The Botneheia Ichthyosaur

by Dr. Michael Maisch


1. Systematics

The specimen belongs to the Ichthyosauria (literally meaning ”fish-lizards”), a large group of marine reptiles that roamed the oceans for most of the Mesozoic. Within ichthyosaurs, the highly derived, externally dolphin-like forms of the Jurassic and Cretaceous like Ichthyosaurus and Stenopterygius are best known. However, in the Triassic there was a wide array of different, more basal ichthyosaurs, some of them less than one meter long, others being the largest marine reptiles ever found. It is among these more “primitive” and early ichthyosaurs that the new find from Svalbard finds its place.

As scientific investigations have just started, it is not yet possible to identify it to genus and species level. As no large ichthyosaurs have so far been described from the Middle Triassic of Svalbard, the probability that one is dealing with a genus and species new to science is quite high.

The specimen is certainly closely related to some of the large ichthyosaur genera of the Middle and Upper Triassic that have been found previously elsewhere in the world. Most famous of these is Shonisaurus. A real graveyard of these animals has been discovered in Nevada in the United States close to a small Wild West ghost town called Berlin. There, numeous specimens, some of them nearly 15 m long, of the species Shonisaurus popularis were discovered in Upper Triassic rocks –thus being somewhat younger than the Botneheia ichthyosaur. Even more spectacular is the recently described Shonisaurus sikkaniensis from British Columbia in Canada, the skull of which alone measured about 5 meters in length. It is the largest marine reptile ever discovered with a total length of 20-25 meters. Surprisingly, it has no teeth!

Another close relative of the Botneheia specimen may be Cymbospondylus, a very elongate animal externally similar to a legendary “sea-snake”. Specimens of this huge ichthyosaur which reached a total length of up to 15 meters have come to light in the Middle Triassic of Nevada and Switzerland and many other places. A fragmentary specimen was also described form the lowermost Upper Triassic of Svalbard in the 1980ies, but its attribution to the genus is somewhat doubtful because of its fragmentary state.

Until the new specimen gets a scientific name, some time will pass, as it has to be investigated in detail and compared to other large Triassic ichthyosaurs described previously by scientists from all over the world. Only then can it be decided whether it represents a genus already known, or something completely new, and we will then also know who its closest cousins were.

2. Length of the specimen

It is rather difficult to provide a reliable estimate on the total length of the Botneheia ichthyosaur. Whereas most Jurassic and Cretaceous ichthyosaurs looked very much alike in external morphology, body shape and proportions, diversity was much higher in the Triassic forms. There were rather compact and stout animals similar to the later forms, but also very elongate ones. As the Botneheia specimen is incomplete, we have no good idea of what its skull or the anterior portion of its body looked like. Most importantly, we have no reliable data on the number of vertebrae. The number of presacral vertebrae –those that are situated anterior to the pelvis- varies tremendously among the large Triassic ichthosaurs, from about 45 to more than 80, even in rather closely related forms. From what we have of the skeleton of the Botneheia ichthyosaur we can therefore roughly estimate a minimal and a maximal length, using either the lowest (about 45) or highest (about 80) number of presacral vertebrae known in comparable genera of which complete skeletons have been found. The truth should lie somewhere in between, although it can not be completely excluded that the number of presacral vertebrae was even lower or even higher than in the forms hitherto known. This latter possibility is, however, rather unlikely. If we use these assumptions, and if we also assume that the size of the skull relative to the rest of the body was similar to other known large Triassic forms like Cymbosponylus or Guizhouichthyosaurus, we can assume that the specimen, if complete, would have been about 10 m long at minimum and more than 12 m long at maximum.


3. Contemporaries and diet of the Botneheia ichthyosaur.

The Botneheia formation contains a fauna of invertebrates rich in individuals but rather poor in genera and species. This low diversity points to the fact that the environment did not offer favourable conditions to a large number of animals. Bottom waters and sediment were most or all of the time depleted in or even free of oxygen during the deposition of the Botneheia Formation. This were deadly conditions for most of the usual sea-floor dwellers, and accordingly we do not find their fossils. Only one genus of bivalve is very common: Daonella, which probably had a very special life style that allowed it to tolerate these conditions. Similar Daonella fossils have been found in other black shales that formed under oxygen-poor conditions elsewhere in the world during the Middle and Upper Triassic. These black shales include the famous fossil localities of Monte San Giorgio in Switzerland and Guizhou in China, were numerous marine reptiles have also been found.
Apart of Daonella, bottom-dwelling organisms are practically absent from the Botneheia formation. Instead, one finds a rich fauna of ammonoids and rare nautiloids. Ammonoids were nektonic animals, living in the upper part of the water column were there was a normal supply of oxygen. The oxygen-poor environment on the sea floor was therefore no problem for them, and accordingly they lived in great numbers in the Botneheia sea. Several ammonoid specimens were found in close association with the ichthyosaur, and also in the rock layers below and above it.
Fish are, in contrast to the ammonoids, almost absent. Except for a single jaw, no remains of them were found during the excavation. The question therefore arises: what did the Botneheia ichthyosaur, which was probably the largest predator in its time and place, eat (and we can assume that it was a predator, no herbivorous ichthyosaur has ever been found)?

Did it eat the Daonella bivalves and ammonoids? That would be a possibility. We do not know the skull of the animal and we therefore also do not know its teeth. If it was living on such organisms with a hard shell, one would assume that its teeth showed some adaptations to crushing such shells, being blunt, low and wide rather than needle- or blade-like and pointed. Although pointed teeth are widely distributed among ichthyosaurs, we know some Triassic forms with crushing teeth. One of them is Grippia longirostris, a small species that was discovered in the Lower Triassic of Svalbard. However, all other ichthyosaurs with crushing teeth are rather small as well, being 2 m in total length at maximum. If the Botneheia ichthyosaur had such a dentition, it would have been an exception to this rule.

The other possibility is that as the majority of large ichthyosaurs known it had a typical carnivore’s dentition and was feeding on fish, soft-bodied cephalopods and other, smaller marine reptiles. From some findings in the Triassic and Cretaceous and numerous ones in the Jurassic we know that ichthyosaurs fed on a variety of things, including all kinds of fish great and small, crocodiles, other ichthyosaurs, turtles, birds, sea-lilies (crinoids) and –most of all- non-ammonoid cephalopods. The hooklets that are positioned on the tentacles of these animals (called onychites by the scientists) have been found by the thousands in the stomachs of Triassic, Jurassic and Cretaceous ichthyosaurs. These fast-swimming predatory invertebrates were certainly not easy to catch, but nevertheless seem to have been the favourite ichthyosaur food through the ages. Whether this is also true for the Botneheia ichthyosaur we cannot possibly say, as we have no evidence of its fossilised stomach content. A find of one of its Lower Triassic relatives, probably belonging to a closely related genus, Merriamosaurus, has however been made on Svalbard which supports the idea of a cephalopod diet. In its stomach numerous cephalopod hooklets have been found, as it was recently described by French scientists.

4. Reproduction

How did ichthyosaurs reproduce? We know a lot about this, due to the extraordinary findings of pregnant ichthyosaur mothers with the skeletons of the unborn embryos still preserved in the body cavity that have been made since the 18th century at the famous Jurassic Holzmaden locality in Germany. These findings unequivocally demonstrate that, like mammals but totally unlike typical “reptiles”, ichthyosaurs did not lay eggs but gave birth to living young. They had to develop this kind of reproduction early in their history, because their entire skeleton was so strongly adapted to swimming that even the oldest and most primitive ichthyosaurs known were biomechanically totally incapable of moving on dry land. And as a lung-breathing reptile you must lay your eggs on dry land –as the sea-turtles are doing it today. If you laid them in water, the young would certainly die inside the eggshells.
We know for certain, that ichthyosaurs as old and even more primitive than the Botneheia ichthyosaur were already definitely viviparous. A pregnant female of the small and very basal ichthyosaur Mixosaurus form the Monte San Giorgio locality in Switzerland has clearly demonstrated this. Therefore, even though we have no direct evidence, we can safely assume that our Botneheia ichthyosaur did not hatch from an egg, as a small dinosaur would have done. Instead, it started its life as a small baby ichthyosaur born in the ocean by its mother.
We have no idea whether ichthyosaurs cared for their young, such as it is assumed for some dinosaurs, and as crocodiles still do it today. Ichthyosaurs had pretty large brains for reptiles, they were probably among the most clever reptiles that ever existed, but that must not necessarily mean that they had any kind of social behaviour. From the fossil record there is some slight evidence that at least a few ichthyosaur species might have been gregarious, living together in larger groups. But again, this is no direct evidence for parental care at all. Certainly a small ichthyosaur was a rather helpless creature in an ocean filled almost entirely with huge sea monsters the like of which is not found today. This must have been particularly true in the Jurassic and Cretaceous, when huge pliosaurs, marine crocodiles, bony fish and sharks, as well as other, larger ichthyosaurs were probably hunting the youngsters. And they could not swim as fast as the adults could. When a young ichthyosaur was born, its tailfin, the main organ of locomotion, was not fully developed. It did so only after a long time of growth, and just then they could reach the maximum speeds and escape their enemies. Before that, they were thus very easy prey. And ichthyosaurs did not have many babies as well. Usually there were only one or two, probably per year. It is therefore highly likely that at least the Jurassic and Cretaceous ichthyosaurs protected their young to a certain extent, simply because it is hardly conceivable how else the ichthyosaur populations could have survived. Whether this is also true for the Triassic forms, we will probably never know, but it can not be excluded that our Botneheia ichthyosaur reached its enormous size also because somebody took care for it when it was a juvenile.

5. Death

All living things die, sooner or later. Microorganisms that reproduce themselves by cell splitting potentially enjoy an eternal life, but the individual cells also die after some time. Even though the Botneheia ichthyosaur grew to an enormous size, being the most formidable predator in its environment with no competition or enemies –except from others of its species, parasites and microorganisms and probably attained an age of 20 or 30 years, it died eventually.
For what reason will probably remain a mystery forever. We can exclude, nevertheless, the possibility that it fell victim to another predator with a high degree of confidence. What we have of the skeleton is virtually complete and largely undisturbed. It has no visible injuries. Nobody bit it, nobody even fed on its carcass. And who in the Botneheia ocean should have attacked this huge animal? There simply was nothing larger or more dangerous that we know of. The ichthyosaur probably died unspectacularly from old age or disease. Very often it is the smallest of living beings –microorganisms like bacteria- who are the downfall of the giants, so maybe it was just a simple infection that brought an end to the life of the Triassic sea monster.
At any rate its carcass sank to the bottom of the sea in the end. It must have sunken so deep that the carcass did not rise again from the sea floor, a prerequisite for its complete preservation, because otherwise it would have floated and disintegrated bit by bit, also falling victim to scavengers of all kinds.
Instead it lay in a black, soupy, slimy, probably rather stinky mud in a zone of death without enough oxygen to sustain any life forms except for the occasional Daonella bivalve. It was therefore save from scavengers and not subject to any further destruction.
To preserve it that intact, it was however also necessary that there were no strong water currents at the sea floor and, particularly, that it was covered by sediment relatively fast, so that any further disturbance of the carcass or loss of bones was prevented. It was not buried instantly. There are some dislocations of bones, particularly the smaller and lighter bones of the paddles, the gastral ribs and haemapophyses. These show that some time passed before the skeleton was completely covered by sediment, but not enough time to destroy any vital part of it or to transport parts of it far away. After the skeleton was completely embedded it was only a matter of time –much time- until the stinky and slimy black mud around it consolidated and became the shales of the Botneheia formation, containing the remains of ammonoids, Daonella bivalves and a large ichthyosaur. Only after ages had passed the rock thus formed was exposed again by the uplifting of the former sea floor and the erosion of wind, ice and sea, so that eventually the skeleton was discovered and rescued by scientists. Its head and the front part of the body were, however, already gone at that time, completely destroyed beyond recognition. We will not know what they looked like until we find another, more complete specimen of the same species, so –at least for the time being- we can feel free to a certain extent to use our imagination.

6. How did it swim, was it fast or slow?

It is always difficult to estimate the speed of an extinct animal. We simply do not know the structure of its muscles, ligaments and sinews, of the cartilage covering the articulation sufaces of the bones, and many other points in its anatomy which are necessary to investigate before we can even attempt to create a reliable model. And even then we can only reconstruct it, usually. In ichthyosaurs, at least in some species, we know a little more than in most other extinct vertebrates. Particularly at the famous Holzmaden locality in Germany not only ichthyosaur skeletons have been preserved, but also fossilised soft tissues, including some specimens with their entire skin and body outline present. We know preservation of cartilage and even of muscle fibers in these specimens, so we have quite an unusually complete set of data.
Only from these specimens, the first of which was discovered at the end of the 19th century, do we know that ichthyosaurs had a fin on their back (dorsal fin), just as sharks and dolphins do. That fin is not supported by bones, so from the skeletons alone we would have never known about its presence. Not surprisingly, old reconstructions of ichthyosaurs that were done in the early 19th century show them without the dorsal fin.
The specimens from Holzmaden also showed that these Jurassic ichthyosaurs had a deep, sickle shaped, so-called semilunate tailfin, as today it is found only among the fastest of all swimming animals, like swordfish, tuna or mako-sharks. All these animals use their tail fin as the single means of propulsion under water when they are swimmig fast, and all show a very similar morphology -as do the dolphins and whales, with the major difference that their tail fin is horizontal, not vertical such as in the fish and ichthyosaurs. We call these animals “thunniform swimmers” (swimming more or less like a tuna-fish). From these and other observations and assumptions, American scientists recently concluded that these Jurassic ichthyosaurs were among the fastest swimming vertebrates ever. Certainly there was nothing faster in the Mesozoic oceans, something that may account for their immense evolutionary success.
In Triassic ichthyosaurs things are different, however. Our Botneheia ichthyosaur certainly did not have the sophisticated tailfin of its Jurassic relatives, nor did he have their torpedo-shaped super-streamlined body. Instead, it was a rather elongate, more snake-like animal with a very long tail in a way rather reminiscent of the tail of a crocodile than that of a shark. It is highly likely that this animal rather swam like a gigantic eel, with undulatory lateral movements of most of its body and particularly its very long and laterally flattened tail. The posterior portion of the tail was certainly slightly deflected downwards, creating additional lift during swimming. There may have been a low tailfin as well, increasing the propulsive force of the tail. The four large flippers that the Botneheia ichthyosaur had were use in steering and maneouvering. They also may have served as an additional means of propulsion when it was swimming slowly, maybe approaching its prey in an ambush situation. It was therefore certainly not as fast as its Jurassic relatives, but a capable and good swimmer nonetheless.
At any rate, the patterns of locomotion of our Botneheia ichthyosaur and its Triassic cousins and the more familiar and “sophisticated” Jurassic and Cretaceous forms were fundamentally different. All the ichthyosaurs that did not use the so-called “thunniform” mode of locomotion –i.e. the propulsion exclusively by the semilunate tailfin- went extinct by the end of the Triassic. Only the fast tuna-like swimmers survived and roamed the Jurassic and Cretaceous oceans for another 100 million years.
Was the eel-like, “anguilliform” or “axial unulatory” mode of locomotion that most Triassic ichthyosaurs used a bad one? Was it responsible for the extinction of the Botneheia ichthyosaur and its relatives? After the ichthyosaurs disappeared from the fossil record, another group of marine reptiles, basically giant marine lizards, called the mosasaurs took their chances. They used exactly the same pattern of locomotion that the Triassic ichthyosaurs had, with a tremendous success! Within a few million years they were found all across the globe from Sweden to Antarctica and from California to New Zealand. Thousands of specimens and more than one hundred different species have been discovered. So the most sophisticated thunniform swimmers, the last ichthyosaurs, died out and were replaced by a new group of marine reptiles using the same pattern of locomotion that their long extinct, “primitive” Triassic relatives had. Weird, isn’t it?
This teaches us that it is probably mostly not a matter of “good” or “bad” design that causes the extinction and survival of animals in earth’s history. The thunniform ichthyosaurs were not “superior” to the Botneheia ichthyosaur in any way (in fact they are a very rare and inconspicuous group in the Triassic), nor were they “inferior” to the mosasaurs. They just had good luck once and bad luck at another point. As perfect their design was to survive whatever caused the end-Triassic mass-extinction, during the mass extinction at the Cenomanian-Turonian boundary in the Upper Cretaceous it may have proved disastrous. Or maybe reasons for survival and extinction were completely different and had nothing to do with the pattern of locomotion at all, but were rather related to food preferences, modes and tempo of reproduction, the appearance of new enemies…there are actually hundreds of imaginable reasons and each one –or rather a combination of several- maybe true.