Xenacanthiformes References Xenacanthiformes fossil fish order Ask Anything Homework Help Written by The Information Architects of Encyclopaedia Britannica The Information Architects maintain a master list of the topics included in the corpus of Encyclopædia Britannica, and create and manage the relationships between them. The Information Architects of Encyclopaedia Britannica Britannica AI Ask Anything Learn about this topic in these articles: fish/ Chondrichthyes: sharks and rays…ago, while the freshwater order Xenacanthiformes lasted until the end of the Triassic, about 200 million years ago. The final Devonian order, Heterodontiformes, still has surviving members. Read More…ago, while the freshwater order Xenacanthiformes lasted until the end of the Triassic, about 200 million years ago. The final Devonian order, Heterodontiformes, still has surviving members. Read More