Age of the Dinosaurs III: Life in the Seas

Around 250 million years ago there were already animals living in the oceans. They had evolved back from terrestrial animals and were therefore part of the reptile family. (1) Each period in the Mesozoic (the age of reptiles) had its own specific types of sea life, but all of them fed on fish, shrimps and shellfish. (2)

During the Triassic Period there was a huge ocean called the Tethys Sea which stretched across Southern Europe. The oldest group of reptiles that had adapted to life in this ocean were placodonts, who fed on shell fish and still needed to surface in order to breathe. They shared the water with nothosaurs, whose body was more streamlined for aquatic life. It had fins on its legs, but could still walk on land. (1)


1. Nothosaur from the Triassic Period

From the nothosaurs another group of aquatic reptiles emerged: plesiosaurs. This is possibly the most varied group of swimming reptiles and can be split into two groups. One group, characterized by their short necks, is called pliosaurs, while the long-necked group is called elasmosaurs. Both of these groups had species in all kinds of sizes and they occupied the oceans in the Jurassic and Cretaceous Period (1)

But the most well adapted sea reptiles in the Mesozoic were the ichthyosaurs. These reptiles resembled dolphins with their streamlined bodies, back-fin, paired fins on either side, and large fin on the tail. Like dolphins, they had to surface in order to breathe. Ichthyosaurs developed in the Triassic Period and persisted until the early Cretaceous Period, when they were replaced by mosasaurs until the end of the Mesozoic. (1)


2. Platypterygius kiprijanovi, an ichthyosaur species

Aside from the reptiles in the seas, there was one other major development below the surface. From the Jurassic Period onwards the marine reptiles shared the oceans with numerous fish species. The development of bonefish, where most modern fish species are a part of, had begun, but they were still overshadowed by the older group of fish: ray-finned fish. (3)


References:

1. Dixon, D., In the Sea, 2001, Ticktock Publishing
2. Amersham, B., National Geographic Dinosaurs, 1999, Firecrest Books (page 16)
3. Palmer, D., Atlas of the Prehistoric World, 1999, Marshall, London (page 101)

Picture credits:

All pictures from Wikipedia Commons

Age of the Dinosaurs II: Dinosaurs Walk the Earth

Around 225 million years ago, during the Triassic Period, a new type of small carnivorous animals emerged in Argentina. (1) They evolved from archosaurs and were probably no larger than a large dog. (2) This were the first dinosaurs to walk the Earth. Like all reptiles, these dinosaurs laid eggs. (1)

The world they lived in consisted of one big continent, called Pangaea, and the Earth was warm and dry. There were vast deserts and no polar icecaps. In this world where very wet and very dry periods followed each other, dinosaurs as a group diversified and grew at a very fast rate. By the end of the Triassic Period there were herbivores alongside the carnivores and they populated the entire Earth. (1)


1. Pangaea

The Jurassic Period that followed the Triassic Period saw the world get wetter, although it remained warm. Plants started to colonize the deserts and immense forests of gigantic trees, ferns and other plants emerged. (1) Plants began to diversify and angiosperms evolved. Eventually, this group of plants would dominate the terrestrial vegetation. (3) The continents started to drift apart and between Northern America and Europe, as well as between Europe and Africa large oceans appeared. (1)

In this green world the number of dinosaurs increased rapidly and a lot of new species evolved. Some were big, heavily armored carnivores, while others were large herbivores like the familiar sauropods with their long necks. Carnivorous dinosaurs either hunted alone or in groups, while herbivores used a large variety of protections against them. Some had their size, armor, or horns to defend themselves, while others relied on speed, their senses, or living in a herd. (1)


2. Artist impression of Alamosaurus, a sauropod

At the beginning of the Cretaceous Period that came after the Jurassic Period temperatures on Earth reached a high point, only to decrease again over the next millions of years. (1) Dinosaurs split into two main groups: Saurischia (‘with lizard hips’) and Ornithischia (‘with bird hips). (2) It is in this period that dinosaurs like Tyrannosaurus rex walked the Earth. The T. rex is perhaps the most well-known dinosaur of our age. With its 12 meters long and 6 meters high it was a fearsome predator in Northern America, although some scientists believe the T. rex was a scavenger and not an active hunter. For a long time the T. rex was the largest dinosaur known to man, but today that distinction goes to Spinosaurus, with estimates between 12.6 and 18 meters in length. (4)


3. Reconstruction of Tyrannosaurus rex in walking position

At the end of the Cretaceous Period the continents reached their current positions, although India was an island. Australia, Antarctica and Southern America were still connected together by narrow land-bridges. (1) The primal forests consisting of mainly fern species made place for more modern forests consisting of oaks, beeches, and other broadleaved trees. In between there were groups of coniferous trees and in the underbrush there were flowering herbs. (5) The world was starting to look more and more like it does today.

References:

1. Amersham, B., National Geographic Dinosaurs, 1999, Firecrest Books (page 13-15, 36-46)
2. Ackroyd, Peter, The Beginning, 2003, Dorling Kinderley, London (page 60-82)
3. Palmer, D., Atlas of the Prehistoric World, 1999, Marshall, London (page 99)
4. Dixon, D., Carnivores, 2001, Ticktock Publishing (page 6-16, 28-31)
5. Dixon, D., Herbivores, 2001, Ticktock Publishing

Picture credits:


All pictures from Wikipedia Commons

Age of the Dinosaurs I: Early Reptiles

The first reptiles started appearing in the Carboniferous period. They were small lizard-like creatures. It’s not exactly known how they evolved, but their advantage over amphibians is obvious, as they didn’t need to return to the water to procreate. (1) This caused them to be able to conquer land in a way not seen before.

One of the earliest species of reptiles was Hylonomus, the oldest known ancestor of crocodiles and dinosaurs, and eventually birds. During this period another early ancestor started to appear, but of an entirely different group. Synapsids, a group of egg-laying, vertebrate animals, eventually developed into mammals. (1)


1. Artist impression of Hylonomus lyelli, an early reptile from the Late Carboniferous of Nova Scotia, Canada

During the Permian period all land formed one great continent known as Pangaea. In many areas had a harsh and dry climate, giving the advantage to reptiles and synapsids over amphibians. Both groups of terrestrial animals flourished, but for unknown reasons synapsids were more successful and made up 75 % of vertebrate, four legged terrestrials. (1)

Then the climate began to change and synapsids started spreading from the north in southern direction. One group of these early synapsids was called pelycosaurs. They resembled large lizards with strong jaws. During the Permian period this group started to evolve into therapsids, who were an extremely varied group with many different shapes and sizes. This group contained the first predators. The Permian period also saw the evolution of the two main classes of reptiles: diapsids and anapsids. (1)


2. Artist impression of Pristerognathus vanderbyli, a member of the therapsids, from South Africa

The end of the Permian period was around 248 million years ago. One of the most massive extinctions ever took place then, and over 90 % of all species went extinct. The extinction hit the oceans the hardest, as they warmed up around 95 % of all species living in the oceans died out. Among them were large groups of coral species and trilobites. Land species fared a little better, ‘only’ 70 % died out. (1)

There was no clear cause for this extinction. What we know is that there were significant climate changes. The oceans withdrew and shallow inner seas dried up, which caused a lot of the oceanic creatures to go extinct. Also, due to volcanic activity there was a lot of dust and carbon dioxide in the atmosphere, causing warming of the Earth as well as a lowered oxygen content in sea water. (1) All of this together was too much for most species living at the time.

The time of the early reptiles ended soon after this mass extinction. A group of reptiles called archosaurs, members of the diapsids, became dominant during the Triassic Period and from this group the dinosaurs would evolve, giving rise to the Age of the Dinosaurs. (1)


References:

1. Ackroyd, Peter, The Beginning, 2003, Dorling Kinderley, London (page 49-60)

Picture credits:

All pictures from Wikipedia Commons

Bookreview: The Atlas of the Prehistoric World

Author: Douglas Palmer
Published: 1999
Personal rating: 5/5

This book has three distinct parts that can be read separately, but are also very complimentary to each other. The first part is about fifty pages of world maps, showing the changing land masses with brief information on what changed and how it affected the climate, landscape, and life on Earth. These maps cover the time period from about 620 million years ago until 18.000 years ago. For reference the outline of the modern day map is drawn on top, which takes a bit of getting used to when viewing the maps, but also makes it really easy to see the enormous changes that have taken place. I loved this part of the book, because usually you only see pictures of some of the more important moments, like Pangaea in the Triassic Period and the drifting of continents in the Tertiary Period. This book shows the changes in much more detail, so you can actually see how and when moves were made by landmasses. I also liked that the viewpoint of each map was not solely the ever-present European side of the world. Usually both sides of the world were shown next to each other.

The second part of the book was about twice as long as the first part and dealt with the time period of the beginning of life until 18.000 years ago. It showed the evolution of life in texts, with great illustrations, with a focus on explaining the evolutionary changes as a natural consequence of the changing geography, which made the landscape and climate change as well. There are so many books that either skip that step completely or gloss over it, that it felt like a breath of fresh air to see the focus on the ‘why’ instead of the ‘what’. Sometimes the story jumped a bit, as the topics here are ordered chronologically bit written as self-contained pieces. This makes it so the story doesn’t always flow well when reading this part front to back, but has the advantage that certain periods can be skipped and it makes it easy to look up particular information.

The last part of the book was about forty pages of facts, by which I mean it contained a brief summary of the history of the Earth, bits about different kind of rocks and sediments, geological processes (like tectonics), and fossils, just to name a few things. This part contained great information in a clear and concise format. None of it was necessary to understand the two previous parts, but it was relevant to the topics discussed and fascinating.

The book ends with a list of small biographies of important scientists (both historic and contemporary) in the various fields that contributed to the over-all knowledge in the book, a list os museums and websites to visit, a glossary, and a further literature list. The only thing missing was a reference list, but I expect a lot of the references, if not all, will be in the further literature list.

All in all, this book was really great. I’ve read about ten books on this topic and browsed even more, but this is one of the best out there. Not to be missed!

Short Reviews: (Dinosaur) Non-fiction Books

The Great Atlas of the Universe by Leopold Benaccio

This wonderful book full of stunning pictures takes you on a whirlwind tour of the history of the Earth, starting with the Big Bang and ending with the emergence of early humans. There’s not much text, but what there is, is very clear, concise, and informative. A great book to page through, and stop and sample whatever page draws your eye.

National Geographic Dinosaurs by Paul Barrett

This is a beautiful book with great pictures and easily understood text. It has good general information and a part where the best known and most recently discovered dinosaurs are discussed in more detail. With a publishing date of 2001 it’s a little dated when it comes to some information, but it’s still a great book.

In the Sea by Dougal Dixon

A nice little book covering the entire dinosaur age, focusing exclusively on sea-life during this period. Because of this narrow focus, there’s a lot of room for information that’s usually skipped. I really liked this look under the sea.

In the Sky by Dougal Dixon

A great little book covering all things flying during the dinosaur age. Not only discussing flying dinosaurs, it also takes the time to show the emergence of birds and takes a look at the early birds that were living during this time. I loved the fact that there’s plenty of examples of links between dinosaurs and birds, not only the always mentioned Archaeopteryx, who’s important but by far not the only important link between dinosaurs and modern birds. I loved this book.

Carnivores by Dougal Dixon

A nice little book covering carnivorous dinosaurs. It talks about the emergence and evolution of carnivores and highlights some of the more important and famous carnivores, including of course the T-Rex. Easy to read with good information.

Herbivores by Dougal Dixon

This nice little book covers all kinds of herbivorous dinosaurs. It talks about the evolution and succession of species, as well as taking a closer look at the most important species. There’s also attention for the various (possible) defensive mechanisms, like spikes and horns, and how they evolved. Easy to read, but sometimes it felt a little disjointed, especially at the end where I felt like some topics were just added on because they had to be discussed.

Dinomummy by Phillip Manning

This children’s book is a quick and easy read, but that doesn’t make the story of the life and discovery of Dakota, a dinosaur mummy, any less interesting. The text is clear and simple, but conveys a lot of information. And the pictures are great. I wonder how many were staged for the book and how many were actual pictures taken during the course of the excavation and research. Either way, a nice look behind the scenes of dinosaur research and one of the greatest finds in recent history!

Review: Walking With Dinosaurs (DVD)

Walking with Dinosaurs, produced by the BBC, is perhaps one of the most famous dinosaur documentaries ever made. Originally aired as six episodes in the UK in 1999 and narrated by Kenneth Branagh, they are now all available on a single DVD. Each episode is approximately 45 minutes, perfect for watching one in a free hour. They are chronological and take the viewer from the beginning of the dinosaur era to the mass extinction at the end of the Cretaceous.

The whole documentary is set up like any other nature documentary, as if dinosaurs could just be filmed in their natural habitat. The scenes played out on screen seem so real and are so beautiful; it’s absolutely amazing even more than ten years past the production date. Of course there are plenty of pictures in dinosaur books, but somehow pictures in a book just don’t give a good impression of how the world was all those millions of years ago – something this DVD does.

It’s scientifically very sound, although there some mistakes (listed here), and as time continues to pass and research advances more and more things will be proven wrong. But that doesn’t take away that most if the information is still correct and Walking with Dinosaurs is still the best documentary on the subject there is. I’m therefore not surprised that the BBC is working on producing a 3D movie based on this series. (1, 2)

For another review of this series look here, for a review especially for parents look here.


References:

1. Wikipedia article Walking with Dinosaurs, 1. http://en.wikipedia.org/wiki/Walking_with_Dinosaurs (accessed 20 April 2011)
2. Spicezee, BBC, Reliance Big in movie co-production deal, 2 November 2010, http://swww.spicezee.com/articles/story74600.htm (accessed 20 April 2011)

Newsflash: "Embryo sauropod discovered"

For the first time ever, an American scientist has mapped an embryo of the sauropoda, a group of herbivorous dinosaurs.

It is probably an embryo of a Titanosaurus, a dinosaur that could reach a length of twelve to fifteen meters. Researcher Gerald Grellet-Tinner of the Field Museum in Chicago discovered the remains of the unborn animal by viewing a dinosaur egg using a special scan.

The discovered embryo is fully developed and has a diameter of about nine centimeter, reports the British magazine New Scientist.

Surprise

"I was totally surprised," said Grellet-Tinner. "We have never before found such a fully formed embryo. And we did not know that these dinosaurs laid such extremely small eggs. "

The dinosaur egg in which the embryo has been discovered was found in the sixties during a scientific expedition close to the Gobi Desert in Mongolia. The fossil had landed in the archives of the Field Museum for some reason.

Bacteria

Bacteria have ensured that the dinosaur bones of the unborn are converted from calcium phosphate to calcium carbonate. The rest of the eggshell is also made up of that material.

This made it impossible for the embryo to be detected with X-rays. Grellet-Tinner used a so-called tomography to map the unborn animal. Based on the shape of the body, he concluded that it was a Titanosaurus. He has published his findings in the scientific journal Gondwana Research.

Doubt

However, some scientists doubt the results of the study. They ask themselves whether it is possible to determine a dinosaur species by looking at the shape of an embryo.

"It's very unusual to find an embryo with bones that are shaped exactly the same as in adults," remarked Steve Salisbury of the University of Queensland in New Scientist.

According to the Salisbury it is plausible that it is an embryo of a dinosaur from the group sauropoda. That discovery alone is very special. The age of the egg indicates that these dinosaurs lived in Mongolia 50 million years earlier than previously thought.

Source: http://www.nu.nl/wetenschap/2474792/embryo-van-sauropod-ontdekt--.html

Original article translated by me.