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An artist’s rendering of the hypothetical placental ancestor (by Carl Buell)
Magnolias at the Brooklyn Botanic Garden
Spring has come early this year and the beautiful tulip-like petals of New York City’s magnolia trees are already beginning to fall into great drifts of white and pink. If you stop and pick up one of the pretty petals from such a pile you will be surprised by the leathery resilience of the delicate-looking petals. The durability of the petals of magnolia flowers is not coincidental—the flowers are different from other common flowering trees because Magnoliidae trees were among the first flowering trees to evolve. The earliest known fossils of such flowers date from the upper Cretaceous period around 130 million years ago. Magnoliidae petals are tough because they were originally meant to attract the attention of beetles rather than bees (which do not appear in the fossil record until 100 million years ago). Since there were no insects specially adapted to live as pollinators when magnolia-like trees first appeared, the petals and reproductive structures of these first flowering trees had to be robust to survive attention from the hungry clumsy beetles (toughness which has passed on to the modern ornamental trees).
Beetles on a Magnolia flower by Beatriz Moisset http://pollinators.blogspot.com/2011/06/magnolias-and-beetle-pollination.html
Paeleobotanists have not yet unraveled the entire history of the evolution of flowering plants (indeed, Charles Darwin called the abrupt appearance of flowers in the fossil record “the abominable mystery”) however magnolia-like trees appeared long before the great radiation of angiosperms which occurred approximately 100 million years ago. The first magnoliid trees must have seemed tremendously strange–explosions of color and shape surrounded by great uniformly green forests of gymnosperm trees (like the familiar conifers). Magnolia blossoms betray evidence of their ancient lineage through several “primitive” features: the petals are nearly indistinguishable from the sepals; each flower has many stamens which are arranged in spiral rows; there are multiple pistils; and all of the stamens and pistils are supported by a “fingerlike receptacle.”
By attracting the attention of animals (either through the colorful appearance and appealing scent of flowers, or by the edible nectar and fruit) flowering plants were better able to reproduce themselves. Magnolias spread around the temperate world and began the complicated interdependent relationship which all sorts of animals (including humans) have with flowering plants.
Saint Patrick Expelling the Snakes
Just kidding—aside from zoos and the pet trade, Ireland actually famously has no snakes. It is one the few snake-free large islands on Earth joined only by New Zealand, Iceland, Greenland, and Antarctica (well—everywhere far enough north or south is snake-free: the reptiles don’t really thrive in places where there is permafrost or truly cold winters). Legend has it that it was Saint Patrick who drove the snakes out of Ireland. Standing on a great hill he lifted up his crosier and focused divine energy upon the unlucky reptiles which then writhed en masse into the sea and never returned to the emerald island.
"Ssseriously, why are you doing thisss?"
It has always been a bit unclear to me why Saint Patrick would do such a thing. Ecoystems which undergo such catastrophic changes tend to go haywire with great alacrity! Fortunately the story is entirely a myth. If snakes ever lived in Ireland (and it doesn’t seem like they did), they were long gone by the time the first Christians showed up. The real reason is even more interesting than the dramatic Moses-like power of Saint Patrick, but as with most actual answers it is also more complex.
Evidence suggests that snakes evolved 130 million years ago during the Cretaceous. At the time Ireland was, um, underwater at the bottom of a warm chalky sea. Early snakes slithered their way across landbridges, rafted to islands on washed away logs, and swam (like the sea snakes) from island to island but, during the Mesozoic, there was no Ireland for them to go to.
Europe in the Ice Age (the pale white area was under a huge sheet of ice)
When the Mesozoic era ended in the great ball of fire, the continents again shifted. Snakes went through a substantial evolutionary period during the Miocene and the original python-like snakes evolved into many different forms. These new varieties of snakes slithered into grasslands, deserts, forests, and oceans around the world, but they still could not get to Ireland (now above the waves) because a cold ocean was in their way. Then the end of the Miocene brought an ice age. To quote the National Zoo’s essay on “Why Ireland Has No Snakes”:
The most recent ice age began about three million years ago and continues into the present. Between warm periods like the current climate, glaciers have advanced and retreated more than 20 times, often completely blanketing Ireland with ice. Snakes, being cold-blooded animals, simply aren’t able to survive in areas where the ground is frozen year round. Ireland thawed out for the last time only 15,000 years ago.
So Ireland remains snake-free because of the world’s temperamental geology. The island was underwater or covered by ice during certain eras when the snakes might have arrived–geography has conspired against serpents coming to Eire and setting up shop. The age of humans however has been marked by numerous introduced species cropping up everywhere. I wonder how long Ireland will be snake free when a pet shop accident or crazy hobbyist could unleash a plague of serpents on the green island. The fact that such a thing has yet to happen seems almost as miraculous as the original myth.
Although many people construe the whole story to be an allegory of Saint Patrick driving paganism and the old gods from Ireland (as seen here).
An artist's depiction of a belemnite
This blog has already traveled back 400+ million years to the Ordovician, the era when great mollusks ruled earth’s oceans. The Ordovician ended in ice as Gondwanaland drifted into the Southern Polar regions—a tectonic shift which brought massive terminal cooling to the great reef systems of the time (and also fundamentally changed Earth’s climate and atmosphere), but the cephalopods were hardly done for. They continued to evolve and adapt to the world’s ever changing oceans. Today we pick up the cephalopod story hundreds of millions of years later during the Mesozoic era—the time of dinosaurs.
Artist's depiction of a belemnite school
The reefs and oceans of the Jurassic and Cretaceous were filled with nautiloid cephalopods—ram shelled descendants of the shelled tentacled monstrosities from the Ordovician—but a new cephalopod had also evolved and filled up the shallow limestone seas in giant teaming schools. These were the belemnites which lacked an external shell and superficially resembled squid.
Belemnites were distinct from today’s squids for several reasons. Not only did they possess hard internal shells/skeletons composed of calcium carbonate but they also lacked the pair of specialized hunting tentacles present in modern cuttlefish and squid. Instead the belemnites hunted with ten arms covered in tiny wicked hooks.
An Amzaingly well preserved fossil belemnite from the 155 million year old Jurassic Solnhofen limestones in Germany (notice the details of the animal's soft anatomy)
Belemnites fed on ostracods, crustaceans, and fish. In turn they made up a sizeable portion of diet for, well, the sizeable predators of the time. Fossils of plesiosaurs, pliosaurs, and giant sharks have been discovered with stomachs full of hooks or rostra. It is also thought that the dolphin-like ichthyosaurs survived largely on belemnites. After feeding and digesting the mollusks, the ichthyosaurs probably vomited out the indigestible hooks and rostra of belemnites much in the manner that sperm whales expel the hooks of giant squid!
The bullet shaped rostra of belemnites have survived in vast numbers and are one of the most characteristic of all Mesozoic fossils. These strange tapered cones weathered out of soft chalks nearly intact and proved extremely puzzling to people of past generations. Numerous magical common names and magical folk beliefs grew out of the conical rocks. The English called the fossils “thunderbolts” and believed they were the physical leftovers from lightning strikes. The ancient Scandinavians thought that belemnite rostra were candles dropped by gnomes, elves, and dwarves on the occasions they traveled from their realms through this world. The ancient Chinese called them “sword stones” and believed they were imbued with ancient healing magic.
An opalized fossil of a belemnite rostrum
The end of belemnites was even more astonishing than these myths. The creatures had short lives—which involved a larval phase drifting amidst the microscopic plankton. The immense extraterrestrial bolide which struck the Earth at the end of the Cretaceous ended the dinosaurs and also finished off the belemnites. The little larvae were unable to survive the massive planktonic die-off which accompanied the long dark winter following the strike. Fortunately other cephalopods proved hardier–and the most intelligent mollusks continued to change and adapt right up until today.
An artist's depiction of the Chickzalub bolide impact
Crescent-shaped rudists on the floor af a Cretaceous Sea
When we think of living reefs we are likely to think of coral reefs, since the biotic reefs of today are most often composed of cnidarian corals (and coralline algae). Such has not always been the case –convergent evolution means that other animals have sometimes jumped in and taken over the central reef building role occupied today by corals (indeed there are still oyster reefs in some parts of the ocean although human hunger for oysters has greatly reduced their size). One of the more interesting and successful of these coral analogs was actually a modified colonial mollusk—the rudist. Rudists were bivalve mollusks very similar to the clams you enjoy on your linguini. Like clams, rudists had two shells (or valves) joined at a hinge. However the rudists possessed very different shapes from modern clams. Some had horn-shaped shells which lay flat on the bottom of the ocean shore (the horns prevented currents from flipping the mollusks or washing them away). The other major group had cone-shapes with little hinged lids on top –like a cross between a lidded beer stein and an ice-cream cone). This latter group formed together in huge super colonies.
Rudist Types (with a modern bivalve in the top left for comparison)
Rudists evolved in the Jurassic Era and burgeoned throughout the Mesozoic, but their greatest success came during the Cretaceous when they pushed out corals and sponges to become the major reef-building organisms in the Tethys Ocean and various other warm tropical shelves around the world. It is believed that rudists were so successful because the ocean’s temperature was so much higher during the Cretaceous (as was the salt content of the water). It must have been amazing to see a rudist tropical reef thronged with strange colorful belemnites, ammonites, and unknown teleosts. Huge prehistoric diving birds, mosasaurs, and super sharks would have lurked in the depths beside the reef.
A Fossilized Rudist Reef from the Cretaceous Era
Like the dinosaurs and the ammonites, the rudists were wiped out by the Chicxulub impact. Sometimes I think about the rudists as I fret about coral die-offs. Coral quickly evolved back into the warm shallow tropical niche left open by the extinction of the rudists. Is there some little clam with a big destiny waiting for the corals to falter in the ever-warmer, ever-more-acidic oceans of the present?
Obdurodon--A Miocene Platypus which flourished 15 to 20 million years ago
Ferrebeekeeper has an abiding interest in monotremes including both the poisonous platypus and the enigmatic echidnas (with their advanced frontal cortex). But sadly that is about it as far as it goes for the extant egg-laying mammals: there are only two living families of monotremes (with a scanty total of five species split between them). To learn more about these animals one must turn to paleontology. Unfortunately even in the fossil record, monotremes are extremely rare.
Based on genetic evidence, biologists believe that the first monotremes made their advent in the history of life about 220 million years ago during the Triassic era; however the earliest known fossil monotreme so far discovered was a fossil jaw from the early Cretacious era about 120 million years ago. The bones belonged to Steropodon galmani, which seems to have been a beaked swimmer about 50 cm (20 inches) long which lived in Australia. Steropodon was apparently a giant among Cretacious mammals–most of which seem to have been shrew-sized (so as to better avoid attention from their contemporaries, the dinosaurs). Reconstructions of Steropodon all seem to resemble the platypus, and most paleantologists would probably concede that it was a sort of platypus—as apparently were other Mesozoic fossil monotremes such as Kollikodon and Teinolophos (platypuses and these platypus-like forbears are called the Ornithorhynchida). During the Cretaceous era, the land which is now Australia was in the South Polar regions of the world (approximately where Antarctica is today). Although temperatures were much warmer during the Cretaceous, monotremes must still have been able to deal with terrible cold: it is believed that the extremely efficient temperature control and the deep hibernation mechanism which these animals continue to display first evolved during that time.
An artist's reconstruction of Steropodon
The only monotreme fossil which was not found in Australia was from another platypus-like creature named Monotrematus sudamericanum. The creature’s remains were found in a Patagonian rock formation from the Paleocene era (the era just after the fall of the dinosaurs). Monotremes probably flourished across South America and Antarctica, as well as on Australia, but evidence is still scarce. There are most likely many interesting monotreme fossils throughout Antarctica, but, for some reason, paleontologists have not yet discovered them. Additionally, unlike the marsupials (which still quietly flourish throughout South America), the poor monotremes were wiped out on that continent.
Another artist's vision of Steropodon galmani--Notice how peeved the poor creature looks!
Last week I wrote about the Eocene era and the great proliferation of mammalian types which took place during that warm and fecund time. Although most families of mammals alive today first appeared on the scene during the Eocene, obviously the monotremes were already incredibly ancient. The Eocene does however seem to have been significant time for the monotreme order: the aquatic platypuses were apparently the ancestral monotremes, and echidnas (the Tachyglossidae) probably split off from them during the Eocene. Unfortunately we have no Eocene monotreme fossils so this conclusion is based on genetic evidence and on the suffusion of Miocene monotremes which include representatives of both Ornithorhynchida and Tachyglossidae. Some of these latter creatures are spectacular, like Zaglossus hacketti the giant echidna from the Pleistocene which was about the size of a ram! As Australia dried up so did the monotremes and now there is only one species of platypus left…
The Giant Echidna (Zaglossus hacketti) which lived until 20,000 years ago...
Well, that’s a cursory history of the monotremes based on what we know. I wish I could tell you more but unfortunately there is no fossil evidence concerning the first half of the order. Sometimes I like to imagine the first monotremes—which were probably clunky, furry platypus-looking characters with an extra hint of iguana thrown in. These creatures fished in the alien rivers of the Triassic world in a time when dinosaurs and pterosaurs were also still evolving.
