Darriwilian Age

First macrofossils of bryophytes

The Darriwilian (467–458 Ma) is a time period during the Middle Ordovician, that occurs after the Dapingian, and before the Sandbian (Late Ordovician)

Geologic Age

467.3±1.1–458.4±0.9 Ma

Eon / Era / Period / Epoch

Phanerozoic; Paleozoic; Ordovician; Middle Ordovician

Above/Below: Miospores found from Darriwilian

Above: reconstructed landscape of the Douglas Dam location (from Figure 15, Retallack, 2019)

What happened during this time?

Flora

The oldest known land plant macrofossils are known from this age (13Jul2021)
Bryophyte macrofossils from five different groups discovered at the Douglas Dam locality, Tennessee (Retallack, 2019)

Hornworts

- Casterlorum crispum, in the Leiosporocerotaceae, with a form similar to the living Leiosporoceros dussii

Liverworts

- Cestites mirabilis †, a thalloid liverwort in the Marchantiaceae, with a form similar to the living Marchantia polymorpha
- Janegraya sibylla †, a balloonwort in the Sphaerocarpaceae, with a form similar to the living Sphaerocarpus

Mosses

- Dollyphyton boucotii †, a peat moss in the Sphagnales (Flatbergiaceae?), with a form similar to the living Flatbergium
- Edwardsiphyton ovatum †, a harsh moss in the Pottiales (Pottiaceae?), with a form similar to the living Tortula leucostoma

Above: Drawings of Middle Ordovician bryophyte fossils from the Douglas Dam location (from Fig. 4, Retallack, 2019)

Fungi

Fungal remains are found at the Douglas Dam location (Retallack, 2019)
Endomycorrhiza
- Palaeoglomus strotheri † related to the glomeromycetes
Fungal-like organisms
- Prototaxites honeggeri † were taller than the plants, around 15cm tall

Cryptospores

Many are bryophyte-like spores found in these Middle Ordovician sediments
- Oldest embryophytic spores have a lamellated wall structure of a single Hanadir Member monad (Taylor et al., 2017)
  - Homogeneous walls are characteristic of extant embryophyte sporoderm, which is actively secreted by a tapetum.
This implies that these Ordovician cryptospores developed within a sporangium
These Middle Ordovician sediments possess 8-10 species of meiospores
- Naked fused dyads (i.e., Pseudodyadospora),
- Naked fused tetrads (i.e., Tetrahedraletes)
- Naked unfused tetrads (i.e., Stegambiquadrella)
- Smooth envelope enclosed dyads (i.e., Segestrespora)
- Envelope enclosed ornamented tetrads
- Several other possible meiospore types:
  - Naked laevigate monads
  - Naked monads with pseudo-trilete mark (i.e., Imperfectotriletes)
  - Naked unfused dyads (i.e., Dyadospora),
  - Ornamented envelope enclosed dyads (i.e., Segestrespora)

Fauna

Pentecopterus, the oldest described sea scorpion (eurypterid), lived during this time and could grow to nearly six feet (Lamsdell et al., 2015)

Douglas Dam locality also records evidence of invertebrates (Retallack, 2019)
- An aquatic chelicerate arthropod, Chasmataspis laurenci
- A phyllocarid crustacean, Douglasiocaris collinsi
- Arthropod trackways, named Diplichnites

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