Monday, 31 August 2015

Life and death in the Wessex Formation

The Wessex Formation is a geological formation dating back to the early Cretaceous, 130 million years ago. It is a part of the Wealden Group, which in turn is part of the Wealden Supergroup. This Supergroup also houses the Weald Clay Group and Hastings Beds Group, which, along with the Wessex Formation, were home to some of the first dinosaurs discovered, such as Baryonyx and Iguanodon. During the early Cretaceous, the Wessex Formation, and Wealden Supergroup in general, was part of a large island in the Tethys, where Britain now is. It had a dry, fairly arid climate, with distinct wet and dry seasons, and where temperature differences between summer and winter were stark. Much of the Wessex lowlands during this period would have been mostly treeless, covered in shrubs and other low-lying plants. The uplands and floodplains on the other hand would have been much more verdant, at least for some parts of the year, and plausibly housed a greater diversity of species. Due to these differences in habitats, animals would probably have migrated across the island depending on the seasons, spending the fairly cool and wet winters in the lowlands, and the warm and dry summers in the uplands. In this post I will be covering several of the major groups present in this formation, from the smallest Crocodyliforms to the largest Sauropods.

Polacanthus at a creek, by John Sibbick

Sunday, 30 August 2015

A brief guide to the Paleocene faunas of Europe

66 million years ago, the world was dominated by dinosaurs. Great herds of Hadrosaurs and Ceratopsians migrated across the continents, stalked by hosts of Tyrannosaurs, Dromeosaurs, and in some places Abelisaurs. Then one fateful day, the Chicxulub asteroid smashed into Earth, and in an instant, the age of Dinosaurs was over. When the dust settled, all Dinosaurian lineages except the Avians were extinct, and along with them were the Pterosaurs, Plesiosaurs, Mosasaurs, and a large chunk of pretty much everything else. This event, the K-PG extinction, marked the end of the Cretaceous, and the beginning of the first period in the Cenozoic. The large animals were gone, and the planet was essentially empty. This was the setting of the Paleocene, an odd and depauperate world, in many ways owing more to the Cretaceous than the periods that would follow.

The Chicxulub asteroid impact, marking the end of the Cretaceous

Saturday, 29 August 2015

Lizard Kings: The giant Monitors of prehistoric Australasia

Today, the Komodo dragon is quite a well known animal. As the largest lizard in the world, it carries a prestigious title, and it is indeed an impressive creature. The Komodo dragon is however only one part of a greater puzzle, that being the giant Monitor lizards that once dominated much of Australasia. Not much is known of these enigmatic animals, but the bits and pieces we do have seem to reveal what was previously a widespread and successful group, now mostly extinct.

The most famous of the giant Monitors is obviously Megalania, a huge lizard that inhabited southern Australia up until the arrival of humans, when it was wiped out in the Anthropogenic-extinction. Known only from fairly incomplete remains, despite being a very recent animal, Megalania has been the subject of much debate, chiefly over its size. Original estimates from when it was first discovered placed it at 7 meters in length, what that would have made it a truly enormous animal, but in 2002, Zoologist Stephen Wroe found it to be a great deal smaller, at only 4.5 meters in length. This was again changed in 2009, when Wroe himself along with other researchers upsized it to 5.5 meters. In truth, we have no idea how large Megalania really was, since we do not know of its proportions. Ralph Molnar said in 2004 that if it's proportions were like those of a Komodo dragon, it would have been 7 meters long, while if they were similar to a Lace monitor, it would be upwards of 8.

Varanus priscus, by Vlad Konstantinov

Friday, 28 August 2015

The first Tyrannosaurs and how they lived

Everyone knows Tyrannosaurus rex, the most famous dinosaur of all time. It is the only dinosaur commonly referred to by its scientific name(T. rex), the only dinosaur that you can be almost completely certain everyone you ask will have heard of, and one of the most well known large Theropods specimen-wise. But as famous as T. rex is, far fewer people have heard of its ancestors. Indeed, while Tyrannosaurus was a late Cretaceous genus, the Tyrannosaurids go back to the early cretaceous, and the Tyrannosauroid superfamily all the way to the mid Jurassic. It is the latter that we will be talking about today.

Coelurus by Nobu Tamura

Thursday, 27 August 2015

On Hateg Island

Hateg Island is undoubtedly one of the most important European faunas from the Cretaceous. Many well preserved remains have been found here, and the animals which lived on the isle are textbook examples of how odd insular ecosystems can be. It can be difficult to predict just how life on the island was, as there are no analogous locations today, but in this post I will do my best to try and explain just how the ecosystems of Hateg Island may have worked.

The Location of Hateg Island 90 mio ago

Hateg Island existed from approximately 100 to 66 million years ago, though it may still have been present in the earliest Paleocene. It was surrounded by the Tethys ocean, which covered most of Europe at the time. There is some uncertainty concerning the size of the island, but current estimates put it at 80,000 square kilometers. It was quite geographically isolated, more than 200 kilometers from the nearest coasts, which to the north was the Bohemian Massif, and to the south an island corresponding to the Balkan massif, meaning that interaction with the outside world would be minimal for any animals not capable of flight. The climate of Hateg was sub-tropical, with marked dry and rainy seasons, and an average temperature in the twenties. Lot's of material for seeds and berries has been found in the Hateg sediments, as has pollen for Birch, Walnut and Beech, giving us a good idea of the island's forest structure.

When Europe Was An Ocean

The first post on this blog, let's see if this goes anywhere. When Europe Was An Ocean is both the name of the blog and this post, but it also refers to a specific span of time, namely between the mid Jurassic and Eocene. This is a time-span of approximately 120 million years, two times as much as the distance between the Holocene and the late Cretaceous. The world has obviously changed dramatically through this era, with the European archipelago being home to countless species, it's character drastically shifting over time. This post will be a short summary of the history of ocean-Europe, from it's inception to it's ultimate demise.

Our story begins in the late Jurassic of Germany, in the area now known as Solnhofen. The Solnhofen Limestone is renowned for it's well preserved late Jurassic fossils, giving us a fantastic insight into the area at the time. 150 million years ago, in the latest Jurassic, Solnhofen was part on an archipelago that stretched across much of Western Europe. A Shallow sea covered most of the area, dotted with small atolls and other islands.

What the Solnhofen Archipelago would have looked like

These islands were home to a diverse fauna, but one which included surprisingly few dinosaurs, probably due to their insular nature, and the flying birds not having evolved yet. In turn, they were inhabited by an incredible diversity of Pterosaurs, including animals such as Rhamphorhynchus, Aerodactylus, and even Pterodactylus, the first Pterosaur to be discovered. Two dinosaurs were present in the faunas however, both of them quite famous. One was Compsognathus, and another the perhaps more surprising Archaeopteryx, which while often portrayed as living in dense jungles alongside Allosaurus and Brachiosaurus, was actually an inhabitant of the European archipelago. Also present were several species of Crocodylomorphs, such as the small and terrestrial Alligatorellus, an Atoposaurid, and Geosaurus, a marine crocodile of the Metriorhynchid family.

Archaeopteryx lithographica, from Matthew Martyniuk's fantastic book, Beasts of Antiquity: Stem-birds in the Solnhofen Limestone

During the cretaceous, even as the continents were beginning to approach their current state, Europe continued to be a series of islands and microcontinents. While the smaller islands continued to resemble the Solnhofen archipelago, many of the larger ones had faunas more similar to those of the continents. One example of this is Britain, which was one of the larger isles at the time. All of the first dinosaurs discovered were from here, including Iguanodon, Megalosaurus, and Hylaeosaurus. Other well known british dinosaurs include animals such as the Spinosaurid Baryonyx and the Ornithopod Hypsilophodon. 

A map of Cretaceous Europe, projected over a modern one

Another part of Cretaceous Europe that must be mentioned is Hateg Island, located in present day Romania. This large offshore isle was home to an incredibly unique insular fauna, such as the dwarf Sauropod Magyarosaurus and the Hadrosaur Telmatosaurus. The island was also home to at least a dozen species of small Theropods, but the primary predators on Hateg were in fact giant Azdarchid Pterosaurs of the genus Hatzegopteryx. These giraffe-sized animals would have been more or less uncontested, dwarfing all other animals on the island, including the sauropods. The Hateg faunas existed in the late Cretaceous, up until the K-PG extinction event.

The small Eocene mammal Leptictidium, from Walking With Beasts

The Paleocene of Europe was a rather dim and poorly known time. Relatively few fossil remains are found from this period, but from what we know, it seems to have been populated by a very low diversity of species, a so-called recovery fauna, which slowly adapted and diversified in the time up until the Eocene. These early faunas were essentially composed of late Cretaceous species, but lacking any animals larger than a cat. For the first 10 million years, the orders of Artiodactyla and Carnivora had not yet appeared, though primitive primates were already present. When the modern groups first started to appear in the early Eocene, they would scarcely have been recognizable, as they had not yet settled into their modern roles. Hoofed, predatory Artiodactyls such as Dissacus stalked the undergrowth, along with other archaic groups such as the Condylarths. Interestingly, many of the larger animals during the Paleocene and Eocene of Europe were not in fact mammals, but instead members of multiple other lineages. Dinosaurs such as Gastornis, a large herbivorous bird, would have been some of the biggest animals in the faunas, and crocodiles would have been keystone predators.

Diatryma, a North American relative of Gastornis, by Matthew Martyniuk

The Eocene saw a great diversification of mammals, as the faunas of the world finally recovered after the K-PG extinction event. In Europe, early Carnivorans such as Parodectes became widespread, though they remained small throughout the period. Other familiar animals, such as Bats and Pangolins also appeared, becoming common parts of the Eocene faunas. Other, far stranger animals were also present, and made up most of the megafauna at the time. Creatures such as the hippo-like Coryphodon and the first Perissodactyls arrived on the continent, due to a connection to North America through a land-bridge with Greenland. These early Perissodactyls were more primitive than either horses or rhinos, possessing features ancestral to both. The early Perissodactyls such as Hallensia were only the size of dogs, but increased substantially in size over the course of the Eocene. The first true horses to arrive in Europe were members of the genus Pliolophous, which may in fact have been a descendant of Hallensia. The mid Eocene was a very peculiar time, in which Europe was home to several lineages not typically though of as European, including Marsupials and the aforementioned Pangolins.

Palaeotherium magnum, an archaeic Perissodactyl, related to tapirs and horses

By the late Eocene, the European archipelago was reaching it's end. The development of the first arctic glaciations was slowly causing the sea levels to lower, and the climate was getting colder. The dense, tropical jungles of the early to mid Eocene were gradually being replaced by more open, subtropical woods. Many surviving Paleocene lineages died out, and a faunal turnover began. Among the winners were animals such as Palaeotherium and Hyaenodon, and among the losers were groups like the Leptictids, which died out, leaving no descendants. The Gastornithid birds and terrestrial Crocodiles died out in Europe, and the Artiodactyls became one of the most successful groups. Then finally came the Oligocene, marking the end for the European archipelago, as a landbridge was established with mainland Eurasia, and masses of new species entered Europe. Many of these species had evolved in the more arid inland conditions of Asia, and were more well adapted to the drying climate than the insular faunas of Europe. Thus, a huge number of the endemic European lineages died out and were replaced by Asian immigrants, in an event sometimes called "La Grand Coupre". True Rhinos and Tapirs entered Europe, outcompeting many European herbivores, and several species of Hyaenodon went extinct, though a new species arrived from Asia, ensuring the genus' continued existence in Europe. Arboreal Primates disappeared from Europe, and the Creodonts, which had previously been top predators, steeply declined. Thus ended ocean Europe, and the continent began to take the shape we know today, though it would continue to look quite different for several million years to come.