Are palaeontologists aware of any amniote groups besides synapsids and sauropsida? Is there any palaeontological discussion on if such animals have existed?
The few I see described are only known from a single fossil with uncertain affinity except this study which claims diadectomorphs and seymouriamorphs were amniotes.
Basically title. In the entire permian period I can't find any example of large amniotes which adapted for a fully aquatic lifestyle. Has anyone else ever wondered why it took less than 8 million years in the triassic period for diapsid species to evolve fully aquatic marine lifestyles, but we have no example of synapsid, diapsid, or parareptile being fully aquatic and marine, let alone attaining large size during the Permian? In the cenozoic, it took around 15 mya for a fully aquatic lineage of mammals to appear, so the lack of marine amniotes in the permian is even stranger.
There must have been some ecological pressure to prevent such animals from evolving, or at least being common.
Or are permian marine strata just too rare?
Before the amniote egg could evolve, three things needed to be at place first; internal fertilization, laying eggs on land and the whole larval stage had to be completed inside the egg (or at least most of the larval stage, but it helps to hatch as a fully developed juvenile if the adults are specialized for a terrestrial lifestyle).
And they obviously had to be relatively small so they could lay their eggs inside hollow trunks and other small cavities in the environment that protected the eggs from dangers such as hostile conditions and animals that likes to eat eggs.
But nothing of this is unique. Modern amphibians have several times and independently from one another evolved eggs with internal fertilization which are laid in a terrestrial environment and where the offspring hatch as juveniles, having completed the larval stage inside the egg. But they have never evolved eggs with several internal membranes like the amniotes have.
The amniotic egg has at least two benefits; it egg can be bigger and the gas exchange is easier.
Most amphibian eggs are surrounded by an outer layer of jelly which makes gas exchange less efficient (some who lay their eggs on land have developed a more rubbery layer). The ancestors of the amniotes evolved eggs where the outer layer of jelly disappeared, and the water required for the fetus to grow was located on the inside instead. Instead of a jelly layer, these eggs had a primitive shell to protect its content. To this day many snakes and lizards lay eggs in moist places so they can absorb water from the environment. So it was not an adaptation to drier habitats.
And because these animals were already small, it was not an adaptation to larger eggs. That was an opportunity that was taken advantage of later. After all the dinosaur ancestors of birds did not become bipedal so that their descendants could use the front limbs as wings somewhere in the future. The loss of the gelatinous outer layer would also have happened before the evolution of the inner membranes.
So if it was not to lay larger eggs, or protect them against drought, the most likely explanation that remains is gas exchange. Present day reptiles have a higher metabolism and oxygen requirement than amphibians. We don't know if the first proto-amniotes were the same, but it wouldn't be surprising if it was.
Amphibians that breed in water can laid huge amounts of eggs. They can focus on quantity rather than quality. Tiny larvae emerges from the blobs of jel
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As I understand it, amniotes evolved from amphibians. Were the first amniotes reptiles, and did synapsids then evolve from reptiles or was there a group of amniotes that were neither and diverged into reptiles and synapsids?
I'm having trouble finding a concise answer to this, so any explanation would be appreciated.
How could an amniote evolve to become more like amphibians, with jelly-like, non-amniotic eggs that need to be laid in water, and moist skin covered in mucus and glands used for cutaneous respiration?
The reason asking is because, many taxonomists are using the term βsauropsidβ instead of βreptileβ.
Most spec projects that involve a terraformed world include only one tetrapod or vertebrate. I wanted to restrict the adaptive radiation to a fully terrestrial creature, like a gibbon. In this project there are multiple amphibian species, but only one pure terrestrial species. Pls give me info and ideas.
I hate using the word "re evolve" but that's the only word that I could think of to describe my question.
OH YOU DON'T? WHAT KIND OF PERSON ARE YOU? How do you read your pets transits?
https://www.sciencedaily.com/releases/2019/06/190613143533.htm
Looking at r/creation, because I havenβt seen any recent posts here arguing against evolution or for creation (as if they were necessarily mutually exclusive), I found the beginnings of a couple series.
In one, we have one where they list problems with evolution. The post was long, but the only thing in it that appears to even potentially suggest separate ancestry is how frogs and humans develop unwebbed fingers differently. In frogs (and other amphibians as a monophyletic group) this is done by extending the digits where in humans (and all other amniotes) this is because of cell death between the fingers. The link above explains this difference without it seeming to be much of a problem for evolution. They also claim that we think marsupials and placental mammals are unrelated which contradicts the common ancestry of all amniotes demonstrated by the finger growth study. This is how homology is supposed to show separate ancestry, rather than divergence from a common ancestor. Remember all therian mammals have placenta, give live birth, and several other features common to the group as a whole (with kangaroos having pseudogenes that are no longer functional for producing a placenta). We have external ear flaps, actual nipples, warmer bodies than even monotremes. Placental mammals lack epipubic bones and a pouch, Marsupials still have the ancestral epipubic bones and a pouch that evolved in their lineage that no other mammals have. These similarities place us in the same larger group, these differences show divergence from a common ancestor. Summary: homology isnβt evidence against evolution, nor does it remotely prove it wrong.
The evidence for creationism so far is the first cause argument. So basically deism. Itβs based on the false premise that the Big Bang was a creation ex nihilo event meaning that we start with nothing and then we get a universe. It doesnβt explain the when, where, or how of this causal relationship when you consider there would be no time, space, or energy which are necessary for change to occur anyway. Absolute nothing evidently isnβt possible nor does it make sense for something, much less someone, existing nowhere at no time without potential turning the potential it doesnβt have into a physical result at a location that doesnβt exist so that it changes over time that also doesnβt exist. Even if they could sufficiently demonstrate deism, thatβs a long way from spec
... keep reading on reddit β‘Has anyone here read SCP 1660? If you have, then you might know about SCP 1660-7, which is a sapient stem-mammal with bioluminescence.
this is based largely off of Wikipedia, which i know is not formalized and so confusion like this is inevitable, but its a fast and convenient source of cited information.
The Wikipedia page for Reptile describes it as paraphyletic, composed of all amniotes that are not Birds or Mammals.
the pages for Sauropsids and Synapsids contradicts this, with Sauropsids including (proto/)Reptiles and Birds (as it should be) and Synapsids as (proto/)Mammals
The first definition would imply that there is a common ancestor to both reptiles and Mammals that is defined as a Reptile itself, making the exclusion of mammals notable. However, the distinction between Synapsids and Sauropsids contradicts this, as they encapsulate proto-reptiles and proto-mammals, which as they coexist alongside eachother would make reptiles predating Mammals, especially as to the ancestor of all Mammals being a Reptile
so, whats the truth?
edit: I realize another solution which could be chalked up to poor wording. Wikipedia's definition could be trying to say, albeit poorly, that reptile encapsulates all non-mammal amniotes except for birds
The evolution of the amniotic egg and its membranes allantois, amnion and chorion, made it possible for amniotes to conquer areas too dry for amphibians in general. But the amniotic egg orginated in a damp and moist environment, and most likley absorbed a much of its water from the substrate it was surrounded by, just like many eggs does today.
Apparently it only evolved ones. The amniotic lineage leading to the mammals split from the one leading to the reptiles about 320 million years ago, according to sources. So it must have been present some time before that (but after their ancestors evolved internal fertilization).
The first amniotes were tiny insectivores, and looked like present day salamanders and small lizards. So obvioulsy their eggs were tiny as well. But they had to contain enough nutrients and water (some of it absorbed from the environment) to allow them to go through and eventually skip the whole larval stage inside the egg. When they hatched, they had to be big enough to survive on land.
Today we have amphibians, both frogs, salamanders and caecilians, with internal fertilization that lay their eggs on land and complete their larval stage inside them. While their eggs can have a rubbery shell, they don't have the membranes we find in the amniotic egg. After all these million of years, the amphibians have never evolved their own version of an amniotic egg. And they seem to survive fine without it, even if they can't be laid in dry areas. So why (and how) did our ancestors evolve these membranes? If it was not to prevent desiccation, what was the selection pressure?
Even if the animals were small, their eggs were probably still bigger than terrestrial amphibian eggs laid by same sized animals. The bigger the offspring, the bigger the chance of survival. Could the answer be gas exhange because of a bigger fetus? And/or a way to deal with the waste the fetus produced in its own little pond? A shell would obvioulsy give mechanical support, and if it was relatively dry it would also make it less likely to be attaced by fungus. But modern day amphibians could still benefit from it.
In nature we rarely see new inventions. Most of the time it is just modifications of already existing structures. So what if out ancestors modified structures that were lost in modern amphibians, and when some of them started to lay eggs on land, they could only use what they had left.
Another main difference between amphibians and amniotes is that amphibians
... keep reading on reddit β‘https://www.sciencedaily.com/releases/2019/06/190613143533.htm
Looking at r/creation, because I havenβt seen any recent posts here arguing against evolution or for creation (as if they were necessarily mutually exclusive), I found the beginnings of a couple series.
In one, we have one where they list problems with evolution. The post was long, but the only thing in it that appears to even potentially suggest separate ancestry is how frogs and humans develop unwebbed fingers differently. In frogs (and other amphibians as a monophyletic group) this is done by extending the digits where in humans (and all other amniotes) this is because of cell death between the fingers. The link above explains this difference without it seeming to be much of a problem for evolution. They also claim that we think marsupials and placental mammals are unrelated which contradicts the common ancestry of all amniotes demonstrated by the finger growth study. This is how homology is supposed to show separate ancestry, rather than divergence from a common ancestor. Remember all therian mammals have placenta, give live birth, and several other features common to the group as a whole (with kangaroos having pseudogenes that are no longer functional for producing a placenta). We have external ear flaps, actual nipples, warmer bodies than even monotremes. Placental mammals lack epipubic bones and a pouch, Marsupials still have the ancestral epipubic bones and a pouch that evolved in their lineage that no other mammals have. These similarities place is in the same larger group, these differences show divergence from a common ancestor. Summary: homology isnβt evidence against evolution, nor does it remotely prove it wrong.
The evidence for creationism so far is the first cause argument. So basically deism. Itβs based on the false premise that the Big Bang was a creation ex nihilo event meaning that we start with nothing and then we get a universe. It doesnβt explain the when, where, or how of this causal relationship when you consider there would be no time, space, or energy which are necessary for change to occur anyway. Absolute nothing evidently isnβt possible nor does it make sense for something, much less someone, existing nowhere at no time without potential turning the potential it doesnβt have into a physical result at a location that doesnβt exist so that it changes over time that also doesnβt exist. Even if they could sufficiently demonstrate deism, thatβs a long way from spec
... keep reading on reddit β‘