Sphenodontida
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Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the
tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...
(''Sphenodon punctatus'') of
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
. Despite its current lack of diversity, during the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
rhynchocephalians were a diverse group including a wide array of morphologically distinct forms. The oldest record of the group is dated to the
Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...
around 238 to 240 million years ago, and they had achieved a worldwide distribution by the
Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
. Most rhynchocephalians belong to the group Sphenodontia ('wedge-teeth'). Their closest living relatives are lizards and
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s in the order
Squamata Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species ...
, with the two orders being grouped together in the superorder
Lepidosauria The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species ...
. Many of the niches occupied by lizards today were held by sphenodontians during the
Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
and
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
, although lizard diversity began to overtake sphenodontian diversity in the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
, and they had disappeared almost entirely by the beginning of the Cenozoic. While the modern tuatara is primarily carnivorous, there were also sphenodontians with
omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
(''
Opisthias ''Opisthias'' is a genus of sphenodont reptile. The type species, ''Opisthias rarus'', is known from the Late Jurassic (Kimmeridgian-Tithonian) Morrison Formation of western North America, present in stratigraphic zones 2 and 4–6. Distributi ...
''),
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
( Eilenodontinae), and
durophagous Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil tu ...
(''
Oenosaurus ''Oenosaurus'' is an extinct genus of sphenodontian reptile from the Late Jurassic (Tithonian) aged Mörnsheim Formation of Germany. Description The genus is known from a partial skull preserved in ventral view. Diet and lifestyle It is like ...
'') lifestyles. There were even several successful groups of aquatic sphenodontians, such as pleurosaurs and '' Ankylosphenodon''.


History of discovery

Tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...
were originally classified as
agamid Agamidae is a family of over 300 species of iguanian lizards indigenous to Africa, Asia, Australia, and a few in Southern Europe. Many species are commonly called dragons or dragon lizards. Overview Phylogenetically, they may be sister to the ...
lizards when they were first described by
John Edward Gray John Edward Gray, FRS (12 February 1800 – 7 March 1875) was a British zoologist. He was the elder brother of zoologist George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray (1766–1828). The same is used for ...
in 1831. They remained misclassified until 1867, when
Albert Günther Albert Karl Ludwig Gotthilf Günther FRS, also Albert Charles Lewis Gotthilf Günther (3 October 1830 – 1 February 1914), was a German-born British zoologist, ichthyologist, and herpetologist. Günther is ranked the second-most productive re ...
of the British Museum noted features similar to birds, turtles, and crocodiles. He proposed the order Rhynchocephalia (meaning "beak head") for the tuatara and its fossil relatives. In 1925
Samuel Wendell Williston Samuel Wendell Williston (July 10, 1852 – August 30, 1918) was an American educator, entomologist, and paleontologist who was the first to propose that birds developed flight cursorially (by running), rather than arboreally (by leaping from tr ...
proposed the Sphenodontia to include only tuatara and their closest fossil relatives. ''Sphenodon'' is derived from
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
'wedge' and 'tooth'. Many disparately related species were subsequently added to the Rhynchocephalia, resulting in what taxonomists call a "
wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined ...
". These include the superficially similar (both in shape and name) but unrelated
rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...
s, which lived in the
Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
. These were resolved after use of computer based
cladistics Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...
, which showed the core sphenodontian grouping to be monophyletic.


Classification and anatomy

Sphenodonts, and their sister group
Squamata Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species ...
(which includes lizards,
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s and amphisbaenians), belong to the superorder
Lepidosauria The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species ...
, the only surviving taxon within Lepidosauromorpha. Squamates and sphenodontians have a number of shared traits ( synapomorphies), including fracture planes within the tail vertebrae allowing
caudal autotomy Autotomy (from the Greek ''auto-'', "self-" and ''tome'', "severing", αὐτοτομία) or self-amputation, is the behaviour whereby an animal sheds or discards one or more of its own appendages, usually as a self-defense mechanism to elude a ...
(loss of the tail-tip when threatened), transverse cloacal slits, an opening in the pelvis known as the thyroid fenestra, the presence of extra
ossification centres An ossification center is a point where ossification of the cartilage begins. The first step in ossification is that the cartilage cells at this point enlarge and arrange themselves in rows.Gray and Spitzka (1910), page 44. The matrix in which t ...
in the limb bone
epiphyses The epiphysis () is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the jo ...
, a knee joint where a lateral recess on the femur allows the articulation of the fibula, the development of a sexual segment of the kidney, and a number of traits of the feet bones, including a fused astralago- calcaneun and enlarged fourth distal tarsal, which creates a new joint, along with a hooked fifth
metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...
. Like some squamates, the tuatara retains a
parietal eye A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhyth ...
, which has been lost in the other groups of extant reptiles, the
turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...
s and archosaurs. Rhynchocephalians are distinguished from squamates by a number of traits, including the retention of
gastralia Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In thes ...
( rib-like bones present in the belly of the body, ancestrally present in tetrapods and also present in living
crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...
ns), a narrow
quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper pa ...
, the
temporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets ...
(an opening of the skull) is enclosed or partially enclosed by bone, the jugal bones in the temporal arch touch the
squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral c ...
posteriorly Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
, and a large coronoid
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...
is present on the lower jaw. The complete lower temporal bar of the tuatara, often considered a primitive feature, is actually a derived feature among sphenodontians, with the most primitive lepidosauromorphs and rhynchocephalians having an open lower temporal fenestra. Unlike squamates, but similar to the majority of birds, the tuatara lacks a penis. This is a secondary loss, as a penis or squamate-like hemipenes were probably present in the last common ancestor of rhynchocephalians and squamates. The dentition of most rhynchocephalians is described as
acrodont Acrodonty (from Greek ''akros'' 'highest' + ''dont'' 'tooth') is an anatomical placement of the teeth at the summit of the alveolar ridge of the jaw, without sockets, characteristic of bony fish. Functionally, acrodont tooth implantation may be rela ...
(the condition where the teeth are attached to the crest of the jaw bone, and lack roots), similar to those of acrodontan lizards like agamids. The term "acrodont" has also been used in reference to the absence of tooth replacement or the extent of bone growth around the teeth, causing terminological confusion. The teeth of living tuatara have no roots and are not replaced, and are extensively fused to the jaw bone. The teeth of ''Gephyrosaurus'' are
pleurodont Pleurodont is a form of tooth implantation common in reptiles of the order Squamata, as well as in at least one temnospondyl. The labial (cheek) side of pleurodont teeth are fused (ankylosed) to the inner surface of the jaw bones which host them. T ...
(teeth are weakly attached to the inner part of the mandible with no sockets, and replaced throughout life), like those of most squamates, and this is thought to be the ancestral condition of Lepidosauria. The most primitive sphenodontians have a combination of both pleurodont and acrodont teeth. Some rhyncocephalians differ from these conditions, with '' Ankylosphenodon'' having teeth that continue deeply into the jaw bone, and are fused to the bone at the base of the socket (ankylothecodont). Rhynchocephalians possess palatal dentition (teeth present on the bones of the roof of the mouth). In most rhynchocephalians, the teeth present on the
pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fis ...
are lost, but the lateral tooth row present on the palatine bones are enlarged, and orientated parallel to the teeth of the
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
. During biting, the teeth of the
dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
in the lower jaw slot between the maxillary and palatine tooth rows. This arrangement, which is unique among amniotes, permits three point bending of food items, and in combination with propalinal movement (back and forward motion of the lower jaw) allows for a shearing bite.


Internal systematics

While the grouping of Rhynchocephalia is well supported, the relationships of many taxa to each other are uncertain, varying substantially between studies. In modern cladistics, the clade Sphenodontia includes all rhynchocephalians other than '' Gephyrosaurus'' (as well as some other related genera) which has been found to be more closely related to squamates in some analyses. In 2018, two major clades within Sphenodontia were defined, the
infraorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Eusphenodontia which is defined by the least inclusive clade containing ''
Polysphenodon ''Polysphenodon'' is an extinct genus of clevosaurine reptile from the Late Triassic Keuper Group of Germany,N. C. Fraser and M. J. Benton. (1989) The Triassic reptiles '' Brachyrhinodon'' and ''Polysphenodon'' and the relationships of the ...
, Clevosaurus hudsoni'' and ''Sphenodon'', which is supported by the presence of three synapomorphies, including the presence of clearly visible wear facets on the teeth of the dentary or maxilla, the
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
ry teeth are merged into a chisel like structure, and the palatine teeth are reduced to a single tooth row, with the presence of an additional isolated tooth. The unranked clade Neosphenodontia (previously informally referred to as the "eupropalinals", in reference to the back and forward motion in the mouth during mastication), is defined as the most inclusive clade containing ''Sphenodon'' but not ''Clevosaurus hudsoni,'' which is supported by the presence of six synapomorphies, including the increased relative length of the antorbital region of the skull (the part of the skull forward of the eye socket), reaching 1/4 to 1/3 of the total skull length, the posterior (hind) edge of the
parietal bone The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is nam ...
is only slightly curved inward, the parietal foramen is found at the same level or forward of the anterior border of the supratemporal fenestra (an opening of the skull), the palatine teeth are further reduced from the condition in eusphenodontians to a single lateral tooth row, the number of
pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medi ...
tooth rows are reduced to one or none, and the posterior border of the ischium is characterised by a distinctive process. The family
Sphenodontidae Sphenodontidae is a family within the reptile group Rhynchocephalia, comprising taxa most closely related to the living tuatara of the genus ''Sphenodon''. Historically the taxa included within Sphenodontidae have varied greatly between analyse ...
has been used to include the tuatara and its closest relatives within Rhynchocephalia. However the grouping has lacked a formal definition, with the included taxa varying substantially between analyses. The closest relatives of the tuatara are placed in the clade
Sphenodontinae Sphenodontidae is a family within the reptile group Rhynchocephalia, comprising taxa most closely related to the living tuatara of the genus ''Sphenodon''. Historically the taxa included within Sphenodontidae have varied greatly between analyse ...
, which are characterised by a completely closed termporal bar.


Paleobiology

Rhynchocephalians were once considered to be a morphologically conservative group with little diversity. However, discoveries in recent decades have disputed this, finding a wide array of diversity within the clade. Early rhynchocephalians possess small ovoid teeth designed for piercing, and were probably insectivores. Amongst the most distinct rhynchocephalians are the pleurosaurs, known from the Jurassic of Europe, which were adapted for marine life, with elongated snake-like bodies with reduced limbs, with the specialised Late Jurassic genus '' Pleurosaurus'' having an elongated triangular skull highly modified from those of other rhynchocephalians. Several other lineages of rhyncocephalians have been suggested to have had semi-aquatic habits. Eilenodontines are thought to have been herbivorous, with batteries of wide teeth with thick enamel used to process plant material. ''
Oenosaurus ''Oenosaurus'' is an extinct genus of sphenodontian reptile from the Late Jurassic (Tithonian) aged Mörnsheim Formation of Germany. Description The genus is known from a partial skull preserved in ventral view. Diet and lifestyle It is like ...
'' and ''
Sapheosaurus ''Sapheosaurus'' was an extinct genus of Late Jurassic sphenodont. Its skull was longer and narrower than that of ''Homoeosaurus''. It was classified as a genus of sapheosaur by Michael Benton in 1985. It reached a length of 70 cm from snout ...
'' from the Late Jurassic of Europe possess broad tooth plates unique amongst tetrapods, and are thought to have been
durophagous Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil tu ...
, with the tooth plates being used to crush hard shelled organisms.


Evolutionary history

Rhynchocephalia is estimated to have diverged from Squamata between the
Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...
and earliest Triassic, between 270 and 252 million years ago. The oldest known remains of rhynchocephalians are indeterminate jaw fragments from the Erfurt Formation near
Vellberg Vellberg is a town in the district of Schwäbisch Hall, in Baden-Württemberg, Germany. It is located 10 km east of Schwäbisch Hall, and 15 km southwest of Crailsheim Crailsheim is a town in the German state of Baden-Württember ...
in Southern Germany, dating to the
Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic ...
stage of the
Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...
, around 238-240 million years old. Rhynchocephalians reached a worldwide distribution across
Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
by the end of the Triassic, with the
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
-
Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
genus ''
Clevosaurus ''Clevosaurus'' (meaning "Gloucester lizard") is an extinct genus of rhynchocephalian reptile from the Triassic, Late Triassic and the Jurassic, Early Jurassic Period (geology), periods. Species of ''Clevosaurus'' were widespread across Pangaea, ...
'' having 10 species across Asia, Africa, Europe, North and South America. The earliest rhynchocephalians were small animals, but by the Late Triassic the group had evolved a wide range of body sizes. During the Jurassic rhynchocephalians reached their apex of morphological diversity, including specialised herbivorous and aquatic forms. The only record of Rhynchocephalians from Asia are indeterminate remains of ''Clevosaurus'' from the Early Jurassic (
Sinemurian In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and ...
) aged
Lufeng Formation The Lufeng Formation (formerly Lower Lufeng Series) is a Lower Jurassic sedimentary rock formation found in Yunnan, China. It has two units: the lower Dull Purplish Beds/Shawan Member are of Hettangian age, and Dark Red Beds/Zhangjia'ao Member ar ...
of
Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the C ...
, China. Rhynchocephalians are noticeably absent from younger localities in the region, despite the presence of favourable preservation conditions. Rhynchocephalians disappeared from North America and Europe after the Early Cretaceous, and were absent from North Africa and northern South America by the early
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...
. The cause of the decline of Rhynchocephalia remains unclear, but has often been suggested to be due to competition with advanced lizards and mammals. They appear to have remained diverse in high-latitude southern South America during the Late Cretaceous, where lizards remained rare, with their remains outnumbering terrestrial lizards by a factor of 200. The youngest known remains of rhynchocephalians outside of New Zealand are those of ''Kawasphenodon peligrensis'' from the early
Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...
(
Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretace ...
) of
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...
, shortly after the
Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...
. Indeterminate sphenodontine jaw fragments bearing teeth are known from the early
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
(19-16 million years ago)
St Bathans fauna The St Bathans fauna is found in the lower Bannockburn Formation of the Manuherikia Group of Central Otago, in the South Island of New Zealand. It comprises a suite of fossilised prehistoric animals from the late Early Miocene (Altonian) period, ...
, New Zealand, that are indistinguishable from those of the living tuatara. It is unlikely that the ancestors of the tuatara arrived in New Zealand via
oceanic dispersal Oceanic dispersal is a type of biological dispersal that occurs when terrestrial organisms transfer from one land mass to another by way of a sea crossing. Island hopping is the crossing of an ocean by a series of shorter journeys between isla ...
, and it is thought that they were already present in New Zealand when it separated from
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
between 80 and 66 million years ago.


Gallery


Phylogeny

The following is a
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
of Rhynchocephalia after Rauhut et al., 2012.


References


Further reading

* * * *


External links

* * {{Taxonbar, from=Q15099738 . Taxa named by Albert Günther Tetrapod orders Extant Middle Triassic first appearances Ladinian first appearances Middle Triassic taxonomic orders Late Triassic taxonomic orders Early Jurassic taxonomic orders Middle Jurassic taxonomic orders Late Jurassic taxonomic orders Early Cretaceous taxonomic orders Late Cretaceous taxonomic orders Paleocene taxonomic orders Eocene taxonomic orders Oligocene taxonomic orders Miocene taxonomic orders Pliocene taxonomic orders Pleistocene taxonomic orders Holocene taxonomic orders