An early specimen of ‘AMMONITES Walcotii’ and Sowerby’s ‘Mineral Conchology’

A version of this article is published in Depositsmag.

A fascinating aspect of palaeontology is the history of early descriptions and the process of assigning and revising the scientific names of fossils. A recently discovered nineteenth century ammonite specimen discussed here provides a vivid illustration of the sometimes tortuous process and can be connected with several illustrious naturalists and geologists from the seventeenth to nineteenth centuries.

Geology in the first quarter of the nineteenth century

The first quarter of the nineteenth century was a particularly important time in the evolution of geological thinking. In Britain, the first long stratigraphic sections were being published, the Geological Society was founded in 1807, the first nationwide geological map was published in 1815, and detailed investigations were underway across the country.

A correspondent in the Philosophical Magazine (‘A Constant Reader’ 1815) promoted the work of James Sowerby and contemporary "travellers in search of Geological facts, like Messrs. Smith, Farey, Bakewell, Greenough, and many others”.

The writer behind the name ‘A Constant Reader” may have been the president of the Royal Society, Sir Joseph Banks, writing under a pseudonym (Smith 2024). On Sowerby, he wrote: "I have been induced by what I have … read regarding Geology, to become a reader and very zealous promoter of Mr. James Sowerby’s work connected with this interesting subject entitled ‘Mineral Conchology,’ published every two months: and in order that I may have the opportunity of recommending many more Ladies and Gentlemen in every part of Britain to become Collectors of Fossil Shells.”

He continued with a plea for participation by the public: "A sight … with which I was favoured, of Mr. William Smith’s Collection of Fossil Shells and other Organic Remains, arranged in the order in which they are found in the several Strata described by colours on his Map of England, and each Specimen distinctly marked with the name of the Place from whence it was taken, at once convinced me, that what had been achieved, by the perseverance of a plain and moderately lettered Man, in a great measure if not totally unacquainted with the technical knowledge above mentioned, might be followed by others …”

An ammonite from the Yorkshire Jurassic

The fossils of the Yorkshire coast have been collected for centuries and several species from here were named in Sowerby’s (1818) beautifully illustrated second volume of ‘Mineral Conchology’. These included some of the most celebrated ammonites known from the vicinity of Whitby.

An early specimen of one of these fossils, labelled Am[monites] Walcottii (Fig. 1), 7cm in diameter, recently turned up in an online sale, having been found in a flea market. Ammonites Walcotii was the name given by Sowerby in 1818 (he capitalised this species name) to what we now know as Hildoceras bifrons. The ammonite has been cut in half and polished to display the internal structure. The external view, with clear spiral groove, confirms that this is an example of Hildoceras bifrons, and not Hildoceras lusitanicum Meister, 1913, a related form lacking such a clearly defined groove.

Fig. 1. A nineteenth century specimen of ‘Ammonites Walcotii’, with species name spelled ‘Walcottii’. Sowerby (1818, opposite p. 7) presented an illustration of a similar specimen (Fig. 2), also cut in half and polished.

Fig. 2. Illustration of ‘Ammonites Walcotii’ in Sowerby (1818).

Sowerby’s description was as follows: "Involute, depressed; volutions four, three-fourths exposed, with a concentrate furrow; lunate undulations over half the sides; front with a carina between two furrows”.

He noted several localities where this form has been found, including: "in balls in the dark pyritaceous or Alum Clay at Whitby." "The insides are divided by various crystallizations of Carbonate of Lime or Iron, or more solid or earthy, and more or less distinct in the divisions or chambers, agreeably to the nature of the stratum in which the specimens are found.”

Very similar internal details are clearly shown in the nineteenth century specimen illustrated here (Fig. 3). Early entry of mud into ammonite chambers is seen and, in the chambers which had remained unfilled by sediment, a sequence from early fringing isopachous cements to late sparry calcite cements.

Fig. 3. Detailed view of the polished side of the nineteenth century ‘Ammonites Walcotii’. Notice how the septa are coated by brown isopachous rimming cements with a later stage infill of colourless sparry calcite. In places, the compartments have been filled with sediment (grey), through openings in the outer shell wall. The plane of section has not included the siphuncle.

Sowerby’s specimen was found at Bath. He did not explain the origin of the species name, but it could derive from the locality of Walcot, Bath, noted for exposures of ‘Lias Upper Marl’ sediments by Lonsdale (1832, p. 243) or, perhaps more probably be named after John Walcott (omitting the last ‘t’), who published a book in 1779 on the ‘petrefactions’ found around Bath during the major phase of building in the city. Walcott illustrated an example of what is now known as Hildoceras bifrons as his No. 41. (Fig. 4), with no name, but with the following description (Walcott 1779 p. 32): "The outward volution for half its breadth next the back is transversely ribbed, their ends bending towards the mouth of the shell: the inner volutions, and the outward one for half its breadth next them, are smooth: diameter near two inches: shell thin of a brown color.”

Walcott noted that: "The recent shell has not yet been discovered, one reason given for their not having been found is, that they are bred in the inmost; and deepest parts of the sea.” This was a thoughtful explanation, which avoided any suggestion that ammonites might be extinct.

Sowerby (1818, p. 8) referred to Walcott’s illustration as follows: "Walcot’s [sic] figure (Bath Petrifactions, fig. 41, p. 32) appears a worn specimen, the inner whorls being destitute of transverse costae.”

Fig. 4. Illustration of an unnamed ammonite in Walcott (1779). This form would later be named Ammonites bifrons in Bruguière (1789), Ammonites Walcotii in Sowerby (1818), then Hildoceras bifrons in Hyatt (1867).

Fig. 5. Lister’s 1678-81 illustration (Tab: VI, fig. 2) of ‘Ammonis Cornu’, representing what was later known as Hildoceras. The apparent absence of a spiral groove in the specimen illustrated later caused confusion for Italian authors, who used the illustration as a guide to identifying Hildoceras bifrons (Ridente 2023).

Naming changes and potential confusion

Sowerby’s Ammonites Walcotii was not the earliest name assigned to the ammonite we now know as Hildoceras. Lister (1678-81) presented it under the name Ammonis Cornu (Fig.5). Lister was a polymathic individual, who published on medicine, spiders, snails, fossils, archaeology and statistics among other subjects, and was one of the ‘York Virtuosi’ (Unwin 1995). He proposed and described the method of creating geological maps (Lister 1684).

More than a century later, Bruguière (1789, p. 40) named this form Ammonites bifrons. The current name, Hildoceras bifrons, was assigned by Alpheus Hyatt (1867, p. 99), defining the name of the genus Hildoceras “After St. Hilda”. He recognised two species, being Hildoceras bifrons and Hildoceras walcotii, but did not discuss their differentiating features.

Hunton (1837, p. 220), in his discussion of the vertical distribution of fossils on the Yorkshire coast, recorded Ammonites Walcotii from the Upper Lias of Yorkshire, as did Williamson (1837), although in one place (p. 227), he misspelled the species name as Ammonites Walcotti. The label on the specimen shown here also misspells the species name, but as Walcottii.

By 1856 (Wright 1856), this form was recognised as ‘Ammonites bifrons, Brug. (Walcotii, Sow.)’.

Ridente (2023) pointed out that Lister’s (1678-81) illustration of Ammonites Cornu was never formally invalidated as the holotype of Hildoceras bifrons and that this led to confusion in subsequent identification of Hildoceras species,whether exhibiting or lacking a clear spiral groove (Fig. 6).

The specimen illustrated in Lister (1678-81) seemingly lacked the spiral groove of what is currently recognised as Hildoceras bifrons, whereas the “Topotype and worthy to be Neotype” example presented by Buckman (1918) does show the spiral groove. The form lacking the clear groove is known today as Hildoceras lusitanicum Meister, 1913 and a form with subdued spiral groove and finer ribbing is known as Hildoceras semipolitum Buckman, 1902.

Fig. 6. Recently found specimens of (A) Hildoceras bifrons, 12 cm diameter (RS.P.723) and (B) Hildoceras lusitanicum, 11.5cm diameter (RS.P724) from near Whitby, North Yorkshire, the former with a pronounced spiral groove (like Sowerby’s Ammonites Walcotii) and one without (like Lister’s Ammonites Cornu). (C) shows a specimen of Hildoceras bifrons (6.5cm diameter) from the Beacon Limestone Formation near Ilminster, Somerset, in a very different sedimentary facies from the Yorkshire examples. This specimen is comparable with the examples from the vicinity of Bath illustrated by Walcott (1779) and Sowerby (1818) (and see Wright 1856). (D) shows a polished section from the Beacon Limestone with sediment-filled chambers as in Sowerby's (1818) illustration.

Snakestones

At Whitby (Fig. 7), souvenirs were once made (often for pilgrims to the abbey) with stylised snake heads carved on fossils of Hildoceras bifrons, but more usually another well-known ammonite from this stretch of coast, Dactylioceras commune. Sowerby (1818) referred to the legend as follows: "The Ammonites are called in common Snake-stones, and superstition has accounted for their having been found constantly without heads, saying, the curse of St. Cuthbert was the cause of it; but as some of the dealers felt it a possible inconvenience, they were determined to be less barbarous, and compassionately supplied some with heads. I was so curious as to desire to see what sort of heads might be substituted, and Lady Wilson kindly procured me a specimen when at Whitby.”

More recently, the ‘curse’ is typically attributed to St Hilda rather than St Cuthbert (Taylor 2016).

Sowerby (1818) also illustrated Dactylioceras commune, naming it Ammonites communis (Fig. 8). Once again, it was Hyatt (1867) who changed the name to Dactylioceras, referring to the Greek for a ring.

Fig. 7. The site of the legendary petrification of a plague of snakes, either by the curse of St Cuthbert or St Hilda. Lower to Middle Jurassic strata are visible in the cliff. Drone image by the author.

Fig. 8. Sowerby’s illustration of Dactylioceras ammonites, then named Ammonites communis and Ammonites angulatus. 2. (bottom left) shows the addition of a simple carved snake head.

Dating the collection of the specimen

Can the approximate time of collection be constrained by the antiquated name on the label? Well, firstly, the label must post-date Sowerby’s 1818 publication. It probably also pre-dates Wright’s 1856 revision of the species name from Walcotii to bifrons, and Hyatt’s 1867 revision from Ammonites to Hildoceras. However, it is always possible that collector labels lagged the publications in the scientific literature (which is certainly the case in the present day). An approximate 1820-1860 date range is probably an appropriate estimate, with a later date also a possibility.

Conclusions

An ammonite specimen with a nineteenth century label affixed was probably collected between about 1820 and 1860. The antiquated name on the label leads to connections with a sequence of early naturalists and geologists from Lister, Walcott, Bruguière, Sowerby, Lonsdale and Wright to Hyatt. The specimen is thus both a relic of a long extinct animal in fossil form and a cultural artefact.

Acknowledgements

Martin Rigby is gratefully acknowledged for finding and donating the specimen (RS.P1981) discussed here, and my thanks go to Andreas Schmidt for reading the draft of this article.

References

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