Jurassic Park Period Part 4

Fauna - Reptiles

During the Jurassic, dinosaurs came to dominate the animal world, but they were not the only type of animals. The first birds appeared, evolving from a branch of theropod (hollow-boned) dinosaurs, to share the skies with pterosaurs, the dominant flying vertebrates. Lizards made an appearance and have been with us ever since. Therian mammals evolved, meaning creatures that gave birth to live young, and that includes marsupials. Crocodylomorphs (which eventually gave rise to modern crocodylia, but not during the Jurassic) transitioned from a terrestrial to an aquatic life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs.

This is a lot of ground to cover (so to speak), so I'm going to start in the oceans and work my way to land and sky.

The Triassic/Jurassic extinction event decimated crocodile-like reptilian diversity, with crocodylomorphs (which originated during the last half of the Triassic) being the only group to survive. Even the herbivorous aetosaurs died out. [Can you imagine if they had survived, and we had vegetarian crocodiles raiding our gardens?] The diversity of crocodylomorphs during the Early Jurassic was about the same as those of the Late Triassic, but they occupied different ecological niches.

A group of predominantly marine crocodylomorphs became a prominent part of marine ecosystems. Within that group, some became highly adapted for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin.

Turtles - Turtles (Testudinata) diversified during the Jurassic. The Jurassic turtles are believed to have formed 2 more advanced groups, the Mesochelydia (which were aquatic), and the Perichelydia. There are 2 modern groups turtles (the Testudines), which are terrestrial and had diverged by the Middle Jurassic. The Thalassochelydia is a diverse lineage of sea turtles, and is known from the Late Jurassic of Europe and South America.

Lepidosaurs - The tuatara is a reptile native only to New Zealand, and is the sole living representative of the Rhynchocephalians, which had achieved a global distribution by the beginning of the Jurassic. The Rhynchocephalians occupied a wide range of lifestyles, including the aquatic pleurosaurs with long snake-like bodies and reduced limbs, the herbivorous eilenodontines, and the Oenosaurus, which had broad tooth plates indicative that they ate creatures that were hard-shelled or had an exo-skeleton, such as corals, shelled mollusks and crabs. Rhynochocephalians disappeared from Asia after the Early Jurassic. The last common ancestor of living squamates (which includes lizards and snakes) is estimated to have lived around 190 million years ago during the Early Jurassic. Squamates first appear in the fossil record during the Middle Jurassic and included early members of a snake lineage. However, many Jurassic squamates have unclear relationships to living groups. Eichstaettisaurus from the Late Jurassic of Germany has been suggested to be an early relative of geckos and displays adaptations for climbing.

Ichthyosaurs - The Ichthyosaurs suffered an evolutionary bottleneck during the Triassic/Jurassic extinction event, with all but one group of them becoming extinct. Ichthyosaurs reached its apex of species diversity during the Early Jurassic, including the huge apex predator Temnodontosaurus and the swordfish-like Eurhinosaurus. However, Early Jurassic ichthyosaurs were significantly less morphologically diverse than their Triassic counterparts

Plesiosaurs - The Plesiosaurs originated at the end of the Triassic Period. At least 6 lineages of plesiosaur crossed the Triassic-Jurassic boundary, so they were already diverse in the Earliest Jurassic. Early plesiosaurs were generally small-bodied, with body size increasing later. There appears to have been a strong turnover as the middle of the Jurassic Period began, with the extinction of 2 groups that had been widespread, and the first appearance of the Cryptoclididae group, which became the dominant group of the latter half of the Jurassic. During this time, the thalassophonean pliosaurs, which had ancestrally been small-headed and long-necked, evolved short necks and large heads. Some species, such as the Pliosaurus, had skulls up to 2 metres (6 ft) in length, with body lengths estimated around 10-12 meters (30-36 feet), making them the apex predators of Late Jurassic oceans. Small-bodied plesiosaurs also invaded freshwater environments during the Jurassic, as shown by remains found in freshwater sediments from China and Australia.

Pterosaurs - Pterosaurs first appeared in the Late Triassic, but a major group of Jurassic pterosaurs is the Rhamphorhynchidae, which first appeared in the Early Jurassic. They ate fish. Another group, the Anurognathids, first appeared in the Middle Jurassic. They had short heads and densely furred bodies, and were probably insectivores. Short-tailed pterodactyloids first appeared in the at the beginning of the Late Jurassic. These include the ctenochasmatids, which have closely spaced needle-like teeth that were presumably used for filter feeding. The Late Jurassic Cycnorhamphus had a jaw with teeth only at the tips, with bent jaws like those of living openbill storks, that may have been used to hold and crush hard invertebrates.

Some of these animals could be found on land, as indicated in the above paragraphs by what they ate. But I'm fairly confident that they had branches of relatives living in the oceans. I am sorry for the use of huge tongue-twisting names, but there were so many names, I would have gotten completely bogged down trying to describe the various species.

There you have some of the reptiles that lived in the oceans and other waterways. This has been a long post, so I am going to end it here and take up fish next time. Yes, there were fish in the waters, too.

There will not be a quiz on the names used in this blog. Class dismissed.

https://en.wikipedia.org/wiki/Jurassic

https://en.wikipedia.org/wiki/Crocodylomorpha

Triassic Period Part 2

 Now let's take a look at the inhabitants of the Triassic Period.

Three categories of organisms can be distinguished in the Triassic record: survivors from the Permian–Triassic extinction event, new groups which flourished briefly, and other new groups which went on to dominate the Mesozoic Era.

To go back to the beginning, after the extinction event just before the Triassic Period began, the Earth's biosphere was impoverished. It was well into the middle of the Triassic before life recovered its former diversity. Therapsids (including what would become mammals) and archosaurs (including crocodilian reptiles) were the chief terrestrial vertebrates of this period. A specialized subgroup of archosaurs, called dinosaurs, first appeared late in the Triassic, but did not become dominant until the succeeding Jurassic Period.

The first true mammals also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who were a specialized subgroup of archosaurs.

In marine environments, new types of corals appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of modern times. The shelled ammonites (whose shell resembled that of the modern nautilus, but is not an ancestor) recovered, diversifying from a single line that survived the Permian-Triassic extinction.

The fish fauna was remarkably uniform, with many families and genera exhibiting a global distribution in the wake of the mass extinction event. There were also many types of marine reptiles. The first of the lizard-like animals appeared in the Early Triassic seas and soon diversified, and some developed to huge size during the Late Triassic.

On land, the surviving plants included ginkos, ferns, and horsetails, among others. Seed plants came to dominate the terrestrial flora. In the northern hemisphere, conifers and ferns flourished. A seed fern genus would dominate Gondwana throughout the period.

Many groups of terrestrial fauna appeared in the Triassic period or achieved a new level of evolutionary success during it. They include lungfish, Temnospondyls (early amphibians that had mostly been replaced by reptiles, they made a come-back in this period), Rhynchosaurs (the primary large herbivores in many Triassic ecosystems), Phytosaurs (looked like crocodiles, but unrelated), Aetosaurs (heavily armored and mostly herbivorous), Rauisuchians (the keystone predators of most Triassic terrestrial ecosystems), Theropods (dinosaurs but not the large kind that would come later; most were 1-2 meters long), and Cynodonts (a large group that includes true mammals, complete with hair and a large brain).

Some amphibians were among those groups that survived the Permian-Triassic extinction event. The first ancestors of frogs are known from the Early Triassic, but did not become common until the Jurassic (which comes next).

Among reptiles, the earliest turtles appeared during the Late Triassic Period.

During the Triassic, archosaurs displaced therapsids as the dominant amniotes. This may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammalia-form successors to live as small, mainly nocturnal insectivores. Nocturnal life may have forced the mammaliaforms to develop fur and a higher metabolic rate.

Though the end-Triassic extinction event was not equally devastating in all terrestrial ecosystems, several important clades of large reptiles disappeared, as did most of the amphibians, groups of small reptiles, and others (except for the proto-mammals). Some of the early, primitive dinosaurs also became extinct, but more adaptive ones survived into the Jurassic. Surviving plants that went on to dominate the Mesozoic Era included modern conifers.

The cause of the Late Triassic extinction in uncertain. It was accompanied by huge volcanic eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago, forming one of the largest known inland volcanic events since the planet had first cooled and stabilized. Another possible but less likely cause for the extinction event might be global cooling.

 

 

https://en.wikipedia.org/wiki/Triassic

Triassic Period Part 1

 The Triassic Period spans 50.6 million years, from 251.9 million years ago to 201.4 million years ago. It is the first and shortest period of the Mesozoic Era. It both started and ended with a major extinction event.

The Permian–Triassic extinction devastated terrestrial life. Diverse communities with complex food-web structures took 30 million years to reestablish.

The Triassic period ended with a mass extinction which was particularly severe in the oceans. All the marine reptiles disappeared except for the ichthyosaurs and plesiosaurs. Invertebrates like molluscs were severely affected. In the oceans, 22% of marine families and possibly half of marine genera went missing.

The vast supercontinent of Pangaea continued until the mid-Triassic, after which it began to gradually split into two separate landmasses, Laurasia to the north and Gondwana to the south.

During this time period, almost all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator and spanning from pole to pole. The Tethys Sea penetrated the east side of this continent for a good distance along the equator. There was an older branch of the ocean (called the Paleo-Tethys Ocean) north of the Tethys Sea that was now closed off by a group of moving islands that became a strip of land.

During the mid-Triassic, a similar sea penetrated along the equator from the west coast. This sea was not named in the article I read. All the rest of Pangaea's shores were surrounded by the world-ocean known as Panthalassa. Although it was not stated, my guess is that these 2 long seas coming from the east and the west along the equator finally met, and Pangaea was no more.

The sea level was consistently low compared to the other geological periods. The beginning of the Triassic saw the sea level at around present sea level, rising to about 10-20 m (30-60 ft) above sea level during the Early and Middle Triassic. Then the sea level began to rise, with it reaching up to 50 metres (150 ft) above the present sea level. It then began to decline, reaching a low of 50 metres below the present sea level, which continued into the next time period.

The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. There is no evidence of glaciation at or near either pole. In fact, the polar regions were apparently moist and temperate, providing a climate suitable for forests and vertebrates, including reptiles. Pangaea's large size limited the moderating effect of the global ocean; it's continental climate was highly seasonal, with very hot summers and cold winters. The strong contrast between Pangea and the global ocean triggered intense monsoons.

The climate shifted and became more humid as Pangaea began to split apart. The Triassic may have mostly been a dry period, but evidence exists that it was punctuated by several episodes of increased rainfall in tropical and subtropical latitudes of the Tethys Sea and its surrounding land. It may be that volcanic activity helped trigger climate change during this period.

Next we'll take a look at the inhabitants of Earth during the Triassic Period.

https://en.wikipedia.org/wiki/Triassic

Siderian & Rhyacian Periods

 

Siderian Period

There are 4 periods in the Paleoproterozoic Era, the first being the Siderian Period. This period lasted from 2,500 to 2,300 million years ago.

Early in this period is when banded iron formations peaked. As I explained before, cyanobacteria produced waste oxygen, which initially combined with iron that was in the sea, forming magnetite (Fe3O4), an iron oxide, in a crystal structure rock. This process removed iron from the oceans, presumably turning the greenish water clear.

Then, with no remaining iron in the sea to serve as an oxygen sink, the oxygen escaped the ocean and built up the oxygen level in the atmosphere. This led to the oxygen catastrophe, wherein a great deal of the life then existing on the Earth was wiped out because they could not tolerate such high levels of oxygen.

Some geologists believe the high level of oxygen also triggered the Huronian glaciation. This glaciation started in mid-Siderian (2,400 million years ago) and extended into the next period, lasting until 2,100 million years ago. It was apparently caused when free oxygen combined with the methane in the atmosphere to form carbon dioxide and water, which do not retain heat as well as methane does. With far less of this greenhouse gas in the atmosphere, a great chilling took place, also known as the Huronian glaciation. I don’t know if the entire planet froze, and the article stated that this glaciation caused a mass extinction. I’m waiting for a geologist I know to clarify whether there were 2 mass extinctions so close together, or just one, with both the presence of oxygen and the cooling temperatures to blame.

 

Rhyacian Period

The Rhyacian Period is the 2nd geologic period in the Paleoproterozoic era. It lasted from 2,300 to 2,050 million years ago. And that is just about all the wikipedia article had to say on the subject. Oh, there were a bunch of rock formations created, and the Huronian glaciation lasted 100 million years, but that still leaves 150 million years at the end of the period during which, apparently, absolutely nothing of note happened.

Oof! What was the tipping point that caused the end of the glaciation? For that matter, did it cover the entire Earth? Was there an explosion of new species afterwards?

Maybe they don’t know. What about theories? Doesn’t anybody have any theories? Well, without sitting my geologist friend down and picking his brain clean, I guess that’s as far as I can go with this period. Maybe the next 2 period of the Paleoproterozoic Era will have more meat to them.

 

https://en.wikipedia.org/wiki/Siderian#:~:text=The%20Siderian%20Period%20(%20%2Fsa%C9%AA,these%20dates%20are%20defined%20chronometrically.

https://en.wikipedia.org/wiki/Rhyacian