Abstract
The Bełchatów Lignite Mine of Poland is a treasure-cove for mid-to late Miocene plant and animal fossils, deposited in a slow-flowing river valley with swamps and oxbow lakes. Here, we report the finding of abundant fossil anomopod cladocerans. Some are three-dimensionally preserved, including the taxonomically important trunk limbs. They pertain to the families Chydoridae and Bosminidae, with species similar to but distinct from modern ones. All are members of the zooplankton, though some are littoral while others are pelagic in nature. Morphological stasis in these families is not outspoken as in the Daphniidae and the stasis hypothesis, based on ephippia only, is challenged. The absence of Daphnia is conspicuous and ascribed to a combination of fish predation and local water chemistry. Its place in the oxbow lakes is taken by at least two Bosmina species, one of which is undescribed. We consider this a case of paleo-competitive release. For Bosminidae, these are the first certified fossils predating the Pleistocene.
Highlights
The Bełchatów Lignite Mine of Poland is a treasure-cove for mid-to late Miocene plant and animal fossils, deposited in a slow-flowing river valley with swamps and oxbow lakes
The fossil-bearing deposits belong to a clayey-sandy (I-P) unit considered to be of mid to late Miocene age[1,2]
This age is supported by fission track dating, and fossils of different animal and plant groups[1,2,3,4,5,6,7]
Summary
Moina (a water flea related to Daphnia) ephippia have been recovered from the early Miocene Barstow formation[12,13,14] In the latter place, fossils are three-dimensional, like in our case in Bełchatów. That we recovered no daphniid fossils may refine our insight into the nature of the Bełchatów aquatic environment: We favour the idea of a series of shallow oxbow lakes in a climate warmer than todays, with at least locally an abundance of macrophytes. Chydorids thrive in such environments, and the genus Simocephalus. Their absence gives these small crustaceans a chance to prosper and dominate the open waters
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