An Upper Triassic Ramble - part 2

A short paddle later
I’m pleased you mentioned those ‘crocodiles’ madam. They are quite small but thoroughly vicious. There are some larger, three metre ones around as well. Fortunately, these animals are far enough away, so there’s probably no reason for concern. Although, especially at this distance, they look more like crocodiles than anything else, they’re not actually even reptiles. These are amphibians called capitosaurs. They’re not fussy about what they eat and nor are the phytosaurs. I can see one of those heading in our direction. Phytosaurs are reptiles. They’re still more crocodile-like, but not closely related either.

There are a couple of obvious distinctions between phytosaurs and crocs. Perhaps the most significant is that these animals are due for extinction. Even at this distance, you’ll notice the phytosaur snout is narrower, as it cuts through the water. The bulk of the upper half is built from a different jaw bone. This is the premaxilla rather than the maxilla, should anybody have received an anatomy book for Christmas. As that specimen’s getting close enough for a further distinction to be visible, (the nostrils are towards the eyes rather than in proximity to the front of the mouth), I think we should wade towards the shore with more urgency. That one can’t even be a couple of metres in length and my stun gun would immobilize it instantly. At least, that’s what it says in the brochure.

Now look, sir, this isn’t a good time for a discussion on anatomy. You may have recently been on holiday in South Africa but I assure you, it isn’t a crocodile. This is the Triassic not the Transkei. It’s a phytosaur. Presently, most crocs are small things, and many run around on two legs. They’re typically found on land, and I think we should join them with haste. That thing’s catching us up. I hope there are batteries in this stun gun, because I didn’t actually check. Come along please.

All ashore
I’m sorry about any cuts and bruises, but we only had to scramble up a low cliff. If some know-all hadn’t started shouting about his holiday, we wouldn’t have needed to rush at all. As if a three-week bloody holiday makes him an expert! Anyway, somebody would’ve fared far worse in the water than a few cuts and bruises, and I have a personal preference as to whom. Pardon? Complain as loudly as you like. As I said: please feel free to ignore any instructions, but be it at your own risk. And if you’re going to walk off in a huff, sir, then that’s your privilege. However, you’re 215 million years from home, and you’ll find your golden credit cards don’t work here. Now please, either enjoy this once-in-a-lifetime view or at least stop moaning. You’re spoiling things for everybody else. Am I right, ladies and gentlemen? I thank you for the applause.

It’s a very warm day, but they generally are at this time of global history. As you can see, it’s a more arid landscape than the French Tourist Board would wish for. The plants are extremely un-Gallic. I can’t actually tell you what any of them are, because no fossils of terrestrial flora will be found in that bonebed. I can say what some aren’t. We’re far too early for most of our familiar vegetation. In our time, the majority of plants is provided by a group called angiosperms; flowering plants in the broadest sense. These include flowers, grasses, vegetables, fruit and many trees. It’s just as well we brought along a supply of coffee, wine and orange juice. None would otherwise have been available. I expect the landscape’s dominated by ferns, conifers, ginkgoes and other more exotic vegetation, but I’m not sure.

A sea view
Tropical storms can be very violent, but the surface of the sea is beautifully calm today. It’s a picture postcard view, with the gentle waves glistening in the sunlight. It’s perfect weather for fishing, and that’s what those pterosaurs are up to. These animals are some of the earliest representatives to have been spotted so far, and should the ornithologist in Bochum ever leap out at one, then his databank would require some drastic modifications, and his rubbish tip would be buried beneath a layer of baffled paleontologists. Hollywood would be disappointed at the size, but these pterosaurs are nevertheless attractive to watch as they swoop down to the water. There’s one trying its luck now. What a sight! Oh, it’s flown off empty handed. Never mind. There are plenty more fish in the sea, but there’s not a great variety of them. Although common, the vast majority of fish fossils represent the same species for some reason.

Only pterosaur teeth will be available here for researchers. As these are very similar to the contents of contemporary mouths found in Italy, they’ll be assigned to the same genus; Eudimorphodon. We know they enjoyed fishing because: a. the teeth have widely-spaced spikes which are excellent for keeping hold of slippery prey; b. we can see them at it.

If you’d care to look over towards those trees, there are smaller pterosaurs hunting on and just above the ground. They’re trying to eradicate the insects, although these animals aren’t particularly experienced operatives. Should any of your homes be blessed with infestations, then I’d ring the town hall rather than this lot. These are juvenile Eudimorphodon. The teeth differ in accordance with age, and that indicates differing diets for kids and adults. This is common enough in our own time. Young iguanas are insectivores, while mature animals are generally herbivores. Should you require more convincing, then gatecrash a five-year-old’s birthday party, but be prepared for the joys of jelly with ketchup.

As with the plants, I can’t tell you anything about the insects, as no remains of those will be known either. However, their presence is certain enough. There’s a large variety of insect eaters in the local fauna, and that points to a plentiful supply of food. Besides, you could have a picnic on the moon and wasps would still somehow track your jam sandwiches down. As it happens, evidence of wasps in the Triassic is debateable. You’d probably be better off eating here than lunar lunching, but the travelling costs are out of this world in comparison.

Local labourers
Madam, why are you taking snapshots in the wrong direction? The cute Eudimorphodon are towards the nondescript trees I took the trouble of mentioning. Yes, of course I can see those ‘huge monsters’. I’m not the one with defective eyesight and a diminished attention span. They’re only half-a-dozen of the local gardeners. There are thirty or forty baby pterosaurs, so it’d make more sense to watch them. Oh very well, but the things really aren’t of much interest. These are plant-eating dinosaurs called Plateosaurus. They aren’t even particularly big. The longest can’t quite manage seven metres. If you hang around for sixty million years, there’ll be sauropods four times that size.

Plateos are prosauropods, and they’ve spread all over the world. (Did I mention we’re still in the days of Pangaea? Most the landmasses on the planet happened to crash into each other about forty million years ago. What with that and the most catastrophic mass-extinction in history, it was a bad hair day for biodiversity. Still, Pangaea is fracturing, so things will become more varied as the Mesozoic progresses.)

Anyway, prosauropods provide the largest land animals on the planet, and they do some of the gardening. End of story. Oh, there are at least three more herbivorous dinos around who help out. And I suppose I might as well mention the dozen meat-eaters who try to be disruptive. These are dinosaurs and near-relatives. They’re generally a metre or two in length, although five metres has been reported from elsewhere in Europe. That’s not too surprising. Somebody has to keep Plateosaurus on its toes. If they were left totally unmolested, these prosauropods would get little exercise and their meat wouldn’t be worth eating. Actually, as it’ll be getting dark in an hour, I think we should head back to the craft. The caterers shoved one in the oven a few hours ago, so our Victorious Eucynodonts' Celebrationary Supper should nearly be ready by the time we arrive.

I said eucynodonts, sir. Is deafness also part of your impressively wide range of impairments? This is a Mesozoic Eucynodont Safari. It’s written on the cover of the tour guide. Perhaps somebody would help out by reading it to him, as I doubt he could manage something so onerous. It’d probably be best to read it very slowly though; Eu-cyn-o-don’t. Notice how ‘eu’ should be pronounced like ‘you’.

Of course I haven’t shown you any! They’re predominantly nocturnal. That means they come out when the sun has gone to bed. Given the rest of your defects, I doubt you’re fitted with infra-red vision. Now stop being disruptive or you can bloody well stay here. However, be it at your own risk. By the looks of you, there’s not enough meat for a decent meal, but some of the local wildlife are stupid enough to try anything, no matter how unappetising. This would be a very bad place to be stranded in.

That reminds me. I think this is a suitable time to pass round a hat. Should anybody wish to show their appreciation, then any loose change would be welcome. Of course, nobody should feel obliged to give anything, but we still have to wade back through water infested with big, ravenous amphibians and phytosaurs, and it pays to indulge me. There may be a connection between generosity and personal survival. Thank you, madam, but I think you accidentally left something in your purse, and that’s a very nice watch you’re wearing.

The Victorious Eucynodonts’ Celebrationary Supper
I must say, although Plateosaurus is a most uninteresting animal, the caterers know how to bring out the flavour. That was the most expensive meal you’re ever likely to have, and it didn’t taste too bad.

Right this moment, back on land, some truly fascinating animals are coming out to hunt. Their remains are the rare treasures in the Saint-Nicolas-de-Port trove. They will be known here only from tiny teeth. These animals are eucynodonts, ‘true dog teeth’, and so am I. Eucynodonts include mammals and their nearest non-mammalian relatives. Many of you may never have heard the word before today, but most should nonetheless be capable of appreciating it. For the sake of familiarity, let’s say it our loud together; Eu-cyn-o-donts. Well done.

Despite operating under the cloak of darkness and being very small, over twenty different species will be identified. Probably the majority are non-mammals, but it’s not entirely clear in all cases. Drawing a line between mammals and their most immediate relatives is literally a trivial pursuit. The demarcation is a faint shade of grey, and it actually gets placed in various positions.

One strict approach is to define Mammalia as being the most recent common ancestor of a duckbilled platypus, an echidna and myself, and all of its descendants. When so seen, then none of the animals scampering around nearby would qualify. I prefer to be more inclusive. According to my own unqualified, informal opinion, mammals began with the first critter who could suckle and replaced its teeth no more often than once. Of course, you can’t directly tell that from isolated molars, so it’s just as well fuller information is known from elsewhere. Slightly more generous definitions are also available. None of the local residents give a damn about whether they’re mammals or not, and I respect their views on this matter. It’s not important.

Bleak future
Nevertheless, according to any available definition, many of the eucynodonts here are small representatives of what used to be called ‘mammal-like reptiles’, and that phrase may sound familiar. But, as that lineage could actually have emerged before reptiles, (and the available evidence strongly suggests I had no reptilian ancestors), that name has been abandoned for synapsids. We eucynodonts are probably the only synapsids to have survived beyond about 225 million years before my birth. Previously, our relatives dominated the land. Here, at the end of the Triassic, we’re small creatures living in the shadows of dinosaur tyranny, and their dictatorship is growing ever more repressive. At least the diversity at Saint-Nicolas-de-Port indicates we have some kind of future, but it looks highly restricted and squeaky. We have to survive mainly on a diet of grubs, worms and insects. The richer pickings are reserved for the stomachs of our oppressors. Even should we eucynodonts unite and rise in rebellion, we wouldn’t stand a cat in hell’s chance. Of course, if we can hold out, things might somehow change in the future, but it’d probably require a miracle.

One miracle later
As we’ve just feasted our attentions on a Plateosaurus, the miraculous happened. At this point in time though, we’d have to wait 150 million years for it. However defined, at least two-thirds of mammalian history is Mesozoic. This is not widely appreciated.

Heroes of Saint-Nicolas-de-Port
I’m now going to give a brief introduction to the resident eucynodonts, starting with the non-mammals. Any suggestion of their body sizes will be wobbly guesses based on isolated teeth, and not necessarily appropriate comparisons with fuller material from elsewhere. Whether correct or not, if all you have are tiny molars, they definitely weren’t donated by something the size of a fox or a tiger.

Non-mammalian carnivores
The local fauna contains at least six genera (and eight species) of non-mammalian meat-eaters. One of them is the largest relevant resident. None of them are known to have survived beyond the Triassic. (A few non-mammalian insectivores will reach the Lower Jurassic, but they are members of a family not found here and quickly vanish from the fossil record.) A good explanation for these disappearances is provided by mammals. Their tastes must be very similar. A family of non-mammalian plant-eaters will fare better and make it to the Lower Cretaceous.

Our local giant is called Meurthodon. The molars have similarities with earlier fossils from South America. However, they’re a bit more mammal-like in that they have two roots. The division of those roots begins below the gum line. If it began at the gum line, the crown was somewhat more complex, and the uppers and lowers were properly aligned, then these teeth would be mammalian. (A bit of shelving at the sides for a few small cusps would’ve been beneficial, but Meurthodon doesn’t have that.) The size range of specimens is between 1.85 and 4.25 millimetres. Based on the largest, I’m prepared to guess the owner might grow to over 30 centimetres in length, and perhaps even 40. Meurthodon is possibly up to kitten-sized, and that’s our local giant. It’s the only eucynodont in the area which could have much of a chance, when it comes to making a meal of small vertebrates. I don’t know what prey it favours, but smaller nocturnal critters is a possibility that comes to mind.

The other non-mammalian meat-eaters can only be insectivores, and they presumably come in shrew to rat formats. The collection of molars includes specimens which are reminiscent of the basal mammal style, but they’re not quite near enough. The closest are three species of a genus called Tricuspes, and they’ve been referred to as mammals on some occasions. The distinctions are small but real. Tricuspes could be a very close relative of Mammalia. However, unless or until more substantial fossils are found, it wouldn’t be advisable to place large bets on that. What’s clear is these molars are broadly similar to the teeth I would expect to find in the mouths of my ancient ancestors. Expectations can’t always be relied upon.

Plant lovers
As well as the enthusiastic entomologists, our community also includes half-a-dozen botanists. Three of them are the most recent available evidence of animals called traversodonts. That family emerged by the start of the Middle Triassic and it prospered. The only continents where none have yet been found are Antarctica and Australasia. During the earliest part of the Upper Triassic, some traversodonts attained lengths of a couple of metres, and the family was a serious candidate for developing megaherbivores. As things turned out, they mostly disappeared in a wave of extinctions about 225 million years before I was born. The rise of herbivorous dinosaurs occurred at a similar time. These shrew-sized Europeans seem to be the last pipsqueaks of a once promising line. Even their closest friend call them dwarfs.

Among the more common of the local eucynodonts are three species of herbivores known as haramiyids. This group will reach the Jurassic, and their emergence could account for the extinction of the similarly sized dwarf traversodonts. The timing’s right. It’s uncertain as to quite what these animals are. Apart from some jaw and pieces of bone from Greenland, fossil evidence is restricted to teeth. These are so distinctive, that it’s not yet possible to pinpoint their wider relationships with certainty. It’s not even clear whether they can be fitted into Mammalia. Remains mostly come from Europe but some have turned up in Inner Mongolia. Haramiyid teeth will be fairly numerous in Lower Jurassic rock, but then become rarer. The line seems destined to run out in the Upper Jurassic of Tanzania. Haramiyid-like gnashers will be identified there in the late 20th century.

The star of the show

So far, ladies and gentlemen, the only eucynodonts we’ve actually seen have been derived forms known as humans. As this is a Mesozoic Eucynodont Safari that’s unfair but it’s not my fault. The animals here are small, nocturnal and only represented by isolated teeth. Given those factors, how could I show you a living specimen?

The answer’s obvious enough. I could cheat. While we were sinking our highly sophisticated choppers into that Plateosaurus, (traversodonts should’ve filled the ecological niche, so the usurper deserved to be eaten!), a couple of assistants dashed off to the Lower Jurassic of China. I’ve just had a signal that their mission was successful. I’m now going to walk over to that small curtain and show you what they brought back. Please, try not to cheer or clap too loudly. Our star isn’t used to the sounds of excited primates. I’m sweating and shaking with tension, and I’ve seen this before. I can well appreciate how the adrenalin must by racing in all of you. We’re all doubtlessly close to, if you’ll permit the comparison, orgasm. Yes madam, that’s the word I used. This sight promises to be as thrilling as the greatest sex you’ve ever had, but try not to shout out in joy and exaltation. Oh, you’ve never had… In your case, madam, that’s something which nobody would blame me for. We’ve spared no effort to provide you with this arousing climax, as you’ll surely appreciate from the details supplied with the supplementary bill.

Before I pull this drawstring, kindly shut up. This is a moment which demands the deepest reverence. I can’t introduce the earliest mammal. The diversity in the local fauna suggests it’s already been dead for a long time. However, I can show you a very close descendant. It has agreed to represent the first mammal. The teeth in this beauty match some from Saint-Nicholas-de-Port extremely closely. Ladies and gentlemen, I now present our stand in for the Big Mamma of all Mammalia!

Raising the curtain on Big Mamma
There she is! What d’you mean, where? She’s in the corner of the twilight simulating aquarium, hiding in that little tunnel. If you look very carefully, you can make out the tip of her tail. While we were ashore, I collected up a few grubs and insects in a matchbox. I’m going to let them run and wriggle around just by the entrance. That might entice her out.

It’s working. The tail’s been withdrawn, she’s turned around, and you can see her delightful little nose beginning to snuffle. She’s coming out to play. This is none other than Morganucodon. Look at that fine snout. The mighty skull reaches a length of 2.5 centimetres, and the beautiful body brings the count towards ten. Morganucodon is the size of a mouse. How lovely, she’s decided to attack one of the creepy crawlies. She’s swallowing it rapaciously. She may be hungry after the journey, but it’s mainly because she’s not all that good at chewing. Actually, she can chew food far more effectively than almost anything else that ever lived before, but there’s still plenty of scope for refinement.

Morganucodon means ‘Morgan’s tooth’, and the first fossils will be found in Lower Jurassic Glamorgan. These will be mostly jaws and teeth with other bits and pieces. Later, Triassic teeth will turn up in various European locations including here. I sent my assistants to China because a number of complete skulls will be recovered, and a further species will be identified in Arizona. As much of the landmass of the world is presently in one block, such a wide range isn’t too surprising. Indeed, close relatives will also reach South Africa and India.

Basal Mammalia
This animal has the most primitive molars in the mammalian repertoire. The lowers feature a straight line of three main cusps running along the centre from front to back, and the middle of them is by far the largest. It’s also got some neat shelving at the sides and extra small cusps. For the molars which have two roots (not all do) the separation begins at the gum line. The way the teeth are arranged is also important. Unlike in non-mammals, the uppers and lowers are directly aligned, (occlusion). That means they operate as a team rather than an assemblage of individuals. And that helps to explain why this animal can chew relatively effectively, (albeit not when compared to more derived mammals).

However, this also raises a couple of difficulties. If she kept replacing teeth, then the alignment would be severely disrupted. A tooth cannot usefully occlude with an empty gap. Plenty of jaws are available and none provide any evidence of multiple replacement. (Some signs would be expected from a reasonably wide sample.) Morganucodon has only two sets of dentition; milk and adult teeth. Furthermore, because the molars directly occlude, they bash against each other with regularity. This produces well-defined wear facets, which aren’t found on non-mammalian teeth. If it weren’t for strengthened enamel, the uppers and lowers would rapidly smash each other into ruins. As it happens, the enamel of Morganucodon is lousy. She deals with the problem by using a different strategy. She dies of starvation due to thoroughly wrecked molars. Actually, they usually get killed before that happens. If you’ve got a short life span, then the best enamel in the world would be of very limited help.

Another dental innovation is the specialisation of postcanine teeth into two distinct kinds. This animal has both molars and premolars, and that's a mammalian monopoly.

Take a look at those legs!
How dare you, sir? She doesn’t look weird. You’re just not used to it. Her legs are beautiful. They’re meant to stick out to the sides. That’s how they’re made. It might mean she runs in a jerky waddle, but she was far too fast for that worm, which is now being demolished and gulped down. At least, I think it was a worm. It’s beyond recognition. If we could just increase the size by about 50 times, Plateosaurus would be in severe trouble. In the modern world, should your tastes be for ferocity, than don’t waste time with lions and sharks. Go for small mammalian insectivores. They require plenty of fuel, have to kill frequently, and their victims can sometimes be bigger and heavily armoured. If a lone lion fails with 80% of its attacks, it’ll have more than enough to eat. A shrew can’t afford to be so unsuccessful. It needs three times its own bodyweight per day. James Dean was a slow coach when it came to living fast and dying young.

Jawing about ears
I’ve heard several people muttering about the ears. It’s true. She doesn’t appear to have any. The reality is that’s she’s got the bee’s knees when it comes to acoustics, but no sticky up ears. I’ve got three little bones for processing sound. Well, six to be accurate, as I’ve got a pair of ears. These bones are the stapes, malleus and incus.

There will now be a few funny words, but there’s no requirement to remember them. If anybody so wishes, they can be referred to subsequently for finding more information. My entire lower jaw is a single bone called the dentary. She’s got a few other bones still attached to it, but they’re very small. I keep my jaw connected to the skull with the help of an upper bone called the squamosal. ‘Morgan’s tooth’ has the same arrangement. However, she retains a vestigial second joint as well; the articular-quadrate. Those two bones are also used for listening. Later in evolutionary history, they’ll be pushed a bit to the side and become completely incorporated into the ear. They’ll be the malleus and incus. Something very similar happened to me. As I was an embryo at the time, I can’t truthfully claim to remember the experience. Her hearing may not be as well-developed as mine, but it’s high-tech for the age, and a damned sight better than some of you lot can manage.

Watching this beautiful mammal scamper around really is giving me an incredible feeling of orgasm, madam. How was it for you? Oh, sorry, I forgot. Wow. I think I’m about ready for a cigarette.

Post natal
As I’m sure you’ve gathered, I could extol the virtues of ‘Morgan’s tooth’ for a great many hours. My spirit is willing me to continue, but my flesh is weak and time is drawing on. Saint-Nicolas-de-Port is clearly not the birth place of Mammalia. Somewhat older fossils have been reported from other locations. A few possibly mammalian fossils have ages of 225 million years. (Note: possibly implies possibly not.) Even if we rudely ignore the enigmatic, plant-munching haramiyids, that still leaves at least another six species of mammal in this assemblage. That alone shows the first mammal must have appeared earlier, but an Upper Triassic birth date is probable. (The available evidence now leaves no room for serious doubt that all mammals are literal descendants of a single common ancestor.)

The rest of the gang Two of the other local mammals are close relatives of delicious Morganucodon. They’re variations on a similar theme. Another pair are harder to place. They could be forerunners of a group called docodonts. These animals will develop highly complex molars on very archaic jaws, and they’ll be most widespread during the Upper Jurassic.

The final couple are ferociously known as kuehneotherians, and are sometimes called symmetrodonts. According to one train of thought, Kuehneotherium (‘Kuehne’s beast’) and Co give rise to all living mammals with the exceptions of the platypus and echidnas. The evidence for this is less than overwhelming. There’s a significantly different arrangement of the three main cusps on the lower molars, and it enhanced the efficiency. However, as it’s a relatively simple adjustment, a similar change could happen on several occasions. Nevertheless, Kuehneotherium teeth are more similar to those of most later mammals, than is the case for Morganucodon.

I mentioned a central line of three main cusps, and it’s not difficult to illustrate; x X x. If the middle cusp was pushed towards the side of the molar, (up or down in that depiction), then the three would form a triangle. A triangulated blade happens to be a more effective cutter than a straight one. You get more cut per bite. Most subsequent mammals, (and virtually all our modern mammals), either have this triangulated pattern in one form or another, or are descended from animals who possessed it. As the apex of the triangle is always on the external side of the tooth, (as in Kuehneotherium), this characteristic must be present in their most recent common ancestor. It cannot have arisen independently in each lineage.

The final question
It’s amazing what can be found in or beneath a load of rubbish. If you’ve followed half of that, you’ve got the basis of a reasonable introduction to early Mesozoic mammalian evolution. Before we return to the future, one important question requires an answer. Which of you is going to do the washing up?

Back to the Introduction

The author, and a few links

Links
More information on Mesozoic mammals and their closest relatives can be found at: Mammal Shorts .
This page offers a few highly-accessible articled on mammals and relatives.

Further eucynodont fossil sites are explored at:
Mesozoic Eucynodonts, Location Summaries
These articles are written in various styles, and they include a less humorous summary of Saint-Nicolas-de-Port with a listing of the eucynodont species.

Mesozoic Eucynodonts, an internet directory .
It's an extensive project, and some parts are likely to be challenging for the uninitiated. However, baffling words can be looked up or ignored. This has recently been recommended as suitable further reading for students in a standard university textbook, so it can't be too bad.

Humorous assaults on sense and understanding can be experienced at:
Dykesian Humour
Some is slightly off track while most is in hitherto unexplored territory.

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