| Ahvaytum | |
|---|---|
 | |
| Skeletal reconstruction | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha (?) |
| Genus: | †Ahvaytum Lovelace et al.,2025 |
| Species: | †A. bahndooiveche |
| Binomial name | |
| †Ahvaytum bahndooiveche Lovelace et al., 2025 | |
Ahvaytum (/ɑːˈveɪtəm/ah-VAY-tum;lit. 'long ago') is anextinct genus of probablebasalsauropodomorphsaurischian dinosaurs from theLate TriassicPopo Agie Formation ofWyoming, United States. The genus contains asingle species,A. bahndooiveche, known from fragmentary hindlimb bones.Ahvaytum represents the oldest known named dinosaur of the ancientLaurasian landmass.
TheAhvaytum fossil material was discovered in 2013 in outcrops of the lowerPopo Agie Formation (Garrett's Surprise locality) in west-central Wyoming, United States.[1][2] Theholotype specimen,UWGM 1975, is an isolated leftastragalus. Specimen UWGM 7549, a partial leftfemur (proximal end) was referred toAhvaytum since it was found within a 5 metres (16 ft)radius of the holotype and its anatomy is consistent with saurischians.[3]
Prior to the formal naming ofAhvaytum, the fossil material was noted in a 2020conferenceabstract, where it was initially interpreted as an early-divergingtheropod closely related to theNeotheropoda.[4]
In 2025, Lovelace et al.describedAhvaytum bahndooiveche as a new genus and species of early sauropodomorphs based on these fossil remains. Thegeneric name,Ahvaytum (Shoshoni pronunciation:[ɑβɑjttum]), means "long ago", referring to the specimen's old age. Thespecific name,bahndooiveche (Shoshoni pronunciation:[pɑnduiβitʃi̥]), literally translates to "water's young man", and is the term used to refer to both dinosaurs and the colorful nativesalamanders. The full binomial (intended to mean "long ago dinosaur") was created byEastern Shoshone elders and students in their native language, intended to counteract the perceivedcolonialism associated with the erection of names derived from European languages.[3]
Ahvaytum notably represents the oldest dinosaur from the ancient landmass ofLaurasia (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 ofGondwana, althoughAhvaytum shows that this clade had already dispersed more widely.[3]
Ahvaytum is a small sauropodomorph, estimated to be 3 feet (0.91 m) long and 1 foot (0.30 m) tall.[1]Eoraptor, a close relative from Argentina, is known from a larger and more complete skeleton with a total body length of around 1.3 metres (4.3 ft).[5] The fossil material assigned toAhvaytum is interpreted as belonging to at least one individual that had grown past the juvenile ontogenetic stage and was still slowly growing.[3]
In theirphylogenetic analyses, Lovelace et al. (2025) consistently recoveredAhvaytum as closely affiliated with theGondwanan sauropodomorphsEoraptor andBuriolestes. Using maximum parsimony, their analysis placed these taxa, along with the AfricanMbiresaurus, as members of the familySaturnaliidae. The authors noted that these results, displayed in thecladogram below, indicate a more inclusive grouping of saturnaliids than traditionally recognized:[3]
In 2024, Deckman, Lovelace, and Holland suggested that the Popo Agie Formation represents a common river environment, specifically a distributivefluvial system.[6] The formation's lower unit from whichAhvaytum is known has also yielded fossils of sulcimentisaurian 'silesaurids', the largetemnospondylsAnaschisma andBuettnererpeton and thephytosaurParasuchus. TherhynchosaurBeesiiwo, thepseudosuchiansHeptasuchus andPoposaurus, and thedicynodontEubrachiosaurus are known from other layers of this formation.[3]
