2024-03-12 21:00:00
Onyconicteris restoration diagram.
There is probably no other animal that is as unfair as a bat. A representative example is the misconception that day rats and night birds are vampires. The daytime mouse all night long began with Aesop’s fable. When birds and wild animals were fighting for supremacy in the forest, bats would stand on the side of the birds if the birds seemed to be superior, and if the wild animals seemed to be superior, they would stand on the side of the wild animals, but in the end, they were driven out by both the birds and the wild animals.
People believe that bats spread diseases by using heat sensors on their noses to find blood vessels and sucking blood from animals. There are actually vampire bats. Three species of vampire bats live in Mexico, Central America, and the equatorial regions of South America. There are no vampire bats in other areas. The fact that the word vampire was included in the Oxford Dictionary in 1734, when almost all Europeans had not even encountered a vampire bat, must have meant that humans had an unfounded dislike for bats.
It is unfortunate that people have recently become the target of ‘extreme hatred’ in relation to COVID-19. But bats are one of the most successful mammals. There are 1,421 species of modern bats in 21 families under the order Bat. Considering that there are over 5,400 species of mammals in 28 orders and 153 families, the diversity is truly enormous. One out of four species of mammals is a bat. Great diversity means that it exists in all kinds of ecosystems. In fact, they live everywhere except the North and South Poles (there are over 2,000 species of rodents, accounting for 40% of all mammal species; naturally, they are distributed over a wider area than bats).
All five front toes have claws
Stronger bones than modern bats, unique skeleton
High-frequency echolocation capability is very primitive.
Appeared in the Eocene, the warmest period on record
Insect food supply, 3D habitat possible
Feeding activity relies on other senses
As it got colder at the end of the Eocene, the ecosystem changed drastically.
Emergence of new species with echolocation capabilities
They are pushed out of competition for food and eventually become extinct.
What makes bats one of the most successful and widespread mammals on Earth? What innovations have bats achieved? It became the only mammal that flies and the only land mammal with echolocation. There are mammals that glide from tree to tree. Things like flying squirrels. Bats do not glide, but fly through the sky by flapping their wings like birds.
An animal emits sound waves through its mouth or nostrils, listens to the echoes returned by the sound waves hitting an object, measures the distance between itself and the object, or distinguishes the shape of the object, which is called echolocation. The only mammals capable of echolocation are cetaceans and bats. Both are animals that chose unfamiliar habitats for mammals, namely the sea and the sky.
Clawed Bat, Onyconicteris
Understanding the evolution of bats has been of great interest to biologists and paleontologists because it provides insight into how complex traits such as powered flight and echolocation arose over millions of years. Which gave bats the ability to fly or echolocation first? Or did they occur simultaneously? Bat fossils have been discovered over a period of 50 million years, but there has been no fossil that can explain the evolution of bats.
The paper that would solve the clue was published in ‘Nature’ in February 2008. A fossil bat discovered in 2003 from the early Eocene Green River Formation in Wyoming, USA, dating back 52.5 million years, is one of the oldest primitive bats ever discovered. The remarkable preservation of the fossils allowed us to analyze their physical characteristics, such as skeletal structure and wing shape, to reveal how primitive bats flew and navigated their environment.
Onychonicteris fossil. You should pay attention to the long tail and the claws at the ends of the front toes of the wings. These are two features that modern bats have lost. Source: Nature
Fossil bats were much more primitive and had interesting features than the bats we know. The most striking feature of bat fossils from Wyoming’s Eocene strata was the claws. Most modern bats have claws only on their thumbs, and only some species have claws on their index fingers. However, the newly discovered fossil bat had claws on all five front toes. Researchers gave the bat the scientific name Onychonycteris finneyi. The genus name Onyconicteris comes from onycho- meaning claws and fingernails and -nycteris meaning bat, and the species name Finney is named following Bonnie Finney, who first discovered the fossil. . If I had to translate it into Korean, it would be something like ‘clawed bat.’
The second characteristic was its unique skeletal structure. Onychonicteris had harder bones, unlike the lighter bones of modern bats. Also, unlike modern bats that fly efficiently by supporting thin wing membranes with long limbs and toes, Onychonicteris had short limbs and toes, which resulted in low flight efficiency.
Onyconicteris also had wings, but they were shorter and wider. The length of both outstretched wings is short at 30cm, but the width is 1.7 times wider than the length. Unlike modern bats, which show a high degree of mobility through gliding flight, they would have alternated between flapping wings and gliding, more like birds. It is an evolutionary intermediate between gliding and powered flight. If modern bats are pilots who perform aerial acrobatics, Onyconicteris barely had a flight license.
A third characteristic is that the ear morphology associated with echolocation is underdeveloped. Unlike the echolocation system of modern bats, which are characterized by large, complex ears and a special laryngeal structure for producing high-frequency sounds, Onychonicteris’ ears were small and simple. Although the pars hyaline bone in the throat is connected to the ear region of the skull, it is very primitive. This means that Onyconicteris either had no echolocation ability or, if it had one, it was very primitive. Onychonicteris would have had to rely on other senses instead of echolocation to find food. This conclusively tells us that flight occurred first and echolocation occurred later.
The tail membrane that extends between the tail and hind legs of modern bats plays an important role in bat behavior. The tail membrane expands the surface area of the body, increasing aerodynamic efficiency during flight and allowing it to fly more stably. It can make sharp turns, sudden stops, and aerobatic maneuvers stably, allowing it to cut through vegetation, avoid obstacles, and catch prey. It also serves as a net to catch flying insects. The tail membrane detects changes in air flow, maintains body temperature, and is also used in courtship activities. However, Onyconicteris does not have this tail membrane.
Paleocene-Eocene thermal maximum
Onyconicteris had the ability to fly, although it was much inferior to that of modern bats. This is a characteristic that no other mammal has. Why did these characteristics occur? We must picture the environment at that time in our minds. The Eocene is the second period of the Cenozoic Era. The Eocene, which followed the Paleocene, the first period of the Cenozoic Era that began 66 million years ago, lasts from 56 million to 32.9 million years ago. The Green River Formation, where the fossils were discovered, was characterized by a warm climate.
A warming trend occurred during the Eocene when Onyconicteris occurred, peaking at the Paleocene-Eocene Thermal Maximum (PETM). The early Eocene was the warmest period in Earth’s history since the extinction of the dinosaurs. A greenhouse climate was formed, so there were no ice caps even in the polar regions, and most of the Earth was covered with dense forests.
A variety of life forms flourished in the early Eocene environment. The warm climate and extensive forests provided a variety of ecological niches for mammals, birds, reptiles, and insects. The biodiversity of the early Eocene Eocene is fully recorded in fossils following the extinction event (fifth mass extinction) at the end of the Cretaceous period of the Mesozoic Era. At this time, mammals rapidly diversified. During this period, several families of modern mammals emerged and spread, including the early ancestors of horses, whales, and primates. At the same time, primitive bat species such as Onyconicteris evolved.
Global warming has melted polar ice, causing sea levels to be much higher than they are today. As a result, a shallow sea was formed within the continent, making the ecosystem at that time more diverse. The ice-free, forested terrain provided a new challenge, flight, to mammals that had lived on the ground all their lives.
At this time, Onychonicteris was provided with abundant food to help with the evolution of flight, and a three-dimensional habitat environment was provided. Instead of going to the ground, they were able to go up into the air and hide while feeding as much as they wanted. Onyconicteris had short, wide wings that allowed it to maneuver in forested environments, but it was not able to pursue prey with the agility and speed of modern bats for long periods of time.
The teeth of Onyconicteris, which are no different from modern bats, indicate that it ate insects that were abundant in the Eocene forests. Onyconicteris might collect insects from leaves, twigs, or the ground. Foraging did not require fast flight, and there were many insects in the dense forest. Of course, you might also catch insects in flight. Onychonicteris may have been able to intercept slow-moving prey in flight in open spaces or forest edges, although not as adeptly as modern bats with echolocation.
Onyconicteris played an important role in regulating insect populations within its habitat. However, as can be inferred from the shape of the ears, since it did not have a sophisticated echolocation function, Onychonicteris would have relied on other senses to find food, unlike modern bats. Unlike modern bats, they were probably mainly active during the day when there was plenty of light. However, given that nocturnal tendencies are a key adaptation for exploiting ecological niches with low competition and predators, it can be assumed that Onyconicteris was also active during transition periods such as early evening and dawn.
weather change
The period when Onyconicteris lived was subject to severe climate fluctuations. After experiencing the Paleocene-Eocene thermal maximum, it gradually became colder toward the end of the Eocene. Climate change has dramatically altered the habitat ecology of Onyconicteris. As forests adapted to cold, dry environments, the ecological niche occupied by Onyconicteris shrank. Survival has become more difficult as places to hide and find food have decreased.
As the ecosystem changed and new bat species emerged that successfully evolved, Onyconicteris began to lose out in the competition for resources. The new species of bat was equipped with a cool device called echolocation. It is the same way that traditional fishing boats cannot compete with fishing boats equipped with fish finders. In the end, Onychonicteris, which did not have an echolocation function, was unable to participate in the competition for food and became extinct.
But it doesn’t concern us. This is because modern bats with echolocation have evolved to protect our ecosystem in abundance. Are bats flying mice? Bats are distantly related to rats. Rather, they are closer to primates such as monkeys and humans. Let’s not hate too much. Rather, we should learn from the innovations of bats.
Author Lee Jeong-mo
I believe that humanity, which is facing its sixth mass extinction, must learn from past extinction events in order to be even a little more sustainable. Although he studied biochemistry at graduate schools such as Yonsei University and researched organic chemistry at the University of Bonn in Germany, he is not a Ph.D. He has worked at the Seodaemun Museum of Natural History, the Seoul Science Museum, and the Gwacheon National Science Museum, and is currently writing, lecturing, and broadcasting to promote science to the public. <과학이 가르쳐준 것들> <과학관으로 온 엉뚱한 질문들> <살아 보니, 진화> <달력과 권력> <공생 멸종 진화> etc. was written.
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