A Silurian short-great-appendage arthropod

Area of Science:

• Paleontology
• Evolutionary Biology
• Arthropod Research

Background:

• The phylogenetic position of the extinct arthropod group Megacheira (short-great-appendage arthropods) has been debated, with interpretations including stem chelicerates or stem euarthropods.
• Megacheirans have primarily been known from Cambrian strata, with their presence in younger rocks being uncertain.

Purpose of the Study:

• To describe a new Silurian arthropod taxon, Enalikter aphson gen. et sp. nov.
• To reassess the phylogenetic position of Megacheira using new fossil evidence.
• To investigate the evolutionary history and survival of the Megacheira group.

Main Methods:

• Description of a new fossil arthropod, Enalikter aphson, from the Silurian Herefordshire Lagerstätte.
• Phylogenetic analysis incorporating Enalikter and Bundenbachiellus into a comprehensive morphological database.
• Comparative analysis of morphological data to determine evolutionary relationships.

Main Results:

• Enalikter aphson is described from the Silurian (Wenlock Series), representing the first megacheiran found in strata younger than the mid-Cambrian.
• Phylogenetic analysis, including Enalikter and Bundenbachiellus, strongly supports a stem euarthropod position for Megacheira.
• Enalikter is the only fully three-dimensionally preserved stem-group euarthropod, offering insights into euarthropod origins.
• The recognition of Enalikter and Bundenbachiellus confirms that megacheirans persisted for nearly 100 million years beyond the mid-Cambrian.

Conclusions:

• Megacheirans are confirmed as stem euarthropods, clarifying their evolutionary placement.
• The discovery of Enalikter and Bundenbachiellus extends the known temporal range of Megacheira significantly.
• This research provides crucial data for understanding the early evolution and diversification of euarthropods.