| Orthomerus | |
|---|---|
 | |
| Skeletal model | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Hadrosauridae |
| Genus: | †Orthomerus Seeley,1883 |
| Type species | |
| †Orthomerus dolloi | |
Orthomerus (meaning "straightfemur") is agenus ofdubioushadrosauriddinosaur from theLate Cretaceous of theNetherlands. It is today an obscure genus, but in the past was conflated with the much better knownTelmatosaurus.
Thetype speciesOrthomerus dolloi was in 1883 named by the well-knownBritishpaleontologistHarry Govier Seeley. The genus name is derived from the Greek ὀρθός (orthos), "straight", and μηρός (meros), "thigh". Thespecific name honours the French/Belgian paleontologistLouis Dollo, who had identified the bones in August 1882, during a visit to London.
Thetype specimen, formed by thesyntypesBMNH 42954-57, was probably found in the chalkstone quarries of theSint-Pietersberg near the city ofMaastricht, The Netherlands. It mainly consists of partialjuvenile skeletal elements. These remains are from theMaastricht Formation of the lateMaastrichtian stage of theLate Cretaceous, about 66 million years old. The type bones include the straight left and right femora that moved Seeley to give it its name. A left tibia and a metatarsal also discovered in the collection ofJacob Gijsbertus Samuël van Breda acquired by theBritish Museum of Natural History in 1871, were referred by him to the species.[1] The leg bones are only about half the size of those belonging to the then largely unknownNorth American andAsian duckbills, with the femur 50 cm (20 in) long.[1] Other more fragmentary hadrosaurid remains have been found, some of them in The Netherlands, where the species is sometimes presented as a rare "Dutch dinosaur", others perhaps in Belgium where in 1882 Dollo acquired two hadrosaurid tail vertebrae nearZichen, a Belgian border village inBelgian Limburg. It is hard to establish whether such finds belonged to the same species and not all of them have been explicitly referred toOrthomerus dolloi. Later Belgian finds included a left third metatarsal, NHMM 1996001 discovered by J.H. Kuypers nearEben Emael, where a larger right third metatarsal was also collected, NHMM RD 241, and a right maxillary tooth, NHMM 1999012, found by E. Croimans. Some phalanges and a left ulna have been reported from private collections, lacking an inventory number.
The Dutch finds include two tail vertebrae collected in the nineteenth century. A second individual dating from just below theCretaceous–Paleogene boundary was in September 1967 discovered in a quarry nearGeulhem by L. de Heer; it consists of a fragmentary left femur (MND K 21.04.003), left tibia (MND K 21.04.004) and left fibula (MND K21.04.005). Later found limb bone fragments are OGP 0196 and OGP 2111. NHMM 2002067, a partial tibia, seems not to be cospecific with the other finds, suggesting two hadrosaurid species were present in the formation. In a quarry nearBemelen a partial right dentary was found, specimen NHMM 198027, that however lacked any teeth. However, isolated teeth have been found: NHMM 1997274 by J. Vollers nearSibbe and left dentary tooth NHMM RD 214 fromBerg en Terblijt, were also dentary tooth NHMM RN 28 was discovered. Finally the collection of theTeylers Museum atHaarlem features a partial right humerus, TM 11253.[2][3]
A second species,Orthomerus weberi, was first described byAnatoly Nikolaevich Riabinin in 1945 for hindlimb elements from an unnamed Maastrichtian-ageformation in theCrimea of what is nowUkraine (then a part of theSoviet Union).[4] These were found by Gertruda Weber who is honoured in the specific name. As Weber was femaleLev Nesov in 1995 emended the name toOrthomerus weberae.[5] In 2015 it was made the type species of the new genusRiabininohadros,[6] which was not formally named until 2020.[7]
What is sometimes listed as a third species,O. transsylvanicus, is actually thetype species ofTelmatosaurus, whichFranz Nopcsa in 1915 referred toOrthomerus, an assignment still accepted byAlfred Sherwood Romer in his review of reptiles.[8] In recent publicationsTelmatosaurus is seen as a separate genus, though.[9][10] IfOrthomerus would be identical toTelmatosaurus the latter would be its junior synonym. Forgetting this, in 1984 Dutch geologistEric Mulder renamedO. dolloi intoTelmatosaurus dolloi.[11] A fourth species name isOrthomerus hillii, a renaming in 1915 by Nopcsa ofIguanodon hillii Newton 1892, based on a tooth fragment. It is today seen as anomen dubium.
In 2019, a study designated the right thighbone as thelectotype. The left thighbone would be of a smaller individual.[12]
The right thighbone has a length of about fifty centimetres. In 2019, noautapomorphies nor a unique combination of traits could be established. That would makeOrthomerus anomen dubium.[12]
Usually,Orthomerus was considered a member of theHadrosauridae. However, the 2019 study included acladistic analysis indicating thatOrthomerus, though a possible hadrosaurid, was more likely placed more basal in theHadrosauroidea, close toGilmoreosaurus andBactrosaurus in the evolutionary tree, outside of the Hadrosauridae.[12]
As a hadrosaurid,Orthomerus would have been abipedal/quadrupedalherbivore, eatingplants with a set of ever-replacingteeth placed in jaw bones with limited mobility that provided grinding action.[10]
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Media related toOrthomerus at Wikimedia Commons
