Europasaurus

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Europasaurus
Temporal range:
Ma
↓
Restored mount of the holotype specimen
Reconstructed skeleton, Aathal Dinosaur Museum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Clade: †Sauropoda
Clade: †Macronaria
Clade: †
Camarasauromorpha
Genus: †Europasaurus
Mateus et al. in Sander et al., 2006[1]
Species:
†E. holgeri
Binomial name
†Europasaurus holgeri
Mateus et al. in Sander et al., 2006[1]

Europasaurus is a basal

herbivorous dinosaur. It lived during the Late Jurassic (middle Kimmeridgian, about 154 million years ago) of northern Germany, and has been identified as an example of insular dwarfism resulting from the isolation of a sauropod population on an island within the Lower Saxony
basin.

Discovery and naming

Preparation of the fossil bones

In 1998, a single sauropod tooth was discovered by private fossil collector Holger Lüdtke in an active quarry at

Lower 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 20–28 of 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 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.[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 the Europasaurus fossil material got damaged or destroyed by arson fire in the night from the 4th to the 5th of 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]

Block with partially prepared bones of specimen DFMMh/FV 709

In

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.[3]

Description

Europasaurus is a very small sauropod, measuring only 5.7–6.2 m (19–20 ft) long and weighed 750–800 kilograms (1,650–1,760 lb) as an adult.[1][8][9] 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 3.7 m (12 ft) to the youngest juvenile at 1.75 m (5.7 ft).[1][2]

Distinguishing characteristics

Life restoration
of Europasaurus in its habitat

Aside from being a very small

centra of cervical vertebrae, the scapula has a prominent process on the posterior surface of its body, and the astragalus (an ankle bone) is twice as wide as tall.[1]

When compared to Camarasaurus, Europasaurus has a different morphology of the

Cetiosaurus humerocristatus (named Duriatitan), which has a deltopectoral crest that is less prominent and extends across less of the humerus.[1]

Skull

Reconstructed skull

Nearly all external skull bones have been preserved among Europasaurus specimens, except the

nasal fenestra, whereas the nasal opening is significantly reduced in derived titanosaurs (Rapetosaurus, Tapuiasaurus and Nemegtosaurus).[10]

Teeth of the upper jaw

A single maxilla is present in the well-preserved material of Europasaurus, 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 except Rapetosaurus. The nasal process is elongate and covers the anterior and ventral rim of the

mesial edges. A small amount of the posterior tooth crowns are slightly twisted (~15º), but much less than in brachiosaurids (30–45º).[10]

Skulls of two dicraeosaurids in dorsal view, showing the placement of the parietal fenestra and the postparietal foramen

Among the nasal bones of Europasaurus, several are known, but few are complete or undistorted. The nasals are overlapped posteriorly by the

infratemporal fenestra.[10]

Skull of Massospondylus with fenestrae labelled. The jugal is similar in form to that of Europasaurus

Multiple jugals are known from Europasaurus, which are more similar in morphology to basal

synapomorphy of Brachiosauridae, although it is also found in some Camarasaurus individuals. The two quadratojugal processes diverge at a nearly right angle (90º), although the dorsal process curves as it follows the shape of the quadrate. Squamosals found from Europasaurus show the same approximate shape in lateral view as Camarasaurus, that of a question 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 and medial
process.[10]

There are thirteen preserved elements of the

ectopterygoid. The quadrates articulate with the palate and braincase bones, as well as the external skull bones. They are similar in shape to those of Giraffatitan and Camarasaurus, 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 and palatine) with the maxilla. Ectopterygoids are L-shaped, with an anterior process attaching to the maxilla, and a dorsal process that meets the pterygoid.[10]

Vertebrae

Articulated neck-vertebrae of specimen DFMMh/FV 838

The cervical vertebrae of Europasaurus are the best preserved and most represented of the vertebral column. However, not the entire neck is known, so the cervical number could be between Camarasaurus (12 vertebrae) and Rapetosaurus (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 and opisthocoelous (anterior end is ball-shaped), with a notch in the top of the rear end of the centrum. This feature was described as characteristic of Europasaurus but is also known in Euhelopus and Giraffatitan. In the side of the centra of Europasaurus there is an excavation which opens into the internal pneumaticity of the vertebrae. Unlike in Giraffatitan 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]

Two back-vertebrae

Front dorsal vertebrae are strongly opisthocoelous like the cervicals, and can be placed in the series based on the absence of the hypantrum and low parapophysis placement. The internal structures are open and camerate like Camarasaurus, Giraffatitan and Galvesaurus, but unlike these taxa this pneumaticity does not extend into the middle and posterior dorsal vertebrae. The arrangement and presence of anterior laminae in Europasaurus 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 the neural arch, like in Barapasaurus, Cetiosaurus, Tehuelchesaurus, and Camarasaurus. 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. These pleurocoels are wide anteriorly, and narrow to become acutely angled posteriorly. The neural spine of Europasaurus stands vertically, a basal feature not seen in Brachiosaurus or more derived sauropods.[7]

A series of all complete sacral 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 the sacrum. 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 of Plateosaurus. The fifth sacral, fused behind the primordial pair, is a caudosacral, migrated from the tail into the pelvis in taxa around Leonerasaurus. 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]

Skin

Among macronarians, fossilized skin impressions are only known from

Brontosaurus excelsus and intermediate diplodocoids, such dermal structures are probably widespread throughout Neosauropoda.[11]

Classification

When it was first named, Europasaurus was considered to be a taxon within Macronaria that didn't fall within the

Titanosauriformes). The results of the favoured analysis of Sander et al. (2006) are shown below on the left:[2]

Back-vertebra in front view

During a description of the vertebrae of Europasaurus by Carballido & Sander (2013), another phylogenetic analysis was conducted (right column above). The cladistic matrix was expanded to include more sauropod taxa, such as

Taylor (2009[16]). 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.[7]

Placement as a brachiosaurid

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

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.[17]

Skull compared to that of related Giraffatitan

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.[18]

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.[19] 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.[20] 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.[21]

Paleobiology

Growth

Lower jaws at various growth stages

It was identified that Europasaurus was a unique dwarf species, and not a juvenile of an existing taxon like Camarasaurus, by a

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.[1][2]

These combinations of growth factors show that Europasaurus developed its small size because of a largely reduced growth rate, gaining size slower than larger taxa such as Camarasaurus. This slowing growth rate is the opposite of the general trend of sauropods and

theropods, who reached greater sizes with increased growth rates.[1] Some of the close relatives of Europasaurus represent the largest dinosaurs known, including Brachiosaurus and Sauroposeidon. Marpmann et al. (2014) proposed that the small size and reduced growth rate of Europasaurus was an effect of pedomorphism, where the adults of taxa retain juvenile characteristics, such as size.[10]

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.[22]

Dwarfism

Reconstructed adult and juvenile skeletons; note humans for scale

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 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 of Europasaurus.

hadrosaur Telmatosaurus.[1][23][24] 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.[24][25] 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.[25] The dwarfism in Europasaurus represents the only significant rapid body mass change in derived Sauropodomorpha, with the general trend of taxa being a growth in overall size in other groups.[26]

Palaeoecology

Late Jurassic terrestrial localities in Europe. '7' indicates the Langenberg Quarry

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.

bivalve fossils, as well as echinoderms and microfossils present in the limestone of the quarry, although many of the animals and plants were terrestrial.[29]

Many marine taxa are preserved at Langenberg, although they would not have co-existed often with Europasaurus. There are at least three

crocodyliforms are known from Langenberg, Machimosaurus and Steneosaurus, which likely fed off turtles and fish, and the amphibious crocodyliform Goniopholis has also been found.[34]

Skeleton of coexisting Knoetschkesuchus

tidal zone and drowned.[27] While the dominant large-bodied animal present is Europasaurus, there is also material from a diplodocid sauropod, a stegosaurian, 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 in Ceratosauridae.[27] Isolated teeth show that there were at least four different types of theropods present at the locality, including the megalosaurid Torvosaurus sp. as well as an additional megalosaurid and indeterminate members of the Allosauridae and Ceratosauria; and there are also the oldest teeth known from Velociraptorinae.[36][37]

Besides the dinosaurs, many small-bodied terrestrial vertebrates are also preserved in the Langenberg quarry. Such animals include a well-preserved three-dimensional

Teutonodon).[27][38]

Extinction

Size comparison of the native torvosaur (blue) and arriving theropod (green)

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 5 m (16 ft) 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 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 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.[39][40]

References

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Further reading

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