CT-SCANNING THE LONDON CLAY FLORA: A NONINVASIVE TECHNIQUE FOR REVEALING THE 3-DIMENSIONAL ORGANIZATION OF TISSUES IN PYRITIZED FRUITS AND SEEDS

Traditionally, there have been three major methods for studying anatomy of permineralized fruits and seeds: scanning electron microscopy of fractured surfaces; wafered or thin sections, and, if material has sufficient organic material, cellulose acetate peels. All three of these techniques are destructive and each is limited in what materials it can optimally benefit. Some of the most significant Tertiary fossil fruits and seeds come from the Early Eocene London Clay flora, an assemblage of fossils highly subject to pyrite decay that can be manipulated only in limited ways (e.g., SEM). The historic nature of many specimens which come from no longer productive localities, and the small number of specimens for many taxa prohibit the use of destructive techniques. In collaboration with the University of Texas High Resolution X-ray CT Facility (UTCT), we examined London Clay fruits for 3-dimensional study using X-ray Computed Tomography (CT-scanning). This technique reveals the 3-dimensional organization of tissues in both fruit and seeds. No critical sections of the fruit wall or seeds are lost as in serial sectioning, and once the specimen has been scanned, it can be studied in virtually any plane. Cost is not prohibitive, as the specimens are small and scan times are relatively short. An advantage of using CT imaging to study London Clay fruits and seeds is that the specimens can be studied directly within the vials of silicone oil in which they are stored. The oil fills spaces within the specimen and provides contrasting boundaries detected by CT imagining. Silicone oil also acts as a calibration baseline and helps in the imaging process. We compared one London Clay fruit type, the guava-like Palaeorhodomyrtus to the closely related genus Paleomyrtinaea known from permineralized Paleocene Almont and Beicegel Creek localities of North Dakota and the middle Eocene Princeton Chert. Cellulose acetate peels reveal excellent cellular detail of both seed and fruit wall in fruits that can be peeled (e.g., Beicegel Creek); in contrast the Almont material which lacks sufficient organic material for the peels to reveal details of seed anatomy, but are shown with wafered sections. SEM is useful in all cases. Comparable information can be obtained from fossils with different preservational modes, if optimal techniques for a given matrix type are chosen.