Abstract Detail

Paleobotany

Dorn, Shanelle [1], Abidi, Shayda [2], Bippus, Alexander [3], Matsunaga, Kelly K.S. [4], Tomescu, Alexandru [5].

Microconchid-plant interactions in the Early Devonian wetlands of Wyoming (Beartooth Butte Formation, Lochkovian-Pragian).

Microconchids are extinct aquatic invertebrates classified as phoronid lophophorates. They are sessile encrusters, producing coiled calcareous tubes on various hard substrates, including plants. Consequently, they can provide insights on the living and depositional environments, and taphonomy of fossil plants. However, microconchids, identified as a distinct group only recently, are still poorly understood in terms of taxonomy, living environments, stratigraphic and geographic distribution. Additionally, interactions between microconchids and plant substrates have yet to be studied in detail. The Early Devonian Beartooth Butte Formation records the oldest occurrence of microconchids colonizing plants, in Lochkovian-Pragian fossil assemblages studied at Cottonwood Canyon (Wyoming). This is also the most abundant occurrence of microconchids associated with plants known to date. As such, the Cottonwood Canyon assemblages provide an opportunity to explore the relationships between microconchids, plants, and their living environments, and can enhance our understanding of these enigmatic invertebrates. At Cottonwood Canyon, plant fossils are preserved as coalified compressions, alongside fish and eurypterid arthropods, in channel fill deposits. The most abundant plant fossil is Sengelia radicans, a robust lycophyte preserved in extensive in situ mats. Flood deposits alternate with Sengelia mats preserving fossils of zosterphylls, trimerophytes, thalloid gametophytes, protolepidodendralean lycophytes and sterile axes assigned to several morphotypes. Microconchids are extremely abundant on the shoots of Sengelia and moderately abundant on two sterile axis morphotypes. The occurrence of microconchids on these plants indicates that they lived in areas that were temporarily submerged. The rich assemblages of Sengelia have allowed us to understand the relationship between this plant and microconchids in great detail. In comparisons of different Sengelia shoot size classes, larger-diameter shoots have substantially greater microconchid density than smaller shoots. This, coupled with the presence of a substantial number of Sengelia specimens that lack microconchid colonization, suggests that Sengelia populations experienced repeated (possibly periodical) episodes of submergence that led to progressive accumulation of microconchids on older shoots. Further investigation of microconchid distribution on plants at Cottonwood Canyon is ongoing and will allow us to understand the dynamics of microconchid colonization on the other plant types. The abundant colonization of plants by microconchids at Cottonwood Canyon also provides insight into the habitats of these invertebrates, suggesting that they had the capacity to live in unstable brackish to freshwater environments during the Early Devonian. Together, these highlight the importance of studies on microconchid-plant interactions which will enrich our understanding of the natural history and ecology of microconchids and plants.

1 - Humboldt State University, Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA
2 - Humboldt State University, 1 Harpst Street, Arcata, CA, 95521, United States
3 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, United States
4 - University Of Michigan, Earth and Environmental Sciences, 1100 North University Avenue, Ann Arbor, MI, 48109, USA
5 - Humboldt State University, Department Of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA

Keywords:
Devonian
fossil
Paleobotany
plant-animal interactions
paleoecology
wetland
microconchid.

Presentation Type: Oral Paper
Session: 16, Cookson/Moseley and Paleozoic paleobotany
Location: Sundance 4/Omni Hotel
Date: Monday, June 26th, 2017
Time: 4:30 PM
Number: 16004
Abstract ID:172
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award