Trilobites - Antecedents and Successors: QUESTIONS

[Joachim Schlick]

I’ve searched your Forum for the word ‘trilobite’ and it came up with ‘no matches found’.

I found this description of the trilobite on the Net (Wikipedia – which believes as a matter of editorial policy that evolution is proved and that intelligent design is nonsense. I summarise).

I have some questions for the expert evolution scientists on this Forum - see below.

For one of the earliest creatures in the fossil record - its developing a very precise 543 million years ago according to the article – the trilobite seems to have a surprising number of very well developed features.

I’ll list some of these key features:

1. A head with several segments
2. A thorax with ‘freely articulating segments’
3. A tail with fused-together segments
4. The ability to ‘curl up’
5. A pair of antennae
6. A multiple set of legs each with six segments, one with a ‘feather-like epipodite’ used both for respiration and swimming
7. Three sets of lobes, two pleural, one axial - hence ‘trilobite’
8. An armoured ‘exoskelton’ on top composed of calcite
9. A pair of crescent-shaped ‘compound’ eyes with up to 15,000 tiny lenses, each being formed in the shape of an elongated prism, mostly apparently capable of seeing in the dark ocean depths, some having a ‘doublet’ structure said to give ‘a superb depth of field’, and arranged hexagonally
10. Horns
11. The ability to survive and flourish thousands of feet under the sea.

Now some genuine questions:

A. What is known about the evolutioanry antecedents of the trilobite, and is there any evidence of them in the fossil record?

B. Whay creatures if any were the evolutionary successors of the trilobite, and is there any evidence of them in the fossil record?

C. By what known genetic mechanism did trilobites gain up to 15,000 elongated prism-shaped lenses arranged hexagonally and capable of seeing in the dark?

D. How much DNA would be needed to code for 15,000 prism-shaped lenses arranged hexagonally and capable of seeing in the dark?

E. Which creature first developed eyes - and how and when did
they do so?

F. By what evolutionary mechanism did trilobites acquire ‘feather-like epipodites’ to help them breathe and swim?

G. Is it a scientific statement - or not - to say: “I consider that the
data relating to the trilobite is better evidence for intelligent design than for evolution”?
And finally:

H. By what mechanism did non-life become life and when (roughly) did this happen?

WIKIPEDIA ARTICLE ON TRILOBITES

Physical description

The bodies of trilobites are divided into three parts (tagmata): a cephalon (head), composed of the two preoral and first four postoral segments completely fused together; a thorax composed of freely articulating segments; and a pygidium (tail) composed of the last few segments fused together with the telson. The pygidia are still fairly rudimentary in the most primitive trilobites.

The thorax is fairly flexible—fossilised trilobites are often found curled up like modern woodlice for protection.
Trilobites had a single pair of preoral antennae and otherwise undifferentiated biramous limbs. Each exopodite (walking leg) had six segments, analogous to those of other early arthropods. The first segment also bore a feather-like epipodite, or gill branch, which was used for respiration and swimming.

The limbs were covered by lateral projections called pleural lobes, extending outward from a central axial lobe. Contrary to popular belief, it is this longitudinal tripartite division into left and right pleural lobes and a central axial lobe that gives trilobites their name, not the division into cephalon, thorax and pygidium.

The name "trilobite" (meaning "three-lobed") is not based on the body sections cephalon, thorax and pygidium, but rather on the three longitudinal lobes: a central axial lobe, and two symmetrical pleural lobes that flank the axis.

The trilobite body is divided into three major sections, a cephalon with eyes, mouthparts and sensory organs such as antennae, a thorax of multiple similar segments (that in some species allowed enrollment), and a pygidium, or tail section.

Although trilobites were only armored on top, they still had a fairly heavy exoskeleton, composed of calcite and calcium phosphate minerals in a protein lattice of chitin. Unlike other groups of armored arthropods, which resorb most of their skeletal minerals prior to molting, a trilobite would cast off a fully mineralized moult.

Thus a single trilobite animal could potentially have left multiple well-mineralized skeletons behind -- further enhancing the apparent abundance of trilobites in the fossil record. During moulting, the exoskeleton generally split between the head and thorax, which is why so many trilobite fossils are missing one or the other: many trilobite fossils are actually moulted exoskeletons rather than dead trilobites. In most groups there were two facial sutures on the cephalon to make shedding easier.

The cheeks of the cephalon usually also supported a pair of crescent-shaped compound eyes, which were surprisingly advanced in some species. In fact, trilobites were the first animals to evolve true eyes, about 543 million years ago; the evolutionary appearance of eyes has been postulated as a trigger for the Cambrian Explosion.

Some trilobites such as those of the order Lichida evolved elaborate spiny forms, from the Ordovician until the end of the Devonian period. Examples of these specimens have been found in the Hamar Laghdad formation of Alnif in Morocco.

Collectors of this material should be aware of a serious counterfeiting and fakery problem with much of the Moroccan material that is offered commercially. Spectacular spined trilobites have also been found in western Russia; Oklahoma, USA; and Ontario, Canada. These spiny forms could possibly have been a defensive response to the evolutionary appearance of fish.

According to New Scientist magazine (May 2005), "some... trilobites... had horns on their heads similar to those of modern beetles." Based on the size, location, and shape of the horns, Rob Knell, a biologist at Queen Mary, University of London and Richard Fortey of London's Natural History Museum, concluded that the most likely use of the horns was combat for mates, making trilobites the earliest exemplars of this behavior. While this study only covered the raphiophorid family, the conclusions can be applied to other groups as well, such as the tridentate phacopide trilobite Walliserops trifurcatus.

Trilobites range in length from one millimeter to 72 cm (1/25 inch to 28 inches), with a typical size range of two to seven centimetres (1 to 3½ inches). The world's largest trilobite, Isotelus rex, was found in 1998 by Canadian scientists in Ordovician rocks on the shores of Hudson Bay.

Sensory organs

The trilobite Metacryphaeus caffer from the Devonian of Bolivia
Many trilobites had eyes; they also had antennae that perhaps were used for taste and smell. Some trilobites were blind, probably living too deep in the sea for light to reach them. Others, such as Phacops rana, had eyes that were quite large.

The eyes of trilobites were made of calcite (calcium carbonate, CaCO3). Pure forms of calcite are transparent, and some trilobites used a single crystallographically oriented, clear calcite crystal to form each lens of each of their eyes. In this, they differ from most other arthropods, which have soft or chitin-supported eyes.

The rigid calcite lenses of a trilobite eye would have been unable to accommodate to a change of focus like the soft lens in a human eye would; however, in some trilobites the calcite formed an internal doublet structure, giving superb depth of field and minimal spherical aberration, as rediscovered by Dutch physicist Christiaan Huygens many millions of years later. A living species with similar lenses is the brittle star Ophiocoma wendtii.

The trilobite eyes were typically compound, with each lens being an elongated prism. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in a single eye. In these compound eyes, the lenses were typically arranged hexagonally.

Cyphaspis tafilalet - trilobites of the order Proetida

Holochroal eyes

Holochroal eyes had a great number of (tiny) lenses (sometimes over 15,000), and are found in all orders of trilobite. These lenses were packed closely together (hexagonally) and touch each other. A single corneal membrane covered all lenses. These eyes had no sclera, the white layer covering the eyes of most modern arthropods.

Schizochroal eyes

Schizochroal eyes typically had fewer (and larger) lenses (to around 700), and are found only in Phacopida. The lenses were separate, with each lens having an individual cornea which extended into a rather large sclera.

Abathochroal eyes

Abathochroal eyes had few (and small) lenses (to around 70), and are found only in Cambrian Eodiscina. Each lens was separate and had an individual cornea. The sclera was separate from the cornea, and did not run as deep as the sclera in schizochroal eyes.

Development

An egg hatched to give a tiny larva called a protaspid, in which all segments are fused into a single carapace. Subsequent thoracic segments were added just ahead of the pygidium ("pygidial release") in successive molts during an intermediate stage called meraspid, until finally the adult number of segments was reached, at which point the animal is called a holaspid. In many species, molting continued during the holaspid stage with no changes in segment number. Trilobite larvae are reasonably well known and provide an important aid in evaluating high-level phylogenetic relationships among trilobites.

REST OF ARTICLE SNIPPED

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[tomrees]

I'm no trilobite expert, but I could hazard an answer to at least some of your questions. But there is a fundamental error in your line of reasoning, so let's assume for the sake of the argument that the answers to your questions A-F are "None" and "Don't know" as appropriate.

Then the answer to your question G is that it is not a scienitifically valid claim. You are confusing an absence of evidence for one hypothesis as evidence for another, unrelated hypothesis.

If you don't know the answer to a question, the correct response is "I don't know". Not "It must've been done by some kind of magic".

One of the problems with proving your hypothesis (intelligent design) is that it has been constructed in such a way that you can never get positive evidence for it. It's untestable (and deliberately so). That's why it is fundamentally unscientific.

[SeaLion]

... the Net (Wikipedia – which believes as a matter of editorial policy that evolution is proved and that intelligent design is nonsense....

The Wikipedia has no such policy. It endeavours to enforce an NPOV (neutral point of view) on matters of controversy. It is a useful first port of call in many instances; where you have a genuine academic interest in a topic, you need to go rather further than Google and the Wikipedia

That evolution has occured among living species of our planet is not controversial among scientists. And neither, any more, is the neo-Darwinian theory which gives a good account entirely consistent with the established fact of evolution. It would be difficult (if not impossible) to name a scientific theory buttressed by more data points than ToE.

The 'controversy' is a political one, got up by a minority with a religious/political agenda. As 'science', ID is indeed 'nonsense' -- as ID is not science.

[jon_12091]

B. Whay creatures if any were the evolutionary successors of the trilobite, and is there any evidence of them in the fossil record?

Trilobites bought the farm in the Permian mass extinction (I think), and as such have no recognised evolutionary successors.

As for evolution of the trilobite, the earliest confirmed microfossils are around 3600 million years old while trilobites appeared around 543 million years ago, that gives over 300 million years for for the trilobite to develop all those useful bits & pieces. The evolutionary history of primates, and therefore us, can be traced back some 60 million years. Primates and bats share a common ancestor which probably lived during the late Cretaceous (~99-65 million years ago). Modern humans are less than 150,000 years old - the entire history of the human race can therefore be fitted into the period between the first microfossils and the emergence of the trilobites some 2000 times over!

[SeaLion]

Is it a scientific statement - or not - to say: “I consider that the data relating to the trilobite is better evidence for intelligent design than for evolution”?

Not.

By what mechanism did non-life become life and when (roughly) did this happen?

You are aware, of course, that this is a question about Abiogenesis rather than Evolution?

[Chris Sergeant]

There are some likely ancestors to Trilobites. Thus the Burgess Shale (around 505m years) has creatures like Trilobites, but without the hard exoskeleton and other differences. For example Naraoia compacta. The legs are very similar to Trilobites.
Chengjiang (around 525m) has Naraoia like creatures. I think there is debate whether to classify them as Trilobites or not.
Always worth remembering the Evolution is like a twiggy bush, not a ladder. Soft bodied Tribobites do not need to go extinct everywhere, just because hard exoskeletons have evolved.

I always find the phrase "non-life to life" slightly misleading. It suggests that there is always an obvious division between the two. However there are materials with some of the properties that consititute life. The Viking missions to Mars had experiments to detect life, but the results were not clear.

[Roger Stanyard]

A. What is known about the evolutioanry antecedents of the trilobite, and is there any evidence of them in the fossil record?

Already been answered - the Burgess shales have yielded examples.

B. Whay creatures if any were the evolutionary successors of the trilobite, and is there any evidence of them in the fossil record?

None. Trilobites became extinct. They were rare before final extinction. There is no reason why evolutionary successors to trilobites should have developed. The horse shoe crab is generally considered to be a relative of trilobites and is in existance today.

C. By what known genetic mechanism did trilobites gain up to 15,000 elongated prism-shaped lenses arranged hexagonally and capable of seeing in the dark?

The same broad genetic mechanism which results in other features - randon mutations, natural selection and genetic drift.

D. How much DNA would be needed to code for 15,000 prism-shaped lenses arranged hexagonally and capable of seeing in the dark?

Not known. We have no trilobite DNA - whoever said trilobites could see in the dark?

The form of a structure is not directly related to the number of genes involved in the sense of the more complex it appears, the more genes are necessarily required. It is theoretically possible that the answer is zero because indivudal genes or sets of genes can control more than one feature. What there isn't is a single gene that determines each element of the feature. If you are thinking that it needs at least 15,000 genes, you are way off understanding basic genetics.

E. Which creature first developed eyes - and how and when did
they do so?

Don't know but it is widely believed that eyes generally orginated as light sensitive patches. You need to ask someone with a better knowledge of pre-Cambrian life to answer this. I would guess that the first eyes were in this period and there is some evidence that collections of free swimming single cell organisms included organisms that were more light sensitive than others. That, perhaps, suggests that the origins of eyes date back well before the Cambrian period.

F. By what evolutionary mechanism did trilobites acquire ‘feather-like epipodites’ to help them breathe and swim?

The same broad genetic mechanism which results in other features - randon mutations, natural selection and genetic drift. It is also possibly, I guess, that polyploidy may have played a significant role.

G. Is it a scientific statement - or not - to say: “I consider that the
data relating to the trilobite is better evidence for intelligent design than for evolution”?

No. Intelligent Design is not science. There is no scientific theory (explanation, if you like) of Intelligent Design. Even its proponents at the Discovery Institute admit this. Moreover we also have evidence of transitional trilobite fossils (bearing in mind that most fossils are of transitional species). The fossil record shows, for example, transitions between species of Phacops (a trilobite; Phacops rana is the Pennsylvania state fossil; Eldredge 1972; 1974; Strapple 1978). ID does not explain this.

ID is a a religious position indistinguishable from creationism. The fossil record of trilobites points massively away from creationism as there are no such fossils later than the Permian.

And finally:

H. By what mechanism did non-life become life and when (roughly) did this happen?

This is a seperate subject, abiogenesis. We don't yet know all the full answers although we have gone a long way towads that objective. As far as I am aware, the consensus appears to be that we are around 10-20 years off having a relatively complete understanding.

My understanding is that the 1st evidence of life dates back 3.5 billion years.

[Roger Stanyard]

I’ve searched your Forum for the word ‘trilobite’ and it came up with ‘no matches found’.


A. What is known about the evolutioanry antecedents of the trilobite, and is there any evidence of them in the fossil record?

The Wikipedia entry provided a brief answer to this question -

Based on morphological similarities, it is possible that the trilobites have their ancestors in arthropod-like creatures such as Spriggina, Parvancorina, and other trilobitomorphs of the Ediacaran period of the Precambrian. There are many morphological similarities between early trilobites and other Cambrian arthropods known from the Burgess Shale and other fossiliferous locations. These are investigated further here: [1] It is reasonable to assume that the trilobites share a common ancestor with these other arthropods prior to the Ediacaran-Cambrian boundary.

[Roger Stanyard]

I’ve searched your Forum for the word ‘trilobite’ and it came up with ‘no matches found’.

So?

I found this description of the trilobite on the Net (Wikipedia – which believes as a matter of editorial policy that evolution is proved and that intelligent design is nonsense. I summarise).

Crap. Wikipedia has no such policy.

I have some questions for the expert evolution scientists on this Forum - see below.

All these can be answered with a relatively limited knowledge of biology and/or paleontology. Try a couple of A level text books from you local library.

[jon_12091]

AID is a a religious position indistinguishable from creationism. The fossil record of trilobites points massively away from creationism as there are no such fossils later than the Permian.

Unless of coarse the trilobites missed the boat.... along with dragons, unicorns, dionsaurs, mammoths, giant sloths, creationists...

[Paula Thomas]

The form of a structure is not directly related to the number of genes involved in the sense of the more complex it appears, the more genes are necessarily required. It is theoretically possible that the answer is zero because indivudal genes or sets of genes can control more than one feature. What there isn't is a single gene that determines each element of the feature. If you are thinking that it needs at least 15,000 genes, you are way off understanding basic genetics.

After all all the differences between men and women are the result of the presence or absence of one gene.

Paula

[George Jelliss]

After all all the differences between men and women are the result of the presence or absence of one gene.

Delete gene, insert chromosome?

I don't have even O-level biology, but even I know that!

[Paula Thomas]

After all all the differences between men and women are the result of the presence or absence of one gene.

Delete gene, insert chromosome?

I don't have even O-level biology, but even I know that!

AH except that the chromosome only has one active gene on it!!!!

[tomrees]

After all all the differences between men and women are the result of the presence or absence of one gene.

Delete gene, insert chromosome?

I don't have even O-level biology, but even I know that!

AH except that the chromosome only has one active gene on it!!!!

The Y chromosome? Has 78 genes http://genome.wellcome.ac.uk/doc_wtd020714.html

But the difference between men and women is down to the x chromosome too!

[Paula Thomas]

After all all the differences between men and women are the result of the presence or absence of one gene.

Delete gene, insert chromosome?

I don't have even O-level biology, but even I know that!

AH except that the chromosome only has one active gene on it!!!!

The Y chromosome? Has 78 genes http://genome.wellcome.ac.uk/doc_wtd020714.html

But the difference between men and women is down to the x chromosome too!

But only the SRY gene is active in sex discrimination [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&rid=gnd.section.156]