Lotheridium is an extinct genus of deltatheroidan mammals that lived in what is now Asia during the Late Cretaceous, about 72–66 million years ago. The genus contains a single species, Lotheridium mengi, named in 2015 after paleontologist Jin Meng. It is known from a single fossil specimen—a skull with associated lower jaws—found in the Qiupa Formation of Henan Province, China and housed in the collections of the Zhejiang Museum of Natural History. The skull measures 67.3 mm (2.65 in) in length, suggesting Lotheridium was large compared to most other deltatheroidans. Though the preserved skull is almost complete, it has been flattened and the skull roof was crushed during fossilization. Lotheridium is believed to be a carnivore. It had a short snout and 46 teeth, among which the upper canines are the largest and most elongated. Though its lower canines are far smaller than the upper pair, they are still large enough that there are small gaps in the upper jaw to hold them when the mouth is closed. Its molars are adapted for shearing flesh. They bear unique cusps which can be used to differentiate it from its relatives. As with all deltatheroidans, its closest living relatives are the marsupials. As the first deltatheroidan found in central China, Lotheridium showed that the group was more widespread across Asia than previously known. Deltatheroidans are otherwise known from North American adn elsewhere in Asia, and debate exists over which continent the group first evolved in before spreading the other. Dating to the Maastrichtian age, the Qiupa Formation represents a tropical to subtropical depositional environment with a shallow lake and braided river delta. Lotheridium lived alongside a many different species such as dinosaurs, lizards, turtles, and other mammals.
Discovery and naming
In 2015, a team of four Chinese paleontologists reported the discovery of an almost complete fossilized skull in Henan Province, China. The skull was excavated from Late Cretaceous-aged rock deposits of the Qiupa Formation in Haoping Village, Luanchuan County, and was deposited at the Zhejiang Museum of Natural History under the specimen number ZMNH M9032. After studying this fossil, the team concluded that it represented a previously unknown genus and species of prehistoric mammal which they named Lotheridium mengi. They designated the skull as the holotype (name-bearing) specimen. The generic name combines the name of Luoyang (the prefecture Luanchuan County is part of) with the Ancient Greek word theridion (meaning "small beast"). The specific name honors Jin Meng (a paleontologist who studies Mesozoic mammals).
Description Lotheridium is currently known from only one specimen: the holotype skull with associated lower jaws. The specimen is nearly complete, but has been flattened during the process of fossilization such that the skull roof has been crushed. This skull has a total length of 67.3 mm (2.65 in), suggesting that Lotheridium was much larger than most other deltatheroidans with the exception of Deltatheroides. As all the teeth are erupted and worn, this skull likely belongs to a full-grown adult.
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