The book "Imprints of life. 25 steps of evolution and the whole history of the planet "
Hello! We have expanded our New Science series with a new book:
Donald Protero, the author of many bestsellers, has transformed the scientific description of twenty-five famous well-preserved fossils into a fascinating history of life on Earth.
The twenty-five fossils discussed in this book demonstrate life in all evolutionary splendor, showing how one species turns into another. We see all the diversity of extinct plants and animals, from microscopic to gigantic sizes. We will tell you about fantastic land and sea creatures that have no analogues in modern nature: the first trilobites, giant sharks, huge sea reptiles and feathered dinosaurs, the first birds, walking whales, giant hornless rhinos and Australopithecus "Lucy".
The story of life on Earth is amazingly complex. Currently, there are between 5 and 15 million species of living creatures on our planet. Since over 99% of ever-existing species have already become extinct, it can be concluded that hundreds of millions of biological species have lived on Earth, if not more, since life began — and this happened 3.5 billion years ago or even earlier.
Therefore, choosing only 25 fossils to represent hundreds of millions of extinct species by their example is not an easy task. I focused on the fossil record of evolutionary history. They demonstrate the key stages of the emergence of large groups of biological species or illustrate evolutionary transitions from one group to another. In addition, life is not just the emergence of new groups of species, but a striking manifestation of various adaptations, during which the size of the organisms, the ecological niches and habitats they occupied changed. Therefore, I chose several “extreme” fossil forms that demonstrate what biology can achieve. You will get acquainted with the largest land animal, and with the largest land predator, and with some of the giant sea creatures that once plied the ocean.
Naturally, such a complex approach forces us to ignore many creatures, so I painfully chose whom to describe and whom to skip. I tried to pick up fossils, relatively well-preserved and known. Thus, many species were excluded, whose remains are too fragmented to be interpreted with confidence. Given the interests of a wide range of readers, I preferred dinosaurs and vertebrates. I apologize to all my friends paleobotanists and micropalleontology - for having deprived of their disciplines, having devoted both of them to the whole chapter.
I hope you forgive me for my sins, acts and non-actions and pay attention to beings, stories about which I want to tell you. May they make your life brighter!
Ichtiologist at the pleyorbala
Gill slits, lingual cartilage, synaptic, endostil and chord. You can’t argue that all these organs distinguish protochord fish from marine fish and indicate to them, as well as to us, their low origin. The thyroid and thymus gland, the rod under the chord - this is what unites us with the lampreys, the katrans and the herring, few of those that have long diversified our table.
Walter Garstang, "Larval Forms with Other Zoological Verses"
HU MILLER AND ANCIENT RED SANDY
Along with the rest of the mammals, we humans, as well as birds, reptiles, amphibians and fish are vertebrates, that is, animals that have a ridge. Where did the vertebrates come from? What can ancient fossil fish tell about the origin of our type? To get answers to these questions, you need to go back to Scotland at the end of the XVIII century.
At the end of the 18th century, a new young scientific discipline, geology, began to develop mainly in Great Britain. One of the first Scottish naturalists, James Hutton, laid the foundations of modern geology based on his own travels in Scotland. Their outcome in 1788 was the publication of Theory of Earth (Theory of the Earth), where Hutton set forth a scientific approach to the question of the origin of the Earth.
Among the British stratigraphic units that Hutton studied carefully, there was a powerful series of sandy rocks known as ancient red sandstone. It is widely distributed in Scotland, also found in many parts of eastern and central England. The more Hatton studied it, the clearer the traces of a huge mountain range loomed before him, which completely collapsed, and its rocks were separated by streams and rivers, deposited in the form of pebble and sandstone of this formation. In many places, it runs almost horizontally through the erosion surface, cutting into more ancient rocks, which were first torn out and then eroded from a horizontal to a vertical position. Such an example of angular disagreement convinced Hutton that the world was incredibly old and originated "in times immemorial." The world turned out to be obviously older than 6,000 years — its age according to the Bible; This assessment at the time of Hatton was generally recognized.
The guess of the scientist was not far from the truth. Today, the ancient red sandstone dates from the Devonian period (about 345 million years ago). Overturned rocks below the angular disagreement on age belong to the Silurian (about 425 million years ago) and appeared during the times of the Caledonian folding (Caledonia is the ancient Roman name of Scotland). This folding unfolded when the core of Europe (the so-called Baltic shield) collided with another tectonic plate, which now includes northern Canada and Greenland. In the course of this titanic act of mountain building, all Silurian rocks that had been formed shortly before were erased into powder. The resulting Caledonian mountains quickly collapsed, turning into river sand, which eventually crystallized in the form of ancient red sandstone.
One generation after Hutton, the ancient red sandstone gained fame due to the fact that it was noticed by a humble Scottish stonecutter named Hugh Miller. He was the son of a captain, but attended school only until he was 17 years old, that is, he did not receive a systematic education sufficient to study fossils. The portraits portrayed him as a strong, broad-shouldered, strong man (he probably acquired such a figure, working for many years with a stone), who wore thick curls and the same lush sideburns (Fig. 8.1). Miller spent his young years in stone quarries, primarily on ancient red sandstone. In the months off from work, he combed the coastal outcrops of sandstone, where one after another found beautiful petrified fish. Other workers who worked there, too, soon also collected a lot of samples, and Miller undertook to study the finds.
Fig. 8.1 Portrait of Hugh Miller (illustration from the Wikimedia Commons)
Even with a limited education, he became one of the first popular science authors in the history of paleontology. In 1834, Miller published Scenes and Legends of North Scotland (“Sketches and Legends of Northern Scotland”) - a real bestseller about the geology and natural history of Scotland, written for the ever-widening readership in those years, interested in natural science. He continued to work in 1841, writing the book The Old Red Sandstone: New Walks in an Old Field (“Old Red Sandstone, or New Walk through the Old Places”), where he describes this stratigraphic unit, its amazing fossil fish and “sea scorpions” . Miller independently illustrated this book (Fig. 8.2). The following passage allows you to fully appreciate its style:
The walls in my closet are half hung with fancy fossils from Lower Ancient red sandstone; indeed, a stranger collection of different creatures was hardly gathered anywhere; beasts, even the type of which is lost, outlandish and inconsistent - so much so that the naturalist will not easily assign them to one or another class. Animals like boats with oars and oarlocks; armored fish, resembling turtles above and below, in solid bone armor, topped, at best, with a single, ball-like fin; fish are not so ambiguous forms, but with fins, densely covered with scales. The beasts, seated with thorns, are different, shining with enamel-covers, as if someone had polished them exquisitely. The tail of all specimens is one of the most recognizable parts of the body, but it is also uneven - in modern fish the tails diverge in symmetrical halves on both sides of the ridge, and in these creatures the tail grows downwards from the decreasing spine, which extends down to the very tip of the fin. From all these forms emanates deep antiquity, a period "that has long been out of fashion."
Thanks to his books, Miller soon became a real celebrity among natural scientists, although he was not a professional paleontologist. Fortunately, at a meeting of the British Association for the Advancement of Scientific Progress, he met the legendary Swiss paleo-ichthiologist Louis Agassis. Miller was able to transfer his samples to a person who was able to analyze them. Agassiz did indeed soon describe and name all the wonderful Miller fossils.
In his books, Miller promoted his own religious beliefs and fought against the interest from evolutionary theories coming from France that were ready to flourish in Britain. His book The Foot-prints of the Creator: or, The Asterolepis of Stromness (The Footsteps of the Creator, or Stromness Asterolepis) was published in 1849 and attacked the sensational evolutionary ideas that in his book Vestiges of the Natural History of Creation ("Relics of the Natural History of Creation"), published in 1844, was developed by the Scottish publisher Robert Chambers.
Fig. 8.2 Lob-colored fish gliptolepis (distantly related to amphibians) and the fossil double-breathing fish dipterus (engraving from the book Hugh Miller, The Old Red Sandstone, or, New Walks in an Old Field (Edinburgh: Johnstone, 1841))
However, Miller was not a supporter of the literal interpretation of the Bible. Like most of the British geologists of his time, he considered Noah's flood a local event that covered only Mesopotamia, and interpreted the fossil record as successive acts of creation and destruction, not mentioned in the Bible. Recognizing that chronological changes can be traced in the fossil record, he nevertheless did not agree that later species came from earlier ones.
Unfortunately, at the age of 54, strange severe headaches and mental confusion began to torment Miller, and he shot himself as soon as he sent the publisher his proof-reading of his latest book, The Testimony of Rocks. The scientific world mourned him, in honor of Miller staged one of the most ambitious funeral processions in the history of Edinburgh. David Brewster wrote: "Mr. Miller is one of the few representatives of Scottish science who was able to rise above the routine of his modest profession and the power of his genius, as well as an outstanding character, to occupy a relatively high place in the social hierarchy." Various fossils were named after him, including the “sea scorpion” Hughmilleria and a primitive fish, today called Millerosteus, as well as many species of milleri fish in the name.
Ancient red sandstone was formed in the Devonian period - in the fish age, therefore it reflects the evolution of the fish that lived at that time. Not only sharks and ray-finned fishes that have survived to this day are found there, but many lobe-plucked and, in particular, double-breathing fishes (see Fig. 8.2). Primitive maxillary (so-called shellfish) fish were spread, their heads and breasts were covered with dense shields. Carapace fish completely extinct by the end of the Devonian.
These fossils gave the first evidence in favor of the large-scale prevalence of armored jellyfish. In the 1830s – 1840s, Agassis described some of them, including pteraspis (Pteraspis) and cephalaspis (Cephalaspis) (Fig. 8.3). Miller claimed that the fish fossils he discovered were not proof of evolution, but he was not a good anatomist to judge. Nevertheless, the presence of these jawless vertebrates in the Devonian testified that modern jawbone fishes from jawless invertebrates are separated by several turns of evolution.
Fig. 8.3 Shellfish jawfish cephalaspis (engraving from Hugh Miller, The Old Red Sandstone, or, New Walks in an Old Field (Edinburgh: Johnstone, 1841))
Fig. 8.4 The family tree of jawless fish showing different groups (Carl Bewell's drawing from Donald R. Prothero, Evolution: New York: Columbia University Press, 2007), fig. 9.8)
Figure. 8.5 Jawless carapace fish pteraspis, heterostracan: (A) head shield; (B) reconstruction of live fish (illustration (A) from the Wikimedia Commons fund; illustration (B) presented by Nobumichi Tamura)
Soon, the fossils of these armored jaws were found in many other regions. They once again showed how maxillary vertebrates evolved from jawless ancestors (see Fig. 8.4). Pteraspis and his relatives (heterostrakans) usually had a streamlined body covered with a shell, resembling a torpedo. Long spikes stuck out of the sides and backs of such fish, and the tail with the main fin looked down (see Fig. 8.5). The heterostrakans had a tiny mouth that looked like a slit, and there were no jaws, just as there were no strong muscular fins that would serve as a rudder. They probably swam like tadpoles, sucking up water and filtering nutrient particles that passed through the mouth and gills. On the contrary, cephalaspis (see fig. 8.3 and 8.4) and related osteostrakans (also called ostracoderms) had a sloping head with a flat bottom, and the main fin on their tail looked up (like modern sharks). It is believed that they floated at the bottom and rummaged in the mud in search of food, filtering the sediment through the jawless maw.
Over the years, scientists have found more and more fossils of shellfish jawbone in Devonian, and then in Silurian sediments around the world. But the only part of their body that was easily fossilized was the outer shell. Like sharks and most primitive fish, they did not have a bone skeleton, only cartilage, which is poorly preserved in fossils. If it were not for the shell, none of these fish could have been preserved in the fossil record.
For quite a long time there was no evidence of the existence of jawless (and any other) fish previously Silurian. Large predators dominated the Ordovician seas, for example, the nautiloidea, 5.5 m long. However, despite the abundance of Ordovician fossil marine fauna, no trace of bones could be found there. The only hints of their existence were rare finds, as in Harding sandstone near Canyon City (Colorado). This breed dates from the Middle Ordovician and contains a mass of fragments of bone shell, which belonged to jawless astrapis fish (Astrapis). By the 1970s – 1980s, it was possible to find complete specimens of these ancient vertebrates, for example, the arandaspis (Arandaspis) from Australia and the sakambaspis from South America, later also discovered in Australia.
Fig. 8.6 Separately taken small fragment of the plate (about a millimeter in diameter) from the leathery shell of the Cambrian jawless fish of Anatolepis (Anatolepis) - one of the oldest vertebrates, which had bones (illustration provided by the US Geological Survey)
All these Ordovician jawless fish were arranged no more complicated than filter feeders covered with thin plates of bone shell. Their wide flat bodies almost had no outstanding parts - any fins or spines. Only a slit mouth for sucking water, which was abundant in food, and a simple asymmetrical tail. Instead of a lamellar shell, like that of a pteraspis, these fish were covered with hundreds of tiny bone pieces that resembled chain mail. Tiny eyes and rows of tubules on the surface of the body (lateral lines) allowed them to catch the movement of water around. All of these Ordovician fish are extremely rare compared to most other animals of the time. It was also disheartening that not a single fish from the Cambrian was known.
Finally, in the 1970s, Jack Repecki, a paleontologist from the United States Geological Survey, began working with micro-stone, the so-called conodont, from the Deadwood sandstone in Wyoming, dating from the late Cambrian. Dissolving calcified fossils in search of conodonts (composed of calcium phosphate, like vertebrate bones), he found fragments of an interesting shape and realized that before him were pieces of leathery shell of jawless fish of Anatolipis (see Fig. 8.6). Later, there were long disputes about whether these samples actually belong to the vertebral. As a result, they resolved, and today Anatolepis is considered the oldest known vertebrate, from which there are bone fossils.
So, gradually finding vertebrate fossils in more and more ancient rocks, we finally find ourselves in sediments that formed before the appearance of bones. At present, fragments of the leathery shell of anatolepis are still the oldest fossils of a creature with bones. More and more ancient animals were soft, consisted of cartilage and less durable tissues that could be fossilized only occasionally, under the most favorable conditions.
Since there were no further discoveries of bone fossils, biologists and paleontologists tried to connect the evolutionary links between the vertebrates and their ancestors, and decided to do it from the bottom up.
Here we do not have a shortage of material, since many intermediate organisms connecting vertebrates with the rest of the animal kingdom have survived to this day, and numerous fossils have remained from the others. Mammals, birds, reptiles, amphibians and fish belong to the type of chordates, which are so called because their embryos (and sometimes adults) have a long flexible cartilage string (chord) that runs along the back and supports the entire body. Chord - the precursor of the spine.
The closest relatives of chordates belong to another type, semi-chordates (Fig. 8.7). Today, they are represented by intestinal and pistostozhabernymi. The intestinal breathing (they are also intestinal glands) resembles the usual worms to an unprepared observer, but their embryos have the beginnings of the notochord and the real pharynx (pharynx) that all chordates have. In addition, their nerve trunk goes along the back, and the digestive tract - along the belly; such a configuration is characteristic of most chordates, whereas in invertebrates it is opposite: the nerve trunk runs along the belly, the digestive tract along the back. This anatomical similarity is supported by the embryological features characteristic of the chord. Finally, DNA molecular analysis shows that semi-chordae are very close to the common ancestor of all vertebrates,
The next link on the way to the vertebrates is the group represented by more than 2,000 species living in the oceans of the whole world. It is about sheaths or ascidians (Fig. 8.7). Like intestinal breathing, ascidians do not resemble an inexperienced fish watcher, but the external impression is deceptive. The adults in them are clumsy, resemble a bag of jelly and filter seawater through their body baskets. But the larvae of tunicates are very similar to fish or tadpoles; they have a well-developed chord, a long muscular tail with paired muscles, and a head with a big throat. These are just some of their most important features. Again, the direction of evolution can be traced at the level of embryos, and embryological evidence is supported by molecular, clearly demonstrating that the tunicates are closer to vertebrates than any other marine invertebrates.
The last link connecting invertebrates with vertebrates is lancelet (Branchiostoma) (see Fig. 8.7). This inconspicuous piece of flesh usually has only a few centimeters in length, but if you look at it, it turns out that it is very similar to fish, even though it is not fish. The lancetniki have a long flexible chord supporting the body and equipped with a multitude of V-shaped muscular ligaments located along the entire length of the animal; thanks to these bundles it floats perfectly. The nerve fibers of the lancelet run along the back, and the digestive tract along the belly, as in all chordates. There are no jaws or teeth, but the mouth leads to the throat with the gill sac, where the animal takes food. The lancetniki have no real eyes, only a light-sensitive spot on the anterior tip of the body, allowing them to distinguish between light and shade. These creatures spend their entire lives
Fig. 8.7 Origin of chordates from invertebrates; the original version described by Walter Garstang and Alfred S. Romer more than a century ago. Variants of the structure of many adult individuals (for example, adult tunicates) turned out to be dead-end evolutionary branches, but the larvae of tunicates retain a long tail and other features that later played an important role in the origin of more advanced chordates (Carl Buell’s drawing from Donald R. Fossils Say and Why It Matters (New York: Columbia University Press, 2007), fig. 9.4)
Finally, several well-preserved lancelet fossils demonstrate that these animals already existed in the early Cambrian, precisely at the time when the evolution of fish began. Among these fossils is Pikaia, found in the Burgess shale in Canada (see Chapter 6), and a similar fossil of Yunnanozoon, belonging to the Shenyang fauna (China), dated by the early Cambrian (518 million years ago).
More information about the book can be found on the website of the publisher .
For readers of this blog 25% discount coupon - Life Imprints
Donald Protero, the author of many bestsellers, has transformed the scientific description of twenty-five famous well-preserved fossils into a fascinating history of life on Earth.The twenty-five fossils discussed in this book demonstrate life in all evolutionary splendor, showing how one species turns into another. We see all the diversity of extinct plants and animals, from microscopic to gigantic sizes. We will tell you about fantastic land and sea creatures that have no analogues in modern nature: the first trilobites, giant sharks, huge sea reptiles and feathered dinosaurs, the first birds, walking whales, giant hornless rhinos and Australopithecus "Lucy".
Foreword
The story of life on Earth is amazingly complex. Currently, there are between 5 and 15 million species of living creatures on our planet. Since over 99% of ever-existing species have already become extinct, it can be concluded that hundreds of millions of biological species have lived on Earth, if not more, since life began — and this happened 3.5 billion years ago or even earlier.
Therefore, choosing only 25 fossils to represent hundreds of millions of extinct species by their example is not an easy task. I focused on the fossil record of evolutionary history. They demonstrate the key stages of the emergence of large groups of biological species or illustrate evolutionary transitions from one group to another. In addition, life is not just the emergence of new groups of species, but a striking manifestation of various adaptations, during which the size of the organisms, the ecological niches and habitats they occupied changed. Therefore, I chose several “extreme” fossil forms that demonstrate what biology can achieve. You will get acquainted with the largest land animal, and with the largest land predator, and with some of the giant sea creatures that once plied the ocean.
Naturally, such a complex approach forces us to ignore many creatures, so I painfully chose whom to describe and whom to skip. I tried to pick up fossils, relatively well-preserved and known. Thus, many species were excluded, whose remains are too fragmented to be interpreted with confidence. Given the interests of a wide range of readers, I preferred dinosaurs and vertebrates. I apologize to all my friends paleobotanists and micropalleontology - for having deprived of their disciplines, having devoted both of them to the whole chapter.
I hope you forgive me for my sins, acts and non-actions and pay attention to beings, stories about which I want to tell you. May they make your life brighter!
Excerpt from a book
Ichtiologist at the pleyorbala
Gill slits, lingual cartilage, synaptic, endostil and chord. You can’t argue that all these organs distinguish protochord fish from marine fish and indicate to them, as well as to us, their low origin. The thyroid and thymus gland, the rod under the chord - this is what unites us with the lampreys, the katrans and the herring, few of those that have long diversified our table.
Walter Garstang, "Larval Forms with Other Zoological Verses"
HU MILLER AND ANCIENT RED SANDY
Along with the rest of the mammals, we humans, as well as birds, reptiles, amphibians and fish are vertebrates, that is, animals that have a ridge. Where did the vertebrates come from? What can ancient fossil fish tell about the origin of our type? To get answers to these questions, you need to go back to Scotland at the end of the XVIII century.
At the end of the 18th century, a new young scientific discipline, geology, began to develop mainly in Great Britain. One of the first Scottish naturalists, James Hutton, laid the foundations of modern geology based on his own travels in Scotland. Their outcome in 1788 was the publication of Theory of Earth (Theory of the Earth), where Hutton set forth a scientific approach to the question of the origin of the Earth.
Among the British stratigraphic units that Hutton studied carefully, there was a powerful series of sandy rocks known as ancient red sandstone. It is widely distributed in Scotland, also found in many parts of eastern and central England. The more Hatton studied it, the clearer the traces of a huge mountain range loomed before him, which completely collapsed, and its rocks were separated by streams and rivers, deposited in the form of pebble and sandstone of this formation. In many places, it runs almost horizontally through the erosion surface, cutting into more ancient rocks, which were first torn out and then eroded from a horizontal to a vertical position. Such an example of angular disagreement convinced Hutton that the world was incredibly old and originated "in times immemorial." The world turned out to be obviously older than 6,000 years — its age according to the Bible; This assessment at the time of Hatton was generally recognized.
The guess of the scientist was not far from the truth. Today, the ancient red sandstone dates from the Devonian period (about 345 million years ago). Overturned rocks below the angular disagreement on age belong to the Silurian (about 425 million years ago) and appeared during the times of the Caledonian folding (Caledonia is the ancient Roman name of Scotland). This folding unfolded when the core of Europe (the so-called Baltic shield) collided with another tectonic plate, which now includes northern Canada and Greenland. In the course of this titanic act of mountain building, all Silurian rocks that had been formed shortly before were erased into powder. The resulting Caledonian mountains quickly collapsed, turning into river sand, which eventually crystallized in the form of ancient red sandstone.
One generation after Hutton, the ancient red sandstone gained fame due to the fact that it was noticed by a humble Scottish stonecutter named Hugh Miller. He was the son of a captain, but attended school only until he was 17 years old, that is, he did not receive a systematic education sufficient to study fossils. The portraits portrayed him as a strong, broad-shouldered, strong man (he probably acquired such a figure, working for many years with a stone), who wore thick curls and the same lush sideburns (Fig. 8.1). Miller spent his young years in stone quarries, primarily on ancient red sandstone. In the months off from work, he combed the coastal outcrops of sandstone, where one after another found beautiful petrified fish. Other workers who worked there, too, soon also collected a lot of samples, and Miller undertook to study the finds.
Fig. 8.1 Portrait of Hugh Miller (illustration from the Wikimedia Commons)
Even with a limited education, he became one of the first popular science authors in the history of paleontology. In 1834, Miller published Scenes and Legends of North Scotland (“Sketches and Legends of Northern Scotland”) - a real bestseller about the geology and natural history of Scotland, written for the ever-widening readership in those years, interested in natural science. He continued to work in 1841, writing the book The Old Red Sandstone: New Walks in an Old Field (“Old Red Sandstone, or New Walk through the Old Places”), where he describes this stratigraphic unit, its amazing fossil fish and “sea scorpions” . Miller independently illustrated this book (Fig. 8.2). The following passage allows you to fully appreciate its style:
The walls in my closet are half hung with fancy fossils from Lower Ancient red sandstone; indeed, a stranger collection of different creatures was hardly gathered anywhere; beasts, even the type of which is lost, outlandish and inconsistent - so much so that the naturalist will not easily assign them to one or another class. Animals like boats with oars and oarlocks; armored fish, resembling turtles above and below, in solid bone armor, topped, at best, with a single, ball-like fin; fish are not so ambiguous forms, but with fins, densely covered with scales. The beasts, seated with thorns, are different, shining with enamel-covers, as if someone had polished them exquisitely. The tail of all specimens is one of the most recognizable parts of the body, but it is also uneven - in modern fish the tails diverge in symmetrical halves on both sides of the ridge, and in these creatures the tail grows downwards from the decreasing spine, which extends down to the very tip of the fin. From all these forms emanates deep antiquity, a period "that has long been out of fashion."
Thanks to his books, Miller soon became a real celebrity among natural scientists, although he was not a professional paleontologist. Fortunately, at a meeting of the British Association for the Advancement of Scientific Progress, he met the legendary Swiss paleo-ichthiologist Louis Agassis. Miller was able to transfer his samples to a person who was able to analyze them. Agassiz did indeed soon describe and name all the wonderful Miller fossils.
In his books, Miller promoted his own religious beliefs and fought against the interest from evolutionary theories coming from France that were ready to flourish in Britain. His book The Foot-prints of the Creator: or, The Asterolepis of Stromness (The Footsteps of the Creator, or Stromness Asterolepis) was published in 1849 and attacked the sensational evolutionary ideas that in his book Vestiges of the Natural History of Creation ("Relics of the Natural History of Creation"), published in 1844, was developed by the Scottish publisher Robert Chambers.
Fig. 8.2 Lob-colored fish gliptolepis (distantly related to amphibians) and the fossil double-breathing fish dipterus (engraving from the book Hugh Miller, The Old Red Sandstone, or, New Walks in an Old Field (Edinburgh: Johnstone, 1841))
However, Miller was not a supporter of the literal interpretation of the Bible. Like most of the British geologists of his time, he considered Noah's flood a local event that covered only Mesopotamia, and interpreted the fossil record as successive acts of creation and destruction, not mentioned in the Bible. Recognizing that chronological changes can be traced in the fossil record, he nevertheless did not agree that later species came from earlier ones.
Unfortunately, at the age of 54, strange severe headaches and mental confusion began to torment Miller, and he shot himself as soon as he sent the publisher his proof-reading of his latest book, The Testimony of Rocks. The scientific world mourned him, in honor of Miller staged one of the most ambitious funeral processions in the history of Edinburgh. David Brewster wrote: "Mr. Miller is one of the few representatives of Scottish science who was able to rise above the routine of his modest profession and the power of his genius, as well as an outstanding character, to occupy a relatively high place in the social hierarchy." Various fossils were named after him, including the “sea scorpion” Hughmilleria and a primitive fish, today called Millerosteus, as well as many species of milleri fish in the name.
THE EPOCH OF FISH
Ancient red sandstone was formed in the Devonian period - in the fish age, therefore it reflects the evolution of the fish that lived at that time. Not only sharks and ray-finned fishes that have survived to this day are found there, but many lobe-plucked and, in particular, double-breathing fishes (see Fig. 8.2). Primitive maxillary (so-called shellfish) fish were spread, their heads and breasts were covered with dense shields. Carapace fish completely extinct by the end of the Devonian.
These fossils gave the first evidence in favor of the large-scale prevalence of armored jellyfish. In the 1830s – 1840s, Agassis described some of them, including pteraspis (Pteraspis) and cephalaspis (Cephalaspis) (Fig. 8.3). Miller claimed that the fish fossils he discovered were not proof of evolution, but he was not a good anatomist to judge. Nevertheless, the presence of these jawless vertebrates in the Devonian testified that modern jawbone fishes from jawless invertebrates are separated by several turns of evolution.
Fig. 8.3 Shellfish jawfish cephalaspis (engraving from Hugh Miller, The Old Red Sandstone, or, New Walks in an Old Field (Edinburgh: Johnstone, 1841))
Fig. 8.4 The family tree of jawless fish showing different groups (Carl Bewell's drawing from Donald R. Prothero, Evolution: New York: Columbia University Press, 2007), fig. 9.8)
Figure. 8.5 Jawless carapace fish pteraspis, heterostracan: (A) head shield; (B) reconstruction of live fish (illustration (A) from the Wikimedia Commons fund; illustration (B) presented by Nobumichi Tamura)
Soon, the fossils of these armored jaws were found in many other regions. They once again showed how maxillary vertebrates evolved from jawless ancestors (see Fig. 8.4). Pteraspis and his relatives (heterostrakans) usually had a streamlined body covered with a shell, resembling a torpedo. Long spikes stuck out of the sides and backs of such fish, and the tail with the main fin looked down (see Fig. 8.5). The heterostrakans had a tiny mouth that looked like a slit, and there were no jaws, just as there were no strong muscular fins that would serve as a rudder. They probably swam like tadpoles, sucking up water and filtering nutrient particles that passed through the mouth and gills. On the contrary, cephalaspis (see fig. 8.3 and 8.4) and related osteostrakans (also called ostracoderms) had a sloping head with a flat bottom, and the main fin on their tail looked up (like modern sharks). It is believed that they floated at the bottom and rummaged in the mud in search of food, filtering the sediment through the jawless maw.
TRACK IN THE PAST
Over the years, scientists have found more and more fossils of shellfish jawbone in Devonian, and then in Silurian sediments around the world. But the only part of their body that was easily fossilized was the outer shell. Like sharks and most primitive fish, they did not have a bone skeleton, only cartilage, which is poorly preserved in fossils. If it were not for the shell, none of these fish could have been preserved in the fossil record.
For quite a long time there was no evidence of the existence of jawless (and any other) fish previously Silurian. Large predators dominated the Ordovician seas, for example, the nautiloidea, 5.5 m long. However, despite the abundance of Ordovician fossil marine fauna, no trace of bones could be found there. The only hints of their existence were rare finds, as in Harding sandstone near Canyon City (Colorado). This breed dates from the Middle Ordovician and contains a mass of fragments of bone shell, which belonged to jawless astrapis fish (Astrapis). By the 1970s – 1980s, it was possible to find complete specimens of these ancient vertebrates, for example, the arandaspis (Arandaspis) from Australia and the sakambaspis from South America, later also discovered in Australia.
Fig. 8.6 Separately taken small fragment of the plate (about a millimeter in diameter) from the leathery shell of the Cambrian jawless fish of Anatolepis (Anatolepis) - one of the oldest vertebrates, which had bones (illustration provided by the US Geological Survey)
All these Ordovician jawless fish were arranged no more complicated than filter feeders covered with thin plates of bone shell. Their wide flat bodies almost had no outstanding parts - any fins or spines. Only a slit mouth for sucking water, which was abundant in food, and a simple asymmetrical tail. Instead of a lamellar shell, like that of a pteraspis, these fish were covered with hundreds of tiny bone pieces that resembled chain mail. Tiny eyes and rows of tubules on the surface of the body (lateral lines) allowed them to catch the movement of water around. All of these Ordovician fish are extremely rare compared to most other animals of the time. It was also disheartening that not a single fish from the Cambrian was known.
Finally, in the 1970s, Jack Repecki, a paleontologist from the United States Geological Survey, began working with micro-stone, the so-called conodont, from the Deadwood sandstone in Wyoming, dating from the late Cambrian. Dissolving calcified fossils in search of conodonts (composed of calcium phosphate, like vertebrate bones), he found fragments of an interesting shape and realized that before him were pieces of leathery shell of jawless fish of Anatolipis (see Fig. 8.6). Later, there were long disputes about whether these samples actually belong to the vertebral. As a result, they resolved, and today Anatolepis is considered the oldest known vertebrate, from which there are bone fossils.
CONNECTING LINKS
So, gradually finding vertebrate fossils in more and more ancient rocks, we finally find ourselves in sediments that formed before the appearance of bones. At present, fragments of the leathery shell of anatolepis are still the oldest fossils of a creature with bones. More and more ancient animals were soft, consisted of cartilage and less durable tissues that could be fossilized only occasionally, under the most favorable conditions.
Since there were no further discoveries of bone fossils, biologists and paleontologists tried to connect the evolutionary links between the vertebrates and their ancestors, and decided to do it from the bottom up.
Here we do not have a shortage of material, since many intermediate organisms connecting vertebrates with the rest of the animal kingdom have survived to this day, and numerous fossils have remained from the others. Mammals, birds, reptiles, amphibians and fish belong to the type of chordates, which are so called because their embryos (and sometimes adults) have a long flexible cartilage string (chord) that runs along the back and supports the entire body. Chord - the precursor of the spine.
The closest relatives of chordates belong to another type, semi-chordates (Fig. 8.7). Today, they are represented by intestinal and pistostozhabernymi. The intestinal breathing (they are also intestinal glands) resembles the usual worms to an unprepared observer, but their embryos have the beginnings of the notochord and the real pharynx (pharynx) that all chordates have. In addition, their nerve trunk goes along the back, and the digestive tract - along the belly; such a configuration is characteristic of most chordates, whereas in invertebrates it is opposite: the nerve trunk runs along the belly, the digestive tract along the back. This anatomical similarity is supported by the embryological features characteristic of the chord. Finally, DNA molecular analysis shows that semi-chordae are very close to the common ancestor of all vertebrates,
The next link on the way to the vertebrates is the group represented by more than 2,000 species living in the oceans of the whole world. It is about sheaths or ascidians (Fig. 8.7). Like intestinal breathing, ascidians do not resemble an inexperienced fish watcher, but the external impression is deceptive. The adults in them are clumsy, resemble a bag of jelly and filter seawater through their body baskets. But the larvae of tunicates are very similar to fish or tadpoles; they have a well-developed chord, a long muscular tail with paired muscles, and a head with a big throat. These are just some of their most important features. Again, the direction of evolution can be traced at the level of embryos, and embryological evidence is supported by molecular, clearly demonstrating that the tunicates are closer to vertebrates than any other marine invertebrates.
The last link connecting invertebrates with vertebrates is lancelet (Branchiostoma) (see Fig. 8.7). This inconspicuous piece of flesh usually has only a few centimeters in length, but if you look at it, it turns out that it is very similar to fish, even though it is not fish. The lancetniki have a long flexible chord supporting the body and equipped with a multitude of V-shaped muscular ligaments located along the entire length of the animal; thanks to these bundles it floats perfectly. The nerve fibers of the lancelet run along the back, and the digestive tract along the belly, as in all chordates. There are no jaws or teeth, but the mouth leads to the throat with the gill sac, where the animal takes food. The lancetniki have no real eyes, only a light-sensitive spot on the anterior tip of the body, allowing them to distinguish between light and shade. These creatures spend their entire lives
Fig. 8.7 Origin of chordates from invertebrates; the original version described by Walter Garstang and Alfred S. Romer more than a century ago. Variants of the structure of many adult individuals (for example, adult tunicates) turned out to be dead-end evolutionary branches, but the larvae of tunicates retain a long tail and other features that later played an important role in the origin of more advanced chordates (Carl Buell’s drawing from Donald R. Fossils Say and Why It Matters (New York: Columbia University Press, 2007), fig. 9.4)
Finally, several well-preserved lancelet fossils demonstrate that these animals already existed in the early Cambrian, precisely at the time when the evolution of fish began. Among these fossils is Pikaia, found in the Burgess shale in Canada (see Chapter 6), and a similar fossil of Yunnanozoon, belonging to the Shenyang fauna (China), dated by the early Cambrian (518 million years ago).
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