Namaste friends! Welcome to another post of the “history of earth” series. Drum rolls for the new period of an entirely new era. If Paleozoic was fun for you I bet Mesozoic will be enthralling. We are entering the era of reptiles and the first post is on the Triassic period- the gateway for reptilian heaven. Mesozoic had such a high reptilian diversity and our beloved dinosaurs that it is named the era of reptiles preceding the Cenozoic era the mammalian time. There is so much to write and read about the Mesozoic era let alone dinosaurs. Let us go for the first period following the biggest extinction on earth.
Triassic is the first period of the Mesozoic era followed by the Jurassic and cretaceous periods. After it took a while for surviving life forms to make a comeback in the Triassic period. The ripples of a catastrophe had remained in the atmosphere for long. When Triassic had started showing its diversity then it became clear that reptiles would own the stage. synapsids, the dominant fauna of Permian, had not survived the great dying except cynodonts that had given rise to mammals in the Late Triassic. While reading the texts I have come across some anomalies.
few important Points…
Firstly, we do read and study that animals had evolved from amphibians to reptiles to birds and then mammals. The later part of this equation is incorrect. Mammals had evolved from synapsids and sauropsids have given rise to reptiles from which birds had evolved. Prominent studies even indicate that mammals have first appeared between the late Triassic and early Jurassic. On the other hand, birds have appeared in the Cretaceous period. In this way, mammals predate the birds. Secondly, it is incorrect to think that dinosaurs had left no descendants because birds are the direct descendants of dinosaurs. We have started calling birds avian dinosaurs. The extinction at the end of the Cretaceous had killed all the nonavian dinosaurs but avian dinosaurs had survived.
A little back story…
The Triassic period began 251 million years ago after the Permian period and ended 199.6 million years ago. The Mesozoic era had started with the supercontinent Pangaea and ended when continents were in a modern configuration. Its start and end are laced with two of the big five mass extinctions, the (the great dying) and the end cretaceous extinction. In the late Triassic, Pangea started to disintegrate into separate continents. Climate was majorly warm and dry except in coastal regions that were wet. Plate movements were still and dormant. This early Triassic was very much like the middle and late Permian period. This all had started to change in the late Triassic and the pioneer of this change was again plate tectonics.
At the end of the Triassic period continents began to drift apart and ocean water had started to invade the coastal areas creating shallow seas. Newly formed shallow seas were colonized by new marine invertebrates and marine reptiles. In the carboniferous when continents were farther apart shallow marine basins were home to varied kinds of animal life. This diversity had suffered in the Permian period. When these landmasses began to move away again in the late Triassic it was good news for life and diversity. After the great dying at the start of the Triassic lifeforms had bounced back and occupied the empty niches.
To better understand the Triassic environment it’s better to divide it into two parts, the early Triassic and late Triassic periods. The middle Triassic was more like a transition zone which was similar to neither of the above. The early Triassic was like the end Permian period, dry and warm. The continents were combined as Pangaea. Pangaea was in C shape configuration from east to west direction. That means on the eastern boundary it was inwardly curved. Tethys Sea was situated on the eastern boundary between Africa and western Asia. In the late Triassic, Pangaea had started to break apart in Laurasia and Gondwanaland ending into the present configuration near the end of the Cretaceous period.
as you see in the above gif Pangea, on its western boundary Panthalassa. Along on its eastern boundary cradled between Africa and Asia Tethys sea.
So, we were discussing the early Triassic and this breaking bad hadn’t started yet. The early Triassic environment mainly had possible coastal forests and vast interior deserts. The Polar Regions were colder and as you moved towards lower latitudes it was drier and warmer. The late Triassic however, was different and the beginning of the ever-changing continental cycle.
Few important points again…
I want to state one thing here. Although dinosaurs had ruled over most of the Mesozoic era their dominance had changed over again and again. In Jurassic and subsequent cretaceous different species had ruled over different regions and continents. For example, entirely new species of the Late Jurassic had replaced the dominant ones of the early Jurassic. The Triassic had exotic reptiles but not dinosaurs until the very end. When Triassic had ended with the end Triassic extinction road was clear for dinosaurs to take over. The Mesozoic was a very active period in the name of life forms and continents. The Pangaea had started to separate in the late Triassic and this continues till the end cretaceous period. I do believe that was a major reason for this.
Continents were on a constant voyage from 199.6 million years ago till 65 years ago. This certainly had affected the climate conditions constantly from one type to another and back again. Maybe it was the reason why species were losing power to each other within a few million years. The early Triassic had fewer distinct climate zones in comparison to the ever-changing late Triassic.
Paleogeography of Triassic period
In the early Triassic, there was only one supercontinent Pangaea. Panthalassa, the superocean had surrounded it. Tethys sea that will become large following the breakup of Pangaea was situated on the east side. Pangea had stretched from 85 degrees north to 90 degrees south covering one-quarter of the earth’s surface. If one could divide Pangea into two parts it would be the northern supercontinent Laurasia and southern supercontinent Gondwana. Laurasia had all the northern continents, North America, Europe, Asia (minus India as it was part of Gondwana). Gondwanaland on the other hand has all the southern continents South America, Africa, India, Australia, and Antarctica. When Pangea had first started to drift apart it had separated in Laurasia and Gondwana first which then further separated into the present configuration. Panthalassa was as wide as double the equator width of the present pacific ocean.
Tectonic motions and separation
There were many volcanic islands in the eastern Panthalassa near the western boundary of Pangaea. It was a little like present-day Hawaii islands near the west coast of America and Canada. During the time of Pangaea breakage when Laurasia had moved westward, the Panthalassa plate was moving eastwards, in a simple words collision course. As we have discussed in the plate tectonics and continental drift oceanic plate is denser than the continental plate so it subducts underneath the continental plate. When the Panthalassa plate had subducted underneath the western boundary of Pangaea small volcanic islands had collided with the North American west coast. This collision had created the Cordilleran belt of North America.
At the eastern boundary of Pangaea smacked between Africa and Asia was Tethys sea. When Pangaea started to break apart in the late Triassic Tethys seaway had extended westwards until it reached the eastern Panthalassa in late Jurassic separating Laurasia and Gondwana. There are many ways we can calculate the voyage of the supercontinent like pale magnetic data, continental margins like South America and Africa, mountain building events, and fossil plants or animals like glossopteris.
When continents break apart and start to move away huge amounts of clastic sediments flow in the nearby water bodies piling on the ocean floor. Shale and sedimentary rocks commonly form as the result of these events. In the later Triassic, the continents began to move apart and it had given plenty of space for ocean water to invade the coastal lands.
The Triassic period, especially the early Triassic, had homogeneous climate conditions. Although it is controversial, evidence points to no glaciers in Triassic. All continents were grouped as one so the climate variation was not extreme. Due to the existence of the supercontinent, the coastline was less in comparison to the present. This all had led to low diversity in the Triassic period.
For surety Pangaea had fewer water bodies on the surface because it must have been extremely difficult for clouds to reach most of its landmass. The early Triassic had high seasonality with warm days and cold nights. However, evidence like alluvial deposits, riverine sediments, and clay-rich clastic material points towards a monsoonal climate in the middle and late Triassic. There are some coal deposits that date back to the Triassic period which seems counterintuitive because Triassic was dry. Well near the late Triassic lush forests might have developed in the higher latitudes. Climate was favorable for the growth of swampy rainforests which gradually transformed into peat.
Ocean circulation must have simple. Ocean water had to travel far to deliver heat and nutrients which had attributed to seasonality. The Eastern boundary of Pangaea was warmer and there was a constant influx of nutrients in Tethys to support its relatively rich shallow marine life. Tethys might have rich coral systems in its sunlit waters. In Polar Regions, the animal distribution was low relative to the tropics similar to modern times. With the plethora of knowledge to share it is better to talk about animals in the next blog post. However, just a little trailer.
- The biggest help as a post for the Triassic period is one by the Natural history Museum.
- Another good post you can go for is the Triassic period by Britannica.com.
The Triassic period was in nutshell a promising sighting of the glorious future. The early Triassic biota was very Palaeozoic in nature but later Triassic had Mesozoic kind biota. We shall see how this story started from an extinction ended on extinction shall go. Stay tuned and Do Revelation.