| Modern vertebrates are classified into two major groups, the gnathostomes and the agnathans. |
| The repeated appearance of higher grades was true long before primates, before mammals, or any vertebrates. |
| In insects, as in all arthropods, the main nerve cord lies ventrally, rather than dorsally as in vertebrates. |
| One of the most prominent characteristics of early vertebrates is the elongate caudal fin bearing fin rays. |
| In modern classification schemes, living vertebrates consist of two main groups, the jawless Agnatha and the jawed Gnathostomata. |
| Their eggs are large, green, and poisonous to warm-blooded vertebrates, including humans. |
