Cloverly Formation

The Cloverly Formation is a geological formation of Early Cretaceous age (Aptian to Albian stage)[2] that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on the eastern side of the Bighorn Basin in Wyoming by N.H. Darton in 1904.[1][3] The sedimentary rocks of formation were deposited in floodplain environments and contain vertebrate fossils, including a diverse assemblage of dinosaur remains. In 1973, the Cloverly Formation Site was designated as a National Natural Landmark by the National Park Service.[4]

Cloverly Formation
Stratigraphic range: Aptian-Albian
Cloverly Fm
Brightly colored strata of the Himes Member of the Cloverly Formation near Shell, Wyoming
TypeGeological formation
UnderliesThermopolis Shale
OverliesMorrison Formation
Thickness150–400 ft (46–122 m)
Lithology
PrimaryMudstone
OtherConglomerate, sandstone
Location
RegionWyoming, Montana, Colorado, Utah
Country USA
Type section
Named forCloverly post office, Wyoming
Named byNelson Horatio Darton, 1904[1]

Stratigraphy

The Cloverly Formation rests disconformably on the Morrison Formation and is conformably overlain by the Thermopolis Shale. It is subdivided into a variety of members, depending on the location.[3][5] In the Bighorn Basin along the Montana-Wyoming border, the Cloverly is divided into the following three members:

  • The Pryor Conglomerate lies at the base and contains abundant black chert. It is named from thick beds exposed on the west side of the Pryor Mountains.
  • The Little Sheep Member lies in the middle and is composed of pale-purple, gray to almost white, bentonitic mudstone.
  • The uppermost unit is the Himes Member, which contains some coarse-grained channel sandstone deposits, but consists primarily of brightly multicolored (variegated) mudstones.

Age

Radiometric dating by the fission track method has yielded dates of 115 ± 10 Ma (million years ago) for the lower part of the Little Sheep Member[2] and 108.5 ± 0.2 Ma near the top of that member,[6] confirming that the Cloverly Formation is of Aptian to Albian age.

Depositional environment

The sediments of the Cloverly Formation were deposited in alluvial and floodplain environments. The basal conglomerates probably represent braided river deposits, while the sandstones were deposited in fluvial channels. The mudstones that contain most of the fossils represent overbank, lacustrine, and pedogenic deposits.[3][5][7]

Vertebrate fauna

Animals recovered include the dinosaurs Deinonychus, Microvenator, Tenontosaurus, Zephyrosaurus and Sauropelta as well as fragmentary remains of Titanosaurs and Ornithomimids. As well, two genera of turtle Naomichelys and Glyptops and the lungfish Ceratodus.

Dinosaur eggs have been found in Montana.[8]

References for data: Ostrom 1970; Cifelli et al. 1998; Cifelli 1999; Nydam and Cifelli 2002. Possible goniopholidid remains are known from the formation.

Ornithischians

Deinonychus (Raptor Prey Restraint)
Zephyrosaurus being attacked by Deinonychus

Saurischians

Theropod eggshell fragments are known from the formation. Unidentifiable ornithomimmid remains are present and most commonly represented by toe bones.[10] Indeterminate allosauroid remains are known from the formation. Remains identified by John Ostrom as Ornithomimus are suspected by Jack Horner to be of a new ornithomimid genus.[10]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Mammals

Turtles

Turtles reported from the Cloverly Formation
Genus Species State Stratigraphic position Material Notes

Glyptops[10]

G. pervicax[10]

Naomichelys[10]

N. speciosa[10]

Bony fish

Indeterminate amiiformes are known from the formation.

See also

Footnotes

  1. ^ a b Darton, N.H. 1904. Comparison of the stratigraphy of the Black Hills, Bighorn Mountains, and Rocky Mountain Front Range. Geological Society of America Bulletin, v. 15, p. 379-448.
  2. ^ a b Chen, Z.-Q. and Lubin, S. 1997. A fission track study of the terrigenous sedimentary sequences of the Morrison and Cloverly Formations in northeastern Bighorn Basin, Wyoming. The Mountain Geologist 34: 51-62.
  3. ^ a b c U.S. Geological Survey (1993). "Geologic Unit: Cloverly". Retrieved 2014-12-23.
  4. ^ "National Natural Landmarks - National Natural Landmarks (U.S. National Park Service)". www.nps.gov. Retrieved 2019-03-22. Year designated: 1973
  5. ^ a b Moberly, R.M., Jr., 1960, Morrison, Cloverly, and Sykes Mountain formations, northern Bighorn basin, Wyoming and Montana: Geological Society of America Bulletin, v. 71, no. 8, p. 1137-1176.
  6. ^ Burton, D., Greenhalgh, B.W., Britt, B.B., Kowallis, B.J., Elliott, W.S., and Barrick, R. 2006. New radiometric ages from the Cedar Mountain Formation, Utah and the Cloverly Formation, Wyoming: implications for contained dinosaur faunas. Geological Society of America Abstracts with Programs 38(7): 52.
  7. ^ May, M.T. 1992. Intra- and extrabasinal tectonism, climate and intrinsic threshold cycles as possible controls on Early Cretaceous fluvial architecture, Wind River basin, Wyoming. In: Sundell, K.A., and Anderson, T.C., eds., Rediscover the Rockies: Wyoming Geological Association Field Conference Guidebook, 43rd Annual Field Conference, Casper, WY, September 12–19, 1992, no. 43, p. 61-74.
  8. ^ a b "3.11 Montana, United States; 1. Cloverly Formation," in Weishampel, et al. (2004). Page 556.
  9. ^ Andrew A. Farke, W. Desmond Maxwell, Richard L. Cifelli & Mathew J. Wedel (2014) A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America, and the Biogeography of Neoceratopsia. PLoS ONE 9(12): e112055. doi:10.1371/journal.pone.0112055 http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0112055
  10. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag Horner. Pp. 93-100.
  11. ^ "Table 17.1," in Weishampel, et al. (2004). Page 365.
  12. ^ a b c d "3.12 Wyoming, United States; 2. Cloverly Formation," in Weishampel, et al. (2004). Page 556.
  13. ^ a b c d e f D'Emic, Michael D.; Melstrom, Keegan M.; Eddy, Drew R. (2012). "Paleobiology and geographic range of the large-bodied Cretaceous theropod dinosaur Acrocanthosaurus atokensis". Palaeogeography, Palaeoclimatology, Palaeoecology. 333–334: 13–23. doi:10.1016/j.palaeo.2012.03.003.
  14. ^ "Table 8.1," in Weishampel, et al. (2004). Page 167.
  15. ^ "Table 5.1," in Varricchio (2001). Page 44.
  16. ^ a b c "3.11 Wyoming, United States; 1. Cloverly Formation" and "3.12 Montana, United States; 2. Cloverly Formation," in Weishampel, et al. (2004). Page 556.
  17. ^ a b c D. Cary Woodruff (2012). "A new titanosauriform from the Early Cretaceous Cloverly Formation of Montana". Cretaceous Research. 36: 58–66. doi:10.1016/j.cretres.2012.02.003.
  18. ^ D'Emic, M.D., and B.Z. Foreman. (2012). The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming. Journal of Vertebrate Paleontology 32(4):883–902.
  19. ^ Frederickson J.A. and Cifelli R.L. (2016) New Cretaceous lungfishes (Dipnoi, Ceratodontidae) from western North America. Journal of Paleontology.

References

  • Burton, D., Greenhalgh, B.W., Britt, B.B., Kowallis, B.J., Elliott, W.S., and Barrick, R. 2006. New radiometric ages from the Cedar Mountain Formation, Utah and the Cloverly Formation, Wyoming: implications for contained dinosaur faunas. Geological Society of America Abstracts with Programs 38(7): 52.
  • Chen, Z.-Q. and Lubin, S. 1997. A fission track study of the terrigenous sedimentary sequences of the Morrison and Cloverly Formations in northeastern Bighorn Basin, Wyoming. The Mountain Geologist 34:51-62.
  • Cifelli, R.L. 1999. Tribosphenic mammal from the North American Early Cretaceous. Nature 401:363-366.
  • Cifelli, R.L., Wible, J.R., and Jenkins, F.A. 1998. Triconodont mammals from the Cloverly Formation (Lower Cretaceous), Montana and Wyoming. Journal of Vertebrate Paleontology 18: 237-241.
  • Horner, John R. Dinosaurs Under the Big Sky (Cloverly Formation). Mountain Press Publishing Company. pp. 93–100. ISBN 0-87842-445-8.
  • Nydam, R.L., and Cifelli, R.L. 2002. Lizards from the Lower Cretaceous (Aptian-Albian) Antlers and Cloverly Formations. Journal of Vertebrate Paleontology 22: 286-298.
  • Ostrom, J. H. 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana. Peabody Museum Bulletin 35:1-234
  • Varricchio, D. J. 2001. Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana. pp. 42–57 in D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life. Indiana University Press, Indianapolis, Indiana.
  • Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.
1970 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 1970.

Acrocanthosaurus

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.

Albian

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.

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.

Aptian

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.

Deinonychus

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.

Gobiconodon

Gobiconodon is an extinct genus of carnivorous mammal from the early Cretaceous. It weighed 10–12 pounds (4.5–5.4 kg) and measured 18–20 inches (460–510 mm). It was one of the largest mammals known from the Mesozoic. Like other gobiconodontids, it possesses several speciations towards carnivory, such as shearing molar teeth, large canine-like incisors and powerful jaw and forelimb musculature, indicating that it probably fed on vertebrate prey; rather uniquely among predatory mammals and other eutriconodonts, the lower canines were vestigial, with the first lower incisor pair having become massive and canine-like. Like the larger Repenomamus there might be some evidence of scavenging.

Microvenator

Microvenator (meaning "small hunter") is a genus of dinosaur from the Early Cretaceous Cloverly Formation in what is now south central Montana. Microvenator was an oviraptorosaurian theropod. The holotype fossil is an incomplete skeleton, most likely a juvenile, with a living length of about 1.2 m. The adult size of Microvenator is estimated to be closer to 3 m long. Microvenator celer is primitive and may be the "sister taxon to all other oviraptorosaurs."

Barnum Brown collected the type specimen (AMNH 3041) of this animal in 1933 and included what are now known to be Deinonychus teeth with the specimen, and thought that his new animal had a small body with an unusually large head. Thus, he informally dubbed it "Megadontosaurus" ("big-toothed lizard"). He had illustrations made of it, but never published the name, a fate shared with several other Cloverly dinosaurs (Deinonychus, Sauropelta and Tenontosaurus). AMNH 3041 includes parts of the skull. hand, foot, left fibula, 23 vertebrae, 4 ribs, and fairly complete ilia, pubes, femora, tibiae, the left ankle, left humerus, radius, and ulna. In 1970 John Ostrom described the type specimen and gave it its formal name. Ostrom also referred a single tooth from the Yale Peabody Museum collection, YPM 5366, to this new species. The illustrations that Brown had prepared were finally published in a detailed and exhaustive monograph by Mackovicky and Sues in 1998. They were unable to confirm that YPM 5366 belongs to Microvenator. They confirmed that Microvenator is an oviraptorosaurian, and that it is the earliest known member of this group from North America.

Nodosaurinae

Nodosaurinae is a group of ankylosaurian dinosaurs named in 1919 by Othenio Abel.

Orodrominae

Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.

Rugocaudia

Rugocaudia is a potentially dubious extinct genus of basal titanosauriform sauropod dinosaur known from the Early Cretaceous of Montana, United States.

Sauropelta

Sauropelta ( SAWR-o-PEL-tə; meaning 'lizard shield') is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species (S. edwardsorum) has been named although others may have existed. Anatomically, Sauropelta is one of the most well-understood nodosaurids, with fossilized remains recovered in the U.S. states of Wyoming, Montana, and possibly Utah. It is also the earliest known genus of nodosaurid; most of its remains are found in a section of the Cloverly Formation dated to 108.5 million years ago.

It was a medium-sized nodosaurid, measuring about 5.2 metres (17.1 ft) long. Sauropelta had a distinctively long tail which made up about half of its body length. Although its body was smaller than a modern black rhinoceros, Sauropelta was about the same mass, weighing in at about 1,500 kilograms (3,300 lb). The extra weight was largely due to its extensive covering of bony armor, including the characteristically large spines projecting from its neck.

Sauroposeidon

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.

Shell, Wyoming

Shell is a census-designated place (CDP) in Big Horn County, Wyoming, United States. The population was 83 at the 2010 Census.

The community is named for the abundance of fossil shells located in the area. Nearby exposed formations such as the Cloverly Formation and the Morrison Formation have yielded numerous fossils of dinosaurs and other animals. Located to the west of the town is the Red Gulch Dinosaur Tracksite, a rare collection of dinosaur tracks from the Jurassic.

Shell is home to the University of Nebraska-Lincoln & Iowa State University geology field station.

Tatankacephalus

Tatankacephalus is a basal genus of nodosaurid dinosaur that lived during the Early Cretaceous.

Its fossil has been collected from the Cloverly Formation (Aptian-Albian) of central Montana, USA, during 1996, 1997 and 1998, in the region of the Middle Dome in Wheatland County. The type species is T. cooneyorum, described by William L. Parsons and Kirsten Parsons in 2009. The genus name is derived from Oglala tatanka, "bison" and Greek kephale, "head", in reference to the rounded head form. The specific name honours the family of John Patrick Cooney. The holotype is MOR 1073, a partial skull with an estimated total undamaged length of 32 centimetres, lacking the lower jaws. Also some ribs, osteoderms and a tooth have been recovered. The front of the snout is missing. The specimen is that of an adult individual.According to the authors the fossil has not been deformed by compression, allowing to distinguish it from Sauropelta edwardsorum, another akylosaurian found in the same formation. The head is domed and the eye-sockets are round. A large bone ridge runs transversely across the back of the head. The fossil skull itself no longer had any teeth in it but a single tooth was found, lacking the cingulum. Two osteoderms were found; one was intact. It has a length of 137 and a width of 115 millimetres. It is hollow and conical.A cladistic analysis showed that Tatankacephalus was a basal member of the Ankylosauridae and relatively closely related to Gastonia. Basal traits include the retention of premaxillary teeth in the front of the upper jaws and a skull opening, the lateral temporal fenestra, that was not covered by the skull armour. A new cladistic analysis performed by Thompson et al., 2011 suggests that Tatankacephalus is a basal nodosaurid.

Tenontosaurus

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.

Thermopolis Shale

The Thermopolis Shale is a geologic formation which formed in west-central North America in the Albian age of the Late Cretaceous period. Surface outcroppings occur in central Canada, and the U.S. states of Montana and Wyoming. The rock formation was laid down over about 7 million years by sediment flowing into the Western Interior Seaway. The formation's boundaries and members are not well-defined by geologists, which has led to different definitions of the formation. Some geologists conclude the formation should not have a designation independent of the formations above and below it. A range of invertebrate and small and large vertebrate fossils and coprolites are found in the formation.

Timeline of dromaeosaurid research

This timeline of dromaeosaurid research is a chronological listing of events in the history of paleontology focused on the dromaeosaurids, a group of sickle-clawed, bird-like theropod dinosaurs including animals like Velociraptor. Since the Native Americans of Montana used the sediments of the Cloverly Formation to produce pigments, they may have encountered remains of the dromaeosaurid Deinonychus hundreds of years before these fossils came to the attention of formally trained scientists.In 1922 Matthew and Brown named the new genus and species Dromaeosaurus albertensis, considering it a new type within the family Deinodontidae, a now defunct family name that once applied to the tyrannosaurs. Not long after, Velociraptor was discovered in Mongolia by the Central Asiatic Expedition. Dromaeosaur research was fairly quiet until the 1960s, when John Ostrom described the new genus and species Deinonychus antirrhopus. This discovery played a major role in setting off the Dinosaur Renaissance because Deinonychus was obviously a vigorous, active animal, and exhibited characteristics linking it to the origin of birds. As such it brought support for controversial reinterpretations of dinosaurs as warm-blooded and ancestral to birds. Its distinct nature and similarity to Dromaeosaurus led Ostrom to follow Edwin Colbert and Dale Russel's suggestion that the Dromaeosaurinae be regarded as its own family separate from the Deinodontidae.After Ostrom's initial research on Deinonychus, evidence continued to mount for a close evolutionary relationship between dromaeosaurids and birds. The dromaeosaurid Sinornithosaurus milennii, described in 1999 by Xu, Wang, and Wu, is a notable example as the fine-grained Chinese limestone from which it was collected preserved its life covering of feathers. Discoveries of feathered dromaeosaurids continued into the 2000s. Xu, Zhou, and Wang named the new genus Microraptor in 2000. Three years later, Xu and others would report a new species in this genus that exhibited a bizarre "four winged" body plan with long pennaceous flight feathers on both its front and hind limbs.

Zephyrosaurus

Zephyrosaurus (meaning "westward wind lizard") is a genus of orodromine ornithischian dinosaur. It is based on a partial skull and postcranial fragments discovered in the Aptian-Albian-age Lower Cretaceous Cloverly Formation of Carbon County, Montana, USA. New remains are under description, and tracks from Maryland and Virginia, also in the USA, have been attributed to animals similar to Zephyrosarus.

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