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Astigmatid mite in Baltic amber

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Uploaded on Nov 13, 2011

Astigmatid mite in Baltic amber

A 44-Million-Year-Old Hitchhiker
http://news.sciencemag.org/sciencenow...

Talk about a ride gone wrong. This tiny mite climbed onto a spider's back at least 44 million years ago, but the spider stumbled into a glob of sticky tree sap. That makes the duo the oldest known fossil evidence of hitch-hiking behavior, or phoresy, in a large group of mites called the Astigmata. Immature mites still use the method to migrate to new habitats—although today, they usually ride on insects, not spiders. Researchers had tried to study the fossilized mite before, but they couldn't see it clearly through the amber. (It's a small bump on the center of the spider's back in the color photo above.) To make matters worse, its underside was hidden against the spider. So a team of biologists, paleontologists, and materials scientists used a method known as high-resolution phase-contrast computed tomography to take thousands of x-ray images and compile them into a digital model of the two arachnids. At less than two-tenths of a millimeter long, the mite (left image) pushed the limits of the method. But the resulting images, published online today in Biology Letters, provide enough detail to tentatively identify the mite and even see the suckers it used to hold onto its ride.

Reference
A minute fossil phoretic mite recovered by phase-contrast X-ray computed tomography
Biol. Lett. November 9, 2011, doi: 10.1098/rsbl.2011.0923
http://rsbl.royalsocietypublishing.or...

Abstract
High-resolution phase-contrast X-ray computed tomography (CT) reveals the phoretic deutonymph of a fossil astigmatid mite (Acariformes: Astigmata) attached to a spider's carapace (Araneae: Dysderidae) in Eocene (44--49 Myr ago) Baltic amber. Details of appendages and a sucker plate were resolved, and the resulting three-dimensional model demonstrates the potential of tomography to recover morphological characters of systematic significance from even the tiniest amber inclusions without the need for a synchrotron. Astigmatids have an extremely sparse palaeontological record. We confirm one of the few convincing fossils, potentially the oldest record of Histiostomatidae. At 176 µm long, we believe this to be the smallest arthropod in amber to be CT-scanned as a complete body fossil, extending the boundaries for what can be recovered using this technique. We also demonstrate a minimum age for the evolution of phoretic behaviour among their deutonymphs, an ecological trait used by extant species to disperse into favourable environments. The occurrence of the fossil on a spider is noteworthy, as modern histiostomatids tend to favour other arthropods as carriers.

Video: Astigmatid mite in Baltic amber
This video shows a tiny asigmatid mite (Histiostomatidae) attached to the carapace of a spider found in ca. 44-49 million year old Baltic amber. This detailed reconstruction was achieved using phase contrast X-ray computed tomography.
Fonte: RoyalSociety http://www.youtube.com/user/RoyalSociety

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