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Life span and growth rate of Middle Jurassic mesohibolitid belemnites deduced from rostrum microincrements

Wierzbowski H.

Volumina Jurassica

2013

Vol. 11, no. 1

1--18

The microincrements of nine Middle Jurassic mesohibolitid belemnite rostra (Hibolithes jurensis, Pachybelemnopsis fusiformis and Pachybelemnopsis “subhastatus”) were analysed to measure the ontogenic age and growth rate of the belemnites. The microincrements are interpreted to have been formed daily based on analogy with extant coleoid cephalopods and the frequency of circadian rhythms in animal activity. The mesohibolitid belemnites are found to have had a short life span of ca. 1 year. The short life span of the belemnites studied is similar to the life span of modern coleoids (squids, cuttlefishes and common octopuses). It restricts the utility of belemnite rostra as a proxy for average secular seawater temperatures and chemistry. Short-lived cycles (2–8 days) in the belemnite growth rate are linked to variations in the metabolic activity of these animals. Minor diagenetic alteration revealed by the dull cathodoluminescence of some rostra is found to have no effect on the preservation of the growth rings.

Fossil wood from the Roztocze region (Miocene, SE Poland) : a tool for palaeoenvironmental reconstruction

Kłusek M.

Geological Quarterly

2006

Vol. 50, No. 4

465-474

This article presents the results of anatomical and growth ring analyses of Badenian fossil wood from the Roztocze region. All the wood specimens examined are classified as Taxodioxylon taxodii Goth. The growth rings of these woods are very narrow, and they vary considerably in width. Tracheids have large diameters and thin cell walls.The latewood zone is wide; the transition between early and latewood is gradual. Both false and wedge rings and also reaction wood zones are often found. These characteristics of the fossil wood make it a suitable aid to reconstructing the environmental conditions prevailing while the trees were alive. The environmental requirements of these ancient Roztocze trees are interpreted by comparison with those of their nearest living relatives, with the conclusion that they lived in waterlogged or temporarily flooded stands under seasonally changing environmental conditions and with a long growing season. The climate was warm and humid and characterized by significant variability, mainly as regards the amount of precipitation.