''Seitaad'' 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 ...

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...

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 ...

which lived during the Early

Jurassic period The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

in what is now southern

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. ''Seitaad'' is known from an

articulated An articulated vehicle is a vehicle which has a permanent or semi-permanent pivot joint in its construction, allowing it to turn more sharply. There are many kinds, from heavy equipment to buses, trams and trains. Steam locomotives were sometim ...

partial

postcrania Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated sk ...

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

skeleton referred to as UMNH VP 18040. The skeleton is missing its head, neck and tail. It was collected from the

Lower Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma&nb ...

Navajo Sandstone The Navajo Sandstone is a geological formation in the Glen Canyon Group that is spread across the U.S. states of southern Nevada, northern Arizona, northwest Colorado, and Utah as part of the Colorado Plateau province of the United States.Anonymo ...

, the uppermost unit of the

Glen Canyon Group The Glen Canyon Group is a geologic group of formations that is spread across the U.S. states of Nevada, Utah, northern Arizona, north west New Mexico and western Colorado. It is called the Glen Canyon Sandstone in the Green River Basin of C ...

, dating to the

Pliensbachian The Pliensbachian is an age (geology), age of the geologic timescale and stage (stratigraphy), stage in the stratigraphic column. It is part of the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series an ...

stage, near

Comb Ridge Comb Ridge ( nv, ) is a linear north to south-trending monocline nearly 80 miles long in Southeastern Utah and Northeastern Arizona. Its northern end merges with the Abajo Mountains some eleven miles west of Blanding. It extends essentially du ...

, San Juan County. A phylogenetic study of ''Seitaad'' found it to be a plateosaur sauropodomorph, placing it in

Massospondylidae Massospondylidae is a family (biology), family of early massopod dinosaurs that existed in Asia, Africa, North America, South America and AntarcticaHellert, Spencer M. "A New Basal Sauropodomorph from The Early Jurassic Hanson Formation of Antarc ...

or alternatively (a less probable position) in

Plateosauridae Plateosauridae is a family of plateosaurian sauropodomorphs from the Late Triassic of Europe, Greenland, Africa and Asia. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosauridae is now restric ...

, but its placement within the

Plateosauria Plateosauria is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous. The name Plateosauria was first coined by Gustav Tornier in 1913. The name afterwards fell out of use until the 1980s. Classificat ...

is not well understood. In a

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analysis, presented by Apaldetti and colleagues in November 2011, ''Seitaad'' was found to be within

Massopoda Massopoda is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to Late Cretaceous epochs. It was named by paleontologist Adam M. Yates of the University of the Witwatersrand in 2007. Massopoda is a stem-based taxon, define ...

, just outside Anchisauria. ''Seitaad'' was first described by Joseph J. W. Sertich and Mark A. Loewen in 2010 and the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

is ''Seitaad ruessi''. The generic name is derived from ''Séít‘áád'' (

Navajo language Navajo or Navaho (; Navajo: or ) is a Southern Athabaskan language of the Na-Dené family, through which it is related to languages spoken across the western areas of North America. Navajo is spoken primarily in the Southwestern United Stat ...

), a mythological sand monster from the Diné folklore who buried its victims in dunes. ''Seitaad'' appears to have been entombed by the collapse of a sand dune. The specific name honours

Everett Ruess Everett Ruess (March 28, 1914 – ''c.'' November 1934) was an American artist, poet, and writer. He carried out solo explorations of the High Sierra, the California coast, and the deserts of the American Southwest. In 1934, he disappeared while ...

, a young artist, poet and naturalist, who mysteriously disappeared in 1934 while exploring southern Utah. ''Seitaad'' is the second basal sauropodomorph dinosaur to have been identified in North America.

References

Fossil taxa described in 2010 Early Jurassic dinosaurs of North America Massopoda Paleontology in Utah {{Sauropodomorph-stub