Alamosaurus
Artistic live representation of Alamosaurus
- North America (New Mexico, Texas, Wyoming, Utah)
- Alamosaurus sanjuanensis
Is a genus of sauropod alamosaurus dinosaur from the Late Cretaceous of North America. Fossils of this dinosaur come from the U.S. states of New Mexico, Texas, Wyoming and Utah, and are dated to the Maastrichtian (before approximately 72-66 million years).
Alamosaurus is one of the better-known and most popular Titanosauria and is - in addition to numerous isolated bones discovered - through several fragmentary skeletons known. This genus is considered to be the only sauropod that lived in the time of the late Cretaceous in North America today. It was a medium sized sauropods of about 21 meters in length, although new findings point to a significantly larger body size. The only way is Alamosaurus sanjuanensis.
Description
Like all sauropods had Alamosaurus a four-legged herbivore with a long neck and tail. It was a medium sized Titanosauria with an estimated length of about 21 meters. The weight was estimated to be about 30 tonnes. However, still in the pipeline study describes much larger bones, which can be one of the largest sauropods ever include: A huge cervical vertebra was about as large as the corresponding vertebra of the giant Titanosauria Futalognkosaurus and Puertasaurus.
The neck was approximately 13 cervical vertebrae longer than some related Titanosauria as Saltasaurus. The dorsal spine probably consisted of 10 vertebrae, while the sacrum had six vertebrae. The tail is in the fossil record with 30 vertebrae. Skull bones have not been found - but there are teeth thinner and pin-like shape known. Although various Alamosaurus findings have been described, a lack of any evidence of skin bony plates ( osteoderms ), as found in some other Titanosauria as Saltasaurus. It is believed that Alamosaurus actually no osteoderms possessed, and that these dermal bones repeatedly trained independently during the evolution of the Titanosauria.
From other genera can be Alamosaurus by several unique features ( autapomorphies ) limitations: So Hämalbögen missing from the ninth caudal vertebrae, while the breastbone ( sternum) shows a sharp craniolateralen extension.
Discoveries and naming
Fossils of Alamosaurus come from numerous sites in the southwestern United States. However, most of these findings consists only of isolated discovered elements of the limbs and was not adequately described scientifically. Sullivan and Lucas (2000 ) note that it is at Alamosaurus a sort of " trash species" (form genus), the numerous sauropod fossils from the Upper Cretaceous of North America are provisionally attributed, although many of these assignments may not be justified.
The scientific description was in 1922 by Charles W. Gilmore. The holotype consists of a shoulder blade (scapula ), sitting legs ( sciatic ) and sacral vertebrae, which originate from the Ojo -Alamo Formation ( or Kirtland Formation) of New Mexico. Later, in 1946, Gilmore described a more complete skeleton from the North Horn Formation of Utah, which consists of a complete tail, a right front leg, chest, legs and seat legs. Further findings were reported from the Javelina Formation, the El Picacho Formation and the Black Peaks Formation of Texas. In 2002, the fragmentary skeleton of a young animal from the Black Peaks Formation has been described.
Alamosaurus ( spanish alamo - " poplar ", gr sauros - " lizard" ) is after a geological formation of the Ojo -Alamo Formation, named - not, as is often assumed, after the famous Alamo in Texas. The Fund layer is now attributed to the Kirtland Formation. The second part of the species name, sanjuanensis is named after the San Juan County in New Mexico.
System
Alamosaurus considered as derived ( advanced ) Representatives of Titanosauria. Most phylogenetic analyzes come to the conclusion that Alamosaurus was closely related to the Mongolian genus Opisthocoelicaudia. Both genera are sometimes grouped together as Opisthocoelicaudiinae and another group, the Saltasaurinae, compared. Other researchers classify both genera as outgroups the Saltasaurinae, where they consider the Opisthocoelicaudiinae as paraphyletic. The Saltasauridae and Alamosaurus and Opisthocoelicaudia be summarized as Saltasauridae. In contrast to most other recent analyzes comes Curry Rogers (2005 ) found that Alamosaurus Opisthocoelicaudia and were related merely removed with the Saltasaurinae. Upchurch and colleagues ( 2004) consider Alamosaurus other hand, as sister taxon of Pellegrinisaurus and so only as a distant relative of Opisthocoelicaudia.
Here are two examples Cladogram - with monophyletic Opisthocoelicaudiinae ( Wilson 2002, left) and with paraphyletischer Opisthocoelicaudiinae ( Calvo and González Riga, 2003, right):
Opisthocoelicaudia
Alamosaurus
Saltasaurus
Opisthocoelicaudia
Alamosaurus
Neuquensaurus
Saltasaurus
Age and paleobiogeography
Alamosaurus is one of the last dinosaurs. Its fossils have long dated exclusively to the late Maastrichtian, the last section of the Cretaceous period immediately below the Cretaceous - Tertiary boundary. Since Alamosaurus fossils are relatively common, they were used as marker fossils. Their presence was considered a proof that this layer is to be classified in the late Maastrichtian.
In recent years, however, recognized that various formations are actually older with Alamosaurus fossils; For example, the Javelina Formation at a newly dated to about 69 million years (late early Maastrichtian ). The oldest find dates from the Kirtland Formation of New Mexico and is dated to an age of 72 million years ( early Maastrichtian ).
From the Cenomanian, ie the beginning of the Upper Cretaceous, sauropod fossils disappear from the fossil record of North America and occur only in the early Maastrichtian with the oldest Alamosaurus fossils again. This gap is interpreted by various researchers that sauropods became extinct in the early Late Cretaceous in North America and migrated again until the Campanian, probably from Asia or South America.