Alamosaurus (/ˌæləmoʊˈsɔːrəs/; meaning "Ojo Alamo lizard") is a genus of titanosaurian sauropod dinosaurs, containing a single known species, Alamosaurus sanjuanensis, from the late Cretaceous Period of what is now southern North America. Isolated vertebrae and limb bones indicate that it reached sizes comparable to Argentinosaurus and Puertasaurus, which would make it the largest dinosaur known from North America. Its fossils have been recovered from a variety of rock formations spanning the Maastrichtian age of the late Cretaceous period. Specimens of a juvenile Alamosaurus sanjuanensis have been recovered from only a few meters below the Cretaceous-Paleogene boundary in Texas, making it among the last surviving non-avian dinosaur species.
|Restored skeletons of Alamosaurus and Tyrannosaurus at Perot Museum|
Alamosaurus was a gigantic quadrupedal herbivore with a long neck and tail and relatively long limbs. Its body was at least partly covered in bony armor.The total length of Alamosaurus is estimated to be 30 meters (98 ft) long. Though most of the complete remains come from juvenile or small adult specimens, three fragmentary specimens, SMP VP−1625, SMP VP−1850 and SMP VP−2104, suggest that adult Alamosaurus could have grown to enormous sizes comparable to the largest known dinosaurs like Argentinosaurus, which has been estimated to weigh 73 metric tons (80 short tons). Scott Hartman estimates Alamosaurus being slightly shorter at 28–30 m (92–98 ft) and is equal in weight to other massive titanosaurs such as Argentinosaurus and Puertasaurus. However, he says that at the moment, scientists do not know whether the massive tibia belongs to an Alamosaurus or a completely new species of sauropod.
Though no skull has ever been found, rod-shaped teeth have been found with Alamosaurus skeletons and probably belonged to this dinosaur. The vertebrae from the middle part of its tail had elongated centra. Alamosaurus had vertebral lateral fossae that resembled shallow depressions. Fossae that similarly resemble shallow depressions are known from Saltasaurus, Malawisaurus, Aeolosaurus, and Gondwanatitan. Venenosaurus also had depression-like fossae, but its "depressions" penetrated deeper into the vertebrae, were divided into two chambers, and extend farther into the vertebral columns. Alamosaurus had more robust radii than Venenosaurus.
Alamosaurus remains have been discovered throughout the southwestern United States. The holotype was discovered in June 1921 by Charles Whitney Gilmore, John Bernard Reeside and Charles Hazelius Sternberg at the Barrel Springs Arroyo in the Naashoibito Member of the Ojo Alamo Formation (or Kirtland Formation under a different definition) of New Mexico which was deposited during the Maastrichtian stage of the Late Cretaceous Period. Bones have also been recovered from other Maastrichtian formations, like the North Horn Formation of Utah and the Black Peaks, El Picacho and Javelina Formations of Texas. Undescribed titanosaur fossils closely associated with Alamosaurus have been found in the Evanston Formation in Wyoming. Three articulated caudal vertebrae were collected above Hams Fork, and are housed at the Museum of Paleontology, University of California, Berkeley. These specimens have not been described.
Smithsonian paleontologist Gilmore originally described the holotype, USNM 10486, a left scapula (shoulder bone), and the paratype USNM 10487, a right ischium (pelvic bone) in 1922, naming the type species Alamosaurus sanjuanensis. Contrary to popular assertions, the dinosaur is not named after the Alamo in San Antonio, Texas, or the battle that was fought there. The holotype, the specimen the name was based on, was discovered in New Mexico and, at the time of its naming, Alamosaurus had not yet been found in Texas. Instead, the name Alamosaurus comes from Ojo Alamo, the geologic formation in which it was found and which was, in turn, named after the nearby Ojo Alamo trading post (since this time there has been some debate as to whether to reclassify the Alamosaurus-bearing rocks as belonging to the Kirtland Formation or whether they should remain in the Ojo Alamo Formation). The term alamo itself is a Spanish word meaning "poplar" and is used for the local subspecies of cottonwood tree. The term saurus is derived from saura (σαυρα), Greek for "lizard" and is the most common suffix used in dinosaur names. There is only one species in the genus, Alamosaurus sanjuanensis, which is named after San Juan County, New Mexico, where the first remains were found.
In 1946, Gilmore posthumously described a more complete specimen, USNM 15660 found on June 15, 1937 on the North Horn Mountain of Utah by George B. Pearce. It consists of a complete tail, a right forelimb complete except for the fingers — which later research showed do not ossify with the Titanosauridae — and both ischia. Since then, hundreds of other bits and pieces from Texas, New Mexico, and Utah have been referred to Alamosaurus, often without much description. Despite being fragmentary, until the second half of the twentieth century they represented much of the globally known titanosaurid material. The most completely known specimen, TMM 43621-1, is a recently discovered juvenile skeleton from Texas, which allowed educated estimates of length and mass.
Some blocks catalogued under the same accession number as the relatively complete and well-known Alamosaurus specimen USNM 15660, and found in very close proximity to it based on bone impressions, were first investigated by Michael Brett-Surman in 2009. In 2015, he reported that the blocks contained osteoderms, the first confirmation of their existence on Alamosaurus.
No skull material is known, except for a few slender teeth.
Gilmore in 1922 was uncertain about the precise affinities of Alamosaurus and did not determine it any further than a general Sauropoda. In 1927 Friedrich von Huene placed it in the Titanosauridae.
Alamosaurus was in any case an advanced, or derived, member of the group Titanosauria, but its relationships within that group are far from certain. The issue is further complicated by some researchers rejecting the name Titanosauridae and replacing it with Saltasauridae. One major analysis unites Alamosaurus with Opisthocoelicaudia in a subgroup Opisthocoelicaudinae of the Saltasauridae. A major competing analysis finds Alamosaurus as a sister taxon to Pellegrinisaurus, with both genera located just outside Saltasauridae. Other scientists have also noted particular similarities with the saltasaurid Neuquensaurus and the Brazilian Trigonosaurus (the "Peiropolis titanosaur") which is used in many cladistic and morphologic analyses of titanosaurians. A recent analysis published March 15, 2016, by Anthony Fiorillo, Ron Tykoski et al indicates that Alamosaurus was a sister taxon to the Lognkosauria and therefore to species such as Futalognkosaurus and Mendozasaurus and lay outside the Saltasauridae (possibly being descended from close relations to the Saltasauridae), based on synapomorphies of cervical vertebral morphologies and two cladistic analyses. The same study also suggests that the ancestors of Alamosaurus hailed from South America, rather than Asia.
Alamosaurus fossils are most notably found in the Naashoibito member of the Ojo Alamo Formation (dated to between about 69–68 million years old) and in the Javelina Formation, though the exact age range of the latter has been difficult to determine. A juvenile specimen of Alamosaurus has been reported to come from the Black Peaks Formation, which overlies the Javelina in Big Bend, Texas, and which straddles the Cretaceous-Paleogene boundary. The Alamosaurus specimen was reported to come from a few meters below the boundary, dated to 66 million years ago, though the position of the boundary in this region is uncertain. Only one geological site in the Javelina Formation has thus far yielded the correct rock types for radiometric dating. The outcrop, situated in the middle strata of the formation about 90 meters (300 ft) below the K-Pg boundary and within the local range of Alamosaurus fossils, was dated to 69.0±0.9 million years old in 2010. Using this date, in correlation with a measured age from the underlying Aguja Formation and the likely location of the K-Pg boundary in the overlying Black Peaks Formation, the Alamosaurus fauna seems to have lasted from about 70–66 million years ago, with the earliest records of Alamosaurus near the base of the Javelina formation, and the latest just below the K-Pg boundary in the Black Peaks Formation.
Skeletal elements of Alamosaurus are among the most common Late Cretaceous dinosaur fossils found in the United States Southwest and are now used to define the fauna of that time and place, known as the "Alamosaurus fauna". In the south of Late Cretaceous North America, the transition from the Edmontonian to the Lancian faunal stages is even more dramatic than it was in the north. Thomas M. Lehman describes it as "the abrupt reemergence of a fauna with a superficially 'Jurassic' aspect." These faunas are dominated by Alamosaurus and feature abundant Quetzalcoatlus in Texas. The Alamosaurus-Quetzalcoatlus association probably represent semi-arid inland plains.
The appearance of Alamosaurus may have represented an immigration event from South America. Alamosaurus appears and achieves dominance in its environment very abruptly, which might support the idea that it originated following an immigration event. Other scientists speculated that Alamosaurus was an immigrant from Asia. However, critics of the immigration hypothesis note that inhabitants of an upland environment like Alamosaurus are more likely to be endemic than coastal species, and tend to have less of an ability to cross bodies of water. Further, Early Cretaceous titanosaurs are already known, so North American potential ancestors for Alamosaurus already existed.
Contemporaries of Alamosaurus in the American southwest include the tyrannosaurid Tyrannosaurus, the oviraptorid Ojoraptorsaurus, the hadrosaurids Gryposaurus alsatei and cf. Kritosaurus, the armored nodosaur Glyptodontopelta and the chasmosaurinae ceratopsids cf. Torosaurus utahensis, Bravoceratops, and Ojoceratops. Non-dinosaur species that had shared the same environment with Alamosaurus included the giant pterosaur Quetzalcoatlus, various species of fishes and rays, amphibians, lizards, turtles like Adocus, and multiple species of multituberculates like Cimexomys and Mesodma.
Aeolosaurini is an extinct clade of titanosaurian dinosaurs known from the late Cretaceous period of Argentina and Brazil. Thomas Holtz (2011) assigned Adamantisaurus, Aeolosaurus, Gondwanatitan, Muyelensaurus, Panamericansaurus, Pitekunsaurus and Rinconsaurus to Aeolosauridae. Rodrigo M. Santucci and Antonio C. de Arruda-Campos (2011) in their cladistic analysis found Aeolosaurus, Gondwanatitan, Maxakalisaurus, Panamericansaurus and Rinconsaurus to be aeolosaurids.Austroposeidon
Austroposeidon is an extinct genus of titanosaurian sauropod dinosaur from the Late Cretaceous Presidente Prudente Formation of Brazil. It contains one species, Austroposeidon magnificus.Black Peaks Formation
The Black Peaks Formation is a geological formation in Texas whose strata date back to the Late Cretaceous. Dinosaur remains (from the sauropod Alamosaurus) have been among the fossils reported from the formation. The boundary with the underlying Javelina Formation has been estimated at about 66.5 million years old. The formation preserves the rays Rhombodus and Dasyatis, as well as many gar scales.Charles W. Gilmore
Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the National Museum of Natural History). Gilmore named many dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus ovatus (now Rubeosaurus) and Thescelosaurus.Diamantinasaurus
Diamantinasaurus is an extinct genus of non-lithostrotian titanosaurian sauropod from Australia that lived during the early Late Cretaceous, about 94 million years ago. The type species of the genus is D. matildae, first described and named in 2009 by Scott Hocknull and colleagues. Meaning "Diamantina lizard", the name is derived from the location of the nearby Diamantina River and the Greek word sauros, "lizard". The specific epithet is from the Australian song Waltzing Matilda, also the locality of the holotype and paratype. The known skeleton includes most of the forelimb, shoulder girdle, pelvis, hindlimb and ribs of the holotype, and one shoulder bone, a radius and some vertebrae of the paratype.Futalognkosaurus
Futalognkosaurus ( FOO-tə-long-ko-SAW-rəs; meaning "giant chief lizard") is a genus of titanosaurian dinosaur. The herbivorous Futalognkosaurus lived approximately 87 million years ago in the Portezuelo Formation, in what is now Argentina, of the Coniacian stage of the late Cretaceous Period. The fish and fossilized leaf debris on the site, together with other dinosaur remains, suggest a warm tropical climate in Patagonia during this period.Javelina Formation
The Javelina Formation is a geological formation in Texas. Dating has shown that the strata date to the Maastrichtian stage of the Late Cretaceous, approximately 70 to 66.5 million years old. The middle part of the formation has been dated to about 69 million years ago plus or minus 1 Ma and the top situated near the Cretaceous–Paleogene boundary (in the overlying Black Peaks Formation), dated to 66 Ma ago. Dinosaur remains are among the fossils that have been recovered from the formation.Lancian
The Lancian was a North American faunal stage of the Late Cretaceous. It was the final stage of the Cretaceous period in North America, lasting from approximately 68 to 66 million years ago.Lithostrotia
Lithostrotia is a clade of derived titanosaur sauropods that lived during the Early Cretaceous and Late Cretaceous. The group was defined by Unchurch et al. in 2004 as the most recent common ancestor of Malawisaurus and Saltasaurus and all the descendants of that ancestor. Lithostrotia is derived from the Ancient Greek lithostros, meaning "inlaid with stones", referring to the fact that many known lithostrotians are preserved with osteoderms. However, osteoderms are not a distinguishing feature of the group, as the two noted by Unchurch et al. include caudal vertebrae with strongly concave front faces (procoely), although the farthest vertebrae are not procoelous.Malawisaurus
Malawisaurus (meaning "Malawi lizard") was a genus of sauropod dinosaur (specifically a titanosaurian). It lived in what is now Africa, specifically Malawi, during the Aptian age of the Early Cretaceous Period. It is one of the few titanosaurs for which skull material has been found.Nemegtosaurus
Nemegtosaurus (meaning 'Reptile from the Nemegt') was a sauropod dinosaur from Late Cretaceous Period of what is now Mongolia. Nemegtosaurus was named after the Nemegt Basin in the Gobi Desert, where the remains — a single skull — were found. The skull resembles diplodocoids in being long and low, with pencil-shaped teeth. However, recent work has shown that Nemegtosaurus is in fact a titanosaur, closely related to animals such as Saltasaurus, Alamosaurus and Rapetosaurus.Opisthocoelicaudia
Opisthocoelicaudia is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is Opisthocoelicaudia skarzynskii. A well-preserved skeleton lacking only the head and neck was unearthed in 1965 by Polish and Mongolian scientists, making Opisthocoelicaudia one of the best known sauropods from the Late Cretaceous. Tooth marks on this skeleton indicate that large carnivorous dinosaurs had fed on the carcass and possibly had carried away the now-missing parts. To date, only two additional, much less complete specimens are known, including a part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4–13 metres (37–43 ft) in length. Like other sauropods, it would have been characterised by a small head sitting on a very long neck and a barrel shaped trunk carried by four column-like legs. The name Opisthocoelicaudia means "posterior cavity tail", alluding to the unusual, opisthocoel condition of the anterior tail vertebrae that were concave on their posterior sides. This and other skeletal features lead researchers to propose that Opisthocoelicaudia was able to rear on its hindlegs.
Named and described by Polish paleontologist Maria Magdalena Borsuk-Białynicka in 1977, Opisthocoelicaudia was first thought to be a new member of the Camarasauridae, but is currently considered a derived member of the Titanosauria. Its exact relationships within Titanosauria are contentious, but it may have been close to the North American Alamosaurus. All Opisthocoelicaudia fossils stem from the Nemegt Formation. Despite being rich in dinosaur fossils, the only other sauropod from this rock unit is Nemegtosaurus, which is known from a single skull. Since the skull of Opisthocoelicaudia remains unknown, several researchers have suggested that Nemegtosaurus and Opisthocoelicaudia may represent the same species. Sauropod footprints from the Nemegt Formation, which include skin impressions, can probably be referred to either Nemegtosaurus or Opisthocoelicaudia as these are the only known sauropods from this formation.Opisthocoelicaudiinae
Opisthocoelicaudiinae is a clade of titanosaurian dinosaurs from the Late Cretaceous, ranked as a subfamily. Opisthocoelicaudiines are known from China, Mongolia, and the United States (New Mexico, Texas, and Utah). Three genera have been assigned to Opisthocoelicaudiinae: Alamosaurus, Borealosaurus, and Opisthocoelicaudia (the type genus). It was named by John S. McIntosh in 1990. The hands of opisthocoelicaudiines lacked wrist bones and phalanges.Quetzalcoatlus
Quetzalcoatlus northropi is a pterosaur known from the Late Cretaceous of North America (Maastrichtian stage) and one of the largest known flying animals of all time. It is a member of the family Azhdarchidae, a family of advanced toothless pterosaurs with unusually long, stiffened necks. Its name comes from the Mesoamerican feathered serpent god, Quetzalcoatl.Saltasauridae
Saltasauridae (named after the Salta region of Argentina where they were first found) — a family of armored herbivorous sauropods from the Upper Cretaceous. They are known from fossils found in South America, Asia, North America, and Europe. They are characterized by their vertebrae and feet, which are similar to those of Saltasaurus, the first of the group to be discovered and the source of the name. The last and largest of the group and only one found in North America, Alamosaurus, was thirty-four metres (112 feet) in length and the last sauropod to go extinct.
Most of the saltasaurids were smaller, around fifteen metres (49 feet) in length, and one, Rocasaurus, was only eight metres (26 feet) long. Like all sauropods, the saltasaurids were quadrupeds, their necks and tails were held almost parallel to the ground, and their small heads had only tiny, peg-like teeth. They were herbivorous, stripping leaves off of plants and digesting them in their enormous guts. Although large animals, they were smaller than other sauropods of their time, and many possessed distinctive additional defenses in the form of scutes along their backs.Saltasaurinae
Saltasaurinae is a subfamily of titanosaurian sauropods known from the late Cretaceous period of South America, India and Madagascar. They are considered to be the most derived of all sauropods.Tangvayosaurus
Tangvayosaurus (meaning "Tang Vay lizard") is a genus of sauropod dinosaur from the Aptian-Albian age Lower Cretaceous Grès Supérior Formation of Savannakhet, Laos. It was a basal somphospondylan, about 15 m long, and is known from the remains of two or three individuals.Titanosauria
Titanosaurs (members of the group Titanosauria) were a diverse group of sauropod dinosaurs which included Saltasaurus and Isisaurus of Africa, Asia, South America, Europe and Australia. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thriving at the time of the extinction event at the end of the Cretaceous. The group includes the largest land animals known to have existed, such as Patagotitan—estimated at 37 m (121 ft) long with a weight of 69 tonnes (76 tons)—and the comparably sized Argentinosaurus and Puertasaurus from the same region. The group's name alludes to the mythological Titans of Ancient Greece, via the type genus (now considered a nomen dubium) Titanosaurus. Together with the brachiosaurids and relatives, titanosaurs make up the larger clade Titanosauriformes.Venenosaurus
Venenosaurus ( ven-EN-o-SOR-əs) was a sauropod dinosaur. The name literally means "poison lizard", and it was named so after the Poison Strip Member of the Cedar Mountain Formation in Utah, United States, where the fossils were discovered by a Denver Museum of Natural History volunteer Tony DiCroce in 1998. Venenosaurus dicrocei was first described as a new species in 2001 by Virginia Tidwell, Kenneth Carpenter, and Suzanne Meyer. Venenosaurus is a relatively small (probably around 10 m (33 ft) long) titanosauriform sauropod, known from an incomplete skeleton of an adult and a juvenile. The holotype is DMNH 40932 Denver Museum of Natural History. The specimen consisted of tail vertebrae, the left scapula, right radius, left ulna, metacarpals, forefoot phalanges, right pubis, left and right ischia, metatarsals, chevrons, and ribs.