Josephoartigasia

Josephoartigasia is an extinct genus of enormous dinomyid rodent from the Early Pliocene to Early Pleistocene of Uruguay. It is named after the Uruguayan national hero José Artigas and is closely related to the living pacarana. Scientists have identified two species of Josephoartigasia: J. magna, found in 1966, and J. monesi, discovered in 2008.

The species J. monesi is the biggest rodent ever discovered. Its skull was about 53 cm long, similar to that of a beef cow. Based on this, scientists estimate that J. monesi could have been about 262.8 cm long and weighed between 480 and 500 kg. This makes it much larger than today’s largest rodent, the capybara.

Josephoartigasia lived in forested areas near water, together with many other large ancient animals like ground sloths, glyptodonts, and terror birds. These giant rodents mostly ate leaves and fruits, but their strong jaws could also help them crack nuts or dig for food.

Discovery and etymology

The rodent was first described based on fossils found in the sea cliffs near Kiyú beach in Uruguay. These fossils include parts of a lower jaw and teeth. In 1966, Uruguayan scientists named it Artigasia magna after the Uruguayan hero José Artigas.

In 2007, the name was changed to Josephoartigasia because another scientist had already used the name Artigasia for a type of parasite. In 2008, scientists found and described an almost complete skull, naming the new species J. monesi to honor another scientist who studied South American rodents.

Classification

Josephoartigasia belongs to the family Dinomyidae, a group of special rodents from South America called hystricognaths. These rodents are mainly found in Argentina, Colombia, Venezuela, and Uruguay. The only living member of this family today is the pacarana, which is one of the largest rodents in the world, weighing about 15 kilograms or 33 pounds.

Josephoartigasia is part of a subgroup called Eumegamyinae within the Dinomyidae family. This family is not very well understood because scientists mostly know about these rodents from pieces of their teeth and jaws, making it hard to tell how all the different species are related.

Age and taphonomy

In 1965, scientists Frances and Mones divided the rock layers in Barrancas de San Gregorio into three parts and dated them to different time periods, linking them to the Montehermosan, Chapadmalalan, and Pampean (Ensenadan) Ages based on the South American land mammal age geological timescale. These correspond to the Upper Pliocene and the Pleistocene on the international geologic time scale.

The fossil of J. magna was not found in its original spot, but scientists believed it came from one of the older rock layers, possibly the San José Formation, due to its large size. The San José Formation includes materials carried by rivers and streams, along with certain types of sandstones and other minerals. Later, in 1966, geologists Goso and Bossi defined the Raigón Formation, and in 2002, it was suggested that this formation could span a long time period from the Montehermosan to the Ensenadan. The fossil of J. monesi was found in a specific rock layer made of siltstone, claystone, and sandstone.

Description

Josephoartigasia is an extinct genus of huge rodents from Uruguay, closely related to the modern pacarana. It is named after José Artigas, a Uruguayan national hero.

The teeth of Josephoartigasia grew continuously, like all rodents. It had a dental formula of 1.0.1.3¹.0.1.3, meaning it had one incisor, no canines, one premolar, and three molars in each half of each jaw. The grinding teeth had special ridges called lophs, with varying amounts of enamel on their surfaces.

The skull of J. monesi was massive, measuring about 53 cm (1 ft 9 in) long—bigger than the skulls of modern beef cows and larger than any previously known rodent skull. The skull bones were fused together in some areas, and it had a strong muscle attachment for powerful biting. The body mass estimates for J. monesi vary widely, but all suggest it was the largest known rodent, possibly weighing over a ton.

Paleobiology

Scientists have studied how strong the bite of Josephoartigasia was. They found that this huge rodent could bite with a force similar to large carnivores like polar bears and jaguars. Its strong incisors and reinforced skull suggest it could either dig for food or defend itself against predators like terror birds.

Early guesses about its diet thought it ate soft plants, but later studies showed it could eat a wide variety of foods, both hard and soft. Analysis of its teeth suggests it ate leaves and fruits, similar to modern capybaras.

Paleoecology

Josephoartigasia lived in what is now Uruguay during the time between the Pliocene and Pleistocene epochs. Scientists have found fossils of this giant rodent along with many other ancient animals, including large ground sloths, glyptodonts like Glyptodon, a big darter bird called Giganhinga, and the vampire bat Desmodus draculae. These findings suggest the area was a forested environment near water.

The climate during this period changed from dry to warmer and more humid, which helped forests grow. This change happened around the time the world entered what is known as the Quaternary glaciation.