Agriodontosaurus

{{Short description|Genus of extinct reptiles}} {{Speciesbox | fossil_range = [[Middle Triassic]]<br>([[Anisian]]), {{fossilrange|244|241.5|~244–241.5 [[Year#Megaannus|Ma]]}} | image = Agriodontosaurus (holotype, BRSUG 29950-14).png | image_caption = Holotype specimen (a, b) and reconstructed skeleton (c) | display_parents = 3 | genus = Agriodontosaurus | parent_authority = Marke et al., [[2025 in reptile paleontology|2025]] | species = helsbypetrae | authority = Marke et al., 2025 }}

'''''Agriodontosaurus''''' (meaning "fierce-toothed lizard") is an [[extinct]] genus of early [[rhynchocephalia]]n reptiles known from the [[Middle Triassic]] ([[Anisian]] age) [[Helsby Sandstone Formation]] of England. The genus contains a [[Monotypic taxon|single species]], '''''Agriodontosaurus helsbypetrae''''', known from a partial skull and skeleton. It is the oldest known definitive rhynchocephalian and currently the oldest known member of [[Lepidosauria]], the broader group including the modern [[tuatara]] (the only living rhynchocephalian) and snakes and lizards ([[Squamata]]).<ref name="Agriodontosaurus">{{Cite journal |last1=Marke |first1=Daniel |last2=Whiteside |first2=David I. |last3=Sethapanichsakul |first3=Thitiwoot |last4=Coram |first4=Robert A. |last5=Fernandez |first5=Vincent |last6=Liptak |first6=Alexander |last7=Newham |first7=Elis |last8=Benton |first8=Michael J. |author8-link=Michael Benton|date=September 10, 2025 |title=The oldest known lepidosaur and origins of lepidosaur feeding adaptations |journal=[[Nature (journal)|Nature]] |language=en |doi=10.1038/s41586-025-09496-9 |issn=0028-0836 |doi-access=free|pmc=12629995 }}</ref>

== Discovery and naming == The ''Agriodontosaurus'' [[holotype]] specimen, BRSUG 29950-14, was discovered excavated by Robert A. Coram in 2015 in a [[sandstone]] bed representing the Pennington Point Member of the [[Helsby Sandstone Formation]] in [[Sidmouth]], [[Devon]], [[South West England]]. Natural weathering had exposed part of the specimen's dorsal surface when it was collected, and later physical [[Fossil preparation|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 (anatomy)|rostrum]] (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, [[Sacrum|sacral]], and caudal (tail) vertebrae, a complete left [[pectoral girdle]] ([[scapula]], [[coracoid]], [[clavicles]], and [[interclavicle]]) and parts of the right one, forelimb bones (both [[humeri]] and fragments possibly representing pieces of the [[radius]] and [[ulna]]), most of the [[pelvic girdle]] ([[Ilium (bone)|ilia]], [[pubes]], and [[ischia]] from the left and/or right sides), and hindlimb bones (both [[femora]], and part of a [[tibia]] and [[fibula]]).<ref name="Agriodontosaurus" />

In 2025, Marke and colleagues [[Species description|described]] ''Agriodontosaurus helsbypetrae'' as a new genus and species of early rhynchocephalians based on these fossil remains. The [[Genus|generic name]], ''Agriodontosaurus'', combines a reference to [[Agrionius]] ({{gloss|fierce}}), an [[Ancient Greek]] epithet of the god [[Dionysus]], with the Greek words {{lang|grc|donto}}, meaning {{gloss|tooth}}, and [[wikt:σαῦρος#Etymology|σαῦρος]] ({{lang|grc|sauros}}), meaning {{gloss|lizard}}. The [[Specific name (zoology)|specific name]], ''helsbypetrae'', references the discovery of the specimen in the Helsby Sandstone Formation, combined with the [[latinized Greek]] {{lang|grc|petra}}, meaning {{gloss|rock}}.<ref name="Agriodontosaurus" />

== Description == [[File:Agriodontosaurus (holotype skull).png|thumb|Holotype skull]]''Agriodontosaurus'' is one of the smallest known rhynchocephalians, with a body around {{Convert|10|cm|in}} long,<ref name="Agriodontosaurus" /> and a skull around {{Convert|1.5|cm}} long.<ref>{{Cite web |title=Newly found fossils of lizard-like animal are the oldest ever discovered {{!}} Natural History Museum |url=https://www.nhm.ac.uk/discover/news/2025/september/newly-found-fossils-lizard-like-animal-oldest-ever-discovered.html |access-date=2025-09-11 |website=www.nhm.ac.uk |language=en}}</ref> ''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]] (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]] with the [[quadrate bone]].<ref name="Agriodontosaurus" />

== Classification == To determine the affinities and relationships of ''Agriodontosaurus'' with other reptiles, Marke et al. (2025) scored this taxon into two [[phylogenetic]] matrices. In the dataset of Tałanda et al. (2022),<ref name= "Bellairsia2022">{{Cite journal |last1=Tałanda |first1=Mateusz |last2=Fernandez |first2=Vincent |last3=Panciroli |first3=Elsa |last4=Evans |first4=Susan E. |last5=Benson |first5=Roger J. |date=2022-10-26 |title=Synchrotron tomography of a stem lizard elucidates early squamate anatomy |journal=[[Nature (journal)|Nature]] |volume=611 |issue=7934 |pages=99–104 |language=en |doi=10.1038/s41586-022-05332-6 |pmid=36289329 |s2cid=253160713 |issn=0028-0836 }}</ref> broadly focused on reptiles with a broad sampling of squamates, ''Agriodontosaurus'' was recovered in an unresolved clade including ''[[Wirtembergia]]'' (the previous oldest-known rhynchocephalian),<ref name="Wirtembergia">{{Cite journal |last1=Sues |first1=Hans-Dieter |last2=Schoch |first2=Rainer R. |date=2023-11-07 |title=The oldest known rhynchocephalian reptile from the Middle Triassic (Ladinian) of Germany and its phylogenetic position among Lepidosauromorpha |journal=[[The Anatomical Record]] |volume=307 |issue=4 |pages=776–790 |language=en |doi=10.1002/ar.25339 |pmid=37937325 |s2cid=265050255 |issn=1932-8486 }}</ref> ''[[Clevosaurus hadroprodon]]'', and ''[[Parvosaurus]]''. This clade diverged after one comprising ''[[Diphydontosaurus]]'' and ''[[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]], again in a more [[Primitive (phylogenetics)|derived]] position than ''Diphydontosaurus'' and ''Gephyrosaurus''. Simplified results of this analysis, following the 50% majority tree, are displayed in the [[cladogram]] below:<ref name="Agriodontosaurus" />

{{clade |{{clade |1=''[[Gephyrosaurus]]'' |2={{clade |1=''[[Penegephyrosaurus]]'' |label2=[[Sphenodontia]] |2={{clade |1=''[[Paleollanosaurus]]'' |2=''[[Vellbergia]]'' |3=''[[Diphydontosaurus]]'' |label4=[[Acrosphenodontia]] |4={{clade |1=''[[Planocephalosaurus]]'' |2={{clade |1=''[[Parvosaurus]]'' |2={{clade |1='''''Agriodontosaurus''''' |2={{clade |1=''[[Theretairus]]'' |2=''[[Sphenocondor]]'' |3=''[[Pamizinsaurus]]'' |4={{clade |1=''[[Lanceirosphenodon]]'' |2=''[[Rebbanasaurus]]'' }} |5={{clade |1=''[[Microsphenodon]]'' |label2=[[Eusphenodontia]] |2={{clade |1=[[Clevosauridae]] |label2=[[Neosphenodontia]] |2={{clade |1=[[Sphenodontidae]] |2=[[Leptorhynchia]] }} }} }} }} }} }} }} }} }} }}|label1=[[Rhynchocephalia]]}}

== Ecology == ''Agriodontosaurus'' is suggested to have probably been an [[insectivore]].<ref name="Agriodontosaurus" />

== See also == * ''[[Feralisaurus]]'', a [[neodiapsid]] reptile from the ''Agriodontosaurus'' bone bed * ''[[Kapes bentoni]]'', a [[procolophonid]] reptile from the ''Agriodontosaurus'' bone bed * [[2025 in reptile paleontology]]

== References == {{Reflist}}

[[Category:Rhynchocephalia]] [[Category:Triassic lepidosaurs]] [[Category:Anisian genera]] [[Category:Middle Triassic reptiles of Europe]] [[Category:Prehistoric reptile genera]] [[Category:Fossil taxa described in 2025]]