| Ovoo Temporal range: Late Cretaceous, 80 Ma |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Family: | Varanidae |
| Genus: | †Ovoo Norell et al., 2008 |
| Species | |
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Ovoo ( /ˈoʊvoʊ/) is an extinct genus of monitor lizard from the Late Cretaceous of Mongolia. It is one of the smallest and earliest monitor lizards. The type and only species, Ovoo gurvel, was named in 2008. Ovoo possesses a pair of two small bones in its skull that are not seen in any other lizard.
Ovoo is only known from a fossilized skull cataloged as IGM 3/767 and designated the holotype of the genus. The skull was discovered in 2001 near the rich Ukhaa Tolgod fossil site in a locality known as Little Ukhaa. The deposits at Little Uhhaa date back to the Campanian stage of the Late Cretaceous. Ovoo was named in 2008 after cairns called ovoos that are found along roads near Little Ukhaa. The type species O. gurvel comes from the Mongolian word for lizard.[1]
Ovoo was very small compared to living monitor lizards, with the exception of the Short-tailed monitor. Nevertheless, the structures of its skull are very similar to those of living monitors. Ovoo shares many similarities with the extinct monitors Aiolosaurus and Cherminotus, which are also known from Little Ukhaa and Ukhaa Tolgod. Differences between these genera are seen in the shape of the bones in the skull. The distinguishing features of Ovoo include:
The most unusual feature of Ovoo is the presence of two small bones that are not present in any other lizard. When it was first described, these structures were called "mystery bones". The two bones are located between the eye sockets. They are positioned behind the nasal bones and in front of the frontal bones. There are no homologous bones in any other animal, making their presence a mystery.[1]
Ovoo is one of many Late Cretaceous lizards belonging to a group called Varanoidea, which includes the living monitor and helodermatid lizards and the extinct mosasaurs. Features linking it with these lizards include a rounded snout and a lack of contact between the maxillae and frontal bones. A phylogenetic analysis conducted with its first description placed it within the monitor subfamily Varaninae. Ovoo is the oldest known member of Varaninae. Of the other Mongolian varanoids, Aiolosauurs was placed as a basal member of Varanidae (the family to which Varaninae belongs) and Cherminotus was placed in Lanthanotinae (another subfamily within Varanidae). Because of their age, Ovoo, Aiolosaurus, and Cherminotus may be representatives of the first radiation of monitor lizards. The Late Cretaceous varanoids Saniwides and Telmasaurus are just as old as these lizards and have traditionally been viewed as the oldest monitors, but they were placed outside the monitor family in the 2008 analysis. Below is a cladogram from the analysis:[1]
| Varanoidea |
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