Josephoartigasia

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

The species J. monesi is the largest rodent ever found. Its skull was about 53 cm long, about the size of a beef cow. Scientists think 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 biggest rodent, the capybara.

Josephoartigasia lived in forests near water, with many other large ancient animals like ground sloths, glyptodonts, and terror birds. These huge 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 found in fossils near Kiyú beach in Uruguay. The fossils included a lower jaw and teeth. In 1966, scientists in Uruguay named it Artigasia magna after the hero José Artigas.

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

Classification

Josephoartigasia belongs to the family Dinomyidae, a group of special rodents from South America. These rodents are found mainly in Argentina, Colombia, Venezuela, and Uruguay. The only living member of this family today is the pacarana. It 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. Scientists do not know much about this family because they only have pieces of teeth and jaws to study. This makes it hard to learn how the different species are related.

Age and taphonomy

In 1965, scientists divided the rock layers in Barrancas de San Gregorio into three parts. They linked these layers to the Montehermosan, Chapadmalalan, and Pampean (Ensenadan) Ages based on the South American land mammal age geological timescale. These layers are from the Upper Pliocene and the Pleistocene on the international geologic time scale.

The fossil of J. magna was not found where it originally lived. Scientists think it came from an older rock layer, possibly the San José Formation, because of its large size. The San José Formation has materials carried by rivers and streams, along with certain types of sandstones and other minerals. Later, in 1966, geologists defined the Raigón Formation. 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 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. This means it had one incisor, no canines, one premolar, and three molars in each half of each jaw.

The skull of J. monesi was very large, measuring about 53 cm (1 ft 9 in) long—bigger than the skulls of modern beef cows. The skull bones were fused together in some areas. The body mass estimates for J. monesi vary, but all suggest it was the largest known rodent, possibly weighing over a ton.

Paleobiology

Scientists studied how strong the bite of Josephoartigasia was. They found this huge rodent could bite as hard as large animals like polar bears and jaguars. Its strong front teeth and strong skull suggest it could dig for food or protect itself from predators like terror birds.

Early ideas about its food thought it ate soft plants. But later studies showed it could eat many kinds of food, both hard and soft. Looking at its teeth suggests it ate leaves and fruits, like modern capybaras.

Paleoecology

Josephoartigasia lived in what is now Uruguay long ago. Scientists found fossils of this giant rodent with other ancient animals. These included large ground sloths, glyptodonts like Glyptodon, a big darter bird called Giganhinga, and the vampire bat Desmodus draculae. This suggests the area had forests near water.

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