Econstudentlog

Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe (2)

Here’s my first post about the book.

I wasn’t quite sure how to rate the book, but I ended up at four stars on goodreads. The main thing holding me back from giving it a higher rating is that the book is actually quite hard to read and there’s a lot of talk about teeth; one general point I learned from this book is that the teeth animals who lived in the past have left behind for us to find are sometimes really useful, because they can help us to make/support various inferences about other things, from animal behaviours to climatic developments. As for the ‘hard to read’-part, I (mostly) don’t blame the author for this because a book like this would have to be a bit hard to read to provide the level of coverage that is provided; that’s part of why I give it four stars in spite of this. If you have a look at the links in the first post, you’ll notice the many Latin names. You’ll find a lot of those in the text as well. This is perfectly natural as there were a lot of e.g. horse-like and rhino-like species living in the past and you need to be clear about which one of them you’re talking about now because they were all different, lived in different time periods, etc. For obvious reasons the book has a lot of talk about species/genera with no corresponding ‘familiar/popular’ names (like ‘cat’ or ‘dog’), and you need to keep track of the Latin names to make sense of the stuff; as well as keeping track of the various other Latin terms used e.g. in osteometry. So you’ll encounter some passages where there’s some talk about the differences between two groups whose names look pretty similar, and you’re told about how one group had two teeth which were a bit longer than they were in the other group and the teeth also looked slightly different (and you’ll be told exactly which teeth we’re talking about, described in a language you’d probably have to be a dentist to understand without looking up a lot of stuff along the way). Problems keeping track of the animals/groups encountered also stem from the fact that whereas some species encountered in the book do have modern counterparts, others don’t. The coverage helps you to figure out which ecological niche which group may have inhabited, but if you’re completely unfamiliar with the field of ecology I’m not sure how easy it is to get into this mindset. The text does provide some help navigating this weird landscape of the past, and the many fascinating illustrations in the book make it easier to visualize what the animals encountered along the way might have looked like, but reading the book takes some work.

That said, it’s totally worth it because this stuff’s just plain fascinating! The book isn’t quite ‘up there’ with Herrera et al. (it reminded me a bit more of van der Geer et al., not only because of the slight coverage overlap), but some of the stuff in there’s pretty damn awesome – and it’s stuff you ought to know, because it’ll probably change how you think about the world. The really neat thing about reading a book like this is that it exposes a lot of unwarranted assumptions you’ve been making without knowing it, about what the past used to be like. I’m almost certain anyone reading a book like this will encounter ideas which are very surprising to them. We look at the world through the eyes of the present, and it can be difficult to imagine just how many things used to be different. Vague and tentative ideas you might have had about how the world used to look like and how it used to work can through reading books like this one be replaced with a much more clear, and much better supported, picture of the past. Even though there’s still a lot of stuff we don’t know, and will never know. I could mention almost countless examples of things I was very surprised to learn while reading this book, and I’m sure many people reading the book would encounter even more of these, as I actually was somewhat familiar with parts of the related literature already before reading the book.

I’ve added a few sample quotes and observations from the book below.

“Europe, although just an appendage of the Eurasian supercontinent, acted during most of its history as a crossroad where Asian, African, and American faunas passed one another, throughout successive dispersal and extinction events. But these events did not happen in an isolated context, since they were the response to climatic and environmental events of a higher order. Thus this book pays special attention to the abundant literature that for the past few decades has dedicated itself to the climatic evolution of our planet.”

“A common scenario tends to posit the early evolutionary radiation of placental mammals as occurring only after the extinction of the dinosaurs at the end of the Cretaceous period. The same scenario assumes a sudden explosion of forms immediately after the End Cretaceous Mass Extinction, filling the vacancies left by the vanished reptilian faunas. But a close inspection of the first epoch of the Cenozoic provides quite a different picture: the “explosion” began well before the end of the Cretaceous period and was not sudden, but lasted millions of years throughout the first division of the Cenozoic era, the Paleocene epoch. […] our knowledge of this remote time of mammalian evolution is much more obscure and incomplete than our understanding of the other periods of the Cenozoic. […] compared with our present world, and in contrast to the succeeding epochs, the Paleocene appears to us as a strange time, in which the present orders of mammals were absent or can hardly be distinguished: no rodents, no perissodactyls, no artiodactyls, bizarre noncarnivorous carnivorans. […] although the Paleocene was mammalian in character, we do not recognize it as a clear part of our own world; it looks more like an impoverished extension of the late Cretaceous world than the seed of the present Age of Mammals.”

“The diatrymas were human-size — up to 2 m tall — ground-running birds that inhabited the terrestrial ecosystems of Europe and North America in the Paleocene and the early to middle Eocene […] Besides the large diatrymas, a large variety of crocodiles — mainly terrestrial and amphibious eusuchian crocodiles — populated the marshes of the Paleocene rainforests. […] The high diversification of the crocodile fauna throughout the Paleocene and Eocene represents a significant ecological datum, since crocodiles do not tolerate temperatures below 10 to 15°C (exceptionally, they could survive in temperatures of about 5 or 6°C). Their existence in Europe indicates that during the first part of the Cenozoic the average temperature of the coldest month never fell below these values and that these mild conditions persisted at least until the middle Miocene.”

“At the end of the Paleocene, approximately 55.5 million years ago, there was a sudden, short-term warming known as the Latest Paleocene Thermal Maximum. Over a period of tens of thousands of years or less, the temperature of all the oceans increased by around 4°C. This was the highest warming during the entire Cenozoic, reaching global mean temperatures of around 20°C. There is some evidence that the Latest Paleocene Thermal Maximum resulted from a sudden increase in atmospheric CO2. Intense volcanic activity developed at the Paleocene–Eocene boundary, associated with the rifting process in the North Atlantic and the opening of the Norwegian-Greenland Sea. […] According to some analyses, atmospheric CO2 during the early Eocene may have been eight times its present concentration. […] The high temperatures and increasing humidity favored the extension of tropical rainforests over the middle and higher latitudes, as far north as Ellesmere Island, now in the Canadian arctic north. There, an abundant fauna — including crocodiles, monitor lizards, primates, rodents, multituberculates, early perissodactyls, and the pantodont Coryphodon — and a flora composed of tropical elements indicates the extension of the forests as far north as 78 degrees north latitude. […] The global oceanic level at the beginning of the Eocene was high, and extensive areas of Eurasia were still under the sea. In this context, Europe consisted of a number of emerged islands forming a kind of archipelago. A central European island consisted of parts of present-day England, France, and Germany, although it was placed in a much more southerly position, approximately at the present latitude of Naples. […] To the east, the growing Mediterranean opened into a wide sea, since the landmasses of Turkey, Iraq, and Iran were still below sea level. To the east of the Urals, the Turgai Strait still connected the warm waters of the Tethys Sea with the Polar Sea. […] Despite the opening of the Greenland-Norwegian Sea, Europe and North America were still connected during most of the early and middle Eocene across two main land bridges […] the De Geer Corridor [and] the Thule Bridge […] these corridors must have been effective, since the European fossil record shows a massive entry of American elements […] The ischyromyid and ailuravid rodents, as well as the miacid carnivores, were among the oldest representatives of the modern orders of mammals to appear in Europe during the early Eocene. However, they were not the only ones, since the “modernization” of the mammalian communities at this time went even further, and groups such as the first true primates, bats (Chiroptera), flying lemurs (Dermoptera), and oddtoed (Perissodactyla) and even-toed (Artiodactyla) ungulates entered onto the scene, in both Europe and North America.”

“Although it was the first member of the horse lineage, Pliolophus certainly did not look like a horse. As classically stated, it had the dimensions of a medium dog (“a fox-terrier”), bearing four hooves on the front legs and three on the hind legs. […] the first rhino-related forms included Hyrachius, a small rhino about the size of a wolf that during the Eocene inhabited a wide geographic range, from North America to Europe and Asia.” (Yep, in case you didn’t know Europe had rhinos for millions and millions of years…) “The artiodactyls are among the most successful orders of mammals, having diversified in the past 10 million years into a wide array of families, subfamilies, tribes, and genera all around the world, including pigs, peccaries, hippos, chevrotains, camels, giraffes, deer, antelopes, gazelles, goats, and cattle. They are easily distinguished from the perissodactyls because each extremity is supported on the two central toes, instead of on the middle strengthened toe. […] The oldest member of the order is Diacodexis, […] a rabbit-size ungulate”

“Although the number of middle Eocene localities in Europe is quite restricted, we have excellent knowledge of the terrestrial communities of this time thanks to the extraordinary fossiliferous site of Messel, Germany. […] several specimens from Messel retain in their gut their last meal, providing a rare opportunity for testing the teeth-inferred dietary requirements of a number of extinct mammalian groups. […] A dense canopy forest surrounded Messel lake, formed of several tropical and paratropical taxa that today live in Southeast Asia”.

“At the end of the middle Eocene, things began to change in the European archipelago. Several late Paleocene and early Eocene survivors had become extinct […] The last part of the middle Eocene saw a clear change in the structure of the herbivore community as specialized browsing herbivores […] replaced the small to medium-size omnivorous/ frugivorous archaic ungulates of the early Eocene and became the dominant species. […] These changes among the mammalian faunas were most probably a response to the major tectonic transformations occurring at that time and the associated environmental changes. During the middle Eocene, the Indian plate collided with Asia, closing the Tethys Sea north of India. The collision of India and the compression between Africa and Europe formed an active alpine mountain belt along the southern border of Eurasia. In the western Mediterranean, strong compression occurred during the late Eocene, […] leading to the final emergence of the Pyrenees. To the south of the Pyrenees, the sea branch between the Iberian plate and Europe retreated”

“The European terrestrial ecosystems at the end of the Eocene were quite different from those inherited from the Paleocene, which were dominated by archaic, unspecialized groups. In contrast, a diversified fauna of specialized small and large browsing herbivores […] characterized the late Eocene. From our perspective, they looked much more “modern” than those of the early and early-middle Eocene and perfectly adapted to the new late Eocene environmental conditions characterized by the spread of more open habitats.”

“during the Eocene […] Australia and South America were still attached to Antarctica, as the last remnants of the ancient Gondwanan supercontinent. Today’s circumpolar current did not yet exist, and the equatorial South Atlantic and South Pacific waters went closer to the Antarctic coasts, thus transporting heat from the low latitudes to the high southern latitudes. However, this changed during the late Eocene, when a rifting process began to separate Australia from Antarctica. At the beginning of the Oligocene, between 34 and 33 million years ago, the spread between the two continents was large enough to allow a first phase of circumpolar circulation, which restricted the thermal exchange between the low-latitude equatorial waters and the Antarctic waters. A sudden and massive cooling took place, and mean global temperatures fell by about 5°C. […] During a few hundred thousand years (the estimated duration of this early Oligocene glacial episode), the ice sheets expanded and covered extensive areas of Antarctica, particularly in its western regions. […] The onset of Antarctic glaciation and the growing of the ice sheets in western Antarctica provoked an important global sea-level lowering of about 30 m. Several shallow epicontinental seas became continental areas, including those that surrounded the European Archipelago. The Turgai Strait, which during millions of years had isolated the European lands from Asia, vanished and opened a migration pathway for Asian and American mammals to the west. […] The tectonic movements led to the final split of the Tethys Sea into two main seas, the Mediterranean Sea to the south and the Paratethys Sea, the latter covering the formerly open ocean areas of central and eastern Europe. […] After the retreat of the Turgai Strait and the emergence of the Paratethys province, the European Archipelago ceased to exist, and Europe approached its present configuration. The ancient barriers that had prevented Asian faunas from settling in this continental area no longer existed, and a wave of new immigrants entered from the east. This coincided with the trend toward more temperate conditions and the spread of open environments initiated during the late Eocene. Consequently, most of the species that had characterized the middle and late Eocene declined or became completely extinct, replaced by herds of Asian newcomers.”

 

February 23, 2015 - Posted by | biology, books, Geology, Paleontology, Zoology

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