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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.

Wstępne badania palinologiczne środkowojurajskiej formacji częstochowskich iłów rudonośnych z odsłonięć w Częstochowie

Hodbod M.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

2009

T. 35, z. 3/1

57-59

Ore Bering Częstochowa Clay Formation (Middle Jurassic) was taken into consideration of spore-pollen analysis. Preliminary research indicates presence of taxa belonging to Lycopodiales, Equisetales, Filicales, Coniferales and Mesozoic pteridosperms. Changes of frequency of sporomorphs possibly indicate variability of climate.