''Placerias'' (meaning 'broad body') is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typic ...

s that lived during the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...

to the

Norian The Norian is a division of the Triassic Period. It has the rank of an age ( geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic ...

age of the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

(230–220 million years ago). ''Placerias'' belongs to a group of dicynodonts called

Kannemeyeriiformes Kannemeyeriiformes is a group of large-bodied Triassic dicynodonts. As a clade, Kannemeyeriiformes has been defined to include the species '' Kannemeyeria simocephalus'' and all dicynodonts more closely related to it than to the species ''Lystros ...

, 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

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

s in the Late Triassic, with large skull measuring long and weighing up to with a powerful neck, strong legs, and a barrel-shaped body. There are possible ecological and evolutionary parallels with the modern

hippopotamus The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two exta ...

, spending much of its time during the wet season wallowing in the water, chewing at bankside vegetation. Remaining in the water would also have given ''Placerias'' some protection against land-based predators such as '' Postosuchus''. ''Placerias'' used its

beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for fo ...

to slice through thick branches and roots with two short

tusk Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine teeth, as with pigs and walruses, or, in the case of elephants, elongated incisors. Tusks share ...

s that could be used for defence and for intra-specific display. ''Placerias'' was closely related to ''

Ischigualastia ''Ischigualastia'' is an extinct genus of large dicynodont therapsids that lived during the Late Carnian age and the Early Norian age of the Late Triassic Period. The genus was found in and named after the Ischigualasto Formation (Cancha de Boc ...

'' and similar in appearance.

Discovery

Fossils of forty ''Placerias'' were found near St. Johns, southeast of the

Petrified Forest Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of '' fossilized wood'', the fossilized remains of terrestrial vegetation. ...

in the

Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In N ...

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

. This site has become known as the 'Placerias Quarry' and was discovered in 1930, by

Charles Camp Charles Lewis Camp (March 12, 1893 Jamestown, North Dakota – August 14, 1975 San Jose, California) was a palaeontologist and zoologist, working from the University of California, Berkeley. He took part in excavations at the 'Placerias Quarry', in ...

and Samuel Welles, of the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant un ...

Sedimentological Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation (erosion and weathering), transport, deposition and diagenesis. Sedimentologists apply their understanding of mo ...

features of the site indicate a low-energy depositional environment, possibly flood-plain or

overbank An overbank is an alluvial geological deposit consisting of sediment that has been deposited on the floodplain of a river or stream by flood waters that have broken through or overtopped the banks. The sediment is carried in suspension, and be ...

. Bones are associated mostly with

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.' ...

s and a layer that contains numerous carbonate nodules. It is also known from the Pekin Formation of

North Carolina North Carolina () is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. The state is the List of U.S. states and territories by area, 28th largest and List of states and territories of the United ...

. ''Placerias'' was originally considered the last of the Dicynodonts until fossil finds from Queensland were reported in 2003 to have revealed that the Dicynodonts survived until the Early Cretaceous. Agnolin ''et al.'' (2010) called for a reconsideration of that Australian specimen, noting its similarity to baurusuchian crocodyliforms such as ''

Baurusuchus pachecoi ''Baurusuchus'' is an extinct member of the ancestral crocodilian lineage, which lived in Brazil from 90 to 83.5 million years ago, in the Late Cretaceous period. Technically, it is a genus of baurusuchid mesoeucrocodylian. It was a terrest ...

''. The Cretaceous dicynodont specimen was eventually discovered to belong to a specimen of ''

Diprotodon ''Diprotodon'' ( Ancient Greek: "two protruding front teeth") is an extinct genus of marsupial from the Pleistocene of Australia, containing one species, ''D. optatum''. The earliest finds date to 1.77 million to 780,000 years ago, but most s ...

'' instead. Another dicynodont ( Lisowicia) have also survived into the Rhaetian

References

External links

Walking with Dinosaurs – Fact File: Placerias

Dinosaur and Paleontology Dictionary: Placerias

Walking with Dinosaurs website
{{Portal bar, Paleontology Anomodont genera Kannemeyeriiformes Carnian genera Late Triassic synapsids Triassic synapsids of North America Triassic Arizona Fossils of the United States Chinle fauna Fossil taxa described in 1904 Taxa named by Frederic Augustus Lucas

Description

Discovery

See also

References

External links