Pulmonoscorpius pp
The Pulmonoscorpius were giant scorpions that lived in the Carboniferous period's Scotland and reached 50-70 centimeters. The reason of why they were so large is the high oxygen level that allowed the arthropods to grow to very large sizes.

They fed on smaller arthropods and tetrapods and they were probably preyed upon by the giant labyrinthodont amphibian Crassigyrinus.