Trilobites in Wales

'A good collection of well-arranged trilobites looks better in the cabinet than perhaps any other fossils', wrote J.E. Taylor in Our Common British Fossils, published in 1885. Such is their popular appeal that trilobites have always been some of the most eagerly sought after of all fossils. Their name, suggested by their singular three-lobed appearance is derived from 'Trilobitae', introduced by the German naturalist Johann Walch in 1771 in his Der Naturgeschichte der Versteinerungen ('Natural History of Petrefactions'). The study of trilobites has particularly long associations with Wales, and the ancient rocks which crop out over much of the Principality have been well known as a rich source of them for nearly 300 years. This article outlines some of the history of their investigation in the area, describes their occurrence there, and discusses aspects of their nomenclature and morphology which are well illustrated by Welsh examples.

Edward Lhuyd, 'flat-fish' and Trinucleum The 17th Century saw the beginnings of the great period of collecting in natural history, and interest in acquiring all kinds of zoological, botanical and geological specimens increased steadily in the 18th and early 19th Centuries, and then much more rapidly during the Victorian era. Whilst many people collected for acquisitive reasons alone, the early naturalists began to prepare detailed monographs, often copiously illustrated with beautifully executed woodcuts and lithographs. The nature of fossils was still a matter of considerable debate in the 17th and early 18th Centuries, when they were often referred to as 'formed' or 'figured' stones. Although few naturalists at that time could explain satisfactorily what they were, several theories were put forward, including origins through supernatural forces, and whilst fossils were commonly compared with living organisms, they were rarely believed to have been originally organic themselves.

The first descriptions and illustrations of trilobites were made by Edward Lhuyd (1660-1709), the famous 17th Century Welsh naturalist. He became an assistant at the Ashmolean Museum, Oxford when it opened in 1683, and worked under Robert Plot, the first Keeper, whom he succeeded in 1691. He travelled extensively throughout the Welsh countryside gathering information for his intended Natural History of Wales for which he drew up 'a design' in 1695, but which unfortunately was never finished. Whilst on his travels Lhuyd wrote letters (many of which were published in the

Philosophical Transactions of the Royal Society) to contemporary scientists in Britain and abroad. In one of these, written to Professor Rivinum in Leipzig from Caldy Island in March 1698, he illustrated trilobites from the Llandeilo district, Carmarthenshire (Dyfed), which he described as Trinucleum and Buglossam curtam strigosam or flatfish. In August 1698 he wrote to Dr. Martin Lister: 'I should have troubled you with some sort of Account of our Travels; which, as you'll find by the inclosed Draughts of Figured Stones, has been tolerably successful. The 8, 9 and 15th we found near the Llan Deilo (Llandeilo) in Carmarthenshire; . . . The 15th whereof we found great plenty must doubtless be referred to the sceleton of some Fiat-Fish; the 8th and 9th I know not at all what to make of. In the following year Lhuyd published the first ever catalogue of fossils, written in Latin and entided Lithophylacii Britannici Ichnographia, in which were reproduced several of the trilobite illustrations included in his letters. Lhuyd's illustrations are sufficiently accurate to enable determination of the trilobites. His flat-fish are now known as Ogygiocarella debuchii. The resemblance of this species to the skeleton of a large flat fish is indeed an apt and striking one when it is considered that no animal closely resembling this fossil is known today. Trinucleum literally means 'three nuts' - reference to the three smooth lobes on the headshield. In terms of modern classification it probably belongs either to Lloydolithus or to Marrolithus (the name Trinucleus is now restricted to a form which occurs abundantly near Llandrindod Wells, and to applied species). The flat-fish and Trinucleum were based upon complete, or nearly complete specimens. Two specimens figured by Lhuyd are incomplete - parts of headshields only - and it is these which completely mystified him (see above). One belongs probably to Marrolithus favus, the other to Atractopyge verrucosa. A specimen of the latter, which is almost certainly Lhuyd's original, was identified some years ago in the collections of the University Museum, Oxford, by the former Curator, Mr. J.M. Edmonds. Lhuyd illustrated both specimens upside down, and as mirror images of the originals (as in many early woodcuts).

A further flat-fish was illustrated by James Parkinson in Volume Three of his Organic Remains of a Former World, published in 1811. He commented as follows: 'Another species of this animal is found in the schistose strata in the neighbourhood of Llanelly (presumably Llandeilo is meant), in Carmarthenshire. . . .the outline of the animal approaches much nearer ro the elliptical than the ovate form. From this latter circumstance, it

Edward Lhuyd, and his Irilobttes from Wales: a, 'Flat-fish'; b, Trinucleum'; c, the 9th and d, the 8th 'Figured Stones' of his letter to Martin Lister; e, part of headshield of Atractopyge verrucosa, almost certainly the original of d {photograph courtesy British Geological Survey, London).

obtains some slight resemblance to a sole, and has therefore been considered by some as the petrifaction of a fish of that tribe. The mutilated remains of this species, in consequence of the fossil being frequently severed transversely, have been regarded as petrified butterflies. . . On the remains of one of these I have perceived a very curious structure: it is in that part of the fossil which presents itself to view on the removal of the external covering, and which was probably the cuticle of the animal. Here the form of the parts appears exactly to correspond with that of the crustaceous covering, being transversely and somewhat obliquely disposed; but, aided by the lens, the eye discovers, that this pellicle is marked by frequent and regular rugae . . .'. This appears to be one of the earliest references to detailed morphology of the dorsal exoskeleton in trilobites. It also brings in a reference to petrified butterflies with which trilobite tails have been commonly associated.

Trilobites similar to Lhuyd's Bat-fish gave rise to a local legend in the Carmarthen area, involving the Arthurian magician Merlin (from whom Carmarthen derives its name), as outlined by W.S. Symonds (1872) in his Record ofthe Rocks: 'An old legend also connects the fossils of Pensarn, and Mount

Photos Trilobite With Naming

Pleasant, with the deeds of the great magician, whose last days were as singular as the earlier portion of his life. He fell in love with an angel sprite, or fair fay, without succeeding however in gaining her affection in return. One summer's day when the birds were singing, and the butterflies flitting, the wizard and the fairy entered a rocky cave, and here by the aid of a spell taught her by Merlin himself, the fairy closed the cavern and entombed the magician and the butterflies. Thus Merlin was "lost to life, and use, and name, and fame," and hence the appearance of the butterflies (or trilobites' tails) in the rocks of Mount Pleasant.' The trilobites in question have a broad resemblance to 0. debuchii, but have recently been shown to belong to a new genus which has been named Merlinia from its association with this legend and from its common occurrence in the Carmarthen area.

The beginnings of modern studies By the end of the 18th Century, it had become generally accepted that fossils were the remains of once living organisms, and through the pioneer work of the English engineer William Smith it became realized in the early 19th Century that fossils occur

19th Century Illustrations Fossils

(left) Plate 2_i ofMurchuon 'r Silurian System (1839), showing trilobites from the Uancleilo an J Caradoc series, (above) Plate 1G of Sedgwick and M'Coy's British Palaeozoic Rocks and fossils

(1851). showing Ordovician trilobites from North Wales and Cumbria. The figures were engraved by J. W. Salter.

through rock strata in a regular order. The two names most intimately connected with establishing the sequence of the ancient rocks of Wales and the fossils occurring in them are those of Adam Sedgwick, Professor of Geology at the University of Cambridge, and Sir Roderick Murchison, a distinguished amateur, who was to become Director General of the Geological Survey of Great Britain. In the 1830s Sedgwick and Murchison began to investigate the geology of north and south Wales, respectively. The results of Sedgwick's work appeared mostly in learned journals, and the large numbers of fossils which he and his colleagues collected were added to the collections of the Sedgwick (then the Woodwardian) Museum, Cambridge. Some of these were described in illustrated catalogues, such as those published in conjunction with F. McCoy and J.W. Salter, and included many fine trilobites from Wales. Murchison's researches were published in a splendid and copiously illustrated memoir, published in 1839 and entitled The Silurian System, founded on geological researches in the counties of Salop, Hereford, Radnor, Montgomery, Caermarthen, Brecon, Pembroke, Monmouth, Gloucester, Worcester and Stafford. Of the 31 plates containing illustrations of the more important fossils, six are devoted to trilobites. It was the work of Sedgwick, Murchison and their colleagues which first brought many of the now famous Welsh trilobite localities to attention; their illustrations include new ones of Lhuyd's Trinucleum and flat-fish, besides a wealth of other kinds. Murchison even proposed naming one locality near Welshpool Trilobite Dingle: 'In a woody dingle . . . the shale abounds with beautifully ornamented trilobites of the genus Trinucleus . . .' (and in footnote): 'As this ravine has not, as far as I could ascertain, any name, I venture to hope that, to mark so interesting a fossil locality, Lord Clive (owner of Powis Castle, in whose grounds the dingle is situated) will call it 'Trilobite Dingle'. The large specimen, Asaphus Powisii (a trilobite), named in honour of the noble family . . . was found at this spot'. The name 'Trilobite Dingle' still survives as an informal name among geologists. Many specimens from this locality found their way to the local Powisland Museum at Welshpool, and in 1962 the material was deposited in the National Museum of Wales on permanent loan.

Along with the commencement of Murchison's and Sedgwick's work, the 1830s saw the establishment of the Geological Survey of Great Britain as a branch of the Ordnance Survey. As officers began to map the country on a systematic scale, fossils, trilobites among them, were collected

J. W. Salter (photograph courtesy of British Geological Survey, London, N.E.R.C. copyright).

as a means of dating and correlating the rocks. For the purpose of investigating these fossils so that they could be used to maximum advantage, the Survey appointed palaeontolgists. Of these, John William Salter was the one most intimately connected with much of the early research on British trilobites. Salter first gained an interest and knowledge of fossils through assisting with illustrations for several major works, including Murchison's Silurian System. In 1842 he worked under Sedgwick in the Woodwardian Museum at Cambridge helping to arrange fossil collections, and during the following three years undertook fieldwork in Wales under Sedgwick's expert guidance. In this way Salter developed a keen interest in Welsh palaeontology in general and in trilobites in particular, and in 1846 became assistant to Professor Edward Forbes, Palaeontologist at the Geological Survey; in 1854 he succeeded Forbes in this post, which he held until 1863. Salter's great interest in trilobites often carried him to Wales, and he made several exciting discoveries, perhaps the most noteworthy of which was that of an enormous trilobite, nearly two feet

Trilobites From Wales

long, at Porth-y-Rhaw, near St. David's in 1862. He informed the Fellows of the Geological Society of London of his discovery in a paper read before them in February 1863 in the following words: 'My object now is to point out the locality and geological place of a giant Trilobite long looked for in Britain, and lately, 1 must say accidentally, found by me. I believed I was working at Solva Harbour, in Llandeilo Flags, but by good fortune I hut) landed instead in a parallel creek a mile to the westward, at the junction of the red and purple Cambrian grits with the Lingula-slates . . . The fry of some large Trilobite first attracted my attention, and then by looking along the ledges, I found fragments (head, body-rings, labrum), but none perfect, of the largest species of Paradoxldes known, scarcely excepting the gteat P. Har/ani, from near Boston. Agnostus accompanied it, as usual, being the smallest as Paradoxides is the largest, Trilobite of the Primordial zone. Saltet's discovery made Porth-y-Rhaw a classic locality for trilobites, but this fame has brought with it successive streams of geologists and collectors, and it is now difficult to obtain more than small fragments of Paradoxides.

Whilst working with the Geological Survey, Salter described and illustrated many trilobites in special Survey publications called Decades. Each of these comprised 10 plates, accompanied by detailed descriptions; Salter produced three Decades dealing with ttilobites, a large proportion of the specimens illustrated originating from Wales and the Welsh Borderland. After leaving the Geological Survey, Salter was able to devote a good deal of his attention to his largest and most important piece of work. This is a monograph in which he intended to illustrate and describe every form of trilobite known from the British Isles. The first part of the work was published in 1864 by the Palaeontographical Society, which was founded in 1847 by professional and amateur geologists with the intention of producing annual volumes devoted to the illustration and desctiption of British fossils, and the series continues to this day. Unfortunately Salter died in 1869 at the early age of 49, long before his monograph was complete, when he had illustrated less than half of the trilobites known at the time. The beautifully produced plates were largely the work of Salter himself, assisted by A. Gawan. Some 500 specimens are illustrated, and of these some 30% originate from Wales, with a further 20% from the Borderland. These figures stress the importance of this area as a source of much of Salter's material.

Apart from his own collecting, and that of Geological Survey Officers, Salter also depended upon a large number of private collectors as a source of many of the specimens that he used. One of these was David Homfray, a fossil collector from Porthmadog, after whom Salter named his giant trilobite from Porth-y-Rhaw Paradoxldes davidis. Another important local amateur was Dr. Henry Hicks, a physician from St. Davids who made a major contribution to unravelling the history of the ancient rocks of that area. Salter named another large trilobite, Paradoxides hicksii, in his honour.

Whilst these early studies were being carried out in the British Isles, European palaeontologists were beginning to investigate trilobites in similar ways. Such was the fame of Welsh trilobites that they soon came to the notice of some of these workers, and it was the French naturalist Alexandre Brongniart who wrote the first full scientific description and gave a formal latinised name to Lhuyd's flat-fish in his Histoire Naturelle des Crustaces fossiles, published in 1822.

Trilobites and Nomenclature

By the 1820s, nomenclature of all organisms, fossil and living, had become more or less stabilized, following the rationalization of the binomial system of nomenclature by the famous Swedish naturalist Carl Linnaeus in 1758, in the 10th edition of his Systema Naturae. This system employs a genus and a species name; with Salter's Paradoxides davidis, Paradoxides is the generic and davidis the specific name. Further examples are well illustrated among trilobites from Wales. Sedgwick, Murchison and Salter are all honoured by trilobite names - e.g. Angelina sedgwickii, Neseuretus murchisoni, and Salterolithus caractaci. Names may be derived from geographical locations, as is the case with Flexicalymene cambrensis (from Cambria, the Roman name for Wales) or they may reflect characteristics intrinsic to the fossils themselves (e.g. Eodiscuspunctatus - with a punctate dorsal exoskeleton; Basilicus tyrannus which is a large species - 'tyrannical'), or, like Olenus they may be derived from mythology. Perhaps the most interesting names applied to trilobites are some of those coined in the early days, which reflect the confusion then existing as to their affinities, as beautifully expressed byJ.E. Taylor in 1885: 'How utterly at sea the majority of naturalists were as to the nature of these singular fossils is indicated by some of their generic names. This statement is borne out by such names as Paradoxides referring to 'strange' or 'contrary to expectation'; Agnostus meaning 'unknown' or 'obscure', Asaphus likewise to 'obscure' or 'baffle', Calymene to 'concealed', and Cryptolithus to 'hidden' or 'concealed'.'

Of all trilobites from Wales none can have had such a complex and chequered nomenclatorial history as Lhuyd's flat fish. Brongniart placed them in Asaphus, but in 1843 Georg August Goldfuss, Professor of Zoology and Mineralogy at Bonn transferred them to Ogygia, to which genus they were usually referred for much of the ensuing threequarters of a century. Ogygia was originally proposed as a trilobite name by Brongniart, but unfortunately he was unaware that it had already been used for a moth by the famous German lepidopterist Hiibner only shortly before. In nomenclatorial rules no two animals, fossil or living, can bear the same generic name, and since the moth received the name firsr, a new one had to be sought for the trilobite. The issue was further compounded by problems of interrelationships between the flat fish and related trilobites. Thus, since 1822 they have been variously called Asaphus debuchii, Asaphus Buchii, Ogygia Buchii, Ogygia buchi, Ogygiocaris buchii and Ogygiocarella debuchii. The last is the currently accepted name.

Fragments, Fakes and Distortion

Problems in understanding and classifying trilobites were made even greater by the often fragmentary nature of the fossils, for trilobites, like their distant cousins the crabs and lobsters, periodically shed their hard exoskeleton in order to accommodate increase in size of the individual. Most trilobite fossils are fragments of discarded exoskeletons - complete specimens generally being rather uncommon.

Fossils were often sold to collectors, either by fellow collectors or by local quarrymen. Complete trilobites have always been particularly desirable, and always commanded a far better price than did fragments. Unscrupulous quarrymen often 'repaired' fragmentary trilobites, and skilfully carved segments betwen detached heads and tails, or added new heads to headless bodies. The end-products were often quite bizarre, combining parts of quite different trilobites. There appear to be no examples of 'repaired' trilobites from Wales, and all the known British examples originate from Dudley in the West Midlands, from where there are two good specimens in the Museum's collection.

The appearance of trilobites can be much altered

Photos Trilobite With Naming
The principal morphological features and terminology of the trilobite exoskeleton. (left) dorsal; (right) ventral
Dingle Slates And Trilobites

by distortion, and many of the ancient rocks in which they occur have suffered severe folding and compression, as in the case with many of those in north Wales. Often all traces of fossils have been obliterated; the slates near Tremadog, however, are rich in trilobites and Angelina sedgwickii is the most distinctive kind from this area. A great variety of distortion is displayed by various examples of this trilobite, some having been compressed from the sides, others from front to back, and others obliquely. The exact proportions of Angelina sedgwickii are still somewhat conjectural, as no completely undistorted examples have been found, although there have been numerous attempts to

'straighten out' specimens, most recently by using an elaborate device involving the superimposing of movable grids shown on a television screen, developed by Dr. R.M. Appleby at University College, Cardiff in the 1970s. Distorted specimens have sometimes misled palaeontologists into thinking that more than one species is present at a locality, as happened to Hicks with trilobites from Bay Ogof Hen, Ramsey Island in the last century. His mistake was only discovered by comparison with better-preserved specimens subsequently found elsewhere.

Trilobite appendages and internal organs It has long been established that trilobites are extinct marine arthropods, a large group of invertebrate animals that includes insects, spiders, crabs and lobsters. Most of the early naturalists appreciated that they were some kind of arthropod; for example, Linnaeus referred to them as Entomolithus ('insect-stone') in 1745, and another Swedish naturalist, G. Wahlenberg called them Entomostracites ('insect-shells') in 1821. Outside the arthropods, trilobites were placed by Walch in 1771 in the molluscs, and in 1808 the French natutalist P.A. Latreille pronounced that if they had had no legs, they must be Venus molluscs, but if legs were found, then they belonged to the Isopoda (woodlice and their allies) - in the words of H. Wendt {Before the Deluge, 1968), 'a truly Solomonic judgement'. The apparent lack of limbs was one of the most perplexing problems for students of trilobites over much of the 19th Century. Only after the discovery of limbs in North America in the latter part of that century could palaeontologists gain a more complete understanding of these fossils. Even today, only a small number are known with remains of limbs, and none have been found in the British Isles. Trilobite appendages ate bitamous, with a walking leg and an upper branch which probably served as a gill; a recent study by Professor H.B. Whittington of Cambridge University has shown how these limbs might have functioned in the living animal, and this work has implications for the interpretation of certain kinds of tracks and trails commonly found as fossils, and which have been assumed to have been

Rusophycus Trails

A trilobite trace-fossil: Rusophycus from Cwm Graianog, Snowdonia (x I), (photograph courtesy of Dr. T.P. Crimes).

Meneviclla venulosa (Salter) from the Cambrian of Porth-y-Rhaw, showing branching diverticulae, possibly belonging to the digestive system (x 8). (Photograph courtesy of Mr. M. Lewis).

Underside of cephalon of Ogygiocarella debuchii (Brongniart), showing hypostome in situ (x 2).

A trilobite trace-fossil: Rusophycus from Cwm Graianog, Snowdonia (x I), (photograph courtesy of Dr. T.P. Crimes).

Underside of cephalon of Ogygiocarella debuchii (Brongniart), showing hypostome in situ (x 2).

produced by the activity of trilobites. One of the best-known of these is Cruziana, a bilobed trail with distinctive diagonal grooves forming a V-pattern, which is very common in the Cambrian rocks in parts of Snowdonia. It had long thought to have been made by a trilobite ploughing through soft mud on the sea bed, but from Whittington's studies it seems unlikely that a trilobite could have generated it. Evidently it was made by some other animal, possibly a soft-bodied one which has left no other trace in the fossil record. Other trails, however, can certainly be ascribed to trilobites, especially some of the ovate, bilobed impressions known as Rusophycus, some of which show clearly impressions of genal spines and the tips of segments. These are evidently shallow burrows excavated by trilobites, perhaps made in search of prey, or for concealment. Well preserved examples have been found at Cwm Graianog in Snowdonia.

Remains of internal organs are even rarer than limbs, although there are specimens known with traces of what appear to be musculature and the digestive tract. Some trilobites show structures on the lateral parts of the headshield which are possibly branching organs belonging to the digestive system called diverticulae. The Welsh Cambrian species Meneviella venulosa, first described by Salter in 1865, shows traces of such diverticulae, and the species name alludes to this character. There is no evidence of a strong jaw apparatus in trilobites, but all bear a rigid plate on the ventral surface of the headshield known as the hypostome, which apparently protected the buccal cavity.

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