Order of fossil sharks with an elongate body, the two dorsal fins each with a spine, e.g. Cladoselache. They lived from the Devonian to the Carboniferous.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。