Europasaurus

Europasaurus, meaning 'Europe lizard', was a type of early sauropod, which were large, four-legged herbivorous dinosaurs. It lived during the Late Jurassic period, around 154 to 151 million years ago, in what is now northern Germany.

This dinosaur is special because it shows a phenomenon called insular dwarfism. This means that the population of Europasaurus lived on an island in the Lower Saxony basin, and because they were isolated, they grew to be smaller than related dinosaurs elsewhere. Europasaurus is a good example of how animals can change size when they live in places far away from others of their kind.

Discovery and naming

In 1998, a single tooth from a large plant-eating dinosaur was found by a fossil collector at Langenberg Mountain in Germany. This was the first time scientists found dinosaur bones from the Jurassic period in northern Germany.

More bones were found later, and scientists began digging up the area. They discovered many dinosaur bones stored in rocks. Some of these rocks had to be broken apart to find the bones inside. By 2001, they had prepared 200 bones, and by 2002, they found the first partial dinosaur skull ever discovered in Europe. Sadly, a fire in 2003 damaged some of the fossils before they could be studied.

In 2006, scientists officially named the dinosaur Europasaurus holgeri. They named it after Europe and the man who found the first tooth. The bones were small, so they first thought they were from baby dinosaurs. But later, they learned these were adult dinosaurs that had grown small because they lived on an island with limited food. Scientists have found over 650 bones from at least 20 different individuals.

Description

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. 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).

Aside from being a very small neosauropod, Europasaurus was thought to have multiple unique morphological features to distinguish it from close relatives by its original describers, Sander et al. (2006). When compared to Camarasaurus, Europasaurus has a different morphology of the postorbital where the posterior flange is not as short, a short contact between the nasal and frontal bones of the skull, the shape of its parietal (rectangular in Europasaurus), and the neural spines of its vertebrae in front of the pelvis are unsplit. Comparisons with Brachiosaurus (now named Giraffatitan) were also mentioned.

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

Among macronarians, fossilized skin impressions are only known from Haestasaurus, Tehuelchesaurus and Saltasaurus. The skin types of Tehuelchesaurus are overall more similar to those found in diplodocids and Haestasaurus than in the titanosaur embryos of Auca Mahuevo.

Classification

When scientists first discovered Europasaurus, they thought it was a special type of dinosaur that didn’t belong to certain groups called Brachiosauridae or Titanosauromorpha. This suggested that its small size came from evolution, not because it was part of a specific group. Many studies looked at Europasaurus and found it to be more advanced than another dinosaur called Camarasaurus, but not part of the Brachiosauridae and Titanosauromorpha groups. Later studies placed Europasaurus close to another group of dinosaurs called titanosaurs.

Some scientists later thought Europasaurus might belong to the Brachiosauridae group. While there was some support for this, Europasaurus didn’t have all the bones needed to be certain. More recent studies still place Europasaurus among the brachiosaurids, but its exact position continues to be studied by scientists.

Paleobiology

Growth

Scientists studied the bones of Europasaurus and found that it was a small dinosaur on purpose, not just a baby. They looked at many fossils and saw that even the biggest ones were smaller than other similar dinosaurs. This shows that Europasaurus grew slower and stayed small.

Dwarfism

Europasaurus might have become small because its ancestors lived on an island that was too tiny to support big dinosaurs. This is called island dwarfism. Other small dinosaurs lived on islands too, but Europasaurus is special because it shows a big, fast change in size compared to its relatives.

Palaeoecology

The Langenberg locality in Germany shows what life was like on an island during the late Jurassic period. Although this area was mostly underwater at the time, many animals and plants from nearby islands were washed into the area. We can see fossils of sea creatures like clams and fish, but most of the animals and plants found there lived on land.

Scientists have found many dinosaur bones at Langenberg, including over 450 bones from Europasaurus. Some of these bones have marks from teeth, likely left by fish or other animals that might have eaten them. Besides Europasaurus, fossils from other dinosaurs like stegosaurs and different types of meat-eating dinosaurs have also been found there.

Extinction

Fossil footprints found above the Europasaurus bones suggest a reason why Europasaurus and other small dinosaurs on the island might have gone extinct. These footprints are from much larger meat-eating dinosaurs that arrived on the island after sea levels dropped. The new, larger dinosaurs may have outcompeted the smaller ones for food and space, leading to the end of Europasaurus and other small dinosaur species on the island.