''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 Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...

). The creatures who made the footprints and tracks were probably pseudosuchian

archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...

s related to the ancestors of the

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...

s. They likely belonged to either

prestosuchidae Prestosuchidae (in its widest usage) is a polyphyletic grouping of carnivorous archosaurs that lived during the Triassic. They were large active terrestrial apex predators, ranging from around in length. They succeeded the Erythrosuchidae as the ...

or rauisuchidae groups, which were both large carnivores with semi-erect gaits.

History

''Chirotherium'' tracks were first found in German Triassic sandstones in 1834, and later in England in 1838. They were found before dinosaurs were known and initial models of the trackmaker proposed that it was a bear or ape, which walked with its feet crossed. This proposal was necessary to explain the toe on the outside. The tracks were also proposed to be from a marsupial. These fossil tracks have now been found on

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, Argentina, North Africa, Europe, and

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

. British paleontologist

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Owe ...

suggested in 1842 that the tracks were made by a

labyrinthodont "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally consid ...

amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...

. 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. In 1965, the skeleton of an animal probably closely related to the trackmaker of ''Chirotherium'' was found, called ''

Ticinosuchus ''Ticinosuchus'' is an extinct genus of suchian archosaur from the Middle Triassic (Anisian - Ladinian) of Switzerland and Italy. Description One of only a handful of fossil reptiles that have been found in Switzerland, ''Ticinosuchus'' (mea ...

''. 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 gender difference ( sexual dimorphism) within the trackmaker species. 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 An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...

sea (the so-called Muschelkalk Sea). In one location, ''Chirotherium'' trackways were found alongside those of early horseshoe crabs. The horseshoe crabs were likely breeding along the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

while the ''Chirotherium'' trackmaker preyed on them during low tide. Smaller reptiles like ''

Macrocnemus ''Macrocnemus'' is an extinct genus of archosauromorph reptile known from the Middle Triassic (Late Anisian to Ladinian) of Europe and China. ''Macrocnemus'' is a member of the Tanystropheidae family and includes three species''. Macrocnemus bass ...

'', represented by the ichnogenus ''

Rhynchosauroides ''Rhynchosauroides'' is an ichnogenus, a form taxon based on footprints. The organism producing the footprints was likely a lepidosaur and may have been a sphenodont, an ancestor of the modern tuatara. The footprint consists of five digits, of w ...

'', likely fed on the horseshoe crabs’ eggs.

References

{{Taxonbar, from=Q311020 Vertebrate trace fossils Fossil trackways

History

Paleobiology

See also

References