Scan Microscope Images Trilobites

Ventral view of a specimen of Triarthrus eatoni (Hall), whose pyritized appendages have been exposed after painstaking preparation by C. E. Beecher (x4.7). From "Beecher's trilobite bed," Utica Shale, Upper Ordovician, Rome, New York. (YPM 219, loaned through courtesy of Dr. J. Cisne.) Photograph obtained while the specimen was totally immersed in xylene.

Radiograph of an adult specimen of

Triarthrus eatoni (Hall) (x4.2). (YPM 228, from a stereo pair of radiographs by J. Cisne.) The biramous appendages can be seen protruding from and underlying the dorsal shield. The pyritized soft parts of the trilobite, as well as the carapace, are more opaque to X-rays than the embedding shale, thus providing high contrast. Details of other soft parts, replaced by fine granules of iron pyrite, yield visible contrast.

The same specimen as in plate 9, this time immersed in xylene. Fine surface details of the structure of the appendages are revealed by this technique.

Another X-ray view of a completely preserved specimen of Triarthrus eatoni, as in the preceding plate (x7.4). (YPM 28253, radiograph by J. Cisne.) These pyritized trilobites are among the most striking fossil records of extinct life ever recaptured.

(a) Pyritized specimen of Phacops sp. from the Lower Devonian Hunsriick Slate, showing the appendages, exposed by mechanical preparation (x2.1); (b) X-ray photograph of the same, by W. Sturmer (WS 295). Both photographs were contributed by W. Sturmer.

Phacops Sketch

All observations had to be carried out with a scanning electron microscope, in view of the minuteness of the complex structures entirely contained within the submillimeter-sized larval shields. From this painstaking body of work, what emerged is a truly astounding reconstruction of the ventral view of this creature, reproduced in figure 6a, together with a sketch of its embryonic-looking dorsal appearance (fig. 6b).

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