Tenontosaurus BW

Restoration of Tenontosaurus

Tenontosaurus ("sinew lizard") is a genus of ornithopod dinosaur from the Early Cretaceous of North America.


Tenontosaurus measured 6.5 to 8 meters long and weighed between 1 to 2 tonnes. It had a particularly long tail, which was stiffened by bony tendons much like its back was.


Tenontosaurus was originally considered a hypsilophodont, but it is now considered a primitive iguanodont.[1] There are two known species, T. tilletti (the type species) and T. dossi (known only from a few specimens in Texas).


The first fossils of Tenontosaurus were discovered in 1903 in Montana. During the next few decades, dozens more were unearthed in the same area. The dinosaur was not formally described at the time, but paleontologist Barnum Brown informally called it "Tenantosaurus", meaning "sinew lizard", referencing the extensive tendons in the back and tail.[2]

In the 1960s, a team from Yale University led by John Ostrom uncovered over 40 new specimens of Tenontosaurus in the Cloverly Formation in Montana. This expedition led to the description of the famous dromaeosaurid Deinonychus[3], but Ostrom also formally described Tenontosaurus at this time, modifying Barnum Brown's original name slightly. Many more specimens have since been reported.[2]


Predatory associationsEdit

Teeth and skeletons that came from the dromaeosaurid dinosaur Deinonychus are often associated with Tenontosaurus remains. In fact, only six sites that contain Deinonychus fossils are found with no Tenontosaurus fossils, and the raptor is rarely found with other potential prey items.[4] Because of this, it is often perceived that Deinonychus was a frequent predator of this dinosaur, although there are other possible scenarios that explain this association, such as cannibalization.[5]



Tenontosaurus was herbivorous, and its diet likely consisted of ferns, shrubs, cycads, and possibly fruits.[2]


In one specimen of Tenontosaurus, medullary bone was found in the animal's thigh and shin. Today, medullary tissue is only found in birds that are laying or going to lay eggs. To date, only two other dinosaurs have been found with this tissue (Tyrannosaurus and Allosaurus), making Tenontosaurus the first ornithischian known to possess it. All three specimens were not fully grown when died, suggesting that all dinosaurs produced this tissue and reached sexual maturity before they reached full size.[6]


  1. Butler, Richard J.; Upchurch, Paul; and Norman, David B. (2008). "The phylogeny of the ornithischian dinosaurs". Journal of Systematic Palaeontology 6 (1): 1–40. doi:10.1017/S1477201907002271.
  2. 2.0 2.1 2.2 Forster, C.A. (1984). "The paleoecology of the ornithopod dinosaur Tenontosaurus tilletti from the Cloverly Formation, Big Horn Basin of Wyoming and Montana." The Mosasaur, 2: 151–163.
  3. Ostrom, J. H. (1970). "Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana". Bulletin of the Peabody Museum of Natural History 35: 1–234.
  4. Maxwell, W. D.; Ostrom, J.H. (1995). "Taphonomy and paleobiological implications of Tenontosaurus-Deinonychus associations". Journal of Vertebrate Paleontology 15 (4): 707–712. doi:10.1080/02724634.1995.10011256. (abstract)
  5. Roach, B. T.; D. L. Brinkman (2007). "A reevaluation of cooperative pack hunting and gregariousness in Deinonychus antirrhopus and other nonavian theropod dinosaurs". Bulletin of the Peabody Museum of Natural History 48 (1): 103–138. doi:10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2.
  6. Lee, Andrew H.; and Werning, Sarah (2008). "Sexual maturity in growing dinosaurs does not fit reptilian growth models". Proceedings of the National Academy of Sciences 105 (2): 582–587. Bibcode 2008PNAS..105..582L. doi:10.1073/pnas.0708903105. PMC 2206579. PMID 18195356.