''Planicoxa'' is a

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 ...

of advanced

iguanodont Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', '' Tenontosaurus'', and the hadrosaurids or "duck-bil ...

ian

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the Early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

of North America. It is known from the partial skeletons of several individual specimens. Its fossils were discovered in

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

. The type species for the genus is ''Planicoxa venenica'', first described by Tony DiCroce and

Kenneth Carpenter Kenneth Carpenter (born September 21, 1949, in Tokyo, Japan) is a paleontologist. He is the former director of the USU Eastern Prehistoric Museum and author or co-author of books on dinosaurs and Mesozoic life. His main research interests ...

in 2001. Its discovery was made in the Poison Strip Sandstone Member of the

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid- Cretaceous. The formation was named for Cedar Mountain in northern Emery County, Utah, where Will ...

in Grand County,

, United States. The generic name, ''Planicoxa'', which means "flat hip", refers to the flat appearance of the ilium formed by horizontal folding over of the postacetabular process (rear portion of the ilium), the defining characteristic of the genus; ''venenica'', the specific name, is Latin for "poison" in reference to the Poison Strip Sandstone Member of the Cedar Mountain Formation where the discovery was made. The taxon is represented by a well-preserved ilium,

femora The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with t ...

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

e, and

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

e, as well as other material. The femora are standard for ornithopods, but the ilium has a short, horizontal postacetabular process that is functionally an antitrochanter. The discovery of ''P. venenica'' added significant information to the

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

fauna of the Cedar Mountain Formation. A second species, ''P. depressa'', was created by Carpenter and Wilson (2008) for material previously named ''Camptosaurus depressus'' by Charles Gilmore in 1909. That material was collected from the

Lakota Formation The Lakota Formation is a sequence of rocks of early Cretaceous ( Berriasian to Barremian) age from Western North America. Located in South Dakota, the name of the formation is derived from the Lakota Native American tribe. There are two units ...

near the town of

Hot Springs, South Dakota Hot Springs (Lakota: ''mni kȟáta''; "hot water") is a city in and county seat of Fall River County, South Dakota, United States. As of the 2020 census, the city population was 3,395. In addition, neighboring Oglala Lakota County contracts the ...

. It too has the odd flat ilium formed by the horizontal postacetabular process. This species differs from ''P. venenica'' in that the ilium is not as arched, has a thicker (more robust) preacetabular process (long, forward projection of the ilium), a shallower acetabular notch (hip-socket), and a proportionally narrower brevis shelf (a shelf for muscles on the inside of the rear part of the ilium). It is known from some vertebrae and two ilia. Isolated iguanodontid bones from the Lakota Formation probably belong to this species. In 2011, it was assigned to its own genus, '' Osmakasaurus''.

References

* DiCroce, T. and K. Carpenter. (2001). "New ornithopod from the Cedar Mountain Formation (Lower Cretaceous) of Eastern Utah". pp. 183–196 in: Tanke, D. & K. Carpenter (eds.) ''Mesozoic Vertebrate Life''. Indiana University Press, Bloomington. * Carpenter, K. and Wilson, Y. (2008). "A new species of ''Camptosaurus'' (Ornithopoda: Dinosauria) from the Morrison Formation (Upper Jurassic) of Dinosaur National Monument, Utah, and a biomechanical analysis of its forelimb". ''Annals of the Carnegie Museum'' 76:227-263. {{Taxonbar, from=Q871981 Early Cretaceous dinosaurs of North America Fossil taxa described in 2001 Iguanodonts Taxa named by Kenneth Carpenter Paleontology in Utah Paleontology in South Dakota Ornithischian genera