Grimmiaceae in the Early Cretaceous: Tricarinella crassiphylla gen. et sp. nov. and the value of anatomically preserved bryophytes

ROTHWELL, GAR W; SAVORETTI, ADOLFINA; TOMESCU, ALEXANDRU M F; BIPPUS, ALEXANDER C; STOCKEY, RUTH A

ANNALS OF BOTANY

OXFORD UNIV PRESS

Año: 2018 p. 1275 - 1286

0305-7364

Background and Aims: Widespread and diverse in modern ecosystems, mosses are rare in the fossil record,especially in pre-Cenozoic rocks. Furthermore, most pre-Cenozoic mosses are known from compression fossils,which lack detailed anatomical information. When preserved, anatomy significantly improves resolution in thesystematic placement of fossils. Lower Cretaceous (Valanginian) deposits on Vancouver Island (British Columbia,Canada) contain a diverse anatomically preserved flora including numerous bryophytes, many of which have yetto be characterized. Among them is the grimmiaceous moss described here.? Methods: One fossil moss gametophyte preserved in a carbonate concretion was studied in serial sectionsprepared using the cellulose acetate peel technique.? Key Results: Tricarinella crassiphylla gen. et sp. nov. is a moss with tristichous phyllotaxis and strongly keeledleaves. The combination of an acrocarpous condition, inferred based on a series of morphological features, i.e.a central conducting strand, a homogeneous leaf costa and a lamina with bistratose portions and sinuous cells,and multicellular gemmae, supports placement of Tricarinella in family Grimmiaceae. Tricarinella is similar toGrimmia, a genus that exhibits broad morphological variability. However, tristichous phyllotaxis and especiallythe lamina, bistratose at the base but not in distal portions of the leaf, set Tricarinella apart as a distinct genus.? Conclusions: Tricarinella crassiphylla marks the oldest record for both family Grimmiaceae and sub-classDicranidae, providing a hard minimum age (136 million years) for these groups. The fact that this fossil could beplaced in an extant family, despite a diminutive size, emphasizes the considerable resolving power of anatomicallypreserved bryophyte fossils, even when recovered from allochthonous assemblages of marine sediments, such asthe Apple Bay flora. Discovery of Tricarinella re-emphasizes the importance of paleobotanical studies as the onlyapproach allowing access to a significant segment of biodiversity, the extinct biodiversity, which is unattainableby other means of investigation.