DIPLOMOCERAS OF HORNBY / JA-DAI-AICH

Diplomoceras sp.

This gorgeous cream and brown big beast of a heteromorph, Diplomoceras (Diplomoceras) sp., (Hyatt, 1900) was found within the 72 million-year-old sediments of the upper Nanaimo Group on the northern Gulf Island of Hornby in southwestern British Columbia, Canada. 

The site is known as Boulder Point to the locals and it has been a popular fossil destination for many years. It is the home of the K'ómoks First Nation, who called the island Ja-dai-aich.

Many of the fossils found at this locality are discovered in concretions rolled smooth by time and tide. The concretions you find on the beach are generally round or oval in shape and are made up of hard, compacted sedimentary rock. 

If you are lucky, when you split these nodules you are rewarded with a fossil hidden within. That is not always the case but the rewards are worth the effort. 

These past few years, many new and wonderful specimens have been unearthed — particularly by members of the Vancouver Island Palaeontological Society. 

And so it was in the first warm days of early summer last year. Three members of the Vancouver Palaeontological Society excavated this 100 cm long fossil specimen over two days in June of 2020. The specimen was not in concretion but rather embedded in the hard sintered shale matrix beneath their feet. It was angled slightly downward towards the shoreline and locked within the rolling shale beds of the island. 

Diplomoceratidae (Spath, 1926) are often referred to as the paperclip ammonites. They are in the family of ammonites included in the order Ammonitida in the Class Cephalopoda and are found within marine offshore to shallow subtidal Cretaceous — 99.7 to 66.043 million-year-old — sediments worldwide. 

I was reading with interest this morning about a new find published by Muramiya and Shigeta in December 2020 of a new heteromorph ammonoid Sormaites teshioensis gen. et sp. nov. (Diplomoceratidae) described from the upper Turonian (Upper Cretaceous) in the Nakagawa area, Hokkaido, northern Japan. This lovely has a shell surface ornamented with simple, straight, sharp-tipped ribs throughout ontogeny, but infrequent flared ribs and constrictions occur on later whorls. Excluding its earliest whorls, its coiling and ornamentation are very similar to Scalarites mihoensis and Sc. densicostatus from the Turonian to Coniacian in Hokkaido and Sakhalin, suggesting that So. teshioensis was probably derived from one of these taxa in the Northwest Pacific during middle to late Turonian.

Much like the long-lived geoducks living in Puget Sound today, studies of Diplomoceras suggest that members of this family could live to be over 200 years old — a good 40-years longer than a geoduck but not nearly as long-lived as the extant bivalve Arctica islandica that reach 405 to 410 years in age. 

Along with this jaw-dropper of a heteromorph, the same group found an Actinosepia, gladius — internal hard body part found in many cephalopods of a Vampyropod. Vampyropods are members of the proposed group Vampyropoda — equivalent to the superorder Octopodiformes — which includes vampire squid and octopus.

The upper Nanaimo Group is a mix of marine sandstone, conglomerate and shale. These are partially exposed in the Campanian to the lower Maastrichtian outcrops at Collishaw Point on the northwest side of Hornby Island.

Along with fossil crabs, shark teeth, bivalves and occasional rare and exquisite saurodontid fish, an ambush predator with very sharp serrated teeth and elongate, torpedo-like body — we also find three heteromorph ammonite families are represented within the massive, dark-grey mudstones interlaminated and interbedded with siltstone and fine-grained sandstone of the upper Campanian (Upper Cretaceous) strata of the Northumberland Formation exposed here: Baculitidae, Diplomoceratidae and Nostoceratidae. 

A variety of species are distinguished within these families, of which only three taxa – Baculites occidentalis (Meek, 1862), Diplomoceras (Diplomoceras) cylindraceum (Defrance, 1816) and Nostoceras (Nostoceras) hornbyense (Whiteaves, 1895), have been studied and reported previously. 

Over the last decade, large new collections by many members of the Vancouver Island Palaeontological Society and palaeontologists working at the Geologic Survey of Canada, along with a renewed look at previous collections have provided new taxonomic and morphometric data for the Hornby Island ammonite fauna. This renewed lens has helped shape our understanding and revamp descriptions of heteromorph taxa. Eleven taxa are recognized, including the new species Exiteloceras (Exiteloceras) densicostatum sp. nov., Nostoceras (Didymoceras?) adrotans sp. nov. and Solenoceras exornatus sp. nov. 

A great variety of shape and form exist within each group. Morphometric analyses by Sandy McLachlan and Jim Haggart of over 700 specimens unveiled the considerable phenotypic plasticity of these ammonites. They exhibit an extraordinarily broad spectrum of variability in their ornamentation and shell dimensions. 

The presence of a vibrant amateur palaeontological community on Vancouver Island made the extent of their work possible. Graham Beard, Doug Carrick, Betty Franklin, Raymond Graham, Joe Haegert, Bob Hunt, Stevi Kittleson, Kurt Morrison and Jean Sibbald are thanked for their correspondence and generosity in contributing many of the exquisite specimens featured in that study. 

These generous individuals, along with many other members of the Vancouver Island Palaeontological Society (VIPS), Vancouver Paleontological Society (VanPS), and British Columbia Paleontological Alliance (BCPA), have contributed a great deal to our knowledge of the West Coast of Canada and her geologic and palaeontological correlations to the rest of the world; notably, Dan Bowen, Rick Ross, John Fam and Pat and Mike Trask, Naomi & Terry Thomas. Their diligence in the collection, preparation and documentation of macrofossils is a reflection of the passion they have for palaeontology and their will to help shape the narrative of Earth history.

Through their efforts, a large population sample of Nostoceras (Nostoceras) hornbyense was made available and provided an excellent case study of a member of the Nostoceratidae. It was through the well-documented collection and examination of a remarkable number of nearly complete, well-preserved specimens that a re-evaluation of diagnostic traits within the genus Nostoceras was made possible. 

The north-east Pacific Nostoceras (Nostoceras) hornbyense Zone and the global Nostoceras (Nostoceras) hyatti Assemblage Zone are regarded as correlative, reinforcing a late Campanian age for the Northumberland Formation. This builds on the earlier work of individuals like Alan McGugan and others. McGugan looked at the Upper Cretaceous (Campanian and Maastrichtian) Foraminifera from the Upper Lambert and Northumberland Formations, Gulf Islands, British Columbia, Canada.

The Maastrichtian Bolivina incrassata fauna (upper part of Upper Lambert Formation) of Hornby Island (northern Comox Basin) is now recognized in the southern Nanaimo Basin on Gabriola and Galiano Islands. The Maastrichtian planktonic index species Globotruncana contusa occurs in the Upper Northumberland Formation of Mayne Island and Globotruncana calcarata (uppermost Campanian) occurs| in the Upper Northumberland Formation of Mayne Island and also in the Upper Lambert Formation at Manning Point on the north shore of Hornby Island (Comox Basin).

Very abundant benthonic and planktonic foraminiferal assemblages from the Upper Campanian Lower Northumberland Formation of Mayne Island enable paleoecological interpretations to be made using the Fisher diversity index, triangular plots of Texturlariina/Rotaliina/Miliolina, calcareous/agglutinated ratios, planktonic/benthonic ratios, generic models, and associated microfossils and megafossils. 

Combined with local geology and stratigraphy a relatively shallow neritic depositional environment is proposed for the Northumberland Formation in agreement with Scott but not Sliter who proposed an Outer shelf/slope environment with depths of 300 m or more.

References & further reading: Sandy M. S. McLachlan & James W. Haggart (2018) Reassessment of the late Campanian (Late Cretaceous) heteromorph ammonite fauna from Hornby Island, British Columbia, with implications for the taxonomy of the Diplomoceratidae and Nostoceratidae, Journal of Systematic Palaeontology, 16:15, 1247-1299, DOI: 10.1080/14772019.2017.1381651

Crickmay, C. H., and Pocock, S. A. J. 1963. Cretaceous of Vancouver, British Columbia. American Association of Petroleum Geologists Bulletin, 47, pp. 1928-1942.

England, T.D.J. and R. N. Hiscott (1991): Upper Nanaimo Group and younger strata, outer Gulf Islands, southwestern British Columbia: in Current Research, Part E; Geological Survey of Canada, Paper 91-1E, p. 117-125.

McGugan, Alan. (2011). Upper Cretaceous (Campanian and Maestrichtian) Foraminifera from the Upper Lambert and Northumberland Formations, Gulf Islands, British Columbia, Canada. Canadian Journal of Earth Sciences. 16. 2263-2274. 10.1139/e79-211. 

Scott, James. (2021). Upper Cretaceous foraminifera of the Haslam, Qualicum, and Trent River formations, Vancouver Island, British Columbia /. 

Sliter, W. & Baker, RA. (1972). Cretaceous bathymetric distribution of benthic foraminifers. Journal of Foraminiferal Research - J FORAMIN RES. 2. 167-183. 10.2113/gsjfr.2.4.167. 

Spath L. F. 1926. A Monograph of the Ammonoidea of the Gault; Part VI. Palaeontographical Society London

Sullivan, Rory (4 November 2020). "Large squid-like creature that looked like a giant paperclip lived for 200 years — 68 million years ago". The Independent. Archived from the original on 4 November 2020.

Urquhart, N. & Williams, C.. (1966). Patterns in Balance of Nature. Biometrics. 22. 206. 10.2307/2528236. 

Yusuke Muramiya and Yasunari Shigeta "Sormaites, a New Heteromorph Ammonoid Genus from the Turonian (Upper Cretaceous) of Hokkaido, Japan," Paleontological Research 25(1), 11-18, (30 December 2020). https://doi.org/10.2517/2020PR016.

Photos: Vancouver Island Palaeontological Society, Courtenay, British Columbia, Naomi and Terry Thomas.