Abstract Detail

Paleobotany

Bippus, Alexander [1], Stockey, Ruth [2], Rothwell, Gar [1].

Permineralized gametophytes from Vancouver Island reveal that peat mosses (Class Sphagnopsida) were anatomically diverse by the Late Cretaceous.

A large number of permineralized peat moss gametophytes from the Late Cretaceous of Vancouver Island provide a rare glimpse of Mesozoic peat moss diversity. Fossils are preserved in a single calcium carbonate concretion collected from a Late Cretaceous (Santonian to Campanian) fossil assemblage from the Trent River Formation. Based on anatomical differences, two peat moss morphotypes are recognized. The first morphotype consists of a single unbranched gametophyte fragment 1.6 mm long. Stems of this morphotype are ca. 300 µm in diameter and have a unistratose hyalodermis (an epidermis of inflated cells), a narrow stereid band comprised of small-diameter cells, and a pith of larger-diameter cells. The unistratose leaves consist of large leucocysts, that are round in cross section, which alternate with much smaller chlorocysts that are narrowly elliptical in cross section. Leucocysts lack pores and fibrils. Because of its size, anatomy, and absence of leucocyst pores and fibrils, this morphotype probably represents a fragment of a stem. The second morphotype is known from two specimens, the largest of which (2.8 mm long) branches twice. Stems of this morphotype are ca. 375 µm in diameter and have a multistratose hyalodermis with at least three layers of inflated cells, a narrow band of stereids, and a central pith comprised of uniformly small-diameter cells. Branches are <150 µm in diameter and have a unistratose hyalodermis with conspicuous retort cells and a pith of small-diameter cells. Stem leaves are unknown, but branch leaves are unistratose throughout with large leucocysts that are broadly elliptical in cross section that alternate with smaller triangular chlorocysts exposed on the abaxial surface of the leaf. Leucocysts lack pores and fibrils. Both of these morphotypes have features diagnostic of Order Sphagnales, and show stem, branch, and leaf anatomy diagnostic of Sphagnum in morphology-based peat moss classifications. Furthermore, these two morphotypes encompass much of the anatomical variation in stem anatomy known among extant Sphagnum species. The Trent River Formation fossils are only the fifth report of peat mosses from Mesozoic deposits and represent the first permineralized fossils of the group ever discovered. As such they provide a search image for anatomically preserved peat mosses. This discovery represents a critical step towards finding more pre-Cenozoic fossils that are needed to understand the diversification of this ancient and ecologically important lineage of plants.

1 - Oregon State University, Department Of Botany And Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331, United States
2 - Oregon State University, Department Of Botany And Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331.0, United States

Keywords:
fossil
moss
Cretaceous
Sphagnum
bryophyte.

Presentation Type: Oral Paper
Session: PAL1, Cookson Award Session I
Location: Virtual/Virtual
Date: Monday, July 27th, 2020
Time: 10:15 AM
Number: PAL1002
Abstract ID:662
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award