With a claw of about 20 (!) centimeters, the crab – which lived about 8.8 million years ago – is in a class of its own.

Researchers – including a scientist from Utrecht University – write this in New Zealand Journal of Geology and Geophysics. Their study concerns a fossil crab discovered on a beach located on the northern island of New Zealand. “I continuously research fossil crabs that are new or interesting to science,” says researcher Barry van Bakel Scientias.nl. “But such a large fossil crab is unique.”

Extremely large
The fossil remains reveal that the crab possessed scissors about 20 centimeters long. His shield was even slightly larger. And that makes the crab ‘extremely large’, at least compared to other fossilized crabs, according to Bakel. The crab is slightly less impressive when we look at its only living descendant. Because it can become even bigger, says Van Bakel. “Its modern relative, the Giant Southern Crab or Tasmanian giant crab, will grow at least twice as big! We think that this fossil ancestor could also have grown larger, but we are waiting for additional material to be found.”

New species
Pending more material and research, scientists can conclude that the fossil giant crab belongs to a previously undescribed species. The researchers have named this one Pseudocarcinus karlraubenheimeri datum.

Unique
The fact that the researchers have been able to describe the new species is quite unique. “Firstly, because these (crabs, ed.) do not easily fossilize completely, but also because it was unexpected that we encountered this group in New Zealand.” This is how the on lives P. karlraubenheimeri related Tasmanian crab only found in Australian waters.

Habitat
In addition P. karlraubenheimeri of course also unique because of its size. “The size is unique and requires special circumstances,” says Van Bakel. Thus, such giant crabs require the presence of quite a bit of food and minerals in the water. The water must also have a certain temperature. “This is a precise mix that occurs almost nowhere.” But it seems like 8.8 million years ago P. karlraubenheimeri near what is now the northern island of New Zealand, everything was in such order that it could reach the enormous size mentioned earlier. “Its habitat, which we investigated and reconstructed, was unique,” ​​says Van Bakel. “Several million years before this crab lived, an undersea volcanic chain spread a lot of volcanic material (ash) over the area. There were a lot of gases in the seabed. Where these rose, ‘volcanic pipes’ formed, with warmer, nutritious water. There a small fauna emerged with shells, snails, and small crabs and hermit crabs.” And they prepared the menu P. karlraubenheimeri. “He cracked these animals with his large scissors with robust ‘teeth’.”

Implications
The research by Van Bakel and colleague Àlex Ossó not only results in the description of a new species. But also in a fairly detailed description of the ecosystem of which he was part. “We have become aware of a unique ecological community from prehistoric New Zealand,” says Van Bakel. In addition, the research also provides more insight into the history of the giant crabs belonging to the genus Pseudocarcinus. “The geological history of this special group of giant crabs has become clear in one go.”

Whether scientists can expect more of these types of meaningful discoveries in New Zealand is doubtful and therefore makes the work of Van Bakel and colleagues even more unique. “We suspect that these giant crabs – and large crabs in New Zealand in general – went extinct after the Miocene. The environment changed mainly due to the inactivity of volcanism and the drifting away of Australia. I would therefore expect new discoveries sooner in Australia.”




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