The oldest type of mineralized vertebrate tissues (known to date) is:
a. The test (tunic) of the Urochordata (tunicates)
b. Vertebral elements of early vertebrates
c. Dermal denticles of the Chondrichthyes
d. Tooth-like odontodes in agnathans (e.g. conodonts and ostracoderms)
e. The lingual cartilage of the Petromyzontiformes
