Abstract
Larvae of malacostracan crustaceans represent a large fraction of modern day zooplankton. Plankton is not only a major part of the modern marine ecosystem, but must have played an important role in the ecosystems of the past as well. Unfortunately, our knowledge about plankton composition of the past is still quite limited. As an important part of today’s zooplankton, malacostracan larvae are still a rarity in the fossil record; many types of malacostracan larvae dominating the modern plankton have so far not been found as fossils. Here we report a new type of fossil malacostracan larva, found in the 150 million years old lithographic limestones of southern Germany (Solnhofen Lithographic Limestones). The three rather incomplete specimens mainly preserve the telson. A pronounced middle spine on the posterior edge of these specimens indicates that they are either larval forms of a clawed lobster or of an axiidean lobster, or of a closer relative to one of the two groups. The tergo-pleura are drawn out into distinct spines in one specimen, further supporting the interpretation as a larva of a clawed lobster or an early relative. The telson morphology also shows adaptations to a prolonged planktic life style, the latero-posterior edges are drawn out into distinct spines. Similar adaptations are known in larvae of the modern homarid lobster Nephrops norvegicus, not necessarily indicating a closer relationship, but convergent life styles. The new finds provide an important new insight into the composition of Mesozoic zooplankton and demonstrate the preservation potential of lithographic limestones.
Highlights
Plankton describes the entirety of organisms floating in the water column without the ability to actively swim against the current
For long-time comparisons of changes in plankton composition, data of fossil plankton is of major interest
Specimens were originally found in the Birkhof quarry in the Blumenberg area near Eichstätt (Solnhofen Lithographic Limestones, Upper Jurassic, Tithonian, Hybonotum zone, Riedense subzone; Schweigert, 2007)
Summary
Plankton describes the entirety of organisms floating in the water column without the ability to actively swim against the current. Plankton has been recognised as an important basis for marine ecosystems in modern seas. Our understanding of changes in plankton composition are important in modern conservation biology and ecology, but are of economic importance (e.g., Duffy & Stachowicz, 2006; Torres et al, 2013; Sardet, 2015). Plankton must have been important in the past as it is today. Our knowledge of plankton in the past is often limited to very specific groups of organisms, namely those with strongly sclerotised and/or mineralised morphological structures, or those composed of certain decay-resisting substances such as resting cysts
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