The taphonomic puzzle of Notothylacites filiformis: reinterpretation of bryophyte fossils from the Late Cretaceous of Czechia reveals co-occurrence of hornworts and liverworts.

Abstract

Background and aims: Hornworts are rarely found in the fossil record, so each new find provides important insights regarding their evolution and diversity. Here we revisit a controversial genus, Notothylacites, described from the Late Cretaceous of Central Europe, which has liverwort morphology, but bears hornwort spores.

Methods: The fossil material was originally studied in 1970 by Pacltová using pollen preparation techniques. Using a single grain method, we extracted the spores from the preparation matrix, and observed them with SEM. For comparison, we studied the spores of the extant hornwort genus Notothylas.

Key results: We reinterpret the original N. filiformis holotype as a conglomerate of two fossils: a hornwort, Notothylacites, and a liverwort, which we designate as a new species Ricciopsis pacltovae. Notothylacites filiformis was lectotypified, using material from seven slides and the original drawing, which emphasized a key character - a sporangium with apical longitudinal dehiscence slit containing psilate, trilete spores. Ricciopsis pacltovae, erected based on comparisons to seven already described species, is a liverwort that closely resembles extant Riccia, with a prostrate circular thallus consisting of dichotomously branched, linear segments, up to six dichotomies per branch, each branch with a pronounced narrow medial sulcus. These and other morphological traits distinguish it from previously described species in the genus.

Conclusions: Notothylacites filiformis is reinterpreted as one of the rare examples of a fossil hornwort sporophyte. Gametophyte material previously assigned to N. filiformis is assigned to a new fossil liverwort species, Ricciopsis pacltovae. Hornworts frequently grow on wet soil together with Riccia liverworts. The co-occurrence of the two fossil species further highlights the presence of bryophyte diversity in the Late Cretaceous that mirrors extant ecological associations. This study corrects decades of taxonomic confusion, demonstrating how taphonomic mixing can mislead interpretations, and emphasizes the importance of re-examining collections with modern methods.