Stegosaurus stenops

Stegosaurus stenops was a large, four-legged herbivore from Late Jurassic western North America. Short forelimbs and longer hind limbs produced its distinctive arched profile, while large dermal plates rose in two rows along the neck, back and front of the tail. Four keratin-covered spikes armed the tail tip. Several unusually informative skeletons make S. stenops the anatomical standard for its genus: the flattened but articulated holotype USNM V4934 and the three-dimensionally preserved London specimen NHMUK PV R36730, nicknamed Sophie.

Its fossils occur between approximately 155 and 150 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

Holotype USNM V4934 preserves an articulated skeleton, skull, plates, tail spikes and a patch of small rounded ossicles beneath the throat. Burial compressed much of it into a slab, so not every bone retains its original three-dimensional shape. Sophie complements it with a largely complete, three-dimensionally preserved young-adult skeleton. Together these specimens show a small, low skull; a deep torso; column-like hind limbs; spreading, weight-bearing forefeet; two plate rows; and a flexible, muscular tail ending in four spikes.

• Small, long and low skull ending in a keratinous beak
• Small, leaf-shaped teeth set behind the beak
• Short forelimbs and much longer hind limbs creating an arched back
• Two rows of large dermal plates along the neck, back and tail base
• Four long tail spikes, probably covered by keratin in life
• Broad, weight-bearing forefeet and compact hind feet
• Pebble-like throat ossicles preserved with the holotype

Marshall P. Felch uncovered the articulated holotype at Felch-Marsh Quarry near Garden Park, Colorado, in 1886. Othniel Charles Marsh named Stegosaurus stenops in 1887; stenops refers to its narrow face. Charles W. Gilmore's 1914 monograph provided the first comprehensive description of the Smithsonian skeleton. Because the original type species S. armatus rested on much poorer material, the International Commission on Zoological Nomenclature formally made S. stenops the type species of Stegosaurus in 2013.

Discovery credit: Marshall P. Felch.

Naming authors: Othniel Charles Marsh.

S. stenops lived on the seasonally dry river floodplains represented by the Morrison Formation. River channels, ponds and wetter lowlands crossed more open areas carrying conifers, cycads, ferns, horsetails and other low plants. It shared this ecosystem with sauropods such as Diplodocus and Camarasaurus, ornithopods including Camptosaurus, and predators including Allosaurus and Ceratosaurus.

Its beak, small teeth and jaw mechanics support cropping low to medium-height vegetation rather than chewing like a mammal. The tail spikes were mechanically capable defensive weapons, although no fossil records a particular strike by this individual species. Plate function is less settled: display, species recognition and heat exchange have all been proposed, and the vessels visible in plate bone do not by themselves identify one purpose. Trackways and limb anatomy show an obligate quadruped; speed estimates remain model dependent.

• The informal name 'thagomizer' for a stegosaur's spiked tail began as a joke in Gary Larson's The Far Side and was later adopted by many palaeontologists.
• Sophie is a nickname only: the specimen's biological sex is unknown.
• The holotype was preserved almost like roadkill in stone—flattened, articulated and with plates close to their original positions.
• S. stenops became the official type species of Stegosaurus 126 years after Marsh named it.
• The name 'roofed lizard' reflects Marsh's early idea that the plates lay flat like roof shingles; articulated fossils later helped establish their upright arrangement.

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1. 01
   The Paleobiology Database

   Open source
2. 02
   Principal characters of American Jurassic dinosaurs; Part IX, The skull and dermal armor of Stegosaurus

   Othniel Charles Marsh · American Journal of Science · 1887

   Open source
3. 03
   Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus Stegosaurus

   Charles W. Gilmore · Bulletin of the United States National Museum 89 · 1914

   Open source
4. 04
   Opinion 2320 (Case 3536): Stegosaurus Marsh, 1877—type species replaced with Stegosaurus stenops Marsh, 1887

   International Commission on Zoological Nomenclature · Bulletin of Zoological Nomenclature · 2013

   Open source
5. 05
   The postcranial skeleton of an exceptionally complete individual of the plated dinosaur Stegosaurus stenops from the Upper Jurassic Morrison Formation of Wyoming, U.S.A.

   Susannah C. R. Maidment, Charlotte Brassey, Paul M. Barrett · PLOS ONE · 2015

   Open source
6. 06
   Body mass estimates of an exceptionally complete Stegosaurus: comparing volumetric and linear bivariate mass estimation methods

   Charlotte A. Brassey, Susannah C. R. Maidment, Paul M. Barrett · Biology Letters · 2015

   Open source
7. 07
   Decoupled form and function in disparate herbivorous dinosaur clades

   Stephan Lautenschlager, Charlotte A. Brassey, David J. Button, Paul M. Barrett · Scientific Reports · 2016

   Open source
8. 08
   Stegosaurus stenops Marsh, 1887 (USNM V4934)

   Smithsonian National Museum of Natural History

   Open source
9. 09
   Earth Hall and Stegosaurus

   Natural History Museum, London

   Open source