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Author Topic:   What would a transitional fossil look like?
caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 6 of 403 (850293)
04-05-2019 1:25 PM
Reply to: Message 5 by Diomedes
04-05-2019 9:58 AM


Interestingly, the fossil record for whales is actually one of the better ones when it comes to transitional fossils. I remember watching an episode of the show 'Paleoworld' back in the 90s and they showcased many of the specimens they had regarding how whales evolved from terrestrial animals known as Mesonychids. Was very fascinating.

I think that's a bit out of date though. Now that many more early whale fossils have been discovered, and now we have a better understanding of mammal interrelationships in general, it's no longer clear that mesonychids are closely related to whales. They might be, but it's a matter of some dispute.


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(2)
Message 160 of 403 (850787)
04-14-2019 12:55 PM
Reply to: Message 152 by Faith
04-14-2019 12:03 PM


Re: Thought Experiment for Faith
All those phenomena are what I'm calling "superficial, that is they are not structural.

We've discussed this before, and I still struggle to see where you're coming from. Yes, trilobites are all three-lobed; this is the basic underlying structure of a trilobite; though within this structure there is enormous variety. You see this variation as superficial for reasons that make no sense to me.

If this was a statement alone we could just leave things there - you just have an odd interpretation of what 'superficiality' means. But you then go on to insist upon the supposedly deep structural differences between dogs and cats, which is simply bizarre. Structurally, dogs and cats are almost identical. You say below in your response to PaulK that you're talking about skeletal structure, not about internal organs. This is somewhat arbitrary, but not a problem - let's take a look at cat and dog skeletons.

Cats and dogs both have a vertebral column. In both this develops initially in the foetus as a collagen rod, which is later replaced by bone - the remaining collagen forming disks between the vertebrae. Cats have seven next vertebrae, thirteen chest vertebrae, 7 lumbar vertebrae, and 3 sacral vertebrae (can't think of a common name for 'lumbar' or 'sacral'). Dogs, exactly the same.

From the vetebrae come four limbs, in both dogs and cats. The limbs are made up of one long, thick bone; then two thinner long bones, then four carpal or tarsal bones, then the toe or finger bones - on which the animal stands. This is exactly the same in cats and dogs. There is a bone covering the joint between the thick long bone and the two thinner long bones in the hind legs, but not in the forelegs; in both dogs and cats. There is usually a fifth toe or finger bone, which is much smaller than the rest and not used in walking, in both dogs and cats.

Dogs usually have 13 pairs of ribs. Cats usually have 13 pairs of ribs.

Then we can look at the skull. Dogs and cats have quite distinctive skulls, compared to other mammals. But not compared to each other. Exactly the same bones fuse to form a skull in cats as in dogs. Now, the bones are not quite the same shape - dogs usually have a much more extended maxilla, example. But, thanks to human selective breeding, this is not always the case - look at a French bulldog for example.

But this is where I fail to see your distinction from trilobites. Trilobites all have three lobes, yes - but their relative size and shape, their internal subdivisions, their articulations and their degree of flexibility vary enormously. And all this variation you see as merely superficial.

Dogs and cats have exactly the same skeletons. The similarities here are much deeper and more fundamental than an overall concept like being made of three lobes - we're talking a few hundred bones with exact counterparts in dogs and cats in exactly the same place. And yet, in contrast to trilobites, you consider small variations in the size and shape of these bones to be fundamental differences. Except this is no longer the case when we look at the variation in size and shape of the bones between different breeds of dogs - despite the fact that the variation here is greater than that between cats and wolves.

You mention flexibility as some kind of deep, fundamental difference. Now, I'm not sure if it's actually true that cats are bendier than dogs, but even if it were - why is a slight difference in exactly the same bone structure to allow it to bend more fundamental? And why, if it's fundamental for cats and dogs, is it not for trilobites; since there the variation is much greater. There are trilobites whose three lobes are connected in such a way that they would have been perfectly rigid and straight, and others that could roll up into a ball.

I think that you view the differences between cats and dogs as being more fundamental than those between different families of trilobites only because they're so much more familiar to you.


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(1)
Message 162 of 403 (850790)
04-14-2019 1:10 PM
Reply to: Message 154 by Faith
04-14-2019 12:12 PM


Re: Thought Experiment for Faith
Further to my previous post:

cats move with their heads below their shoulders but dogs' heads are above their shoulders.

If this were true, how on earth would this be fundamental; when all that is required is exactly the same bones joined at a slightly different angle.

And of course it's not even true. Cats often move with their heads held high

and vice versa

In another post I think you wrote 'stalking', rather than simply moving, but if that's what you meant then of course all dogs and cats go low when stalking

Incidentally, with regards to the last picture, awwwww.


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 164 of 403 (850792)
04-14-2019 1:11 PM
Reply to: Message 161 by Faith
04-14-2019 1:07 PM


Re: Thought Experiment for Faith
Structure basically means skeleton, basic build, basic structure; "Superficial" characteristics are like fur color, eye color, things that vary regularly from generation to generation, including such things as changes in overall size, or elongation of the body and so on: they don't change the basic structure, just stretch or compress it. A chart of all the dog breeds shows the same skeletal structure in all of them.

Did you read my post? It's point was that cats, too, have the same basic skeletal structure.

Edited by caffeine, : Added the word 'skeletal'


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(2)
Message 191 of 403 (850845)
04-15-2019 2:50 PM
Reply to: Message 166 by Faith
04-14-2019 1:54 PM


Re: Thought Experiment for Faith
I'm sorry, I do get impatient. So far you haven't but others accuse me of stuff that is false and everybody seems to have to find some nitpicky way what i'm saying is wrong whereas if you just read what I wrote and thought about it I don't think it would look that way to you. Cats' bodies are flexibility, dogs' are not.

I understand your frustration; you have to put up with a lot of petty sniping on these boards. But a lot of that sniping stems from others being equally frustrated. You feel that others are not really reading what you wrote and trying to understand; I can assure you they feel the same about you.

I am reading what you're saying; I'm not ignoring it - it just doesn't make sense. You think trilobites are all one kind; while cats and dogs are different kinds; but you're not applying consistent criteria to the two.

All trilobites are three-lobed. The shape and size of these lobes varies enormously. All cats and dogs share about 300 bones. The shape and size of these bones varies much, much, much less than the shape and size of the lobes of different trilobite classes. And the fact that we're talking aboutn 300 specific bones rather than just a general overarching structure like in trilobites bespeaks a much closer relationship.

Cats are more flexible than dogs. Some trilobites were completely rigid while others could roll up into balls - the range of flexibility here is much greater for trilobites.

I'm not disputing that cats are different than dogs - of course they are; that's why we have different names. I'm disputing that these differences are somehow greater than the differences between trilobites.

--------------------------------------------------

To avoid a double post, I'll add here a response to your later post:

I'm still big on the argument that you have to run out of genetic variability with strong selection that produces dramatic new gene frequencies in a reproductively isolated population, but just from the point of view of how a given creature is put together and how it behaves there is certainly enough reason to consider this a likely definition of a Kind, and recognizing that the basic structure doesn't change (HOX genes) while many other changes occur from generation to generation and all the more so under selection pressure and the formation of reproductively isolated populations, similarly points to a built in limit to evolution.

HOX genes are shared by all bilaterian animals; not just closely related ones. What they do, to simplify dramatically, is to ensure that genes express differently at different points along the body axis - they are what makes the same genes produce an arm at your shoulder but a leg at your knee; for example.

I was thinking about these in trying to think how to respond to an earlier post of yours (can't find it now), because it seemed to show a fundamental misunderstanding you had of how genes work. You were talking about an animal evolving by removing the genes for an arm and replacing them with the genes for a flipper - but that's not how it works. Genes don't code for body parts; and the same genes are working in making an insect's antenna, its jaws and its legs. What changes is that regulatory genes change the pattern of expression of these genes in different parts of the body.

Genes do not code for specific traits, as you've mentioned a few times. They just make proteins. Changing the rate at which different genes do so at different parts of the body changes the whole complicated cascade of chemical reactions which make an organism.


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 192 of 403 (850847)
04-15-2019 2:58 PM
Reply to: Message 189 by Faith
04-15-2019 2:28 PM


The bodies I have in mind are identical, not merely similar, except that they may vary in proportions: size and length and that sort of thing. But all dogs have a rigid skeleton with the same kind of feet, all of them, and dogs all bark and wag their tails etc etc etc. Cats have somewhat similar skeletons but they are very flexible. If you pick one up it will drape floppily over your arm unless you support it whereas a dog doesn't bend. Cats also have retractable claws that are not at all like a dog's toenails, and they meow. Etc etc etc. Your comparisons are ludicrous, the similarities are really broad and there is no way you are going to get a seal from a penguin. Sheesh.

Not all dogs bark. Nor do all cats have retractile claws (using 'cat' in the wider sense since I've understood you're including all felids in the 'cat kind'). Cheetahs' claws are non-retractile.

Aside from the retractability of lack of it, though, I don't see how cat's claws are 'not at all like' dog's claws. They look pretty much the same to me, and the similarity is not just apparent - they're structurally the same. It's a hard keratin sheath surrounding a a mass of connective tissue innervated with blood vessels and nerves; in basically the same shape.

Edited by caffeine, : No reason given.


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(7)
Message 216 of 403 (850896)
04-16-2019 3:03 PM
Reply to: Message 194 by Faith
04-15-2019 3:07 PM


Re: Thought Experiment for Faith
I'm happy to hear about regulatory genes that determine what the HOX genes do in a given creature. That makes sense.

Sorry for not being clear - HOX genes are regulatory genes; by which it's meant that they regulate the expression of other genes.

Yes genes make proteins but particular alleles make particular proteins that form particular traits. Are you going to argue with that?

Yes, I am

Genes do not make proteins for a particular trait - you're thinking about HOX genes in the wrong way. Their 'role' is not to produce a flipper in one creature and a leg in another. It's to produce an arm in one creature and a leg at a different place of the same creature. It's exactly the same genes making an arm as making a leg, but the same genes can produce quite different structures depending on the pattern of their expression. Hox genes were first discovered by scientists playing around with fruit fly genetics; who noted that mutations to HOX genes could do things like this:

In case you can't see it well, that's a fruit fly with legs growing where its antenna should be. There are not different genes building legs to building antennae; it's just a matter of changing their pattern of expression. If the same genes can produce legs, antennae, mandibles and pincers, then why not a leg and a slightly different kind of leg (eg, a dog's leg and a cat's leg). After all, dogs' and cats' legs are much more similar to one another than a fly's leg is to its antenna.

To see that genes do not code for specific traits in the way you seem to think, it's good to look at specific examples. OCA2 is a very well-known gene in humans, because it's the gene 'for' blue eyes. What we mean by that is that one of the first things uncovered about OCA2 back in the early days of genetics was that people with a certain form of the gene usually have blue eyes.

To conclude from this that OCA2 is a gene 'for' eye colour is to completely misunderstand genetics, however. What the gene is for is a protein involved in the transport of small molecules across cell membranes. Changing how it works can have an effect on pigmentation; because one of the molecules it helps to transport (tyrosine) is a precursor of melanin - the pigment responsible for darker colours in a lot of organisms.

There's a fantastic website which maps the expression of genes across different tissues in humans. Here you can see the expression pattern for OCA2. Note how it's significantly expressed in gonads, ovaries, bone marrow and the gastrointestinal tract. This is nothing to do with eye colour, because there are no genes for eye colour. There are genes for proteins, and the same proteins do all sorts of different things. We are built of the same proteins as cats and dogs are.

Edited by caffeine, : typos


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(1)
Message 258 of 403 (851017)
04-18-2019 1:58 PM
Reply to: Message 230 by mike the wiz
04-18-2019 9:07 AM


As usual Mike, the information about fossils used to support your arguments is woefully incorrect. I'm guessing it's things you've either misremembered or misunderstood; or it's some nonsense you've taken for granted from a creationist source.

Basically the same things unchanged, that turn up no matter how far back you go, and some are even specialised examples such as the funnel-nose ray or the giant salamander or the platypus.

Giant salamanders do not go back 'as far as you go'. They're known from the Jurassic onwards (about 160 million years). Prior to this - there are no salamanders in the fossil record.

Platypuses don't go back very far at all - the oldest known fossils are about 60 million years old. And the fossil record is very poor - it consists of one partial skull, a few fragments, and teeth. It's hard to quantify how much they've changed based on such scanty materials. The modern and ancient platypus skulls differ in quite a few features, however (below). Significantly, modern platypus don't have teeth.

ABE - for some reason the platypus skull pictures don't embed properly. This is the fossil skull. These are modern.

I'm not sure what a funnel nose ray is - this doesn't seem to be a particularly common name for type of ray, so it's hard to know what you're being wrong about here.

Do we find any ancestors for the cambrian phyla? They're conspicuously absent. What about angiosperms? Conspicuously absent. What about dinosaurs? Conspicuously absent.

I don't know a great deal about plants, but to say that dinosaur ancestors are 'conspicuously absent' is just bizarre. There are plenty. Here's one (the below is of course a model, but I selected Marasuchus because it's a remarkably complete fossil - most of the model below is based on actual fossil bones; not speculative reconstruction).

Edited by caffeine, : No reason given.


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(1)
Message 263 of 403 (851028)
04-18-2019 2:20 PM
Reply to: Message 246 by ringo
04-18-2019 1:19 PM


That doesn't follow. It is possible for the same pattern to evolve from different sources. Note the seal's flipper and the penguin's flipper, very similar in form and function, yet the seal is more closely related to other mammals and the penguin is more closely related to other birds. The evolution does not depend on birds and mammals having a common ancestor.

I think you're misunderstanding Mike's point here. He's not saying whales and ichthyosaurs should have evolved from the same land ancestor if they both evolved flippers. He's pointing out that ichthyosaurs have extremely weird, derived phalanges that do not have the same immediately obvious homology with those of land animals that you see in cetaceans.

Fortunately, we have early (dare I say, transitional) ichthyosaur fossils such as the below Chaohusaurus from the early Triassic of China whose phalanges still look like finger bones.

Edited by caffeine, : No reason given.


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caffeine
Member
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(2)
Message 403 of 403 (851800)
05-02-2019 3:27 PM
Reply to: Message 312 by Faith
04-20-2019 9:33 PM


You fail to take into account that the scientists who study these things are first of all dedicated to the ToE which colors how they think about all these things, and if the ToE is wrong, which of course it is, they are being misled. It isn't as if they approach their study without bias. I'm not so hampered. However, if I run across a seriously different trilobite body plan I may have cause to rethink things.

Recognising the diversity of trilobites does not require being blinded by Darwinist propaganda. We know this because trilobites are abundant as fossils and have been studied since long before Darwin. The work of classifying them into their various species, genera, families and orders was begun by creationists.

The name 'trilobite' is usually attributed to Johann Ernst Immanuel Walch; a Protestant theologian at the University of Jena. In addition to his work on the history of Christianity and the gospels, he had an interest in fossils and wrote what was, at the time, the most detailed account of trilobites in existence. He declined to make a formal, Linnean classification of different trilobite species because he felt there wasn't enough evidence to do it properly (specifically that he had very few articulated fossils to work with and so did not know which heads went with which tails). Nevertheless, despite having nowhere near the amount of materials we work with today, and despite being a creationist theologian, he clearly recognised the huge diversity of species.

quote:
This head, or to state it more clearly, this shell under which the head of the animal is hidden as under a helmet, has forms so varied in the Kingdom of Fossils, that it becomes troublesome to report and determine all these variations. (....) We do not find these horns in all the animals found, nor in any which British authors havewritten about in the Philosophical Transactions; this difference, as well as several others which we have already noticed on the head shield of this animal, informs us that the Trilobite is a widespread type of animal consisting of a very large number of species and subordinate species.

One of the most important early figures in classifying trilobites was John W Salter, an Evangelical Protestant who lost his job as senior palaeontologist at the Geological Survey of Great Britain over his bitter arguments with the atheist Thomas Henry Huxley. His classification of trilobites (published several years before Origin of Species) introduced some of the orders we still use today. I'm unsure what Salter thought about Darwin's ideas; but he'd spent years classifying trilobites into different families before he ever heard them.

I find your approach to trilobites a bit odd. You have no problem with other animals sharing the same body plan and yet representing different kinds - cats and dogs are much more alike in body plan than different families of trilobites and yet you're happy classing them into different kinds. I know you deny this to be true since, in the case of dogs and cats the angle of the neck is somehow enough to denote a fundamentally different body plan; but let's note that it wasn't evolutionary scientists that first noted this fact - creationists like Georges Cuvier could easily see that cats and dogs belonged in the same order (unlike trilobites). What difference does it make if there are many kinds of trilobite?

Edited by caffeine, : No reason given.


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