|Aturia angustata, Lower Miocene, WA|
There are seven living nautiloid species in two genera: Nautilus pompilius, N. macromphalus, N. stenomphalus, N. belauensis, and the three new species being described from Samoa, Fiji, and Vanuatu (Ward et al.). We have specimens of fossil nautiloids dating to the Turonian of California, and possibly the Cenomanian of Australia. There has also been a discovery of what might be the only known fossil of Allonautilus (Ward and Saunders, 1997), from the Nanaimo Group of British Columbia, Canada.
|Aturia in the Collection of Rick Ross, VIPS|
Aturia lived in cooler water in the Cenozoic, preferring it over the warmer waters chosen by their cousins. Aturia, are commonly found as fossils from Eocene and Miocene outcrops. That record ends with their extinction in the late Miocene. This was a fierce little beast with jaws packed with piranha-like teeth. They grew at least twice that of the largest known Nautilus living today.
Aturia is characterized by a smooth, highly involute, discoidal shell with a complex suture and subdorsal siphuncle. The shell of Aturia is rounded ventrally and flattened laterally; the dorsum is deeply impressed. The suture is one of the most complex within the subclass Nautiloidea. Of all the nautiloids, he may have been able to go deeper than his brethren.
Nautiloids are known for their simple suturing in comparison to their ammonite cousins. This simplicity of design limited their abilities in terms of withstanding the water pressure experienced when several atmospheres below the sea. Nautiloids were not able to compete with their ammonite cousins in this regard.
Instead of elaborate and complex sutures capable of withstanding the pressures of the deep, nautiloids have simpler sutures that would have them enfold on themselves and crush at depth.
|Aturia angustata; Rick Ross Collection|
The siphuncle is moderate in size and located subdorsally in the adapical dorsal flexure of the septum. Based on the feeding and hunting behaviours of living nautiluses, Aturia most likely preyed upon small fish and crustaceans.
I've found a few of these specimens along the beaches of Clallam Bay and nearby in a local clay quarry. I've also seen calcified and chalcedony — microcrystalline quartz — agatized beauties of this species collected from river sites within the Olympic Peninsula range. In the bottom photos, you can see Aturia from Washington state and one (on the stand on the left) from Oregon, USA. These beauties are in the collections of the deeply awesome Rick Ross, Vancouver Island Palaeontological Society.
References: Ward, P; Haggart, J; Ross, R; Trask, P; Beard, G; Nautilus and Allonautilus in the Nanaimo Group, and in the modern oceans; 12th British Columbia Paleontological Symposium, 2018, Courtenay, abstracts; 2018 p. 10-11