| Europasaurus | |
|---|---|
 | |
| Reconstructed skeleton,Aathal Dinosaur Museum | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Camarasauromorpha |
| Genus: | †Europasaurus Mateus et al. in Sanderet al.,2006[1] |
| Species: | †E. holgeri |
| Binomial name | |
| †Europasaurus holgeri Mateuset al. in Sanderet al., 2006[1] | |
Europasaurus (meaning 'Europe lizard') is a basalmacronariansauropod, a form ofquadrupedalherbivorousdinosaur. It lived during the LateJurassic (middleKimmeridgian, from about 154 to 151 million years ago) of northernGermany, and has been identified as an example ofinsular dwarfism resulting from the isolation of a sauropod population on an island within theLower Saxony basin.
In 1998, a single sauropod tooth was discovered by private fossil collector Holger Lüdtke in an active quarry atLangenberg Mountain, between the communities ofOker,Harlingerode andGöttingerode in Germany. TheLangenberg chalk quarry had been active for more than a century; rocks are quarried using blasting and are mostly processed into fertilisers. The quarry exposes a nearly continuous, 203 m (666 ft) thick succession ofcarbonate rocks[2] belonging to theSüntel Formation, that ranges in age from the earlyOxfordian to lateKimmeridgianstages and have been deposited in a shallow sea with a water depth of less than 30 m (98 ft). The layers exposed in the quarry are oriented nearly vertically and slightly overturned, which is a result of the ascent of the adjacentHarz mountains during theLower Cretaceous. Widely known as a classical exposure among geologists, the quarry had been extensively studied, and visited by students of geology for decades. Although rich in fossils of marine invertebrates, fossils of land-living animals had been rare. The sauropod tooth was the first specimen of a sauropod dinosaur from the Jurassic of northern Germany.[3]
After more fossil material was found, including bones, excavation of the bone-bearing layer commenced in April 1999, conducted by a local association of private fossil collectors. Although the quarry operator was cooperative, excavation was complicated by the near-vertical orientation of the layers that limited access, as well as by the ongoing quarrying. The sauropod material could not be excavated directly from the layer but had to be collected from lose blocks that resulting from blasting. The exact origin of the bone material was therefore unclear, but could later be traced to a single bed (bed 83).[3][4] An excavation conducted between July 20 and 28, 2000, rescued ca. 50 t (49 long tons; 55 short tons) of bone-bearing blocks containing vertebrate remains.[5] Fossils were prepared and stored in theDinosaur Park Münchehagen (DFMMh), a private dinosaur open-air museum located close toHanover. Due to the very good preservation of the bones, consolidating agents had to be applied only occasionally, and preparation could be conducted comparatively quickly as bone would separate easily from the surrounding rock. Bones of simple shape could sometimes be prepared in less than an hour, while the preparation of asacrum required a workload of three weeks. By January 2001, 200 single vertebrate bones had already been prepared. At this point, the highest bone density was found in a block measuring 70 x 70 cm, which contained ca. 20 bones.[4] By January 2002, preparation of an even larger block had revealed a partial sauropod skull – the first to be discovered in Europe. Before complete removal of the bones from the block, a silicon cast was made of the block to document the precise three-dimensional position of the individual bones.[5]
Part of theEuropasaurus fossil material got damaged or destroyed by arson fire on the night of 4–5 October 2003. The fire destroyed the laboratory and exhibition hall of the Dinosaur Park Münchehagen, resulting in the loss of 106 bones, which account for 15% of the bones prepared at the time. Furthermore, the fire affected most of the still unprepared blocks, with firefighting water hitting the hot stone causing additional crumbling.[6] Destroyed specimens include DFMMh/FV 100, which included the best preserved vertebral series and the only complete pelvis.[7][6]
In2006, the new sauropodtaxon was formally described asEuropasaurus holgeri. The givenetymology for thegenus name is "reptile from Europe", and the specific name honours Holger Lüdtke, the discoverer of the first fossils.[1] Given the comparatively small size of the bones, it was initially assumed that they stem from juvenile individuals. The 2006 publication, however, established that the majority of specimens were adult, and thatEuropasaurus was an island dwarf.[3] The number of individual sauropod bones had increased to 650 and include variously articulated individuals; the material was found within an area of 60–80 m (200–260 ft) squared.[2] From these specimens, theholotype was selected, a disarticulated but associated individual (DFMMh/FV 291).[2] The holotype includes multiplecranial bones (premaxilla,maxilla andquadratojugal), a partialbraincase, multiplemandible bones (dentary,surangular andangular), large amounts of teeth,cervical vertebrae,sacral vertebrae andribs from the neck and torso. At least 10 other individuals were referred to the same taxon based on overlap in material.
A large-scale excavation campaign commenced in the summer of 2012, with the goal to excavateEuropasaurus bones not only from lose blocks but directly from the rock layer. Access to the bone-bearing layer required the removal of some 600 tons of rock using excavators and wheel loaders, and the constant pumping out of water from the base of the quarry. Excavations continued in spring and summer 2013. The campaign resulted in the discovery of new fish, turtle, and crocodile remains, as well as valuable information of the bone-bearing layer; additionalEuropasaurus bones, however, could not be located. By 2014, around 1300 vertebrate bones had been prepared from bed 83, the majority of which stemming fromEuropasaurus; an estimated 3000 additional bones await preparation. A minimum number of 20 individuals was identified based on jaw bones.[3]
Europasaurus is a very small sauropod, measuring only 5.7–6.2 m (19–20 ft) long and weighed 750–2,100 kilograms (1,650–4,630 lb) as an adult.[1][8][9][10][11][12] This length was estimated based on a partial femur, scaled to the size of a nearly completeCamarasaurus specimen. Younger individuals are known, from sizes of 3.7 m (12 ft) to the youngest juvenile at 1.75 m (5.7 ft).[1][2]
Aside from being a very smallneosauropod,Europasaurus was thought to have multiple unique morphological features to distinguish it from close relatives by its original describers, Sanderet al. (2006[1]). The nasal process of the premaxilla was thought to curve anteriorly while projecting upwards (now known to be preservational[13]), there is a notch on the upper surface of thecentra of cervical vertebrae, thescapula has a prominent process on the posterior surface of its body, and theastragalus (an ankle bone) is twice as wide as tall.[1]
When compared toCamarasaurus,Europasaurus has a different morphology of thepostorbital where the posterior flange is not as short, a short contact between thenasal andfrontal bones of the skull, the shape of itsparietal (rectangular inEuropasaurus), and theneural spines of its vertebrae in front of thepelvis are unsplit. Comparisons withBrachiosaurus (now namedGiraffatitan) were also mentioned, and it was identified thatEuropasaurus has a shorter snout, a contact between the quadratojugal andsquamosal, and ahumerus (upper forelimb bone) that has flattened and alignedproximal anddistal surfaces. There were finally quick comparisons to the potential brachiosauridLusotitan, which has a differentilium and astragalus shape, andCetiosaurus humerocristatus (namedDuriatitan), which has adeltopectoral crest that is less prominent and extends across less of the humerus.[1]
Nearly all external skull bones have been preserved amongEuropasaurus specimens, except theprefrontals. Some additional bones are only represented by very fragmented and uninformative fossils, such as thelacrimals. Eight premaxillae are known, with a generally rectangular snout shape as found inCamarasaurus. The anterior projection of the premaxilla identified in Sanderet al. (2006[1]) was re-identified as a preservational artifact in Marpmannet al. (2014[13]), similar to the anatomy found inCamarasaurus andEuhelopus to a lesser degree. Thedorsal projection of the premaxilla, the one which contacts the nasal bone, begins as a postero-dorsal projection, before becoming straight vertical at the point of the subnarialforamen, until it reaches the nasal. This weak "step" is seen inCamarasaurus andEuhelopus, and is present more strongly inAbydosaurus,Giraffatitan and a possible skull ofBrachiosaurus. These latter taxa also have a longer snout, with more distance from the first tooth until the nasal process of the premaxilla. As well,Europasaurus shares with the basalcamarasauromorphs (brachiosaurids,Camarasaurus,Euhelopus andMalawisaurus) a similarly sizedorbit andnasal fenestra, whereas the nasal opening is significantly reduced in derived titanosaurs (Rapetosaurus,Tapuiasaurus andNemegtosaurus).[13]
A single maxilla is present in the well-preserved material ofEuropasaurus, DFMMh/FV 291.17. This maxilla has a long body, with two elongate processes, a nasal and a posterior process. There is only a weak lacrimal process, like in most sauropods exceptRapetosaurus. The nasal process is elongate and covers the anterior and ventral rim of theantorbital fenestra. This process extends about 120º from the horizontaltooth row. The base of the nasal process also forms the body of the lacrimal process, and at their divergence is the antorbital fenestra, similar in shape to those ofCamarasaurus,Euhelopus,Abydosaurus andGiraffatitan, but about 1/2 taller proportionally. The pre-antorbital fenestra, a small opening in front of or beneath the antorbital opening, is well developed in taxa likeDiplodocus andTapuiasaurus, is nearly absent, like inCamarasaurus andEuhelopus. There were about 12–13 total teeth in the maxilla ofEuropasaurus, fewer than in more basal taxa (16 teeth inJobaria and 14–25 inAtlasaurus), but falling within the range of variation in Brachiosauridae (15 inBrachiosaurus to 10 inAbydosaurus). All of the unworn teeth preserved display up to four smalldenticles on theirmesial edges. A small amount of the posterior tooth crowns are slightly twisted (~15º), but much less than in brachiosaurids (30–45º).[13]
Among the nasal bones ofEuropasaurus, several are known, but few are complete or undistorted. The nasals are overlapped posteriorly by thefrontal bones, and towards the side, they articulate bluntly with the prefrontals. Unlike the nasals ofGiraffatitan, those inEuropasaurus project horizontally forwards, forming a small portion of the skull roof over the antorbital fenestrae. Four frontals are known fromEuropasaurus, three being from the left and one being from the right. Because of their disarticulation, it is likely that the frontals never fused during growth, unlike inCamarasaurus. The frontals form a portion of the skull roof, articulating with other bones such as the nasals, parietals, prefrontals andpostorbitals, and they are longer antero-posteriorly than they are wide, a unique character among aeusauropodan. Like in diplodocoids (Amargasaurus,Dicraeosaurus andDiplodocus), as well asCamarasaurus, the frontals are excluded from the frontoparietal fenestra (or parietal fenestra when frontals are excluded). The frontals are also excluded from thesupratemporal fenestra margin (a widespread character in sauropods more derived thanShunosaurus), and they only have a small, unornamented participation in theorbit. Several parietal bones are known inEuropasaurus, which show a rectangular shape much wider than long. the parietals are also wide when viewed from the back of the skull, being slightly taller than theforamen magnum (spinal cord opening). The parietals contribute to about half the post-temporal fenestra (opening above the very back of the skull) border, with the other region enclosed by thesquamosal bones and some braincase bones. Parietals also form part of the edge of the supratemporal fenestra, which is wider than long inEuropasaurus, like inGiraffatitan,Camarasaurus andSpinophorosaurus. Besides the before mentioned fenestra, the parietals also have a "postparietal fenestra", something rarely seen outside ofDicraeosauridae. A triradiate postorbital bone is present inEuropasaurus, which evolved as the fusion of the postfrontal and postorbital bone of more basal taxa. Between the anterior and ventrally projecting processes the postorbital forms the margin of the orbit, and between the posterior and ventral processes it borders theinfratemporal fenestra.[13]
Multiple jugals are known fromEuropasaurus, which are more similar in morphology to basalsauropodomorphs than other macronarians. It forms part of the border of the orbit, infratemporal fenestra and the bottom edge of the skull, but does not reach the antorbital fenestra. The posterior process of the jugal are very fragile and narrow, showing a bone scar from the articulation with the quadratojugal. There are two prominences projecting from the back of the jugal body, which diverge at 75º and form the bottom and front edges of the infratemporal fenestra. Like inRiojasaurus andMassospondylus, two non-sauropod sauropodomorphs, the jugal forms a large part of the orbit edge, from the back to the front bottom corner. This feature has been seen inembryos of titanosaurs, but no adult individuals. Thequadratojugal bone is an elongate element that has two projecting arms, one anterior and one dorsal. Like in other sauropods, the anterior process is longer than the dorsal, but inEuropasaurus the arms are more similar lengths. The horizontal process is parallel to the tooth row ofEuropasaurus, similar to inCamarasaurus but unlike inGiraffatitan andAbydosaurus. There is a prominent ventral flange on the anterior arm of the bone, which is a possiblesynapomorphy of Brachiosauridae, although it is also found in someCamarasaurus individuals. The two quadratojugal processes diverge at a nearly right angle (90º), although the dorsal process curves as it follows the shape of thequadrate. Squamosals found fromEuropasaurus show the same approximate shape in lateral view asCamarasaurus, that of aquestion mark. The squamosals articulate with many skull bones, including those of the skull roof, those of the ventral skull, and those of the braincase. Like the postorbitals, the squamosals are triradiate, with a ventral, anterior andmedialprocess.[13]
There are thirteen preserved elements of thepalate ofEuropasaurus, including the quadrate,pterygoid andectopterygoid. The quadrates articulate with the palate and braincase bones, as well as the external skull bones. They are similar in shape to those ofGiraffatitan andCamarasaurus, and have well-developed articular surfaces. A single shaft is present for a majority of the quadrates length, with a pterygoid wing along the medial side. Pterygoids are the largest of the sauropod palate bones, and it has a triradiate shape, like the postorbitals. An anterior projection contacts the opposite pterygoid, while a lateral wing contacts the ectopterygoid, and a posterior wing supports the quadrate and basipterygoid (a bone that provides connection between the palate and the braincase). The ectopterygoid is a small palate bone, which articulates the central palate bones (pterygoid andpalatine) with the maxilla. Ectopterygoids are L-shaped, with an anterior process attaching to the maxilla, and a dorsal process that meets the pterygoid.[13]
The cervical vertebrae ofEuropasaurus are the best preserved and most represented of the vertebral column. However, not the entire neck is known, so the cervical number could be betweenCamarasaurus (12 vertebrae) andRapetosaurus (17 vertebrae). Additionally, the multiple cervical vertebrae come from different-aged individuals, and the centrum length and internal structure are known to change throughout development. The adult cervical centra are elongated andopisthocoelous (anterior end is ball-shaped), with a notch in the top of the rear end of the centrum. This feature was described as characteristic ofEuropasaurus but is also known inEuhelopus andGiraffatitan. In the side of the centra ofEuropasaurus there is an excavation which opens into the internalpneumaticity of the vertebrae. Unlike inGiraffatitan and brachiosaurids,Europasaurus does not have thin ridges (laminae) dividing this opening.Europasaurus shares laminae features on the upper vertebrae with basal macronarians and brachiosaurids. Differing from the anterior and middle cervicals, the posterior cervical vertebrae are less elongate, and taller proportionally, like in other macronarians, with significant changes in the positions of articular surfaces.[7]
Front dorsal vertebrae are strongly opisthocoelous like the cervicals, and can be placed in the series based on the absence of thehypantrum and lowparapophysis placement. The internal structures are open andcamerate likeCamarasaurus,Giraffatitan andGalvesaurus, but unlike these taxa this pneumaticity does not extend into the middle and posterior dorsal vertebrae. The arrangement and presence of anterior laminae inEuropasaurus is similar to other basal macronarians, but unlike more basal taxa (e.g.Mamenchisaurus,Haplocanthosaurus) and more derived taxa (e.g.Giraffatitan). The middle dorsals possess a pneumatic cavity that extends upwards into theneural arch, like inBarapasaurus,Cetiosaurus,Tehuelchesaurus, andCamarasaurus. The ventral edge of this opening is rhomboidal and well-defined. In the posterior vertebrae, the lateral pneumatic cavity has shifted higher on the centrum, a change seen in other basal macronarians. Thesepleurocoels are wide anteriorly, and narrow to become acutely angled posteriorly. Theneural spine ofEuropasaurus stands vertically, a basal feature not seen inBrachiosaurus or more derived sauropods.[7]
A series of all completesacral vertebrae is only known from a single specimen, DFMMh/FV 100, which was destroyed in a fire in 2003. All five vertebrae, the characteristic number of more basal neosauropods, are incorporated into thesacrum. The third and fourth sacrals represent the primordial sacrals, present in all dinosaur groups. The second, S2, is the ancestral sauropodomorph sacral that was added in basal sauropodomorphs, who all share three sacrals to the exception ofPlateosaurus. The fifth sacral, fused behind the primordial pair, is a caudosacral, migrated from the tail into the pelvis in taxa aroundLeonerasaurus. The first sacral, articulated with the ilium but not fused to the other vertebrae, represents the dorsosacral, bringing the count to five vertebrae found in all neosauropods. The level of fusion of the dorsosacral confirms the evolutionary history of the sauropod sacral count: the primordial pair incorporating first a dorsal (total of three), then a caudal (total of four), then another dorsal to make a total of five vertebrae.[7]
Among macronarians, fossilized skin impressions are only known fromHaestasaurus,Tehuelchesaurus andSaltasaurus. BothTehuelchesaurus andHaestasaurus may be closely related toEuropasaurus, and the characteristics of all sauropod skin impressions are similar.Haestasaurus, the first dinosaur known from skin impressions, preservedintegument over a portion of the arm around the elbow joint.[14] Dermal impressions are more widespread in the material ofTehuelchesaurus, where they are known from the areas of the forelimb, scapula and torso. There are no bony plates or nodules, to indicate armour, but there are several types of scales. The skin types ofTehuelchesaurus are overall more similar to those found in diplodocids andHaestasaurus than in the titanosaur embryos ofAuca Mahuevo.[15] As the shape and articulation of the preserved tubercles in these basal macronarians are similar in other taxa where skin is preserved, including specimens ofBrontosaurus excelsus and intermediate diplodocoids, such dermal structures are probably widespread throughout Neosauropoda.[14]
When it was first named,Europasaurus was considered to be a taxon within Macronaria that didn't fall within thefamily Brachiosauridae or thecladeTitanosauromorpha. This indicated that the dwarfism of the taxon was a result of evolution, instead of being a characteristic of a group.[1] Three matrices were analysed with the inclusion ofEuropasaurus, that of Wilson (2002[16]) and Upchurch (1998[17]) and Upchurchet al. (2004[18]). All analyses resulted in similar phylogenetics, whereEuropasaurus placed more derived thanCamarasaurus but outside a clade of Brachiosauridae and Titanosauromorpha (now namedTitanosauriformes). The results of the favoured analysis of Sanderet al. (2006) are shown below on the left:[2]
During a description of the vertebrae ofEuropasaurus by Carballido & Sander (2013), another phylogenetic analysis was conducted (right column above). The cladistic matrix was expanded to include more sauropod taxa, such asBellusaurus,Cedarosaurus andTapuiasaurus. The taxonBrachiosaurus was also separated into trueBrachiosaurus (B. altithorax) andGiraffatitan (B. brancai), based onTaylor (2009[19]). Based on this newer and more expansive analysis,Europasaurus was found to be in a similar placement, as a basal camarasauromorph closer to titanosaurs thanCamarasaurus. However,Euhelopus,Tehuelchesaurus,Tastavinsaurus andGalvesaurus were placed betweenEuropasaurus and Brachiosauridae.[7]
In a 2012 analysis of the phylogeny of Titanosauriformes, D'Emic (2012) consideredEuropasaurus to belong to Brachiosauridae, instead of being basal to the earliest brachiosaurids. The phylogeny resolved the most true brachiosaurids to date, although several potential brachiosaurids were instead determined to belong toSomphospondyli (Paluxysaurus,Sauroposeidon andQiaowanlong). However, D'Emic was tentative in consideringEuropasaurus to be a confirmed brachiosaurid. While there was strong support in the phylogeny for its placement,Europasaurus, one of few basal macronarians with a skull, lacks multiple bones that display characteristic features of the group, such as caudal vertebrae. The cladogram below on the left illustrates the phylogenetic results of D'Emic (2012), withEuhelopodidae and Titanosauria collapsed.[20]
A later analysis on titanosauriformes agreed with D'Emic (2012) in the placement ofEuropasaurus. It formed apolytomy withBrachiosaurus and the "FrenchBothriospondylus" (namedVouivria) as the basalmost brachiosaurids. Next most derived in the clade wasLusotitan, withGiraffatitan,Abydosaurus,Cedarosaurus andVenenosaurus forming a more derived clade of brachiosaurids. The "twisted" teeth ofEuropasaurus were found to be one of the unique features of Brachiosauridae, which could mean a confident referral of isolated sauropod teeth to the clade.[21]
A further phylogenetic analysis was performed on Brachiosauridae, based on that of D'Emic (2012). This phylogeny, conducted by D'Emicet al. (2016), resolved a very similar placement ofEuropasaurus within Brachiosauridae, althoughSonorasaurus was placed in a clade withGiraffatitan, andLusotitan was placed in a polytomy withAbydosaurus andCedarosaurus. The remaining tree was the same as in D'Emic (2012), althoughBrachiosaurus was collapsed into a polytomy with more derived brachiosaurids.[22] Another phylogeny, Mannionet al. (2017) found similar results to D'Emic (2012) and D'Emicet al. (2016).Europasaurus was the basalmost brachiosaurid, with the "French Bothriospondylus", orVouivria, as the next most basal brachiosaurid.Brachiosaurus was placed outside of a polytomy of all other brachiosaurids,Giraffatitan,Abydosaurus,Sonorasaurus,Cedarosaurus andVenenosaurus.[23] A 2017 phylogeny, that of Royo-Torreset al. (2017), resolved more complex relations within Brachiosauridae. BesidesEuropasaurus as the basalmost brachiosaurid, there were two subgroups within the clade, one containingGiraffatitan,Sonorasaurus andLusotitan, and another including almost all other brachiosaurids, as well asTastavinsaurus. This second clade would be termedLaurasiformes under the group's definition.Brachiosaurus was in a polytomy with the two subclades of Brachiosauridae. The phylogeny of Royo-Torreset al. (2017) can be seen above, in the right column.[24]
It was identified thatEuropasaurus was a unique dwarf species, and not a juvenile of an existing taxon likeCamarasaurus, by ahistology analysis of multiple specimens ofEuropasaurus. The youngest specimen (DFMMh/FV 009) was shown by this analysis to lack signs of aging such as growth marks orlaminar bone tissue, and is also the smallest specimen at 1.75 m (5.7 ft) in length. Such bone tissue is an indicator of rapid growth, so the specimen is probably a young juvenile. A larger specimen (DFMMh/FV 291.9) at 2 m (6.6 ft) shows large amounts of laminar tissue, with no growth marks present, so is likely a juvenile as well. The next smallest specimen (DFMMh/FV 001) has shows the presence of growth marks (specificallyannuli), and at the length of 3.5 m (11 ft) is possibly a subadult. Further larger, DFMMh/FV 495 displays matureosteons as well as annuli, and is 3.7 m (12 ft). The second largest analysed specimen (DFMMh/FV 153) also shows growth marks, but they are more frequent. This specimen is 4.2 m (14 ft). A single partial femur represents the largest knownEuropasaurus individual, at a body length of 6.2 m (20 ft). Unlike all other specimens, this one (DFMMh/FV 415) shows the presence oflines of arrested growth, indicating it died after reaching full body size. The internal bone is also partiallylamellar, which shows it had stopped growing recently.[1][2]
These combinations of growth factors show thatEuropasaurus developed its small size because of a largely reduced growth rate, gaining size slower than larger taxa such asCamarasaurus. This slowing growth rate is the opposite of the general trend of sauropods andtheropods, who reached greater sizes with increased growth rates.[1] Some of the close relatives ofEuropasaurus represent thelargest dinosaurs known, includingBrachiosaurus andSauroposeidon. Marpmannet al. (2014) proposed that the small size and reduced growth rate ofEuropasaurus was an effect ofpedomorphism, where the adults of taxa retain juvenile characteristics, such as size.[13]
Examinations of the inner ears of infantEuropasaurus suggest they were precocial, and it is suggested that they would have been reliant on the protections of adults in a herd to some degree, something not seen in larger sauropods due to the massive size difference in parent and offspring. The structure and long length of the inner ear in this genus also suggests that they had good senses of hearing, withEuropasaurus. Intraspecific communication was also apparently important to this sauropod, based on these studies, suggesting this sauropod displayed clear, gregarious behavior.[25]
It has been suggested that an ancestor ofEuropasaurus would have quickly decreased in body size after emigrating to an island that existed at the time, as the largest of the islands in the region around northern Germany was smaller than 200,000 km (120,000 mi) squared, which may not have been able to support a community of large sauropods. Alternately, a macronarian may have shrunken concurrently with a larger landmass, until achieving the size ofEuropasaurus.[1] Previous studies on insular (island) dwarfism are largely restricted to theMaastrichtian ofHaţeg Island inRomania, home to the dwarf titanosaurMagyarosaurus and the dwarfhadrosaurTelmatosaurus.[1][26][27]Telmatosaurus is known to be from a small adult, and although it is very small,Magyarosaurus specimens of small sizes are known to be from adult to old individuals.[27][28]Magyarosaurus dacus adults were a similar body size toEuropasaurus, but the largest of the latter had longer femora than the largest of the former, whileMagyarosaurus hungaricus was significantly larger than either taxon.[28] The dwarfism inEuropasaurus represents the only significant rapid body mass change in derivedSauropodomorpha, with the general trend of taxa being a growth in overall size in other groups.[29]
The Langenberg locality in Germany, from the early Oxfordian to late Kimmeridgian, displays the variety of plant and animal life from an island ecosystem from the late Jurassic.[30] During the Kimmeridgian the locality would have been marine, being located between the Rhenisch, Bohemian, and London-BrabantMassifs. This does not indicate that the taxa present weremarine, as the animals and plants may have been depositedallochthonously (albeit only by a short distance) from the surrounding islands.[31] The sediments to show that there was an occasional influx of fresh orbrackish water, and the fossils preserved display that. There are large numbers of marinebivalve fossils, as well asechinoderms and microfossils present in the limestone of the quarry, although many of theanimals andplants were terrestrial.[32]
Many marine taxa are preserved at Langenberg, although they would not have co-existed often withEuropasaurus. There are at least threeturtle genera,Plesiochelys,Thalassemys and up to two unnamed taxa.[30][33][34]Actinopterygian fish are abundant, being represented byLepidotes,Macromesodon,Proscinetes,Coelodus,Macrosemius,Notagogus,Histionotus,Ionoscopus,Callopterus,Caturus,Sauropsis,Belonostomus, andThrissops.[35] Also present are at least five distinct morphologies ofhybodont sharks, theneoselachiansPalaeoscyllium,Synechodus andAsterodermus.[36] Two marinecrocodyliforms are known from Langenberg,Machimosaurus andSteneosaurus, which likely fed off turtles and fish, and the amphibious crocodyliformGoniopholis has also been found.[37]
Conifer cones and twigs can be identified as thearaucarianBrachyphyllum, from the terrestrial fossils of the site. Deposited in the locality are many taxa, including a large accumulation ofEuropasaurus bones and individuals. At least 450 bones fromEuropasaurus were recovered from the Langenberg Quarry, with about 1/3 bearing tooth marks.[30] Of these tooth marks, the sizes and shapes match well with the teeth offish, crocodyliforms or other scavengers, but no confirmed theropod marks.[30][38] The high number of individuals present suggests that a herd ofEuropasaurus was crossing atidal zone and drowned.[30] While the dominant large-bodied animal present isEuropasaurus, there is also material from a diplodocid sauropod, astegosaurian, and multiple theropods. Three cervicals of the diplodocid are preserved, and from their size it is possible that the taxon was also a dwarf. The stegosaurian and variety of theropods only preserve teeth, with the exception of a few bones possibly from a taxon inCeratosauridae.[30] Isolated teeth show that there were at least four different types oftheropods present at the locality, including themegalosauridTorvosaurus sp. as well as an additional megalosaurid and indeterminate members of theAllosauridae andCeratosauria; and there are also the oldest teeth known fromVelociraptorinae.[39][40]
Besides the dinosaurs, many small-bodied terrestrial vertebrates are also preserved in the Langenberg quarry. Such animals include a well-preserved three-dimensionalpterosaur skeleton fromDsungaripteridae, and isolated remains fromOrnithocheiroidea andCtenochasmatidae; aparamacellodidlizard; and partial skeletons and skulls from a relative ofTheriosuchus now named as the genusKnoetschkesuchus.[30][31][33] Teeth fromdryolestid mammals are also preserved, as well as adocodont, a taxon inEobaataridae, and amultituberculate with similarities toProalbionbataar (now namedTeutonodon).[30][41]
Dinosaur footprints preserved at the Langenberg Quarry display a possible reason for the extinction ofEuropasaurus, and potentially other insular dwarfs present on the islands of the region. The footprints are located 5 m (16 ft) above the deposit ofEuropasaurus individuals, which shows that at least 35,000 years after that deposit there was a drop in sea level which allowed for a faunal overturn. The inhabiting theropods of the island, that coexisted withEuropasaurus, would have been about 4 m (13 ft), but the theropods that arrived over the land bridge preserve footprints up to 54 cm (21 in), which indicates a body size between 7 and 8 m (23 and 26 ft) if reconstructed as anallosaurian. It was suggested by the describers of these tracks (Jens Lallensack and colleagues), that these theropod taxa likely made the specialized dwarf fauna extinct, and the bed from which the footprints originated (Langenberg bed 92) is probably the youngest in whichEuropasaurus is present.[42][43]
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