Hi, I'm Thesaurus, and welcome to this new video
Oh my.. It's been a while since I said something like this
And yes, I'm sorry about that
and if you want to know more about my absence on Youtube and the reasons behind it
and also about the changes I made on the channel... Well, just watch this video until the end.
For now, let's focus on the "real" topic of this video,
because it's a really interesting one, actually, maybe one of the most interesting
among all the other stuff I already talk about.
Because today I' m going to talk about two groups of animals, or should I say ,
One group and one species in paticular of tetrapoda animals
( vertebrates animals with 4 limbs)
that, at some point of their evolutionary path, "decide" to go back into the water ...
This video is part of a new series with it's own playlist
with the name of "Water Reptiles"
But now let's talk about the first group of animals: the Mesosaurus' one
The order of "Mesosauria" comprise a small number of genus and species and genera
all with acquatic lifestyles
It's uncertain if these animal lived on the coast
(according to old theories the mesosaurus were fresh water animals)
or hypersaline lakes
Well.
even if these animals may appear menacing
with a terrified look,
because of their very big head full of sharp teeth
However we have to remember that,
even if these animals may look menancig,
we probably would not find them scary
'cause they weren't bigger than 1 meter long
One important feature of these animals,
and wich will be common among the creatures of this series,
it's the position of the nostrils on the top of their head
this allows the animals to breath, since the nostrils stay outside the water
while its body remained underwater
and this help these animals to hide from the predators
and from the prey too
Besides the big head and the jaws full of elongated teeth
we also have to take a look at their tails
which they were probably used to swim
since they were long and flattened.
Their limbs of the mesosaurus were not capable of
sustaining their own weight out of the water
and if they were capable of actually move on land,
they would probably be very slow and clumsy like the sea turtles
So we are unsure about wether or not they actually ever get out of the water
and how many time would they spend out of the water
But we can say that on the land they would probably move around only by crawling
Another interesting feature about these animals is something that we can't see from the outside
it's a very peculiar condition called "pachyostosis"
With "pachyostosis" we identify a condition in which the bones are very thick
this occurs in some aquatic animals
but it's not an exclusive of them
Anyway an example of pachyostosis in modern aquatic animals are the "sirenians"
the order that comprise manatees and the dungong
Interestingly, this condition gave the name to a genus of the Mesosauria order
in which this condition its particular evident:
"Stereosternum" that means "thick chest"
Other genus of this order are,
besides Mesosaurus itself
(that it's like the "representative" of the family):
Brazilosaurus, Stereosternum of course, and also
Noteosaurus but this is a "numen dubium"
which means that we are not sure if the genus is valid or not
or even a separate species
since with the fossil evidences that we have
don't allow us to determinate the validity of this genus,
Since (spoiler) the mosasaurs were not too fast in the water either
for some time we thought that these animals,
even because of a wrong reconstruction of
their jaws caused by a wrong interpretation,
were filter feeders
"Nice" (don't ask me why)
In fact we actually find out that these animals
simply fed on crustaceans like the pygocephalomorphs.
We already said that their movement on land were very slow
but what about their movement... in the water ?
Well...they were pretty bad here too
In fact they were kinda slow
And maybe it's also because of that... Well, they went extinct. Or it simply was a cause of their decline.
In fact they didn't have such an evolutionary fortune
They lived from 299 to 270 milion years ago
and, after that, they just went extinct
Another peculiarity of these group it's their distibution:
they were, in fact, present in South America and South Africa.
Well...
this, among other things, "helped" Alfred Wegener
with his theory of continental drift,
because by guessing that this animal would not be capable of crossing the ocean
to travel from one continent to another.
He theorized that these continents, at the time, were attached one another
or even just near to one, another in ancient times
and, as we know, it's true
So we could actually say that "Mesosaurus" helped Wegener with his theory...
Or, better, with the formulation of the "theory of continental drift"
One last thing before proceeding with the classification of Mesosaurus
and the entire Mesosauria order by extension,
it's that now we know, thanks to some new paleontological discoveries,
that these animals, were most likely, ovoviviparous or viviparous
Probably, as I represented in this drawing
they being born tail-first
like the ichthyosaurs
and also some modern animals like the dolphins
Well...
This new paleontological discovery it's also very important because these fossil embryos
are the first ever discovered of an amniota,
the group that comprise the Sauropsida (reptiles)
and the Synapsida (mammals, their ancestors and their extinct relatives
I mentioned earlier that the mesosaurus went extinct without leaving any descendants
but I didn't say nothing about
any existing relatives still alive today
but just because there aren't any of them.
Actually the classification of the entire order of the Mesosauria
it's unclear
but there are two key assumptions:
in the first one they are just a part of the "Parareptilia" group
"What are the Parareptilia? What are these parareptiles?" you may ask...
Well,
they are one of the two groups comprised in "Sauropsida"
the other one it's "Eureptilia";
which comprise all the modern-day reptiles, the birds
and all their ancient relatives and their ancestors
( hence the name, which means "true reptiles);
while "Parareptilia"
(which means "similar to reptiles")
aren't closely related to any living reptiles or, in general, modern day organism
( even if they resemble modern day reptiles and share with them a common ancestor)
because they didn't leave any still-living descendants.
Anyway, the other theory about their classification suggests that
Mesosauria and Parareptilia are two distinct groups,
two sister groups with a common ancestor,
but stiil, two distinct groups
This theory is confirmed by the conformation of the skull:
in fact, the Mesosaurus have a "temporal fenestra"
( basically, an opening on the side of the skull )
while the Parareptiles have none
they are all anapsida
( with no opening on the skull )
In the Euereptilia group
there are both anapsida
and diapsida creatures.
However, over the time, some diapsida have developed various modifications
like the turtles [ I should have said "Chelonii" or "Testudines", my bad ].
( Oh, right...)
( I didn't specify it before but...
the Diapsida have two temporal fenestrae,
hence the name, " two openings")
Turtles, even if are just modified diapsida,
have a skull without any temporal fenestra
so they have actually an anapsida skull type...
Yeah, I know, It's kinda messy...
Anyway, back to the Mesosauria,
according to some scientist this temporal fenestra is a primal trait
and so the Parareptilia and the Eureptilia lost these characteristic
and then some Eureptilia evolved two temporal fenestra
So, this charachteristic is actually a basal trait of all the Sauropsida
and the ancestor of all Sauropsida had one temporal fenestra
But according to the other theory
the one according to which the Mesosauria are included in the group of the Parareptilia
and the Mesosauria simply evolved this characteristic successively
( usually the temporal fenestra have the function of lightening the weight of the cranium)
and so this characteristic would not be an ancestral trait but an evolved one "by" the mesosaurus
And now let's talk about the other "protagonist" of this video:
"Spinoaequalis"
So, let's put the parareptiles behind us,
we don't need them for now,
and proceed with the Eureptilia
and, besides all the modern reptiles, a lot of extinct groups are part of this clade
and let's see the group of Diapsida
which it's divided into two branches
the one of the Neodiapsida
( which comprehend modern day reptiles and birds)
and the other one which comprehend less-evolved life-forms
like the "Aeroscelidia"
and Spinoaequalis it's part of this group
and we are going to talk of "him" very soon.
Now, generally speaking, the Aeroscelida
aren't well known among people who didn't have a great knowledge
of "prehistory and prehistoric animals" .
This because they are not too much interesting [sorry guys]
They are similar in appearance to modern lizards
They probably were almost all arborial or terrestrial
(like lizard, yes)
I said "almost", yes.
Anyway the most important representatives of this group are:
Petrolacosaurus, one of the eldest memebers of this group,
and Aeroscelis,
which the whole group is named after.
But they are not important for now,
because we are [ finally ] going to talk about Spinoaequalis
Now, the name of the genus "Spinoaequalis"
comes from a characteristic
which made use theorize that this animal was actually a fully acquatic one
or even just a semi-aquatic life forms.
In fact "Spinoaequalis" means
"equal spines"
"But, which spines?" you may ask...
Well, the haemal arches ( the hind parts of the vertebrae),
which are the "spines" on the bottom of the tail,
and the neural arches (the spines on the top of the tail)
have the same size in this animal.
Because of that, the tail seems flattened
similar to a leaf, we could say.
This suggest that this animal
could have used its tail to move into the water
So scientists assume that this animal would be an acquatic one "just" from that.
In fact we don't have any other evidence confirm this claim
but if that it's actually true
that would make the Spinoaequalis, probably, the first tetrapod to go back into the water
In fact, Spinoaequalis lived during the Carboniferous,
roughly from 305 to 300 milions years ago
way before than Mesosaurus and all the mesosaurus
and that it's what makes Spinoaequalis so special:
it's the first of its kind
Anyway, we still have to remember that
we didn't have any other evidence
that suggest that this animal had a full-acquatic or even an amphibian lifestyle
Some scientist suggested that
the tail could have helped the animal in life-threatening situation
by giving the chance of losing the predator by leaping into the water
What's the truth?
Saddly we don't know for sure
since we didn't have enough fossil evidences
to confirm the hypothesis of the acquatic/ semi-acquatic Spinoaequalis
or the whole "just a stratagem to escape from predator" one
About its natural range,
its fossil were found in Kansas, North America
There's nothing much to say about this animal...
Except that the genus Spinoaequalis
have only one species "Spinoaequalis schultzei"
so we could say that its really one of a kind [ Yeah, I know, it's an awful """"joke"""" ]
And with that we could end...
So... See ya' :D
Oh, before I go,
I just want say that I was absent for a number of reasons related to
my university, my family ( of course, I won't specify what)
and various personal problem
Anyway, I'm back,
and maybe you have noticed that I changed something about the channel, like the name
from "Tèsaurus" to "Thesaurus"
which means "Thesaurus" [ Yeah, I know, for all you of this explanation it's useless]
this was made to increase the extent of the pubblic
and because, as I rediscovered the sparking cider,
the tea take second place [ "Tè" is "Tea" in italian]
and this is the only TRUE justification [ I'm joking... maybe :D]
Also I want to give a more original concept at the base of the channel
In fact, all started when I opened my Facebook page
(a really old page about now old memes)
and, among the various names I've given to it,
called "Il Salotto del Tèsaurus Rex"
Because, at the time the whole joke: "Teasaurus/Tyrannosaurus"
with the Tyrannosaurus drinking the tea, was not so exploited like it is now
The joke is very used, almost seasoned
Which, for me it's not the case of the "Tyrannosaurus/Thesaurus"
And maybe it's just my opinion but I think that it's not so "utilised"
as the "Teasaurus/Tyrannosaurus"
I've also changed something in the graphic aspects of the channel
About the music, right now you are probably listening a free-copyrights music
[ pot... pizza-english with some blabbering]
But next time you might listen something different
because a friend of mine (Hi Michele Spata :D )
offered to make me some background music for the channel
Nothin much to say, except...
"Are you still here?" Like Netflix says
If the answer it's "Yes" well... Thank you very much :3
It's just that, you know... you can waste your life in better ways
I'm telling you this for your own sake...
Bye :D
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