In pursuit of understanding: Fossils that do not fit our world-view

John St James Stewart Buckeridge (Australia)

It is through observation and categorisation of the living and inanimate objects around us that we develop an acceptable world-view of our environment. But what happens when something we observe does not fit a recognised category? This is less common today perhaps, because we have confidence in our scientific knowledge.

However, there are still uncertainties and these are most apparent when we try to unravel the past – especially the nature of extinct organisms. This article revolves around some very unusual southern hemisphere fossils that, for a long time, did not fit any known category. This is the Waiparaconus enigma – a tale that began in New Zealand during the second half of the nineteenth century.

An enigmatic fossil

In 1871, the Prussian geologist Sir Julius von Haast, while working for the Canterbury government in the New Zealand colony, reported seeing some curious fossils from the Waipara Gorge in mid Canterbury (Fig. 1 and 2). These fossils, which Haast considered to be allied to the rudistid bivalve Radiolites, were found in the “… thick greensand strata overlying the Septarian clays” (Haast, 1871:45).

On the basis of this tentative taxonomy, Haast concluded that the strata were late Cretaceous. However, the beds – today known as the Waipara Greensand – are now recognised to be of Palaeocene age (McGregor, 1986). The unusual fossils were essentially long tubular structures, comprised of micritic calcite (Buckeridge, 1993). That they are organic is clear, the delicacy, morphologic envelope and disposition being testament to a living organism (Figs. 3, and 4).

For the next 60 years, these fossils remained incertae sedis, until English palaeontologist Thomas Withers, working at the British Museum (Natural History) examined some specimens presented to the museum as “problem fossils” – with a request to clarify their taxonomic location. Withers was a fossil barnacle expert, and had wide experience of the variety and distribution of these crustaceans. He had recently been studying fossils of the stalked barnacle Euscalpellum from North America, and saw sufficient similarities between this New Zealand material and the American to identify the Waipara Gorge material as “monstrously developed peduncles of Euscalpellum” (Withers, 1951: 153). For the time being, the palaeontological world accepted this placement.

Revisiting the site

In the middle 1970s, while undertaking fieldwork in mid Canterbury on the east coast of New Zealand’s South Island, I had an opportunity to visit the Waipara Gorge. I was particularly interested in rocks of latest Cretaceous to early Palaeocene age, for it was at this time that acorn barnacles (which were the object of my research) first appeared in the fossil record. Although fossiliferous rocks of Palaeocene age are rare anywhere in the world, some of the best are known from shallow water lithologies in the Palaeocene of New Zealand.

I knew of Withers’ work, purporting that barnacles were abundant in Middle Waipara Gorge lithologies, so I was relatively confident of finding some there. The quest for any definitive barnacle fossils was unsuccessful, although I did find unusual calcareous tubes exposed in vertical glauconitic sandstone beds (Fig. 2). These were the remains that Withers had identified as scalpelliform barnacles and had called Euscalpellum zealandicum. However, as I soon found, these fossils did not easily lie within the Crustacea, far less the Cirripedia (barnacles).

There were problems with Withers’ assignment – his reconstruction showed that growth would have proceeded in the opposite direction to that of all known stalked barnacles. The solid nature of the tubes too would have been unique among barnacles and, strangely (and importantly), there was no evidence of any of the capitular plates that characterise scalpelliform barnacles such as Euscalpellum. There are at least 14 of these thick, calcareous plates that protect the capitulum of species like Euscalpellum and Trianguloscalpellum (Fig. 5).

Further, they are generally the only remains found of fossil scalpelliform barnacles and, as such, significant numbers of them could be expected to have been entrapped between the numerous stalks (see Figs. 3 and 4). They were not. Nonetheless, it seems that Withers was confident in his identification.

Some 30 years later, in my 1983 monograph, when explaining why they could not be cirripedes, I made the cardinal mistake of asserting no formal taxonomic assignation; rather, these fossils were left as incertae sedis, with a suggestion that perhaps they could be annelids (Buckeridge, 1983: 116).

Revisiting the taxonomic placement

By concluding that a fossil is “not something” but failing to suggest exactly what it is, did little to advance science. “… perhaps it could be included within the Annelida” was, in hindsight, not likely to be useful to anybody describing the palaeontology of the region. Others, such as Seilacher & Seilacher-Drexler (1986), did not help either – with no further support for a barnacle origin, they simply accepted Withers’ interpretation and included reference to the material as E. zealandicum.

This prompted a re-think on my behalf and, ignoring helpful comments from family as to what these fossils really were (Fig. 6), I undertook further collecting and evaluation. This also provided an opportunity to study new material, attributed to this taxon from the Antarctic and Western Australia (both of late Cretaceous age). A careful observation of the material demonstrates that the “imbricating scales” (i.e., the overlapping calcareous plates) are much more clearly defined at the sharper end of the tube; importantly, these are successively buried (or covered) as one moves towards the broader end.

This is demonstrated particularly well in Waiparaconus from the late Cretaceous Gingin Chalk of Western Australia (Fig. 7).

The Western Australian material has fewer imbricating “scales” than many of the specimens from New Zealand and the Antarctic (Fig. 8).

However, they can be shown to be part of a continuum – an overlapping morphological series. Those specimens with extended smooth basal sections, from all localities, also possess fine, longitudinal striae on the smoother surfaces (Fig. 7).

Importantly, even though the wider (basal) portion of the tubes is older, it is not more corroded, as would be expected if it were exposed. Indeed, a tube of this nature would be a great place for encrusting organisms to settle, unless of course it was a sub-surface anchor (as Seilacher & Seilacher-Drexler proposed). But even if it were an anchor, almost certainly part of it, or adjacent dead specimens could have eventually been exposed on the seabed – as they are very abundant (Fig. 2). However, there is no indication at all of effects that would be associated with exposure, leading to the conclusion that, upon death, these heavy structures would simply settle into the sediment.

Further, a series of longitudinal thin sections through the tube demonstrated that Waiparaconus is made up of a series of calcareous cones, the apical end directed towards the end with the greatest abundance of scales and the wider end thinning at the base, to progressively cover older cones (and “scales”) as they are added. On the basis of this, I argued that the structure was most likely internal (Buckeridge, 1993).

My conclusions are that an invertebrate produced the structure. It was bottom dwelling, living in areas of low clastic input and surprisingly with few or no other associated organisms with mineralised skeletons. All the material collected comes from glauconite-rich sands or glauconitic marls and this led me to conclude that they lived an area of low biodiversity, somewhere between middle to outer shelf (Buckeridge, 1993).

The New Zealand site is the most prolific and is the only location where Waiparaconus comprises distinct beds. Due to its proximity to thin horizons of scour and fill, the material may have undergone some sorting and transportation. However, although all specimens lie parallel or sub parallel to bedding, this is not necessarily evidence of transport as such, it is simply a natural position of repose. It is likely that transport would have been very minor, as material of this nature would quickly break up. I also confirmed that the minor weathering that occurs on the surface of the Waipara material was diagenetic, being due to solution pitting at the quartz grain calcite interface (Buckeridge, 1993).

The task then became one of determining what could have had an internal skeleton such as this. I did not wish to repeat the same mistake as in 1983 – placing it in incertae sedis!

Drawing the threads together

Effective taxonomic placement needs to start broadly, but then quickly focus on the most realistic options. Of the available phyla to accommodate organisms like this, the Echinodermata were eliminated, primarily due to the nature of the calcite. The Annelida possess nothing quite like this, nor were there any similar forms in the Porifera, Arthropoda, Brachiopoda, Bryozoa or Mollusca (the lack of a “lid” being an important reason why it could not be a rudistid).

If we leave out the unlikely conclusion that it is a representative of a new, and otherwise unknown phylum, the group that has most appeal is the Cnidaria, in particular the Octocorallia: Pennatculacea (sea pens) and, therefore, I assigned it to this group (Buckeridge, 1993). Although mineralised peduncles of sea pens are not known, examples such as shown in Fig. 9, if mineralised, would be not unlike Waiparaconus.

In this specimen, the individual polyps are present on the curved dark-red part. This is the only part of the sea pen that would be visible (that is, above the water-sediment interface) and is here interpreted as being the apical end of Waiparaconus. In Waiparaconus, each scale would have been the site for a polyp attachment or for a rachis (an extended branch) of polyps. The smooth, lower end of the specimen in Fig. 9 does not have an exact corollary in Waiparaconus, although this may simply be represented by the basal part of the fossil. Much or all of the lower (wider) part of the Waiparaconus tube was likely covered in tissue during the lifetime of the animal and would have assisted with anchoring it in the sediment.

As noted, there is always the option to erect a new phylum to accommodate unusual forms. In this case, there is sufficient evidence not only to place it within the Cnidaria, but also to drill down to subclass level. Octocorals are uncommon in shallow waters and living examples typically lack a mineralised skeleton. Nonetheless, octocorals are corals, and there is a precedent for mineralisation – many fossil octocorals, such as Graphularia, recorded from the Tertiary of Australasia, Europe and North America, possess a mineralised skeleton. Therefore, it is most unfortunate and confusing to read in the compendium produced by Sepkoski (2002) that Waiparaconus is a recognised taxon, but that its location within the Cirripedia is both “valid” and an “opinion”. Hedging one’s bets? Indeed!

References

Buckeridge, J. S., 1983. The fossil barnacles (Cirripedia: Thoracica) of New Zealand and Australia. New Zealand Geological Survey, Paleontological Bulletin 50, 151 pp.

Buckeridge, J. S., 1993. A re-evaluation of the Gondwanan invertebrate Waiparaconus as a coelenterate. Records of the Western Australian Museum,16: 221–233.

Haast, Sir Julis von, 1871. On the Geology of the Amuri District, in the Provinces of Nelson and Marlborough. Geological Survey of New Zealand Reports of Geological Exploration 1870-1, 6: 25-46.

Seilacher, A and E. Seilacher-Drexler, 1986. Sekundäre Weichbodenbewohner unter den Cirripediern. Paläontologie Zeitschrift 60: 75-92.

Sepkoski, J. J. 2002. A compendium of fossil marine animal genera. Bulletins of American Paleontology 363:1–560

(As both “opinion” and “valid taxa”) In online Paleobiology Database:

http://paleodb.org/cgi-bin/bridge.pl?user=Guest&action=displayPage&page=OSA_1_marine_animals )

Withers, T. H. 1951. Cretaceous and Eocene peduncles of the cirripede Euscalpellum. Bulletin of the British Museum (Natural History) Geology, 1: 149-162.

McGregor, E. 1987. (Compiler) Bibliographic index of New Zealand stratigraphic names to 31 December 1986. New Zealand Geological Survey Bulletin 102, 258 pp.