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Phytosaurs (Φυτόσαυροι in
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 ...
) are an
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
group of large, mostly
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...
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 ...
archosauriform Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthier ...
reptiles. Phytosaurs belong to the
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent groupings containing the same species, but some studies have identified non-phytosaurid phytosaurians. Phytosaurs were long-snouted and heavily armoured, bearing a remarkable resemblance to modern
crocodilian 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 livin ...
s in size, appearance, and lifestyle, as an example of
convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that ...
or parallel evolution. The name "phytosaur" means "plant reptile", as the first fossils of phytosaurs were mistakenly thought to belong to plant eaters. The name is misleading because the sharp teeth in phytosaur jaws clearly show that they were predators. For many years, phytosaurs were considered to be the most basal group of
Pseudosuchia Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...
(crocodile-line
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avia ...
s), meaning that they were thought to be more closely related to the crocodilians than to birds (the other living group of archosaurs). Then some studies of the evolutionary relationships of early archosauriforms suggested that phytosaurs evolved before the split between crocodile- and bird-line archosaurs and are the
sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
of Archosauria. The most recent study retains the former way of classifying phytosaurs as pseudosuchians. Phytosaurs had a nearly global distribution during the Triassic. Fossils have been recovered from
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,
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,
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,
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,
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,
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
,
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...
and
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
. Fossils attributed to phytosaurs have been found in Early Jurassic rocks, possibly extending their temporal range beyond the Triassic-Jurassic boundary.


Description

Phytosaurs are known from many different morphologies, specifically with vastly different skull forms. These changes relate to the feeding and habits of the animals, not completely evolutionary modifications. Dolichorostral ("long snouted") phytosaurs have a long, slender snout with many
conical A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines c ...
teeth that are
homodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example, ...
(all the same). These taxa were most likely piscivores that were well adapted to capture fast aquatic prey, but not terrestrial animals. ''
Paleorhinus ''Paleorhinus'' (Greek: ''"Old Nose"'') is an extinct genus of widespread basal phytosaur known from the Late Triassic (late Carnian stage). The genus was named in 1904 based on the type species ''Paleorhinus bransoni'', which is known from Wyo ...
'', ''
Rutiodon ''Rutiodon'' ("Wrinkle tooth") is an extinct genus of phytosaur belonging to the family Parasuchidae. It lived during the Late Triassic period, and was about in length. ''Rutiodon'' is known from the eastern United States ( North Carolina, ...
'' and ''
Mystriosuchus ''Mystriosuchus'' (meaning "spoon-crocodile")
Retrieved on May 25th, 2008.
is an
'' are dolichorostral phytosaurs, but do not form a distinct group of taxa (named Mystriosuchinae of
Friedrich von Huene Friedrich von Huene, born Friedrich Richard von Hoinigen, (March 22, 1875 – April 4, 1969) was a German paleontologist who renamed more dinosaurs in the early 20th century than anyone else in Europe. He also made key contributions about v ...
) as other morphotypes such as '' Pseudopalatus'' are more closely related to ''
Mystriosuchus ''Mystriosuchus'' (meaning "spoon-crocodile")
Retrieved on May 25th, 2008.
is an
'' than it is to the other long-snouted taxa. Brachyrostral ("short snouted") forms are the opposite, having a massive, broad snout, and very strong skulls and jaws. They are
heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For exampl ...
, as the front teeth are prominent fangs, and the rear teeth are blade-like for slicing food into chunks that can be swallowed easily. Taxa like this, such as ''
Nicrosaurus ''Nicrosaurus'' (/nɛkroʊˈsɔrəs/) is an extinct genus of phytosaur reptile existing during the Late Triassic period. Although it looked like a crocodile (and probably lived like the more terrestrial crocodylomorphs), it was not closely rel ...
'' and ''
Smilosuchus ''Smilosuchus'' (meaning "chisel crocodile") is an extinct genus of leptosuchomorph parasuchid from the Late Triassic of North America. History The type species was first described in 1995 as a replacement generic name for ''Leptosuchus gre ...
'', were powerful taxa that fed on stronger prey, such as terrestrial animals that came to the water to drink. Altirostral ("high snouted") animals are intermediate between the two distinct types. They had heterodont dentition but not as extremely developed as the brachyrostral type. ''Pseudopalatus'' is an altirostral phytosaur, and was most likely a generalist feeder. Modern crocodilians exhibit a similar morphological diversity, for example the broad snouted altirostral
alligator An alligator is a large reptile in the Crocodilia order in the genus ''Alligator'' of the family Alligatoridae. The two extant species are the American alligator (''A. mississippiensis'') and the Chinese alligator (''A. sinensis''). Additional ...
and the long snouted dolichorostral gavial. Various phytosaurs have crests and similar ornamentions in their snouts. ''
Nicrosaurus ''Nicrosaurus'' (/nɛkroʊˈsɔrəs/) is an extinct genus of phytosaur reptile existing during the Late Triassic period. Although it looked like a crocodile (and probably lived like the more terrestrial crocodylomorphs), it was not closely rel ...
'' has a ridge along the snout that would have supported a keratinous crest in life, while ''
Mystriosuchus westphali ''Mystriosuchus'' (meaning "spoon-crocodile")
Retrieved on May 25th, 2008.
is an
'' has several bony crests.


Differences from crocodiles

Despite their great similarities in appearance and lifestyle, there are still a number of minor differences that distinguish phytosaurs from true crocodiles. For one thing, the phytosaur
ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joi ...
structure is much more primitive than that of any crocodile. Also, phytosaurs lack the bony
secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medi ...
that enables crocodiles to breathe even when the mouth is full of water. However, it is possible that phytosaurs had a fleshy palate, as many Mesozoic crocodiles are presumed to have had. Phytosaurs were even better armoured than crocodiles, protected by heavy bony
scute A scute or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior po ...
s (often found as fossils), and the belly reinforced with a dense arrangement 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 ...
(abdominal ribs). Finally, and most noticeably, phytosaurs had nostrils placed near or above the level of the eyes, in contrast to crocodiles where the nostrils are near the end of the snout. This adaptation may have developed to allow them to breathe while the rest of the body was submerged.


Teeth

Unlike most crocodilians, phytosaurs have tooth serrations. In a 2001 study of the biomechanics of the dinosaur '' Albertosaurus'''s teeth, William L. Abler also examined a phytosaur's teeth, finding that it had had serrations so fine that they resembled a crack in the tooth. '' Albertosaurus'' had similarly crack-like serrations, but, at the base of each serration Abler discovered a round void, which would have functioned to distribute force over a larger
surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ...
. This void, termed an ampulla, would hinder the ability of the "crack" formed by the serration to propagate through the tooth. The phytosaur was found to lack
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
s for preventing its dental "cracks" from propagating. Abler examined another sort of prehistoric predator, ''
Dimetrodon ''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodont ...
'', and found that it also lacked adaptations for guarding against crack propagation. Based on their teeth, most phytosaur genera are carnivorous, piscivorous, or a combination of the two. However, two taxa show slight adaptations towards hunting and consuming harder invertebrates. A study on phytosaur microwear patterns has found ''
Mystriosuchus ''Mystriosuchus'' (meaning "spoon-crocodile")
Retrieved on May 25th, 2008.
is an
'' to line with soft invertebrate consumers, ''
Nicrosaurus ''Nicrosaurus'' (/nɛkroʊˈsɔrəs/) is an extinct genus of phytosaur reptile existing during the Late Triassic period. Although it looked like a crocodile (and probably lived like the more terrestrial crocodylomorphs), it was not closely rel ...
'' with hard invertebrate consumers and ''
Smilosuchus ''Smilosuchus'' (meaning "chisel crocodile") is an extinct genus of leptosuchomorph parasuchid from the Late Triassic of North America. History The type species was first described in 1995 as a replacement generic name for ''Leptosuchus gre ...
'' and ''
Machaeroprosopus ''Machaeroprosopus'' is an extinct genus of mystriosuchin leptosuchomorph phytosaur from the Late Triassic of the southwestern United States. ''M. validus'', once thought to be the type species of ''Machaeroprosopus'', was named in 1916 on ...
'' with carnivores and piscivores.


Locomotion and terrestriality

Phytosaurs have been traditionally held as rather "primitive" animals in regards to terrestrial locomotion, particularly in regards to archosaurs such as
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, lacking the erect
gait Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. ...
seen in these, other
pseudosuchia Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...
ns,
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s and
pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...
s. However, the ''
Apatopus ''Apatopus'' is an ichnogenus, or a name based on footprints, that may have been from a phytosaur. The trackmaker lived in the early Triassic. It was named by Baird in 1957. Of special relevance in regard to its phytosaurian identity is the fac ...
''
ichnofossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
shows that the animals did in fact have an erect gait like their archosaur relatives. Most phytosaurs are thought to be aquatic animals, and indeed most do show adaptations for such a lifestyle; swim tracks attributed to phytosaurs, for example, are known.Stocker, M. R. & Butler, R. J. 2013
Phytosauria
Geological Society, London, Special Publications 379, 91–117. Link is broken.
However, at least ''
Nicrosaurus ''Nicrosaurus'' (/nɛkroʊˈsɔrəs/) is an extinct genus of phytosaur reptile existing during the Late Triassic period. Although it looked like a crocodile (and probably lived like the more terrestrial crocodylomorphs), it was not closely rel ...
'' seems to have evolved towards a secondarily terrestrial lifestyle, developing longer limb bones, straighter femora and a deeper pelvis, and indeed occurs in terrestrial or marginal lacustrine settings. Combined with its deep upper jaw, it probably led a similar lifestyle to terrestrial predatory
crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cr ...
like sebecians. Inversely, some dolichorostral forms like ''
Mystriosuchus ''Mystriosuchus'' (meaning "spoon-crocodile")
Retrieved on May 25th, 2008.
is an
'' have become further specialised to life in the water, and occurred in marine environments. A skeleton of ''Mystriosuchus planirostris'', found in a marine setting and with evidence of little post-mortem transportation – indicating that it died either at sea or in a freshwater environment nearby – shows that this animal had paddle-like limbs, less adapted for terrestrial locomotion than in most other phytosaurs. Furthermore, the tail of ''
Mystriosuchus ''Mystriosuchus'' (meaning "spoon-crocodile")
Retrieved on May 25th, 2008.
is an
'' was laterally compressed and could have been used in propulsion.


Endocast Studies

Scans on various phytosaur braincases suggest that these animals generally had long olfactory tracts, weakly demarcated cerebral regions, dorsoventrally short endosseous labyrinths and various sinuses, including large antorbital and dural venous ones; the general bauplan is vaguely similar to that of crocodilians, but differs significantly in the presence of multiple sinuses, smaller cerebral hemispheres and smaller endosseous labyrinths. The similarities are considered to be plesiomorphic in relation to the ancestral archosauriform design, lacking many features seen in
avemetatarsalia Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. ...
ns, though convergence in terms of lifestyle might also play a role.


Reproduction

No phytosaur eggs have been found so far. There are pits associated with footprints in the
Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In N ...
, but these "nests" are apparently the result of
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...
weathering. A recent study suggests they might have had parental care.


History

When the first phytosaur fossils were found, it was not immediately obvious what kind of animal/species they were. The first phytosaur species known to science was named ''Phytosaurus cylindricodon'' – "plant lizard with cylindrical teeth" – by G. Jaeger in 1828 because he mistakenly believed that petrified mud fillings in the jaw were herbivore teeth. The specimen is too poor to be diagnostic, and this species name is no longer valid. The name of the group – Phytosauria – was coined by the German paleontologist
Hermann von Meyer Christian Erich Hermann von Meyer (3 September 1801 – 2 April 1869), known as Hermann von Meyer, was a German palaeontologist. He was awarded the 1858 Wollaston medal by the Geological Society of London. Life He was born at Frankfurt am Ma ...
in 1861, on the basis of this first species. The next species to be described was ''Belodon plieningeri'' by von Meyer in von Meyer and Plieninger 1844. The altogether more appropriate name Parasuchia ("alongside the crocodiles", as they resembled crocodiles to a great degree) was coined by
Thomas Huxley Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist specialising in comparative anatomy. He has become known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. The stori ...
in 1875 along with his discovery and naming of the Indian species ''Parasuchus hislopi'' (Chatterjee, 1978), on the basis of a partial snout. The specimen also is usually considered non-diagnostic, and the name ''Parasuchus'' replaced by ''
Paleorhinus ''Paleorhinus'' (Greek: ''"Old Nose"'') is an extinct genus of widespread basal phytosaur known from the Late Triassic (late Carnian stage). The genus was named in 1904 based on the type species ''Paleorhinus bransoni'', which is known from Wyo ...
''. Although the names Parasuchidae and Phytosauridae are variously still used by different specialists, "phytosaur" is the standard generic name for these animals, despite the fact that these animals have been clearly shown to be
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
.


Evolutionary history

Phytosaurs first appeared during the
Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...
or ?Ladinian age, evolving from an unknown crurotarsan ancestor. There are no clear intermediate forms, as even the earliest known phytosaurs are highly specialized aquatic animals, unlike most contemporary archosauriforms that were terrestrial. However, a recent study has suggested that '' Diandongosuchus'' is a basal phytosaur. If this is the case, this taxon offers more of a bridge between phytosaurs and earlier Archosauriformes. The earliest phytosaurs are traditionally classified in the genus ''
Paleorhinus ''Paleorhinus'' (Greek: ''"Old Nose"'') is an extinct genus of widespread basal phytosaur known from the Late Triassic (late Carnian stage). The genus was named in 1904 based on the type species ''Paleorhinus bransoni'', which is known from Wyo ...
'', now thought to be polyphyletic. ''
Parasuchus ''Parasuchus'' is an extinct genus of basal phytosaur known from the Late Triassic (late Carnian to early Norian stage) of Andhra Pradesh and Madhya Pradesh, India. At its most restricted definition, ''Parasuchus'' contains a single specie ...
'' and related basal species were widely distributed, meaning that phytosaurs dispersed across
Pangea 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 ...
early on and there were probably few geographical barriers for their distribution; only in the southernmost regions are they rare, possibly due to increased aridity. A somewhat more advanced and larger form, ''Angistorhinus'' appears at the same time or soon after. Later in the Carnian, both these animals were replaced by more specialised forms like ''
Rutiodon ''Rutiodon'' ("Wrinkle tooth") is an extinct genus of phytosaur belonging to the family Parasuchidae. It lived during the Late Triassic period, and was about in length. ''Rutiodon'' is known from the eastern United States ( North Carolina, ...
'', ''
Leptosuchus ''Leptosuchus'' is an extinct genus of leptosuchomorph phytosaur with a complex taxonomical history. Fossils have been found from the Dockum Group and lower Chinle Formation outcropping in Texas, New Mexico, and Arizona, USA, and date back to th ...
'', and the huge ''
Smilosuchus ''Smilosuchus'' (meaning "chisel crocodile") is an extinct genus of leptosuchomorph parasuchid from the Late Triassic of North America. History The type species was first described in 1995 as a replacement generic name for ''Leptosuchus gre ...
'' (Lucas 1998). The Carnian-Norian extinction meant that these animals died off, and the Early
Norian The Norian is a division of the Triassic Period. It has the rank of an age ( geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic ...
sees new genera like ''
Nicrosaurus ''Nicrosaurus'' (/nɛkroʊˈsɔrəs/) is an extinct genus of phytosaur reptile existing during the Late Triassic period. Although it looked like a crocodile (and probably lived like the more terrestrial crocodylomorphs), it was not closely rel ...
'' and ''Pseudopalatus'', both of which belong to the most derived clade of phytosaurs, the
Pseudopalatinae Mystriosuchini, historically known as Pseudopalatinae, is an extinct tribe (formerly subfamily) of derived phytosaurs in the clade Leptosuchomorpha. As with all other phytosaurs, mystriosuchins lived during Late Triassic. The name is derived fr ...
. Later in the middle Norian the advanced and specialised fish-eater ''Mystriosuchus'' appears. Fossil remains of this widespread animal is known from Germany, northern Italy, and Thailand. Finally the large ''
Redondasaurus ''Redondasaurus'' is an extinct genus of phytosaur from the Late Triassic (221.5 to 201.6 million years ago) of the southwestern United States. It was named by Hunt & Lucas in 1993, and contains two species, ''R. gregorii'' and ''R. bermani''. ...
'' in south-west North America and the long-snouted (altirostral) '' Angistorhinopsis ruetimeyeri'' in Europe continued the group into the
Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest a ...
. Phytosaur footprints (the ichnotaxon ''Apatopus'') are also known from the latest Rhaetian of the East Coast of USA (the Newark Supergroup) (Olsen ''et al.'' 2002). This indicates that phytosaurs continued as successful animals until the very end of the Triassic, when, along with many other large crurotarsan reptiles, they were killed off by the end Triassic extinction event, about 200 Ma ago. There have been reports of phytosaur remains found in lowermost Jurassic rocks. Several teeth from Early Jurassic deposits in France have been identified as phytosaur teeth, but other studies argue they have either been misidentified or were reworked from Late Triassic into Early Jurassic deposits. In 1951, a partial upper jaw was discovered in the Early Jurassic
Lower Lufeng Series 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 Membe ...
in
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
and described as a new genus of phytosaur, '' Pachysuchus'', but a study in 2012 reinterpreted the fossil as a sauropodomorph dinosaur. A fragment of a lower jaw from a longirostrine archosaur has been described from early
Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassi ...
strata in the town of
Watchet Watchet is a harbour town, civil parish and electoral ward in the county of Somerset, England, with a population in 2011 of 3,785. It is situated west of Bridgwater, north-west of Taunton, and east of Minehead. The town lies at the mouth of ...
in
Somerset ( en, All The People of Somerset) , locator_map = , coordinates = , region = South West England , established_date = Ancient , established_by = , preceded_by = , origin = , lord_lieutenant_office =Lord Lieutenant of Somerset , lor ...
, England. While
teleosaurid Teleosauridae is a family of extinct typically marine crocodylomorphs similar to the modern gharial that lived during the Jurassic period. Teleosaurids were thalattosuchians closely related to the fully aquatic metriorhynchoids, but were les ...
thalattosuchia Thalattosuchia is a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are colloquially referred to as marine crocodiles or sea crocodiles, though they are not members of Cro ...
ns had similar longirostrine jaws to phytosaurs and were common in the Jurassic, they do not appear in the earliest Jurassic rocks. The mandible is more similar to those of known phytosaurs than to thalattosuchians, and likely belongs to a phytosaur closely related to the genus ''Mystriosuchus''. The presence of phytosaurs in the earliest Jurassic may have prevented thalattosuchians from occupying similar ecological niches at that time. However, more recent work suggests that the jaw fragment came from a pre-Hettangian rock unit, and is therefore Late Triassic in age. Also, if the age of the Magnesian Conglomerate does extend into 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 ...
(
Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassi ...
), then it is possible that '' Rileyasuchus'' survived into the Early Jurassic.Hunt, A.P. (1994). Unpublished doctoral dissertation
discussed here
/ref>


Classification


Genera


Phylogeny

Phytosaurs are generally regarded as the most basal group of Crurotarsi, a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
of archosaurs that includes crocodilians and their extinct relatives. Phytosaurs are often excluded from a clade called
Suchia Suchia is a clade of archosaurs containing the majority of pseudosuchians (crocodilians and their extinct relatives). It was defined as the least inclusive clade containing '' Aetosaurus ferratus'', '' Rauisuchus tiradentes'', '' Prestosuchus c ...
, which usually encompasses all other crurotarsans, including
aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivoro ...
s, rauisuchians, and
crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cro ...
s. Some studies have found polytomies between phytosaurs and other groups, like
Ornithosuchidae Ornithosuchidae is an extinct family of pseudosuchian archosaurs (distant relatives of modern crocodilians) from the Triassic period. Ornithosuchids were quadrupedal and facultatively bipedal (e.g. like chimpanzees), meaning that they had the a ...
and Suchia. In these cases, it is unclear whether phytosaurs are the most basal crurotarsans. In one of the earliest studies of crurotarsan phylogeny, Sereno and Arcucci (1990) found Crurotarsi to be a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...
grouping consisting of phytosaurs, ornithosuchids, and the more
derived Derive may refer to: *Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguation ...
suchians, but produced a trichotomy between the three groups in their tree. In resolving this trichotomy, Parrish (1993) placed ornithosuchids, not phytosaurs, as the most basal crurotarsans. However, most other studies, such as Sereno (1991) and Benton ''et al.'' (2010), recover phytosaurs in a basalmost position among crurotarsans. Below is a cladogram modified from Benton ''et al.'' (2010) showing the widely accepted phylogenetic relationships of phytosaurs: A phylogenetic analysis of early archosaurs by paleontologist Sterling Nesbitt (2011) found strong support for a
sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
relationship between phytosaurs and Archosauria. If this is the case, phytosaurs would be placed outside Pseudosuchia in a more basal position among archosauriforms. Phytosaurs would be considered closely related to the ancestors of both crocodilians and
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s. Furthermore, the definition of the clade Crurotarsi would change, as it is often defined by the inclusion of phytosaurs. Thus, Crurotarsi would include phytosaurs and all other archosaurs —including dinosaurs— under this phylogeny. Below is a cladogram showing the placement of phytosaurs from Nesbitt (2011): The phylogenetic analysis of Stocker (2010) placed ''Paleorhinus'' outside Phytosauridae as a basal phytosaur. Under this phylogeny, Phytosauridae and Phytosauria are not synonymous. Stocker also erected the clade Leptosuchomorpha for derived phytosaurs, including ''Leptosuchus'' and ''Smilosuchus''. Ezcurra (2016) updated Nesbitt's analysis and found that Phytosauria was once again a group of basal pseudosuchian archosaurs. His study analyzed the ten phylogenetic traits which Nesbitt claimed were lacking in phytosaurs but not archosaurs, thus excluding phytosaurs from Pseudosuchia. Four of the traits (well-developed palatal processes of the maxilla which meet at the midline, an elongated cochlear recess, a tuber on the lateral side of the
ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
, and a particular orientation of the
calcaneal In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. S ...
tuber) were confirmed to support Nesbitt's placement of Phytosauria. However, one of the ten traits was found in '' Euparkeria'' (an
abducens nerve The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocu ...
exit foramen only present in the prootic) and another was found in proterochampsians (a swollen biceps tubercule), so their lack in phytosaurs may be reversals rather than basal traits. Another one of the traits (an antorbital fossa contacting the horizontal process of the maxilla) was found in the basal phytosaur ''
Parasuchus ''Parasuchus'' is an extinct genus of basal phytosaur known from the Late Triassic (late Carnian to early Norian stage) of Andhra Pradesh and Madhya Pradesh, India. At its most restricted definition, ''Parasuchus'' contains a single specie ...
.'' One trait (short metacarpals compared to metatarsals) was difficult to analyze in any crurotarsan, and another (a medial tuber on the
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates ...
) was found in both proterochampsids and ''Parasuchus''. One trait (a divided tibial facet of the astragalus) was also lacking in '' Marasuchus'' and ''
Nundasuchus ''Nundasuchus'' is an extinct genus of crurotarsan, possibly a suchian archosaur related to Paracrocodylomorpha. Remains of this genus are known from the Middle Triassic Manda beds of southwestern Tanzania. It contains a single species, ''Nund ...
'', and therefore had a variable existence in Archosauria. This reanalysis, along with the observance of many traits linking Phytosauria with pseudosuchians, concluded that it was more likely that phytosaurs were pseudosuchians than non-archosaur archosauriforms. The following cladogram is a simplified version the fourth strict reduced consensus tree of Ezcurra's third phylogenetic analyses within his study. This cladogram only shows taxa from the group Eucrocopoda.


Footnotes


Sources

* Abler, W.L. 2001. A kerf-and-drill model of tyrannosaur tooth serrations. p. 84–89. In: ''Mesozoic Vertebrate Life''. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press. * Carroll, R.L. (1988). ''Vertebrate Paleontology and Evolution'', WH Freeman & Co. * Chatterjee, S. (1978). A primitive parasuchid (phytosaur) reptile from the Upper Triassic Maleri Formation of India, ''Palaeontology'' 21: 83–127 * Hungerbühler, A. (2002). The Late Triassic phytosaur ''Mystriosuchus'' Westphali, with a revision of the genus. ''Palaeontology'' 45 (2): 377–418 * Jaeger, G.F. 1828. Über die fossilen Reptilien, welche in Würtemberg aufgefunden worden sind. Metzler, Stuttgart. * Kimmig, J. & Arp, G. (2010) Phytosaur remains from the Norian Arnstadt Formation (Leine Valley, Germany), with reference to European phytosaur habitats. ''Palaeodiversity'' 3: 215–224 * Lucas, S.G. (1998). Global Triassic tetrapod biostratigraphy and biochronology. ''Paleogeog. Palaeoclimatol., Palaeoecol.'' 143: 347–384. * * Olsen, P.E., Kent, D.V., H.-D.Sues, Koeberl, C., Huber, H., Montanari, E.C.Rainforth, A., Fowell, S.J., Szajna, M.J., and Hartline, B.W., (2002). Ascent of dinosaurs linked to an iridium anomaly at the Triassic-Jurassic boundary. ''Science'' 296: 1305–1307. * * Ballew, K.L. (1989). A phylogenetic analysis of Phytosauria from the Late Triassic of the Western United States. ''Dawn of the age of dinosaurs in the American Southwest'': pp. 309–339. * Gregory, J.T. (1962). Genera of phytosaurs. ''American Journal of Science'', 260: 652–690. * Long, R.A. & Murry, P.A. (1995). Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. ''New Mexico Museum of Natural History and Science Bulletin'', 4: 1–254.


External links


Translation and Pronunciation Guide






– cladistic tree

– some material on phytosaurs {{Taxonbar, from=Q131343 01 Late Triassic reptiles Carnian first appearances Rhaetian extinctions