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Anodontosaurus is an extinct genus of ankylosaurid within the subfamily Ankylosaurinae. It is known from the entire span of the Late Cretaceous Horseshoe Canyon Formation (mid Late Campanian to "middle" Maastrichtian stage, about 72.8-67 Ma ago) of southern Alberta, Canada, and is also known from the Dinosaur Park Formation (75.6 Ma ago). It contains two species, A. lambei and A. inceptus.
In 1986 Coombs examined specimen AMNH 5266, at the time by him referred to Euoplocephalus, and determined that it was a juvenile. It consists of five vertebral centra, a Vertebral arch, one dorsal and two sacral ribs, the right ischium, the complete right hindlimb, the right pes, an incomplete left pes, and various other fragments. AMNH 5266 was discovered in 1912 at Red Deer River and was collected by Barnum Brown with assistance from Peter Kaisen, George Olsen, and Charles M Sternberg in the sediments from the Horseshoe Canyon Formation.Coombs, W.P., Jr. (1986, June). A Juvenile Ankylosaur Referable to the Genus Euoplocephalus (Reptilia, Ornithischia). Journal of Vertebrate Paleontology, 6(2), 162-173.
Coombs supported the assertion that specimen AMNH 5266 represented a juvenile by citing that the vertebral centra were not fused to their neural arches, and that sacral ribs were likewise not fused to vertebrae and to the ilium. Other morphological characters supporting that this is a juvenile specimen include (a) long bones that feature smooth surfaces, which are not marked by the rugosities characteristic of adult bone; (b) the head of the femur is less spherical in shape and is clearly delimited from the adjacent part of the femoral shaft; (c) the distal ends of the tibia and the fibula are not fused to the astragalus and the calcaneum; and (d) the ungual phalanx of the manus is not widest at the proximal articular end as is observed in adults.
The validity of Anodontosaurus was formalized in three studies. The first, published by Paul Penkalski and William T. Blows in 2013, re-validated Scolosaurus as well. The second study, by Penkalski (2013), named and described Oohkotokia from Montana on the basis of remains that were originally thought to be referable to Euoplocephalus. Penkalski (2013) performed a small phylogenetic analysis of some ankylosaurine specimens. The only Anodontosaurus specimen that was included in this analysis was its holotype. Anodontosaurus was placed in a polytomy with the holotype of Euoplocephalus and some specimens that are referred to it, while Oohkotokia was placed in a clade with Dyoplosaurus, and specimens that are thought to represent either Dyoplosaurus or Scolosaurus. In a study based on the results of her 2010 SVP abstract, Arbour along with Philip Currie formalized the revalidation of Anodontosaurus, and one specimen from the Dinosaur Park Formation, TMP 1997.132.1, was referred to Anodontosaurus
/ref> The DPF specimen, however, was later made the holotype of a new species, A. inceptus.
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The following cladogram is based on a 2015 phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie:
See also
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