Xenoposeidon

Xenoposeidon (meaning "strange or alien Poseidon", in allusion to Sauroposeidon) is a genus of rebbachisaurid sauropod dinosaur from the Early Cretaceous of England, living about 140 million years ago. It is known from a single partial vertebra with unusual features, unlike those of other sauropods. This bone was first discovered in the early 1890s but received little attention until it was found by University of Portsmouth student Mike Taylor, who formally described and named it in 2007 with Darren Naish.

Xenoposeidon
Temporal range: Early Cretaceous,140 Ma
Xenoposeidon proneneukos.jpeg
Holotype vertebra in multiple views
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Clade: Sauropoda
Family: Rebbachisauridae
Genus: Xenoposeidon
Taylor & Naish, 2007
Species:
X. proneneukos
Binomial name
Xenoposeidon proneneukos
Taylor & Naish, 2007

Description

Xenoposeidon laminae unidentified wrinkles
Close up of v-shaped laminae on NHMUK R2095. The feature of the wrinkles are unknown[1]

Xenoposeidon is based on BMNH R2095, a partial posterior back vertebra. The specimen lacks the anterior face of the centrum and the upper portion of the neural arch. The centrum is estimated at 200 millimetres (7.9 in) long, and the height of the preserved portion of the vertebra is 300 millimetres (11.8 in). The average diameter of the posterior face of the centrum is 165 millimetres (6.50 in), with a concave surface. This concavity is deep enough to suggest that the anterior faces of vertebrae from this part of the dinosaur's spine would have been convex to articulate with such a shape.[2]

The specimen displays several distinguishing characteristics. The base of the neural arch covers the length of the centrum and is continuous with the centrum's posterior face. The neural arch leans anteriorly at 35° and there are broad areas of featureless bone on the lateral surfaces of the arch. The neural canal is large and teardrop-shaped anteriorly but small and circular at its posterior opening. The various bony struts and sheets that make up the arch have a distinctive configuration.[2]

Classification

Lydekker 1893 Wealden Sauropod Vertebrae
Illustration of the vertebra by Richard Lydekker in 1893
Xenoposeidon Rebachisaurid 2017
Hypothetically restored as a rebbachisaurid

Xenoposeidon's distinct suite of vertebral characteristics is unlike those found in other groups of sauropods, which differ in various proportional and structural features. So unique is the vertebra that when Taylor and Naish attempted to classify it using a phylogenetic analysis, they found that, although a neosauropod, it didn’t fit ‘comfortably’ into any of the established groups, Diplodocoidea, Camarasauridae, Brachiosauridae and Titanosauria. Xenoposeidon could be a derived member of one of the known groups, or may even represent a new group. The authors left it as a neosauropod of uncertain affinities.[2] The titanosauriform phylogeny by D'Emic established Xenoposeidon as a nomen dubium due to its basis on nondiagnostic material.[3] However, Mike Taylor has disagreed with these findings online. According to a study published in 2018, X. proneneukos is a basal member of Rebbachisauridae, and 10 million years older than the next oldest member of the family, Histriasaurus.[4]

The below majority rules cladogram was found in the analysis of Xenoposeidon. Without the genus, the support for each group except Flagellicaudata was considerably higher.[2]

Eusauropoda

Shunosaurus

Barapasaurus

Patagosaurus

Omeisaurus

Mamenchisaurus

Losillasaurus

Haplocanthosaurus

Neosauropoda
Diplodocoidea

Nigersaurus

Rebbachisaurus

Limaysaurus

Flagellicaudata

Apatosaurus

Barosaurus

Diplodocus

Suuwassea

Amargasaurus

Dicraeosaurus

Macronaria

Jobaria

Camarasaurus

Titanosauriformes

Brachiosaurus

Xenoposeidon

Euhelopus

Titanosauria

Discovery and history

Michael P. Taylor
Describer Michael P. Taylor with the vertebra of Xenoposeidon

Fossil collector Phillip James Rufford discovered the vertebra that would be later named Xenoposeidon in the early 1890s. It was found near Hastings in East Sussex, England, in rocks of the Hastings Bed Group. This formation dates to the Lower Cretaceous, and is within the Berriasian and Valanginian Stages. The vertebra was probably from the Berriasian portion of the Ashdown Beds within the Hastings, although precise information about the locality and stratigraphy have been lost if such data were ever recorded.[2]

The partial posterior back vertebra, cataloged as NHMUK R2095, was briefly described by English naturalist and paleontologist Richard Lydekker in 1893. He thought that it might belong to Cetiosaurus brevis, better known today as Pelorosaurus conybearei.[2] The bone attracted little attention for decades, sitting on a shelf at the British Natural History Museum in London for 113 years. Mike Taylor, a sauropod vertebra specialist, stumbled upon it and became interested in the unusual specimen, entering into a description of it with Darren Naish.[5]

The new genus was first announced by the British Palaeontological Association on November 15, 2007. The genus consists of the single species Xenoposeidon proneneukos. The generic name combines Greek xenos, "strange", with a reference to Poseidon, the "earth-shaker". The specific name means ‘forward sloping’ in Greek, in recognition of the anterior sloping of the neural arch. This unusual characteristic, along with its other distinctive features, prompted the authors to erect the new genus.[2]

Paleobiology

Xenoposeidon Skeletal
Skeletal reconstruction of Xenoposeidon as a rebbachisaurid

Like other sauropods, Xenoposeidon would have been a large quadrupedal herbivore.[6] It was relatively small for a sauropod. Extrapolating from the vertebra suggests that the type individual of Xenoposeidon could have been about 15 metres (50 ft) long and weighed approximately 7.6 tonnes (8.4 short tons), if it resembled Brachiosaurus, to 20 m (65 ft) long and 2.8 tonnes (3.1 short tons), if it was built like the longer, lighter Diplodocus.[2]

References

  1. ^ Taylor, M.P. (2009-02-17). "Xenoposeidon week, day 8 (somewhat belatedly): those wrinkles". Sauropod Vertebra Picture of the Week.
  2. ^ a b c d e f g h Taylor, Michael P.; Naish, Darren (2007). "An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England" (PDF). Palaeontology. 50 (6): 1547–1564. doi:10.1111/j.1475-4983.2007.00728.x.
  3. ^ D'Emic, M. D. (2012). "The early evolution of titanosauriform sauropod dinosaurs". Zoological Journal of the Linnean Society. 166 (3): 624–671. doi:10.1111/j.1096-3642.2012.00853.x.
  4. ^ Taylor MP. (2018) Xenoposeidon is the earliest known rebbachisaurid sauropod dinosaur. PeerJ 6:e5212 https://doi.org/10.7717/peerj.5212
  5. ^ Naish, Darren (2007-11-15). "The world's most amazing sauropod". Tetrapod Zoology. ScienceBlogs. Archived from the original on December 22, 2007. Retrieved 2007-11-21.
  6. ^ Upchurch, Paul; Barrett, Paul M.; Dodson, Peter. (2004). "Sauropoda". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 259–322. ISBN 978-0-520-24209-8.

External links

Brasilotitan

Brasilotitan is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous (early Maastrichtian) Adamantina Formation of Brazil. The type species is Brasilotitan nemophagus.

Cetiosauridae

Cetiosauridae is a family of sauropod dinosaurs. While traditionally a wastebasket taxon containing various unrelated species, some recent studies have found that it may represent a natural clade. Additionally, at least one study has suggested that the mamenchisaurids may represent a sub-group of the cetiosaurids, which would be termed Mamenchisaurinae.

Daxiatitan

Daxiatitan is a genus of titanosaur dinosaur from the Lower Cretaceous of Lanzhou Basin, Gansu Province, northwestern China. It is known from fossils including several neck vertebrae, a shoulder blade, and a thigh bone.It was a very large dinosaur, estimated at 23–30 meters (75–98 feet). Like both Euhelopus and Huanghetitan, it had an enormously long neck.

Diplodocinae

Diplodocinae is an extinct subfamily of diplodocid sauropods that existed from the Late Jurassic to Early Cretaceous of North America, Europe and South America, about 161.2 to 136.4 million years ago. Genera within the subfamily include Tornieria, Supersaurus, Leinkupal, Galeamopus, Diplodocus, Kaatedocus and Barosaurus.Cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015).

Ferganasaurus

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Flagellicaudata

Flagellicaudata is a clade of Dinosauria. It belongs to Sauropoda and includes two families, the Dicraeosauridae and the Diplodocidae.

Gravisauria

Gravisauria is a clade of sauropod dinosaurs consisting of some genera, Vulcanodontidae and Eusauropoda.

Huangshanlong

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Jiutaisaurus

Jiutaisaurus is a genus of sauropod dinosaur from the Quantou Formation of China. Jiutaisaurus was a sauropod which lived during the Cretaceous. The type species, Jiutaisaurus xidiensis, was described by Wu et al. in 2006, and is based on eighteen vertebrae.

Kaijutitan

Kaijutitan (meaning "Kaiju titan" after the type of Japanese movie monsters) is a genus of basal titanosaur dinosaur from the Sierra Barrosa Formation from Neuquén Province in Argentina. The type and only species is Kaijutitan maui.

Michael P. Taylor

Michael P. Taylor (born 12 March 1968) is a British computer programmer with a Ph.D in palaeontology. To date, he has published 18 paleontological papers and is co-credited with naming three genera of dinosaur (Xenoposeidon in 2007 with Darren Naish, Brontomerus in 2011 with Matt J. Wedel and Richard Cifeli, and Haestasaurus in 2015 with Paul Upchurch and Phil Mannion).Along with paleontologists Darren Naish and Matt Wedel, he founded the paleontology blog Sauropod Vertebra Picture of the Week, where he blogs as Mike Taylor.

He lives in Ruardean, Gloucestershire, England.

Microcoelus

Microcoelus is a dubius genus of small Titanosaurian sauropod dinosaur native to Argentina. It is known from only a single dorsal vertebra. A left humerus was formerly referred to this species, but it is now considered to belong to Neuquensaurus. This species may be a synonym of the contemporary sauropod Neuquensaurus australis.It was described by British paleontologist Richard Lydekker in 1893.

Oceanotitan

Oceanotitan is a genus of titanosauriform sauropod known from the Upper Jurassic Praia da Amoreira-Porto Novo Formation of Portugal. It contains one species, Oceanotitan dantasi.The holotype consists of the scapula, almost all of the pelvis, a complete leg sans the toes, and nine caudals.

Pilmatueia

Pilmatueia is a diplodocoid sauropod belonging to the family Dicraeosauridae that lived in Argentina during the Early Cretaceous.

Rebbachisauridae

Rebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, North America, and Europe.

Tambatitanis

Tambatitanis is an extinct genus of titanosauriform dinosaur from the Early Cretaceous (probably early Albian) of Japan. It is known from a single type species, Tambatitanis amicitiae. It was probably around 14 meters long and its mass was estimated at some 4 tonnes. It was a basal titanosauriform and possibly belonged to the Euhelopodidae.

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Valanginian

In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian stage succeeds the Berriasian stage of the Lower Cretaceous and precedes the Hauterivian stage of the Lower Cretaceous.

Vulcanodontidae

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