Clinging On

As the human world reels under the malign influence of Coronavirus, my thoughts turn to Cretaceous barnacles. 

This sudden interest in extinct cirripedia is prompted by a paper published a month ago by Professor Andy Gale: New thoracican cirripedes (Crustacea) from the Cretaceous of Europe and North Africa.[1] It announces the discovery of new extinct genera and species of barnacle. There are two sorts: the acorn/wart-type (sessile) barnacles familiar from rocky shores and the stalk-type (pedunculate) 'goose barnacles' sometimes found attached to drift wood. 

I have never really thought about these crustacea before. They are easily overlooked - that is until you gash your hands or feet on them at the seaside, or eat them in a Portuguese restaurant. What crystallises my interest in them now is that one of the Zeugmatolepadid family now bears my name: Subsecolepas holtwilsoni. It is a lepadid barnacle - one of the stalked type. My thanks go to Andy for the honour. I think its taxonomic status is:

Phylum - Arthropoda

Clade - Mandibulata

Clade - Pancrustacea

Subphylum - Crustacea

Class - Maxillopoda

Infraclass - Cirripedia

Superorder - Thoracica

Order - Pedunculata

Suborder - Scalpelliformes

Clade - Thoracicalcarea

Family - Zeugmatolepadidae

Subfamily - Martillepadinae

Genus - Subsecolepas

Species - holtwilsoni 

Andy Gale is one of a very small band of palaeontological researchers active in the field of fossil cirripedes. Their most illustrious forebear is Charles Darwin. Thomas Withers was active from 1910 to the 1960s, and catalogued the fossils specimens at the Natural History Museum, London. " There can be no doubt the Wither's 'Catalogues' are to fossil lepadomorph and verrucomorph barnacles what Darwin's 'Monographs' are to Recent barnacles."[2] Andy has been one of the most prolific cirripede researchers in recent decades, focusing on the Cretaceous Chalk and publishing many papers. He says that S.holtwilsoni is common in chalk of the Upper Campanian stage in the UK, and that 400 fossil specimens have been found at various old pits in the Norwich area. He named it after me for helping him dig in these pits and for having been involved in their conservation, including Keswick, Catton, Cringleford and Whitlingham.

Collecting samples at Keswick, 2015

I have not visited any chalk pits lately. Britain today is in emergency 'lock-down', and I feel sorry for city-dwellers cooped up in flats and terraced houses. At least I have an extensive wildlife garden to ramble in, and I also enjoy exploring the meaning of our geological heritage.

Crustaceans of the Campanian seas are a great imaginative diversion - a dépaysement, as the French say. Geology and palaeontology call us out of our own time and down into the profound depths of planetary and biological evolution. I try to imagine the lifeworld of the extinct species that now bears my name.  

Here are photos of the type specimens of S.holtwilsoni, variously sourced from chalk pits at Keswick and Cringleford, and all are now archived in the Natural History Museum. They show elements of the set of hard, calcareous plates which enclose the head of the barnacle. 

Type specimens of Subsecolepas holtwilsoni. Image courtesy Andy Gale [1]

Stalked barnacles from JG Wood: 'The Illustrated Natural History'; Routledge, London, 1863

Darwin's drawing of a Middle Jurassic stalked barnacle Pollicipes concinnus,
as found attached to the shell of an ammonite.[3]

Contemporary stalked barnacles attach themselves to floating objects, particularly driftwood, turtles and ships. According to Andy Gale, S.holtwilsoni and other Zeugmatolepadids probably had a similar lifestyle, attaching to the shells of free-swimming ammonites and seabed-dwelling inoceramid bivalves as well as floating wood.[1, p.245] There must have been a steady rain of their plates falling into the carbonate-rich mud of the sea floor, perhaps 100 to 500 metres down.[4] 

The Campanian stage spans from 83.6 to 72.2 million years ago.[5], and chalk of this age is well-represented in Norfolk and Suffolk. I have visited many quarries of this period in the Gipping valley and Norwich areas. At Keswick and Cringleford I helped clear the chalk exposures so that Andy Gale could record the geological succession and take samples. The samples are treated with glauber's salt and freezing in a repeat process until the miniscule fossil fragments - echinoid spines, bits of coral, fish scale, shell, etc - are freed from their chalky matrix and can be examined under a microscope.  

Fossil residues from the Chalk (40x magnification)

  

The contrast between the physical reality of an old chalk pit, with its crumbly, scrub-infested chaos, and the clarified world of knowledge compiled by over 150 years of scientific research into the Chalk is remarkable. We now know much about the Earth's geography during the Campanian, for example that Europe was an archipelago of islands.[6] We know much about biodiversity and details of climate and chemistry.[7; 8]  

 

The world as it was in the late Cretaceous. Image courtesy Andy Gale [1]

All this is wonderful, radical stuff to explore during COVID-19 lock-down. Like astronomy, geology has the power to frame human life against an almost infinite scale of time and space. Like pedunculate cirripedes, we cling for a few seasons to our floating attachment points and then - like them - our debris will inevitably find its way to the metaphorical sea floor. Perhaps only our names, inscriptions and genetic coding will survive us, for a century or two at most. The history of taxonomic revision makes clear that not even species names backed up with diligent taxonomic description may be proof against time. 

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REFERENCES

[1] - Gale, A.S. New thoracican cirripedes (Crustacea) from the Cretaceous of Europe and North Africa. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 295 Heft 3 (2020), pp.243-282. [Link accessed May 2020]
[2] - Southward, AJ. Barnacle Biology. CRC Press, 1987; chapters 2.1 and 2.2.
[3] - Darwin, CR. A monograph on the fossil Lepadidæ, or pedunculated cirripedes of Great Britain. Palæontographical Society, London, 1851 Plate 3, Fig.1. Downloadable here. [Link accessed May 2020]
[4] - Rawson, PF. Cretaceous: Sea Levels peak as the North Atlantic Opens, in: Brenchley, PJ & Rawson, PF (eds). The Geology of England and Wales. The Geological Society, 2006; 2nd Edition. 
[5] - Lee, JR, et al (eds). British Regional Geology. East Anglia. British Geological Survey, Fifth Edition, 2015.
[6] - Csiki-Sava, Z et al. Island life in the Cretaceous - faunal composition, biogeography, evolution, and extinction of land-living vertebrates on the Late Cretaceous European archipelago. Zookeys, no.469, January 2015, pp.1-161. [Link accessed May 2020]
[7] - Jarvis, I, et al. Late Cretaceous (Campanian) carbon isotope events, sea-level change and correlation of the Tethyan and Boreal realms. Palaeogeography, Palaeoclimatology, Palaeoecology, no.188, 2002, pp.215-248.
[8] - Skelton, PF et al (eds). The Cretaceous World. The Open University / Cambridge University Press, 2003.

THANKS TO

• Andy Gale, for naming the extinct beastie.
• Gilbert Addison, for suggesting the title of this article.