Ankylosaurus magniventris
- 演化之聲
- 3 days ago
- 4 min read
Updated: 19 hours ago
Age
Cretaceous（Maastrichtian）
68-66 Ma
Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Ornithischia
Family: Ankylosauridae
Subfamily: Ankylosaurinae
Genus: Ankylosaurus
Species: Ankylosaurus magniventris
Morphological description
Ankylosaurus magniventris was a heavily built, low-slung, and broad-bodied ankylosaurid dinosaur. It was a quadruped, with the back and sides of the body covered by numerous osteoderms, and the tail ended in a large club. Its total length is estimated to have reached about 6 to 8 metres.
The skull was low and broad, and in dorsal view it was triangular. The top of the skull and the facial region were covered by large, flat, polygonal bony plates, giving the head a broader and flatter appearance than that seen in earlier ankylosaurs. Multiple prominent horn-like bony projections were present along the posterolateral region of the skull, and there were also large projecting bony elements above the orbits and behind the cheek region.
The premaxillae and nasal region contained highly developed internal cavities and sinus spaces, producing an enlarged snout. The maxillae expanded laterally, giving the cheeks a broad appearance; the tooth rows were positioned more medially, while the outer side formed a platform-like area. On this basis, researchers have suggested that these animals probably possessed soft cheek tissues in life, which would have helped prevent food from spilling out of the mouth during chewing. The number of maxillary teeth was relatively high for an ankylosaurid, with about 34 to 36 teeth on each side of the upper jaw, although these teeth were proportionally smaller than those of many close relatives.
At the front of the neck there was a cervical half-ring made up of several large osteoderms, forming a strong protective band across the front of the shoulder and neck region. Other parts of the body bore osteoderms of various shapes, some comparatively smooth and others marked by distinct keels. At the end of the tail, several stiffened caudal vertebrae and enlarged osteoderms together formed a low, broad, and massive tail club. The handle vertebrae were wide and robust, indicating that the tail club was a very solid structure.
Etymology
Genus name Ankylosaurus: This name was first established by Barnum Brown in 1908. It is derived from the Greek ankylos (αγκυλος), meaning "bent," "stiff," "fused," or "hooked," and sauros (σαυρος), meaning "lizard." The name therefore means "stiff lizard" or "fused lizard."
Species name magniventris: This name is derived from the Latin magnus, meaning "large," and ventris, meaning "belly" or "abdomen." It thus means "large-bellied."
Biological description
Ankylosaurus magniventris lived during the latest part of the Late Cretaceous, in the Maastrichtian, and was one of the largest ankylosaurid dinosaurs in the dinosaur faunas of western North America. In its ecosystem, Ankylosaurus magniventris lived alongside famous dinosaurs such as Tyrannosaurus, Triceratops, and Edmontosaurus. Its fossils are known from what are now Montana and Wyoming in the United States, as well as Alberta and Saskatchewan in Canada. These remains come mainly from the Hell Creek Formation, Lance Formation, Scollard Formation, and Frenchman Formation, all of which are closely associated with the final interval of the Cretaceous. This means that Ankylosaurus magniventris lived very close to the Cretaceous-Palaeogene extinction event.
Ankylosaurus magniventris was a low browser. Its low head posture, body carried close to the ground, and broad, blunt beak all support the idea that it mainly fed on vegetation growing near ground level. More traditional interpretations have pictured it as feeding only on low plants such as ferns, small angiosperms, and tender shoots from the lower parts of shrubs. However, more recent work has pointed out that the snout and nasal region of Ankylosaurus magniventris did not resemble those of modern rooting animals such as pigs or aardvarks. Instead, they may have been more similar to the shovel-like snouts seen in burrowing squamates capable of pushing through soil. On that basis, researchers have proposed that Ankylosaurus magniventris may also have used its snout to obtain food resources from shallow soil, including roots, tubers, and perhaps even small invertebrates or other nutritionally rich foods.
Evidence from the hyoid apparatus and tongue muscle attachments has also led to the suggestion that ankylosaurids may have had relatively well-developed and powerful tongues, which would have helped them manipulate more unusual food items within the mouth. In addition, the comparatively low rate of tooth formation in ankylosaurs has raised the possibility that their diet did not consist entirely of highly abrasive leaves in large quantities. For this reason, Ankylosaurus magniventris may have been better interpreted as an opportunistic and broad-feeding animal lying near the boundary between herbivory and omnivory.
The feature most often emphasized in Ankylosaurus magniventris is the tail club. As part of a powerful defensive system, these animals likely did not rely on speed to escape predators. Instead, they would have turned to face danger, stabilized their posture, protected vulnerable parts of the body, and counterattacked with the tail. However, some studies have suggested that the tail club may not have been used only against predators. Differences in tail club size, shape, and structure may also have been related to interactions between members of the same species, meaning that it may have played a role in intraspecific competition, intimidation, and contests over status.
Compared with many earlier North American ankylosaurines, Ankylosaurus magniventris had already diverged markedly in skull structure, dentition, nasal anatomy, and body size. It had evolved into a highly specialized late form in functional terms, and this may indicate that it occupied a more specialized way of using resources within its ecosystem. Such a combination of traits is also entirely plausible in an environment shared with giant tyrannosaurids.
（Author: Shui-Ye You）
References
Arbour VM and Mallon JC. (2017). Unusual cranial and postcranial anatomy in the archetypal ankylosaur Ankylosaurus magniventris. FACETS.
Carpenter K. (2004). Redescription of Ankylosaurus magniventris Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America. Canadian Journal of Earth Sciences.
Hu T. (2024). Defensive Adaptations and Paleoecology of Ankylosaurus: Insights into the Armor and Lifestyle of a Cretaceous Armored Dinosaur. Preprints.org.