- Cephalopods diversified to a variety of shapes and sizes (see Figure 03). Eventually, a lineage progressed to ammonites in the late Silurian period.
- Also in the picture is a group of sea lilies (right); in front of them lie rounded clumps of flat corals and a few skeletons of horn-shaped (wrinkled) rugosa corals.
- FA of jawed fish - Placoderms (=plate skin) are armored by their extensive dermal skeleton. These dermal bones (or plates) form head and thoracic shields that are either articulated by distinctive joints or fused into a single unit. Pectoral fins are typically well developed. Bony shearing or crushing structures on the jaws substitute for true teeth, which are absent. The jaw joint is simple.
- At the end of the Silurian period, swamps and marshes beside the sea were already occupied by low vegetation composed of the most primitive types of vascular plants that reproduce like ferns.