New spider family discovered in Europe

First Record of the spider family Hersiliidae from the Mesozoic of Europe

Summarized by Devan Legendre, a geology major at the University of South Florida. He is currently a senior in his last semester. Once he earns his degree, he plans to work in the geotechnical industry and gain experience to actively promote himself within the field. When he’s not studying geology, he enjoys running long distances to clear his head and gain new insight. 

Hypothesis: The aim of this study is to describe a new male spider found in ajkaite (sulfur-bearing resin found in brown coal) from the Ajka Coal Formation in Hungary and place the male spider in a new taxonomic group. The climate and the environment in which the resin was found was used to evaluate the current environmental description for the Ajka Coal Formation and better predict past environments. 

Data used: Arachnid fossils that are found preserved in amber resin offer a unique glimpse into the build of arachnid fossils, which usually don’t have their legs preserved.  The amber provides a preservation that is often entirely complete, shows the entire body build, and has a level of detail not often found in other methods of preservation for fossils. This can also help to understand the behavior and ecology of arachnids. The amber fossils used in this study are from the Ajka Coal Formation in Hungary that is one of two areas known for Mesozoic amber inclusions dated between 86 to 83 million years of age.

Methods: The chunk of ajkaite resin for this study was almost completely opaque, making it too dark for examination by light microscope. An X-ray tomograph from the University of Pannonia in Veszprem, Hungary was used to scan the large chunk of ajkaite. Upon scanning, multiple arthropod inclusions were discovered inside the chunk, including a relatively large sized spider. To achieve a better resolution scan on the spider, the ajkaite was broken to a smaller size for easier scans. A micro-computed tomography scanner in Hamburg, Germany used multiple images taken at various specifications along with specialized computer programs in Matlab, and the Astra Toolbox. 

Results: The images taken allowed scientists to identify a short third pair of legs and lateral spinnerets unique to the Hersiliidae family of spiders, that differs from the extinct and extant families. The specimen can be seen in Figure 1.  This is why scientists proposed the Hungarosilia genus to accommodate the new arachnid fossil. Based on drill cores samples, the climate for the Ajka Coal Formation has been projected as tropical, with large amounts of rain. The forests were likely fern dominated in the subtropical or tropical environment.

A dark mass with multiple protruding stick like objects (the spider body and limbs), as well as two pointy objects coming from the rear of said dark mass. The pointy objects are the spinnerets, it appears. Entire body is about 3 mm in height; with legs, about 6 mm in width.
An image of the spider scanned from the amber inclusion, that was found in the Ajka Coal Formation in Europe. Hails from the Mesozoic time period. Scale bar = 2 mm

Why is this study important? This specimen is unique in that it is a new genus of spider from the Mesozoic. The only other genera in this spider family that have been described so far are Burmesiola and Spinasilia, both of which were found in amber from Myanmar. These two genera have distinct differences that set them apart from the newly found specimen, which differs mainly with the longer rear end, triangular separation between the spinnerets, and short middle section. 

Broader implications beyond this paper: Up until this specimen was found, there have been very few spiders or spider-related inclusions found in the Ajka Coal Formation . With the identification of this specimen, the Hersiliidae family of spider establishes the oldest known record for this family in Europe, as well as being the second record of this fossil from the Mesozoic. The discovery of this specimen has greatly improved the knowledge on the Mesozoic diversity of the family Hersiliidae, and the Ajka Coal formations paleoenvironment. Further specimens may help to expand the diversity of spiders in the Mesozoic of Europe.

Citation: Szabo, Marton, Jörg U. Hammel, Danilo Harms, Ulrich Kotthoff, Emese Bodor, Janos Novak, Kristof Kovacs, and Attila Ősi. “First record of the spider family Hersiliidae (Araneae) from the Mesozoic of Europe (Bakony Mts, Hungary).” Cretaceous Research 131 (2022): 105097.