Ovoo (genus)
Encyclopedia
Ovoo 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.
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 cairn
s called ovoo
s that are found along roads near Little Ukhaa. The type species O. gurvel comes from the Mongolian word for lizard.
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 bone
s. There are no homologous bones in any other animal, making their presence a mystery.
, which includes the living monitor and helodermatid lizards and the extinct mosasaur
s. 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:
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of monitor lizard
Monitor lizard
Monitor lizards are usually large reptiles, although some can be as small as in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known...
from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
of Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
. It is one of the smallest and earliest monitor lizards. The type
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
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.
Description and history
Ovoo is only known from a fossilized skull cataloged as IGMMongolian Academy of Sciences
The Mongolian Academy of Sciences is Mongolia's first centre of modern sciences. It was founded in 1921, when the government established an Institute of Literature and Script, which was later upgraded to Institute of Science. Later, in 1961, it was reconstituted as the Mongolian Academy of Sciences...
3/767 and designated the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of the genus. The skull was discovered in 2001 near the rich Ukhaa Tolgod
Djadochta Formation
The Djadochta Formation is situated in central Asia and dates from the Late Cretaceous Period. Laid down in the early Campanian, possibly starting in the latest Santonian, it is dated somewhat uncertainly at about 84-75 mya...
fossil site in a locality known as Little Ukhaa. The deposits at Little Uhhaa date back to the Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stage of the Late Cretaceous. Ovoo was named in 2008 after cairn
Cairn
Cairn is a term used mainly in the English-speaking world for a man-made pile of stones. It comes from the or . Cairns are found all over the world in uplands, on moorland, on mountaintops, near waterways and on sea cliffs, and also in barren desert and tundra areas...
s called ovoo
Ovoo
An ovoo is a type of shamanistic cairn found in Mongolia, usually made from rocks or from wood. Ovoos are often found at the top of mountains and in high places, like mountain passes...
s that are found along roads near Little Ukhaa. The type species O. gurvel comes from the Mongolian word for lizard.
Ovoo was very small compared to living monitor lizards, with the exception of the Short-tailed monitor
Short-tailed monitor
The short-tailed monitor, or the pygmy goanna, is the smallest living monitor lizard, and may be the smallest species of monitor that has ever existed with a maximum length of 25 cm...
. Nevertheless, the structures of its skull are very similar to those of living monitors. Ovoo shares many similarities with the extinct monitors Aiolosaurus
Aiolosaurus
Aiolosaurus is an extinct genus of monitor lizard from the Late Cretaceous of Mongolia. The type and only species, A. oriens, was named in 2000 from Ukhaa Tolgod, a rich fossil site in the Campanian-age Djadochta Formation.-Description and history:...
and Cherminotus
Cherminotus
Cherminotus is an extinct genus of monitor lizard from the Late Cretaceous of Mongolia. The type and only species, C. longifrons, was named in 1984.-Description and history:...
, 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:
- NasalsNasal boneThe nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
, located behind the nostril openings, that are divided into two bones (in living monitors they are fused into one bone). - The large size of a pair of holes called premaxillaPremaxillaThe incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
ry fenestrae in front of the nostril openings. - A bone called the septomaxilla that separates the premaxilla (the bone at the very tip of the snout) from the maxillaMaxillaThe maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
(the bone that makes up the upper jaw). - The small size of a hole in the septomaxilla bone called the septomaxillary foramen.
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 bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
s. There are no homologous bones in any other animal, making their presence a mystery.
Classification
Ovoo is one of many Late Cretaceous lizards belonging to a group called VaranoideaVaranoidea
Varanoidea is a superfamily of lizards, including the well-known family Varanidae . Also included in the Varanoidea are such extinct marine and semi-aquatic forms as mosasaurs and dolichosaurs, the venomous helodermatids , the Lanthanotidae , and the extinct Necrosauridae.Throughout their long...
, which includes the living monitor and helodermatid lizards and the extinct mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
s. 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
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...
. Ovoo is the oldest known member of Varaninae. Of the other Mongolian varanoids, Aiolosauurs was placed as a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
member of Varanidae
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...
(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
Telmasaurus
Telmasaurus is an extinct genus of varanoid lizard from the Late Cretaceous of Mongolia. Fossils have been found from the Djadokha and Barun Goyot Formations that date between the early and middle Campanian stage from approximately 80 to 75 million years ago. The type species T...
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
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
from the analysis: