CLADOGRAM OF THE CRANIATE CLASSES AFTER BENTON (2005)

This is a simplification of Benton (2005) by 21 craniate groups that I interpret at the class-level. The 12 extinct taxa are given in red letters. The two extant agnathan classes are clearly members of different clades. The agnathans (Myllokunmingiida – Cephaloaspidomorphi), in general, grade gradually to the gnathostomes (Placodermi – Archosauromorpha). The gnathostome fishes (Placodermi – Osteichthyes) grade to the tetrapods (Stegocephali – Archosauromorpha). The tetrapods have three major extant clades: the Batrachomorphs (tetrapods with an aquatic larval form), Mammals (tetrapods with a lower jaw made of a single bone and three bones associated with the middle ear), and the Sauromorphs (Anapsida – Archosauromorpha).

1. Animals with a hollow dorsal nerve cord, notochord, and pharyngeal gill slits. 2. Body elongate, myomeres. 3. Brain encapsulated, or at least partially so, by a cartilaginous or bony cranium. 4. Vertebrae, associated with or replace notochord. 5. Head shield of dermal bone; bony scales. 6. Paired spines or fins. 7. Neurocranium encloses brain dorsally. 8. Mouth formed by articulated jaws. 9. Teeth erupt from dental lamina. 10. Paired fin radials barely extend beyond body. 11. Gills covered by an operculum. 12. Pectoral and pelvic girdles anchored to vertebral column. 13. Digits reduced to 5 or fewer; radius as long as the ulna. Operculum lost. 14. Premaxilla less than 2/3 skull width. 15. Egg with an outer amnion membrane. 16. One temporal fenestra formed by the squamosal and jugal bones. 17. Large post-temporal fenestra; suborbital foramen in palate. 18. Two temporal fenestrae; upper one formed by the squamosal and postorbital bones. 19. Trunk ribs single-headed, end of humerus robust.

By Jack R. Holt. Last revised: 01/14/2010