I’ve been quiet for two reasons. One is that I’m trying to put something complicated in simple terms about madness and the state of the human race. I’ve written quite a lot on this but haven’t published it yet. The other is that we’re about to leave England, probably for good, and that takes a lot of doing. Given the state of things, it seems insensitive to write about anything else than the madness afflicting the West, if indeed “afflicting” is the right word.
Nonetheless, something has come to occupy my mind and operate as a distraction from the insanity, and perhaps put it in context. Whereas we’re in the midst of a mass extinction which may shortly bring the lives of all vertebrates to an end, we are at the end of a long history more than half an aeon in length with its own ups and downs. The biggest of these was the end-Permian mass extinction, whose causes are still not established, but involved the extinction of all but four percent of all species and leading to what’s been described as “a world of pigs”, since Pangaea became dominated by pig-like animals called Lystrosaurs for a long time. This was followed by the end-Triassic mass extinction many millions of years later, which had the surprising result of wiping out most of the mammaliforms and leading to the dominance of the up until then rather insignificant dinosaurs. Something like 120 million years after that came the K-T Event, which I’m often tempted to call the “left hand down a bit” disaster for reasons which reveal possible first-hand experience of the aforementioned mental condition of the world, but which basically involved a massive chunk of something rich in iridium hitting the Gulf of Mexico and killing every animal with a mass over twenty-five kilogrammes. I want now to talk about what happened after that.
I’ve mentioned multituberculates before as the most long-lived ever order of mammals, first appearing 167 million years ago and surviving in some form until millions of years after the extinction of non-avian dinosaurs in the late Eocene, 130 million years later. In other words they lasted longer than the non-avian dinosaurs. These are impressive and could be quite large, fox- or beaver-sized, and superficially resembled rodents although they weren’t closely related, but I haven’t come here to talk about that today. No, I want to talk about pantodonts, because I’ve recently had a bit of a revelation about them.
Pantodonts are somewhat enigmatic early Cenozoic mammals. I should explain that surviving mammals today comprise three main types. There are the monotremes, including the echidnas and the duck-billed platypus, whose group is unclear. The other two are the marsupialiformes and the eutheria, both of which are classed as theria. Multituberculates were in a different group again, the allotheria. Marsupials and their close relatives are well-known for having very short pregnancies and often keeping their young in a pouch physically attached to their nipples. The eutheria include all placental mammals, such as humans, but also other mammals who are not placental. Their traits include skeletal details such as a large malleolus at the bottom of the tibia, and although nowadays all eutheria are placental, there was a time when there were non-placental eutheria distinguished by those other characteristics, and probably more but soft parts are not preserved and there’s no surviving genome from them to work out the fine details. There was once a native New Zealand mammal, who went extinct in the Miocene and may or may not have been therian or eutherian but not placental. I mention all this because pantodonts may have been non-placental eutherians.
Tom Stoppard wrote a play called ‘Rosencrantz And Guildenstern Are Dead’, concentrating on the minor characters from ‘Hamlet’ in question, who are really just a footnote in the play. Stoppard’s play focusses on the random, arbitrary nature of the world and the framing of events in narratives, when something else is also going on. I’ve long since sworn off literary criticism but I tentatively venture to suggest that a major point of the piece is that while the big drama between the “important” people is going on, every bit part player portrays a potential main character who is central to her own life. For another example, consider Regina Spektor’s ‘Samson’:
Samson went back to bed,
not much hair left on his head.
ate a slice of wonder bread, and went right back to bed.
oh, we couldn’t bring the columns down,
yeah, we couldn’t destroy a single one,
and history books forgot about us,
and the Bible didn’t mention us, not even once.
All we “know” about Samson is from the Biblical narrative, but who knows who else was important to him? What about all the other routes not taken in our lives, all the people we knew vaguely as acquaintances but could’ve got to know better, and the various decisions we took and events which overtook us? Something which preoccupies me at times is that I could’ve gone to university in Sheffield instead of Leicester and maybe would still be living there today for all I know, but instead I did go to Leicester, met Sarada, we had children and now have grandchildren and for some reason I don’t understand, somehow I have never been to Sheffield, not even once. I know Leeds well, regularly go to Doncaster, have visited York a few times, have been to Bradford a fair bit, have stayed in Huddersfield and so on, but I have never, ever been to Sheffield. But in another world, Sheffield is my home city, and presumably in that world I’ve never been to Leicester instead of living there for thirty-two years. There are also, I guess, hundreds of people who have lived or do live in Sheffield whom I would’ve got to know, loved, hated, just vaguely known. As it is, I know two people in Sheffield and about two hundred in Leicester.
The pantodonts are like Sheffield, or Rosencrantz and Guildenstern, with respect to the dominant narrative of prehistory. The multituberculates are also like this to some extent. We have this popular view that there was a time we call the Age Of Dinosaurs, where giant reptiles dominated the planet on land and sea while mammals were tiny and insignificant, then an asteroid collided with us and wiped out all the giant reptiles, who were then replaced by mammals who became dominant. This is partly true, but the details are wrong. The multituberculates, along with various other species related to mammals, were around for a hundred million years before most of the dinosaurs were killed. After the event, it’s possible that hadrosaurs survived for a million years or so, but this is very doubtful. Less doubtful is the somewhat surprising survival of cursorial crocodiles. These were predatory like other crocodiles but with running underslung legs like those of dinosaurs, and terrestrial. Technically they weren’t dinosaurs but this didn’t matter to them or any of the prey they chomped down on for millions of years. At the same time, it would be equally false to over-emphasise these apparent anomalies, because that’s still what they are. And that brings me back to the pantodonts.
Apart from the multituberculates, and for some reason also the cursorial crocodiles, the post-apocalyptic landscape left by the Chicxulub Impactor was probably devoid of any large animals. This situation wouldn’t last, but I don’t want to pass over the immediate aftermath without comment. After the rather dramatic cock-up one Tuesday in May seen as killing off all the large animals here, including the ones living in the seas and oceans, it’s possible that a few scavengers such as pterosaurs survived and actually did really well for a bit and also that there were in fact a few dinosaurs dotted about here and there who had by some happy-ish accident not been killed, but never met another member of their species again and failed to breed. There was also a major rodent “problem”. The rodents, who had evolved in the late Cretaceous, proliferated like anything along with other small mammals, able to thrive in such an environment with few predators. Many of them were largely herbivorous, which helped. The ancestors of today’s hoofed mammals were there too, though they had yet to become hoofed and remarkably a lot of them were going to evolve into apparent apex predators and weren’t herbivorous at all.
By three million years after the K-T Event, one of the earliest pantodonts had appeared. This was Bemalambda:
Source: Own work. Author: ДиБгд
As can be seen from this picture, Bemalambda was around a metre long, so about the size of many dogs or perhaps a badger. It was herbivorous, but not a grazer because although grass did exist back then, grasslands didn’t. Grass was just one type of plant among many and much of the planet was covered in forest by then, so grazing didn’t happen and running either after prey or away from predators was difficult over long distances. By the way, this is my view and may not be backed up by evidence. Suppose this animal lived an average of ten years. There are therefore 300 000 generations maximum between the K-T Event and the presence of this specific animal. That’s a mean increase in length by a millimetre every nine thousand years, assuming the original ancestor to be infinitely small, which is obviously false – this is along the lines of “assume a spherical cow”. The significance of these animals is that they were to become the earliest large herbivorous mammals. At this point, this largest herbivorous mammal was the same size as the largest multituberculates had been, so the record was about to be broken.
Relatives and perhaps descendants included Barylambda, Pantolambda and Coryphodon. The occurrence of the word “lambda”, i.e. “Λ”, is incidentally to do with the arrangement of the cusps on their teeth. Speaking of teeth, unlike multituberculates or the more modern rodents, lagomorphs, even-toed ungulates and odd-toed ungulates, pantodonts didn’t have a gap in their teeth between their incisors and molars but just had a load of the primitive canines and premolars between them without any spaces at all. Just to cover the details a bit, they lived in North America and Eurasia but managed to spread to South America and became almost ubiquitous on land except for Antarctica, India (a continent at the time) and Australasia. The smaller species were Asian – one even lived in trees – and the larger North American. At the time, North America seems to have had very different fauna, since a few million years later our own ancestors the omomyids evolved on that continent. I envisage a continent covered in tropical rain forests.
Barylambda was a late Palaeocene ground sloth-like animal weighing two thirds of a tonne and apparently able to rear up on her hind legs, since she had a heavy tail.
Pantolambda was smaller at up to 178 kilogrammes but there was a smaller species of the same genus whose mass was only twenty-eight or lower. She was found in both North America and Eurasia and seems to have eaten soft plants in the summer and leaf litter and fungi in the winter, bearing in mind that she lived in the Arctic, which despite having what we would perceive as semi-tropical forests still had 24-hour daylight in the summer and completely nocturnal conditions in the winter, possibly for months on end, during which apparently loads of mushrooms grew. This particular fact about the Arctic in the early Cenozoic always does my head in: yes there were basically tropical rain forests inside the Arctic circle and yes they had twenty-four hours of darkness in the winter and permanent daylight in the summer.
Coryphodon was about two metres long and more common in North America though also present in Europe and the rest of Eurasia. They’re remarkable for having tiny brains. The body weighs up to seven hundred kilogrammes and the brain only ninety grammes, a ratio of nearly eight thousand to one. This compares to the human figure of about forty-five to one and the rhino’s of about five thousand, which is the same as a whale’s, and a bovine’s is about a thousand. This kind of brain size is quite extreme for a mammal and doesn’t compare even to contemporary or earlier such animals.
It seems that the chief means of defence offered by pantodonts was their sheer size compared to the predators, since it seems unlikely they were intelligent enough to outwit them and they couldn’t run, something I’ll get back to. Their chief mammalian threat was the mesonychids, as at this point the predatory artiodactyls and creodonts had yet to evolve. Ankalagon was an early mesonychid appearing soon after the K-T Event and was the size of a bear.
The possibility that the pantodonts were not placental mammals but were eutherian might provide extra information regarding their nature. First of all, today’s ungulates are precocial. That is, their young can stand and walk (or swim in the case of whales) almost immediately after they’re born, possibly because they may have to escape predators very early on. Human babies, by contrast, are altricial. We are helpless at birth and can’t possibly fend for ourselves for a very long time. Although for humans this relates directly to the way we use our intelligence and technology, many other mammals are also altricial, such as dogs and mice. Pantodonts, having less advanced placentae, may have been altricial too, and this is not a good combination with being potential prey living out in the open from birth. It seems unlikely they lived in burrows and in most cases they couldn’t have climbed trees, so they’d have to tend their young and prevent them from being picked off by mesonychids or cursorial crocodilians (dinosaurs in all but name really) to some extent, although presumably thick undergrowth helped. Maybe they had nests? Once artiodactyls had evolved, with their precocial young, they would’ve had a big advantage over them, hence their early extinction.
There may be another way of understanding this group corresponding to the ancestry and nature of other clades of mammals. Pantodonts were graviportal. That is, they moved as slowly as tortoises or sloths, and this last is crucial. Before sophisticated DNA sequencing and maybe other more accurate techniques, a lot of guesswork was involved in tracing the ancestry of species. In the case of placental mammals, it was thought for a long time that there was a group called the “insectivores” who were close to the ancestors of all placental mammals. It’s still possible this is true, but “insectivores” no longer exist. Tupaias, colugos, tenrecs and elephant shrews, for example, were all placed within this order as well as hedgehogs, moles and shrews. It turns out that elephant shrews are more closely related to actual elephants, tupaias and colugos are close to primates and also rodents and tenrecs, despite being almost indistinguishable from hedgehogs, actually have no connection to them and are almost as distantly related as they could be and still be placental mammals. Almost, and this is where it gets a bit more relevant.
The group of placental mammals least closely related to the others is the xenarthra, formerly known as the edentates or “toothless mammals”. This description is completely wrong as in fact the armadillos have more teeth than any other species of mammals. They’re apparently in three groups: armadillos, anteaters and sloths. Nowadays, armadillos are grouped separatedly from the other two, who are considered to belong to the same order, but the three still have much in common with each other, rather like rodents and lagomorphs have. Xenarthrans diverged from the rest of us placental mammals around a hundred million years ago, and of course since then they have been evolving just like the rest of us, but they also have unusual features compared to others. They have the lowest metabolic rate, no milk teeth, often no teeth at all, no colour vision, seem to have regulated their temperature by burrowing in the past, extra vertebral joints (lost in sloths) to stiffen the spine and aid burrowing, no enamel on their teeth and sloths have either more or fewer neck vertebrae than other mammals and several times the number of ribs at fifty-six.
Sloths are particularly unusual. They sleep most of the time, their claws relax in a grasping position meaning that when they die they may not fall from the branch they were living on, they’re capable of starving with a full stomach because their bodies may get too cold for their digestive enzymes to work, and have algae living on the side of their fur away from the Sun. Ground sloths in particular somewhat resemble Barylambda:
It’s thought that the very first mammals were not able to control their body temperatures internally, because the growth patterns in their teeth seem to indicate that they lived about as long as lizards of the same size. Monotremes also have quite labile body temperatures, marsupials somewhat so and xenarthrans also to some extent. I think, not rigorously or scientifically but I have a hunch, that pantodonts and probably other mammals at the time who were not closely related to any of the eutherian mammals around today, shared characteristics with sloths and that the other placental mammals have lost them.
Here, then, is a scenario: pantodonts were sloth-like. They moved extremely slowly, might have had algae growing on the side away from the equator and had quite variable body temperatures. Their metabolism was sufficiently slow that they wouldn’t be able to digest food below a certain temperature, although in the Eocene this probably didn’t matter because practically the whole planet was too hot to endanger them. They also gave birth to tiny, naked and helpless young after short pregnancies whom they tended away from predators as far as possible but weren’t very good at keeping them safe, and once the true ungulates came along they couldn’t compete and died out. They’re really quite unlike most of the mammals Europeans would be familiar with. Those are my thoughts on the subject, and they’re quite unscientific and involve quite a few leaps of logic, but we’re never going to know.
Most of the time when people think about prehistoric animals, they think of dinosaurs, giant dragonflies, sea monsters, mammoths, trilobites and various other species, and all of those are very interesting, but I don’t think many people think about pantodonts even though they were of record-breaking size at the time, managed to evolve very quickly just after the non-avian dinosaurs died and were the first browsing herbivores. Hence, as I said, they’re the Rosencrantz and Guildenstern of the mammal world and they’re excluded because we tend to tell certain stories which miss details out. Thus their significance is akin to me not going to Sheffield and not meeting anyone there whom I might otherwise have got to know and Regina Spektor’s imaginary first lover of Samson. Like her, (pre)history books forget about them and the “Bibles” of palaeontology don’t really mention them, but for millions of years they existed before they vanished without trace. In a way, they’re like the Goths. I make a point of mentioning people’s names to those who never met them but whom I used to know because I think their existence should be honoured. Likewise, I mentioned the pantodonts here.
A Box Of Chocolates 