Final answer:
The 11 generalized synapomorphies of gnathostomes, including placoderms, are jaws, paired appendages/fins, bone/dermal skeleton, vertebrate column, internal gill slits, internal fertilization, ectothermy, neural crest cells, specialized teeth, olfactory organs, and higher metabolic rate.
Step-by-step explanation:
The 11 generalized synapomorphies (shared derived characteristics) of gnathostomes, including placoderms, are:
- Jaws
- Paired appendages/fins (pectoral and pelvic fins)
- Bone/dermal skeleton
- Vertebrate column (backbone)
- Internal gill slits
- Internal fertilization
- Ectothermy (cold-bloodedness)
- Neural crest cells
- Specialized teeth
- Olfactory organs
- Higher metabolic rate
These characteristics are important milestones in the evolution of vertebrates that allowed gnathostomes to diversify and become successful in various environments.