Paramylodon is an extinct genus of ground sloth of the family Mylodontidae endemic to North America during the Pliocene through Pleistocene epochs, living from around ~4.9 Mya–12,000 years ago. Within the genus only two species are recognised: Paramylodon harlani, also known as Harlan's ground sloth known from Early Pleistocene to the Late Pleistocene (Irvingtonian–Rancholabrean) and the earlier Pliocene–Early Pleistocene (Blancan) species Paramylodon garbanii, though the placement of the latter in the genus has been questioned by some authors. The first fossil findings date back to the beginning of the 1830s. They go back to Richard Harlan, in whose honor the species was named. The genus Paramylodon was introduced by Barnum Brown in the early 20th century. Over 150 years after the description of the first species, the finds that are now attributed to Paramylodon were repeatedly placed in with other genera, first with Mylodon, but since the 1950s increasingly with Glossotherium. Paramylodon shares numerous features that suggest a close relationship with Glossotherium. Only since the 1990s have both genera been considered distinct, with Glossotherium restricted to South America, while Paramylodon inhabited North America. The species Paramylodon harlani is known from remains found across North America, with abundant remains known from the La Brea Tar Pits in California. Like some other mylodontids, Paramylodon had osteoderms embedded within its skin. Paramylodon lived in open landscapes, sometimes also in mountainous locations, and were grazers or mixed feeders. Preserved footprints are known. The morphology of the forelimbs has led to suggestions that Paramylodon may have engaged in burrowing. Like other ground sloths, Paramylodon became extinct around 14–12,000 years ago as part of the Late Pleistocene megafauna extinctions of most large mammals across the Americas. Paramylodon overlapped in time with Paleoindians, the earliest human inhabitants of the Americas, who may have hunted Paramylodon. Its extinction may be the result of climatic change, hunting, or a combination of both factors.
Taxonomy Paramylodon is an extinct genus of sloth from the extinct family Mylodontidae. Mylodontidae is grouped together with modern two-toed sloths of the family Choloepodidae and the extinct Scelidotheriidae, in the superfamily Mylodontoidea, with the former family being their closest living relatives. Paramylodon is usually considered closely related to both Mylodon and Glossotherium. In contrast, a study presented in 2019 by Luciano Varela and other involved scientists, which includes numerous fossil forms of the entire sloth suborder, partially challenged this. In this study Paramylodon and Glossotherium were found to be closely related, Mylodon, on the other hand, forms the basis of the advanced mylodonts and Lestodon clades with some forms from northern South America. In the same year, a more-detailed phylogenetic analysis of the mylodonts was published by a research group led by Alberto Boscaini. According to the study, Paramylodon, Glossotherium, and Mylodon form a closer relationship within the Mylodontinae. This view also finds support from the aforementioned biochemical data, also presented in 2019. Detailed morphological analyses published as early as 2009 by Robert K. McAfee also suggest that Paramylodon and Glossotherium are very closely related and share a close common ancestor. Below is a phylogenetic tree of the Mylodontidae, based on the work of Boscaini et al.. 2019, showing the position of Paramylodon.
History of research
Discoveries in North and South America
The research history of Paramylodon is complex and characterized by more than 150 years of confusion with Mylodon and Glossotherium. The history begins with the first discoveries of Richard Harlan (1796–1843) at Big Bone Lick in Boone County in the U.S. state of Kentucky in 1831, which included a right mandible and a clavicle. Harlan recognized that they were remains of an extinct sloth and referred them to Megalonyx, which was already known from North America at the time, and within the genus to the species Megalonyx laqueatus that he had established shortly before. The finds were originally preserved in New York, but are now lost. Between the years 1831 and 1836, Charles Darwin made his pioneering voyage on HMS Beagle to South America and brought back from there a large number of fossils. These were then studied by Richard Owen, one of the most important explorers of the Victorian era, and the results published. In a first publication on mammalian remains in general in 1840, he introduced the genus Mylodon with the species Mylodon darwinii. The genus and species were based on a mandible Darwin found in Punta Alta in the Argentina Buenos Aires province. As a special characteristic, a total of four molar-like teeth per tooth row stood out. At the same time, Owen also noted similarities in tooth structure between Harlan's mandible and that of Mylodon darwinii. Inferring this, he discarded the name coined by Harlan, Megalonyx laqueatus, and created a new species, Mylodon harlani. The genus name Paramylodon is composed of the Greek παρα (para meaning "beside" or "near"), μύλη (myle "molar") and ὀδούς (odoús "tooth"), thus translates as "molar tooth". Harlan commented two years later on the use of the name because, in his opinion, it did not describe any outstanding characteristic of the animal and could mean any extinct mammal because almost all of them had the posterior molars. In the same year, 1842, Owen presented a comprehensive description of a skeleton of a mylodont that came from the flood plains of the Río de la Plata north of Buenos Aires; he established for it the new species Mylodon robustus. At this point, then, the genus Mylodon consisted of three species, two of which occurred in South America and one in North America. Furthermore, it should prove problematic that Owen identified Mylodon darwinii as the type species of the genus, although, as he admitted, this was the second known and described species after Mylodon harlani. Accordingly, Mylodon harlani would actually be entitled to the status of type species. Subsequently, different type species were assigned to Mylodon, for example, Johannes Theodor Reinhardt in 1879 considered it to be Mylodon robustus, Richard Lydekker in 1887, on the other hand, considered it to be Mylodon harlani.
Paramylodon and the Mylodon–Glossotherium problem
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