Complex brain and optic lobes in an early Cambrian arthropod

Area of Science:

• Paleontology
• Evolutionary Biology
• Neuroscience

Background:

• Understanding arthropod evolutionary relationships relies heavily on nervous system data.
• Fossil preservation of neural tissue is rare, limiting insights into early arthropod sensory and motor capabilities.
• Previous analyses of early arthropods' nervous systems focused on external features.

Purpose of the Study:

• To investigate the neuroanatomy of the stem-group arthropod Fuxianhuia protensa from the Cambrian period.
• To provide compelling fossil evidence for arthropod nervous system evolution.
• To resolve debates regarding the ancestral state of insect brains.

Main Methods:

• Exceptional preservation of fossilized neural tissue (brain and optic lobes) in Fuxianhuia protensa.
• Detailed analysis of neuroanatomical structures, including optic centres, deutocerebrum, and tritocerebrum.
• Comparative neuroanatomical analysis with extant arthropod groups (Malacostraca, Insecta, Branchiopoda).

Main Results:

• Fuxianhuia protensa exhibits a tripartite pre-stomodeal brain with three nested optic centres, similar to extant Malacostraca and Insecta.
• The deutocerebrum is innervated by antennal nerves, and a tritocerebral component is identified.
• This complex brain structure in early arthropods suggests sophisticated visual behaviors were possible.
• Fuxianhuia's neuroanatomy supports cladistic analyses, indicating Branchiopoda evolved from a malacostracan-like ancestor with subsequent brain simplification.

Conclusions:

• The complex brain of Fuxianhuia protensa demonstrates that sophisticated nervous systems were present in early-diverging arthropods.
• This fossil evidence challenges molecular analyses suggesting simpler ancestral states for Hexapoda.
• The early evolution of complex brains likely drove versatile visual behaviors in Cambrian arthropods.