Before dinosaurs dominated the world, at the top of the Palaeozoic Era, the land was dominated by the synapsids. The synapsids (the vertebrate line that has mammals) were a extremely productive cluster that occupied most niches throughout the late Carboniferous and also the geological period periods, however at the top of the Palaeozoic Era most families were destroyed by the Permian-Triassic mass extinction (around 252 million years ago) with solely the class line living to this day. during this entry we’ll inspect a number of the additional peculiar synapsid reptile teams, that have junction rectifier to the evolution of mammals like us.
SYNAPSIDS CHARACTERISTICS AND EVOLUTIONARY TRENDS
The biological group subclass Synapsida includes mammals and every one alternative amniotes additional closely associated with them than to reptiles. The synapsids were the primary amniotes to diversify and appeared concerning 320 million years past, at the center of the geological period. These initial synapsids were characterised by the presence of only 1 temporal orifice behind every orbit through that the jaw muscles pass. subclass Synapsida virtually means that “fused arches” referencing to the feature arches (because within the past person believed that synapsids had evolved from diapsid reptile reptiles so their arches were thought to be “fused”).
Other characteristics that appeared through their evolution were:
- Differentiation of differently-shaped (heterodont) teeth.
- Lower jaw formed by fewer bones.
- Acquisition of a more erect posture and an endothermic metabolism.
The first teams of additional primitive or “reptile-like” synapsids ar informally known as pelycosaurs, whereas the latter additional advanced forms ar known as therapsids (clade order Therapsida, that in truth derived from pelycosaurs). As we are going to see, the evolution of synapsids is of the type of “one cluster, which has consequent cluster, which has consequent group”.
THE ORIGIN OF SYNAPSIDS, THE PELYCOSAURS
The first synapsids had a sprawling limb posture, low slung bodies and were probably ectothermic. If we look at the skull morphology, the earliest groups of synapsids were the caseasaurians (clade Caseasauria) characterized by their small heads, an overdeveloped snout and their huge bodies (they were probably ectothermic and slow-moving creatures). Yet, if we look at the postcranial skeleton, the earliest synapsids were two groups called the varanopids and the ophiacodontids (Varanopidae and Ophiacodontidae families) which were similar to varanids (through convergent evolution), and while the former were quite small and agile creatures, the latter developed bigger forms with huge heads.
Just before the appearance of the more advanced therapsids, the last two groups of “pelycosaurs” evolved and occupied most land ecosystems. Both groups shared a tall sail along their backs (similarly to Spinosaurus) formed by tall neural spines. In life, this sail probably was covered in skin and had plenty of blood vessels. Although it’s believed that these two groups were still ectothermic, this sail was probably used to gain or lose heat more easily.
The first of these groups is the Edaphosauridae family. Unlike most basal synapsids, the edaphosaurids were herbivorous and, along with the caseasaurians, they were among the first large amniotes to adopt a vegetarian lifestyle. The sails of edaphosaurids were covered with spiny tubercles, of which their function is still debated.
The other group, the Sphenacodontidae family, were the sister group of the therapsids, inside the clade Sphenacodontia. While all other pelycosaur clades had their teeth loosely set in the jaw, the sphenacodontians had their teeth set in deep sockets. Most sphenacodontids were carnivorous, with strong jaws and well-developed caniniform teeth. Some species became the top predators on land before the apparition of the therapsids.