THE FINEST STEGOSAURUS SPECIMEN TO COME TO MARKET, DISTINGUISHED BY ITS INCREDIBLE SIZE, VIRTUAL COMPLETENESS, AND EXCEPTIONAL LEVEL OF PRESERVATION.

The sale of “Apex” marks a significant moment, as the first instance of an auction house working to bring a dinosaur specimen to market, starting from the day of its discovery. Sotheby's collaborated closely with the owner to document the entire process, from discovery and excavation to restoration, preparation, and mounting, ensuring that the documentation and sale of the specimen is handled with the highest standards and transparency.

Introducing “Apex”

The Stegosaurus is the best-known member of the armored dinosaurs (Thyreophorans), characterized by the distinctive shape and arrangement of dermal armor on the back, extending from the neck to the tail and terminating into a multi-spiked tail weapon.

Fossils belonging to the family Stegosauridae are known from Jurassic-Cretaceous localities throughout Eurasia, North America, and Africa.

GEOLOGY & LOCATION

"Apex" was discovered on privately owned land in Moffat County, Colorado, near the town of Dinosaur, so named due to its proximity to the Dinosaur National Monument. This region is the richest source of dinosaur fossils in the United States due to its location in the Morrison Formation, a sequence of Upper Jurassic sedimentary rock centered in the states of Colorado and Wyoming, with portions running through the states of New Mexico, Utah, Idaho, Arizona, Oklahoma, Texas, Kansas, Nebraska, North & South Dakota, and Montana. Found alone, with no other fossils nearby, "Apex" represents a singular specimen as it lived.

Morrison Formation Stegosaur species have been placed in two genera, Stegosaurus and Hesperosaurus. In the postcranial morphology, Stegosaurus and Hesperosaurus are distinguished primarily on the shape of the dorsal plates. In Stegosaurus the dermal plates are taller and can take on a rounded triangular shape rising to a point, while the plates of Hesperosaurus tend to be wider and more rounded. Both genera share a set of four spikes at the end of the tail, used as a weapon, but only Stegosaurus is known to have throat armor, often referred to as ossicles. The taxonomic distinctions between these two genera and their species remain a topic of ongoing debate.

CONDITION & ANATOMY

“Apex” represents an important palaeontological discovery as it ranks high among the most complete skeletons ever found. Overall, the bones are preserved in exquisite detail, exhibiting little distortion, and retaining much of their original shape and surface characteristics. The fossilization is superb, with even small, delicate bones being preserved in fine detail including seldom preserved skin impressions, fragile cervical dermal plates, and throat armor. The bone is thoroughly mineralized, dense, and heavy, with its surface coloration being dark grey to black, colors consistent with fossils originating from the Morrison Formation in Colorado.

The skeleton was preserved in hard sandstone, which protected the bones from being distorted, resulting in an informative specimen with a high degree of integrity and distinction. Importantly, the bones in this skeleton represent a single individual without composite elements added.

Skull

Generally the bones of the skull are preserved in good detail, showing no discernable distortion and retaining much of their original shape and surface detail, with approximately 36 cranial elements preserved. The skull has much of the posterior elements (neurocranium) preserved intact. The orbits, infratemporal, and superatemporal fenestrae including the surrounding bones (supraorbital, postorbital, jugal, quadrate, etc.) of these openings are mostly intact on both sides of the skull.

Many of the exterior bones on both right and left sides of the skull are preserved, and on the right side, these elements are beautifully preserved together with the frontals, parietals, squamosals, supraoccipitals, and the basioccipital.

In the lower jaws, the dentaries, including the surangular, splenial, angular, and coronoids are present and well preserved.

POST CRANIAL SKELETON

The virtually complete axial skeleton is well represented by cervical (12), dorsal (11), sacral (4, fused together), and caudal (48) vertebrae nicely preserved with most centra and neural processes intact. There are 43 chevrons associated with the tail vertebrae.

Associated with the dorsal vertebrae are 25 dorsal ribs belonging to both sides. Associated with the fused sacral vertebrae are complete sets of hipbones including both right and left pelvic elements (ilia, pubes, and ischia) all preserved in very good condition, with little to no distortion.

Most of the appendicular skeleton is represented. Remarkably, the preserved limb elements; right and left scapula, coracoid, humeri, radii, femora ilia, pubis, and ischia are without significant crushing or damage. The right scapula/coracoid, distal end of right humerus, left radius and ulna, and part of the shaft of the left femur, have been accurately restored.

Foot bones include: Between the left and right Manus, 8 metacarpi, 4 phalanges, 3 unguals, both radiale, and 1 ulnare; and between the left and right Pes, 5 metatarsi and 3 unguals; several hoofs are perfectly preserved.

ARMOR

The bony armor includes 17 dorsal plates of which five have been partially restored. The first two very fragile cervical dermal plates are remarkably preserved intact, and to preserve their integrity, 3D printed replicas have been placed on the mount, while the originals have been stored separately.

Two tail spikes are complete, with one being restored and the other more so.

NECK ARMOR/OSSICLES

There are several throat ossicles present in the skin impressions that are preserved with the skeleton (see below).

SKIN IMPRESSIONS

Fossilized skin impressions provide a glimpse into the outer appearance of these never seen dinosaurs. This intriguing and rare fossil displays the surface texture of skin (integument) belonging to Stegosaurus. The fossil skin was found as part of the skeleton. The natural casts and mold (positive and negative) are from the same individual from near the neck region.

CENSUS

By comparison, there are very few substantially complete Stegosaurus skeletons representing a single individual, mounted and exhibited comparable to “Apex”. The Yale Peabody Museum, and American Museum of Natural History Stegosaurus skeletons are composites of partial skeletons. The skeletons exhibited at the Sauriermuseum in Aathal, Switzerland are Hesperosaurus mjosi.

The most complete and best-known Stegosaurus examples are:

-United States National Museum, Washington DC, (USNM 4934), an almost complete skeleton with skull and holotype of S. stenops

-Carnegie Museum of Natural History, Pittsburgh, Pennsylvania (CM 11341) near complete skeleton with no skull

-The Natural History Museum, London, UK (NHMUK PV R36730) S. stenops “Sophie” nearly complete with skul

-Brigham Young University Museum, Salt Lake City, Utah (BYU12290)

-University of Wyoming Geological Museum, Sub-adult partial skeleton Stegosaurus

-Dinosaur National Monument, Jensen, Utah, (DNM 2438) S. ungulates partial skeleton

-Denver Museum of Nature and Science, Denver, Colorado, (DMNS 2818) Skull and skeleton

REFERENCES

• Carpenter, K., Miles, C.A, Cloward, K., 2001. "New Primitive Stegosaur from the Morrison Formation, Wyoming". In: Carpenter, Kenneth (ed.). The Armored Dinosaurs. Indiana University Press. pp. 55–75.
  
• Christiansen, N., & Tschopp, E. (2010). “Exceptional stegosaur integument impressions from the Upper Jurassic Morrison Formation of Wyoming”, in: Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0026-0
  
• Galton, P.M. 1982a. “Juveniles of the stegosaurian dinosaur Stegosaurus from the Upper Jurassic of North America”. In: Journal of Vertebrate Paleontology 2: 47–62.

  
• Gilmore, Charles W. 1914. "Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus Stegosaurus." Bulletin of the United States National Museum. i–xi, 1-143, 73 figs, 37 pls.
  
• Maidment SC, Brassey C, Barrett PM. The Postcranial Skeleton of an Exceptionally Complete Individual of the Plated Dinosaur Stegosaurus stenops (Dinosauria: Thyreophora) from the Upper Jurassic Morrison Formation of Wyoming, U.S.A. PLoS One. 2015 Oct 14;10(10):e0138352. doi: 10.1371/journal.pone.0138352. PMID: 26466098; PMCID: PMC4605687.
  
• Maidment S. C. R., Woodruff D. C., et al (2018) A new specimen of the ornithischian dinosaur Hesperosaurus mjosi from the Upper Jurassic Morrison Formation of Montana, U.S.A., and implications for growth and size in Morrison stegosaurs, Journal of Vertebrate Paleontology 38 1, e1406366: 1-22 doi:10.1080/02724634.2017.1406366
  
• Saitta, E.T. 2015. Evidence for sexual dimorphism in the plated dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper Jurassic) of western USA. PloS ONE 10: e0123503.
  
• Ostrom, John H. and McIntosh, John S. Marsh’s Dinosaurs. The Collections from Como Bluff. New Haven and London: Yale University Press, 1999. Pp. 248-363