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Earth 5 million years from now

The Osteodontia are a large and diverse group of primarily herbivorous reptiles. Having evolved from within the Rynchocephalians, Osteodonts are sometimes classified in the clade Rynchocephalomorpha. Initially appearing as small, lizard-like creatures, Osteodonts eventually diversified into one of the most successful orders of reptiles in natural history. Throughout the many identified families, these reptiles have taken up the roles of many former ungulates, rodents, marsupials, and sirenians.

Evolution Edit

Osteodonts can trace their evolution back to the Rhynchocephalians, an order that was once prevalent and diverse in the Mesozoic, but eventually declined to the tuataras of New Zealand by the Holocene. Despite being threatened by invasive species such as rats, the tuatara populations began to gradually increase through conservation efforts placed by humans. Following the ice age near the end of the Cenozoic, five million years in the future, the Tuatara had been introduced to most of mainland New Zealand, as well as some parts of Australia, where they would develop a more omnivorous diet than their island ancestors.

The tuatara's descendants, the Rynchocephalomorphs, would retain a form similar to lizards through the Postocene, with some species evolving into forms similar to prehistoric Rhynchocephalians, such as Priosphenodon, having also developed an entirely herbivorous diet. However, following the Postocene-Neogene extinction that would wipe out most large mammal species, the Rynchocephalomorphs would diverse, eventually evolving into the first true Osteodonts by the Megistocene.

Although the Osteodonts would originally be undermined by other herbivorous reptiles, such as the Scutosquamids, they would eventually outcompete them and diversify across Borealia by the end of and after the Basilozoic. This is due to their unique dentition; unlike other reptiles, their Rhynchocephalian ancestors had two rows of teeth on the upper jaw, which overlap with a single row of teeth on the lower jaw. While these teeth are projections of the skull itself, and thus cannot be replaced if broken, this dentition allows the tuatara, and its Osteodont descendants, to chew its food more than any other reptile, making them more like mammals in this manner. Thus, the Osteodonts can diversify into the main herbivores of Borealia, and fill niches in numerous ecosystems.

Trianychia Edit

Trianychids ("three claws") are Osteodonts that are characterized by three toes, and the equal distribution of weight on either one of all of these toes. The claws have been developed into a more nail-like structure, which further developed into a structure similar to the hooves of ungulate mammals. Some Trianychids (Elaphosaurids and Suisaurids) have one large 'hoof' and two dewclaws; other Trianychids (Bysaurids) have three distinct hooved or heavily nailed toes. Unlike Pentanychids, Trianychids are obligate quadrupeds.

Elaphosauridae Edit

With their name meaning "Deer Lizards", Elaphosaurids fit their name perfectly; nimble, agile grazers that live in herds, these are almost convergently identical to the deer, antelope and horses of the Cenozoic era. Being found throughout the majority of what is today Africa, Eurasia and N. America, they are the most widespread of the Osteodonts, with a possible number of over 500 species identified. They range in size from the small, shrub-foragers of the North American and Central African forests, standing at about 14-19 inches tall at the shoulder, to the gigantic grazers of the Eurasian Steppes, which stand at almost 89 inches tall (2.26 meters), making them larger than the tallest breed of horse.

Bysauridae Edit

Named for their Bovine-like adaptations, Bysaurids are the largest Trianychids. Largely found about nothern Borealia, particularly modern day N. America and Asia, Bysaurids are reminiscent of present-day Bovines and Rhinos, with characteristically large heads, short necks and broad chests. Most species are solitary animals, with a few exceptions, whom travel in migratory herds across the continent.

Suisauridae Edit

Suisaurids, as their name implies, are similar to modern day pigs and peccaries, both in behavior and anatomy. Like the Bysaurids, Suisaurids have large heads and short necks, but they have characteristically daintier and lighter builds, allowing them to be more agile. Their most unique feature, however, if their omnivorous diets; unlike other families, which are purely herbivores, Suisaurids supplement their diet with invertebrates, small lizards, birds and mammals, and even carrion. Some species are even more carnivorous than herbivorous, actively hunting out smaller animals while supplementing their diet with foliage.

Pentanychia Edit

Pentanychids ("five claws") are Osteodonts that have retained their ancestors' five toes, and lack the 'hoof' of Trianychids. While they're less advanced than Trianychids, Pentanychids are also less restricted in their movement; they're aren't obligate quadrupeds, and in fact contain a number of purely bipedal species.

Mysauridae Edit

The Mysaurids, or "Mice Lizards", consists of the smallest and most primitive of the Osteodonts. They are the most like their distant sphenodontian ancestors, retaining their small stature and sprawling posture, even though they act more like rodents than lizards. Resembling smaller Anomodonts, such as Diictodon, Mysaurids are sociable, burrowing animals that often feed on low-lying grasses and plant roots, although some have taken up arboreal lifestyles. As such, most are found in parts of Borealia closer to the equator, with more vegetation and stable climates and humidity, although some can be found as far north as northern Eurasia and N. America, much closer to the North Pole.

Elegansauridae Edit

The Elegansauridae consists of species convergent with herbivorous marsupials, such as kangaroos and wallabies, with a bipedal, hopping gate instead of a quadrupedal stance like their relatives. Ironically, most of these species are found throughout the peninsula that was once modern day Australia, like the marsupials they resemble, but they aren't uncommon in Asia and Africa either. Elegansaurids have smaller forelimbs, being bipedal, but they are still used to grasp objects, such as plants.

Dynamisauridae Edit

Dynamisaurids are perhaps the most bizarre family of Osteodonts. These reptiles are characterized by a burly, robust build (hence their name, "Robust Lizards"), smaller heads and long arms adorned with strong, sharp claws. These specialized creatures are convergent with a number of other animals, such as the extinct giant ground sloths or chalicotheres, and even therizinosaurid dinosaurs like Nothronychus. Like all of these creatures, Dynamisaurids are herbivores adapted to grasp tree branches with their powerful limbs to feed on the succulent leaves. Thus, these reptiles are only relatively common in more forested regions, although a few species have made their home in more arid regions.

Hydrosauridae Edit

The Hydrosauridae consist of reptiles completely adapted for life in the water, with a sleek, smooth build, fins and flukes for better locomotion, and a viviparous mode of reproduction. Convergent with modern day marine mammals, such as cetaceans and sirenians, Hydrosaurids are the first purely aquatic herbivorous reptiles in history, having become fully aquatic around 99 MyF. These reptiles, having little competition for the various species of sea plants that fill the waters of the future, are as successful as their cousins on land. They range from the smallest species of 177.8 cm (70 in), often found in freshwater or coastal mangrove environments, to 12 meter (40 foot) long giants that often roam in more open oceans. Hydrosaurids can be found throughout the oceans, although they are generally more common in southern waters, closer to the equator where more flora can be found.

Tetranychia Edit

Tetranychids ("four claws") are Osteodonts characterized by having four toes on each foot. These Osteodonts are significantly larger than their Pentanychid and Trianychid relatives, with some Tetranychids being the largest land animals of their time, growing to the size of even some sauropod dinosaurs.

Cyrtodontidae Edit

Cyrtodontids are characterized by having the front teeth on both the upper and lower jaws curve forward, creating two pairs of slicing 'incisors' adept at cutting through vegetation. These Osteodonts are fairly small for their suborder (still larger than most other families), with the largest being a little larger than a hippo. They also live like hippos as well; spending large amounts of time in water, feeding on aquatic plants or cooling down in the heat. Cyrtodontids are primarily found around the equator, often in areas with abundant amounts of vegetation.

Dolichirhisidae Edit

The "long-nosed lizards", as their name implies, are characterized by having an elongated proboscis, as well as a pair of teeth that have formed into tusks. Dolichirhisids have developed the same adaptations as advanced proboscideans for feeding, using their trunks and tusks to grasp plants, making them adept foragers and browsers of all but the tallest of vegetation. These Osteodonts are often found in northern Borealia, particularly Eurasia and North America, although some species can be found much farther to the south, and even on some coastal islands.

Decaspondylusidae Edit

Decaspondylusids are named for their ten neck vertebrae, which have developed to support an elongated neck. The smallest of these Osteodonts can grow to the size of a moose, while the largest reach and even surpass some sauropod dinosaurs in size, making Decaspondylusids the largest land animals of their time, and among the largest animals in natural history. Unlike their relatives, they have a cosmopolitan distribution, often feeding on the highest trees that even Dolichirhisids, the next largest herbivores, can reach.

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