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Lotheridium
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.
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).
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.
The snout of Lotheridium is short and makes up under a third of the skull's length. The short premaxilla bone forms the tip of the upper jaw and bears all the upper incisor teeth, in addition to forming the front margin of the socket for the upper canine tooth. This bone has a large indentation between where the canine and hindmost incisor are positioned, which the tip of the lower canine fits into when the mouth is shut. Most of the incisive foramen (an opening on the hard palate) is also present on the premaxilla. The hind margin of this foramen is on the maxilla bone, as is most of the upper canine socket. This bone has a large opening called the infraorbital foramen, in front of which the maxilla depresses inward, possibly to serve as an attachment point for facial muscles. Behind the maxilla is the lacrimal bone, located behind the eye socket and expanding greatly onto the face. The middle of the skull roof is made up of the frontal bones, and the hind part of the roof is formed by the larger parietal bones. Each frontal bears a bony projection called a postorbital process and a ridge behind it called the temporal line. These ridges converge towards the back of the bone and join each other at the border of the frontal and parietal bones, forming a sagittal crest. The cheek bones are strongly arched, forming a structure known as the zygomatic arch on each side of the skull. The arch is mostly made up of a bone called the jugal (though the lacrimal and squamosal bones also contribute to it), which has a projection halfway down its length marking the back of the eye socket. At the hind part of each zygomatic arch is a depression called the mandibular fossa (where the lower jaw articulates), and behind this depression is a bony projection called the postglenoid process.
Forming the middle of the underside of the skull is a wide, flat bone called the basisphenoid, with raised ridges on either side of it. Behind it is the basioccipital bone, which makes up the base of the skull and has a V-shaped indentation at its hind part. On either side of the notch is a large, rounded protrusion called an occipital condyle. Part of the middle ear is housed by a hollow, bulging protrusion of the petrosal bone called a promontorium, which bears a groove for a facial nerve and an oval window that opens to the side. Like that of the related Deltatheridium, the promontorium of Lotheridium has no grooves for blood vessels. The supraoccipital bone at the back of the skull has a prominent, backward-pointing structure called a lambdoidal crest.
The robust mandible (lower jaw) is deepest at the point where the third molar is attached, and its underside is slightly curved. Two small openings called mental foramina can be seen from the side of the jaw, located below the first molar and second premolar teeth respectively. The coronoid process of the mandible (a projection behind the teeth) is prominent, its front margin forming a 135° angle with the corresponding tooth row. A depression where the masseter muscle would attach (known as the masseteric fossa) is visible below it. The point where the jaw articulates with the rest of the skull, called the mandibular condyle, is low and almost level with the teeth. On the lingual side of the mandible (the surfaces facing the tongue), the mandibular symphysis (where the two halves of the lower jaw join together) is unfused and an inward-facing bony projection is present at each angle.
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Lotheridium
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.
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).
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.
The snout of Lotheridium is short and makes up under a third of the skull's length. The short premaxilla bone forms the tip of the upper jaw and bears all the upper incisor teeth, in addition to forming the front margin of the socket for the upper canine tooth. This bone has a large indentation between where the canine and hindmost incisor are positioned, which the tip of the lower canine fits into when the mouth is shut. Most of the incisive foramen (an opening on the hard palate) is also present on the premaxilla. The hind margin of this foramen is on the maxilla bone, as is most of the upper canine socket. This bone has a large opening called the infraorbital foramen, in front of which the maxilla depresses inward, possibly to serve as an attachment point for facial muscles. Behind the maxilla is the lacrimal bone, located behind the eye socket and expanding greatly onto the face. The middle of the skull roof is made up of the frontal bones, and the hind part of the roof is formed by the larger parietal bones. Each frontal bears a bony projection called a postorbital process and a ridge behind it called the temporal line. These ridges converge towards the back of the bone and join each other at the border of the frontal and parietal bones, forming a sagittal crest. The cheek bones are strongly arched, forming a structure known as the zygomatic arch on each side of the skull. The arch is mostly made up of a bone called the jugal (though the lacrimal and squamosal bones also contribute to it), which has a projection halfway down its length marking the back of the eye socket. At the hind part of each zygomatic arch is a depression called the mandibular fossa (where the lower jaw articulates), and behind this depression is a bony projection called the postglenoid process.
Forming the middle of the underside of the skull is a wide, flat bone called the basisphenoid, with raised ridges on either side of it. Behind it is the basioccipital bone, which makes up the base of the skull and has a V-shaped indentation at its hind part. On either side of the notch is a large, rounded protrusion called an occipital condyle. Part of the middle ear is housed by a hollow, bulging protrusion of the petrosal bone called a promontorium, which bears a groove for a facial nerve and an oval window that opens to the side. Like that of the related Deltatheridium, the promontorium of Lotheridium has no grooves for blood vessels. The supraoccipital bone at the back of the skull has a prominent, backward-pointing structure called a lambdoidal crest.
The robust mandible (lower jaw) is deepest at the point where the third molar is attached, and its underside is slightly curved. Two small openings called mental foramina can be seen from the side of the jaw, located below the first molar and second premolar teeth respectively. The coronoid process of the mandible (a projection behind the teeth) is prominent, its front margin forming a 135° angle with the corresponding tooth row. A depression where the masseter muscle would attach (known as the masseteric fossa) is visible below it. The point where the jaw articulates with the rest of the skull, called the mandibular condyle, is low and almost level with the teeth. On the lingual side of the mandible (the surfaces facing the tongue), the mandibular symphysis (where the two halves of the lower jaw join together) is unfused and an inward-facing bony projection is present at each angle.