Josephoartigasia monesi

Josephoartigasia monesi Temporal range: Pliocene to Early Pleistocene 4–2Ma PreЄ Є O S D C P T J K Pg N ↓
Life restoration of J. monesi
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Dinomyidae
Genus:	†Josephoartigasia
Species:	†J. monesi Rinderknecht & Blanco, 2008
Binomial name
Josephoartigasia monesi Rinderknecht & Blanco, 2008

Josephoartigasia monesi, an extinct species of South American caviomorph rodent, is the largest rodent known, and lived from approximately 4 million BC to 2 million BC during the Pliocene to early Pleistocene.^[1][2] The species is one of two in the Josephoartigasia genus, the other being J. magna.^[1] J. monesi is sometimes called the giant pacarana, after its closest living relative, the pacarana (Dinomys branickii) in the family Dinomyidae.^[1] The species may have weighed a ton, considerably larger than its closest living relative, the pacarana.^[1]

Description

Reconstruction of J. monesi head

The skull of the holotype is 53 cm (21 in) long, and the remaining incisor is more than 30 cm (12 in) in length. The total estimated body length is 3 m (10 ft), with a height of 1.5 m (5 ft).

Body mass

There is no dispute that J. monesi replaces Phoberomys pattersoni, a related and somewhat older species that lived in Venezuela during the Late Miocene, as the largest rodent. However, size comparisons are difficult because previous estimates of 400 and 700 kg (880 and 1,540 lb) for P. pattersoni were based on forelimb and hindlimb elements, which are not present in the J. monesi specimen.^[1]

By comparing the skull with various extant species of rodent, the authors of the original paper estimated a mass between 468 and 2,586 kg (1,032 and 5,701 lb), with a median estimate of 1,211 kg (2,670 lb).^[1] A later researcher revisited the numbers and came up with a more conservative estimate of 350 to 1,534 kg (772 to 3,382 lb), with a median of 900 kg (2,000 lb).^[3]

Discovery

J. monesi is known from an almost complete skull, which was recovered from the San José Formation on the coast of Río de la Plata in Uruguay.^[1] Discovered in 1987, but not scientifically described until 2008, the specimen is preserved in Uruguay's National History and Anthropology Museum.^[4]

Paleobiology

The rodent's fearsome front teeth and large size may have been used to fight over females for breeding rights and may also have helped defend against predators, including carnivorous marsupials, saber-toothed cats, and terror birds.^[5]

The rodent may have lived in an estuarine environment or a delta system with forest communities,^[1] and may have eaten soft vegetation.^[6] It has been stated that J. monesi probably fed on aquatic plants and fruits, because its molars are small and not good for grass or other abrasive (vegetation). Larger mammals also have the advantage of access to low-quality food resources, such as wood, that smaller species are unable to digest.^[5]

References