Mastodonsaurus (meaning "teat tooth lizard") is an extinct genus of temnospondyl amphibian from the Middle Triassic of Europe. It remains one of the largest amphibians known in the fossil record, and may have exceeded 6 meters (20 feet) in length. Mastodonsaurus belongs to a Triassic group of stereospondyl temnospondyls called Capitosauria, characterized by their large body size, large flattened skulls, and probably predatory aquatic lifestyles analogous to some later crocodilian reptiles.
The gigantic size of Mastodonsaurus made it a top predator in lakes, swamps, river deltas, and other freshwater and brackish aquatic ecosystems. Huge jaws equipped with enlarged fangs and tusks, along with a powerful tail, suggest it was an underwater ambush hunter. Mastodonsaurus would have preyed mainly on fish and on smaller amphibians, but likely took on terrestrial animals that ventured into water as well. Given its heavy body mass and its relatively small limbs, Mastodonsaurus likely could not crawl onto land after reaching larger growth stages.
Description
Like those of many other capitosaurs, the head of Mastodonsaurus was triangular, reaching about in the largest specimens. 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 lines 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 tusks 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.
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.Friends of Crystal Palace Dinosaurs: Labyrinthodon statues https://cpdinosaurs.org/blog/post/neglected-labyrinthodon-in-crystal-palace-park The Artwork of Zdenek Burian. Mastodonsaurus (1955) http://zburian.blogspot.com/2012/03/mastodonsaurus.html 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.Mastodonsaurus model from 1996 at the American Museum of Natural History with a short, broad body
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. Some of the bones showed evidence of being rolled and transported a long distance. Working from the rich Kupferzell finds, German paleontologist Rainer Schoch 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. 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.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
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.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 The total length of the largest individuals is about . Isolated teeth up to 14 cm (6 in) long indicate that old individuals grew even larger.
Paleobiology
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. 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.Kupferzell fossil site geological layers, showing paleoenvironments in which Mastodonsaurus lived https://ars.els-cdn.com/content/image/1-s2.0-S0031018222003510-gr13.jpg
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.
Mastodonsaurus fed mainly on fish, whose remains have been found in its fossilized coprolites.Benes, Josef. Prehistoric Animals and Plants. Prague, Artia, 1979. 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 archosaurs 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.
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. 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.
History and naming
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. 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).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 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. 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
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 proboscidean mastodon, supposedly to suggest gigantic size ("mastodon(-size) lizard"), the false meaning given in some sources.
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.