Teraterpeton
Encyclopedia
Teraterpeton is an extinct genus
of basal
archosauromorph. A partial skeleton was described from the Late Triassic
Wolfville Formation
of Nova Scotia
in 2003. It has many unique features seen in no other related form, including an elongated, toothless snout and large openings for the nostrils. Because of this, Teraterpeton was placed in its own family
, Teraterpetidae.
and prefrontal bone
s. At the back of the jaws, the small, sharp teeth are closely spaced. They continue below the level of the eye, an unusual trait among early archosauromorphs. The upper tooth row does not run along the edge of the jaw, but is inset closer to mouth. An additional tooth row on the palate
runs alongside the maxilla
ry tooth row of the upper jaw. The teeth of the upper jaws fit closely, or occlude, with the teeth of the lower jaw. The upper jaw teeth have sharp cusps with indentations in front of them, while the lower jaw teeth have cusps with indentations behind them. The cusps of the upper teeth fit into the indentations of the lower teeth, while the cusps of the lower teeth fit into the indentations of the upper teeth.
Teraterpeton is unique among all archosauromorphs in having a euryapsid-type skull. Euryapsids have a single hole at the back of the skull called the supratemporal fenestra, which is located toward the top of the head. Teraterpeton evolved from diapsid
reptiles with two holes at the back of their skull, the supratemporal fenestra and an infratemporal fenestra below it. Although it lacks an infratemporal fenestra, Teraterpeton still belongs to Diapsida because it is a descendant of true diapsids. Other euryapsids such as the marine plesiosaur
s and ichthyosaur
s are not closely related to Teraterpeton.
Another unusual feature of Teraterpeton is the large size of its narial fenestra, a hole in the skull that serves as the opening for the nostril
. This hole is positioned directly in front of the eyes and extends to the level of the toothless portion of the snout. It is positioned where the antorbital fenestra
would normally be. In fact, the namer of Teraterpeton first considered the hole to be an antorbital fenestra. The anterior margin of the antorbital fenestra is usually bound by the maxilla near the end of the snout and the lacrimal near the eye socket. However, the maxilla of Teraterpeton has moved closer to the eye socket, touching the lacrimal and closing off the antorbital fenestra. Comparable in size to the antorbital fenestrae of many other archosauromorphs, the narial fenestra of Teraterpeton is even longer than the eye socket.
skeleton referred to as NSM 999GF041. This skeleton was found in a sea cliff in Burntcoat Head, Nova Scotia
. The deposit from which it was found is part of the late Carnian
Wolfville Formation, comprising a section of the larger Newark Supergroup that stretches across Canada
and the eastern United States
. The formation is located in the Fundy Basin
, a rift basin which, like other Newark basins, opened as Pangaea
began to break apart at the end of the Triassic. The Wolfville Formation contains a diverse assemblage of Triassic tetrapods that includes temnospondyl amphibians, procolophonid
reptiles, and traversodont
cynodont
s. Based on the presence of the temnospondyl Koskinonodon
(a common Triassic index fossil
), the assemblage is dated to the Carnian
stage of the Late Triassic.
The type species of Teraterpeton, T. hrynewichorum, was named in 2003. It is named after George P. Hrynewich and his son Sandy Hrynewich, fossil collectors who discovered the bones at Burntcoat Head in 1999.
as the closest relative of the genus. Together, these two forms comprise an archosauromorph clade that is more derived
than prolacertiforms and more basal
than rhynchosaur
s. Below is a cladogram
modified from the 2003 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 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:...
archosauromorph. A partial skeleton was described from the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
Wolfville Formation
Wolfville Formation
The Wolfville Formation is a Mesozoic geologic formation of Nova Scotia. The formation is late Carnian to early Norian in age. Fossils of small land vertebrates have been found in the formation, including procolophonid and early archosauromorph reptiles and cynodonts...
of Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
in 2003. It has many unique features seen in no other related form, including an elongated, toothless snout and large openings for the nostrils. Because of this, Teraterpeton was placed in its own family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, Teraterpetidae.
Description
Teraterpeton has a very different appearance from other early archosauromorphs. It has a long skull with no teeth at the ends of the upper and lower jaws. Over the eye sockets, two bony projections are formed by the lacrimalLacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
and prefrontal bone
Prefrontal bone
The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls. It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most modern and extinct lungfish, amphibians and reptiles...
s. At the back of the jaws, the small, sharp teeth are closely spaced. They continue below the level of the eye, an unusual trait among early archosauromorphs. The upper tooth row does not run along the edge of the jaw, but is inset closer to mouth. An additional tooth row on the palate
Palate
The 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...
runs alongside 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...
ry tooth row of the upper jaw. The teeth of the upper jaws fit closely, or occlude, with the teeth of the lower jaw. The upper jaw teeth have sharp cusps with indentations in front of them, while the lower jaw teeth have cusps with indentations behind them. The cusps of the upper teeth fit into the indentations of the lower teeth, while the cusps of the lower teeth fit into the indentations of the upper teeth.
Teraterpeton is unique among all archosauromorphs in having a euryapsid-type skull. Euryapsids have a single hole at the back of the skull called the supratemporal fenestra, which is located toward the top of the head. Teraterpeton evolved from diapsid
Diapsid
Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
reptiles with two holes at the back of their skull, the supratemporal fenestra and an infratemporal fenestra below it. Although it lacks an infratemporal fenestra, Teraterpeton still belongs to Diapsida because it is a descendant of true diapsids. Other euryapsids such as the marine plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
s and ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
s are not closely related to Teraterpeton.
Another unusual feature of Teraterpeton is the large size of its narial fenestra, a hole in the skull that serves as the opening for the nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
. This hole is positioned directly in front of the eyes and extends to the level of the toothless portion of the snout. It is positioned where the antorbital fenestra
Antorbital fenestra
An antorbital fenestra is an opening in the skull, in front of the eye sockets. This skull formation first appeared in archosaurs during the Triassic Period. Living birds today possess antorbital fenestrae, but the feature has been lost in modern crocodilians...
would normally be. In fact, the namer of Teraterpeton first considered the hole to be an antorbital fenestra. The anterior margin of the antorbital fenestra is usually bound by the maxilla near the end of the snout and the lacrimal near the eye socket. However, the maxilla of Teraterpeton has moved closer to the eye socket, touching the lacrimal and closing off the antorbital fenestra. Comparable in size to the antorbital fenestrae of many other archosauromorphs, the narial fenestra of Teraterpeton is even longer than the eye socket.
History
Teraterpeton is known from a single partial 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...
skeleton referred to as NSM 999GF041. This skeleton was found in a sea cliff in Burntcoat Head, Nova Scotia
Burntcoat Head, Nova Scotia
Burntcoat Head is an unincorporated Canadian community in Hants County, Nova Scotia and is known internationally as the site where it was officially recorded that the Bay of Fundy, and specifically Burntcoat, has the highest tides in the world.- Highest Tides in the World :Burntcoat Head has a...
. The deposit from which it was found is part of the late Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
Wolfville Formation, comprising a section of the larger Newark Supergroup that stretches across Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and the eastern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The formation is located in the Fundy Basin
Fundy Basin
The Fundy Basin is a sediment-filled rift basin on the Atlantic coast of southeastern Canada. It contains three sub-basins; the Fundy sub-basin, the Minas Basin and the Chignecto Basin. These arms meet at the Bay of Fundy, which is contained within the rift valley. From the Bay of Fundy, the Minas...
, a rift basin which, like other Newark basins, opened as Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
began to break apart at the end of the Triassic. The Wolfville Formation contains a diverse assemblage of Triassic tetrapods that includes temnospondyl amphibians, procolophonid
Procolophonid
The Procolophonids - family Procolophonidae - are a group of small reptiles. Skulls have been discovered, roughly 5 cm in diameter....
reptiles, and traversodont
Traversodontidae
Traversodontidae is a family of herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe and eastern North America. Traversodonts first appeared in the Middle Triassic, diversified...
cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
s. Based on the presence of the temnospondyl Koskinonodon
Koskinonodon
Koskinonodon is an extinct genus of large temnospondyl amphibian, formerly named Buettneria. It was very common during the Late Triassic in what is now the American Southwest.-External links:*...
(a common Triassic index fossil
Index fossil
Index fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...
), the assemblage is dated to the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
stage of the Late Triassic.
The type species of Teraterpeton, T. hrynewichorum, was named in 2003. It is named after George P. Hrynewich and his son Sandy Hrynewich, fossil collectors who discovered the bones at Burntcoat Head in 1999.
Classification
A phylogenetic analysis was provided in the original description of Teraterpeton in 2003. It placed TrilophosaurusTrilophosaurus
Trilophosaurus was a lizard-like Triassic diapsid reptile related to the archosaurs. It was a herbivore up to 2.5 meters long. It had a short, unusually heavily-built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting up tough plant material...
as the closest relative of the genus. Together, these two forms comprise an archosauromorph clade that is more 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...
than prolacertiforms and more 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:...
than rhynchosaur
Rhynchosaur
Rhynchosaurs were a group of Triassic diapsid reptiles related to the archosaurs.-Description:Rhynchosaurs were herbivores, and at times abundant , with stocky bodies and a powerful beak...
s. 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...
modified from the 2003 analysis: