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Dromaeosauroides

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Dromaeosauroides
Temporal range:Early Cretaceous,140Ma
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Cast of the holotype tooth (DK 315),Geological Museum, Copenhagen
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Dromaeosauridae
Clade: †Eudromaeosauria
Subfamily: †Dromaeosaurinae
Genus: †Dromaeosauroides
Christiansen & Bonde,2003
Type species
†Dromaeosauroides bornholmensis
Christiansen & Bonde, 2003

Dromaeosauroidesis agenusofdromaeosauridtheropoddinosaurfrom theEarly Cretaceousof what is nowDenmarkand possibly alsoEngland.It was discovered in theJydegaard Formationin the Robbedale valley, on the island ofBornholmin theBaltic Sea.This is the only likely place for dinosaur remains to be discovered on Danish territory, since theMesozoicdeposits exposed in the rest of the country are marine.Dromaeosauroidesis the first known dinosaur from Denmark, and the only one which has been scientifically named. It is one of the oldest known dromaeosaurs in the world, and the first known uncontested dromaeosaur from the Early Cretaceous of Europe.

It is known from two teeth, the first of which was found in 2000 and the second in 2008. Based on the first tooth (theholotype), the genus and speciesDromaeosauroides bornholmensiswas named in 2003. The genus name means "Dromaeosaurus-like ", due to the similarity to the teeth of that genus, and the species name means" from Bornholm ". After this discovery, remains and tracks of more dinosaurs were found in several formations on Bornholm. Some teeth from the United Kingdom that have been referred to the genusNuthetesmay also belong to this animal.Coprolitescontaining fish remains found in the Jydegaard Formation may belong toDromaeosauroides.

The holotype tooth is 21.7 millimetres (0.85 in) long, and the second tooth is 15 millimetres (0.59 in). They are curved and finely serrated. In life,Dromaeosauroideswould have been 2 to 3 metres (7 to 10 ft) in length, and weighed about 40 kilograms (88 lb). As a dromaeosaur it would have been feathered, and had a large sickle claw on its feet like its relativesDromaeosaurusandDeinonychus.It lived in a coastal lagoon environment withsauropods,as evidenced by a possibletitanosaurtooth.

Discovery and naming

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Fewdinosaurremains have been found inScandinavia.The mainland of western Denmark is an unlikely region to find dinosaur remains, since the Mesozoic sediments there are marineMaastrichtianchalk.Fossils of non-dinosaurian marine animals, includingmosasaursandplesiosaurs,have been found in these deposits.[1]Mesozoic deposits inScania,Sweden, are much richer in fossils, including those of dinosaurs. The Danish island ofBornholmin theBaltic Seawas part of the same land mass as Scania (the Scandinavian-Russian continent), and has a similar geology. The southwestern part of the island is the only place in Denmark which has yielded dinosaur remains.[2]

Map of area where dinosaur teeth were found
Map showing Denmark (A) andBornholm(B), with "Carl Nielsen's sandpit" whereDromaeosauroideswas found indicated by a red dot

During the 1990s, the Fossil Project (disbanded in 2005) was formed by a group of unemployed people who received funding from Denmark and theEECto maintain geological sites on Bornholm.[2]One of these, "Carl Nielsen's sandpit" in the Robbedale valley (not to be confused with theRobbedale Formation,where no vertebrate remains have been found), is part of theJydegaard Formation.This formation is 140 million years old, dating to theLate Berriasian(or Ryazanian) stage of theEarly Cretaceousperiod. The Fossil Project sifted sand at these sites in cooperation with theNaturBornholminterpretation centre,which exhibited the fossils discovered. In September 2000, DanishpalaeontologistsPer ChristiansenandNiels Bondetaught a field course at the site, "The Hunt for Danish Dinosaurs". During the course, geology student Eliza Jarl Estrup found atheropodtooth, the first dinosaur discovered on Danish territory, and the find was recorded by a local television station.[1][3]

The tooth was presented at the 45th annual meeting of thePalaeontological Associationin 2001, and identified as adromaeosaur.[4]In 2003 the tooth (MGUH 27218/DK 315) was made theholotype specimenofDromaeosauroides bornholmensis—named and described by Christiansen and Bonde. Thegenusname combinesDromaeosauruswith theGreek-ides( "in the form of" ), referring to the resemblance between the teeth of the two genera. Thespecific namerefers to Bornholm.[5]The nameDromaeosaurusitself has been translated as "swift" or "running reptile".[6][7]Bonde and Christiansen had expected the first Danish dinosaur remains to be teeth of herbivorous dinosaurs such ashypsilophodontsorIguanodon,and were surprised to find a dromaeosaur tooth instead, since these are rare in Early Cretaceous formations; herbivores would have been more abundant than carnivores.[1][8]Because the dromaeosaur seems to have been large, they expected that resilient bones, such as claws, might be found in the future. The palaeontologists did not expect bones of larger dinosaurs to be discovered in the formation (since these would most likely have been found when the sand was commercially exploited), but hoped the remains of a Mesozoic mammal would be found.[1]The holotype tooth has been illustrated in several books and research articles. It was certified"Danekræ"( "Danish creature", according to a 1990 Danish museum law securing important fossils) when its scientific importance was evaluated by theGeological Museum in Copenhagen.[1][2]

Feathered dinosaur with large head, claws and rudimentary wings
Hypotheticallife restoration,based on relatedgenera

In late summer 2008, ranger Jens Kofoed found a second dromaeosaurid tooth.[9]This specimen (DK 559) was found in the same location, and later assigned toD. bornholmensisas well.[2]Kofoed explained that the finds were surprising because people had been unsuccessfully searching for dinosaur remains in Denmark for years, and it was like finding a "needle in a haystack".[10]In a press release, the second dromaeosaur tooth was also certifiedDanekræby theNatural History Museum of Denmark,which compared the animal to the raptors in the filmJurassic Park,noting that the animals, unlike the film's raptors, would have been feathered.[9]

Since the discovery ofDromaeosauroides,evidence of more dinosaurs has been found on Bornholm. In 2002, a tooth thought to belong to a juveniletitanosauriansauropodwas found in the Jydegaard Formation. Footprints of a sauropod and athyreophoranwere reported from theMiddle JurassicBagå Formationin 2005.[2]Small dromaeosaur and indeterminatemaniraptoranteeth from the Early CretaceousRabekke Formationwere reported in 2008,[11]and sauropod tracks were also reported from the formation that year.[12]In 2011, footprints of a sauropod, a thyreophoran and a theropod were reported from the Bagå Formation.[13]Lower Jurassictracks reported form the Rønne Formation in 2014 are the earliest evidence of dinosaur activity in Denmark.[14]A tooth from themultituberculateSunnyodonwas found in the Rabekke Formation in 2004, making it the first known Danish and Scandinavian Mesozoic mammal.[15]A tooth of aturiasauriansauropod was reported from the Lower JurassicHasle Formationin 2023.[16]

In 2012, Jesper Milàn and colleagues described twocoprolites(fossilised faeces) containing fish scales and bones. They were found in the Jydegaard Formation, the first such fossils found in Danish continental Mesozoic deposits. Although the producer of these faeces cannot be identified with certainty, marine turtles and dromaeosaurids such asDromaeosauroidesare the most likely candidates.[17]

Description

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Dinosaur head and body, compared with human for size
Estimated size ofDromaeosauroides,and possible placement of the two known teeth

Fossil theropod teeth are typically identified according to features including size, proportion, curvature of the crown and themorphologyand number ofdenticles(serrations). The holotype ofD. bornholmensisis atooth crown21.7 millimetres (0.85 in) long, 9.7 millimetres (0.38 in) from front to back and 6.6 millimetres (0.26 in) wide at the base. The front part of the tooth was worn, indicating that it was shed when the animal was alive. It was further affected bytaphonomicwear; the base of the tooth is irregular, so it may have been slightly longer in life.[1]The curvature and length of the holotype tooth and the length of its hindmost cutting edge (carina) indicates it was in the front of the jaw.[8]

The tooth is recurved with a backward bend, and is oval in cross-section. Its front and back cutting edges are finely serrated, extending two-thirds down each edge.[8]There are six denticles per millimeter (0.04 in), and each denticle is square and chiseled. The overall form of the tooth, its width and shape in cross-section and its curvature resemble those in themaxilla(upper jawbone) andmandibleof the speciesDromaeosaurus albertensisfromNorth America.Blood grooves are indistinct or absent, also similar toDromaeosaurus,and differing from members of theVelociraptorinaesubfamily.Dromaeosauroidesdiffers fromDromaeosaurusin that the cutting edge at the front side is further from the middle of the tooth. Although the tooth is larger and the denticles similar, each denticle was smaller than those ofDromaeosaurus,which had only 13–20 denticles per 5 millimetres (0.20 in), instead ofDromaeosauroides'30.[1]The second known tooth is smaller—15 millimetres (0.59 in)—with the same features as the holotype.[2]

The holotype tooth is roughly 25 percent larger than equivalentDromaeosaurusteeth, from which a body length of 3 metres (120 in) or more was estimated forDromaeosauroides;it may have been as long as 3 to 4 metres (9.8 to 13.1 ft).[1][8]In an interview, Christiansen estimated its skull to be 35 centimetres (14 in) long and the animal's weight 40 kilograms (88 lb); aBengal tigerof the same length would weigh 150 to 180 kilograms (330 to 400 lb) by comparison.[18]As a dromaeosaur,Dromaeosauroideswould have had a large sickle claw on its highly mobile second toe, like its relativesDromaeosaurus,VelociraptorandDeinonychus.That group is closely related tobirds,and the NaturBornholm interpretive centre houses a roughly life-sized sculpture ofDromaeosauroidescovered in feathers. Later Chinese finds of well-preserved feathered dromaeosaurs indicate that the sculpture should have more and longer feathers to be accurate. Although some smaller dromaeosaurs may have been able to fly, flight was unlikely for an animal the size ofDromaeosauroides.[8]

Classification

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Dinosaur skull in museum with jaw propped open, showing its teeth
Skull cast of the similar relativeDromaeosaurus,Geological Museum

Several features of the tooth are only known from members of the family Dromaeosauridae of theropod dinosaurs.[8]Dromaeosauroideswas classified as a member of theDromaeosaurinaesubfamilywithin the Dromaeosauridae, due to its similarity toDromaeosaurus.Despite the resemblance,Dromaeosauroidesis not considered part of that genus. It is unlikely that a genus would survive for 60 million years;Dromaeosauroideslived during the Early Cretaceous, andDromaeosaurusduring theLate Cretaceous.The differences between their denticles also indicate they should be kept separate.[1]

According to Bonde,Dromaeosauroidesis one of the oldest known dromaeosaurs in the world; older remains, for the most part, have only tentatively been referred to Dromaeosauridae.Dromaeosauroideswas the first definite dromaeosaurid known from the Early Cretaceous of Europe, depending on the identity ofNuthetesfrom theMiddle Purbeckformation of the United Kingdom (which may slightly predate the Jydegaard Formation). It is uncertain whether the juvenile holotype specimen ofNutheteshas dromaeosaurid characteristics.[1]Large specimens referred toNuthetesappear to belong to true dromaeosaurs, and may belong toDromaeosauroidesrather thanNuthetes.These specimens measure 15 to 18 millimetres (0.59 to 0.71 in).[2]

Dromaeosauroideswas considered an indeterminate dromaeosaur by Johan Lindgren and colleagues in 2008.[11]Bonde responded that since the teeth differ from those of other dromaeosaurs from the Early Cretaceous (and later members of the group, includingDromaeosaurus), it should be considered valid. He also said that these scientists had provided incorrect information about the location, strata and age of the specimen, and that the circumstances of its naming were no different from those of other tooth-based taxa.[2]Oliver W. M. Rauhut and colleagues cautioned in 2010 that theropod teeth from the Late Jurassic/Early Cretaceous similar to those of dromaeosaurids may instead have belonged to the smalltyrannosauroidProceratosaurusor related taxa.[19]Nicholas R. Longrich and colleagues stated in 2021 thatDromaeosauroidesmay have been an earlyeudromaeosaur.[20]

Palaeoenvironment

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NuthetesattackingEchinodon,based on teeth from the UK that may belong toDromaeosauroides

Only a corner of the Jydegaard Formation is exposed today; the remainder is overgrown. Jydegaard is part of theNyker Group,which includes three formations (Rabekke, Robbedale, and Jydegaard) ranging from the Berriasian to theValanginianages of the Early Cretaceous. Jydegaard consists of sediments deposited in a fresh-to-brackishlagoonfacing a coastal strip. In addition toDromaeosauroidesand a possible titanosaur, remains ofhybodont sharks,fish such asLepidotesandPleuropholis,turtles, lizards, thecrocodilePholidosaurusand thin bone fragments from birds orpterosaurshave been found in the deposit.[1]The bivalveNeomiodonis found in abundance in the sediments below (theNeomiodonBed), indicating mass mortality, perhaps due todinoflagellatetoxins.[21]

The fish and bivalves were found in clay which was probably a lagoon, and the dinosaurs and lizards in sand which probably was land, perhaps a beach; turtles and crocodiles were found in both. Freshwater snails were found in clay that may have been shallow, drying lakes behind a sandy barrier between lagoon and sea, in a setting perhaps similar to theFlorida Keysor the southwestern coast ofJutland.[2]Dinosaurs may have fed there, based on the remains of plants and small land animals, and theropods may have hunted along the shore.[1]Bornholm and Scania appear to be the only places were remains of the Scandinavian-Russian fauna of the Early Cretaceous can be found. Further investigations there may show whether this fauna has European or Asian affinities.[2]

Based on possible dromaeosaur coprolites from the Jydegaard Formation, which contained scales of the fishLepidotes,Milàn and colleagues speculated that some dromaeosaurids were able to catch fish with the enlarged sickle claw on the second digit of the foot, similar to the "spear fishing" that has been proposed for the theropodBaryonyxand its enlarged thumb claw. The larger of the two coprolites has evidence ofcoprophagousorganisms.[17]

See also

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References

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  1. ^abcdefghijklBonde, N.; Christiansen, P. (2003). "New dinosaurs from Denmark".Comptes Rendus Palevol.2(1): 13–26.Bibcode:2003CRPal...2...13B.doi:10.1016/S1631-0683(03)00009-5.
  2. ^abcdefghijBonde, N. (2012)."Danish Dinosaurs: A Review".In Godefroit, P. (ed.).Bernissart Dinosaurs.Indiana University Press. pp. 435–449.ISBN9780253005700.
  3. ^Estrup, E. J. (2007)."Jurassic Park Denmark"(PDF).Scient.4 (in Danish).1:12–14.[dead link]
  4. ^Bonde, N. (2001). "A Berriasian" Wealden fauna "from Bornholm, Denmark".Palaeontological Association 45th Annual Meeting.4.
  5. ^Christiansen P. & Bonde N. (2003). "The first dinosaur from Denmark".Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen.227(2): 287–299.doi:10.1127/njgpa/227/2003/287.
  6. ^Holtz, T. R. Jr. (2012).Dinosaurs: The Most Complete, Up-to-date Encyclopedia for Dinosaur Lovers of All Ages.New York: Random House. p.384.ISBN978-0-375-82419-7.
  7. ^Norman, D. B. (1985). "Dromaeosaurids".The Illustrated Encyclopedia of Dinosaurs: An Original and Compelling Insight into Life in the Dinosaur Kingdom.New York: Crescent Books. p. 56.ISBN978-0-517-46890-6.
  8. ^abcdefBonde, N.; Andersen, S.; Hals, N.; Jakobsen, S.T. (2008).Danekræ – Danmarks bedste fossiler(in Danish). Gyldendal. pp. 28–32.ISBN9788702049855.
  9. ^ab"Sensationelt dinosaurfund på Bornholm"(in Danish). Jyllands-Posten. 2009. Archived fromthe originalon 2013-06-16.
  10. ^Barslev, K. (2008)."Tand fra dinosaur fundet på Bornholm"(in Danish). Kristeligt Dagblad. Archived fromthe originalon 2012-08-30.
  11. ^abLindgren, J.; Currie, P. J.; Rees, J.; Siverson, M.; Lindström, S.; Alwmark, C. (2008). "Theropod dinosaur teeth from the lowermost Cretaceous Rabekke Formation on Bornholm, Denmark".Geobios.41(2): 253–262.Bibcode:2008Geobi..41..253L.doi:10.1016/j.geobios.2007.05.001.
  12. ^Surlyk, F.; Milàn, J.; Noe-Nygaard, N. (2008)."Dinosaur tracks and possible lungfish aestivation burrows in a shallow coastal lake; lowermost Cretaceous, Bornholm, Denmark"(PDF).Palaeogeography, Palaeoclimatology, Palaeoecology.267(3–4): 292–304.Bibcode:2008PPP...267..292S.doi:10.1016/j.palaeo.2008.07.004.
  13. ^Milàn, J. (2011)."New theropod, thyreophoran, and small sauropod tracks from the Middle Jurassic Bagå Formation, Bornholm, Denmark"(PDF).Bulletin of the Geological Society of Denmark.59:51–59.doi:10.37570/bgsd-2011-59-06.Archived(PDF)from the original on 2016-06-16.Retrieved2013-11-05.
  14. ^Clemmensen, L. B.; Milàn, J.; Pedersen, G. K.; Johannesen, A. B.; Larsen, C. (2014). "Dinosaur tracks in Lower Jurassic coastal plain sediments (Sose Bugt Member, Rønne Formation) on Bornholm, Denmark".Lethaia.47(4): 485–493.Bibcode:2014Letha..47..485C.doi:10.1111/let.12073.
  15. ^Lindgren, J.; Rees, J.; Siverson, M.; Cuny, G. (2004). "The first Mesozoic mammal from Scandinavia".GFF.126(4): 325–330.Bibcode:2004GFF...126..325L.doi:10.1080/11035890401264325.S2CID129740267.
  16. ^Milàn, Jesper; Mateus, Octávio (2023)."A turiasaurian (Dinosauria, Sauropoda) tooth from the Pliensbachian Hasle Formation of Bornholm, Denmark, shows an Early Jurassic origin of the Turiasauria".Diversity.16(1): 12.doi:10.3390/d16010012.
  17. ^abMilàn, J.; Rasmussen, B. W.; Bonde, N. (2012)."Coprolites with prey remains and traces from coprophagous organisms from the Lower Cretaceous (Late Berriasian) Jydegaard Formation of Bornholm, Denmark"(PDF).New Mexico Museum of Natural History and Science. Bulletin.57:235–240.Archived(PDF)from the original on 2013-09-23.Retrieved2013-09-21.
  18. ^Ejsing, J. (2003)."Fortidsmonstre ser dagens lys"(in Danish). Berlingske.Archivedfrom the original on 2015-09-23.Retrieved2013-04-26.
  19. ^Rauhut, Oliver W. M.; Milner, Angela C.; Moore-Fay, Scott (2010)."Cranial osteology and phylogenetic position of the theropod dinosaurProceratosaurus bradleyi(Woodward, 1910) from the Middle Jurassic of England ".Zoological Journal of the Linnean Society.158(1): 155–195.doi:10.1111/j.1096-3642.2009.00591.x.
  20. ^Longrich, Nicholas R.; Martill, David M.; Jacobs, Megan L. (2022). "A new dromaeosaurid dinosaur from the Wessex Formation (Lower Cretaceous, Barremian) of the Isle of Wight, and implications for European palaeobiogeography".Cretaceous Research.134:105123.Bibcode:2022CrRes.13405123L.doi:10.1016/j.cretres.2021.105123.S2CID245324247.
  21. ^Bonde, N. (2004). "An early Cretaceous (Ryazanian) fauna of" Purbeck-Wealden type "at Robbedale, Bornholm, Denmark". In Arratia, G.; Tintori, A. (eds.).Mesozoic Fishes 3 – Systematics, Paleoenvironments and Biodiversity.Verlag Dr. Friedrich Pfeil. pp. 507–528.ISBN9783899370539.
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