Hello folks,
This is @jasladin here today.
I guess school work got me hibernating in Steemit, but hey! I am back and this is my first steemstem post.
Biology has always been interesting, challenging, confusing, especially with the tongue biting names.
Though I remember jumping through the window in my senior high 1, during biology class, not because the names were too big to pronounce or memorize,
it was not, because I was not good at neat drawing, since the teacher said, my drawing should not be artistic but rather simple and neat, no, not that, not even because the class was a give away time to meet my science boys (smiles memories), but because I had to pee and the teacher won't allow it. 😁
Hope you were not thinking I was a bad student.
Today I want to share with you on something simple, yet facilitating.
Have you ever wondered where bones are from?
Let's take a flash back to biology and bones.
I will be sharing with you based on bony and cartilaginous fish.
Bonyfishes are fishes that belongs to the class called OSTEICHTHYES I know the pronouncing it can be tongue biting, so this is how you pronounce it ahs tee IHK thees
This means bony fish.
Examples of bony fishes are Fishes, You know, tuna and whatnot, trout, catfish, perch, guppies, salmon and most other familiar fishes.
The bony fishes as the name implies have skeleton of bones instead of cartilage.
Bony fishes first appeared more than 400 years ago, although bony fishes are now more abundant in fresh water and salt water, I believe they probably appeared first in fresh water.
Let's go with the shark.
They belong to the CHONDRICHTHYES class, pronounced as Kahn DRIHK thees.
The skeleton here are composed of of flexible substance called cartilage.
When you get the chance to touch a cartilaginous fish such as shark, rays, you'll get to feel the rough sand paper-like skin. This is as a result of the many scales that are embedded in the skin.
Now aside from the current day where humans are rendering them extinct within a century or so in order to enjoy some tasteless soup, sharks have thrived for millions of years, unchanged and unevolved that whole time.
Or so we thought 🤔
The problem is, cartilage doesn't preserve as well as bone, so it's a lot harder to keep a good track record of their history.
Cartilage is more of a kind of rubbery tissue that in bony creatures, gets replaced with bones once the 'frame' is set (aside from like, our noses and whatever).
For a long time, researchers just kind of assumed sharks were a primitive remnant, a 'living fossil' as they like to say.
They simply managed to survive with old material.
But recently, this has been entirely overturned.
After 60 years of coming up blank, one archaeological site in Western Australia, the Gogo Formation brought up some ancient shark fossils that were very interesting indeed. Not only was it a unique find in an ocean of fossils that were rich in fauna but up to this point lacking in sharks, but they found that the 380 million year old cartilage was very much like modern day shark's cartilage.
On top of this, the matrix holding the cartilage together had bone cells visible within its structure - something absent in modern day sharks.
Bones have only been around about half a billion years, and has served very useful not just as a structural tool, but a defensive one.
Unique to vertebrates, studies suggest bone wasn't even a possible option for the longest time, and the reason is likely to do with oxygen.
Today, our atmosphere is about 20% oxygen, but back in the day, this number was closer to 0.1%.
Then, a so far mysterious period called The Great Oxygenation Event occurred about 2.5 billion years ago, and oxygen started to rise significantly. boom, just like that. I guess a little more complicated.
This changed the chemistry of the oceans, rocks and beyond. For example, Dolomite (CaMg(CO3)2) was a mineral dominating rocks before the oxygen rise, but these rocks were largely replaced by limestone, a rock rich in both Aragonite and Calcite (CaCO3 - two different crystal forms of the same mineral).
This was an important advancement for the formation of bone (I bet you thought I was going off on some unrelated tangent), because Calcium Carbonate crystals can form quickly and with little energy compared to that of Dolomite. To add to this, the continental erosion of I suppose billions of tonnes of Calcium would have washed away and filled the seas with the much needed ingredients.
This new technology was now abundant and animals were (in perspective) quick to take advantage in a kind of skeleton revolution. This has been confirmed in the fossil records, with soft bodied creatures in the days of Dolomite and skeleton animals during the later Limestone days. After that, evolution continued to do its work and, well, here we are!
War between the bones and cartilages, who wins?
In the family tree of life, both bony and cartilage fish evolved from a common ancestor called Placoderms, an armour plated fish that represents one of the earliest jawed fish dating back to about 420 million years ago - well into the oxygenation bony era.
In 2013, a fossil was found in Qujing, China called Entelognathus.
This animal is interesting in that it seems somewhat hybridised. the neck, body and tail are reminiscent of the Placodermi, but the head and its bone patterns looked like modern day fish.
This gave some insight as to howskeletons formed; It all began with the head.
The timeline was once thought to be something along the lines of the placodermi evolving a primitive bony structure, animals then losing this and then re-evolving modern-day bones. Meanwhile, sharks and other cartilaginous fish didn't bother and just lived with their rubbery bones.
Our new understanding shows that the Placodermi skeleton simply evolved into modern day skeletons face first, this also adds to the argument that sharks are actually more evolved in this regard than we, having since done away with bones in favour of cartilage at some later date which, if you remember above, was probably around 380 million years or so ago compared to bones at 420 mya.
Bone evolved when the chemical properties of the earth were changed by some currently unexplained event allowing bones to form, and modern bones formed face first in an old fish. Cartilaginous skeletons actually came after the bony structures, split from us on the evolutionary tree to sharks, and we continued with the old model.
I'd like to point out once again that much of this information is buried in questions, controversy and mystery that we are, as a species slowly picking apart and becoming increasingly objective towards
Well the more we learn, the more questions arise I guess that's why we keep evolving in knowledge.
And so many questions keep coming to mind.
When exactly did bones come to exist?
Did bones evolve once, or multiple times?
What molecular mechanisms made our soft tissue become hard? And so on.
I am pretty sure the answers are fourth coming as technology advances, and I hope to be alive to witness the era.
