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Visualizzazione dei post da Giugno, 2008

NANNOFOSSILI: scoperta nuova specie vissuta tra 40 e 35 Milioni di anni fa.

A new Eocene Chiasmolithus species: hypothetical reconstruction of its phyletic lineage
Davide Persico*, Giuliana Villa
Dipartimento di Scienze della Terra, Università degli Studi di Parma, Viale GP Usberti, 157A, 43100 Parma, Italy; *
Chiasmolithus is abundant in Southern Ocean Ocean Drilling Program Sites 738, 689 and 748, and consequently provides an opportunity to study, in detail, evolutionary lineages and investigate the biostratigraphic distributions of some of the species. In particular, in the Middle to Late Eocene, a new species, Chiasmolithus eoaltus, has been recognised and distinguished from C. altus. Quantitative analysis highlights a gap between the last occurrence of C. eoaltusin the Upper Eocene and the first occurrence of C. altus in the Lower Oligocene. The morphological similarity is probably the result of convergent evolution. Additionally, the evolutionary process that has marked the phylogenesis of Chiasmolithus species during the Middle Eoce…