# Agriodontosaurus

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Genus of extinct reptiles

Agriodontosaurus Temporal range: Middle Triassic (Anisian), ~244–241.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N Holotype specimen (a, b) and reconstructed skeleton (c) Scientific classification Kingdom: Animalia Phylum: Chordata Class: Reptilia Order: Rhynchocephalia Suborder: Sphenodontia Genus: †Agriodontosaurus Marke et al., 2025 Species: †A. helsbypetrae Binomial name †Agriodontosaurus helsbypetrae Marke et al., 2025

***Agriodontosaurus*** (meaning "fierce-toothed lizard") is an [extinct](/source/Extinct) genus of early [rhynchocephalian](/source/Rhynchocephalia) reptiles known from the [Middle Triassic](/source/Middle_Triassic) ([Anisian](/source/Anisian) age) [Helsby Sandstone Formation](/source/Helsby_Sandstone_Formation) of England. The genus contains a [single species](/source/Monotypic_taxon), ***Agriodontosaurus helsbypetrae***, known from a partial skull and skeleton. It is the oldest known definitive rhynchocephalian and currently the oldest known member of [Lepidosauria](/source/Lepidosauria), the broader group including the modern [tuatara](/source/Tuatara) (the only living rhynchocephalian) and snakes and lizards ([Squamata](/source/Squamata)).[1]

## Discovery and naming

The *Agriodontosaurus* [holotype](/source/Holotype) specimen, BRSUG 29950-14, was discovered excavated by Robert A. Coram in 2015 in a [sandstone](/source/Sandstone) bed representing the Pennington Point Member of the [Helsby Sandstone Formation](/source/Helsby_Sandstone_Formation) in [Sidmouth](/source/Sidmouth), [Devon](/source/Devon), [South West England](/source/South_West_England). Natural weathering had exposed part of the specimen's dorsal surface when it was collected, and later physical [preparation](/source/Fossil_preparation) was carried out to reveal more of the anatomy. The specimen, which remains fully contained in the sandstone block it was collected in, is well preserved and partially articulated. It comprises much of the mandible and skull, although it is distorted and missing the [rostrum](/source/Rostrum_(anatomy)) (snout region) and much of the right side, in addition to an articulated series of eight cervical (neck) vertebrae and the succeeding few dorsal (back) vertebrae, various disarticulated dorsosacral, [sacral](/source/Sacrum), and caudal (tail) vertebrae, a complete left [pectoral girdle](/source/Pectoral_girdle) ([scapula](/source/Scapula), [coracoid](/source/Coracoid), [clavicles](/source/Clavicles), and [interclavicle](/source/Interclavicle)) and parts of the right one, forelimb bones (both [humeri](/source/Humeri) and fragments possibly representing pieces of the [radius](/source/Radius) and [ulna](/source/Ulna)), most of the [pelvic girdle](/source/Pelvic_girdle) ([ilia](/source/Ilium_(bone)), [pubes](/source/Pubes), and [ischia](/source/Ischia) from the left and/or right sides), and hindlimb bones (both [femora](/source/Femora), and part of a [tibia](/source/Tibia) and [fibula](/source/Fibula)).[1]

In 2025, Marke and colleagues [described](/source/Species_description) *Agriodontosaurus helsbypetrae* as a new genus and species of early rhynchocephalians based on these fossil remains. The [generic name](/source/Genus), *Agriodontosaurus*, combines a reference to [Agrionius](/source/Agrionius) ('fierce'), an [Ancient Greek](/source/Ancient_Greek) epithet of the god [Dionysus](/source/Dionysus), with the Greek words *donto*, meaning 'tooth', and [σαῦρος](https://en.wiktionary.org/wiki/%CF%83%CE%B1%E1%BF%A6%CF%81%CE%BF%CF%82#Etymology) (*sauros*), meaning 'lizard'. The [specific name](/source/Specific_name_(zoology)), *helsbypetrae*, references the discovery of the specimen in the Helsby Sandstone Formation, combined with the [latinized Greek](/source/Latinized_Greek) *petra*, meaning 'rock'.[1]

## Description

Holotype skull

*Agriodontosaurus* is one of the smallest known rhynchocephalians, with a body around 10 centimetres (3.9 in) long,[1] and a skull around 1.5 centimetres (0.59 in) long.[2] *Agriodontosaurus* has robust, conical teeth at the front of the upper and lower jaws, which become more triangular towards the posterior. The front teeth are [acrodont](/source/Acrodont) (attached to the apex of the jaw), while the back teeth are pleuracrodont, fused to the jaw but on a residual shelf. *Agriodontosaurus* lacks a complete temporal bar/arcade connecting the [jugal bone](/source/Jugal_bone) with the [quadrate bone](/source/Quadrate_bone).[1]

## Classification

To determine the affinities and relationships of *Agriodontosaurus* with other reptiles, Marke et al. (2025) scored this taxon into two [phylogenetic](/source/Phylogenetic) matrices. In the dataset of Tałanda et al. (2022),[3] broadly focused on reptiles with a broad sampling of squamates, *Agriodontosaurus* was recovered in an unresolved clade including *[Wirtembergia](/source/Wirtembergia)* (the previous oldest-known rhynchocephalian),[4] *[Clevosaurus hadroprodon](/source/Clevosaurus_hadroprodon)*, and *[Parvosaurus](/source/Parvosaurus)*. This clade diverged after one comprising *[Diphydontosaurus](/source/Diphydontosaurus)* and *[Gephyrosaurus](/source/Gephyrosaurus)*. Using the dataset of Chambi-Trowell et al. (2021), which is more precisely focused on rhynchocephalians, *Agriodontosaurus* was found to occupy an early-diverging position within the [Sphenodontia](/source/Sphenodontia), again in a more [derived](/source/Primitive_(phylogenetics)) position than *Diphydontosaurus* and *Gephyrosaurus*. Simplified results of this analysis, following the 50% majority tree, are displayed in the [cladogram](/source/Cladogram) below:[1]

Rhynchocephalia Gephyrosaurus Penegephyrosaurus Sphenodontia Paleollanosaurus Vellbergia Diphydontosaurus Acrosphenodontia Planocephalosaurus Parvosaurus Agriodontosaurus Theretairus Sphenocondor Pamizinsaurus Lanceirosphenodon Rebbanasaurus Microsphenodon Eusphenodontia Clevosauridae Neosphenodontia Sphenodontidae Leptorhynchia

## Ecology

*Agriodontosaurus* is suggested to have probably been an [insectivore](/source/Insectivore).[1]

## See also

- *[Feralisaurus](/source/Feralisaurus)*, a [neodiapsid](/source/Neodiapsid) reptile from the *Agriodontosaurus* bone bed

- *[Kapes bentoni](/source/Kapes_bentoni)*, a [procolophonid](/source/Procolophonid) reptile from the *Agriodontosaurus* bone bed

- [2025 in reptile paleontology](/source/2025_in_reptile_paleontology)

## References

1. ^ [***a***](#cite_ref-Agriodontosaurus_1-0) [***b***](#cite_ref-Agriodontosaurus_1-1) [***c***](#cite_ref-Agriodontosaurus_1-2) [***d***](#cite_ref-Agriodontosaurus_1-3) [***e***](#cite_ref-Agriodontosaurus_1-4) [***f***](#cite_ref-Agriodontosaurus_1-5) [***g***](#cite_ref-Agriodontosaurus_1-6) Marke, Daniel; Whiteside, David I.; Sethapanichsakul, Thitiwoot; Coram, Robert A.; Fernandez, Vincent; Liptak, Alexander; Newham, Elis; [Benton, Michael J.](/source/Michael_Benton) (September 10, 2025). ["The oldest known lepidosaur and origins of lepidosaur feeding adaptations"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12629995). *[Nature](/source/Nature_(journal))*. [doi](/source/Doi_(identifier)):[10.1038/s41586-025-09496-9](https://doi.org/10.1038%2Fs41586-025-09496-9). [ISSN](/source/ISSN_(identifier)) [0028-0836](https://search.worldcat.org/issn/0028-0836). [PMC](/source/PMC_(identifier)) [12629995](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12629995).

1. **[^](#cite_ref-2)** ["Newly found fossils of lizard-like animal are the oldest ever discovered | Natural History Museum"](https://www.nhm.ac.uk/discover/news/2025/september/newly-found-fossils-lizard-like-animal-oldest-ever-discovered.html). *www.nhm.ac.uk*. Retrieved 2025-09-11.

1. **[^](#cite_ref-Bellairsia2022_3-0)** Tałanda, Mateusz; Fernandez, Vincent; Panciroli, Elsa; Evans, Susan E.; Benson, Roger J. (2022-10-26). "Synchrotron tomography of a stem lizard elucidates early squamate anatomy". *[Nature](/source/Nature_(journal))*. **611** (7934): 99–104. [doi](/source/Doi_(identifier)):[10.1038/s41586-022-05332-6](https://doi.org/10.1038%2Fs41586-022-05332-6). [ISSN](/source/ISSN_(identifier)) [0028-0836](https://search.worldcat.org/issn/0028-0836). [PMID](/source/PMID_(identifier)) [36289329](https://pubmed.ncbi.nlm.nih.gov/36289329). [S2CID](/source/S2CID_(identifier)) [253160713](https://api.semanticscholar.org/CorpusID:253160713).

1. **[^](#cite_ref-Wirtembergia_4-0)** Sues, Hans-Dieter; Schoch, Rainer R. (2023-11-07). "The oldest known rhynchocephalian reptile from the Middle Triassic (Ladinian) of Germany and its phylogenetic position among Lepidosauromorpha". *[The Anatomical Record](/source/The_Anatomical_Record)*. **307** (4): 776–790. [doi](/source/Doi_(identifier)):[10.1002/ar.25339](https://doi.org/10.1002%2Far.25339). [ISSN](/source/ISSN_(identifier)) [1932-8486](https://search.worldcat.org/issn/1932-8486). [PMID](/source/PMID_(identifier)) [37937325](https://pubmed.ncbi.nlm.nih.gov/37937325). [S2CID](/source/S2CID_(identifier)) [265050255](https://api.semanticscholar.org/CorpusID:265050255).

v t e Rhynchocephalia Kingdom: Animalia Phylum: Chordata Class: Reptilia Superorder: Lepidosauria Sauropsida see Sauropsida Lepidosauromorpha see Lepidosauromorpha Rhynchocephalia see below↓ Rhynchocephalia Rhynchocephalia †Wirtembergia †Gephyrosauridae? Gephyrosaurus Penegephyrosaurus Deltadectes Sphenodontia †Diphydontosaurus †Godavarisaurus †Micromenodon †Parvosaurus †Pelecymala †Rebbanasaurus †Sphenocondor Incertae sedis †Paleollanosaurus †Whitakersaurus Acrosphenodontia †Planocephalosaurus †Godavarisaurus? Eusphenodontia †Lanceirosphenodon †Microsphenodon †Opisthiamimus †Polysphenodon †Clevosauridae Brachyrhinodon Clevosaurus Polysphenodon? Neosphenodontia †Colobops? †Homoeosaurus †Lanceirosphenodon? †Pamizinsaurus †Rebbanasaurus? †Sphenocondor? †Sphenodraco †Theretairus †Zapatadon †Kallimodon †Leptosaurus †Sapheosauridae Piocormus Sapheosaurus Oenosaurus "Eupropalinal sphenodonts" †Lamarquesaurus †Sigmala †Tingitana †Vadasaurus †Pleurosauridae? Palaeopleurosaurus Pleurosaurus Tingitana? Vadasaurus? Sphenodontidae †Ankylosphenodon †Cynosphenodon †Derasmosaurus †Kawasphenodon? †Navajosphenodon †Notosphenos †Pamizinsaurus? Sphenodon †Sphenofontis †Sphenovipera? †Theretairus? †Tika †Zapatadon? †Opisthodontia Alamitosphenos Fraserosphenodon Kawasphenodon? Opisthias Pelecymala? Trullidens Pleurosauridae? Sapheosauridae? Eilenodontinae Eilenodon Kaikaifilusaurus Patagosphenos Priosphenodon Sphenotitan? Toxolophosaurus

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Adapted from the Wikipedia article [Agriodontosaurus](https://en.wikipedia.org/wiki/Agriodontosaurus) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Agriodontosaurus?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.