Sprecher
Beschreibung
The bryophyte fossil record is notoriously scarce due to different biases, most of which are associated with their size and the lack of researchers specialized in this group. Among the ~650 fossil bryophyte taxa recognized to date, hornworts (Anthocerotophyta) are represented by only four taxa, of which two are only tentatively assigned to the group. Here we report new fossil hornwort specimens from Miocene strata (~7 Ma) in eastern Romania. The fossils are found in a 1-meter-thick layer of grey clayey marls that represents a shallow lacustrine to paludal depositional environment.
The gametophyte thalli, up to 6-7 mm across and ~1 mm thick, are rosette shaped with lobed outline and their anatomy is well preserved. Multiple large empty chambers (0.5-1.0 mm) present close to the lobe tips probably correspond to mucilage cavities. There is no dorsiventral differentiation in the histology of thalli, but there is a system of radiating narrow canals that dichotomizes following the general morphology of the thallus. The sporophytes, >5mm long, have bases deeply embedded in the gametophyte thalli. They have a central tissue resembling a columella forming a bundle of 16 cells and a surrounding layer of variable thickness (mostly 1-2 cells thick). The variable thickness of this layer indicates that the sporophytes are probably missing some of the outermost cell layers. These new hornwort fossils represent a 25% increase in the number of known fossil hornworts (now with five fossil types) and represent the only fossil record of Cenozoic age for the group.