Proplatynotia
Encyclopedia
Proplatynotia is an extinct genus
of varanoid
lizard from the Late Cretaceous
of Mongolia
. Fossils have been found in the Barun Goyot Formation
, which is mid-Campanian
in age. The type
and only species, P. longirostratia, was named in 1984.
skull cataloged as ZPAL MgR-I/68. The skull is mostly complete except for damage in the posterior area. Rounded plates of osteoderm
s cover the top surface and would have been covered in scales in life.
Compared to other Cretaceous varanoids, Proplatynotia was medium-sized with a skull about 4 centimetres (1.6 in) long. Its skull is long and slender, giving the type species P. longirostratia its name, which means "long snout." Bones in the back of the skull called parietals
are enlarged, indicating that it may have had larger jaw muscles and a stronger bite than most monitor lizards. Proplatynotia has many primitive varanoid features, including nostrils that are placed near the tip of the snout. The nostrils have expanded and moved backward in later varanoids, separating the maxilla
and nasal bone
. In Proplatynotia, these bones still touch. Other characteristic features of Proplatynotia include:
n lizard. Platynota is the group that includes monitor lizards and sometimes snakes and mosasaur
s. It includes all members of the superfamily Varanoidea
. Along with other Cretaceous lizards from Mongolia like Parviderma and Gobiderma
, Proplatynotia was called a necrosaurian. Necrosaurians were an evolutionary grade
of varanoid lizards that had generalized morphologies, lacking the derived
features of monitor lizards and snakes. They were the most primitive platynotans.
Since the first description of Proplatynotia, some features have been recognized that separate it from other platynotans. The teeth of Proplatynotia are smooth and lack plicidentine, folded layers of dentine around the center pulp cavity
of the tooth. Plicidentine, while rare in land-living vertebrates, is characteristic of monitor lizards and their closest extinct relatives. The lack of plicidentine in Proplatynotia led to an early hypothesis that it was not a platynotan, but evolved platynotan features through convergence
.
Despite its non-platynotan features, Proplatynotia is usually classified as one of the most basal
platynotans. In most recent studies, Platynotia includes monitor lizards, helodermatids, and their close extinct relatives, but not snakes. Below is a cladogram
from a 2008 phylogenetic study showing the relationships of Proplatynotia:
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 varanoid
Varanoidea
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...
lizard 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...
. Fossils have been found in the Barun Goyot Formation
Barun Goyot Formation
The Barun Goyot Formation , dating from the Late Cretaceous Period, is located within and is widely represented in the Gobi Desert basin, in the Ömnögovi Province of Mongolia....
, which is mid-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 ...
in age. 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, P. longirostratia, was named in 1984.
Description
Proplatynotia was named in 1984 from a single holotypeHolotype
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...
skull cataloged as ZPAL MgR-I/68. The skull is mostly complete except for damage in the posterior area. Rounded plates of osteoderm
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
s cover the top surface and would have been covered in scales in life.
Compared to other Cretaceous varanoids, Proplatynotia was medium-sized with a skull about 4 centimetres (1.6 in) long. Its skull is long and slender, giving the type species P. longirostratia its name, which means "long snout." Bones in the back of the skull called parietals
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
are enlarged, indicating that it may have had larger jaw muscles and a stronger bite than most monitor lizards. Proplatynotia has many primitive varanoid features, including nostrils that are placed near the tip of the snout. The nostrils have expanded and moved backward in later varanoids, separating the maxilla
Maxilla
The 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...
and nasal bone
Nasal bone
The 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....
. In Proplatynotia, these bones still touch. Other characteristic features of Proplatynotia include:
- The elongation of a hole beneath the eye socket called the suborbital fenestra.
- The large size of a pair of holes at the tip of the snout called the 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 foramina. - The narrowness of two holes in the palatePalateThe palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
called interpterygoid vacuities. - The extension of the internal naris (the part of the nasal cavity that opens in the mouth) far back in the palate.
Classification
When Proplatynotia was named in 1984, it was classified as a platynotaPlatynota
Platynota is a group of anguimorph lizards. Since it was named in 1839, it has included several groups, including monitor lizards, snakes, mosasaurs, and helodermatids. Its taxonomic use still varies, as it is sometimes considered equivalent to the group Varanoidea and other times viewed as a...
n lizard. Platynota is the group that includes monitor lizards and sometimes snakes and 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. It includes all members of the superfamily Varanoidea
Varanoidea
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...
. Along with other Cretaceous lizards from Mongolia like Parviderma and Gobiderma
Gobiderma
Gobiderma is an extinct genus of Late Cretaceous lizard whose fossils are known from the Gobi Desert in southern Mongolia. It was first discovered as a result of a joint Polish-Mongolian Paleontological Expedition, and formally named in 1984...
, Proplatynotia was called a necrosaurian. Necrosaurians were an evolutionary grade
Evolutionary grade
In alpha taxonomy, a grade refers to a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.-Definition:...
of varanoid lizards that had generalized morphologies, lacking the derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
features of monitor lizards and snakes. They were the most primitive platynotans.
Since the first description of Proplatynotia, some features have been recognized that separate it from other platynotans. The teeth of Proplatynotia are smooth and lack plicidentine, folded layers of dentine around the center pulp cavity
Pulp (tooth)
The dental pulp is the part in the center of a tooth made up of living connective tissue and cells called odontoblasts.- Anatomy :Each person can have a total of up to 52 pulp organs, 32 in the permanent and 20 in the primary teeth....
of the tooth. Plicidentine, while rare in land-living vertebrates, is characteristic of monitor lizards and their closest extinct relatives. The lack of plicidentine in Proplatynotia led to an early hypothesis that it was not a platynotan, but evolved platynotan features through convergence
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
.
Despite its non-platynotan features, Proplatynotia is usually classified as one of the most 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:...
platynotans. In most recent studies, Platynotia includes monitor lizards, helodermatids, and their close extinct relatives, but not snakes. 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 a 2008 phylogenetic study showing the relationships of Proplatynotia: