Unraveling the insect head: Segmentation and pancrustacean homologies

Area of Science:

• * Evolutionary developmental biology
• * Comparative morphology
• * Arthropod phylogeny

Background:

• * The segmental composition of arthropod heads, especially insects, is a complex and debated topic.
• * Fusion and modification of segments during insect development obscure their postembryonic segmentation patterns.

Purpose of the Study:

• * To propose a novel interpretation of insect head morphology and segmentation.
• * To reconcile current genetic and embryological data with morphological interpretations.

Main Methods:

• * Utilized 3D-reconstruction techniques on a Cretaceous thripidan fossil.
• * Reassessed the 'anterior tentorial arm' in light of developmental processes.
• * Analyzed mandibular articulation and labrum morphology in Pancrustacea.

Main Results:

• * Identified intercalary segment remnants (intercalates), providing evidence for a revised head segmentation model.
• * Interpreted the 'anterior tentorial arm' as part of a lateral segmental suture.
• * The two-jointed mandibular articulation is proposed as symplesiomorphic for Insecta, challenging the monophyly of Dicondylia.

Conclusions:

• * The proposed reinterpretation aligns with existing genetic and embryological data.
• * The findings necessitate a re-evaluation of insect head segmentation and the definition of the Dicondylia clade.
• * New perspectives are offered on the evolution of the labrum in Pancrustacea.