{{Short description|Extinct genus of dinosaurs}} {{speciesbox | name = ''Agilisaurus'' | fossil_range = Middle Jurassic, {{Fossil range|168|164}} | image = Zigong Dinosaur Museum Agilisaurus louderbacki.jpg | image_caption = Mounted skeleton at the Zigong Dinosaur Museum | display_parents = 2 | genus = Agilisaurus | parent_authority = Peng, 1990 | species = louderbacki | authority = Peng, 1990<ref name=Peng1990/> }}
'''''Agilisaurus''''' ({{IPAc-en|ˌ|æ|dʒ|ᵻ|l|ᵻ|ˈ|s|ɔː|r|ə|s}}; 'agile lizard') is a genus of ornithischian dinosaur from the Middle Jurassic Period of what is now eastern Asia. The only named species is '''''A. louderbacki''''', recovered from the Lower Shaximiao Formation of Sichuan, China. It was about {{cvt|1.2-1.7|m|ft}} in length, {{cvt|60|cm|ft}} in hip height, and {{cvt|40|kg|lb}} in weight.<ref>Paul, G.S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press</ref> It has leaf-shaped teeth that were well-adapted to its abrasive, plant-based diet. Most surprisingly, the wavy enamel of the teeth of this genus (and all other ornithopods), presumed to make them more resistant to wear, was previously thought to be exclusive to hadrosaurs.<ref name=Jun/> This is also the case for ''Changchunsaurus'' from the Cretaceous Period.<ref name=Jun>Jun Chen, Aaron R. H. LeBlanc, Liyong Jin, Timothy Huang, Robert R. Reisz. Tooth development, histology, and enamel microstructure in Changchunsaurus parvus: Implications for dental evolution in ornithopod dinosaurs. PLOS ONE, 2018; 13 (11): e0205206 DOI: 10.1371/journal.pone.0205206</ref>
==Discovery and history== [[File:Zigong Dinosaur Museum Agilisaurus.jpg|left|thumb|Holotype specimen in Zigong Dinosaur Museum]] There is one named species (''A. louderbacki''), named after Dr. George Louderback, an American geologist and the first to recognize dinosaur fossils from the Sichuan Province of China in 1915. The holotype, which is the only known specimen, was discovered in 1984, during the construction of the Zigong Dinosaur Museum. Both genus and type species were named by Chinese paleontologist Peng Guangzhou in very brief fashion in 1990,<ref name=Peng1990>{{cite journal | last1 = Peng | first1 = G. | year = 1990 | title = A new small ornithopod (''Agilisaurus louderbacki'' gen. et sp. nov.) from Zigong, China | journal = Newsletter of the Zigong Dinosaur Museum | volume = 2 | pages = 19–27 |language=zh}}</ref> then described in further detail by Peng in 1992.<ref>{{cite journal | last1 = Peng | first1 = G. | year = 1992 | title = Jurassic ornithopod ''Agilisaurus louderbacki'' (Ornithopoda: Fabrosauridae) from Zigong, Sichuan, China | journal = Vertebrata PalAsiatica | volume = 30 | pages = 39–51|language=zh }}</ref>
The name is derived from the Latin "''agilis"'' meaning 'agile' and the Greek "''sauros"'' meaning 'lizard', and refers to the agility suggested by its lightweight skeleton and long legs. The species epithet, ''louderbacki'', honors the late U.S. geologist Dr. George D. Louderback the first to discover fossils within the Sichuan Basin in 1915.<ref>{{cite web|title=George Davis Louderback, 1874–1957|website=University of California Museum of Paleontology|author=Taliaferro, N.|author2=Buck, T.|author3=Lenzen, V.F.|url=http://www.ucmp.berkeley.edu/museum/louderbackfund/aboutlouderback.php}}</ref>
A single complete skeleton of ''A. louderbacki'' is known to science, one of the most complete small ornithischian skeletons ever found. Only a few parts of its left fore limb and hind limb are missing, and those can be reconstructed from their counterparts on the right side.<ref name=Peng1990/><ref name=Peng1992/>
This skeleton was actually discovered during the construction of the Zigong Dinosaur Museum, in which it is now housed.<ref>{{cite web |first=Dirk |last=Meissner |url=https://www.cbc.ca/news/canada/british-columbia/prehistoric-dinosaur-highway-discovered-in-northeastern-b-c-1.3049475 |title=Prehistoric dinosaur highway discovered in northeastern B.C. |publisher=CBC |date=2015-04-26}}</ref> This museum features many dinosaurs recovered from the famous Dashanpu Quarry<ref>Li, K; Liu, J.; Yang, C.; Hu, F. (2011). "Dinosaur assemblages from the Middle Jurassic Shaximiao Formation and Chuanjie Formation in the Sichuan-Yunnan Basin, China". Volumina Jurassica. 9 (9): 21–42.</ref> outside the city of Zigong, in the Chinese province of Sichuan, including ''Agilisaurus'', as well as'' Xuanhanosaurus'',<ref>Dong, Z. (1984). "A new theropod dinosaur from the Middle Jurassic of Sichuan Basin". ''Vertebrata PalAsiatica'' 22(3):213-218</ref> ''Shunosaurus'',<ref>Dong, Z., Zhou, S. & Zhang, Y. 1983. [Dinosaurs from the Jurassic of Sichuan]. ''Palaeontologica Sinica'', New Series C 162(23): 1-136</ref> and ''Huayangosaurus''.<ref>Dong, Z., Tang, Z. and Zhou, S.W. (1982). ["Note on the new Mid-Jurassic stegosaur from Sichuan Basin, China"] (in Chinese). ''Vertebrata PalAsiatica'' 20 (1) :83-87</ref> This quarry preserves sediment from the Lower Shaximiao Formation (sometimes called "Xiashaximiao") which ranges from the Bathonian through Callovian stages of the Middle Jurassic Period, or from about 168 to 161 million years ago.<ref>See for a detailed geologic timescale Gradstein et al. (2004)</ref>
==Description== [[File:Agilisaurus life restoration.jpg|thumb|left|Life restoration]] Its tibia (lower leg bone), at {{cvt|20.7|cm|in}} in length, was slightly longer than its femur (upper leg bone), at {{cvt|19.9|cm|in}} in length, which indicates that it was an extremely fast bipedal runner, using its long tail for balance, although it may have walked on all fours when browsing for food.<ref name=Peng1992/> It was a small herbivore, and like all ornithischians, it had a beak-like structure on the ends of both upper and lower jaws to help it crop plant material.<ref name=Peng1992>{{cite journal | last1 = Barrett | first1 = P.M. | last2 = Butler | first2 = R.J. | last3 = Knoll | first3 = F. | year = 2005 | title = Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China | journal = Journal of Vertebrate Paleontology | volume = 25 | issue = 4| pages = 823–834 | doi=10.1671/0272-4634(2005)025[0823:sodftm]2.0.co;2}}</ref> Because it lacks tail-stiffening interwoven bony struts, some paleontologists think it may have been a burrow dweller.<ref name=Peng1992/>
==Classification== thumb|right|Skeletal reconstruction Despite its completeness, ''Agilisaurus'' has been placed in many different positions in the ornithischian family tree. It was originally placed in the family Fabrosauridae, which is no longer considered valid by most paleontologists.<ref name=Peng1990/>
Several recent studies, including cladistic analyses, find ''Agilisaurus'' to be the most basal member of the group Euornithopoda, which includes all ornithopods more derived than the family Heterodontosauridae.<ref>{{cite journal | last1 = Butler | first1 = R.J. | year = 2005 | title = The 'fabrosaurid' ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho | journal = Zoological Journal of the Linnean Society | volume = 145 | issue = 2 | pages = 175–218 | doi=10.1111/j.1096-3642.2005.00182.x| doi-access = free }}</ref> <ref name=Butler>{{cite journal |last=Butler |first=Richard J. |author2=Upchurch, Paul|author3=Norman, David B.|author3-link=David B. Norman|title=The phylogeny of the ornithischian dinosaurs|journal=Journal of Systematic Palaeontology |volume=6 |issue=1 |year=2008 |pages=1–40 |doi=10.1017/S1477201907002271|bibcode=2008JSPal...6....1B |s2cid=86728076 }}</ref>
However, heterodontosaurs are not universally considered to be ornithopods and have been considered more closely related to the suborder Marginocephalia, which includes ceratopsians and pachycephalosaurs. In one recent cladistic analysis, ''Agilisaurus'' was found in a position basal to heterodontosaurs in the branch leading to Marginocephalia.<ref name=Xu2006/>
''Agilisaurus'' has been recovered in other positions as well, including as an ornithischian basal to both ornithopods and marginocephalians.<ref name=Butler/><ref name=Xu2006>{{cite journal | last1 = Xu | first1 = X. | last2 = Forster | first2 = C.A. | last3 = Clark | first3 = J.M. | last4 = Mo | first4 = J. | year = 2006 | title = A basal ceratopsian with transitional features from the Late Jurassic of northwestern China | journal = Proceedings of the Royal Society B: Biological Sciences | volume = 273| issue = 1598 | pages = 2135–40| doi = 10.1098/rspb.2006.3566 | pmid=16901832 | pmc=1635516}}</ref>
thumb|right|Size compared to a human In his more thorough 1992 description, Peng added a new species to the genus ''Agilisaurus''.<ref name=Peng1992/> This species had previously been known as ''Yandusaurus multidens''. Because this species did not belong in the genus ''Yandusaurus'' and due to similarities with ''A. louderbacki'', it was assigned the name ''Agilisaurus multidens''.<ref name=Peng1992/>
Other scientists were not convinced that this species belonged to either ''Yandusaurus'' or ''Agilisaurus'', and in 2005, it was once again reassigned, this time to its own newly created genus. It is now known as ''Hexinlusaurus multidens''.<ref name=Barrett2005>{{cite journal |last=Barrett|first=P.M. |author2=Butler, R. J. |author3=Knoll, F. |year=2005|title= Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China|journal=Journal of Vertebrate Paleontology|volume= 25|issue=4 |pages=823–834 |doi=10.1671/0272-4634(2005)025[0823:sodftm]2.0.co;2}}</ref> Several studies agree that this species is slightly more derived than ''Agilisaurus''.<ref>Norman, D.B., Sues, H-D., Witmer, L.M., & Coria, R.A. (2004). "Basal Ornithopoda". In: Weishampel, D.B., Dodson, P., & Osmolska, H. (eds.) ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. pp. 393–412.</ref><ref name=Barrett2005/>
==Paleobiology== Comparisons between the scleral rings of ''Agilisaurus'' and modern birds and reptiles suggest that it may have been diurnal, unlike larger herbivorous dinosaurs that were inferred to be cathemeral,<ref>{{cite journal | last1 = Weishampel | first1 = D.B. | last2 = Jianu | first2 = C.-M. | last3 = Csiki | first3 = Z. | last4 = Norman | first4 = D.B. | title = Osteology and phylogeny of ''Zalmoxes'' (n.g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania | journal = Journal of Systematic Palaeontology | year = 2003 | volume = 1 | issue = 2 | pages = 65–123 | doi=10.1017/s1477201903001032| bibcode = 2003JSPal...1...65W | s2cid = 86339025 }}</ref> being active throughout the day at short intervals.<ref>{{cite journal|author1=Schmitz, L. |author2=Motani, R. |year=2011 |title=Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology |journal=Science |volume=332 |issue= 6030|pages= 705–8|doi=10.1126/science.1200043 |pmid=21493820|bibcode=2011Sci...332..705S |s2cid=33253407 }}</ref>
==References== {{Reflist}}
==External links== {{Portal|Dinosaurs}} *[https://web.archive.org/web/20071210135323/http://www.nhm.ac.uk/jdsml/nature-online/dino-directory/detail.dsml?Genus=Agilisaurus Agilisaurus] in the [http://www.nhm.ac.uk/jdsml/nature-online/dino-directory/ Dino Directory], NHM.ac.uk.
{{Ornithischia|O.}} {{Taxonbar|from=Q131319}}
Category:Neornithischia Category:Dinosaur genera Category:Callovian dinosaurs Category:Shaximiao Formation Category:Dinosaurs of China Category:Fossil taxa described in 1990