Land of giants

89.4 – 84.6 million years ago

The sauropods of the Jurassic and Cretaceous are the largest land animals ever, more than an order of magnitude larger (in estimated body mass) than the largest terrestrial mammals.

And sauropods evolved enormous body size multiple times.

How did they get to be so big? Paleobiologist Martin Sanders recruited a multidisciplinary team of more than twenty researchers in fields ranging from engineering and materials science to animal nutrition and paleontology. They present their results in a review article (whence the figures above) and a book. It doesn’t look like Mesozoic ecology was unusual enough to favor sauropod gigantism on its own. Instead, the long neck of the sauropods was a key innovation, allowing a much greater food intake. The long neck in turn was allowed by a small head with limited chewing capacity and a lightly built pneumatized skeleton going along with avian-style lungs. Other features, including reproduction via many small fast maturing offspring, and a high metabolic rate, also contributed to the complex. The argument is summarized in this chart.

Compare: cold-blooded reptiles don’t command enough energy to grow large quickly. And mammals have taken another path, committed to more thorough mastication rather than sheer volume of food, and to bearing and caring for live young.

No other animal group before or since has had the suite of characters that favored gigantism in sauropods. Their like will not be there again.

Slime had they for mortar

“And slime had they for mortar” Genesis 11:3

The last blog post was about a major transition in evolution, the origin of social insect colonies, in which individual ants and bees work together to make up something like a superorganism. Around the same time that this was happening we find evidence for another venture in higher-level evolution, the slime molds. (The evidence is in the form of a recently discovered 100 million year old fossil, although slime molds were probably around long before this.)

John Tyler Bonner, who died in 2019, spent 70 years of a very long life studying cellular slime molds. Here are some weirdly beautiful movies he made. Cellular slime molds switch between being single cell organisms and multicellular organisms. Most of the time they live alone, looking and acting much like non-social amoebae. But when times get tough, and local food resources are exhausted, the cells start sending out chemical signals indicating they are ready to shift to another state. Individual cells aggregate to form a mass, which is capable of moving around, seeking out new food sources, even learning. (In cellular slime molds, cells retain their identity as separate cells. In plasmodial slime molds, the cells merge to form one super cell.) The mass may raise up a fruiting body atop a stem. The spores in the fruiting body may blow away, perhaps being carried some distance to a better home, where the survivors disperse and feast as the cycle begins again. There is an interesting sociobiological puzzle here: the cells forming the stalk are sacrificing themselves for the sake of the spore cells. This is probably an instance of kin selection.

Both social insects and slime molds may carry lessons for human social life, which, on a large scale, is radically different from the social life of our primate near relations. Both social insects and humans commonly build enormous social organizations with high levels of cooperation. These organizations are too large for their members to recognize one another as individuals. Instead they rely on signals to show others that they are the right sort. With social insects, these are mostly chemical signals. With humans these are the various insignia – letters of commission, uniforms, shibboleths, etc. – that mark the bearer as the occupant of a particular social role, independently of his personal character. (“You salute the uniform, not the man.”) For more on this topic, check out Mark Moffett’s The Human Swarm: How Our Societies Arise, Thrive, and Fall.

And, as with slime molds, humans seem to go through characteristic alternations in their social lives, on a time scale of multiple generations. With slime molds there is an alternation between solitary and social phases. With humans there is an alternation between phases of lesser and greater social solidarity (asabiya). Borrowing from Max Weber, we might call this an alternation between routine and charisma. In phases of routine, people learn the rules of their society, and do their best to get ahead by following the rules, or working around them. But in times of crisis, the old ways no longer serve. While slime molds secrete pheromones to instigate aggregation in hard times, humans secrete cosmologies. Prophets arise, with visions of a new order, taking their cues from divine visions, or the Book of Daniel or Revelations, or theories of political economy or race science. The great majority of such projects are stillborn, but occasionally one succeeds, subduing doubters and infidels, overthrowing the established order or leading a chosen people to a new land. The world we live in – the civilizational landscape of Eurasia, the cultural geography of the United States (I write this in Salt Lake City, Utah) – is in some degree the legacy of such projects.

The quotation above from Genesis 11:3 was used by Eric Hoffer in his book The True Believer: Thoughts on the Nature of Mass Movements, published in the early years of the Cold War, still worth reading today.

Related, here’s me on the sociobiology of “ethnic group selection.”

Consider her ways

99.9 – 95.6 million years ago.

Here is my obituary for Ed Wilson (1929 – 2021) and below some thoughts about ants.

There are some pieces of paleontology that really stand out in the popular imagination. Dinosaurs are so cool that even if they hadn’t existed we would have invented them. (Maybe we did, in the form of dragons. And look ahead (or back) to early April for the dinosaur-griffin connection.) Also, as I suggested in a previous post, transitions from one form of locomotion to another – flightless dinosaurs to birds, fish to tetrapods, land mammals to whales – really grab the imagination (and annoy creationists) because the largest and most distinctive named folk categories of animals (snakes, fish, birds) are built around modes of locomotion.

Evolutionary biologists tend to see things differently. Turning fins into legs, legs into wings, and legs back into flippers is pretty impressive. But the really major evolutionary transitions involve the evolution of whole new levels of organization: the origin of the eukaryotic cell, for example, and the origin of multicellular life. From this perspective, the really huge change in the Mesozoic – sometimes called the Age of Dinosaurs – is the origin of eusociality among insects like ants and bees. An ant nest or a bee hive is something like a single superorganism, with most of its members sterile workers striving – even committing suicide — for the colony’s reproduction, not their own. (100 million years ago – corresponding to March 28 in Logarithmic History — is when we find the first bee and ant fossils, but the transition must have been underway before that time.)

Certainly the statistics on social insects today are impressive.

The twenty thousand known species of eusocial insects, mostly ants, bees, wasps and termites, account for only 2 percent of the approximately one million known species of insects. Yet this tiny minority of species dominate the rest of the insects in their numbers, their weight, and their impact on the environment. As humans are to vertebrate animals, the eusocial insects are to the far vaster world of invertebrate animals. … In one Amazon site, two German researchers … found that ants and termites together compose almost two-thirds of the weight of all the insects. Eusocial bees and wasps added another tenth. Ants alone weighed four times more than all the terrestrial vertebrates – that is, mammals, birds, reptiles, and amphibians combined. E. O. Wilson pp 110-113

E. O. Wilson, world’s foremost authority on ants, and one of the founders of sociobiology, thinks that the origin of insect eusociality might have lessons for another major evolutionary transition, the origin of humans (and of human language, technology, culture, and complex social organization). In his book The Social Conquest of Earth he argues that a key step in both sets of transitions was the development of a valuable and defensible home – in the case of humans, a hearth site. Wilson returns to this argument in his recent book Genesis: The Deep Origin of Human Societies. On the same topic, Mark Moffett’s book The Human Swarm: How Human Societies Arise, Thrive, and Fall,  asks how it is that we somehow rival the social insects in our scale of organization.

One trait found in both ants and humans is large-scale warfare. Wilson gives an idea of the nature of ant warfare in fictional form in his novel Anthill. It’s an interesting experiment, but also disorienting. Because individual recognition is not important for ants, his story of the destruction of an ant colony reads like the Iliad with all the personal names taken out. But Homer’s heroes fought for “aphthiton kleos,” undying fame (and got some measure of it in Homer’s poem). The moral economy of reputation puts human cooperation in war and peace on a very different footing from insect eusociality. (Here’s my take on “ethnic group selection,” which depends on social enforcement, perhaps via reputation.)

“Consider her ways” is the title of a short story by John Wyndham, about a woman from the present trapped in a future ant-like all-female dystopia. It was made into an episode of Alfred Hitchcock Presents. The title is from Proverbs 6:6, “Go to the ant, thou sluggard, consider her ways and be wise.”

Other science fiction authors have taken a cheerier view of a world without men.

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.

Amborella Day

1 galactic revolution ago

The Triassic ends 201 million years ago with another major mass extinction (the fourth, by the usual count, after the end-Ordovician, end-Devonian, and end-Permian). Not quite as bad as the end-Permian (“only” 75% of species go extinct). This coincides with the formation of the Central Atlantic LIP (Large Igneous Province), which now includes a lot of eastern North America, northeast Amazonia, and western North Africa. So the end Triassic mass extinction may be the result of volcanoes spewing lava and carbon dioxide as Pangaea splits into Laurasia (North America, most of Eurasia) and Gondwanaland (South America, Africa, Antarctica, India, Australia).

The succeeding Jurassic Period will be when dinosaurs become the dominant vertebrates on land. The mammals around are mostly shrew-sized and nocturnal.

Not as conspicuous is another evolutionary innovation: the ancestors of Amborella, a rare shrub found in the wild only on New Caledonia, split off from the other angiosperms, ancestors of all other flowering plants, 200 million years ago. (This was suspected for a while, and confirmed in 2012 with the sequencing of the Amborella genome.) We can call this the origin of flowers. Amborella has clusters of small white flowers, with male and female separate.

Spring is gearing up in the Northern hemisphere; some dwarf irises are in flower in my front yard, and the daffodils, celebrating global warming, are about to let loose. If you’re lucky you’ll be able to smell the flowers on Amborella Day, and take your mind off catastrophes past and present.

The worst of times

260 million years ago: the Capitanian mass extinction

A capsule summary of the evolution of life on Earth goes like this: There is steady progress in adaptation, driven especially by arms races, sometimes involving competitors, sometimes predators and prey. But this progress is interrupted from time to time by catastrophes – mass extinctions resulting from extrinsic causes, sometimes astronomical, but more often geological. (We’ll see much later in the year that a similar summary of human history goes like this: steady progress in the scale of cooperation driven by arms races, with occasional catastrophic interruptions, often associated with the spread of epidemic diseases.)

The geological causes of mass extinctions have been coming into focus lately. Many mass extinctions co-occur with the formation of Large Igneous Provinces (LIPS), regions where vast amounts of lava have flowed out of the earth, triggering a whole cascade of changes: the destruction of the ozone layer by halogen gases, global warming induced by CO2 and methane, and anoxic seas.

Large Igneous Provinces aren’t always associated with mass extinctions. What makes some episodes of massive lava flow particularly destructive is that they produce short circuits in the “planetary fuel cell.” The development of complex life has depended on the separation between an oxygen-rich, electron-hungry atmosphere and a reducing, electron-stuffed planetary interior. Some of the biggest setbacks to complex life have happened when  lava flows from deep in the Earth’s interior punch through carbon deposits on their way up, and bridge this chemical gap between surface and interior.

The mass extinction 260 million years ago, the Capitanian, is not one of the classic five greatest mass extinctions, and has been overshadowed by the mother of all mass extinctions, the end-Permian, which happened just 8 million years later. But it took a major toll on living things, from marine organisms to dinocephalians. (The dinocephalians – more closely related to mammals than to dinosaurs, ranging up to hippo sized, and including both herbivores and carnivores – went entirely extinct with the Capitanian. See picture.) The Capitanian extinctions coincide with, and were probably caused by, the formation of the Emeishan LIP, now in southwest China.

A book published recently, The Worst of Times, pulls together the latest evidence that the Capitanian was the beginning of an 80 million year period in which mass extinctions were exceptionally common. Apparently the formation of the supercontinent of Pangaea and the Panthalassic superocean made living things particularly vulnerable to volcanically induced extinctions. Once Pangaea breaks up, mass extinctions are less frequent, and generally have different causes.  The death of the dinosaurs had an extra-terrestrial cause, and the mass extinction we’re in the middle of results from the activities of one very unusual species.

Coals to Newcastle

274 – 260 million years ago

It seems like Gaia really went on a bender in the late Carboniferous, getting drunk on oxygen. By some estimates, the atmosphere was over 30% oxygen back then, compared to 21% today. Living things took advantage of the opportunity. Insects apparently face an upper limit in size because they rely on diffusion through tracheas instead of forced respiration through lungs to get oxygen into their bodies. With more oxygen in the air, this limit was raised. The Carboniferous saw dragonflies with a wingspan up to 70 centimeters, and body lengths up to 30 centimeters, comparable to a seagull.

This happened because plants were turning carbon dioxide into organic matter and free oxygen, and the organic matter was accumulating. With carbon dioxide being removed from the atmosphere, the late Carboniferous and subsequent early Permian saw a reduced greenhouse effect, and global cooling. This was another Ice Age, with ice caps around the southern pole.

A lot of organic carbon ended up being buried. Much of the world’s coal, especially high quality anthracite, has its origin in Carboniferous tropical forests. Western Europe and eastern North America lay in the tropics at the time, and got a particularly generous allotment of coal. Three hundred million years later this bounty would fuel the early Industrial Revolution. (Thanks partly to some of my Welsh ancestors, who helped dig it up back in the day.) And here’s a song about coal mining, Dark as a Dungeon.

Devonian days

405 – 384 million years ago

(posted a day late)

Lots going on in the Devonian.

Forests are spreading. These early trees, genus Wattieza, are kin to ferns and horsetails. They stand 10 meters tall. No leaves yet, just fronds. The first forests will absorb carbon dioxide, and cool the planet.

Life is moving onto land. Tiktaaklik roseae, the “fishapod” discovered in 2006, is as nice a link between fish and amphibians as one could hope for, with both lungs and gills. Here’s a book by Neil Shubin, the co-discoverer.

You can see a lot further in the air than underwater. This may be one of the early selective pressures for evolving a proper neck and sticking one’s head out of water. Eventually, for some, the rest of the body would follow.

And evolution seems to be generally speeded up on land. It’s not just that animals and plants develop adaptations for life on land (obviously). But there is also a more general acceleration in the pace of evolution. Major innovations come at a faster pace among terrestrial organisms.