included families, including the largest notoungulates, share several dental, auditory and tarsal specializations. The g ...

typotheres Typotheria is a suborder of the extinct mammalian order Notoungulata and includes five families: Archaeopithecidae, Campanorcidae, Interatheriidae, Mesotheriidae, and Oldfieldthomasiidae. CifelliCifelli, Richard L. 1993. The phylogeny of the ...

, and

litopterns Litopterna (from grc, λῑτή πτέρνα "smooth heel") is an extinction, extinct order of fossil hoofed mammals from the Cenozoic era. The order is one of the five great orders of Meridiungulata, South American ungulates that were endemic to ...

, as well as modern reptiles such as iguanas and birds such as rheas, geese, and hawks. Giant phorusrachid "terror birds" lived in the region and may have been the top predators. Like most extinct

sloths Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their l ...

it is categorized as a ground sloth, but it is believed that the smaller size of ''Hapalops'' allowed it to engage in some climbing behaviors.

Classification

The genus is classified within the Megatherioidea, which includes the

megalonychid Megalonychidae is an extinct family of sloths including the extinct ''Megalonyx''. Megalonychids first appeared in the early Oligocene, about 35 million years (Ma) ago, in southern Argentina (Patagonia). There is actually one possible find dating ...

and the nothrotheriid sloths. While it is generally represented as an outgroup to Nothrotheriidae and a genus of uncertain relationships, it shows most of the character states that diagnose Nothrotheriidae and may be a close relative. At least 26 species in this genus have been named from the same Santa Cruz formation, a biological impossibility largely based on assigning new species names to fossil fragments. The genus awaits revision.

References

Bibliography

* {{Taxonbar, from=Q2261453 Prehistoric sloths Prehistoric placental genera Miocene xenarthrans Miocene mammals of South America Huayquerian Chasicoan Mayoan Laventan Colloncuran Friasian Santacrucian Neogene Argentina Fossils of Argentina Neogene Bolivia Fossils of Bolivia Neogene Brazil Fossils of Brazil Neogene Colombia Fossils of Colombia Honda Group, Colombia Fossil taxa described in 1887 Taxa named by Florentino Ameghino