Mastodonsaurus

{{Short description|Extinct genus of temnospondyls}} {{Automatic taxobox | fossil_range = {{fossilrange|Middle Triassic}} | image = Mastodonsaurus giganteus.JPG | image_caption = Skeleton of ''Mastodonsaurus giganteus'' in the [[Staatliches Museum für Naturkunde Stuttgart]] | taxon = Mastodonsaurus | authority = Jaeger, 1828 | type_species = {{extinct}}'''''Mastodonsaurus giganteus''''' (Jaeger, 1828) | subdivision_ranks = Other species | subdivision = * {{extinct}}'''''M. cappelensis''''' Wepfer, 1923 * {{extinct}}'''''M. torvus''''' Konzhukova, 1955 | synonyms = *''[[Batrachosaurus]]''? Fitzinger, 1837 *''Heptasaurus'' Säve-Söderbergh, 1935 (likely synonym) *''Labyrinthodon'' Owen, 1841 *''Salamandroides'' Jaeger, 1828 }}

'''''Mastodonsaurus''''' (meaning "teat tooth lizard") is an [[Extinction|extinct]] [[genus]] of [[temnospondyl]] [[amphibian]] from the [[Middle Triassic]] of [[Europe]]. It belongs to a Triassic group of temnospondyls called [[Capitosauria]], characterized by their large body size, large flattened skulls, and probably mainly aquatic lifestyles. ''Mastodonsaurus'' remains one of the largest amphibians known, and may have exceeded 6 meters (20 feet) in length.

==Description== [[File:Маст череп1.jpg|thumb|left|Illustration of ''Mastodonsaurus'' skull, showing the "third eye" pineal foramen in the skull roof and the pairs of orbits, nostrils, and mandible tusk openings, as well as sensory sulci on the face and the otic notches and the double condyle to attach to the neck vertebrae at the back of the skull. The left half shows the pitted texture of the skull surface while the other half indicates the separate bones that make up the skull.]] {{multiple image | perrow = 2/1 | total_width = 250 | image1 = Mastodonsaurus giganteus 2.JPG | image2 = Mastodonsaurus_giganteus_fangs.JPG | footer = Jaws and teeth of ''Mastodonsaurus'', with skull seen from below (left) showing the double rows of small teeth along the sides, the palate with pairs of large fangs, and two openings at the tip for the pair of tusks (right) at the front end of the lower jaws, which have a single row of small teeth on each side | align = left }}

Like those of many other capitosaurs, the head of ''Mastodonsaurus'' was triangular, reaching about {{convert|1.5|m|ft}} in the largest specimens.<ref name=SRR98>{{cite journal |last=Schoch |first=R.R. |year=1999 |title=Comparative osteology of ''Mastodonsaurus giganteus'' (Jaeger, 1828) from the Middle Triassic (Lettenkeuper: Longobardian) of Germany (Baden-Württemberg, Bayern, Thüringen) |journal=Stuttgarter Beiträge zur Naturkunde Serie B |volume=278 |pages=1–175 |url=https://www.researchgate.net/publication/235732311}}</ref> Narrow grooves on the surface of the skull bones called sulci show it had sensory organs that could detect vibrations and pressure under water, similar to the [[lateral line]]s on fish. The large, oval eye sockets are midway along the skull with the nostrils near the tip of the snout. Small ear holes (otic notches) are indented on either side of the back of the skull. The upper surface of the skull bones of ''Mastodonsaurus'' bore an intricate pattern of pits and ridges, a feature found in many temnospondyls. The function of this rugged ornamentation is not fully understood. As with other capitosaurs, ''Mastodonsaurus'' had a [[pineal foramen]] (opening) between the [[parietal bones]] behind the orbits on the roof of the skull, which would have contained a light-sensing [[parietal eye]] linked to the [[pineal gland]] to regulate the circadian sleep-wake cycle and hormone production related to body temperature for a cold-blooded ([[ectotherm]]) animal and to reproduction.

The sides of upper jaw are lined with a double row of small conical teeth, while the lower jaw has a single row of similar small teeth. The upper and lower arrangement of small, narrow teeth could function like a trap for small prey when ''Mastodonsaurus'' closed its mouth. The tip of the upper jaw has a set of larger teeth. Behind these teeth at the front end of the palate on the underside of the skull are sets of small teeth and multiple pairs of large fangs or tusks (about 8 in all). Two large [[tusk]]s project up from the end of the lower jaw, fitting through openings on the [[palate]] and emerging out from the top of the skull in front of the nostrils when the jaw is closed. The tusk-like teeth on the palate and in the lower jaw could bite and hold bigger prey.[[File:Mastodonsaurus giganteus fangs 45.jpg|thumb|left|''Mastodonsaurus giganteus'' fangs]]

The exact number of vertebrae in the skeleton is still not known but recent research shows that ''Mastodonsaurus'' had about 28 trunk vertebrae and a relatively long tail, revised from the squat body shape and short tail assumed in earlier reconstructions.<ref name=Schoch2015>{{cite journal |author=Schoch, R.R. |year=2015 |title=Amphibien und Chroniosuchier des Lettenkeupers |trans-title=Amphibians and chroniosuchians from the Lettenkeuper|journal=Palaeodiversity |series=Supplement |volume=1 |issue=Special Issue: der Lettenkeuper – ein Fenster in die Zeit Vor den Dinosauriern [The Lettenkeuper – a Window on the Time before the Dinosaurs] |language=de |pages=203–230 | url=http://www.palaeodiversity.org/pdf/08Suppl/09Palaeodiversity_SB_Schoch.pdf }}</ref><ref name="Folie6">Reconstructed ''Mastodonsaurus'' skeleton with a longer tail based on recent research https://lehrerfortbildung-bw.de/u_matnatech/bio/gym/bp2016/fb9/1_evolution/1_belege/3_fossilien/1_bilder/pix/Folie6.PNG </ref> The total length of the largest individuals is about {{convert|4|to|6|m|ft}}.<ref name="SRR98"/> Isolated teeth up to 14 cm (6 in) long indicate that old individuals grew even larger.

==Paleobiology== [[File:Mastodonsaurus giganteus 9743.jpg|thumb|Fossil remains of ''M. giganteus'' at the Muschelkalkmuseum|left|260x260px]] {{multiple image | perrow = 1/1 | total_width = 250 | image1 = Mastodonsaurus DB.jpg | image2 = Mastodonsaurus Scale.svg | footer = Life restoration with exposed tusks (top) and scale diagram (bottom) – the tail was likely longer than depicted. | align = right }} The marked reduction of the limbs, the strong tail and sensory grooves on the head called sulci show that ''Mastodonsaurus'' was an aquatic animal that rarely, if ever, ventured on land. ''Mastodonsaurus'' may have been completely unable to leave the water, as large quantities of bones have been found that suggest individuals died en masse when pools dried up during times of [[drought]].<ref name="Benes, Josef 1979" /> It normally inhabited freshwater to brackish swamps, lakes, and river deltas. Fossil skull remains found in marine sediments suggest it also may have entered into saltier environments on occasion.<ref name=Schoch2015/><ref>Kupferzell fossil site geological layers, showing paleoenvironments in which ''Mastodonsaurus'' lived https://ars.els-cdn.com/content/image/1-s2.0-S0031018222003510-gr13.jpg</ref>

Its tail was likely thickened with a fleshy fin for propulsion. The stronger tail in combination with small limbs, a trunk section stiffened with long, broadened, overlapping ribs, and extra-heavy bones would indicate that ''Mastodonsaurus'' was an aquatic ambush predator that lurked on the bottom in wait for prey, making sudden, rapid attacks with its giant mouth and impaling tusks, propelled by its tail.<ref name=Schoch2015/><ref name=Rainer2014>{{cite book |author=Schoch, R.R. |title=Amphibian Evolution: The Life of Early Land Vertebrates |year=2014 |publisher=Wiley-Blackwell |pages=1–288|bibcode=2014aele.book.....S }}</ref>

''Mastodonsaurus'' fed mainly on fish, whose remains have been found in its fossilized [[coprolite]]s.<ref name="Benes, Josef 1979">Benes, Josef. Prehistoric Animals and Plants. Prague, Artia, 1979.</ref> The fossils of some smaller [[temnospondyls]] bear tooth marks made by ''Mastodonsaurus''-like animals and there is evidence for cannibalism by adults on juveniles of ''Mastodonsaurus''. It probably also ate land-living animals, such as small [[archosaur]]s that ventured into or along the edge of water. Bite marks on ''Mastodonsaurus'' bones show that the large terrestrial archosaur ''[[Batrachotomus]]'' actively preyed on the giant amphibians, entering the water or attacking individuals stranded in pools during droughts.<ref name="Mujal2022" >{{Cite journal|author1= Eudald Mujal |author2= Christian Foth |author3= Erin E. Maxwell |author4= Dieter Seeg|author5= Rainer R. Schoch |year=2022 |title= Feeding habits of the Middle Triassic pseudosuchian ''Batrachotomus kupferzellensis'' from Germany and palaeoecological implications for archosaurs |journal=Palaeontology |volume= 65 |issue= e12597|pages=1–31|doi= 10.1111/pala.12597 |bibcode= 2022Palgy..6512597M |s2cid= 248657885 |url= https://ddd.uab.cat/pub/artpub/2022/258667/Mujal-2022-Feeding-habits-of-the-middle-triass.pdf }} </ref>

''Mastodonsaurus'' was once thought to be responsible for the footprints found in Triassic [[sandstone]]s and described as ''[[Chirotherium]]'', but later research found that the tracks belong to crocodile-like [[pseudosuchian]] reptiles like the aforementioned ''Batrachotomus'' or ''[[Ticinosuchus]]''.<ref name="Benes, Josef 1979"/> Based on the misattributed tracks and misidentified bones from other Triassic animals, early illustrations depicted the giant amphibians (often referred to as "''Labyrinthodon''" at the time) as big froglike creatures that supposedly crossed their legs as they walked since the outer fifth digit on the ''Chirotherium'' footprints resembled a thumb.[[File:Labyrinthodon pachygnathus historical.png|thumb|right|1855 proposed life reconstruction based on paleontologist Richard Owen of a "''Labyrinthodon''" as the maker of ''Chirotherium'' tracks, walking with crossed limbs to match the outer "thumb" impression and with misidentified skeletal parts taken from archosaurs, but with a ''Mastodonsaurus'' skull]]

Most of the skeleton of ''Mastodonsaurus'', apart from skulls and jaws, remained poorly known until recently. Both scientific and popular sources continued to describe ''Mastodonsaurus'' as having a squat, frog-like body and a short tail from the 19th century into the 20th century, including for the ''"Labyrinthodon"'' sculptures by [[Waterhouse Hawkins]] at [[the Crystal Palace]] outside London in 1854 and in a painting of ''Mastodonsaurus'' by the famous Czech paleoartist [[Zdeněk Burian]] in 1955.<ref>Friends of Crystal Palace Dinosaurs: Labyrinthodon statues https://cpdinosaurs.org/blog/post/neglected-labyrinthodon-in-crystal-palace-park </ref><ref>The Artwork of Zdenek Burian. Mastodonsaurus (1955) http://zburian.blogspot.com/2012/03/mastodonsaurus.html </ref> A life-size model put on display for the [[American Museum of Natural History]] Hall of Vertebrate Origins in 1996 also restored ''Mastodonsaurus'' with a short, broad body and a short tail, and so presumably able to crawl on land.<ref>''Mastodonsaurus'' model from 1996 at the American Museum of Natural History with short body and short tail https://www.geol.umd.edu/~jmerck/nature/misc/htmls/cladoselache71034.html#next5</ref>

A site discovered during road construction near the town of [[Kupferzell]] in southern Germany in 1977 provided researchers with important new fossils of ''Mastodonsaurus giganteus'' that included well preserved skulls and disarticulated bones from all parts of the body. Thousands of individual fossils were recovered during a three-month salvage operation before road work resumed, including, in addition to ''Mastodonsaurus'', remains of the temnospondyl ''[[Gerrothorax]]'' and the archosaur ''Batrachotomus'', as well as of many fishes.<ref name="Schoch2022" >{{Cite journal|author1= Rainer R. Schoch |author2= Dieter Seegis |author3= Eudad Mujal |year=2022 |title= The Middle Triassic vertebrate deposits of Kupferzell (Germany): Palaeoenvironmental evolution of complex ecosystems |journal= Palaeogeography, Palaeoclimatology, Palaeoecology |volume= 603 |article-number= 111181 |doi= 10.1016/j.palaeo.2022.111181 |bibcode= 2022PPP...60311181S |s2cid= 251428479 |url= https://ddd.uab.cat/pub/artpub/2022/264843/palpalpal_a2022v603a111181.pdf }}</ref> Some of the bones showed evidence of being rolled and transported a long distance. Working from the rich Kupferzell finds, German paleontologist Rainer Schoch<ref>Rainer Schoch (Paleontologist) (in German) https://de.wikipedia.org/wiki/Rainer_Schoch_(Pal%C3%A4ontologe)</ref> published a revised description of ''Mastodonsaurus'' in 1999 that revealed a longer body and an estimated longer tail, for a larger, more massive animal with a highly aquatic lifestyle.<ref name="SRR98"/> Although no complete and fully articulated skeleton has been found to date, research since 1999 was incorporated into a composite skeletal reconstruction and a fleshed-out model displayed at the [[Staatliches Museum für Naturkunde Stuttgart]] in Germany that give ''Mastodonsaurus'' more crocodile-like proportions, with a lengthened tail for swimming, similar to some other capitosaurs.<ref name="Folie6"/><ref>Updated skeletal reconstruction of ''Mastodonsaurus giganteus'' at the Staatliches Museum für Naturkunde Stuttgart https://www.naturkundemuseum-bw.de/fileadmin/_processed_/f/9/csm_smns-schoch-fig4_83408a397d.jpg</ref><ref name=Schoch2015/>

The growth stages of ''Mastodonsaurus'' are documented from numerous specimens found at Kupferzell and elsewhere in Germany, with skulls that range from about 1.5 cm (~0.5 in) up through 125 cm (50 in) long.<ref>{{Cite journal|author1= Rainer R. Schoch |author2= Florian Witzmann|author3= Raphael Moreno|author4= Ralf Werneburg |author5= Eudald Mujal |year=2024 |title= Growing giants: ontogeny and life history of the temnospondyl ''Mastodonsaurus giganteus'' (Stereospondyli) from the Middle Triassic of Germany |journal=Fossil Record |volume= 27 |issue= 3|pages=401–422|doi= 10.3897/fr.27.125379 |doi-access= free|url= https://fr.pensoft.net/article/125379/ }}</ref> Stereospondyls lacked a true larval stage of development and ''Mastodonsaurus'' followed a slow, conservative ontogenetic pattern with relatively minor changes as it grew so that small juveniles would have resembled adults.<ref name=Rainer2014/>

==History and etymology== {{multiple image | perrow = 2/1 | total_width = 250 | image1 = La terre avant le déluge, 1863 "Labyrinthodon ou Chreirotherium". (4514423604).jpg | image2 = View of a dinosaur in the Dinosaur Trail in Crystal Palace Park ^4 - geograph.org.uk - 4490522.jpg | image3 = Mastodonsaurus.jpg | footer = Reconstructions of ''Mastodonsaurus'' through the 19th century: *top left: "''Labyrinthodon'' or ''[[Cheirotherium]]''" (1863) *top right: ''Labyrinthodon'' at the Crystal Palace (1854) *bottom: ''Mastodonsaurus'' and ''[[Hyperodapedon]]'' (1894) | align = left }} The German paleontologist [[Georg Friedrich von Jaeger]] gave the name ''Mastodonsaurus'' in 1828 to a single large conical fang with vertical striations and a worn-off tip, found in the Triassic Lettenkeuper deposits near [[Gaildorf]] in [[Baden-Württemberg]] in southern Germany.<ref name=Jaeger1828>{{cite book |author=Jaeger, G.F. von |title=Über die fossile Reptilien, welche in Württemberg aufgefunden worden sind. |trans-title=On the Fossil Reptiles, which have been found in Württemberg. |year=1828 |publisher=J.B. Metzler|location=Stuttgart |language=de |pages=1–48 |url=https://commons.wikimedia.org/wiki/File:%C3%9Cber_die_Fossile_Reptilien_Welche_in_W%C3%BCrttemberg_Aufgefunden_Sind.pdf }}</ref> Jaeger assumed the big tooth (a snout fang about 10.4 cm (4.1 in) long as preserved) belonged to a giant reptile and that the indented missing tip was a distinctive natural feature that, when viewed from above, resembled a nipple or teat with a small hole in the middle, which he expressed in the name ''Mastodonsaurus'' or "teat tooth lizard" (from Greek ''mastos'' "breast, nipple" + ''odous'' (''odon'') "tooth" + ''sauros'' "lizard"): "Dieser Zahn ist nämlich besonders ausgezeichnet durch seine zitzenartige Spitze." [This tooth namely is especially distinguished by its teat-like tip.] He illustrated the tooth and its "teat-like" tip in a plate (Plate IV, figure 4).<ref>''Mastodonsaurus'' tooth as illustrated by Jaeger in 1828, figure 4 https://commons.wikimedia.org/w/index.php?title=File%3A%C3%9Cber_die_Fossile_Reptilien_Welche_in_W%C3%BCrttemberg_Aufgefunden_Sind.pdf&page=65 </ref><ref name="RevisionMoser">{{cite journal | doi=10.1111/j.1475-4983.2007.00705.x | title=Revision of the Type Material and Nomenclature of ''Mastodonsaurus giganteus'' (Jaeger) (Temnospondyli) from the Middle Triassic of Germany | year=2007 | last1=Moser | first1=Markus | last2=Schoch | first2=Rainer | journal=Palaeontology | volume=50 | issue=5 | pages=1245–1266 | s2cid=82693035 | doi-access= | bibcode=2007Palgy..50.1245M }}</ref> However, Jaeger did not provide a type species name for ''Mastodonsaurus''.

Also in 1828, Jaeger identified the back part or [[occiput]] of a large skull found in the same area as coming from a giant amphibian-like animal as indicated by the double articulation of the occipital condyles. He gave the creature the genus-species name combination ''Salamandroides giganteus'', meaning "gigantic salamander-like (animal)".

The discovery of a complete skull of ''Mastodonsaurus'' near Gaildorf in 1833 showed that the teeth and occiput came from the same kind of animal, as later noted by Jaeger.<ref>{{cite journal |author=Jaeger, G.F. von |title= Société géologique de France meeting December 17th, 1832; ''Mastodonsaurus'' and ''Salamandroides'': current work in paleontology of Württemberg [in French] |year=1833 |journal=Bulletin de la Société géologique de France |volume= 3 |page= 86 |url= https://www.biodiversitylibrary.org/item/229773#page/108/mode/1up }} </ref><ref>Illustration from 1844 of the complete ''Mastodonsaurus'' skull found near Gaildorf in 1833 https://archive.org/details/bub_gb_f6lAAAAAcAAJ_2/page/n145/mode/1up?view=theater </ref> [[File:Researches_on_the_Structure,_Organization,_and_Classification_of_the_Fossil_Reptilia._VII._Further_Observations_on_Pareiasaurus_(1892)_(14802932243).jpg|thumb|left|Illustration of ''Mastodonsaurus'' holotype occiput, originally identified as ''Salamandroides giganteus'']] [[File:Vestiges 11 fig 39 Labyrinthodon tooth.jpg|thumb|right|19th century illustration of the complex inner structure of a ''Labyrinthodon'' [''Mastodonsaurus''] tooth|227x227px]]

The name ''Mastodonsaurus'' has led to confusion over its intended meaning, and as pointed out by the British paleontologist [[Richard Owen]], the name could be misinterpreted as a reference to the extinct [[Proboscidea|proboscidean]] [[mastodon]], supposedly to suggest gigantic size ("mastodon(-size) lizard"), the false meaning given in some sources.<ref>{{cite journal |last=Owen |first=R. |year=1841|title=XXXII.- Description of parts of the Skeleton and Teeth of five species of the Genus Labyrinthodon (Lab. leptognathus, Lab. pachygnathus, and Lab. ventricosus, from the Coton-end and Cubbington Quarries of the Lower Warwick Sandstone; Lab. Jægeri, from Guy's Cliff, Warwick; and Lab. scutulatus, from Leamington); with remarks on the probable identity of the Cheirotherium with this genus of extinct Batrachians |journal= Transactions of the Geological Society |volume=2 |issue=6 |page=515 |url=https://books.google.com/books?id=S6JSAAAAcAAJ&pg=PA515}}</ref>

Owen noted that the teat-like appearance was not a real diagnostic feature and also objected to the term "saurus" for a "batrachian" (amphibian). He proposed what he thought was the more fitting replacement name ''Labyrinthodon'' or "labyrinth tooth" to refer to the complex maze-like appearance of the inner tooth structure when viewed in cross section. However, the rules of zoological nomenclature require that the earliest name established be used and ''Labyrinthodon'' is a junior synonym of ''Mastodonsaurus''. The maze-like inner tooth structure in ''Mastodonsaurus'' is found in multiple types of extinct amphibians, and Richard Owen created the formal taxonomic category [[Labyrinthodontia]] (published in 1860) as a supposed order of "Reptilia" to unite them. However, the "order" turned out to contain multiple types of animals that are not closely related and the category Labyrinthodontia no longer has recognized scientific status, although the general form "labyrinthodont" is still used as a descriptive term.<ref>{{cite journal |last=Owen |first=R. |year=1860|title=On the Orders of Fossil and Recent Reptilia, and their Distribution in Time |journal=Report of the Annual Meeting of the British Association for the Advancement of Science |volume=29 |pages=153–166 |url=http://www.biodiversitylibrary.org/pdf3/005848800096146.pdf}}</ref>

==Species== [[File:Mastodontosaurus spp DB24.jpg|thumb|left|Three species of ''Mastodonsaurus'' compared in size]] After recognition by Jaeger in 1833 that the original ''Mastodonsaurus'' tooth and the ''Salamandroides giganteus'' occiput fossil were from different individuals of the same species of animal, based on the discovery of the complete skull, most authors used the binomial combination ''Mastodonsaurus giganteus'' as the type species. In recent work, German paleontologist Rainer R. Schoch has recognized ''Mastodonsaurus giganteus'' (Jaeger 1828) as the official type species, with the occiput (GPIT Am 678) as the holotype specimen, considered diagnostic.<ref>{{cite journal|author1= Rainer R. Schoch |author2= Raphael Moreno |year=2024 |title= Synopsis on the temnospondyls from the German Triassic |journal=Palaeodiversity |volume= 17 |issue= 1|pages=9–48|doi= 10.18476/pale.v17.a2 |url= https://bioone.org/journals/Palaeodiversity/volume-17/issue-1/pale.v17.a2/Synopsis-on-the-temnospondyls-from-the-German-Triassic/10.18476/pale.v17.a2.full|url-access= subscription |doi-access= free }}</ref> This revises an earlier reexamination of the genus by Markus Moser and Rainer Schoch in 2007, in which they chose ''M. jaegeri'' Holl from 1829 as the historically oldest type species for ''Mastodonsaurus'', designating Jaeger's original tooth (SMNS 55911) as the lectotype of ''Mastodonsaurus jaegeri''.<ref name="RevisionMoser"/> Holl had treated ''Mastodonsaurus'' and ''Salamandroides'' as distinct and unrelated animals (a reptile (from the tooth) and an amphibian (from the back of a skull) respectively), in line with Jaeger's first descriptions of the fossils in 1828.<ref>{{cite book |author=Holl, Friedrich|title=Handbuch der Petrefactenkunde |year=1829 |publisher=Hilscher |location=Dresden |language=de|volume= 1 |pages=1–155 |url= https://books.google.com/books?id=IXsNkaMrbwgC }}</ref> Schoch now lists ''M. jaegeri'' as a junior synonym of ''Mastodonsaurus giganteus''.

Moser and Schoch (2007) had noted that the best-known species, ''M. giganteus'', could be a senior synonym of ''M. jaegeri'' if the two species are not taxonomically distinct. They also recognized the species ''M. torvus'' from Russia. However, they found that the species ''M. acuminatus'' was a junior synonym to ''M. giganteus'', while the species ''M. tantus'' & ''M. maximus'' were synonyms of ''M. torvus''. The species ''M. andriani'', ''M. indicus'', ''M. laniarius'', ''M. lavisi'', ''M. meyeri'', ''M. pachygnathus'' and ''M. silesiacus'', when reexamined by Moser and Schoch, were not deemed assignable to the genus ''Mastodonsaurus'' due to the fragmentary nature of the type specimens and as such are considered ''[[nomen dubium]]''.<ref name="RevisionMoser"/> Examination of the literature showed ''M. conicus'' to be a senior synonym of the genus ''M. ventricosus''; however this species was never formally published and is thus considered a ''[[nomen nudum]]''.<ref name="RevisionMoser"/>

In 1923, German paleontologist {{ill|Emil Wepfer|de}} described the new species ''Mastodonsaurus cappelensis'' for fossils found near the town of Kappel in [[Baden-Württemberg]] in an older formation than remains of ''Mastodonsaurus giganteus''.<ref name="Wepfer1929">{{cite book |author=Wepfer, Emil|title= Der Buntsandstein des badischen Schwarzwalds und seine Labyrinthodonten |year=1923 |publisher= Monographien zur Geologie und Paläontologie 1|pages=1–101}}</ref> Swedish paleontologist [[Gunnar Säve-Söderbergh]] erected the new genus ''Heptasaurus'' ("seven lizard" for seven skull openings) for the species in 1935.<ref name= Säve-Söderbergh1935>{{cite journal |last= Säve-Söderbergh |first=Gunnar |year=1935 |title= On the dermal bones of the head in labyrinthodont stegocephalians and primitive Reptilia with special reference to Eotriassic stegocephalians from East Greenland. |journal= Meddelelser om Grønland |volume=98 |pages=1–211}}</ref> In his review of ''Mastodonsaurus'', Rainer Schoch (1999) recognized ''Heptasaurus'' as a genus that was distinct from ''Mastodonsaurus'', with "smaller orbits and a markedly broader snout tip", and that was found in the Middle and Upper Buntsandstein Formation, earlier than fossils of ''Mastodonsaurus giganteus''.<ref name=SRR98/>[[File:Heptasaurus kappelensis.jpg|thumb|right|Underside of the skull of ''Mastodonsaurus'' [''Heptasaurus''] ''cappelensis'' in the [[Naturmuseum Senckenberg]] in Frankfurt am Main in Germany]]

This analysis was questioned by Damiani (2001), who used the original name ''Mastodonsaurus cappelensis'' for the species.<ref name=Damiani2001>{{cite journal | doi=10.1111/j.1096-3642.2001.tb00635.x | title=A systematic revision and phylogenetic analysis of Triassic mastodonsauroids (Temnospondyli: Stereospondyli) | year=2001 | last1=Damiani | first1=Ross J. | journal=Zoological Journal of the Linnean Society | volume=133 | issue=4 | pages=379–482 | doi-access=free }}</ref> Moser and Schoch (2007) continued to accept the valid status of the genus ''Heptasaurus'' but noted that the species "could also be re-referred to ''Mastodonsaurus''".<ref name="RevisionMoser"></ref> Rayfield, Barrett & Milner (2009) pointed out that the skull and size differences between ''Heptasaurus'' and ''Mastodonsaurus'' may not be important diagnostic features at a generic level.<ref name="Rayfield2009">{{cite journal | doi=10.1671/039.029.0132 | title=Utility and validity of Middle and Late Triassic 'land vertebrate faunachrons' | year=2009 | last1=Rayfield | first1=Emily | last2=Barrett | first2=Paul | last3=Milner | first3=Andrew | journal=Journal of Vertebrate Paleontology | volume=29 | issue=1 | pages=80–87 1245–1266| bibcode=2009JVPal..29...80R | s2cid=86502146 }}</ref>

In more recent research, Schoch has restored the combination ''Mastodonsaurus cappelensis'' for the geologically older species, noting in 2008 that "present evidence indicates close ties with ''Mastodonsaurus giganteus'', which is why this species is here referred to ''Mastodonsaurus''".<ref name=Schoch2008>{{cite journal |last=Schoch |first=R.R. |year=2008 |title= The Capitosauria (Amphibia): characters, phylogeny, and stratigraphy |journal= Palaeodiversity |volume=1 |pages=189–226 |url= http://www.palaeodiversity.org/pdf/01/Palaeodiversity_1_13_189-226.pdf}}</ref><ref name=Schoch2011>{{cite journal|last=Schoch |first=R.R. |year=2011 |title= How diverse is the temnospondyl fauna in the Lower Triassic of southern Germany? |journal= Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen|volume=261 |issue=1 |pages=49–60|doi=10.1127/0077-7749/2011/0147 }}</ref> A revised description of ''Mastodonsaurus cappelensis'' by Schoch and others in 2023 indicated that the earlier species was 3 meters long and differed from ''M. giganteus'' in having a wider snout and differently shaped orbits, as well as a longer and more gracile humerus. The ''Mastodonsaurus'' lineage evolved larger tusks and stronger jaws over time to deal with more types of prey, becoming a dominant predator in lake-related ecosystems.<ref>{{cite journal|last1=Schoch | first1=R. R. | last2=Milner | first2=A. | last3=Witzmann | first3=F. | last4=Mujal | first4=E. |year=2023 |title= A revision of ''Mastodonsaurus'' from the Anisian of Germany, and the evolutionary history of mastodonsaurid temnospondyls|journal= Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen|volume=309 |issue=2 |pages=123–140|doi=10.1127/njgpa/2023/1154| s2cid=261594499 }}</ref>

[[File:Mastodonsaurus3.jpg|thumb|left|A reconstruction of ''M. torvus''|225x225px]] The species ''Mastodonsaurus torvus'' was described in 1955 by Russian paleontologist Elena Dometevna Konzhukova (wife of paleontologist [[Ivan Yefremov]]) based on a lower jaw fragment (holotype PIN 415/1) and other bones unearthed near the village of Koltaevo in [[Bashkortostan]] in the Southern Urals in Middle Triassic beds that are part of the [[Bukobay Svita]] in [[Russia]].<ref>{{cite journal |last=Konzhukova |first=E.D. |year=1955|title=Permian and Triassic labyrinthodonts of the Volga and Urals region |journal=Trudy Paleontologicheskogo Instituta, Akademiia Nauk SSSR |volume=49 |pages=5–88}}</ref> Additional fossils of very large mastodonsaurids have been discovered as well at Middle Triassic sites in the [[Orenburg Oblast]] in Russia and in northern [[Kazakhstan]]. In 1972, Russian paleontologist [[Leonid Petrovich Tatarinov]] found a complete skull (measuring 1.25 meters long) on an expedition to Koltaevo. The giant skull is on display at the [[Moscow Paleontological Museum|Orlov Paleontological Museum]] (specimen PIN 2867/67) in [[Moscow]] in Russia and has been labeled ''Mastodonsaurus torvus'', although some sources cite the specimen as ''Mastodonsaurus sp.'' instead.<ref>(''Mastodonsaurus sp.'') skull, Orlov Paleontological Museum (in Russian) https://www.paleo.ru/museum/exposure/exhibit.php?ID=11985</ref><ref>The Biggest Amphibian (in Russian) https://elementy.ru/kartinka_dnya/541/Samaya_bolshaya_amfibiya</ref><ref name=Lopatin2012>{{cite book |author=Lopatin A.V. |title=Paleontological Museum Named After Yu. A. Orlov (guidebook in Russian)|year=2012 |publisher=Pin Ran |location=Moscow |isbn=978-5-903825-14-1 |pages=1–320|url=https://www.arran.ru/data/collections/col18.pdf}}</ref><ref name=Ivakhnenko1997>{{cite book|last=Ivakhnenko|first=M.F.|author2=Golubev, V.G.|author3=Gubin, Yurii M.|author4=Kalandadze, N.N.|author5=Novikov, I.V.|author6=Sennikov, A.G.|author7=Radian, A.|editor=Tatarinov, L.L.|title=Trudy Paleontologicheskogo Instituta 268. Permian and Triassic Tetrapods of Eastern Europe (in Russian)|url=https://www.rfbr.ru/rffi/ru/books/o_37911|year=1997|publisher=GEOS|location=Moscow|isbn=5-89118-029-4|pages=1–216|archive-date=2023-05-16|access-date=2022-06-26|archive-url=https://web.archive.org/web/20230516115000/https://www.rfbr.ru/rffi/ru/books/o_37911|url-status=dead}}</ref> A full scientific description has not been published yet, but differences from ''Mastodonsaurus giganteus'' include smaller orbits positioned further back on the skull.[[File:Mastodonsaurus skull.jpg|thumb|right| Complete skull (PIN 2867/67) assigned to ''Mastodonsaurus'', found in 1972 in the Southern Urals, on display at the [[Moscow Paleontological Museum|Orlov Paleontological Museum]] in Moscow ]]

Researchers debate the generic classification of the Russian fossils, sometimes referring to them as "''Mastodonsaurus''" in quotes or with a question mark (?) to indicate that further study may justify a separate giant mastodonsaurid genus.<ref name=NS00>{{cite book|last=Shishkin |first=Mikhail A. |author2=Novikov, Igor V. |author3=Gubin, Yurii M. |editor=Benton, Michael J. |editor2=Shishkin, Mikhail A. |editor3=Unwin, David M. |editor4=Kurochkin, Evgenii N. |title=The Age of Dinosaurs in Russia and Mongolia |url=https://archive.org/details/agedinosaursruss00bent |url-access=limited |year=2000 |publisher=Cambridge University Press |location=Cambridge |isbn=0-521-55476-4 |pages=35–59 |chapter=Permian and Triassic temnospondyls from Russia}}</ref><ref name="Rayfield2009"/>

===Formerly assigned species=== * ''Mastodonsaurus cappelensis'' = valid (or ''[[Heptasaurus]]'') * ''Mastodonsaurus vaslenensis'' = possible "heptasaurid"<ref name="RevisionMoser" /> * ''Mastodonsaurus granulosus'' = ''[[Plagiosternum]]'' * ''Mastodonsaurus arenaceus'' = ''[[Capitosaurus]]'' * ''Mastodonsaurus robustus'' = ''[[Cyclotosaurus]]''<ref name="RevisionMoser" /> * ''Mastodonsaurus durus'' = ''[[Eupelor]]'' (metoposaurid)<ref name="RevisionMoser" /> * ''Mastodonsaurus keuperinus'' = mix of ''[[Metoposaurus]]'' and indeterminate mastodonsaurid material<ref name="RevisionMoser" /> * ''Mastodonsaurus weigelti'' = junior synonym of ''[[Parotosuchus]]''<ref name="RevisionMoser" /> * ''Labyrinthodon leptognathus'' = Stereospondyli indeterminate<ref name=Damiani2001/>

==References== {{Reflist}}

[[Category:Capitosauria]] [[Category:Extinct apex predators]] [[Category:Triassic temnospondyls of Europe]] [[Category:Middle Triassic amphibians of Europe]] [[Category:Fossil taxa described in 1828]]