AST1 Written

The Mesozoic era
What’s left of them today ? !
From a morphological point of of view:!
• Can be linked to actual reptiles with their scaly, resistant skin and strong bone structure.!
• Through them, we can see the stages, visible in their morphology, towards the
acquisition of the mammalian characters, whose accumulation makes the mammal of
today. There was a profusion of species in the Triassic that illustrates the emergence of
these characters.!
Triassic:!
⁃Thrinaxodon: Similar to other synapsids,$Thrinaxodon$adopted a semi-
sprawling posture, an intermediary form between the sprawling position
of$pelycosaurs$(not unlike current$Crocodylia) and the more upright
posture present in current mammals.!
⁃Kannemeyeria: This species has lost almost all of its teeth to develop a
horny beak like turtles!
Jurassic: !
⁃Sauropodes: They consume plants they did not chew, they deliberately
ingested stones and gastroliths as birds do. They grind mixed plants by
contraction of the gizzard. The bolus ferments and produces methane in
the posterior and muscular part of the stomach.!
⁃Archaeopteryx, is a genus of bird-like dinosaurs that is transitional
between non-avian feathered dinosaurs and modern birds. In particular,
they shared the following features with the ( dinosaurs) dromaeosaurids
and troodontids: jaws with sharp teeth, three fingers with claws, a long
bony tail, hyperextensible second toes ("killing claw"), feathers (which
also suggest warm-bloodedness), and various features of the skeleton.
fossils include impressions of feathers. Because these feathers are of an
advanced form (flight feathers). the wings and tail were used for lift
generation, but it is unclear whether Archaeopteryx was capable of
flapping flight or simply a glide.!
⁃Eozostrodon: We observe the presence of a temporal pit on each side of
the skull and confluent with the orbit. One of the important muscles of
chewing goes into this pit to fit on the skull, they are called synapsids.
Its teeth were typically mammalian, being differentiated
into$molars$and$premolars$with triangular cusps.!
⁃Juramaia sinensis: appearance of the tribosphenic molar, one of the
most important characteristics of mammals => plays a role in chewing!
Cretaceous: !

⁃Ornithiscians had a bassin comparable to that of the current birds,
perforated. The bones were spread in length, the pubis is parallel to the
ischium and the prepubis to the back.!
⁃Species of theropods, sauropods and ornithopods, ceratopsians had a
body temperature between 36° and 37°C, which is also the temperature
found in mammals and birds today. !
⁃
⁃They are therefore warm-blooded animals, hemiotherms or endotherms.!
Idées reçu les dinosaures ont disparus: !
-One of the most reknowed families which survived were the theropodes,
the famille of the tyrannosaures, the organisms belonging to this family are
still among us, the birds. When we compare the theropode’s skeleton and
the birds we can clearly see a ressemblance.