TRILOBITE TROUBLE.
by
Bob Williams.

It is believed that Trilobites became extinct during the Permo-Triassic extinction event that occurred 250 million years ago. I will express illustrated thoughts to you that must surely put emphasis on the word ‘believed’! As will hopefully be conveyed to you, there are environments that do still exist on this planet that we call Earth, into which man is only just starting to stick his polluted fingers to bring destruction upon. In those environments are creatures, still living, that have yet to be discovered but, as the days go by, they are being found to add to our knowledge of LIFE.

One of those environments is known to us as the ‘Deep Sea’ environment, into which we are only just beginning to enter. We are doing so a/. by the use of ‘deep sea’ trawl fishing techniques, which have been used for many years. We use them so that we can quite literally destroy what we find by eating it! and b/. by the use of ‘deep sea’ underwater research vessels, used so that we can at least observe and begin to understand what we are finding using the first technique! And it isn’t just small animal types that are being discovered by the use of these processes. The prime example of this was found in 1938, as part of a deep-sea trawl catch. Consequently, it was dead! But the type, which is now known to achieve over 6 feet in length and thought to have been extinct for over 70 million years, still lives in some quantity in the deep-sea environment, that being at depths up to 700 metres, (2,300 feet!). It is known as the Coelacanth, a primitive fish. It is now known as well, (since 1998), that at least 2 species of it still exist, the second species being found in a fish market on an Indonesian island! (What an environment to inhabit!). Previously, the genus had not been thought to live any further east than Madagascar. And scientific progress has now allowed them to be filmed living in their habitats. And this has proved that they are not singular animals by any stretch of the imagination. Well, I hear you ask, ‘What has this got to do with Trilobites?’. If animals as big as that have evaded detection successfully for so long, why couldn’t some trilobite species that lived in the same environment do so as well? The answer must be, ‘Perhaps they have, but, like the Coelacanth, because we haven’t seen any yet, we don’t know they are there!’ Some of you may now be thinking that ‘hope is being made beyond hope’ and perhaps even ‘What the hell is he writing about here’, but read on. The following presentation, which is illustrated by specimens of animal species that still live, may educate you as many of you won’t be aware of their existence and may persuade you to begin to think otherwise! Some of you will have seen the specimens concerned ‘in the flesh’, so to speak, at the AGM Society meeting and favourable comment has already been made on them. Obviously the specimens are not specimens of living trilobites, but the evolutionary influence of Trilobites, certainly in one of the specimens, is plain to see. Where do they come from? Answer … Deep-sea environments! A significant number of previously unknown species is being found in those environments and, as these creatures may now suggest, ‘If they can live there, why can’t real trilobites? It may be that we just have to find them. We found the Coelacanth. We found the Lungfish. We have Horseshoe crabs, (see present day Florida beaches and Jurassic Solnhofen limestone! We have found other animal species thought to be extinct. It would not be correct to say that ‘Trilobites are extinct!’ It would be more accurate to say that ‘Based on current evidence, we believe that trilobites are extinct’, and beliefs can change!

The ‘evidence’ offered here takes the form of 2 species of a creature termed an ISOPOD and 2 types of Trilobite as comparisons. Again, I hear many of you say, ‘What is an Isopod?’ Subconsciously, however, I suspect you will all know. Usual example …………. The Woodlouse, found under compost heaps and wood piles in most gardens. The woodlouse is a small, terrestrial isopod which, as many of you will appreciate, is a type of Arthropod, as were the Trilobites! Lengthen a woodlouse by some 10 inches. Widen it by 4 inches. Place it in a marine, deep-sea environment of over 6,000 feet depth, (2,000 metres), in the Indo-Pacific ocean and you have the first of the Isopod species I wish to present. The second is a little different, as you will see, but has the best similarity of the 2 to a trilobite.

A bit of background info about the specimens first. The larger of the two is named, not surprisingly, Bathynomus giganteus, the second part of the name, the species name, relating to its size. The first of the names is the generic name and this genus has a worldwide distribution, although the other species are, (again surprisingly), smaller in size. Any Bathynomus, (indeed any deep-sea isopod), is uncommon, if not rare (as is B. giganteus). Not because they are so small in population numbers, but because man is such an infrequent visitor to the habitats that they occupy, because of their location and accessibility. My source informs me that they are not to be frequently seen as specimens in museum collections and they are certainly rare in private collections, (he is a zoological associate of the Natural History Museums in Brussels and Paris and tells me that the Oxford University Museum is now trying to obtain a specimen as well!). The specimen was part of a deep-sea trawl catch and, at this point, I wish to stress that it was not killed purely for collection purposes but its life was terminated due to the changes in pressure that occurred in bringing it to the sea surface from such a great depth, which, of course, was not intended for this animal type. Due to the physical stresses encountered in landing the catch, many specimens are damaged in some way but this specimen was somehow landed undamaged. Also, when found in a catch, the fisherman usually just chuck’em back in the sea, but a fortunate contact was made in this case and the specimen was saved. The specimen is illustrated in Fig.A1(upperside) and Fig.A2 (underside).

Fig.A1. Bathynomus giganteus, (upperside).

Fig.A2. Bathynomus giganteus. (Underside). Scale marked in ½ inch divisions.

Many of you will probably be unaware of the appearance of a trilobite from the underside, which is to be expected unless specific texts have been read. It would be safe to say that out of all the many trilobite specimens that I have seen, I have never seen one prepared from the underside and the knowledge that I have acquired about trilobite undersides has been gained from studying pictures like the one shown in Fig A3. This image was gained by the use of X-Ray techniques, the limbs becoming visible because they have been preserved in Iron Pyrites which is much more opaque to x-rays, thereby highlighting them in the picture. Now compare this picture to that shown in Fig.A2. Again, the similarity speaks for itself! (Fig.A3. obtained from the book entitled ‘TRILOBITE! Eye witness to evolution’ by Richard Fortey of the Natural History Museum, London).

"The legs of the Devonian trilobite Phacops preserved in iron pyrites from the Hunsruck Slate, Germany. (Photograph courtesy Prof. W. Haas.) "

Fig.A3.

The next comparison to make is with another picture from the same book, as follows:-

Fig.A4. A Trilobite of the genus Bumastus, from the Silurian deposits of Shropshire in the UK.

Can it be said that the similarity to the Isopod species B. giganteus is only an illusion. I think not! Of course there are variations in anatomical details of the body such as the positioning of the eyes, antennae and other organs, but the overall body morphology is remarkably similar. Just stretch it a bit! And that illustrates the basic content of this article. The similarity of some living Isopod species to some Trilobites. Now for something a bit more eye-opening!

We have covered an ‘opening comparison’. The next comparison, I think, is more striking. The Isopod species now being referred to is of a genus named Serolis, of which a number of species exist which differ only in small detail, eg. size and length of lateral protusions, (spines). The specimen shown here was retrieved from a deep-sea trawl catch made in the Falklands Trench near Tierra del Fuego, South Atlantic, (South America). Once again, it was extremely fortunate to retrieve a specimen in such good quality and specimens such as this are sought after!

(You may wish to go to http://scilib.ucsd.edu/sio/nsf/fguide/arthropoda30.html where there is view of another serolid isopod plus a lot of background information. The whole site is absolutely wonderful and worth book marking for future reference. RC/15/06.)

Fig B.1. Serolis ?? specimen. (upperside). Specimen length approx. 7cms.

Until I saw this specimen, I didn’t know such creatures existed, despite my zoology degree! Having said that, because of the environments in which they live, it may have been that they weren’t known about in 1975 when I graduated. And it is a possibility that this is a specimen of a new species anyway, hence the lack of a second ‘Specific’ scientific name. But these creatures do exist and some have only been discovered very recently. It wasn’t until the Trilobite book aforementioned was read that the ‘very distinct’ similarity was noticed to a Trilobite genus, that genus being Kettneraspis. The picture, Fig.B2, speaks for itself.

Fig B2. The Trilobite specimen Kettneraspis is on the left of the image. The Isopod specimen Serolis sp. is on the right of the image.

This is a similarity that at least one society member saw and commented on when displayed at the AGM. And don’t worry because we aren’t the only ones to make this observation. The same similarity, mentioning the same Isopod Serolis by name, is referred to in at least one text book, ‘CRUSTACEA guide of the world’ by Helmut Dibelius, (a recognised marine biologist), so it has been noted by at least one professional too! And similarities occur with other Trilobite genera as well.

Two questions should now arise. The first is ‘What produces these similarities?’ Processes of evolution have a part to play in answering that. Any environment poses particular problems that must be solved successfully in order to ensure that a species can continue to live successfully in that environment. One method of solving those problems is to adapt and modify the body, or parts of the body, so that the problems are answered successfully and in ways that ensure the survival of the species concerned. Most problems only have one successful answer and so identical problems will be answered in similar ways. This can mean that whole bodies or appropriate parts of a body can be adapted in similar ways in different and unrelated species of animal.

Example A/. (of whole bodies being affected) ……………………………….
The Newt, (Amphibian), and the Alligator, (Reptile). Both have very similar external body forms to cope with the environments in which they live.

Example B/. (of specific body parts being affected) …………………………
The Bird and the Bat, (a mammal). Both animal types have wings. In both examples it is the Forelimbs that have been adapted and evolutionarily modified to ensure survival in an aerial environment. And the result of this evolutionary development is that both creatures have very similar general body forms.

Simple and obvious examples, but examples, nevertheless.

It is this process, known as Convergent evolution, that has resulted in the development of similarities between some Isopods and some Trilobites. And it should be remembered that both types are members of the same animal Phylum, the Arthropoda, so any processes that have an effect are probably more likely to have a similar effect on these creatures. Basically, evolution has resulted in the production of similar animal types; similar environments have posed similar problems which have been answered by nature in similar ways with the production of similar body parts, producing similar animals, although not directly related.

The next question to be asked should be ‘Why have these 2 independent animal types developed such similar body forms?’ Answer ……….. If the bodies have been adapted to cope with a particular environment then it must be that similar environments have resulted in the evolution of the similar body forms. So, if we are now getting to learn about the environments in which Isopods live, are we looking at environments that are similar, or even identical, to those in which Trilobites lived ……… or may still live?

It is, of course, realised that Isopods cannot be the genetic descendants of Trilobites but the thought that must now be expressed is that at least SOME of them are the evolutionary replacements of SOME of the Trilobites! After reading this article, what are your considerations now?

The opening paragraph of this article suggested that it would be an inaccuracy to just state that ‘Trilobites are extinct’ and that it would be far more accurate to state that ‘Based on our current knowledge, it is believed that Trilobites MAY be extinct at this time’. And the grounding for that is that we just don’t know for sure! Man was sure that the Coelacanth was extinct …….. until one was found, having been hidden in an environment that man had very little contact with! If an animal as large as a Coelacanth can remain hidden in that way, there must be the possibility, however small, that smaller animals can do so as well, but more easily. It may indeed be that, somewhere out there, a Trilobite or two are waiting to be discovered as well! Think about it!

END

Postscript. If any member reading this develops a desire to obtain a specimen of the Isopods shown, please speak to Bob Williams. It should be stressed that they are rare and usually in a slightly poorer condition due to the capturing technique employed, (damage to legs, etc. and perhaps minor carapace damage). Species may vary, but that really relates to a smaller size in respect of the Bathynomus genus and a variation in lateral spine size in respect of Serolis. And because of their rarity, they are not cheap!................ (for information, the large Bathynomus was priced at £200, (smaller ones are a bit cheaper) and the Serolis was priced at £75!). And although they are rare, they can be obtained, but not necessarily immediately. Contact will be made with the supplier.

Bob Williams would welcome any constructive discussions on this subject, he can be contacted on bobfosswilliams@hotmail.com. Bob wanted his article included in our Society's newsletter, it was too long and we could never have done the pictures justice. My apologies for editing out some of the pictures supplied by Bob, their source was copyright of third parties. Hope you enjoy the alternative Internet links I hunted down (RC).

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All text © Bob Williams 2005 (Photographs courtesy of Roger Coleman)