| Matheronodon | |
|---|---|
 | |
| Holotype maxilla | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Rhabdodontidae |
| Genus: | †Matheronodon Godefroitet al.,2017 |
| Type species | |
| Matheronodon provincialis Godefroitet al., 2017 | |
Matheronodon (meaning "Matheron tooth") is agenus ofrhabdodontidornithopoddinosaur from the lateCretaceous Period of theGrès à Reptiles Formation inFrance. The genus contains a single species,M. provincialis, which is known from a singlemaxilla and associated teeth. It was named byPascal Godefroit and colleagues in 2017. The teeth ofMatheronodon are large but few in number. The teeth are also in an unusual arrangement, emerging alternatingly from one of a pair of fused tooth sockets in its mouth. In life, the teeth would have functioned like a pair of scissors, allowingMatheronodon to feed on the tough leaves ofmonocot plants.[1]
Like other rhabdodontids,Matheronodon would have been a bipedal herbivore. The length of the genus has been estimated at 5 metres (16 ft) by its lead describerPascal Godefroit.[2]
Themaxilla ofMatheronodon is a short, robust bone. The front portion is particularly shortened and also angled upwards, differentiatingMatheronodon from other rhabdodontids. It measures 22 cm (8.7 in) long, and 10 cm (3.9 in) high. When viewed from the top, the front portion is triangular, and forms a broad rostrodorsal shelf. BothRhabdodon andZalmoxes lack the shelf. There is a bar-like structure on the interior surface, the dorsal bar, which is also present inRhabdodon. Immediately below this bar, there is a horizontal groove, or transverse sulcus. Further behind, the upward-projecting dorsal process is wider and angled further backwards thanRhabdodon, and larger thanZalmoxes. From the base of this process, a "wing" extends backwards to articulate with thejugal bone. Also at the base of the dorsal process is a small triangular projection delimiting the back of theantorbital fenestra, which is shorter thanRhabdodon.[1]
LikeRhabdodon,Zalmoxes, andMochlodon, the maxillary tooth crowns ofMatheronodon are shaped like cleavers. They are unusually large, being up to 5 cm (2.0 in) long. More than these other rhabdodontids, there are at least 25 ridges on the inner surface of each tooth. The ridges are all roughly the same size, and there is no "primary" ridge, identifyingMatheronodon as a rhabdodontid. A singlewear facet is oriented 60° below the horizontal, likeZalmoxes andMochlodon.Enamel covers all sides of the teeth, unlikehadrosaurids, being thicker on the inner surface (particularly on the ridges, compared toEdmontosaurus). Also unlike hadrosaurids, the tubular structure of thedentine below the enamel does not appear to vary in orientation. The scratches on the dentine's surface are vertical likeZalmoxes andMochlodon.[1]
Even though the maxilla is large, it bears only eighttooth sockets.Zalmoxes has up to 10, andRhabdodon has 11. The walls separating adjacent sockets appear to have beenresorbed such that the sockets have fused into four pairs, which is not known in eitherRhabdodon orZalmoxes. Only one functional tooth would have been present in each pair at any time. From the preservedreplacement teeth, it appears that tooth replacement progressed from the back to the front of the jaw, with teeth alternatingly emerging from the front and rear sockets in each pair. The tooth of each front socket would have overlapped those from the rear socket, due to the size of the crowns.[1]
Unlike the teeth of the maxilla, the teeth of the lower jaw are leaf-shaped, and bear a primary ridge displaced backwards from the center of the crown. However, they are also large. The subsidiary ridges flanking the primary ridge are also more numerous thanRhabdodon orMochlodon, with there being at least 12 on each side. These ridges stretch to the bottom edge of the crown, instead of stopping short as inMochlodon.[1]
All specimens ofMatheronodon have been found at the locality of Velaux-La Bastide Neuve, in theAix-en-Provence basin,Bouches-du-Rhône,France. Thesandstones at this locality, which was discovered by Xavier Valentin in 1992,[3] are part of the Begudian regionalstage (whichcorrelates to the lateCampanian epoch, about 74 to 72 million years ago[4]). After their discovery, the fossils were stored in thepaleontology andarchaeology collections of themunicipality ofVelaux, and labelled as belonging to theMusée du Moulin Seigneurial/Velaux-La Bastide Neuve (MMS/VBN). Thetype specimen is MMS/VBN-02-102, a right maxilla; associated with it are maxillary teeth (-93-34, -09-149a, -09-150, and -12-22) and dentary teeth: (-02-11, -09-43c, and -12-A002).[1]
In 2017, the fossil material was described by Godefroit along with Géraldine Garcia, Bernard Gomez, Koen Stein, Aude Cincotta, Ulysse Lefèvre, and Valentin in aresearch paper published by the journalNature Communications. They assigned this material to the genusMatheronodon, with the name being formed fromPhilippe Matheron (who described the first dinosaur fossils found inProvence, or the southeastern region of France) and the suffix-odon, a derivative ofodous (Greek for "tooth"). They also named the type and only speciesM. provincialis, withprovincialis beingLatin for Provence. For the study, aCT scan of the type maxilla was conducted at theUniversity of Liège, and athin section of an isolated maxillary tooth was examined under a microscope.[1]
Inferences regarding the method of feeding inMatheronodon can be made from the unique morphology of its teeth. The hadrosaurs, a contemporary successful group ofornithopods, had a large number of wide, high crowned teeth in tightly-packed rows. These were used in a complex method of chewing, a culmination of continued specialization throughout the evolution ofiguanodonts. Rhabdodontids, which were morebasal, had a far simpler arrangement, with teeth more similar to those of less specialized ornithopods. Fewer teeth were present in the jaw, but they were taller, thinner, and individually larger. In life, they would have functioned like a pair of scissors in powerful but simple slicing bites. The microstructure of the teeth inMantheronodon was also adapted for this action.[1]
These differences would have led to different diets in the two groups of ornithopods. Where they co-occurred, they were likelyecologically partitioned. Rhabdodontids would have had more limited diets, compared to the diverse and likelycellulose-rich and perhapsconifer-based diets of hadrosaurs.Mantheronodon and its relatives may have fed onmonocot plants, such as thepalmsSabalites andPandanites, common in Europe at the time.Sclerenchyma fibres, abundant in monocot leaves but largely absent ineudicots and conifers, result in tougher plant tissue, and would have necessitated the more powerful bites of rhabdodontids to be consumed.[1]
Velaux-La Bastide Neuve represents a continental deposit.[4] However, it was probably close to the shoreline, judging by the presence of claws fromdecapods,[3]gastropods, andunionidmussels at the site. Fossils from the locality are well-preserved and were likely slowly transported.[4] Other dinosaurs discovered at the site include thetitanosaurAtsinganosaurus, in addition to teeth fromnodosauridankylosaurs[3] as well asneoceratosaurian anddromaeosauridtheropods. Additional faunal elements include theeusuchianAllodaposuchus,pterosaurs, the turtlesSolemys andPolysternon,thehybodontelasmobranchMeristonoides, and agar.[4]
It was around five metres long, I guess.
