Bird life

So we rode all around the park until quite late talking and philosophizing quite a lot and I finally told him that I thought, after all, that bird life was the highest form of civilization. So Gerry calls me his little thinker and I really would not be surprised if all of my thoughts will give him quite a few ideas for his novels. Because Gerry says he has never seen a girl of my personal appearance with so many brains. 

“Gentlemen Prefer Blondes” Anita Loos

Maybe bird life is not the highest form of civilization. But a recent book, The Parrot in the Mirror: How Evolving to be Like Birds Makes Us Human, makes the case that primates in general, and humans in particular, are special in ways that show convergent evolution with birds. To wit:

Vision: Mammals in the Mesozoic Era were largely nocturnal. With the great dinosaur extinction, some mammals moved into diurnal niches. Primates take this further than most. Like birds, primates are highly visually oriented. Birds have exceptional color vision, with four types of color-sensitive cone cells in their retinas. Most mammals have just two. But Old World monkeys and apes (and you, unless you are colorblind) have three types of cones. On the other hand, birds and primates are less attuned to smells than most mammals.

Longevity: Birds are long-lived relative to mammals. At any given size, a bird is likely to live maybe twice as long as a typical mammal. (Something to consider when choosing a pet.) Primates are also longer lived than most mammals, and human beings long-lived even among primates. Birds can afford to slow down their life histories and senesce more slowly, because being able to fly puts them at lower risk from predators. Primates too live life in the slow lane, relying on brains and sociality to cut down on the predation and other extrinsic mortality that push many mammals to live fast and die young.

Brains: Birds have relatively small, i.e. light-weight, brains, as part of being lightly built for flight. But their small brains pack in lots of smaller neurons compared a similar size mammal brain.

[C]ompared with mammals, very small birds, with similarly small brains, will have many more neurons than similarly sized mammals. Small songbirds can weigh in at barely a tenth the weight of a common mouse, but sport more than double the number of neurons. Meanwhile, some of the heaviest bird brains, which are found in the macaws, the big, colourful South American parrots, weigh in at perhaps 20–25 grammes. This is a bit bigger than the brain of a common European rabbit. Yet while the rabbit has about half a billion neurons in its whole body, the macaw can have over three billion in its brain alone, a number more in line with much larger giraffes and baboons There are really only four types of animal that get into the billions of neurons: whales, large mammals such as elephants and seals, primates, and brainy birds (parrots and crows).

https://www.amazon.com/Parrot-Mirror-evolving-birds-makes/dp/019884610X/

Pair bonds. Many birds, especially passerines (perching birds, including songbirds = most bird species) pair up, with males and females cooperating to care for offspring. There’s only so much nutrition you can pack into an egg, so baby birds are often pretty helpless, and need two parents to take care of them. Human infants too are pretty helpless; there’s only so big a fetus can get before birth. And children, growing slowly, take a long time to become independent. So human mothers too commonly have to enlist helpers in providing for their offspring.

Vocal communication. Among birds, parrots, hummingbirds, and songbirds show exceptional vocal learning abilities. (Among mammals, the closest nonhuman exemplars are cetaceans.) In birds, vocal learning may happen during juvenile sensitive periods (in humans: think about learning the local accent in childhood) or may be more open-ended (in humans: think about adding to your vocabulary throughout life). Bird vocalizations can be socially transmitted, and different communities can develop distinctive dialects.

And even among birds, parrots are really exceptional. The Parrot in the Mirror gives them a whole chapter to themselves. Parrots are a pinnacle in the evolution of intelligence. 

And they’ve got rhythm.

Life at sea: whales and sailors

48.3 – 45.8 million years ago

The end-Cretaceous mass extinction knocked off not only the dinosaurs (except for birds), but also air-breathing marine predators like mososaurs and plesiosaurs. Birds and mammals started moving into the empty niche: penguins from early on, and eventually whales.

(Cartoon by Sam Gross. Not scientifically accurate.)

People around the world seem to be naturally inclined to distinguish major animal life forms according to whether they walk, fly, swim, slither, or creep, so evolutionary shifts in modes of travel – the origin of flight, the return to the sea – really catch people’s imagination – and provoke Creationists. The whale story is particularly dramatic. When Darwin was tried to account for the evolution of whales from a land-dwelling ancestor, he cited accounts of bears swimming and feeding in water, and wrote “I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale.” This statement attracted so much ridicule that Darwin took it out of later editions of The Origin of Species. But he turns out to have been very much on target. We now have a great sequence of whale ancestors. The sequence runs from today’s Pakicetus — a wolf size meat-and-fish eater that splashed along the shores of the ancient Tethys sea separating Africa from Eurasia — to the “walking whale,” Ambulocetus, and on to true whales. We have even begun to detail some of the genetic changes that went with the return to the sea. Darwin was sort of on the right track thinking of bears, but anatomy and genetics put the ancestors of whales firmly among artiodactyls – hooved animals including hippos, pigs, and cows.

Whales are famously large. Marine mammals in general tend toward bigness: one theory is that large body size (low ratio of surface area to volume), and an insulating layer of blubber, are adaptations to reduce heat loss. Whales, particularly baleen whales, take it further with dietary adaptations that let them get huge.

Remarkably there may be a parallel in human evolution. Polynesians have the largest body sizes of any living people, and this too may be an adaptation to conserve heat in a maritime environment.

The Polynesian people who settled a wide area of the tropical Pacific have a large and muscular body phenotype that appears to contradict the classical biological rules of Bergmann and Allen. However, a scrutiny of the conditions actually experienced by these canoe voyagers and small-island dwellers suggests that in reality the oceanic environment is labile and frequently very cold, and from it tribal technology offered little protection. The Polynesian phenotype is considered to be appropriate to, and have undergone selection for, this oceanic environment.

People of the Wind

John W. Campbell, the editor of Astounding Science Fiction magazine, used to challenge writers with new premises. One of his challenges was to imagine an alien that is to mammals as mammals are to reptiles. Science fiction writer Poul Anderson took up this challenge by inventing the Ythri, flying intelligent aliens of the planet Avalon, for his novel The People of the Wind. The Ythri were able to support the high metabolisms necessary for flight because they had a special system for supercharging their bloodstreams with extra oxygen.

Since Anderson’s time, we’ve learned that birds – and some dinosaurs – are actually somewhat Ythri-like. To begin with, consider non-dinosaur reptiles, like lizards: their sprawling posture means that their legs compress and expand their lungs as they run, so they can’t run and breathe at the same time. (David Carrier, a biologist at the University of Utah, was a main guy to figure this out.) If you had traveled back in time to the Paleozoic, before the dinosaurs took over, and if you had had good endurance training, you would have found the hunting easy, because the sprawling reptiles of the time would not have been able to run away for more than a short sprints. The predators to worry about would have been ambush hunters, not endurance hunters.

Dinosaurs got around these constraints in the first place by running bipedally (although some later reverted to quadrupedalism). And it now looks like at least some of them also had the sort of respiration we find in birds. Lungs are only part of birds’ respiratory systems. Birds also have an extensive network of air sacs running through their bodies, and even air passages in their bones. Air moves in both directions, in and out, like a bellows, through the air sacs, but only one direction through the lungs. This allows for more efficient circulation than mammalian lungs, where air has to move both in and out of the lungs. Just recently (2008), it’s been shown that Allosaurus, only distantly related to birds, had the same system, so it was probably widespread among dinosaurs. This breathing system may have helped dinosaurs to survive low-oxygen crises at the end of the Triassic, and flourish in the low oxygen Jurassic and Cretaceous. It may also have helped one group of dinosaurs to evolve into birds.

Anderson’s book isn’t just about respiratory physiology. It’s also about perennial issues of loyalty and identity. Avalon also has human settlers, who have so absorbed Ythri values — some of them even yearning, impossibly, to be Ythri — that they fight for an independent Avalon against an expanding Terran Empire. (Compare the movie Avatar.)

We’ll have more to say about bipedalism and breathing — and language — when human evolution comes up.

Hotblooded

Were dinosaurs warmblooded? More precisely, were they ectotherms, with low metabolic rates, like living reptiles, or endotherms, with high metabolic rates, like mammals and birds? (Yes, yes, you and I know that birds are dinosaurs, cladistically speaking, but you know what I mean.) And there are other possibilities: were the biggest dinosaurs, the sauropods, gigantotherms, keeping metabolic rates low, but staying warm through sheer size?

Endothermy is a big deal:

Elevated metabolic rates enable animals to remain active year-round at high latitude and altitude. They also enhance physiological performance, improve endurance, increase activity levels and facilitate rapid niche shift during environmental perturbations.

https://www.nature.com/articles/s41586-022-04770-6

Recently, it has become possible to address this question by looking at chemical signals of metabolic rates in fossil bones. The chart below (see link above) summarizes the results.

The upper branch of the tree are the diapsids – reptiles, dinosaurs, birds, and relatives. The lower branch is the synapsids ­– from dimetrodon way back in the day to mammals today. The chart shows that the earliest dinosaurs had high metabolic rates, as did the closely related early pterosaurs. And the sauropods were true endotherms. But some later dinosaurs actually gave up on endothermy: triceratops, stegosaurus, and the hadrosaurs (duck-billed dinosaurs) seem to be secondary ectotherms. Other dinosaurs went for more intense endothermy, like allosaurs and diplodocus and some close bird relatives.

In short, dinosaurs are diverse.

Archaeopteryx, Bird, Fish, Snake

156 – 149 million years ago

The first Archaeopteryx discovered, found in 1861, is the most famous fossil ever (barring maybe some close human relations). It came at the right time, providing dramatic evidence for the theory of evolution.

There may be psychological reasons why Archaeopteryx had the impact it did. Here’s my argument anyway:

According to Jorge Luis Borges, the following is a classification of animals found in a Chinese encyclopedia, the Celestial Emporium of Benevolent Knowledge.

• Those that belong to the Emperor
• Embalmed ones
• Those that are trained
• Suckling pigs
• Mermaids (or Sirens)
• Fabulous ones
• Stray dogs
• Those that are included in this classification
• Those that tremble as if they were mad
• Innumerable ones
• Those drawn with a very fine camel hair brush
• Et cetera
• Those that have just broken a flower vase
• Those that, at a distance, resemble flies

Although some scholars have taken this list seriously (Hi, Michel Foucault!), there’s no evidence that this is anything but a Borgesian joke. Anthropologists have actually spent a lot of time investigating the principles underlying native categorizations of living things, and found they are not nearly as off-the-wall as Borges’ list. These categorizations obey some general principles, not quite the same as modern biologists follow, but not irrational either. Naming Nature: The Clash Between Instinct and Science is good popular review of ethno-biology, the branch of anthropology that studies different cultures’ theories of biology and systems of classification Did you know there are specialized brain areas that handle animal taxonomy? Or try here for a scholarly treatment.

At the highest level is usually a distinction between plants and animals. This doesn’t necessarily match the biologists’ distinction between Plantae and Animalia, but rather usually follows a distinction between things that don’t and do move under their own power. Even babies seem to make a big distinction between shapes on a screen that get passively knocked around, and shapes that move on their own. i.e. are animated.

Among larger animals (non-bugs/worms) the first large scale groups to receive a label of their own are almost always birds, fish, and snakes, in no particular order. These categories are telling: each represents a variety of locomotion (flying, swimming, slithering) other than the stereotypical mammalian walking/running. (Many folk classifications lump bats with birds and whales with fish, and they may also separate flightless birds like the cassowary from others.) So whether a creature moves on its own, and how it moves are central to folk categorizations of living kinds, even if not to modern scientific taxonomy. And so finding an animal that seems to be a missing link between two (psychologically) major domains of life — birds and terrestrial animals — is going to be a Big Deal, cognitively, upsetting people’s intuitive notions that it takes God’s miraculous intervention to create animals that fly, or to condemn the Serpent to slither.

The worst day in the history of the Earth

66.5 million years ago

This April 6 on Logarithmic History marks the most famous mass extinction ever, the one that did in the dinosaurs (okay, okay, the non-avian dinosaurs).

Just a few years back, we had news of one of the most extraordinary fossil discoveries ever, in North Dakota: a graveyard of fish piled on one another by a tsunami-like wave, and mixed with burned trees, and the remains of mammals, mososaurs, ammonites, and insects, and a partial triceratops, formed within hours of the asteroid impact that wiped out most life on Earth. Here is a news release, 66 million-year-old deathbed linked to dinosaur-killing meteor, and here is an article from the New Yorker, The Day the Dinosaurs Died.

The end-Cretaceous extinction isn’t the biggest ever, but it’s the one everybody knows about. The Disney movie Fantasia (1940) did a version of the event, set to Stravinsky (and mixing up Jurassic and Cretaceous dinosaurs). In Terence Malik’s movie The Tree of Life, a predatory dinosaur discovers compassion in an encounter with a hadrosaur just before all their kind are wiped out by an asteroid: mass extinction meets the Book of Job.

The discovery that dinosaurs (and about 70% of all species in total) probably went extinct as a result of an extraterrestrial impact did more than anything else to bolster catastrophism. For most of the history of modern geology, geologists have mostly argued instead for uniformitarianism: the same slow processes we see today caused past geological and evolutionary changes. When evidence for an impact was first discovered – a thin layer of iridium, presumably extraterrestrial — paleontologists were pretty uniformly hostile: no physicist was going to tell them how to do science. But by now the evidence is overwhelming that the asteroid impact that left the Chixculub crater, in what is now the Yucatan, was largely responsible for the end-Cretaceous extinctions (although the volcanic eruptions that created the Deccan traps in India may also have played a role).

But at the same time that evidence has increasingly vindicated the catastrophist position, new discoveries in paleontology have increasingly brought home that one group of dinosaurs survived the extinction. Most people think of birds and dinosaurs as two quite distinct kinds of animal. But birds are just as much dinosaurs as bats are mammals. Many dinosaurs had many of the distinctive features of birds – warm-bloodedness and high metabolic rates (probably), wishbones, an advanced respiratory system, feathers (sometimes brightly colored, sometimes used for courtship), and parental care for nests of eggs and juveniles. It’s even possible that some flightless dinosaurs, like the turkey-sized Caudipteryx, were secondarily flightless, descended from flying ancestors like Archeopteryx. We don’t have to hope for The Lost World or Jurassic Parkto come true to see living dinosaurs; a trip to the park, with The Sibley Guide to Birds (or appropriate guidebook for your region) in hand, will do it.

People of the Wind

123 – 118 million years ago

John W. Campbell, the editor of Astounding Science Fiction magazine, used to challenge writers with new premises. One of his challenges was to imagine an alien that is to mammals as mammals are to reptiles. Science fiction writer Poul Anderson took up this challenge by inventing the Ythri, flying intelligent aliens of the planet Avalon, for his novel The People of the Wind. The Ythri were able to support the high metabolisms necessary for flight because they had a special system for supercharging their bloodstreams with extra oxygen.

Since Anderson’s time, we’ve learned that birds – and some dinosaurs – are actually somewhat Ythri-like. To begin with, consider non-dinosaur reptiles, like lizards: their sprawling posture means that their legs compress and expand their lungs as they run, so they can’t run and breathe at the same time. (David Carrier, a biologist at the University of Utah, was a main guy to figure this out.) If you had traveled back in time to the Paleozoic, before the dinosaurs took over, and if you had had good endurance training, you would have found the hunting easy, because the sprawling reptiles of the time would not have been able to run away for more than a short sprints. The predators to worry about would have been ambush hunters, not endurance hunters.

Dinosaurs got around these constraints in the first place by running bipedally (although some later reverted to quadrupedalism). And it now looks like at least some of them also had the sort of respiration we find in birds. Lungs are only part of birds’ respiratory systems. Birds also have an extensive network of air sacs running through their bodies, and even air passages in their bones. Air moves in both directions, in and out, like a bellows, through the air sacs, but only one direction through the lungs. This allows for more efficient circulation than mammalian lungs, where air has to move both in and out of the lungs. Just recently (2008), it’s been shown that Allosaurus, only distantly related to birds, had the same system, so it was probably widespread among dinosaurs. This breathing system may have helped dinosaurs to survive low-oxygen crises at the end of the Triassic, and flourish in the low oxygen Jurassic and Cretaceous. It may also have helped one group of dinosaurs to evolve into birds.

Anderson’s book isn’t just about respiratory physiology. It’s also about perennial issues of loyalty and identity. Avalon also has human settlers, who have so absorbed Ythri values — some of them even yearning, impossibly, to be Ythri — that they fight for an independent Avalon against an expanding Terran Empire. (Compare the movie Avatar.)

We’ll have more to say about bipedalism and breathing — and language — when human evolution comes up.

Archaeopteryx, Bird, Fish, Snake

154 – 147 million years ago

The first Archaeopteryx discovered, found in 1861, is the most famous fossil ever (barring maybe some close human relations). It came at the right time, providing dramatic evidence for the theory of evolution.

There may be psychological reasons why Archaeopteryx had the impact it did. Here’s my argument anyway:

According to Jorge Luis Borges, the following is a classification of animals found in a Chinese Encyclopedia, the Celestial Emporium of Benevolent Knowledge.

• Those that belong to the Emperor
• Embalmed ones
• Those that are trained
• Suckling pigs
• Mermaids (or Sirens)
• Fabulous ones
• Stray dogs
• Those that are included in this classification
• Those that tremble as if they were mad
• Innumerable ones
• Those drawn with a very fine camel hair brush
• Et cetera
• Those that have just broken a flower vase
• Those that, at a distance, resemble flies

Although some scholars have taken this list seriously (Hi, Michel Foucault!), there’s no evidence that this is anything but a Borgesian joke. Anthropologists have actually spent a lot of time investigating the principles underlying native categorizations of living things, and found they are not nearly as off-the-wall as Borges’ list. These categorizations obey some general principles, not quite the same as modern biologists follow, but not irrational either. (Naming Nature: The Clash Between Instinct and Science is good popular review of ethno-biology, the branch of anthropology that studies different cultures’ theories of biology and systems of classification Did you know there are specialized brain areas that handle animal taxonomy? Or try here for a scholarly treatment.)

At the highest level is usually a distinction between plants and animals. This doesn’t necessarily match the biologists’ distinction between Plantae and Animalia, but rather usually follows a distinction between things that don’t and do move under their own power. Even babies seem to make a big distinction between shapes on a screen that get passively knocked around, and shapes that move on their own. i.e. are animated.

Among larger animals (non-bugs/worms) the first large scale groups to receive a label of their own are almost always birds, fish, and snakes, in no particular order. These categories are telling: each represents a variety of locomotion (flying, swimming, slithering) other than the stereotypical mammalian walking/running. (Many folk classifications lump bats with birds and whales with fish, and they may also separate flightless birds like the cassowary from others.) So whether a creature moves on its own, and how it moves are central to folk categorizations of living kinds, even if not to modern scientific taxonomy. And so finding an animal that seems to be a missing link between two (psychologically) major domains of life — birds and terrestrial animals — is going to be a Big Deal, cognitively, upsetting people’s intuitive notions that it takes God’s miraculous intervention to create animals that fly, or to condemn the Serpent to slither.

Life at sea: whales and sailors

50.2 -47.6 million years ago

The end-Cretaceous mass extinction knocked off not only the dinosaurs (except for birds), but also air-breathing marine predators like mososaurs and plesiosaurs. Birds and mammals started moving into the empty niche: penguins from early on, and eventually whales.

(Cartoon by Sam Gross. Not scientifically accurate.)

People around the world seem to be naturally inclined to distinguish major animal life forms according to whether they walk, fly, swim, slither, or creep, so evolutionary shifts in modes of travel – the origin of flight, the return to the sea – really catch people’s imagination – and provoke Creationists. The whale story is particularly dramatic. When Darwin was tried to account for the evolution of whales from a land-dwelling ancestor, he cited accounts of bears swimming and feeding in water, and wrote “I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale.” This statement attracted so much ridicule that Darwin took it out of later editions of The Origin of Species. But he turns out to have been very much on target. We now have a great sequence of whale ancestors. The sequence runs from today’s Pakicetus — a wolf size meat-and-fish eater that splashed along the shores of the ancient Tethys sea separating Africa from Eurasia — to the “walking whale,” Ambulocetus, and on to true whales. We have even begun to detail some of the genetic changes that went with the return to the sea. Darwin was sort of on the right track thinking of bears, but anatomy and genetics put the ancestors of whales firmly among artiodactyls – hooved animals including hippos, pigs, and cows.

Whales are famously large. Marine mammals in general tend toward bigness: one theory is that large body size (low ratio of surface area to volume), and an insulating layer of blubber, are adaptations to reduce heat loss. Whales, particularly baleen whales, take it further with dietary adaptations that let them get huge.

Remarkably there may be a parallel in human evolution. Polynesians have the largest body sizes of any living people, and this too may be an adaptation to conserve heat in a maritime environment.

The Polynesian people who settled a wide area of the tropical Pacific have a large and muscular body phenotype that appears to contradict the classical biological rules of Bergmann and Allen. However, a scrutiny of the conditions actually experienced by these canoe voyagers and small-island dwellers suggests that in reality the oceanic environment is labile and frequently very cold, and from it tribal technology offered little protection. The Polynesian phenotype is considered to be appropriate to, and have undergone selection for, this oceanic environment.

The worst day in the history of the Earth

66.5 million years ago

This April 6 on Logarithmic History marks the most famous mass extinction ever, the one that did in the dinosaurs (okay, okay, the non-avian dinosaurs).

Just a few years back, we had news of one of the most extraordinary fossil discoveries ever, in North Dakota: a graveyard of fish piled on one another by a tsunami-like wave, and mixed with burned trees, and the remains of mammals, mososaurs, ammonites, and insects, and a partial triceratops, formed within hours of the asteroid impact that wiped out most life on Earth. Here is a news release, 66 million-year-old deathbed linked to dinosaur-killing meteor, and here is an article from the New Yorker, The Day the Dinosaurs Died.

The end-Cretaceous extinction isn’t the biggest ever, but it’s the one everybody knows about. The Disney movie Fantasia (1940) did a version of the event, set to Stravinsky (and mixing up Jurassic and Cretaceous dinosaurs). In Terence Malik’s movie The Tree of Life, a predatory dinosaur discovers compassion in an encounter with a hadrosaur just before all their kind are wiped out by an asteroid: mass extinction meets the Book of Job.

The discovery that dinosaurs (and about 70% of all species in total) probably went extinct as a result of an extraterrestrial impact did more than anything else to bolster catastrophism. For most of the history of modern geology, geologists have mostly argued instead for uniformitarianism: the same slow processes we see today caused past geological and evolutionary changes. When evidence for an impact was first discovered – a thin layer of iridium, presumably extraterrestrial — paleontologists were pretty uniformly hostile: no physicist was going to tell them how to do science. But by now the evidence is overwhelming that the asteroid impact that left the Chixculub crater, in what is now the Yucatan, was largely responsible for the end-Cretaceous extinctions (although the volcanic eruptions that created the Deccan traps in India may also have played a role).

But at the same time that evidence has increasingly vindicated the catastrophist position, new discoveries in paleontology have increasingly brought home that one group of dinosaurs survived the extinction. Most people think of birds and dinosaurs as two quite distinct kinds of animal. But birds are just as much dinosaurs as bats are mammals. Many dinosaurs had many of the distinctive features of birds – warm-bloodedness and high metabolic rates (probably), wishbones, an advanced respiratory system, feathers (sometimes brightly colored, sometimes used for courtship), and parental care for nests of eggs and juveniles. It’s even possible that some flightless dinosaurs, like the turkey-sized Caudipteryx, were secondarily flightless, descended from flying ancestors like Archeopteryx. We don’t have to hope for The Lost World or Jurassic Parkto come true to see living dinosaurs; a trip to the park, with The Sibley Guide to Birds (or appropriate guidebook for your region) in hand, will do it.