Dunkleosteus a very large (up to 33 feet and 4 tons) armoured fish from the Late Devonian 382–358mya.
Ammonoids arose in the Devonian and survived until 66mya.

You will need two skeins of yarn in contrasting colours, 145-155 yds of each. My square weighs c.55 grams.

The pattern is 47sts by 58 rows done in double knitting, and comes out at 10 inches square on 4mm needles.

You could use thicker yarn and larger needles for a larger square if you wish.