Vol. 59, 2020
(update: 2020.07.09; 08.05)
Fossil and Modern Clam Shrimp (Branchiopoda: Spinicaudata, Laevicaudata)
The Fossil Record of the Clam
Shrimp (Crustacea; Branchiopoda)
A. Hegna1,* and Timothy I. Astrop2
of Geology and Environmental Sciences, SUNY Fredonia, 203 Jewett Hall,
280 Central Avenue, Fredonia, NY 14063, USA. *Correspondence: E-mail:
2Fossil Forest Project, Blast Road, Brymbo, Wales,
United Kingdom, LI11 5BT. E-mail: firstname.lastname@example.org (Astrop)
(Received 18 April 2020 / Accepted 26
Special issue (articles 32-46) communicated by Thomas A. Hegna and D.
shrimp (the paraphyletic assemblage of spinicaudatans, laevicaudatans,
cyclestherids and the extinct leaiins) are small, bivalved branchiopod
crustaceans that specialize in ephemeral freshwater habitats. They have
a long fossil record (Devonian onward) that has often been overlooked.
Here we briefly review the fossil record of the major groups of clam
shrimp and clear up some misconceptions in the literature as to their
origin. The dominant group of clam shrimp in the fossil record is the
Spinicaudata, which have a diverse fossil record beginning in the
Devonian. The clam shrimp suborder Laevicaudata are known from the
Permian, with possible soft-part preservation from the Jurassic.
However, owing the character-poor nature of these fossils, it is
impossible to tell if they represent crown group or stem group
laevicaudatans. In contrast, the total group Spinicaudata have a rich
record of mostly carapace fossils—the earliest from the Early Devonian.
The leaiins are an enigmatic extinct diplostracan lineage thought to be
closely related to the spinicaudatans. They have a record that extends
from the Middle Devonian to the Permian. The Cyclestherida have a
somewhat problematic fossil record: there are no examples of
cyclestherids preserved with soft-parts, so the only character used to
assign fossils to this lineage is the carapace shape. According to that
metric, cyclestherids have a record that begins in the Middle Devonian.
Exceptionally preserved clam shrimp are found in the Paleozoic and
Mesozoic. Assessing holistically what is known about the clam shrimp
fossil record along with carapace morphology, carapace ornamentation
and examples of exceptional preservation will ultimately contribute to
a synthetic paleontological and neontological understanding of the
group, its systematics and evolution.
Key words: Laevicaudata,
Spinicaudata, Cyclestherida, Diplostraca, Onychocaudata.
Citation: Hegna TA, Astrop TI. 2020. The
fossil record of the clam shrimp (Crustacea; Branchiopoda). Zool Stud 59:43. doi:10.6620/ZS.2020.59-43.