''Rhizomnium dentatum'' is an extinct

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of moss in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Mniaceae Mniaceae is a moss family in the order Bryales. Taxonomy The family Mniaceae includes the following genera: * '' Cinclidium'' * '' Cyrtomnium'' * '' Epipterygium'' * '' Leucolepis'' * '' Mielichhoferia'' * '' Mnium'' * '' Orthomnion'' ...

. The species is solely known from the

Middle Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "da ...

Baltic amber The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that these forests created more than ...

deposits in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and ...

region of Europe. The genus contains a total of thirteen extant species distributed across the northern hemisphere.

History and classification

''Rhizomnium dentatum'' is known from a small group of fossil

gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...

shoots which are

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s in a transparent chunk of Baltic amber. The amber specimen also contains seven shoots of a '' Pyrrhobryum'' species moss, three shoot fragments of a pleurocarpous, flat laying, hypnalian moss, and part of a centipede. When the fossil was described it was part of the amber collections housed in the American Museum of Natural History. The amber was recovered from fossil bearing rocks in the Baltic Sea region of Europe. Estimates of the age date between 37 million years old, for the youngest sediments and 48 million years old. This age range straddles the middle Eocene, ranging from near the beginning of the Lutetian to the beginning of the Pribonian. The holotype was first studied by a group of five researchers led by Jochen Heinrichs of the Ludwig Maximilian University of Munich. The research group's 2014 type description for the species was published in the paleobotany journal ''Review of Palaeobotany and Palynology''. The specific epithet ''dentatum'' was coined as a reference to the toothed margins of the leaves.

Description

The ''R. dentatum'' specimens the upper portions of a gametophyte shoots, with no lower structures preserved. Overall the stems are up to long, with a noted zig-zag structure that separates it from the described extant species. The leaves are attached at the outer angles of the stem bends. Each of the leaves are up to long and wide. Each of the leaves is oval to oblong, with a margin that is smooth to sparsely toothed.

References

{{Taxonbar, from=Q20817972 dentatum Prehistoric life of Europe Fossil taxa described in 2014 Flora of Europe Eocene plants Baltic amber