Placerias
Template:Short description Template:Speciesbox
Placerias (meaning 'broad body')<ref name="Paleofile">Template:Cite web</ref> is an extinct genus of dicynodonts that lived during the Carnian and Norian stages of the Triassic period (230–215 million years ago). Placerias belongs to a clade of dicynodonts called Kannemeyeriiformes, which was the last known group of dicynodonts before the taxon became extinct at the end of the Triassic.
Description
Placerias was one of the largest herbivores in the Late Triassic, weighing up to Template:Convert.<ref>Template:Cite journal</ref><ref name=FPM2000>Template:Cite journal</ref> The largest skull found had a length of Template:Convert.<ref>Template:Cite journal</ref>
Placerias had a powerful neck, strong legs, and barrel-shaped body with possible ecological and evolutionary parallels with the modern hippopotamus, spending much of its time during the wet season wallowing in the water and chewing at bankside vegetation.<ref name=FPM2000/> Placerias was closely related to Ischigualastia and similar in appearance.<ref>Template:Cite journal</ref> Placerias used its beak to slice through thick branches and roots with two tusk-like flanges that could be used for defence and for intra-specific display. These so-called caniniforms were not true tusks derived from teeth, like in other dicynodonts, but were instead extensions of the skull merely mimicking tusks, likely covered in horn or beak tissue, a trait unique to the Stahleckeriidae family. The genus exhibits two morphs, one with short caniniforms and one with long caniniforms, which is inferred to be sexual dimorphism, with the longer-tusked individuals presumably being males.<ref name="Pinto2024"/>
Discovery
Fossils of forty Placerias were found near St. Johns, southeast of the Petrified Forest in the Chinle Formation of Arizona. This site has become known as the 'Placerias Quarry' and was discovered in 1930, by Charles Camp and Samuel Welles, of the University of California, Berkeley. Sedimentological features of the site indicate a low-energy depositional environment, possibly flood-plain or overbank. Bones are associated mostly with mudstones and a layer that contains numerous carbonate nodules. It is also known from the Pekin Formation of North Carolina.<ref>Template:Cite web</ref>
Placerias was originally considered the last of the dicynodonts, although other Late Triassic dicynodonts, such as Lisowicia<ref>Template:Cite journal</ref> and Pentasaurus<ref name="Kammerer2018"/> have since been discovered.Template:Efn
Palaeobiology
Growth
P. hesternus outer cortical primary bone is generally zonal fibrolamellar in orientation, with a parallel-fibred peripheral layer. This suggests that P. hesternus experienced rapid osteogenesis punctuated by intervals of slower growth. Also, an external fundamental system has been described from a very large P. hesternus tibia, suggesting that this feature developed following the attainment of maximum size and cessation of growth.<ref>Template:Cite journal</ref>