Antlers Formation

The Antlers Formation is a stratum which ranges from Arkansas through southern Oklahoma into northeastern Texas. The stratum is 150 m (490 ft) thick consisting of silty to sandy mudstone and fine to coarse grained sandstone that is poorly to moderately sorted. The stratum is cemented with clay and calcium carbonate. In places the sandstone may be conglomeratic or ferruginous (rich in iron oxides).

Based on correlation with the Trinity Group of Texas, the Antlers Formation is estimated to be late Aptian-early Albian. This age range is supported by the presence of two dinosaurs that are also known from the Cloverly Formation, Deinonychus and Tenontosaurus.

Antlers Formation
Stratigraphic range: Early Cretaceous
TypeGeological formation
RegionOklahoma, Texas
Country United States
Type section
Named byRobert Thomas Hill[1]


Indeterminate frog remains. Possible indeterminate salamander remains.

Basal vertebrates ("Fish")

References: Cifelli et al. 1999; Wedel et al. 2000, Kielan-Jarorowska and Cifelli 2001; Nydam and Cifelli 2002.

Cartilaginous fish

Ray-finned fish

Possible indeterminate amiid remains. Possible indeterminate lepisosteid remains. Possible indeterminate semionotidae remains.

Actinopterygians of the Antlers Formation
Genus Species Location Stratigraphic position Abundance Notes


Gyronchus dumblei


?Palaeobalistum sp.


Possible indeterminate deltatheroidan material. Indeterminate multituberculate remains. Indeterminate tribosphenidan remains.

Mammals of the Antlers Formation
Genus Species Location Stratigraphic position Abundance Notes


Astroconodon sp.


Atokatheridium boreni


Paracimexomys crossi



Possible indeterminate atoposaurid remains. Possible indeterminate goniopholidid remains. Possible indeterminate pholidosaurid remains.


Possible indeterminate scincid remains.

Lepidosaurs of the Antlers Formation
Genus Species Location Stratigraphic position Abundance Notes


Atokasaurus metarsiodon


Bemissartia sp.


Ptilotodon wilsoni



Possible indeterminate bird remains are known from the formation.


Turtles of the Antlers Formation
Genus Species Location Stratigraphic position Abundance Notes


Glyptops sp.


Naomichelys sp.

See also


  1. ^ Hill, R.T. (1894). "Geology of parts of Texas, Indian Territory and Arkansas adjacent to Red River". Bulletin of the Geological Society of America. 5: 303.
  2. ^ "Table 13.1," in Weishampel, et al. (2004). Page 267.

Further reading

  • Cifelli, R. Gardner, J.D., Nydam, R.L., and Brinkman, D.L. 1999. Additions to the vertebrate fauna of the Antlers Formation (Lower Cretaceous), southeastern Oklahoma. Oklahoma Geology Notes 57:124-131.
  • Nydam, R.L. and R. L. Cifelli. 2002a. Lizards from the Lower Cretaceous

(Aptian-Albian) Antlers and Cloverly formations. Journal of Vertebrate Paleontology. 22:286–298.

  • Kielan-Jarorowska, Z., and Cifelli, R.L. 2001. Primitive boreosphenidan mammal (?Deltatheroida) from the Early Cretaceous of Oklahoma. Acta Palaeontologica Polonica 46: 377-391.
  • Wedel, M.J., Cifelli, R.L., and Sanders, R. K. 2000. Sauroposeidon Proteles, A new sauropod from the Early Cretaceous of Oklahoma. Journal of Vertebrate Paleontology 20:109-114.
1950 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1950.


Acrocanthosaurus ( ak-ro-KAN-thə-SAWR-əs; meaning "high-spined lizard") is a genus of theropod dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous. Like most dinosaur genera, Acrocanthosaurus contains only a single species, A. atokensis. Its fossil remains are found mainly in the U.S. states of Oklahoma, Texas, and Wyoming, although teeth attributed to Acrocanthosaurus have been found as far east as Maryland.

Acrocanthosaurus was a bipedal predator. As the name suggests, it is best known for the high neural spines on many of its vertebrae, which most likely supported a ridge of muscle over the animal's neck, back, and hips. Acrocanthosaurus was one of the largest theropods, reaching 11.5 meters (38 ft) in length, and weighing up to 6.2 metric tons (6.8 short tons). Large theropod footprints discovered in Texas may have been made by Acrocanthosaurus, although there is no direct association with skeletal remains.

Recent discoveries have elucidated many details of its anatomy, allowing for specialized studies focusing on its brain structure and forelimb function. Acrocanthosaurus was the largest theropod in its ecosystem and likely an apex predator which preyed on sauropods, ornithopods, and ankylosaurs.


The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 Ma (million years ago). The Albian is preceded by the Aptian and followed by the Cenomanian.


The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), approximately. The Aptian succeeds the Barremian and precedes the Albian, all part of the Lower/Early Cretaceous.The Aptian partly overlaps the upper part of the regionally used (in Western Europe) stage Urgonian.

The Selli Event, also known as OAE1a, was one of two oceanic Anoxic events in the Cretaceous period, which occurred around 120 Ma and lasted approximately 1 to 1.3 million years. The Aptian extinction was a minor extinction event hypothesized to have occurred around 116 to 117 Ma.


Astroconodon is an extinct genus of mammal from the Cretaceous of North America. Part of Eutriconodonta, it was a small sized predator, either a terrestrial insectivore and carnivore, or a semi-aquatic piscivore.

It is the first Cretaceous eutriconodont found.


Astrodon (aster: star, odon: tooth) is a dubious genus of large herbivorous sauropod dinosaur, related to Brachiosaurus, that lived in what is now the eastern United States during the Early Cretaceous period. Its fossils have been found in the Arundel Formation, which has been dated through palynomorphs to the Albian about 112 million years ago. Adults are estimated to have been more than 9 m (30 ft) high and 15 to 18 m (50 to 60 ft) long.


Atokasaurus is an extinct genus of scincomorph lizard from the Early Cretaceous of Oklahoma. The type and only species is Atokasaurus metarsiodon, named in 2002 on the basis of a single isolated lower jaw bone found within the Antlers Formation in Atoka County. It is similar in appearance to extinct lizards in the family Paramacellodidae and may itself be a paramacellodid, although the phylogenetic relationships of the group are uncertain. Atokasaurus differs from other paramacellodids in having teeth in the lower jaw with enlarged bases and an S-shaped profile when viewed edge-on.


Deinonychus ( dy-NON-i-kəs; from Greek: δεινός deinós, 'terrible' and ὄνυξ ónux, genitive ὄνυχος ónuchos 'claw') is a genus of dromaeosaurid theropod dinosaur with one described species, Deinonychus antirrhopus. This species, which could grow up to 3.4 metres (11 ft) long, lived during the early Cretaceous Period, about 115–108 million years ago (from the mid-Aptian to early Albian stages). Fossils have been recovered from the U.S. states of Montana, Utah, Wyoming, and Oklahoma, in rocks of the Cloverly Formation, Cedar Mountain Formation and Antlers Formation, though teeth that may belong to Deinonychus have been found much farther east in Maryland.

Paleontologist John Ostrom's study of Deinonychus in the late 1960s revolutionized the way scientists thought about dinosaurs, leading to the "dinosaur renaissance" and igniting the debate on whether dinosaurs were warm-blooded or cold-blooded. Before this, the popular conception of dinosaurs had been one of plodding, reptilian giants. Ostrom noted the small body, sleek, horizontal posture, ratite-like spine, and especially the enlarged raptorial claws on the feet, which suggested an active, agile predator."Terrible claw" refers to the unusually large, sickle-shaped talon on the second toe of each hind foot. The fossil YPM 5205 preserves a large, strongly curved ungual. In life, archosaurs have a horny sheath over this bone, which extends the length. Ostrom looked at crocodile and bird claws and reconstructed the claw for YPM 5205 as over 120 millimetres (4.7 in) long. The species name antirrhopus means "counter balance", which refers to Ostrom's idea about the function of the tail. As in other dromaeosaurids, the tail vertebrae have a series of ossified tendons and super-elongated bone processes. These features seemed to make the tail into a stiff counterbalance, but a fossil of the very closely related Velociraptor mongoliensis (IGM 100/986) has an articulated tail skeleton that is curved laterally in a long S-shape. This suggests that, in life, the tail could bend to the sides with a high degree of flexibility. In both the Cloverly and Antlers formations, Deinonychus remains have been found closely associated with those of the ornithopod Tenontosaurus. Teeth discovered associated with Tenontosaurus specimens imply they were hunted, or at least scavenged upon, by Deinonychus.

List of fossiliferous stratigraphic units in Oklahoma

This article contains a list of fossil-bearing stratigraphic units in the state of Oklahoma, U.S.

List of fossiliferous stratigraphic units in Texas

This article contains a list of fossil-bearing stratigraphic units in the state of Texas, U.S.

List of stratigraphic units with dinosaur body fossils

This is a list of stratigraphic units from which dinosaur body fossils have been recovered. Although Dinosauria is a clade which includes modern birds, this article covers only Mesozoic stratigraphic units. Units listed are all either formation rank or higher (e.g. group).


Palaeobalistum is an extinct genus of prehistoric ray-finned fish which ranged from the Cretaceous to Eocene periods.


Paracimexomys is a genus of extinct mammals in the also extinct Multituberculata order. Paracimexomys lived during the Cretaceous period. The few fossils remains come from North America. Some Romanian fossils were also tentatively assigned to this genus, though that classification now seems doubtful.The genus Paracimexomys ("beside Cimexomys") was named by Archibald J.D. in 1982. Paracimexomys fossils were originally referred as Cimexomys, until it was realized they were different enough to justify a genus of their own.


Paramacellodidae is an extinct family of scincomorph lizards that first appeared in the Middle Jurassic around 170 million years ago (Ma) and became extinct in the Early Cretaceous about 100 Ma. It was one of the earliest groups of lizards to have undergone an evolutionary radiation, with members found across the supercontinent Laurasia. The phylogenetic relationships and constituent species of Paramacellodidae are uncertain. Many studies regard it to be closely related to Scincoidea, a large group that includes skinks and their closest extinct relatives, and possibly also to Cordyoidea, a group that includes spinytail lizards and relatives. Like modern skinks, paramacelloidids had rectangular bony plates called osteoderms covering most of their bodies, including their backs, undersides, and tails. They also had short and robust limbs.The family was named in 1983 to include two well-known genera, Paramacellodus and Becklesius, from the Late Jurassic and Early Cretaceous of Europe. A third genus, Sharovisaurus, was named in 1984 from the Late Jurassic of Kazakhstan, and a fourth, Mimobecklesisaurus, in 1985 from the Late Jurassic of China. Remains of Paramacellodus were later described from the Morrison Formation in Utah. Possible paramacellodid remains have also been found in Late Cretaceous deposits in Mongolia, as well as the Late Jurassic Tendaguru Formation in Tanzania, which would indicate that the family was also present in Gondwana. Three other early scincomorphs—Pseudosaurillus, Saurillodon, and Saurillus—have also commonly been referred to Paramacellodidae, although some recent phylogenetic studies find them to be non-paramacellodid scincomorphs. Collectively, paramacellodids and taxa formerly referred to Paramacellodidae may represent a paraphyletic grade of basal scincomorphs closely related to Scincoidea. In 2002, the newly named genus Atokasaurus from the Early Cretaceous Antlers Formation in Oklahoma was described as a "paramacellodid-grade" scincomorph to reflect this phylogenetic ambiguity.


Ptilotodon is an extinct genus of teiid lizard from the Early Cretaceous of Oklahoma. The type and only known species is Ptilotodon wilsoni, named in 2002 on the basis of a single lower jaw with four teeth found in the Antlers Formation. The small size of the specimen may be an indication that it belonged to a juvenile.


Sauroposeidon ( SOR-o-po-SY-dən; meaning "lizard earthquake god", after the Greek god Poseidon) is a genus of sauropod dinosaur known from several incomplete specimens including a bone bed and fossilized trackways that have been found in the American states of Oklahoma, Wyoming, and Texas. The fossils were found in rocks dating from near the end of the Early Cretaceous (Aptian–early Albian), a time when sauropod diversity in North America had greatly diminished. It was the last known North American sauropod prior to an absence of the group on the continent of roughly 40 million years that ended with the appearance of Alamosaurus during the Maastrichtian.

While the holotype remains were initially discovered in 1994, due to their unexpected age and unusual size they were initially misclassified as pieces of petrified wood. A more detailed analysis in 1999 revealed their true nature which resulted in a minor media frenzy, and formal publication of the find the following year.Paleoecological analysis indicates that Sauroposeidon lived on the shores of the Gulf of Mexico, in a river delta. Extrapolations based on the more completely known Brachiosaurus indicate that the head of Sauroposeidon could reach 17–18 m (56–59 ft) in height with its neck extended, which would make it the tallest known dinosaur. With an estimated length of 27–34 m (89–112 ft) and a mass of 40–60 t (44–66 short tons), it also ranks among the longest and heaviest. However, this animal may not be as closely related to Brachiosaurus as previously thought, so these estimates may be inaccurate.

While initially described as a brachiosaurid closely related to Brachiosaurus and Giraffatitan, the discovery of additional remains in the Cloverly Formation of Wyoming suggested that it was in fact more closely related to the titanosaurs, in the group Somphospondyli. Analysis of these remains and comparison with others from Texas supported this conclusion, and demonstrated that the more completely known sauropods from the Twin Mountains Formation (including a partial skull and fossil trackways) previously named Paluxysaurus jonesi also belonged to Sauroposeidon. It is the state dinosaur of Texas.


Tenontosaurus ( ti-NON-toh-SOR-əs; meaning "sinew lizard") is a genus of medium- to large-sized ornithopod dinosaur. The genus is known from the late Aptian to Albian ages of the middle Cretaceous period sediments of western North America, dating between 115 and 108 million years ago.

The genus contains two species, Tenontosaurus tilletti (described by John Ostrom in 1970) and Tenontosaurus dossi (described by Winkler, Murray, and Jacobs in 1997). Many specimens of T. tilletti have been collected from several geological formations throughout western North America. T. dossi is known from only a handful of specimens collected from the Twin Mountains Formation of Parker County, Texas.

Twin Mountains Formation

The Twin Mountains Formation, also known as the Twin Mountain Formation, is a sedimentary rock formation, within the Trinity Group, found in Texas of the United States of America. It is a terrestrial formation of Aptian age (Lower Cretaceous), and is notable for its dinosaur fossils. Dinosaurs from this formation include the large theropod Acrocanthosaurus, the sauropod Sauroposeidon, as well as the ornithopods Tenontosaurus and Convolosaurus. It is the lowermost unit of the lower Cretaceous, lying unconformably on Carboniferous strata. It is overlain by the Glen Rose Formation. It is the lateral equivalent of the lower part of the Antlers Formation.


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