Tenontosaurus californicus is about 6.5 to 8 metres (21 to 26 ft) long and 3 metres (9.8 ft) high in a bipedal stance (when fully grown), with a mass of somewhere between 1 to 2 tonnes (1 to 2 short tons). It has an unusually long, broad tail, which like its back is stiffened with a network of bony tendons, and its tail is used mainly for communication and for defense against potential predators. It is a low browser, and an adult has a maximum browsing height of about 3 meters (9 ft) if it adopted a bipedal stance; its main source of food includes ferns, tree ferns, cycads, conifer, and ginkgo trees. Tenontosaurus californicus is a social herd animal that lives in groups up to about 19 at a time. During mating seasons, males fight one another by ramming each other's sides until one backs down, and the winner gets a right to mate. The females lay eggs about 3-4 months after mating seasons, the eggs hatch about 2-3 months after being laid, and the young are cared for by their mothers until they are almost fully grown, when they must fend for themselves in their herds. Unlike most iguanodonts, while Tenontosaurus californicus grows quickly in early life, it grows very slowly in the years approaching maturity.