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Nanosaurus

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Not to be confused with Nanosaur.

Nanosaurus
Temporal range: Late Jurassic, 155–148 Ma
Mounted skeleton, on temporary exhibit in the National Museum of Denmark
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Genasauria
Clade: †Neornithischia
Family: †Nanosauridae
Marsh, 1877
Genus: †Nanosaurus
Marsh, 1877
Species:
†N. agilis
Binomial name
†Nanosaurus agilis
Marsh, 1877
Synonyms
Genus synonymy
  • Drinker Bakker et al., 1990
  • Othnielia Galton, 1977
  • Othnielosaurus Galton, 2007
Species synonymy
  • Drinker nisti Bakker et al., 1990
  • Laosaurus consors Marsh, 1894
  • Nanosaurus rex Marsh, 1877
  • Othnielia rex (Marsh, 1877)
  • Othnielosaurus consors (Marsh, 1894)

Nanosaurus ("small or dwarf lizard") is an extinct genus of neornithischian dinosaur that lived about 155 to 148 million years ago, during the Late Jurassic in North America. Its fossils are known from the Morrison Formation of the south-western United States. The type and only species, Nanosaurus agilis, was described and named by Othniel Charles Marsh in 1877. The taxon has a complicated taxonomic history, largely the work of Marsh and Peter M. Galton, involving the genera Laosaurus, Hallopus, Drinker, Othnielia, and Othnielosaurus, the latter three now being considered to be synonyms of Nanosaurus. It had historically been classified as a hypsilophodont or fabrosaur, types of generalized small bipedal herbivore, but more recent research has abandoned these groupings as paraphyletic and Nanosaurus is today considered a basal member of Neornithischia.

History and taxonomy

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Marsh's original groundwork

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Holotype dentary and ilium

Nanosaurus has had a long and complicated taxonomic history. In 1877, Marsh named two species of Nanosaurus in separate publications, based on partial remains from the Morrison Formation of Garden Park, Colorado. One paper described N. agilis, based on YPM 1913, with remains including impressions of a dentary, and postcranial bits including an ilium, thigh bones, shin bones, and a fibula.[1] The other paper named N. rex, a second species which Marsh based on YPM 1915 (also called 1925 in Galton, 2007), a complete thigh bone.[2][3] He regarded both species as small ("fox-sized") animals.[3] A third species, N. victor, was named, which he soon recognized to be something completely different, and is now known as the small, bipedal crocodylomorph Hallopus.[1][4]

The next year, he named the new genus Laosaurus on material collected by Samuel Wendell Williston from Como Bluff, Wyoming. Two species were named: the type species L. celer, based on parts of eleven vertebrae (YPM 1875);[5] and the "smaller" L. gracilis, originally based on a back vertebra's centrum, a caudal centrum, and part of an ulna (review by Peter Galton in 1983 finds the specimen to now consist of thirteen back and eight caudal centra, and portions of both hindlimbs).[5][6] A third species, L. consors, was established by Marsh in 1894 for YPM 1882, which consists of most of one articulated skeleton and part of at least one other individual.[7] The skull was only partially preserved, and the fact that the vertebrae were represented only by centra suggests a partially grown individual. Galton (1983) notes that much of the current mounted skeleton was restored in plaster, or had paint applied.[6]

Galton's taxonomic revisions

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Type specimen of Nanosaurus agilis Marsh 1877 (YPM VP 1913) as illustrated in 1908 (left) and cast of the bone impressions after the fragmentary bone was removed (right)

These animals attracted little professional attention until the 1970s and 1980s, when Peter Galton reviewed many of the "hypsilophodonts" in a series of papers. In 1973, he and Jim Jensen described a partial skeleton (BYU ESM 163 as of Galton, 2007) missing the head, hands, and tail as Nanosaurus? rex, which had been damaged by other collectors prior to description.[8] By 1977, he had concluded that Nanosaurus agilis was quite different from N. rex and the new skeleton, and coined Othnielia for the latter species. The paper (primarily concerning the transcontinental nature of Dryosaurus) considered Laosaurus consors and L. gracilis synonyms of O. rex without elaboration, and considered L. celer an invalid nomen nudum.[9]

Othniel Charles Marsh's 1896 skeletal restoration of "Laosaurus" consors (now Nanosaurus).

In 1990, Robert Bakker, Peter Galton, James Siegwarth, and James Filla described remains of a dinosaur they named Drinker nisti. The name is somewhat ironic; Drinker, named for renowned palaeontologist Edward Drinker Cope whose infamous "bone wars" with rival Othniel Charles Marsh produced many dinosaur fossils which are world-famous today, was described as a probable close relative of Othnielia, named for Marsh. The species name refers to the National Institute of Standards and Technology (NIST). Discovered by Siegwarth and Filla in upper Morrison Formation beds at Como Bluff, Wyoming, it was based on a partial subadult skeleton (listed as CPS 106 originally, then as Tate 4001 by Bakker 1996[10]) including partial jaws, vertebrae, and partial limbs. Several other specimens found in the same area were assigned to it, mostly consisting of vertebral and hindlimb remains, and teeth.[11] The holotype specimen's current location is unknown; according to Carpenter and Galton (2018), the previous two institutions reported to have had it did not ever curate the specimen, and the collection it was originally said to be in never existed at all.[10]

Several decades later, in his 2007 study of the teeth of Morrison ornithischians, Galton concluded that the holotype femur of Othnielia rex is not diagnostic, and reassigned the BYU skeleton to Laosaurus consors, which is based on better material. As the genus Laosaurus is also based on nondiagnostic material, he gave the species L. consors its own genus, Othnielosaurus. As a result, in practical terms, what had been thought of as Othnielia is now known as Othnielosaurus consors. Regarding Nanosaurus agilis, Galton considered it a potentially valid basal ornithopod, and noted similarities to heterodontosaurids in the thigh bone. He tentatively assigned to it some teeth that had been referred to Drinker.[2]

Skeleton with outdated skull-shape based on Hypsilophodon

Another decade later, in 2018, Galton, alongside Kenneth Carpenter, described a new ornithischian specimen. They found it very similar to the fragmentary holotype of Nanosaurus, but more clear in its anatomical features. Their new specimen was also found to display extreme similarity with the specimens of Othnielosaurus and Drinker. Due to the new data, they concluded that all three species, alongside Othnielia, represented the same animal, united under the name Nanosaurus agilis. This painted a new picture of a singular, very common small dinosaur known from a large amount of material.[10] This conclusion has been recognized by papers since, some of which incorporating the new, all-encompassing taxon into their phylogenetic analyses.[12][13][14]

Description

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Size compared to a human
Life restoration

Nanosaurus is known from material from all parts of the body, including two good skeletons, although the skull is still poorly known.[15] It was a small animal, with specimens previously assigned to Drinker and Othnielosaurus measuring 2–2.2 metres (6.6–7.2 ft) long and weighing 20–30 kilograms (44–66 lb).[16]

It was a bipedal dinosaur with short forelimbs and long hindlimbs with large processes for muscle attachments.[17] The hands were short and broad with short fingers. The head was small. It had small leaf-shaped cheek teeth (triangular and with small ridges and denticles lining the front and back edges), and premaxillary teeth with less ornamentation.[2]

Like several other neornithischian dinosaurs, such as Hypsilophodon, Thescelosaurus, and Talenkauen, Nanosaurus had thin plates lying along the ribs. Called intercostal plates, these structures were cartilaginous in origin.[18]

Classification

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Skull-less skeleton of a juvenile Nanosaurus skeleton (BYU 163)

The cladogram below results from analysis by Herne et al., 2019.[12]

Ornithischia

Paleobiology and paleoecology

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Torvosaurus mounted as if chasing Nanosaurus, Museum of Ancient Life

Nanosaurus was one of the smaller members of the diverse Morrison Formation dinosaur fauna, diminutive in comparison to the giant sauropods.[19] The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains.[20] Vegetation varied from river-lining gallery forests of conifers, tree ferns, and ferns, to fern savannas with rare trees.[21] It has been a rich fossil hunting ground, holding fossils of green algae, fungi, mosses, horsetails, ferns, cycads, ginkgoes, and several families of conifers. Other fossils discovered include bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs, several species of pterosaur, numerous dinosaur species, and early mammals such as docodonts, multituberculates, symmetrodonts, and triconodonts. Such dinosaurs as the theropods Ceratosaurus, Allosaurus, Ornitholestes, and Torvosaurus, the sauropods Apatosaurus, Brachiosaurus, Camarasaurus, and Diplodocus, and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus are known from the Morrison.[22] Nanosaurus is present in stratigraphic zones 2-5.[23]

Typically, Nanosaurus has been interpreted like other hypsilophodonts as a small, swift herbivore,[24] although Bakker (1986) interpreted Nanosaurus as an omnivore.[25]

References

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  1. ^ a b Marsh, Othniel Charles (1877). "Notice of some new vertebrate fossils". American Journal of Science and Arts. 14 (81): 249–256. Bibcode:1877AmJS...14..249M. doi:10.2475/ajs.s3-14.81.249. S2CID 131230859.
  2. ^ a b c Galton, Peter M. (2007). "Teeth of ornithischian dinosaurs (mostly Ornithopoda) from the Morrison Formation (Upper Jurassic) of the western United States". In Carpenter, Kenneth (ed.). Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Bloomington and Indianapolis: Indiana University Press. pp. 17–47. ISBN 978-0-253-34817-3.
  3. ^ a b Marsh, Othniel Charles (1877). "Notice of new dinosaurian reptiles from the Jurassic formations". American Journal of Science and Arts. 14 (84): 514–516. Bibcode:1877AmJS...14..514M. doi:10.2475/ajs.s3-14.84.514. S2CID 130488291.
  4. ^ Marsh, O.C. (1881). "Principal characters of American Jurassic dinosaurs. Part V.". American Journal of Science. 21 (125): 418–423. Bibcode:1881AmJS...21..417M. doi:10.2475/ajs.s3-21.125.417. S2CID 219234316.
  5. ^ a b Marsh, Othniel Charles (1878). "Notice of new dinosaurian reptiles". American Journal of Science and Arts. 15 (87): 241–244. Bibcode:1878AmJS...15..241M. doi:10.2475/ajs.s3-15.87.241. S2CID 131371457.
  6. ^ a b Galton, Peter M. (1983). "The cranial anatomy of Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and East Africa, with a review of hypsilophodontids from the Upper Jurassic of North America". Geologica et Palaeontologica. 17: 207–243.
  7. ^ Marsh, Othniel Charles (1894). "The typical Ornithopoda of the American Jurassic". American Journal of Science. Series 3. 48 (283): 85–90. Bibcode:1894AmJS...48...85M. doi:10.2475/ajs.s3-48.283.85. S2CID 130777820.
  8. ^ Galton, Peter M.; Jensen, James A. (1973). "Skeleton of a hypsilophodontid dinosaur (Nanosaurus (?) rex) from the Upper Jurassic of Utah". Brigham Young University Geology Series. 20: 137–157.
  9. ^ Galton, Peter M. (1977). "The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic". Nature. 268 (5617): 230–232. Bibcode:1977Natur.268..230G. doi:10.1038/268230a0. S2CID 30721851.
  10. ^ a b c Carpenter, Kenneth; Galton, Peter M. (2018). "A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA". Geology of the Intermountain West. 5: 167–207. doi:10.31711/giw.v5.pp167-207. S2CID 73691452.
  11. ^ Bakker, R.T.; Galton, P.M.; Siegwarth, J.; Filla, J. (1990). "A new latest Jurassic vertebrate fauna, from the highest levels of the Morrison Formation at Como Bluff, Wyoming. Part IV. The dinosaurs: A new Othnielia-like hypsilophodontoid". Hunteria. 2 (6): 8–14.
  12. ^ a b Herne, Matthew C.; Nair, Jay P.; Evans, Alistair R.; Tait, Alan M. (2019). "New small-bodied ornithopods (Dinosauria, Neornithischia) from the Early Cretaceous Wonthaggi Formation (Strzelecki Group) of the Australian-Antarctic rift system, with revision of Qantassaurus intrepidus Rich and Vickers-Rich, 1999". Journal of Paleontology. 93 (3): 543–584. Bibcode:2019JPal...93..543H. doi:10.1017/jpa.2018.95.
  13. ^ Li, Ning; Dai, Hui; Tan, Chao; Hu, Xufeng; Wei, Zhaoying; Lin, Yu; Wei, Guangbiao; Li, Deliang; Meng, Li; Hao, Baoqiao; You, Hailu; Peng, Guangzhou (2019). "A neornithischian dinosaur from the Middle Jurassic Xintiangou Formation of Yunyang, Chongqing, China: the earliest record in Asia". Historical Biology. 33 (7): 1–14. doi:10.1080/08912963.2019.1679129. S2CID 209583081.
  14. ^ Wilson, John P.; Varricchio, David J. (2019). "Photogrammetry of the Oryctodromeus cubicularis type locality burrow and the utility of preexisting, standard field photographs for three dimensional digital reconstruction". Historical Biology. 32 (8): 1054–1061. doi:10.1080/08912963.2018.1563783. S2CID 91500384.
  15. ^ Norman, David B.; Sues, Hans-Dieter; Witmer, Larry M.; Coria, Rodolfo A. (2004). "Basal Ornithopoda". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 393–412. ISBN 0-520-24209-2.
  16. ^ Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 306. ISBN 978-1-78684-190-2. OCLC 985402380.
  17. ^ Scott Hartman. "othnielia". Retrieved 2007-01-25.
  18. ^ Butler, Richard J.; Galton, Peter M. (2008). "The 'dermal armour' of the ornithopod dinosaur Hypsilophodon from the Wealden (Early Cretaceous: Barremian) of the Isle of Wight: a reappraisal". Cretaceous Research. 29 (4): 636–642. Bibcode:2008CrRes..29..636B. doi:10.1016/j.cretres.2008.02.002.
  19. ^ Foster, John R. (2003). "Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A.". New Mexico Museum of Natural History and Science Bulletin. 23: 29.
  20. ^ Russell, Dale A. (1989). An Odyssey in Time: Dinosaurs of North America. Minocqua, Wisconsin: NorthWord Press. pp. 64–70. ISBN 1-55971-038-1.
  21. ^ Carpenter, Kenneth (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 131–138.
  22. ^ Chure, Daniel J.; Litwin, Ron; Hasiotis, Stephen T.; Evanoff, Emmett; Carpenter, Kenneth (2006). "The fauna and flora of the Morrison Formation: 2006". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 233–248.
  23. ^ Foster, J. (2007). "Appendix." Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 327-329.
  24. ^ Norman, David B.; Sues, Hans-Dieter; Witmer, Larry M.; Coria, Rodolfo A. (2004). "Basal Ornithopoda". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 393–412. ISBN 0-520-24209-2.
  25. ^ Bakker, Robert T. (1986). The Dinosaur Heresies. New York: William Morrow. p. 180. ISBN 0-14-010055-5.
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