Aegirocassis benmoulae

Overview

Aegirocassis benmoulae is a large marine arthropod with filtering frontal appendages. Swimming flaps along its sides are divided into upper and lower tiers. It has been studied as an animal more than 2 m long that filtered small food particles from water.^[1][2]

Key facts

Each body segment did not carry just one tier of swimming flaps. The researchers described separate dorsal and ventral pairs. Following the body from the side reveals this distinctive two-tier arrangement.^[1]

Time and place

It is known from Early Ordovician Fezouata fossils around 480 million years old. The locality lies in present-day Morocco. The material allows investigation of the structures of a large arthropod from ancient seas.^[2]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

Central and lateral carapace elements are described on the head, with filtering appendages in front. Each body segment has separate pairs of dorsal and ventral swimming flaps. The paper gives a body length exceeding 2 m.^[1]

Habitat and reproduction

The frontal appendages are interpreted as devices for filtering small food particles from water. Considering a large body together with filtering appendages raises the idea that large animals did not necessarily live only by capturing large prey. The arrangement of trunk flaps invites comparison of structures used in water.^[1]

Fossil discovery

Research on the Fezouata material described frontal appendages together with swimming flaps along the trunk. Setal blades at the bases of the dorsal flaps were also described in the captions. A well-preserved large body led to comparisons of arthropod appendage arrangements.^[1][2]

References

1. Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps
2. Institutional guide — A giant Ordovician filter feeder
3. Bicknell et al. (2019) — Euproops specimens preserved together
4. Bicknell·Pates (2020) — An atlas of fossil and living horseshoe crabs

Research questions

What significance might two tiers of lateral flaps have for arthropod evolution? Researchers compared the upper and lower structures with other arthropod appendages. A distinctive structure in a large body added questions about the origins of small body parts.^[1]

Observation

After examining the filtering appendages in front of the head, follow the upper and lower swimming flaps along the body. Remembering that two tiers occur on the same segment makes the body arrangement clearer.^[1]