Tenontosaurus (/"TEN-on-toh-SOR-us"/; "tendon lizard") is a genus of medium-sized ornithopod dinosaur that lived during the Early Cretaceous period, approximately 115-108 million years ago. Its fossils have been primarily discovered in the Cloverly Formation, which spans parts of Montana, Wyoming, and Oklahoma, as well as the Antlers Formation of Texas and Oklahoma. Paleontologist John Ostrom described and named the genus in the 1970s.

Description and Classification

Tenontosaurus belongs to the Ornithopoda, a diverse group of herbivorous dinosaurs that includes iguanodonts and the well-known hadrosaurs (duck-billed dinosaurs). It was a relatively agile, mid-sized dinosaur, estimated to reach lengths of 6-8 meters (20-26 feet) and weights between 1-2 tonnes (1.1-2.2 short tons).

While primarily bipedal, Tenontosaurus likely had the ability to move on all fours when needed, similar to other ornithopods. Its most distinctive feature was its exceptionally long tail, which made up almost half of its total body length. The tail was likely used for balance when running and may have also served as a potential defense weapon against predators.

Distinguishing Features

One of the most notable features of Tenontosaurus is the extensive network of ossified tendons found along its tail and back. These tendons likely provided stiffness and support to these regions, enhancing the dinosaur's locomotion and power. The presence of these ossified tendons is reflected in the genus name, which means "tendon lizard."

Other distinguishing characteristics of Tenontosaurus include:

  • Elongated, narrow skull with a beak-like structure at the front of the jaws.
  • Relatively long, slender neck compared to other ornithopods.
  • Forelimbs that were shorter than the hindlimbs but still well-developed.
  • Hands with five fingers, including a partially opposable thumb, which may have been used for grasping vegetation.
  • Leaf-shaped, serrated teeth adapted for herbivory.

Paleoenvironment and Diet

During the Early Cretaceous, the region inhabited by Tenontosaurus was characterized by a warm, subtropical environment with forests, river systems, and coastal plains. This habitat would have provided a diverse array of plant life to support herbivorous dinosaurs like Tenontosaurus.

As an herbivore, Tenontosaurus would have fed on various types of low-growing vegetation, including ferns, horsetails, and early flowering plants. Its beak-like mouth and specialized teeth were well-suited for cropping and processing tough plant material.

Significance and Ongoing Research

The discovery and study of Tenontosaurus have contributed significantly to our understanding of dinosaur ecology and behavior during the Early Cretaceous period. One notable aspect of Tenontosaurus research is its association with the dromaeosaurid theropod Deinonychus.

Numerous Tenontosaurus fossils have been found in close proximity to Deinonychus remains, strongly suggesting that Tenontosaurus was a common prey item for these agile, pack-hunting predators. The frequency of this association provides some of the earliest compelling evidence for coordinated hunting behavior in dromaeosaurids.

Another intriguing aspect of Tenontosaurus is the discovery of multiple individuals in close association, which has led to speculation about potential herd behavior or social grouping in this genus. While more evidence is needed to confirm this hypothesis, it raises interesting questions about the social dynamics and behavior of ornithopod dinosaurs.

Tenontosaurus also sheds light on the diversity and adaptations of iguanodontid-like ornithopods during the Early Cretaceous of North America. While discussions of this time period often focus on the later hadrosaurs, Tenontosaurus represents a successful and widespread ornithopod lineage that thrived alongside other herbivorous dinosaurs.

Ongoing research on Tenontosaurus includes studies of its anatomy, growth patterns, and biomechanics. Detailed analyses of its skeletal structure and muscle attachments provide insights into its locomotion, feeding mechanics, and overall paleobiology.

Comparative studies with other ornithopods and herbivorous dinosaurs help elucidate the evolutionary relationships and ecological roles of Tenontosaurus within its Early Cretaceous ecosystem. As new fossil discoveries are made and analytical techniques advance, our understanding of this intriguing dinosaur continues to grow, providing a clearer picture of the complex and fascinating world of the Early Cretaceous.



Back to blog