Chirotherium

{{Short description|Trace fossil}} {{Ichnobox | fossil_range = {{fossil range|245|205}} | image = Cheirotherium prints possibly Ticinosuchus.JPG | image_caption = ''Cheirotherium'' trace fossil, displayed in [[Oxford University Museum of Natural History]] | taxon = Chirotherium | authority = [[J.J. Kaup|Kaup]], 1835 | type_ichnospecies = {{extinct}}''Chirotherium barthii'' | type_ichnospecies_authority = [[J.J. Kaup|Kaup]], 1835 | subdivision_ranks = Ichnospecies | subdivision = *{{extinct}}''Chirotherium barthii'' [[J.J. Kaup|Kaup]], 1835 *{{extinct}}''Chirotherium sickleri'' [[J.J. Kaup|Kaup]], 1835 *{{extinct}}''Chirotherium stortonense'' [[George Highfield Morton|Morton]], 1863 *{{extinct}}''Chirotherium vorbachi'' [[H. Kirchner|Kirchner]], 1927 *{{extinct}}''Chirotherium beasleyi'' [[F.E. Peabody|Peabody]], 1948 *{{extinct}}''Chirotherium moquinense'' [[F.E. Peabody|Peabody]], 1956 *{{extinct}}''Chirotherium rex'' [[F.E. Peabody|Peabody]], 1948 *{{extinct}}''Chirotherium lulli'' [[W. Bock|Bock]], 1952 *{{extinct}}''Chirotherium wondrai'' [[F. Heller|Heller]], 1952 *{{extinct}}''Chirotherium swinnertoni'' ([[William Sarjeant|Sarjeant]], 1970) *{{extinct}}''Chirotherium courelli'' [[G.R. DeMathieu|DeMathieu]], 1970 *{{extinct}}''Chirotherium atlensis'' [[P.E. Biron|Biron]] & [[J.-M. Dutuit|Dutuit]], 1981 *{{extinct}}''Chirotherium mediterraneum'' [[G.R. DeMathieu|DeMathieu]] & [[M. Durand|Durand]], 1991 |synonyms = *''Chirosaurus'' [[J.J. Kaup|Kaup]], 1835 *''Cheirotherium'' {{ill|Friedrich Sickler|lt=Sickler|de}}, 1836 *''Cheirotherion'' [[Franz Nopcsa von Felső-Szilvás|Nopcsa]], 1923 *''Krokodilipus'' [[Franz Nopcsa von Felső-Szilvás|Nopcsa]], 1923 *''Saurichnites'' [[H. Kirchner|Kirchner]], 1927 }}{{Distinguish|Chilotherium}} '''''Chirotherium''''', also known as '''''Cheirotherium''''' (‘hand-beast’), is a [[Triassic]] [[trace fossil]] consisting of five-fingered (pentadactyle) footprints and whole tracks. These look, by coincidence, remarkably like the hands of apes and bears, with the outermost toe having evolved to extend out to the side like a thumb, although probably only functioning to provide a firmer grip in mud. ''Chirotherium'' tracks were first found in 1834 in Lower Triassic [[sandstone]] ([[Buntsandstein]]) in [[Thuringia]], [[Germany]], dating from about 243 [[million years ago]] ([[mya (unit)|mya]]).

The creatures who made the footprints and tracks were probably [[pseudosuchia]]n [[archosaur]]s related to the ancestors of the [[crocodile]]s. They likely belonged to either [[prestosuchidae]] or [[rauisuchidae]] groups, which were both large carnivores with semi-erect gaits.

==History== [[File:Fossil track of a Chirotherium. Triassic Period. From England. Kelvingrove Art Gallery and Museum, Glasgow, UK.jpg|thumb|left|Fossil track of a Chirotherium. Triassic Period. From England. Kelvingrove Art Gallery and Museum, Glasgow, UK]] ''Chirotherium'' tracks were first found in German Triassic sandstones in 1834, and later in [[England]] in 1838. They were found before [[dinosaur]]s were known and initial models of the trackmaker proposed that it was a bear or ape, which walked with its feet crossed.<ref name=SWE61>{{cite journal |last=Swinton |first=W.E. |year=1961 |title=The history of ''Chirotherium'' |journal=Geological Journal |volume=2 |issue=3 |pages=443–473 |doi=10.1002/gj.3350020309}}</ref> This proposal was necessary to explain the toe on the outside. The tracks were also proposed to be from a [[marsupial]].<ref name=BTS10>{{cite journal |last=Bowden |first=A.J. |author2=Tresise, G.R. |author3= Simkiss, W. |year=2010 |title=''Chirotherium'', the Liverpool footprint hunters and their interpretation of the Middle Trias environment |journal=Geological Society, London, Special Publications |volume=343 |pages=209–228 |doi=10.1144/SP343.12}}</ref> These [[fossil trackway|fossil track]]s have now been found on [[North America]], [[Argentina]], [[North Africa]], [[Europe]], and [[China]].

British paleontologist [[Richard Owen]] suggested in 1842 that the tracks were made by a [[labyrinthodont]] [[amphibian]].<ref name=BTS10/> Over the following years, new discoveries of archosaurian reptiles indicated that ''Chirotherium'' tracks were made by a pseudosuchian. The print's resemblance to mammals was only superficial; in reality, an external (lateral) ‘thumb’ was commonplace among Triassic archosaurs.

[[Image:Chirotherium.jpg|thumb|left|''Chirotherium'' monument in [[Hildburghausen]], [[Germany]], with reconstruction of the original track-bearing bedding plane based upon which the ichnogenus ''Chirotherium'' was first described in 1834 and named in 1835.]] In 1965, the skeleton of an animal probably closely related to the trackmaker of ''Chirotherium'' was found, called ''[[Ticinosuchus]]''.<ref name=BTS10/> It had the external toe on its hind feet but not on its front feet and was possibly a more derived descendant, whose gait did not require a stabilizing front toe. Footprints of different size and proportions occurring together on one and the same bedding plane probably reflect a sex difference ([[sexual dimorphism]]) within the trackmaker species.<ref name=TG96>{{cite journal |last=Tresise |first=G. |year=1996 |title=Sex in the footprint bed |journal=Geology Today |volume=12 |issue=1 |pages=22–26 |doi=10.1046/j.1365-2451.1996.00005.x|doi-access=free }}</ref>

Other Chirotheriidae include ''[[Isocheirotherium]]''.

==Paleobiology== ''Chirotherium'' trackways have been found in German sandstones that were likely deposited on flood plains. During the Middle Triassic, much of Central Europe was covered by a shallow [[epicontinental]] sea (the so-called [[Muschelkalk|Muschelkalk Sea]]). In one location, ''Chirotherium'' trackways were found alongside those of early [[horseshoe crab]]s. The horseshoe crabs were likely breeding along the [[intertidal zone]] while the ''Chirotherium'' trackmaker preyed on them during low tide. Smaller reptiles like ''[[Macrocnemus]]'', represented by the ichnogenus ''[[Rhynchosauroides]]'', likely fed on the horseshoe crabs’ eggs.<ref name=DCG11>{{cite journal |last=Diedrich |first=C.G. |year=2011 |title=Middle Triassic horseshoe crab reproduction areas on intertidal flats of Europe with evidence of predation by archosaurs |journal=Biological Journal of the Linnean Society |volume=103 |issue=1 |pages=76–105 |doi=10.1111/j.1095-8312.2011.01635.x|doi-access=free }}</ref>

==See also== *[[Ichnite]]

==References== {{Reflist}}

[[Category:Vertebrate trace fossils]] [[Category:Fossil trackways]] [[Category:Ichnotaxa]]