''Alamosaurus'' (; meaning "Ojo Alamo lizard") is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
opisthocoelicaudiine titanosauria
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
n
sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', ' lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s, containing a single known species, ''Alamosaurus sanjuanensis'', from the late
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
Period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
of what is now southern
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 th ...
. Isolated
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
e and limb bones indicate that it reached
sizes comparable to ''
Argentinosaurus
''Argentinosaurus'' is a genus of giant sauropod dinosaur that lived during the Late Cretaceous period in what is now Argentina. Although it is only known from fragmentary remains, ''Argentinosaurus'' is one of the largest known land animal ...
'' and ''
Puertasaurus
''Puertasaurus'' is a genus of sauropod dinosaur that lived in South America during the Late Cretaceous Period. It is known from a single specimen recovered from sedimentary rocks of the Cerro Fortaleza Formation in southwestern Patagonia, Ar ...
'', 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
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the inte ...
age of the late
Cretaceous period
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of t ...
. 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.
Description
''Alamosaurus'' was a gigantic
quadruped
Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...
al
herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
with a long neck and tail and relatively long limbs.
Its body was at least partly covered in bony armor.
In 2012
Thomas Holtz
Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomor ...
gave a total length of or more and an approximate weight of 72.5–80 tonnes (80–88 short tons) or more.
[ ]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 .
Scott Hartman estimates ''Alamosaurus,'' based on a huge incomplete
tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...
that probably refers to it, being slightly shorter at and equal in weight to other massive titanosaurs such as ''
Argentinosaurus
''Argentinosaurus'' is a genus of giant sauropod dinosaur that lived during the Late Cretaceous period in what is now Argentina. Although it is only known from fragmentary remains, ''Argentinosaurus'' is one of the largest known land animal ...
'' and ''
Puertasaurus
''Puertasaurus'' is a genus of sauropod dinosaur that lived in South America during the Late Cretaceous Period. It is known from a single specimen recovered from sedimentary rocks of the Cerro Fortaleza Formation in southwestern Patagonia, Ar ...
''. It is currently the only titanosaur from North America. However, he says that at the moment, scientists do not know whether the massive
tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...
belongs to an ''Alamosaurus'' or a completely new species of sauropod. In 2019
Gregory S. Paul estimated the (SMP VP−1625) specimen at 27 tonnes (30 short tons), and he also mentioned a large partial anterior caudal vertebra which suggests an Alamosaurus specimen that is 15 percent dimensionally larger with similar mass to his ''
Dreadnoughtus'' estimation of 31 tonnes (34 short tons). In 2020 Molina-Perez and Larramendi estimated the size of the largest individual at 26 meters (85.3 ft) and 38 tonnes (42 short tons).
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
Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees.
The chain has three different ...
.
''Alamosaurus'' had vertebral lateral
fossae that resembled shallow depressions.
Fossae that similarly resemble shallow depressions are known from ''
Saltasaurus
''Saltasaurus'' (which means "lizard from Salta") is a genus of saltasaurid dinosaur of the Late Cretaceous period of Argentina. Small among sauropods, though still heavy by the standards of modern creatures, ''Saltasaurus'' was characterized by ...
'', ''
Malawisaurus
''Malawisaurus'' (meaning "Malawi lizard") is an extinct genus of titanosaurian sauropod dinosaur. It is known from the Dinosaur Beds of northern Malawi, which probably date to the Aptian stage of the Early Cretaceous. The type species is ''M. di ...
'', ''
Aeolosaurus
''Aeolosaurus'' (; "Aeolus' lizard") is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now South America. Like most sauropods, it would have been a quadrupedal herbivore with a long neck and tail. ''Aeolos ...
'', and ''
Gondwanatitan
''Gondwanatitan'' (meaning "giant from Gondwana") was a titanosaurian sauropod dinosaur. ''Gondwanatitan'' was found in Brazil, at the time part of the southern supercontinent Gondwana, in the late Cretaceous Period (70 mya). Like some oth ...
''.
''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
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
than ''
Venenosaurus
''Venenosaurus'' ( ) 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 ...
''.
History
''Alamosaurus'' remains have been discovered throughout the
southwestern United States
The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, N ...
. The
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...
was discovered in June 1921 by
Charles Whitney 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 N ...
,
John Bernard Reeside
John is a common English name and surname:
* John (given name)
* John (surname)
John may also refer to:
New Testament
Works
* Gospel of John, a title often shortened to John
* First Epistle of John, often shortened to 1 John
* Seco ...
and
Charles Hazelius Sternberg
Charles Hazelius Sternberg (June 15, 1850 – July 20, 1943) was an American fossil collector and paleontologist. He was active in both fields from 1876 to 1928, and collected fossils for Edward Drinker Cope and Othniel C. Marsh, and for the ...
at the Barrel Springs Arroyo in the Naashoibito Member of the
Ojo Alamo Formation (or
Kirtland Formation
The Kirtland Formation (originally the Kirtland Shale) is a sedimentary geological formation.
Description
The Kirtland Formation is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain th ...
under a different definition) of
New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe, New Mexico, Santa Fe
, LargestCity = Albuquerque, New Mexico, Albuquerque
, LargestMetro = Albuquerque metropolitan area, Tiguex
, Offi ...
which was deposited during the
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the inte ...
stage of the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...
Period.
[ Bones have also been recovered from other Maastrichtian formations, like the ]North Horn Formation
The North Horn Formation is a widespread non-marine sedimentary unit with extensive outcrops exposed in central and eastern Utah. The formation locally exceeds in thickness and is characterized by fluvial, Lacustrine plain, lacustrine, and flood ...
of Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
and the Black Peaks, El Picacho and Javelina
A peccary (also javelina or skunk pig) is a medium-sized, pig-like hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of North ...
Formations of Texas
Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
.[Weishampel, D.B. ''et al.''. (2004). "Dinosaur Distribution (Late Cretaceous, North America)". In Weishampel, D.B., Dodson, P., Oslmolska, H. (eds.). "The Dinosauria (Second ed.)". University of California Press.] Undescribed titanosaur fossils closely associated with ''Alamosaurus'' have been found in the Evanston Formation
The Evanston Formation is a geological formation in Wyoming whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et al. (2004). "Dinosaur distributio ...
in Wyoming
Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...
. Three articulated caudal vertebrae were collected above Hams Fork, and are housed at the Museum of Paleontology, University of California, Berkeley
The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant un ...
. These specimens have not been described.
Smithsonian paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Gilmore originally described the holotype, USNM 10486, a left scapula
The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...
(shoulder bone), and the paratype
In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...
USNM 10487, a right ( pelvic bone) in 1922, naming the type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...
''Alamosaurus sanjuanensis''. Contrary to popular assertions, the dinosaur is not named after the Alamo
The Battle of the Alamo (February 23 – March 6, 1836) was a pivotal event in the Texas Revolution. Following a 13-day siege, Mexican troops under President General Antonio López de Santa Anna reclaimed the Alamo Mission near San Anton ...
in San Antonio
("Cradle of Freedom")
, image_map =
, mapsize = 220px
, map_caption = Interactive map of San Antonio
, subdivision_type = Country
, subdivision_name = United States
, subdivision_type1= State
, subdivision_name1 = Texas
, subdivision_ ...
, Texas
Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
, or the battle
A battle is an occurrence of combat in warfare between opposing military units of any number or size. A war usually consists of multiple battles. In general, a battle is a military engagement that is well defined in duration, area, and for ...
that was fought there. The holotype, the specimen the name was based on, was discovered in New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe, New Mexico, Santa Fe
, LargestCity = Albuquerque, New Mexico, Albuquerque
, LargestMetro = Albuquerque metropolitan area, Tiguex
, Offi ...
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
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...
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
The Kirtland Formation (originally the Kirtland Shale) is a sedimentary geological formation.
Description
The Kirtland Formation is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain th ...
or whether they should remain in the Ojo Alamo Formation). The term ''alamo'' itself is a Spanish
Spanish might refer to:
* Items from or related to Spain:
**Spaniards are a nation and ethnic group indigenous to Spain
**Spanish language, spoken in Spain and many Latin American countries
**Spanish cuisine
Other places
* Spanish, Ontario, Can ...
word meaning "poplar" and is used for the local subspecies of cottonwood tree
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
. The term ''saurus'' is derived from ''saura'' (σαυρα), Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
for "lizard" and is the most common suffix used in dinosaur names. There is only one species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
in the genus, ''Alamosaurus sanjuanensis'', which is named after San Juan County, New Mexico
San Juan County is located in the U.S. state of New Mexico. As of the 2020 census, the population was 121,661 making it the fifth-most populous county in New Mexico. Its county seat is Aztec. The county was created in 1887.
San Juan Count ...
, 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.[
The restored ''Alamosaurus'' skeletal mount at the Perot Museum (pictured right) was discovered when a member of an excavation team at a nearby site had to go around a hill to urinate.
]
Classification
Gilmore in 1922 was uncertain about the precise affinities of ''Alamosaurus'' and did not determine it any further than a general Sauropoda
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
.[ In 1927 ]Friedrich von Huene
Friedrich von Huene, born Friedrich Richard von Hoinigen, (March 22, 1875 – April 4, 1969) was a German paleontologist who renamed more dinosaurs in the early 20th century than anyone else in Europe. He also made key contributions about v ...
placed it in the Titanosauridae
Lithostrotia is a clade of derived titanosaur sauropods that lived during the Early Cretaceous and Late Cretaceous. The group was defined by Upchurch ''et al.'' in 2004 as the most recent common ancestor of '' Malawisaurus'' and '' Saltasaurus'' ...
.
''Alamosaurus'' was in any case an advanced, or derived, member of the group Titanosauria
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
, 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
''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 wa ...
'' in a subgroup Opisthocoelicaudiinae
Opisthocoelicaudiinae is a subfamily of titanosaurian dinosaurs from the Late Cretaceous. It was named by John McIntosh in 1990. Opisthocoelicaudiines are known from Mongolia, Argentina, and the United States. Two genera were assigned to Op ...
of the Saltasauridae
Saltasauridae (named after the Salta region of Argentina where they were first found) is a family of armored herbivorous sauropods from the Upper Cretaceous. They are known from fossils found in South America, Asia, North America, and Europe. T ...
. A major competing analysis finds ''Alamosaurus'' as a sister taxon
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
to ''Pellegrinisaurus
''Pellegrinisaurus'' (meaning ''Lizard from Pelligrini'') is a genus of titanosaurian sauropod dinosaur that lived in South America during the Late Cretaceous period. The holotype was found in the Allen Formation, Argentina.
Discovery and na ...
'', with both genera located just outside Saltasauridae. Other scientists have also noted particular similarities with the saltasaurid ''Neuquensaurus
''Neuquensaurus'' (meaning "Neuquén lizard") is a genus of saltasaurid sauropod dinosaur that lived in the Late Cretaceous, about 80 million years ago in Argentina and Uruguay in South America. Its fossils were recovered from outcrops of the A ...
'' and the Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
ian'' Trigonosaurus'' (the "Peiropolis titanosaur") which is used in many cladistic
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
and morphologic analyses of titanosaurians. A recent analysis published in 2016 by Anthony Fiorillo and Ron Tykoski indicates that ''Alamosaurus'' was a sister taxon to the Lognkosauria
Lognkosauria is a clade of giant long-necked sauropod dinosaurs within the clade Titanosauria. It includes some of the largest and heaviest dinosaurs known.
Description
Lognkosaurians can be distinguished from other titanosaurs by the wide and u ...
and therefore to species such as ''Futalognkosaurus
''Futalognkosaurus'' ( ; 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 ...
'' and ''Mendozasaurus
''Mendozasaurus'' is a genus of titanosaurian sauropod dinosaur. It was a member of Titanosauria, which were massive sauropods that were common on the southern landmasses during the Cretaceous. It is represented by several partial skeletons fro ...
'' 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.
Age
''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
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 abo ...
, though the exact age range of the latter has been difficult to determine.[Sullivan, R.M., and Lucas, S.G. 2006.]
The Kirtlandian land-vertebrate "age" – faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America
" New Mexico Museum of Natural History and Science, Bulletin 35:7–29. 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 below the K-Pg boundary and within the local range of ''Alamosaurus'' fossils, was dated to million years old in 2010.[ Using this date, in correlation with a measured age from the underlying ]Aguja Formation
The Aguja Formation is a geological Formation (geology), formation in North America, exposed in Texas, United States and Chihuahua (state), Chihuahua and Coahuila (state), Coahuila in Mexico, whose strata date back to the Late Cretaceous. Dinosaur ...
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.[
]
Habitat and geographic origin
Skeletal elements of ''Alamosaurus'' are among the most common Late Cretaceous dinosaur fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s found in the United States Southwest and are now used to define the fauna
Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is '' flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. ...
of that time and place, known as the "''Alamosaurus'' fauna". In the south of Late Cretaceous North America, the transition from the Edmontonian
The Edmontonian was a North American faunal epoch occurring during the Late Cretaceous, lasting from approximately 70 to 68 million years ago.
Paleobiogeography
In southern North America, little changed in the transition from the Judithian to t ...
to the 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 70.6 to 66 million years ago.
Geology
Terrestrial sedimentary strata from the Judit ...
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
''Quetzalcoatlus'' is a genus of pterosaur known from the Late Cretaceous period of North America (Maastrichtian stage); its members were among the largest known flying animals of all time. ''Quetzalcoatlus'' is a member of the Azhdarchidae, ...
'' 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 unidentified tyrannosaurids
Tyrannosauridae (or tyrannosaurids, meaning " tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous '' Tyrannosaurus''. The exact number of ...
similar to ''Tyrannosaurus
''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
'', the oviraptorosaur ''Ojoraptorsaurus
''Ojoraptorsaurus'' is a genus of oviraptorosaurian dinosaur from the late Cretaceous. ''Ojoraptorsaurus'' is only known from pubic bones found at the Naashoibito Member of the Ojo Alamo Formation dating to the early Maastrichtian, about 69 mil ...
'', the hadrosaurid '' Kritosaurus'', the armored nodosaur ''Glyptodontopelta
''Glyptodontopelta'' (meaning "''Glyptodon'' shield") is a monospecific genus of nodosaurid dinosaur from New Mexico that lived during the Late Cretaceous (lower to upper Maastrichtian, 69 to 66 Ma) in what is now the Naashoibito member of the ...
'' and the chasmosaurine ceratopsids cf. ''Torosaurus utahensis
''Torosaurus'' ("perforated lizard", in reference to the large openings in its frill) is a genus of herbivorous ceratopsid dinosaur that lived during the late Maastrichtian stage of the Cretaceous period, between 68 and 66 million years ago, ...
'', ''Bravoceratops
''Bravoceratops'' is a genus of large chasmosaurine ceratopsid dinosaur that lived approximately 70 million years ago, and is known from the Late Cretaceous Javelina Formation in what is now Texas, United States.
Discovery and naming
''Brav ...
'', and ''Ojoceratops
''Ojoceratops'' ( meaning "Ojo Alamo horned face") is a genus of ceratopsian dinosaur which lived in what is now New Mexico, United States. ''Ojoceratops'' fossils have been recovered from strata of the Ojo Alamo Formation (Naashoibito Member), d ...
''. Non-dinosaur taxa that had shared the same environment with ''Alamosaurus'' include the giant pterosaur ''Quetzalcoatlus
''Quetzalcoatlus'' is a genus of pterosaur known from the Late Cretaceous period of North America (Maastrichtian stage); its members were among the largest known flying animals of all time. ''Quetzalcoatlus'' is a member of the Azhdarchidae, ...
'', various species of fish
Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
es and rays
Ray may refer to:
Fish
* Ray (fish), any cartilaginous fish of the superorder Batoidea
* Ray (fish fin anatomy), a bony or horny spine on a fin
Science and mathematics
* Ray (geometry), half of a line proceeding from an initial point
* Ray (gra ...
, amphibian
Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...
s, lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia altho ...
s, turtle
Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...
s like ''Adocus
''Adocus'' is an extinct genus of aquatic turtles belonging to the family Adocidae. ''Adocus'' was once considered to belong to the family Dermatemyidae.
Description
Species of the genus ''Adocus'' had flattened and smoothly contoured shells ...
'', and multiple species of multituberculates
Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, a ...
like ''Cimexomys
''Cimexomys'' is an extinct North American mammal that lived from the Upper Cretaceous to the Paleocene. For a while, it shared the world with dinosaurs, but outlived them. It was a member of the extinct order Multituberculata and lies withi ...
'' and ''Mesodma
''Mesodma'' is an extinct genus of mammal, a member of the extinct order Multituberculata within the suborder Cimolodonta, family Neoplagiaulacidae. It lived during the upper Cretaceous and Paleocene Periods of what is now North America. The e ...
''.
References
Notes
{{Taxonbar, from=Q131583
Late Cretaceous dinosaurs of North America
Saltasaurids
Natural history of San Juan County, New Mexico
Fossil taxa described in 1922
Taxa named by Charles W. Gilmore
Paleontology in New Mexico
Paleontology in Utah
Paleontology in Texas
Ojo Alamo Formation
Maastrichtian genus first appearances
Maastrichtian genus extinctions