Wednesday 19 December 2012

Goblin Spiders from Cretaceous Amber.

Goblin Spiders (Oonopidae) are one of the most abundant groups of Spiders, with at least 600 and possibly over 1000 extant species described, though this is generally considered to be a poor representation of their diversity, since the Spiders are tiny (often under 1 mm) and at their most abundant in the tropics. Goblin Spiders have a fossil record that dates back to the Cretaceous, being quite common in amber, though not known from sedimentary rocks. Goblin Spiders have six eyes rather than the eight of most Spiders, though some species have lost additional eyes. The back pair of legs are modified for jumping.

In a paper published in the journal Palaeontology in January 2012, a team of scientists led by Erin Saupe of the Department of Geology & Paleontological Institute at the University of Kansas describe four new Goblin Spider specimens from Cretaceous Amber from France and Spain. All the Spiders are placed in the genus Orchestina, which is still extant. Only two specimens are assigned to species, the other two (probably) being females, which are hard to distinguish to species level in modern specimens.

The first new Spider described is named Orchestina gappi, after Ian Wesley Gapp, a student at the University of Kansas. Orchestina gappi is a 1 mm Goblin spider preserved in a piece of dark brown, opaque amber from the Font-de-Benon Quarry, 1 km east of Archingeay-Les Nouillers in the Charente-Maritime Department of France. The sediments from which the amber was recovered are uppermost Albian–lowermost Cenomanian in age, making the fossil roughly 100 million years old. The specimen is barely visible through the dark amber matrix, but was revealed by synchrotron imaging at the European Synchrotron Radiation Facility in Grenoble.

Synchrotron images of Orchestina gappi. Scale bar is 1 mm. Saupe et al. (2012).

The second specimen is named Orchestina rabagensis, after the Rábago, the municipality in Cantabria, Spain where the fossil was found. Orchestina rabagensis is a 1.1 mm Goblin Spider preserved in light
yellow amber from the El Soplao Outcrop. It is early Albian in age, or about 110-113 million years old.

Orchestina ragagensis: (Top) Photograph and (Bottom) interpretive drawing. Stars indicate the locations of trichobothria, sensitive hairs capable of detecting air movements. Scale bars are 0.5 mm. Saupe et al. (2012).

The first unnamed specimen is a 1.11 mm female(?) Goblin Spider preserved in clear orange amber from the San Just Outcrop at Teruel in Spain. It is Middle Albian in age, or about 105 million years old.

Orchestina sp. from the San Just Outcrop. (Top) Photograph, scale bar is 0.5 mm. (Bottom) Synchrotron images, scale bar is 1 mm. Saupe et al. (2012).

The second unnamed specimen is a female over 1 mm in length from embedded in a piece of clear, dark orange amber, slightly clouded by organic debris. The specimen was found at the Peñacerrada Outcrop in Burgos, Spain. It is early Albian in age, or about 110-113 million years old.

Orchestina sp. from the Peñacerrada Outcrop. (Top) photograph, (Bottom) interpretive drawing. Stars indicate known trichobothria. C = crack, B = bubble. Scale bars represent 0.5 mm. Saupe et al. (2012).

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