Chirotherium
Encyclopedia
Chirotherium, also known as Cheirotherium ('hand-beast'), is the name of a Triassic
archosaur
known only from fossil imprints of its tracks (trace fossil
s). These look, by coincidence, remarkably like the hands of apes, humans, 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. Its tracks were first found in 1834 in red sandstone
in Thuringia
, Germany
, dating from about 243 million years ago (mya).
This creature was probably a pseudosuchia
n archosaur
related to the ancestors of the crocodile
s. It likely belonged to a group of pseudosuchians called the rauisuchia
ns, which were large carnivores with erect gaits.
in 1838. Tracks left by this creature were found before dinosaur
s were known and initial models of the animal 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 track
s have now been found on North America
, Africa
, and Europe
.
British paleontologist Richard Owen
suggested in 1842 that the tracks were made by a labyrinthodont amphibian
. 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 a probably closely related animal was found, called Ticinosuchus
. It had the external toe on its hind feet but not on its front feet and was possibly a more advanced descendant, whose gait had improved enough to reduce the need for a stabilizing front toe. Chirotherium barthii and Ticinosuchus ferox have also been proposed to be the same species, with what may have been a gender difference (sexual dimorphism
) visible in the tracks.
. 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 track maker preyed on them during low tide. Smaller reptiles like Macrocnemus
, represented by the ichnogenus Rhynchosauroides, likely fed on the horseshoe crabs' eggs.
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
known only from fossil imprints of its tracks (trace fossil
Trace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
s). These look, by coincidence, remarkably like the hands of apes, humans, 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. Its tracks were first found in 1834 in red sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
in Thuringia
Thuringia
The Free State of Thuringia is a state of Germany, located in the central part of the country.It has an area of and 2.29 million inhabitants, making it the sixth smallest by area and the fifth smallest by population of Germany's sixteen states....
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, dating from about 243 million years ago (mya).
This creature was probably a pseudosuchia
Pseudosuchia
Pseudosuchia is the name originally given to a group of prehistoric reptiles from the Triassic period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today. A more commonly used name, Crurotarsi, is often substituted for...
n archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
related to the ancestors of the crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s. It likely belonged to a group of pseudosuchians called the rauisuchia
Rauisuchia
Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...
ns, which were large carnivores with erect gaits.
History
Chirotherium tracks were first found in German Triassic sandstones in 1834, and later in EnglandEngland
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in 1838. Tracks left by this creature were found before dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s were known and initial models of the animal 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
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
. These fossil track
Fossil trackway
A fossil trackway is a type of trace fossil, a trackway made by an organism. Many fossil trackways were made by dinosaurs, early tetrapods, and other quadrupeds and bipeds on land...
s have now been found on North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
.
British paleontologist Richard Owen
Richard Owen
Sir Richard Owen, FRS KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...
suggested in 1842 that the tracks were made by a labyrinthodont amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
. 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.
Ticinosuchus
Ticinosuchus is an extinct genus of rauisuchian archosaur from the Middle Triassic of Switzerland and Italy.Ticinosuchus was about long, and its whole body, even the belly, was covered in thick, armoured scutes. The structure of the hips shows that its legs were placed under the body almost...
. It had the external toe on its hind feet but not on its front feet and was possibly a more advanced descendant, whose gait had improved enough to reduce the need for a stabilizing front toe. Chirotherium barthii and Ticinosuchus ferox have also been proposed to be the same species, with what may have been a gender difference (sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
) visible in the tracks.
Paleobiology
Chirotherium trackways have been found in German sandstones that were likely deposited along shorelines. During the Triassic, much of Europe was a chain of islands surrounded by the shallow Tethys OceanTethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
. In one location, Chirotherium trackways were found alongside those of early horseshoe crab
Horseshoe crab
The Atlantic horseshoe crab, Limulus polyphemus, is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs. Horseshoe crabs are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America...
s. The horseshoe crabs were likely breeding along the intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
while the Chirotherium track maker preyed on them during low tide. Smaller reptiles like Macrocnemus
Macrocnemus
Macrocnemus is an extinct genus of prolacertiform reptile from the Middle Triassic of Europe. Two species have been named, the type species M. bassanii and the species M. fuyuanensis....
, represented by the ichnogenus Rhynchosauroides, likely fed on the horseshoe crabs' eggs.