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137 12 12.1. A, BER 296.5, section 1, general view of the apical region (tip) of two small teeth, plus tooth fragment. B, BER 296.5, section 3, detail of possibly the proximal region of a small tooth crown (broken). Irregular large, rounded bays in the dentine may be evidence of biological dentinoclasy linked to tooth replacement. C, BER 296.5, section 3, detail of dentine and enamel along a tooth crown. The thin, highly birefringent enamel is nonprismatic and appears to be divided in four to five superimposed sheets; the numerous dentine canaliculi are obvious. D, Iguanodon bernissartensis from Bernissart (RBINS unregistered specimen “H”), detail of the enamel–dentine junction (EDJ) in a maxillary tooth. The thick enamel shows extensive superimposed zigzagging bright and dark bands, typical of advanced ornithopod enamel; the thickness of the dentine toward the pulp cavity would extend upward over the full height of the plate. E, Bactrosaurus johnsoni maxillary tooth; detail of the EDJ for comparison. Superposition of the bandings in the enamel suggests the fake occurrence of juxtaposed vertical pillars forming the tissue. Histological Assessment of Vertebrate Remains in the 2003 Bernissart Drill Armand de Ricqlès*, Pascal Godefroit, and Johan Yans After the 2003 drilling in the Iguanodon Sinkhole at Bernissart (BER 3 borehole), examination of the column revealed stony dark grayish remains at levels −296.5 m and −309 m, and hence within the Wealden clays levels. Microscopic examinations of the remains (paleohistology) conclusively demonstrate the occurrence of bone and tooth tissues. Whether the histological characteristics of the tissues allow a precise identification, especially whether the remains belong to Iguanodon, is quite another matter. The small teeth material clearly does not belong to ornithopod dinosaurs; however, their precise taxonomic origin cannot be assessed. However, the bony material shows structures compatible with a dinosaurian origin. A survey of the literature devoted to Iguanodon bone and tooth histology, as well as comparisons with Iguanodon bernissartensis bone and tooth material and with Bactrosaurus johnsoni teeth, do not demonstrate that the material definitely belongs to Iguanodon, although the possibility is likely for several reasons, detailed herewith. Comparison between “fresh” (from the borehole) and “old” (kept in the RBINS for more than 130 years under ordinary conditions) Iguanodon bones also allows checking the degradation process experienced by pyritized bones at the tissue level. In 2002–2003, three new boreholes were drilled within and around the Iguanodon Sinkhole at Bernissart. They provided exceptional material used for a multidisciplinary research to improve our knowledge of the Iguanodon-bearing Wealden facies (see Chapter 1 in this book). Detailed examination of the BER 3 column revealed stony dark grayish remains at levels −296.5 m and −309 m, and hence within the Wealden clays levels. The likeliness that those remains could be vertebrate skeletal fragments was high because of their phosphatic nature and because the borehole was drilled at the presumed site where the Bernissart iguanodons were discovered in 1878. Microscopic examinations of these fragments (paleohistology) conclusively demonstrate that these fragments are actually bone and tooth remains. Here, we describe the histology of the skeletal fragments discovered in the BER 3 borehole. Histological comparisons are attempted with data compiled from the literature and also with bone and teeth fragments taken from Iguanodon bernissartensis and Bactrosaurus johnsoni specimens. The “fresh” material from the borehole is also compared with “old” bones discovered at Bernissart between 1878 and 1881 in order to check at the tissue level the degradation process experienced by pyritized bone. Institutional abbreviation. RBINS, Royal Belgian Institute of Natural Sciences, Brussels, Belgium. Introduction Ricqlès et al. 138 Four fragments of a few cubic centimeters each were carefully extracted from the BER 3 column for examination by histological technics. The fragments, numbered Bernissart 3 296.5, Bernissart 3 309 A, Bernissart 3 309 B, and Bernissart 3 309 C, were dried and embedded in resin under gentle vacuum, with the resin temperature monitored to secure a slow polymerization. The resulting blocks were trimmed and sawed with a thin diamond/copper circular blade and further processed to obtain thin sections following routine paleohistological techniques (e.g., Wilson, 1994). For comparative purposes, a fragment of rib and one maxillary tooth from Iguanodon bernissartensis (RBINS unregistered specimen “H”; see Norman , 1986, appendix 1), and maxillary and dentary teeth from Bactrosaurus johnsoni, a basal hadrosaurid from the Iren Dabasu Formation in Inner Mongolia (P.R. China), were also histologically processed. The resulting thin sections were examined under dissecting and compound microscopes, in...

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