''Trilophosaurus'' (
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 ...
for "
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
with three
ridges
A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...
") is a lizard-like
trilophosaurid allokotosaur
Allokotosauria is a clade of early archosauromorph reptiles from the Middle Triassic, Middle to Late Triassic known from Asia, Africa, North America and Europe. Allokotosauria was first described and named when a new monophyletic grouping of spec ...
known from the
Late Triassic
The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...
of North America. It was a
herbivore
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 mouthpart ...
up to 2.5 m 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. Teeth are absent from 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 b ...
and front of the lower jaw, which in life were probably equipped with a horny beak.
The skull is also unusual in that the lower
temporal opening is missing, giving the appearance of a
euryapsid
__NOTOC__
Euryapsida is a polyphyletic (unnatural, as the various members are not closely related) group of Sauropsida, sauropsids that are distinguished by a single temporal fenestra, an opening behind the orbit (anatomy), orbit, under which the ...
skull. Because of this, the trilophosaurs were once classified with
placodont
Placodonts (" Tablet teeth") are an extinct order of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. They were part of Sauropterygia, the group that includes plesiosaurs. Placodonts were genera ...
s within
Sauropterygia
Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became ...
.
Carroll (1988) suggested that the lower opening may have been lost to strengthen the skull.
''Trilophosaurus'' is traditionally thought to include two valid species: the typical ''T. buettneri'' and the more robust ''T. jacobsi''. In 1993, paleontologists
Hans-Dieter Sues
Hans-Dieter Sues (born January 13, 1956) is a German-born American paleontologist who is Senior Scientist and Curator of Vertebrate Paleontology at the National Museum of Natural History of the Smithsonian Institution in Washington, DC.
He receiv ...
and
Paul E. Olsen
Paul E. Olsen (born August 4, 1953) is an American paleontologist and author and co-author of a large number of technical papers. Growing up as a teenager in Livingston, New Jersey, he was instrumental in Riker Hill Fossil Site being named a Na ...
reassigned ''T. jacobsi'', as well as two additional trilophosaurids (''
Tricuspisaurus'' and ''
Variodens''), to
Procolophonidae
Procolophonidae is an extinct family of small, lizard-like parareptiles known from the Late Permian to Late Triassic that were distributed across Pangaea, having been reported from Europe, North America, China, South Africa, South America, Antarc ...
based on similarities between its tricuspid teeth and those of the newly described procolophonid ''
Xenodiphyodon''.
This view persisted in subsequent publications
until the cranial material of ''T. jacobsi'' was described by Heckert ''et al.'' (2006). The new material confirmed the originally classification that ''T. jacobsi'', as well as ''
Tricuspisaurus'' and ''
Variodens'' based on similarities to it, are indeed
trilophosaurids.
Meanwhile, a third species of ''Trilophosaurus'', ''T. dornorum'', was named by Mueller & Parker (2006) based on teeth of a robust individual.
[Müller, B. D. & Parker, W. G., 2006]
A new species of ''Trilophosaurus'' (Diapsida: Archosauromorpha) from the Sonsela Member (Chinle Formation) of Petrified Forest National Park, Arizona
''Museum of Northern Arizona,'' Bulletin 62:119-125. However, Spielmann ''et al.'' (2009) argued that the robustness of the new species is not sufficient to differentiate it from other Trilophosaurus species, especially in light of new robust specimens of ''T. jacobsi''. Therefore, they considered ''T. dornorum'' to be a
junior synonym
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
of ''T. jacobsi'',
[Spielmann, J.A., Lucas, S.G., Heckert, A.B., Rinehart, L.F., and Richards, H.R., III. 2009]
Redescription of ''Spinosuchus caseanus'' (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America
''Palaeodiversity'' 2:283-313. a view that was maintained since in other publications.
Spielmann ''et al.'' (2006) redescribed the type material of ''
Malerisaurus
''Malerisaurus'' is an extinct genus of archosauromorph known from Andhra Pradesh of India and Texas of the USA.
Description
''Malerisaurus'' was a medium-sized archosauromorph which averaged 1.2 meters in length. ''Malerisaurus'' is known from ...
langstoni'' and concluded that it's indistinguishable from ''T. buettneri'', and thus ''M. langstoni'' represents its synonym.
[Spielmann, J.A., Lucas, S.G., Hunt, A.P., and Heckert. 2006]
Reinterpretation of the holotype of ''Malerisaurus langstoni'', a diapsid reptile from the Upper Triassic Chinle Group of West Texas
''The Triassic-Jurassic Terrestrial Transition.'' New Mexico Museum of Natural History and Science, Bulletin 37:543-547.
Nesbitt ''et al.'' (2015) performed a
phylogenetic analysis
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
focusing on relations within
Allokotosauria
Allokotosauria is a clade of early archosauromorph reptiles from the Middle to Late Triassic known from Asia, Africa, North America and Europe. Allokotosauria was first described and named when a new monophyletic grouping of specialized herbivor ...
and recovered ''T. jacobsi'' to be more closely related to ''
Spinosuchus caseanus'' than to the type species of ''Trilophosaurus''. To further test this possibility, the types of ''S. caseanus'' and ''T. jacobsi'' were scored separately from the referred the Kahle ''Trilophosaurus'' Quarry elements (referred to ''T. jacobsi'' by Spielmann ''et al.'' (2008) or to ''S. caseanus'' by Spielmann ''et al.'' (2009)). A phylogenetic analysis recovered the three in 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 gro ...
clade to the exclusion of ''T. buettneri'' based on a single
autapomorphy
In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...
. Furthermore, the types of ''S. caseanus'' and ''T. jacobsi'' as well as the Kahle Quarry material all scored identically, suggesting that ''T. jacobsi'' not only should be reassigned to ''Spinosuchus'', but in fact represents the junior synonym of its type and only species (''S. caseanus''). Nesbitt ''et al.'' (2015) refrained from officially synonymizing the two taxa pending further study of other advanced trilophosaurids.
Sources
*
Benton, M. J. (2000), ''Vertebrate Paleontology'', 2nd ed. Blackwell Science Ltd, p. 144
*
Carroll, R. L. (1988), ''Vertebrate Paleontology and Evolution'', W.H. Freeman & Co. p. 266
*
External links
Archosauromorpha: Rhynchosaurs and ''Trilophosaurus''at Palaeos
Trilophosauria. Beaked, lizard-like reptiles UC Museum of Paleontology
Archive copyfrom 6 February 2019.
{{Taxonbar, from=Q15041841
Allokotosaurs
Prehistoric reptile genera
Late Triassic reptiles of North America
Fossil taxa described in 1928
Taxa named by Ermine Cowles Case