FTIR spectra of resins from selected modern and Eocene conifers and of Baltic amber. Vertical lines indicate spectral bands used to define the ratios subjected to cluster analysis table (1). Shaded area is the Baltic shoulder, which is fully expressed in Baltic amber and S. verticillata and partially in Pseudolarix. Red, fossil resin; green, modern resin; orange, Baltic amber.

Hierarchical cluster analysis based on averaged FTIR spectra for five groupings of modern conifer resins and Baltic amber. (a) Dendrogram based on the six FTIR spectral ratios described in table 1. (b) Dendrogram based on the 169 bands that define the fingerprint region between 650 and 1300 cm⁻¹.

Examples of wavenumber ratios calculated from the FTIR spectral database. (a) The 1159 cm⁻¹/1178 cm⁻¹ ratio reflects the amplitude of the Baltic shoulder and is positive only for modern S. verticillata (S.v.) resin and Baltic amber (B.a.). This ratio is not overprinted strongly by diagenesis. (b) The ratio of maximum C=O absorbance to that of secondary C–H, in contrast, is controlled by oxidation history and retains no chemotaxonomic significance. Additional abbreviations are as follows: C.A., Eocene Canadian Arctic (all Giraffe and Buchanan Lake samples); Pin., Pinaceae; Ara., Araucariaceae; Tax., taxodioid Cupressaceae; Cup., cupressoid Cupressaceae; Cret., Canadian Cretaceous ambers from McKellar et al. (2008).

Baltic amber and S. verticillata. (a) Fragments of Baltic amber in Eocene glauconitic sediments from Kaliningrad Oblast, Russia. (b) Parevania producta, an evaniid (or ensign) wasp preserved in Polish Baltic amber, demonstrating the quality of arthropod preservation witnessed in the deposit. (c) Large Baltic amber block with bark and wood occluded to the specimen by successive resin flows (Schlaube). The bark possesses a cupressoid–taxodioid morphology similar to modern S. verticillata (i), but distinct from either Pinus or Agathis. (d) Wood anatomy from the specimen illustrated in (c) is simple, lacking parenchyma and intercellular canals. Radial walls of xylem tracheids have uniseriate ovoid to circular bordered pits. Vertical tracheids frequently terminate at perpendicular ray parenchymal cells arranged radially in vertical rows of one to eight cells. In each of these aspects, wood anatomy compares favourably with modern Sciadopitys, but bears no resemblance to Agathis, for which bordered pits are multiseriate. (e) Sciadopityspollenites palynomorph from Swedish Baltic amber, compared with modern S. verticillata pollen (f) which is comparable in terms of both size and exine morphology. (g) Conifer needle from Baltic amber showing morphological similarity to modern S. verticillata (h). (j) Resin bled from a severed twig of S. verticillata. (k) Dense resin canals in S. verticillata phloem are well developed for defensive resinosis. Scale bars, (a) 2 cm, (b) 1 mm, (c, i) 10 cm, (d) 250 µm, (e, f) 10 µm, (g, h) 1 cm, (j) 0.5 cm and (k) 100 µm.