Acrocanthosaurus
| Acrocanthosaurus | ||||||||||||
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Acrocanthosaurus , live reconstruction |
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous ( Aptian to Middle Albian ) | ||||||||||||
| 126.3 to 107.5 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Acrocanthosaurus | ||||||||||||
| Stovall & Langston , 1950 | ||||||||||||
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Acrocanthosaurus is a dinosaur belonging to the Carnosauria , a group within the theropods . Its remains, including several partial skeletons and an almost complete skeleton, wererecoveredfrom layers of the Early Cretaceous (Aptian to Middle Albian) in the USA. The only species is A. atokensis .
Acrocanthosaurus was a very large, bipedal carnivore. A major feature are elongated vertebral processes that may have formed a low sail.
General
Acrocanthosaurus is named after its vertebral spines, the name is composed of the Greek akro "high", akantha "sting" and sauros "lizard". The Artepitheth atokensis after Atoka County named where the holotype material was found. In his master's thesis published in 1947 , the paleontologist Wann Langston had initially suggested the name Acracanthus , but the name was changed to Acrocanthosaurus .
The first scientific description of Acrocanthosaurus was carried out in 1950 using two partial skeletons by Langston and his colleague Willis Stovall. The finds ( holotype OMNH 10146 and paratype OMNH 10147), which in addition to other skeletal remains also contain some skull material, had previously been recovered from the layers of the Antlers Formation in Oklahoma .
Since then, two more, more complete skeletons have been described: The first is from the Twin Mountain Formation in Texas . It bears the number SMU 74646 and around 70% of it is preserved, including the incomplete skull. This skeleton was rediscovered in 1990, although it had been excavated more than 40 years earlier. The second skeleton (OMNH 10168) bears the nickname "Fran" and, like the first two skeletons, comes from the Antlers formation from Oklahoma. It is the most complete Acrocanthosaurus skeleton to date , and even the skull is completely intact. Many more individual bones and bone fragments were recovered in Texas and Oklahoma, but also in Utah (Cedar Mountain Formation).
The finds come from the Aptian and Middle Albian, so Acrocanthosaurus lived 126 to 108 million years ago. For example, Deinonychus , Tenontosaurus and Sauroposeidon lived in the same area at the same time . This is one of the richest known dinosaur faunas of the Early Cretaceous, and Acrocanthosaurus was the top predator.
Three dorsal bones from England , which had even higher spines, were initially called Acrocanthosaurus altispinax . However, a separate genus was later described for this find: Becklespinax .
In America, many fossil footprints are traditionally ascribed to Acrocanthosaurus , most notably the famous Glen Rose footprints in Dinosaur Valley State Park in north Texas. It is impossible to say whether these traces really come from Acrocanthosaurus . However, they are about the same age as the bone finds and have the appropriate size, which is why an affiliation to Acrocanthosaurus is quite possible.
Some of the tracks were found on the tracks of a sauropod herd and they point in the same direction as those of herbivores. It is therefore assumed that the carnivores followed the large sauropod herds on their migrations and lay in wait for sick and weak animals. However, this cannot be proven.
description
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The almost complete skeleton "Fran" has a length of 11.5 m. Of this, 129 cm is accounted for by the skull, which is significantly longer than that of its relative Allosaurus . Its weight is therefore estimated at 2–3 tons. This makes Acrocanthosaurus one of the largest known theropods, although it was slightly smaller than the relative Giganotosaurus with up to 13 m.
Important anatomical features of the skull are two additional small skull openings in the upper jaw, in addition to the usual five. In addition, the antorbital window, an opening in the skull located in front of the eye opening, is unusually large at 42 cm. In contrast to many of its relatives, Acrocanthosaurus has no skull horns.
The cervical, dorsal and anterior caudal vertebrae have elongated processes that can be more than 2.5 times higher than the respective vertebrae. These vertebral spines also occur in other dinosaurs, the record is held by the Egyptian Spinosaurus with a spine length of 1.5 m. Perhaps the vertebral spines on Acrocanthosaurus formed a low sail. Or, like those of today's bison , they were surrounded by muscles that formed a high hump on the back.
Systematics
There is still disagreement about the systematic classification within the Allosauroidea , to which Acrocanthosaurus is counted. The Allosauroidea consist of three families, the Allosauridae (e.g. Allosaurus ), the Carcharodontosauridae (e.g. Carcharodontosaurus , Giganotosaurus , Tyrannotitan ) and the Sinraptoridae (e.g. Sinraptor ).
Originally it was classified as an allosauride. Today it is believed by many researchers to be more of a carcharodontosaurid, although this has been questioned by recent studies. Coria and Currie (2003) mean e.g. B. after investigations on the skull cases that Acrocanthosaurus does not have any of the typical carcharodontosaur features and therefore cannot be placed among the carcharodontosaurids. Fanzoza (2002), however, found clear similarities between the Acrocanthosaurus skull boxes and those of Allosaurus and Carcharodontosaurus .
A new family, the Acrodontosauridae , has even been proposed (Molnar, 2001) in which Acrocanthosaurus should be classified along with Carcharodontosaurus . However, this theory is rejected by most researchers.
Brain structure
In 2005 scientists digitized the holotype skull material of the Acrocanthosaurus using computed tomography in order to be able to reconstruct the brain and the nerve ducts. The following observations could be made:
- The olfactory bulbs were large and thick, which indicates a well-developed sense of smell.
- The reconstruction of the semicircular canals of the ear , the "balance organ", showed that the head was held at an angle of 25 degrees below the horizontal.
- The brain is more similar to that of the Carcharodontosaurus and Giganotosaurus than that of Sinraptor or Allosaurus , which should strengthen the classification as Carcharodontosauride.
Computed tomography is a fairly new method in paleontology, which has also been used to reconstruct the brain prints of other large theropods ( Tyrannosaurus , Ceratosaurus , Allosaurus and Carcharodontosaurus ).
Web links
Individual evidence
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, pp. 96-97, ISBN 978-0-691-13720-9 , online .
- ^ J. Willis Stovall, Wann Langston, Jr .: Acrocanthosaurus atokensis, a New Genus and Species of Lower Cretaceous Theropoda from Oklahoma. In: American Midland Naturalist. Vol. 43, No. 3, 1950, ISSN 0003-0031 , pp. 696-728, doi : 10.2307 / 2421859 .
- ↑ Jerald D. Harris: A reanalysis of Acrocanthosaurus atokensis, its phylogenetic status, and paleobiogeographic implications, based on a new specimen from Texas (= New Mexico of Natural History and Science. Bulletin. 13, ISSN 1524-4156 ). New Mexico Museum of Natural History, Albuquerque NM 1998.
- ^ Philip J. Currie , Kenneth Carpenter : A new specimen of Acrocanthosaurus atokensis (Theropoda, Dinosauria) from the Lower Cretaceous Antlers Formation (Lower Cretaceous, Aptian) of Oklahoma, USA. In: Geodiversitas. Vol. 22, No. 2, 2000, ISSN 1280-9659 , pp. 207-246.
- ↑ Jonathan Franzosa, Timothy Rowe : Cranial endocast of the Cretaceous theropod dinosaur Acrocanthosaurus atokensis. In: Journal of Vertebrate Paleontology. Vol. 25, No. 4, 2005, ISSN 0272-4634 , pp. 859-864, doi : 10.1671 / 0272-4634 (2005) 025 [0859: CEOTCT] 2.0.CO; 2 .