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Scientists measuring the mantle width of a large female giant squid of c. 2 m (6.6 ft) ML. Mantle length (ML) is the standard size measure for coleoid cephalopods (shell diameter being more common for nautiluses) and is almost universally reported in the scientific literature.
Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle.Endocerida was a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Silurian.
Cameroceras exhibited a broad range of sizes, and some species were fairly large by extinct cephalopod standards. One species, C. turrisoides from the Boda Limestone of Sweden , [ 2 ] is estimated to have shell around 2 metres (6.6 ft) in length, [ 3 ] while that of C. rowenaense was about 70 centimetres (2.3 ft). [ 1 ]
Cephalopods are widely regarded as the most intelligent of the invertebrates and have well-developed senses and large brains (larger than those of gastropods). [13] The nervous system of cephalopods is the most complex of the invertebrates [14] [15] and their brain-to-body-mass ratio falls between that of endothermic and ectothermic vertebrates.
Endoceratidae is a family of large to very large straight shelled nautiloid cephalopods belonging to the order Endocerida that lived during the Middle and Late Ordovician. They include the largest known Paleozoic invertebrates, represented by Endoceras and Cameroceras. [1] [2]
Flower 1950, in Flower & Kümmel, A Classification of the Nautiloidea, Journal of Paleontology 243 Sept 1950 Flower 1976, Ordovician Cephalopod Faunas and Their Role in Correlation; The Ordovician System; proceedings of a palaeonotlogical Association symposium, Birmingham U.K. 1974.
Nautiluses are much closer to the first cephalopods that appeared about 500 million years ago than the early modern cephalopods that appeared maybe 100 million years later (ammonoids and coleoids). They have a seemingly simple brain, not the large complex brains of octopus, cuttlefish and squid, and had long been assumed to lack intelligence ...
Flower 1950 in Flower and Kummel 1950, A Classification of the Nautiloidea; Journal of Paleontology 24(5):604-616, Sept 1950 Kroger 2008, Brief Report, A new genus of middle Tremadocian orthoceratoids and the Early Ordovician origin of orthoceratoid cephalopods; Acta Palaeontologica Polonica 53 (4): 745–749, 2008