title: Triassic leech cocoon from Antarctica contains fossil bell animal.
abstract: Our understanding of the evolution of life on Earth is limited by the imperfection of the fossil record. One reason for this imperfect record is that organisms without hard parts, such as bones, shells, and wood, have a very low potential to enter the fossil record. Occasionally, however, exceptional fossil deposits that preserve soft-bodied organisms provide a rare glimpse of the true biodiversity during past periods of Earth history. We here present an extraordinary find of a fossil ciliate that is encased inside the wall layer of a more than 200 Ma leech cocoon from Antarctica. The microfossil consists of a helically contractile stalk that attaches to a main body with a peristomial feeding apparatus and a large C-shaped macronucleus. It agrees in every aspect with the living bell animals, such as Vorticella. Vorticellids and similar peritrichs are vital constituents of aquatic ecosystems worldwide, but so far have lacked any fossil record. This discovery offers a glimpse of ancient soft-bodied protozoan biotas, and also highlights the potential of clitellate cocoons as microscopic "conservation traps" comparable to amber.
authors.affiliation: Department of Ecology and Evolutionary Biology and Biodiversity Institute, University of Kansas, Lawrence, KS 66044, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bomfleur
authors.forename: Hans
authors.initials: H
authors.lastname: Kerp
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Taylor
authors.forename: Øjvind
authors.initials: Ø
authors.lastname: Moestrup
authors.forename: Edith L
authors.initials: EL
authors.lastname: Taylor
mesh_terms: D000818:Animals; D000864:Antarctic Regions; D044822:Biodiversity; D005075:Biological Evolution; D017753:Ecosystem; D005580:Fossils; D005843:Geography; D007448:Invertebrates; D007865:Leeches / Q000502:physiology*; D010163:Paleontology / Q000379:methods