| Betasuchus | |
|---|---|
 | |
| Cast of the femur | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | †Neoceratosauria |
| Superfamily: | †Abelisauroidea |
| Family: | †Abelisauridae |
| Genus: | †Betasuchus von Huene, 1932 |
| Species: | †B. bredai |
| Binomial name | |
| †Betasuchus bredai (Seeley, 1883 [originallyMegalosaurus]) | |
| Synonyms | |
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Betasuchus is agenus of probableabelisauridtheropoddinosaur which lived during the LateCretaceous Period.Betasuchus is, besidesOrthomerus, the only dinosaur genus named from remains found inthe Netherlands and the only non-avian theropod found in theMaastrichtian Beds.
Its fossil,holotype BMNH 42997 (now NHM R 42997), a part of a rightfemur, 312 mm long, was found in theNetherlands nearMaastricht, and originally described as a new species ofMegalosaurus in 1883 byHarry Seeley:M. bredai, honouring the late Dutch biologist and geologistJacob Gijsbertus Samuël van Breda, a director of theTeylers Museum, who had collected the fossil at some time between 1820 and 1860 from the chalkstone quarry at theSt Pietersberg. Van Breda did not excavate the remains himself but bought them from quarry workers who in this period dug stone from tunnels at several levels in the mountain; it is therefore impossible to determine the exact temporal horizon, apart from a generalMaastrichtian; however all dinosaurian material from the formation that could be dated, stems from the latest Maastrichtian, 67-66 million years old. Only the top part of the femur has been conserved; of the distal end about eight centimetres are missing as the bone was cleanly cut in two when the chalk block containing it was sawed out. Other saw cuts damaged the head of the thigh bone. The fossil was part of his personal collection, not the museum's, and sold to theBritish Museum of Natural History after his death in 1867. In 1892 Belgian/Dutch/German paleontologistJohan Casimir Ubaghs referred some teeth — probably ofmosasaurs — toM. bredai.Megalosaurus bredai was in 1883 the first terrestrial vertebrate named from Maastrichtian layers.[1]
A re-evaluation of the fossil byFriedrich von Huene in 1926, however, showed that it came from a genus distinct fromMegalosaurus — which in the nineteenth and early twentieth century was a "wastebin taxon" where many unrelated carnivorous dinosaurs were lumped together. Von Huene thought that the fossil actually belonged to anornithomimosaur, and gave it the provisional designation "Ornithomimidorum [sic][2] genus b" (inLatin: genus b of the ornithomimids), being the second of twoMegalosaurus species he was reallocating to Ornithomimidae, the first beingM. lonzeensis as "Ornithomimidorum genus a". "Ornithomimidorum" is sometimes mistakenly listed as a dinosaur genus name. Von Huene referred to this designation when he formally renamedM. bredai in 1932, calling itBetasuchus (or "B crocodile" in Greek).
In 2017 its length was estimated to be 4 meters (13 feet).[citation needed]
Betasuchus is known only from a single incomplete femur, so its exact relationships with other theropods have been difficult to determine. In 1972Dale Russell confirmed Von Huene's opinion thatBetasuchus was an ornithomimosaurid, but also considered the name anomen vanum: a failed emendation. Some workers in reference to the material still useM. bredai instead ofBetasuchus.David Norman in 1990 listedMegalosaurus bredai as anomen dubium.
Jean le Loeuff andEric Buffetaut in 1991 concluded it was a smallabelisaurid, close toTarascosaurus and that it was distinct enough not to consider it anomen dubium: they mentioned a more narrow femoral neck, a lack of orientation of the femoral head towards the front, the lack of an opening, or foramen, under the lesser trochanter and that the anterior face is narrower. Furthermore, at the lower end the beginnings of an anterointernal crest are visible, seeming to be homologous to the supracondylar crest of the femur ofCarnotaurus. They rejected the placement within Ornithomimidae, partly because of the much higher position of the fourth trochanter on the back of the femur.
In 1997Betasuchus was concluded by Carpenter, Russell and Baird to be related toDryptosaurus, atyrannosauroid. In 2004 Tykoski and Rowe placedTarascosaurus within theAbelisauroidea.
A 2022 study suggested thatBetasuchus was a ceratosaur, and likely an abelisaurid.[3] A 2024 study by Buffetaut and colleagues again concluded thatBetasuchus was an abelisaurid.[4]
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