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I don't know what the correct term for "failed animals" is, but I mean those animals which wheren't able to survive due to their "failed" evolution process. Because evolution, as we see it today, has gone through a lot of "this doesn't work" and "this does work" - so the "good" outcomes of mutation have survived and the others haven't.

This is for some an argument against evolution, but just because they don't know really why nothing has been found or that something has been found.

So I want to ask if skeletons of any of those "failed animals" have been found or not. So is there any evidence of animals who had a "really bad" mutation (not illness, but mutation) and haven't survived in the process of evolution?

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    $\begingroup$ Yes I meant those which failed, so not those who really made it or had an impact on creatures today. $\endgroup$ – watchme Mar 23 '18 at 11:56
  • $\begingroup$ You could just say fossil of "organisms that left no descendent today". In fact most, if not all, fossils we find are of individuals that left no descendants today. They might be very closely related to the individuals who left descendants but they are likely not themselves. This is the magic of coalescence. Only very few individuals actually contribute to distant generations. $\endgroup$ – Remi.b Mar 23 '18 at 16:44
  • $\begingroup$ Here's an example of a "failed animal" - the Atacama desert mummy that some people were claiming as an alien - that's been in recent news: theguardian.com/science/2018/mar/22/… $\endgroup$ – jamesqf Mar 23 '18 at 19:18
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Short answer
The dodo and Irish Elk, both going extinct relatively recently, are examples of species that have yielded skeletons and went extinct, at least partly, due to maladaptations.

Background
Extinct animals are an example of an answer to your question, barred those species did not go extinct through a cataclysmic event of course. No species can evolve into a meteor-resistant species. The term you are looking for is, I think, maladaptation.

For example, the Irish elk (Fig. 1) has been proposed to have gone extinct at least partly through a maladaptation. The male Irish elk was grew the biggest antlers ever recorded, (over 10ft (3 m) wide. Irish elk became extinct 10,600 years ago, and the male antlers have been proposed as a possible reason, although this is debated (source: Wikipedia). For example, males might have suffered because they got entangled in thickets. The climate changed at the end of the last Ice Age, causing the woodlands in which elk live to shrink. And food shortage might have resulted in a lack of nutritional support for the hefty antlers. However, extinction of an entire species is always caused by a multitude of cooperative factors, so the antlers alone can't be blamed (source: Love Nature, Wikipedia).

Also the dodo (Fig. 2) can be an example of an answer to your question. While not caused by a natural phenomenon, some animals simply become maladapted due to human influences. The dodo is the classic example. The dodo went extinct in the 1600's. It was adapted to life without ground-dwelling predators, as it nested on the ground and couldn't fly. The plump, slow, flightless birds were unable to escape from the sailors and their dogs, rats and pigs who landed on Mauritius (sources: Smithsonian, Love Nature).

skeleton Irish Elk
Fig. 1. Skeleton of Irish Elk. source: Love Nature

dodo
Fig. 2. Dodo skeleton. source: Physiology

Sources
- Love Nature
- Smithsonian
- Wikipedia page on Irish Elk

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    $\begingroup$ The anon downvoter is prolly thinking that dodos were perfectly well adapted till humans ruined their party. $\endgroup$ – Roni Saiba Mar 23 '18 at 13:00
  • $\begingroup$ @RoniSaiba - Very true - dodos were adapted to their habitat before they encountered humans, as is mentioned in the answer quite explicitly. Since we are currently experiencing a mass extinction event due to us human actions, it might be categorized a cataclysmic event and given my first lines of my answer, the dodo might have been left out of the answer. Nonetheless, I think it serves as an illustrative example of an answer to the question, as it meets all question criteria (maladapted + skeletal proof) $\endgroup$ – AliceD Mar 23 '18 at 13:36
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    $\begingroup$ Well, should have known someone would come along with a more complete and better sourced answer than mine. :) +1. $\endgroup$ – rotaredom Mar 23 '18 at 16:27
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Of course, we don't need evidence of that in the fossil record: we have evidence of that on going. All around us we see mutations which lead to life-impairing or life-removing disease. However, if the mutation causes early death, it never has the chance to reproduce.

Not the most official source, but Wikipedia does say it well:

Alleles that need only be present in one copy in an organism to be fatal are referred to as dominant lethal alleles. These alleles are not commonly found in populations because they usually result in the death of an organism before it can transmit its lethal allele on to its offspring. An example in humans of a dominant lethal allele is Huntington's disease, a rare neurodegenerative disorder that ultimately results in death. A person exhibits Huntington's disease when they carry a single copy of a repeat-expanded Huntingtin allele on chromosome 4.

(Emphasis mine)

It bears mentioning that Hungtington's is a disease which only shows up later in life, giving a carrier the opportunity to pass it on before it shows up. This allows it to be passed on to its offspring.

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    $\begingroup$ Thanks for the upvote above. I didn't vote on yours as I have difficulty seeing how your answer addresses the question? $\endgroup$ – AliceD Mar 23 '18 at 18:53
  • $\begingroup$ @AliceD I was particularly addressing the last paragraph: "... So is there any evidence of animals who had a "really bad" mutation (not illness, but mutation) and haven't survived in the process of evolution?" My point was to point out that evidence of that is going on all around us; finding it in the fossil record wouldn't be evidence for anything tangible. $\endgroup$ – rotaredom Mar 23 '18 at 18:58
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Yes

There are lots of them, at one time scientists were far more entered in them than normal critters. So called aberrations or anomalous creatures. Animals born with two heads, extra limbs, and other deformities, even some congenital defects would count.These of course are most likely to be fond in organisms we have lots and lots of fossils of like invertebrates. Note most of what you find are injuries which makes sense statistically, it is rare to find a modern wild animal that is has no sings of injury.

Below is an example of a skull of a horse with cyclopsia, an entire website is devoted to abnormal trilobites, and here is paper listing known abnormal ammonites.

enter image description here

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