Bactritida

Bactritida Temporal range: 407–231 Ma PreꞒ Ꞓ O S D C P T J K Pg N Pragian (questionable) or early Emsian – Middle Carnian Possible descendant taxon Coleoidea survives to present
Diagram showing evolution of Bactritida to Ammonoidea
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Clade:	Neocephalopoda
Subclass:	†Bactritoidea Shimanskiy, 1951
Order:	†Bactritida Shimanskiy, 1951
Families[1]
†Bactritidae †Parabactritidae †Ammonoidea? Coleoidea? Bactritida incertae sedis †Cochleiferoceras †Cyclobactrites

The Bactritida are a small order of more or less straight-shelled (orthoconic) cephalopods that first appeared during the Emsian stage of the Devonian period (407 million years ago) with questionable origins in the Pragian stage before 409 million years ago, and persisted until the Carnian pluvial event in the upper middle Carnian stage of the Triassic period (231 million years ago). They are considered ancestors of the ammonoids, as well as of the coleoids (octopus, squid, cuttlefish, and the extinct belemnites).

Bactritids are distinguished from the more primitive nautiloids by the small size and globular shape of the protoconch, the so-called embryonic shell. Nautiloids have relatively large embryonic shells, and living species lay a few large eggs. In contrast, bactritids and ammonoids produced large numbers of small eggs, each housing a small embryonic shell.