| Ardetosaurus | |
|---|---|
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| Composite mounted skeleton, Oertijdmuseum | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Superfamily: | †Diplodocoidea |
| Family: | †Diplodocidae |
| Subfamily: | †Diplodocinae |
| Genus: | †Ardetosaurus van der Linden et al.,2024 |
| Species: | †A. viator |
| Binomial name | |
| †Ardetosaurus viator van der Linden et al., 2024 | |
Ardetosaurus is anextinct genus ofdiplodocid sauropod dinosaurs from theLate Jurassic (Kimmeridgian)Morrison Formation of northernWyoming, United States. The genus contains asingle species,Ardetosaurus viator. It was first described in 2024 on the basis of a partial articulated skeleton, including vertebrae from the neck, back, and tail, hip bones, and part of the left hindlimb. The genus is a member of theDiplodocinae, asubfamily of large long-necked dinosaurs with whiplike tails.Ardetosaurus represents one of many distinct sauropod taxa that coexisted in this formation.
TheArdetosaurus holotype was collected in 1993 before being shipped to Switzerland, from which it was later sent to Germany, where it was damaged by a museum fire, and later the Netherlands, where it is now housed. It can be distinguished from other diplodocines based on a unique arrangement oflaminae on its vertebrae.
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TheMorrison Formation is a famousgeological formation with prominentoutcrops throughout the western United States. One notable locality is the Howe Ranch in northern Wyoming'sBighorn Basin, which comprises several fossiliferous sites. One of the most well-known of these is the Howe Quarry, which was first excavated byBarnum Brown and theAmerican Museum of Natural History in 1934. This team uncovered close to three thousand bones representing multiple dinosaur species. Fieldwork did not immediately continue after that year, with much of the collected material being subsequently lost. In 1989,Hans-Jakob Siber and workers from theAathal Dinosaur Museum revisited this location, finding another site later named the Howe-Stephens Quarry. Among the many associated dinosaur skeletons was a partial articulated skeleton of a diplodocid sauropod, found during the extraction of aCamarasaurus specimen nicknamed "E. T." in the summer of 1993. It was subsequently collected in several excavation trips until the fall of 1994. The fossil—originally identified as belonging to the genusDiplodocus—was given the nickname "Brösmeli", meaning "crumbly" inSwiss German, and sent to Europe for preparation and eventual study.[2]
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The Brösmeli specimen was first housed at the Aathal Dinosaur Museum in Switzerland, where it was cataloged as SMA 0013. At an unrecorded date, it was later sent to theDinosaurier Freilichtmuseum in Münchehagen, Germany forpreparation. On October 4–5, 2003, a destructive fire caused bymalicious arson damaged much of the museum's exhibition hall and laboratory. More than 100 bones from different specimens were entirely destroyed, including about 15% of the bones that had been prepared from the Brösmeli specimen.[3] Reviews of field notes and maps indicate that three anterior cervical vertebrae and the field jackets protecting the dorsal vertebrae were mostly lost, with the femur and fibula sustaining significant damage. The tibia exhibits burn marks on the proximal end. Subsequently, the partially-prepared specimen was bought by theOertijdmuseum inBoxtel, the Netherlands, in 2018 and 2019, where it was given the new specimen number MAB011899. The Oertijdmuseum also purchased four other diplodocoid specimens, nicknamed "Aurora", "Triplo", "Twin", and "XL", found in the same quarry as Brösmeli. Final preparation on these specimens was carried out by this museum. The bones referable to MAB011899 comprisecervical vertebrae 13–14,dorsal vertebrae 1–10, severalribs, part of thesacrum, the leftilium, thepubes andischia, the first fivecaudal vertebrae, twochevrons, the leftcoracoid, the partial leftfemur andfibula, the lefttibia.[2]
Once Brösmeli, Triplo, and Twin were fully prepared, the museum organized a mounted composite skeleton based on these specimens, which was completed in March 2022. Most of the skeleton is represented by the three specimens, although they are not all referable to the same taxon.[2]
In 2024, van der Linden et al.describedArdetosaurus viator as a new genus and species of diplodocine sauropods based on MAB011899, theholotype specimen. Thegeneric name,Ardetosaurus is a combination of theLatinardērē, meaning "to burn", and theAncient Greekσαῦρος (sauros), meaning "lizard". This refers to the holotype specimen's history with fire, with some elements having been lost and others still bearing burn marks from the 2003 Dinosaurier Freilichtmuseum fire. Thespecific name,viator, is the Latin word for traveler, referring to the long journey the specimen has gone through to arrive in the Netherlands.[2]
Ardetosaurus is a member of thesauropodfamily Diplodocidae. All sauropods arequadrupedal herbivores with small heads, columnar legs, and long necks and tails. Diplodocids are further characterized by their extremely elongated necks and whip-like tails. Members of this family have thin, cylindrical pencil-like teeth confined to the front of their jaws that may have assisted the animals in effectively stripping leaves from branches. Their nasal openings are situated closer to the eyes than the tip of the snout. The forelimbs of these sauropods are notably smaller than their hindlimbs—a trait that may have facilitated rearing.[4]
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Ardetosaurus can be more precisely classified within the diplodocidsubfamilyDiplodocinae, which includes sauropods more similar toDiplodocus thanApatosaurus. Diplodocines exhibit a vast range of body sizes, including some of the longest known dinosaurs such asSupersaurus, at 35–40 metres (115–131 ft).[5][6][7] Conversely, some were much smaller, such as the ArgentinianLeinkupal at about 9 metres (30 ft).[8] A dorsal rib of theArdetosaurus holotype washistologically sectioned to determine its growth patterns. These analyses indicate that the specimen belonged to a fully mature adult that grew for about 22 years, reaching sexual maturity at about 13 years and skeletal maturity at 17 years. The maturity of this specimen is indicated by the presence of an external fundamental system (EFS), which is a band of tissue that only develops when bone growth slows in older animals.[9] While incomplete, the femur ofArdetosaurus is estimated at around 130 centimetres (51 in) long, with a tibia at 91.5 centimetres (36.0 in).[2] The holotype bones of the skeletally immatureGaleamopus pabsti are comparable in size, including a 116 centimetres (46 in)-long femur and 84.5 centimetres (33.3 in)-long tibia.[10] The subadultGaleamopus pabsti holotype individual is estimated at 18.2 metres (60 ft) long.[11]
Ardetosaurus is a diplodocine sauropod, placing it among several taxa that also lived in the Morrison Formation includingDiplodocus,Galeamopus andSupersaurus. All members of this group are herbivores that lived between 161.2 and 136.4Mya.[2][5]
In their 2024 description of the taxon, van der Linden and colleagues refrained from including aphylogenetic analysis, stating that the description is part of an ongoing project to investigate the systematics of the much broader cladeDiplodocoidea. They mention that a collaborative phylogeny will be published in the future, which will include a number of new diplodocoid specimens. As such, the exact relationships ofArdetosaurus with other diplodocines remain unknown.[2]
The following cladogram of Diplodocidae is simplified from a 2015 analysis by Tschopp and colleagues, illustrating the general relationships of many described diplodocine species.[5]
Ardetosaurus is known from theMorrison Formation, a rock sequence with outcrops throughout the western United States known for its rich dinosaur fauna.[2]Radiometric dating indicates the formation is about 156.3 million years old (Ma) at the base and up to 146.8 million years old at the top, placing it within the latestOxfordian,Kimmeridgian, and earlyTithonian ages of theLate Jurassic epoch.[12][13][1] The Morrison Formation is comparable in age and faunal composition to theLourinhã Formation in Portugal and theTendaguru Formation in Tanzania.[14]
The ancient Morrison Basin region, where many dinosaurs lived, ranged fromAlberta andSaskatchewan in the north toNew Mexico in the south. It was formed when theRocky Mountains precursors began to push up to the west. Rivers carried the east-facing drainage basin deposits into swampylowlands, lakes, river channels, andfloodplains.Thesealluvial and shallow marinedepositional environments have been interpreted as representing asemi-arid environment with separatewet anddry seasons.[15][1]
The Morrison Formation records a very diverse dinosaur fauna in addition to fossils of other animals and plants. It is arguably most famous for its plentiful sauropod fauna. In particular, the Howe-Stephens Quarry from whichArdetosaurus is known has yielded associated skeletons of the sauropodsDiplodocus andCamarasaurus, the armoredStegosaurus, the theropodAllosaurus and the small herbivorousNanosaurus.[2]
In addition toArdetosaurus, other diplodocines of the Morrison Formation includeDiplodocus,Barosaurus,Supersaurus andGaleamopus.Apatosaurines includeApatosaurus—one of the most abundant Morrison sauropods—andBrontosaurus.Dicraeosaurids are less common, comprising isolated specimens ofSmitanosaurus,Dyslocosaurus, andSuuwassea.Amphicoelias (a diplodocid ofuncertain placement),Kaatedocus (a possible diplodocine),Maraapunisaurus (a possiblerebbachisaurid) and the basal diplodocoidHaplocanthosaurus are also known.Macronarian sauropods in the Morrison Formation includeBrachiosaurus but are dominated by the very commonCamarasaurus.[16][17]
Theropods are also common in the Morrison Formation, including the extremely commonAllosaurus, which represents theapex predator in Morrison ecosystems. Other taxa include theallosauroidSaurophaganax,ceratosaursCeratosaurus andFosterovenator,megalosaursTorvosaurus andMarshosaurus, and thecoelurosaursCoelurus,Ornitholestes, andTanycolagreus (all basal forms),Stokesosaurus (a basaltyrannosauroid), andHesperornithoides (atroodontid).[17][18] Morrisonornithischians includestegosaurs (Alcovasaurus,Hesperosaurus, andStegosaurus),[19]ankylosaurs (Gargoyleosaurus andMymoorapelta), theheterodontosauridFruitadens, basalneornithischians (Nanosaurus), andornithopods (Camptosaurus—the most geographically widespread Morrison ornithopod—Dryosaurus—the most temporally widespread Morrison ornithopod—andUteodon).[17]
Non-dinosaurian animals in the Morrison Formation includepterosaurs (Harpactognathus,Kepodactylus,Mesadactylus, andUtahdactylus), in addition to manyray-finned fishes, amphibians, turtles,sphenodontians, lizards, terrestrial and aquaticcrocodylomorphs, and various small mammals.Bivalve and aquatic snail shells can also be found. The contemporary flora of the period comprisedmosses,horsetails, and various families ofcycads,cycadeoid,ginkgo, andconifer. Vegetation varied fromgallery forests of ferns andtree ferns along rivers,woodland savannas of ginkgos and coniferophytes, and fernsavannas with scattered trees.[18][20]
