Encapsulation

Related to permineralized insects from evaporate deposits is a rare form of preservation wherein minerals form around the insect, sometimes a single crystal (Tillyard, 1922a; Schlüter and Kohring, 2001; Schlüter, 2003a). In the latter two studies, dragonfly nymphs were reported entombed in gypsum crystals from the Late Miocene (ca. 5.2 mya) of northern Italy. These were formed during the Messinian Crisis, a period of such extreme aridity that the Mediterranean Sea virtually evaporated. The nymphs are preserved in the crystals as three-dimensional or compressed inclusions with hollow bodies.

The scientifically remarkable biota preserved in the Rhynie Chert, from the Old Red Sandstone in the Devonian of Scotland has a similar preservation, though organisms are not encapsulated within single crystals. Chert is microcrys-talline silica, SiO2, formed in a volcanic process. The chert is translucent and, if pieces are trimmed thinly enough, three-dimensional fragments of tiny organisms can be observed (Figure 5.8). These were trapped in ancient shallow pools created by hot springs and then rapidly silicified (Trewin, 1989). The Rhynie Chert has preserved some of the finest examples of earliest terrestrial life. Similar encapsulation is known from Tertiary onyx (Figure 2.15).

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