This analysis aims to recreate the locomotion of extinct mammals. The ancestors of mammals are thought to be synapsids. Early mammals that evolved from the synapsids are thought to have been small and able to hide from the larger dinosaurs and reptiles around them. However, the mass extinction that occurred 66 million years ago changed the situation dramatically, with large dinosaurs disappearing from the earth, thereby expanding the mammalian niche. The opening of the niche led to the emergence of many lineages of mammals of varying sizes. Many of the mammalian species identified by paleontological studies were so large and had strange body shapes that it is difficult to imagine their locomotion. Therefore, we attempted to reproduce their locomotion in this analysis.
Reproduction method: 1: Incorporation of the skeleton of extinct species; 2: Reproduction of muscles, tendons, and skin based on data from modern species; and 3: Reproduction of locomotion from bone shape and inferred muscle-tendon structure.
In this revised version, we examined skeletons constructed in 3D using photogrammetry for selected species. The skeletons can be seen from various angles on the screen. However, depending on the species, it is difficult to obtain photogrammetric images from all directions, and there are parts where image data is missing.
(Cooperation: National Museum of Nature and Science, Tokushima Prefectural Museum, Gunma Museum of Natural History, Yamaguchi Museum)
Megatherium lived in South America approximately 0.01-5 million years ago. Megatherium was one of the largest mammals, weighing up to 4 tons and measuring up to 6 m. It had a large pelvic girdle and tail and powerful hindlegs. Many skeletons of Megatherium are set in a standing position using support from three points comprising the hindlimbs and tail. The limbs had large, curved claws similar to modern sloths that live in trees. Some researchers have speculated that it performed knuckle walking like an anteater or bipedal walking.
（Tokushima Prefectural Museum)
Glyptodon was an extinct species of Cingulate It lived in South America around 2.5 million years ago, with a body length of 3 m and dome-shaped armor plates. The very heavy and non-movable armor plates significantly reduced locomotion by suppressing the mobility of the spinal column. It has been considered that when moving faster, Glyptodon extend its limbs and increasing the number of steps like as three banded armadillo.
（Tokushima Prefectural Museum)
Toxodon was a larger species in Notoungulata that lived in South America around 0.01-1.1 million ears ago. Notoungulata is an extinct order, and Toxodon was the last and largest species in the order, with body length of 3 m and shoulder height of 1.5 m. Charles Darwin was the first collector of Toxodon fossils. Toxodon had a short neck, wide trunk and pelvis, and its forelimbs were shorter than the hindlimbs. Toxodon kept its pelvic girdle high and head low. Toxodon was said to resemble a rhinoceros or hippopotamus but was different from any extant species. What kind of locomotion did Toxodon perform with its skeleton and body form?
（National Museum of Nature and Science)
Arsinoitherium was a large species in the extinct Embrithopoda that lived in rainforests and mangrove swamps in Africa around 30-36 million years ago, with body length of 3 m and shoulder height of 1.8 m. It was characterized by one large and two smaller paired horns on its head. These horns were made of bone similar to cow, rather than formed from hair like a rhinoceros horn. It is considered that Arsinoitherium was unable to run like a rhinoceros. Hoofed animals with well developed running ability have developed a nuchal ligament that supports the head and neck. The nuchal ligament originates from a spinous process on the thoracic vertebrae (arrowhead) and inserted into the cervical vertebrate and head. The spinous process of thoracic vertebrae in Arsinoitherium was low and the nuchal ligament was unable to support the head and neck during vertical motion when running.
（National Museum of Nature and Science)
Paleoparadoxia was a large aquatic mammal (215 cm in length, 80 cm at shoulder height, 600 kg inweight) that inhabited the Northern Pacific around 10-20 million years ago. Paleoparadoxia is a species in an extinct order, Desmostylia. Paleoparadoxia had a large head, wide body, and short limbs like as hippopotamus. The humeral and femoral bones in skeletal specimens displayed in some museums are arranged horizontally from the shoulder and pelvic girdles. On the other hand, those of the hippopotamus extend vertically How well was Paleoparadoxia able to move on land?
（Kitakyushu Museum of Natural History & Human History)
Moropus had a shoulder height of 2.4 m and large claws and was a species in the perissodactyl, living in North America around 14-20 million years ago. Moropus was species in Chalicotheres characterized by a posture that leant from the shoulder to the buttocks. Some species in Chalicotheres, such as Anisodon had significant inclines to their body axis. However, the tilt angle of the spine of Moropus was small and Moropus could run floating its long claws.
（National Museum of Nature and Science)
Modern whales are thought to have evolved from land mammals. Pakicetus (41-56 million years ago) and Ambulocetus (48-49 million years ago) were ancestors of whales and had limbs. Whales swim by moving their horizontally spread tail fin up and down. The vertical movement of the spine is a movement that appears when mammals run on land and is characteristic of locomotion in mammals. Therefore, whale ancestors must have run. Pakicetus and Ambulocetus are thought to have lived mostly in water but were able to climb onto land. What kind of locomotion did limbed ancestors of whales perform on land?
（National Museum of Nature and Science)
（National Museum of Nature and Science)
Moeritherium was an extinct species of primitive proboscideans living 23-35 million years ago, but it is not thought to be a direct ancestor of modern elephants. This species was significantly smaller than a modern elephant, with a shoulder height of 0.7 m, body length of, and body weight of 200 kg. The modern elephant seems to have grown from a smaller ancestor. Its body was characterized by short limbs and a horizontally elongated body and is often described as similar to a pygmy hippopotamus or tapir. Fossils of Moeritherium were found in Egypt by Charles W. Andrew (1902). From the information gather at the excavation, it was considered that Moeritherium lived close to water. Was Moeritherium a sprinting animal like tapir or trotter like a pygmy hippopotamus?
（National Museum of Nature and Science)