''Ahvaytum'' ( ; ) is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of probable basal

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 lo ...

saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithi ...

n dinosaurs from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

Popo Agie Formation The Popo Agie Formation ( )Locally "po-PO-zha" according to Don Pitcher, 2006, ''Moon Handbooks Wyoming,'' p. 26/ref>More ambiguous transcription of "po-po-zsha" at is a Triassic geologic Formation (geology), formation that outcrop, crops out in ...

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

, United States. The genus contains a single species, ''A. bahndooiveche'', known from fragmentary hindlimb bones. ''Ahvaytum'' represents the oldest known named dinosaur of the ancient

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

n landmass.

Discovery and naming

The ''Ahvaytum'' fossil material was discovered in 2013 in outcrops of the lower

(Garrett's Surprise locality) in west-central Wyoming, United States. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen, UWGM 1975, is an isolated left

astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

. Specimen UWGM 7549, a partial left

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

(

proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

end) was referred to ''Ahvaytum'' since it was found within a

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

of the holotype and its anatomy is consistent with saurischians. Prior to the formal naming of ''Ahvaytum'', the fossil material was noted in a 2020

conference A conference is a meeting, often lasting a few days, which is organized on a particular subject, or to bring together people who have a common interest. Conferences can be used as a form of group decision-making, although discussion, not always d ...

abstract, where it was initially interpreted as an early-diverging

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

closely related to the

Neotheropoda Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodomo ...

. In 2025, Lovelace et al. described ''Ahvaytum bahndooiveche'' as a new genus and species of early sauropodomorphs based on these fossil remains. The generic name, ''Ahvaytum'' (), means "long ago", referring to the specimen's old age. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''bahndooiveche'' (), literally translates to "water's young man", and is the term used to refer to both dinosaurs and the colorful native

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

s. The full binomial (intended to mean "long ago dinosaur") was created by

Eastern Shoshone Eastern Shoshone are Shoshone who primarily live in Wyoming and in the northeast corner of the Great Basin where Utah, Idaho and Wyoming meet and are in the Great Basin classification of Indigenous People. They lived in the Rocky Mountains du ...

elders and students in their native language, intended to counteract the perceived

colonialism Colonialism is the control of another territory, natural resources and people by a foreign group. Colonizers control the political and tribal power of the colonised territory. While frequently an Imperialism, imperialist project, colonialism c ...

associated with the erection of names derived from European languages. ''Ahvaytum'' notably represents the oldest dinosaur from the ancient landmass of

(comprising what is now North America, Europe, and Asia excluding the Indian subcontinent and the Arabian peninsula). Prior to its description, it was assumed that sauropodomorph dinosaurs originated in the landmass of

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

, although ''Ahvaytum'' shows that this clade had already dispersed more widely.

Description

''Ahvaytum'' is a small sauropodomorph, estimated to be long and tall. ''

Eoraptor ''Eoraptor'' () is a genus of small, lightly built, Basal (phylogenetics), basal sauropodomorpha, sauropodomorph dinosaur. One of the earliest-known dinosaurs and one of the earliest sauropodomorphs, it lived approximately 231 to 228 million yea ...

'', a close relative from Argentina, is known from a larger and more complete skeleton with a total body length of around . The fossil material assigned to ''Ahvaytum'' is interpreted as belonging to at least one individual that had grown past the juvenile ontogenetic stage and was still slowly growing.

Classification

In their

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

, Lovelace et al. (2025) consistently recovered ''Ahvaytum'' as closely affiliated with the

n sauropodomorphs ''

'' and ''

Buriolestes ''Buriolestes'' is a genus of early sauropodomorph dinosaurs from the Late Triassic Santa Maria Formation of the Paraná Basin in southern Brazil. It contains a single species, ''B. schultzi'', named in 2016. The type specimen was found alongsid ...

''. Using maximum parsimony, their analysis placed these taxa, along with the African ''

Mbiresaurus ''Mbiresaurus'' (meaning " Mbire reptile") is an extinct genus of basal sauropodomorph dinosaur from the Late Triassic (Carnian) Pebbly Arkose Formation of Zimbabwe. The genus contains a single species, ''Mbiresaurus raathi'', known from a near ...

'', as members of the family

Saturnaliidae Saturnaliidae is a family of basal sauropodomorph dinosaurs found in Brazil, Argentina and possibly Zimbabwe. It is not to be confused with Saturnalidae, a family of radiolarian protists. Classification In 2010, Martin Ezcurra defined the subfam ...

. The authors noted that these results, displayed in the

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below, indicate a more inclusive grouping of saturnaliids than traditionally recognized:

Paleoenvironment

In 2024, Deckman, Lovelace, and Holland suggested that the Popo Agie Formation represents a common river environment, specifically a distributive

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

system. The formation's lower unit from which ''Ahvaytum'' is known has also yielded fossils of sulcimentisaurian '

silesaurids Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compr ...

', the large

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

s ''

Anaschisma ''Anaschisma'' ("ripped up") is an extinct genus of large temnospondyls. These animals were part of the family called Metoposauridae, which filled the crocodile-like predatory Ecological niche, niches in the late Triassic. It had a large skull ab ...

'' and ''

Buettnererpeton ''Buettnererpeton'' is an extinct genus of large temnospondyls known from the Late Triassic Dockum Group in Texas. The type species, ''B. bakeri'', was long classified as part of other genera, such as '' Metoposaurus'' and ''Koskinonodon ' ...

'' and the

phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...

Parasuchus ''Parasuchus'' is an extinct genus of basal phytosaur known from the Late Triassic (late Carnian to early Norian stage) of Andhra Pradesh and Madhya Pradesh, India. At its most restricted definition, ''Parasuchus'' contains a single species, '' ...

''. The

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

Beesiiwo ''Beesiiwo'' (meaning "big lizard") is a genus of Hyperodapedontinae, hyperodapedontine rhynchosaur from the Late Triassic Popo Agie Formation in Western Wyoming. The type and only species is ''B''. ''cooowuse'', known from four specimens consist ...

'', the

pseudosuchia Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...

ns ''

Heptasuchus ''Heptasuchus'' is an extinct genus of loricatan pseudosuchian known from the Middle Triassic, Middle or Late Triassic upper Chugwater Group of Wyoming, United States. It contains a single species, ''Heptasuchus clarki'', the first formally recog ...

'' and ''

Poposaurus ''Poposaurus'' is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern and eastern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, bea ...

'', and the

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

'' Eubrachiosaurus'' are known from other layers of this formation.

References

{{Taxonbar, from1=Q131701579, from2=Q131701585 Sauropodomorpha Dinosaur genera Carnian dinosaurs Dinosaurs of the United States Fossil taxa described in 2025