Europasaurus

Extinct genus of dinosaurs
Speciesbox
|fossil range = Late Jurassic,
|image = Europasaurus holgeri. jpg
|image alt = Restored mount of the holotype specimen
|image caption = Reconstructed skeleton, Aathal Dinosaur Museum
|display parents = 2
|genus = Europasaurus
|parent authority = Mateus et al. in Sander et al., 2006

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). Fossils were prepared and stored in the Dinosaur Park Münchehagen (DFMMh), a private dinosaur open air museum located close to Hanover. 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 a sacrum 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. 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. Destroyed specimens include DFMMh/FV 100, which included the best preserved vertebral series and the only complete pelvis. 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 that Europasaurus was an island dwarf. The holotype includes multiple cranial bones (premaxilla, maxilla and quadratojugal), a partial braincase, multiple mandible bones (dentary, surangular and angular), large amounts of teeth, cervical vertebrae, sacral vertebrae and ribs 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 excavate Europasaurus 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; additional Europasaurus bones, however, could not be located. By 2014, around 1300 vertebrate bones had been prepared from bed 83, the majority of which stemming from Europasaurus; an estimated 3000 additional bones await preparation. A minimum number of 20 individuals was identified based on jaw bones. This length was estimated based on a partial femur, scaled to the size of a nearly complete Camarasaurus specimen. Younger individuals are known, from sizes of to the youngest juvenile at As the shape and articulation of the preserved tubercles in these basal macronarians are similar in other taxa where skin is preserved, including specimens of Brontosaurus excelsus and intermediate diplodocoids, such dermal structures are probably widespread throughout Neosauropoda.

When it was first named, Europasaurus was considered to be a taxon within Macronaria that didn't fall within the family Brachiosauridae or the clade Titanosauromorpha. This indicated that the dwarfism of the taxon was a result of evolution, instead of being a characteristic of a group.) and Upchurch (1998) and Upchurch et al. (2004). All analyses resulted in similar phylogenetics, where Europasaurus placed more derived than Camarasaurus but outside a clade of Brachiosauridae and Titanosauromorpha (now named Titanosauriformes). The results of the favoured analysis of Sander et al. (2006) are shown below on the left:). Based on this newer and more expansive analysis, Europasaurus was found to be in a similar placement, as a basal camarasauromorph closer to titanosaurs than Camarasaurus. However, Euhelopus, Tehuelchesaurus, Tastavinsaurus and Galvesaurus were placed between Europasaurus and Brachiosauridae.

In a 2012 analysis of the phylogeny of Titanosauriformes, D'Emic (2012) considered Europasaurus 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 to Somphospondyli (Paluxysaurus, Sauroposeidon and Qiaowanlong). However, D'Emic was tentative in considering Europasaurus 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), with Euhelopodidae and Titanosauria collapsed. A later analysis on titanosauriformes agreed with D'Emic (2012) in the placement of Europasaurus. It formed a polytomy with Brachiosaurus and the "French Bothriospondylus" (named Vouivria) as the basalmost brachiosaurids. Next most derived in the clade was Lusotitan, with Giraffatitan, Abydosaurus, Cedarosaurus and Venenosaurus forming a more derived clade of brachiosaurids. The "twisted" teeth of Europasaurus were found to be one of the unique features of Brachiosauridae, which could mean a confident referral of isolated sauropod teeth to the clade. A further phylogenetic analysis was performed on Brachiosauridae, based on that of D'Emic (2012). This phylogeny, conducted by D'Emic et al. (2016), resolved a very similar placement of Europasaurus within Brachiosauridae, although Sonorasaurus was placed in a clade with Giraffatitan, and Lusotitan was placed in a polytomy with Abydosaurus and Cedarosaurus. The remaining tree was the same as in D'Emic (2012), although Brachiosaurus was collapsed into a polytomy with more derived brachiosaurids. Another phylogeny, Mannion et al. (2017) found similar results to D'Emic (2012) and D'Emic et al. (2016). Europasaurus was the basalmost brachiosaurid, with the "French Bothriospondylus", or Vouivria, as the next most basal brachiosaurid. Brachiosaurus was placed outside of a poltomy of all other brachiosaurids, Giraffatitan, Abydosaurus, Sonorasaurus, Cedarosaurus and Venenosaurus. A 2017 phylogeny, that of Royo Torres et al. (2017), resolved more complex relations within Brachiosauridae. Besides Europasaurus as the basalmost brachiosaurid, there were two subgroups within the clade, one containing Giraffatitan, Sonorasaurus and Lusotitan, and another including almost all other brachiosaurids, as well as Tastavinsaurus. This second clade would be termed Laurasiformes under the group's definition. Brachiosaurus was in a polytomy with the two subclades of Brachiosauridae. The phylogeny of Royo Torres et al. (2017) can be seen above, in the right column.

It was identified that Europasaurus was a unique dwarf species, and not a juvenile of an existing taxon like Camarasaurus, by a histology analysis of multiple specimens of Europasaurus. The youngest specimen (DFMMh/FV 009) was shown by this analysis to lack signs of aging such as growth marks or laminar bone tissue, and is also the smallest specimen at 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 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 (specifically annuli), and at the length of is possibly a subadult. Further larger, DFMMh/FV 495 displays mature osteons as well as annuli, and is The second largest analysed specimen (DFMMh/FV 153) also shows growth marks, but they are more frequent. This specimen is A single partial femur represents the largest known Europasaurus individual, at a body length of Unlike all other specimens, this one (DFMMh/FV 415) shows the presence of lines of arrested growth, indicating it died after reaching full body size. The internal bone is also partially lamellar, which shows it had stopped growing recently. Examinations of the inner ears of infant Europasaurus 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, with Europasaurus. Intraspecific communication was also apparently important to this sauropod, based on these studies, suggesting this sauropod displayed clear, gregarious behavior.

It has been suggested that an ancestor of Europasaurus 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 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 of Europasaurus. 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. Magyarosaurus dacus adults were a similar body size to Europasaurus, but the largest of the latter had longer femora than the largest of the former, while Magyarosaurus hungaricus was significantly larger than either taxon.

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. The sediments to show that there was an occasional influx of fresh or brackish water, and the fossils preserved display that. There are large numbers of marine bivalve fossils, as well as echinoderms and microfossils present in the limestone of the quarry, although many of the animals and plants were terrestrial. Many marine taxa are preserved at Langenberg, although they would not have co existed often with Europasaurus. There are at least three turtle genera, Plesiochelys, Thalassemys and up to two unnamed taxa. Actinopterygian fish are abundant, being represented by Lepidotes, Macromesodon, Proscinetes, Coelodus, Macrosemius, Notagogus, Histionotus, Ionoscopus, Callopterus, Caturus, Sauropsis, Belonostomus, and Thrissops. Also present are at least five distinct morphologies of hybodont sharks, the neoselachians Palaeoscyllium, Synechodus and Asterodermus. Two marine crocodyliforms are known from Langenberg, Machimosaurus and Steneosaurus, which likely fed off turtles and fish, and the amphibious crocodyliform Goniopholis has also been found. Conifer cones and twigs can be identified as the araucarian Brachyphyllum, from the terrestrial fossils of the site. Deposited in the locality are many taxa, including a large accumulation of Europasaurus bones and individuals. At least 450 bones from Europasaurus were recovered from the Langenberg Quarry, with about 1/3 bearing tooth marks. The high number of individuals present suggests that a herd of Europasaurus was crossing a tidal zone and drowned. Besides the dinosaurs, many small bodied terrestrial vertebrates are also preserved in the Langenberg quarry. Such animals include a well preserved three dimensional pterosaur skeleton from Dsungaripteridae, and isolated remains from Ornithocheiroidea and Ctenochasmatidae; a paramacellodid lizard; and partial skeletons and skulls from a relative of Theriosuchus now named as the genus Knoetschkesuchus.

Dinosaur footprints preserved at the Langenberg Quarry display a possible reason for the extinction of Europasaurus, and potentially other insular dwarfs present on the islands of the region. The footprints are located above the deposit of Europasaurus 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 with Europasaurus, would have been about , but the theropods that arrived over the land bridge preserve footprints
up to , which indicates a body size between if reconstructed as an allosaurian. 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 which Europasaurus is present.