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Fossil record

Morrison Formation
A team of palaeontology students excavating dinosaur fossils in the Upper Jurassic Morrison Formation, Wyoming, USA

As a totally extinct group, stegosaurs are only known from fossils.  Clear stegosaur fossils are known from North America, Europe, Asia, and Africa, while questionable specimens have also been reported from South America, Australia, and India.  Stegosaur fossils have not been reported from Antarctica, which is likely a reflection of sampling bias (little palaeontological work has been carried out on the continent) rather than actual absence.  The earliest known stegosaur body fossils come from the Bajocian, a stage of the Middle Jurassic.  However, putative stegosaur footprints have been reported from the Early Jurassic of France and Australia.  The youngest stegosaur fossils are Early Cretaceous in age, and the absence of stegosaur remains from well-sampled middle-Late Cretaceous units worldwide strongly indicate this group went extinct during the beginning stages of the Cretaceous.  Below are brief descriptions of the stegosaur record on particular continents.

Morrison Formation, USANorth America

The characteristic stegosaur Stegosaurus, as well as Hesperosaurus, are known from the Upper Jurassic Morrison Formation, a series of channel and floodplain sandstones and mudstones that crops out in 13 different states in the western United States.  Taphonomic studies indicate that Stegosaurus fossils overwhelmingly occur in channel sandstones, which some scientists argue indicates that these dinosaurs likely inhabited floodplains and were separated ecologically from sauropods.  Most Stegosaurus fossils are disarticulated elements preserved with disarticulated elements of other dinosaur species, but a spectacular assemblage of nearly complete Stegosaurus fossils at one site in Colorado may reflect drought-induced mass mortality.  In the Morrison, Stegosaurus fossils are found alongside those of several other dinosaurs, including the predatory Allosaurus, as well as Camptosaurus, Apatosaurus, Camarasaurus, and Diplodocus.  The photo shows a team of American scientists working in the Morrison Formation. 


TibetAsia

The highest diversity of stegosaurs comes from Asia, with at least five valid genera (and several fragmentary specimens that questionably have been named) known from the People's Republic of China.  In general, many Chinese stegosaurs are known from more complete specimens than those genera from North America and Europe.  The likely basal stegosaur Huayangosaurus is known from the Middle Jurassic of Sichuan, while most other Chinese stegosaurs are known from the Late Jurassic of this province.  The large number of named China stegosaurs prompted some authors to argue that this group must have originated in Asia, but a recent study by Susannah Maidment finds many of these genera to be based on remains that are too fragmentary to be reliably named.  Thus, this high diversity is somewhat of a mirage, although even with this reassessment there are still more stegosaurs known from Asia than from any other continent.  The photo shows a small village in rural Tibet, which was the site of a stegosaur discovery in the 1970s.

Kentrosaurus, Africa Africa

The stegosaur Kentrosaurus (left, photo courtesy S.C.R. Maidment) is represented by a plethora of specimens from the Upper Jurassic Tendaguru Formation of Tanzania, yet when compared with other Tendaguru dinosaurs this stegosaur is a relatively minor element of the fossil fauna.  Remains of this stegosaur are known from nearshore marine sediments, and some particular quarries have yielded the remains of multiple individuals of several size classes.  Stegosaur material has also been reported from Middle Cretaceous rocks in Morocco, but this referral is disputed.  If substantiated, this specimen would extend the range of stegosaurs and push their known extinction date into the Middle Cretaceous.






Paris MuseumEurope

The earliest descriptions of stegosaurs were based on specimens from the Early Cretaceous of England, described by Gideon Mantell in the 1840s.  As with Mantell's Megalosaurus (one of the first dinosaurs to be discovered, studied scientifically, and named), this stegosaur material is fragmentary, and has led to much taxonomic confusion.  At least three valid stegosaur genera are known from England, however: Dacentrurus, Lexovisaurus, and Craterosaurus.  Dacentrurus and Lexovisaurus have also been reported from France, as have many isolated and fragmentary stegosaur fossils.  Dacentrurus has also been reported from Spain and Portugal. The photo at left was taken of a generalized stegosaur model on display outside the National Museum of Natural History in Paris.







Author: Stephen Brusatte
Last updated: 01/11/2006
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