Here we describe an additional member of the Vitamin K-dependent protease family comprising the Gla-EGF1-EGF2-SP domain architecture. These proteases were found in different vertebrate classes including jawless fish, cartilaginous fish, bony fish, reptiles, birds and marsupials but not in other mammals. We have investigated for the first time the homolog of the garter snake Thamnophis sirtalis and thus called these proteases ‘sirtilins’.