Abstract Detail

Paleobotany

Bippus, Alexander [1], Stockey, Ruth [2], Rothwell, Gar [3].

Uncovering Mesozoic polar bryophyte diversity: A permineralized haplolepideous moss gametophyte from the Late Cretaceous of the north slope of Alaska.

A single permineralized moss gametophyte from the Late Cretaceous of the north slope of Alaska provides a rare glimpse of Cretaceous polar bryophyte diversity. The fossil was recovered from a block of terrestrial limestone collected along the Colville River which also preserves a rich, conifer-dominated vascular plant flora. The gametophyte shoot is 1.4 mm long and consists of a central (175 µm diameter) shoot which bears two smaller (60 µm diameter) branches in an opposite arrangement. Stems consist of an epidermis of 6-8 µm quadrate cells, a cortex of 2-30 µm thin-walled isodiametric cells, and an incompletely preserved central conducting strand. The shoot is isophyllous and leaves are erecto-patent. Leaves are broad (775 µm) and keeled basally, becoming narrower (325 µm) and canaliculate proximally. The costa is narrow and D-shaped in cross section near leaf insertion, becoming stronger proximally. Apically, the costa is excurrent for ca. 200 µm. Costal anatomy is complex with an epidermis, a central layer of large (13-17 um) circular cells that resemble deuters, and adaxial and abaxial patches of smaller (6 µm) isodiametric cells comparable to stereids. Leaf lamina is unistratose and composed of rectangular to isodiametric cells. Alar cells are 17 µm tall x 24 µm wide x 16-21 µm long and rectangular in paradermal section. Median lamina cells are 10-12 µm diameter and isodiametric. Leaf margins are unistratose or bistratose throughout and recurved below the canaliculate portion of the leaf. The branching architecture of the Alaskan fossil resembles that of short turf or cushion forming mosses. Keeled to canaliculate leaves with an excurrent costa that is comprised of deuters, adaxial and abaxial stereids, and an epidermis suggest affinities within the subclass Dicranidae (haplolepideous mosses). Detailed comparison of the fossil with all extant and extinct members of the subclass (ca. 3,000 spp.) is ongoing, but preliminary results suggest that the Alaskan fossil most closely resembles members of the families Dicranaceae, Ditrichaceae, and Pottiaceae. Today, short turf and cushion forming members of these families are conspicuous components of polar floras. The Alaskan fossil reveals that Late Cretaceous haplolepideous mosses had already evolved similar morphological adaptations for ectohydry (compact colonial growth forms, three-dimensionally complex leaf morphology, excurrent costa) like extant members of the lineage, which enable them to survive in physiologically demanding polar environments.

1 - Oregon State University, Botany and Plant Pathology, 2701 SW Campus Way, Corvallis, OR, 97331, USA
2 - Oregon State University, Department Of Botany And Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331.0, United States
3 - Ohio University, and Oregon State University, Environmental and Plant Biology, and Botany and Plant Pathology, 308 Porter Hall, Ohio University, Athens, OH, 45701, USA

Keywords:
moss
fossil
Cretaceous
Alaska
anatomy
haplolepideous.

Presentation Type: Oral Paper
Session: CK2, Cookson Award Session II
Location: Tucson G/Starr Pass
Date: Monday, July 29th, 2019
Time: 10:45 AM
Number: CK2003
Abstract ID:297
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award