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The origin and evolution of the euarthropod labrum
1Department of Earth Sciences, Palaeobiology Programme, Uppsala University, Villavägen 16, Uppsala, SE 752 36, Sweden.
Arthropod Structure & Development
|April 16, 2021
Summary
The labrum in arthropods likely evolved from anterior appendages. New fossil evidence suggests a protocerebral brain was present early in euarthropod evolution, with the deutocerebrum developing later.
Area of Science:
- Evolutionary Biology
- Paleontology
- Arthropod Morphology
Background:
- The labrum, a key feature of euarthropods, is hypothesized to originate from anterior appendages.
- Reconstructions of early euarthropod evolution are complicated by challenges in interpreting fossil appendages.
Purpose of the Study:
- To review evidence for labrum evolution in extant taxa.
- To re-evaluate fossil arthropod interpretations based on labrum evolution.
- To investigate the segmental identity of fossil arthropod head appendages.
Main Methods:
- Review of existing literature on labrum evolution in living arthropods.
- Analysis of fossil evidence, specifically from the Cambrian stem-group euarthropod Parapeytoia.
- Reinterpretation of segmental homologies and central nervous system evolution in fossil arthropods.
Main Results:
- Evidence from living taxa supports the hypothesis of labrum evolution from anterior appendages.
- Fossil evidence from Parapeytoia suggests a persistent protocerebral appendage in early euarthropods.
- This challenges existing models of segmental homologies and brain evolution.
Conclusions:
- The deutocerebrum likely evolved later in euarthropod history.
- A protocerebral brain was likely ancestral to a large part of the euarthropod stem group.
- Revisions to arthropod phylogeny and head evolution models are necessary.
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