Giant dicynodont from the Triassic of Poland

800px-Dicynodont_from_PolandDB

Illustration by Dmitry Bogdanov under the CC BY 3.0 License: source

The giants from the Triassic of Poland

The robust animal in the picture calls attention as the youngest, in the sense of the geologic age, and also the largest member of dicynodonts. The dicynodonts constituted one of the branches of the mammal-like reptiles, which the ancestors of mammals (and hence the remote ancestors of humans) also belonged to. Shortly before the disappearance of the dicynodonts by the late Late Triassic, there had evolved some gigantic forms as the species discovered at the Lisowice site in Poland.

During the last 10 years, the Lisowice site has yielded lots of interesting findings, the most famous of which are two giants: (1) An unnamed yet, robust, 5–6 meters long dicynodont was the biggest known herbivore of its time. (2) The carnivorous dinosaur Smok wawelski, of a comparable length of 5–6 meters, was the largest terrestrial predator of its epoch too. The Lisowice site presents an ecosystem of the Norian or Rhaetian, the Late Triassic, dated back to around 208 million years ago. The epoch of the mammal-like reptiles was about to be finished, leaving nevertheless the legacy of the first mammals, whereas the dinosaurs had recently begun to proliferate.

The giant dicynodont has left for paleontologists its bones, footprints, and scats, which still are being studied. Now, let’s make a preliminary reconstruction of that animal and its habits in the environment of the Triassic of Lisowice.

Ecological niche of the dicynodont

In 2011, during my visit to the site, the paleontologist Grzegorz Niedźwiedzki showed me numerous and enigmatic, oval, dark gray structures, mostly below 10 cm in length. The finding appeared to be exciting as we were talking about possible coprolites, it means fossilized feces of the dicynodont. Herbivore coprolites (or their descriptions) are exceptionally rare on a world scale, but first and foremost these fossils constitute an invaluable source of information about the diet and the physiology of extinct animals whose bone remains we unearth. Three years later came a preliminary publication on this material, whose I’m the first author in collaboration with Krzysztof Owocki and Grzegorz Niedźwiedzki.

dicynodont-coprolite-Lisowice

Although the putative coprolites contain organic matter, in the macroscopic view most of them reveal very few plant remains. The herbivorous diet of their producer was corroborated by analyses of the isotopes of carbon (δ13C) and nitrogen (δ15N). The coprolites enclose several types of pollen and also tissues of gymnosperms. There are also some very rare specimens of another type that are replete with wood fragments.

Sedimentological analyses, it means the study of the deposited sediments, as well as the geochemical analyses, suggest that the Lisowice site represented an environment comparable to the wetlands of the Everglades, Florida. The lack of woody plant elements in the vast majority of the coprolites of the giant dicynodont might be explained simply by the consumption of soft plants.

Now, let’s compare the dicynodont to the hippo. Although the hippopotamuses consume soft aquatic plants, this food resource is insufficient for these sizable animals. At night, the hippos leave the water pools to graze on grasses, but the grasses hadn’t yet evolved in the Triassic. Here, the rare wood-rich coprolites appear interesting. In 2007, Karen Chin described wood-rich coprolites produced by the herbivorous dinosaur Maiasaura from the Cretaceous of Montana. Although it would seem a weird custom in modern animals, Karen Chin suggested that the coprolite producers intentionally ingested rotted, partially decomposed wood and noticed the lack of grasses in the ecosystems of the Cretaceous. The rotting wood might be easily accessible in the wetlands of Lisowice.

Dicynodont coprolites are fairly numerous at the Lisowice site and it’s not ruled out that the dicynodont lived in herds, although scats tend to be abundant around sources of drinking water. In 2013, there were described copious accumulations of dicynodont coprolites from the Triassic of Argentina. The team of researchers led by Lucas Fiorelli suggested that the dungs were made in communal latrines, just as some modern mammals do it, in particular large herbivores. The hippopotamuses form small herds too.

Physiology of the dicynodont

Below, I list the titles of several of the numerous papers of German physiologists that constitute a source of a scientific inspiration for me and allowed a preliminary draft of the physiology of the dicynodont from Lisowice in the publication of 2014. On my blog, in various occasions I will highlight the significance of fossil feces for the understanding of the physiology of extinct animal groups.

To say something about the physiology of the dicynodont, firstly we note that modern reptiles are characterized by a long retention of food in the gastrointestinal tract, i.e. by a slow metabolism. On the other hand, the mammals used to initially triturate the food in the mouth and then it passes rapidly through the gastrointestinal tract. The mammalian groups vary between each other in the digestive strategy too. To eat more not always means to gain more. With the increase of consumption, accelerates the passage of the ingesta through the gastrointestinal tract as well, resulting in a worse digestion. For example, the hippo is capable to consume 45–50 kg of forage a day (I mean a dry matter). Each additional kilogram would paradoxically cause an energetic loss and no longer a gain, so that the hippopotamuses spend only 30% of a day foraging. This phenomenon is minimized in the elephants, which spend 75% of a day foraging.

However, to eat more involves to be less choosy and to ingest foodstuffs of a lower quality. Apart from the mentioned exceptions, the food of the dicynodont from Lisowice used to be non-fibrous and hence it seems that it ate little. It’s important to note that the dicynodont was toothless. In modern herbivorous mammals a better mastication of food allows to increase the total consumption. It can be observed via juxtaposition of different groups of mammals, or mammals with reptiles. We conclude that the dicynodont consumed relatively small amounts of forage and then it was retained for a long time in the gastrointestinal tract. Thus, in this mammal-like reptile we can see a strategy more typical of reptiles than mammals, yet it supports the comparison to the hippopotamus, which is an animal of a low-energy lifestyle.

The coprolites of the dicynodont from Lisowice contain a good deal of quartz grains. So-called gastroliths are hard objects missing a nutritional value that are found in the gastrointestinal tract. It’s very common to highlight the role of gastroliths in the crumbling of food particles in the stomach of some animals. However, such a mechanism seems unsubstantiated in the case of the dicynodont from Lisowice. The mineral grains in the coprolites are rather small and could be swallowed accidentally in large amounts in the wetlands with forage or turbid water. The amounts of sand and small gravel found in the stomachs of hippopotamuses are astonishing, sometimes reaching one third of the weight of their (wet) content.

Finally, we can note that the increase of the body size can serve as a strategy allowing a prolonged food retention in the gastrointestinal tract and a better digestion. The body size of dicynodonts was increasing across the Triassic, and the latest of their members, it is the dicynodont from Lisowice, was a real giant. A super strong digestion of a weak food might explain in general the high fragmentation of the plant remains in the coprolites of the dicynodont (although in part it was caused by destructive processes when the fresh dung was turned into a rock). In mammals, after an initial mastication the ingested plant tissues do not reduce in size significantly during the passage through the gastrointestinal tract. In modern herbivorous reptiles, which are characterized by a much longer digestion, the ingested plant tissues do indeed get crumbled due to the digestive processes. In spite of such a reduction, the residues in the feces of reptiles on average are still of larger dimensions than in feces of herbivorous mammals (of a comparable body mass). Today’s reptiles, as some lizards, are however very small animals and none of them can be compared to the gigantic dicynodont from Lisowice.

As it was noted by the team of Grzegorz Niedźwiedzki in 2011, meanwhile the body size of dicynodonts was increasing during their evolution, the predators were growing too. Tooth marks on the bones of the dicynodont moreover suggest that it was under the pressure of the mentioned carnivorous dinosaur Smok wawelski. It’s very interesting the way the physiological innovations, new feeding strategies, and the expansion into new ecological niches, fitted into the race between herbivores and predators.

Piotr Bajdek

References

Bajdek, P., Owocki, K., and Niedźwiedzki, G. 2014. Putative dicynodont coprolites from the Upper Triassic of Poland. Palaeogeography, Palaeoclimatology, Palaeoecology 411: 1–17. doi: 10.1016/j.palaeo.2014.06.013

Chin, K. 2007. The paleobiological implications of herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana: why Eat Wood? Palaios 22: 554–566. doi: 10.2110/palo.2006.p06-087r

Clauss, M., Streich, W.J., Schwarm, A., Ortmann, S., and Hummel, J. 2007. The relationship of food intake and ingesta passage predicts feeding ecology in two different megaherbivore groups. Oikos 116: 209–216. doi: 10.1111/j.2006.0030-1299.15461.x

Dzik, J., Sulej, T., and Niedźwiedzki, G. 2008. A dicynodont-theropod association in the latest Triassic of Poland. Acta Palaeontologica Polonica 53 (4): 733–738. doi: 10.4202/app.2008.0415

Fiorelli, L.E., Ezcurra, M.D., Hechenleitner, E.M., Argañaraz, E., Taborda, J.R.A., Trotteyn, M.J., Belén von Baczko, M., and Desojo, J.B. 2013. The oldest known communal latrines provide evidence of gregarism in Triassic megaherbivores. Scientific Reports 3, 3348. doi: 10.1038/srep03348

Fritz, J., Hummel, J., Kienzle, E., Streich, W.J., and Clauss, M. 2010. To chew or not to chew: fecal particle size in herbivorous reptiles and mammals. J. Exp. Zool. A Ecol. Genet. Physiol. 313A (9): 579–586.

Martin, R.B. 2005. Transboundary Species Project. Background Study: Hippopotamus. Namibia Nature Foundation, Windhoek.

Niedźwiedzki, G., Gorzelak, P., and Sulej, T. 2011. Bite traces on dicynodont bones and the early evolution of large terrestrial predators. Lethaia 44: 87–92. doi: 10.1111/j.1502-3931.2010.00227.x

Niedźwiedzki, G., Sulej, T., and Dzik, J. 2012. A large predatory archosaur from the Late Triassic of Poland. Acta Palaeontologica Polonica 57 (2): 267–276. doi: 10.4202/app.2010.0045

Schwarm, A., Ortmann, S., Wolf, C., Streich, W.J., and Clauss, M. 2009. More efficient mastication allows increasing intake without compromising digestibility or necessitating a larger gut: comparative feeding trials in banteng (Bos javanicus) and pygmy hippopotamus (Hexaprotodon liberiensis). Comp. Biochem. Physiol. A 152 (4): 504–512.

Wings, O., Hatt, J.M., Schwarm, A., and Clauss, M. 2008. Gastroliths in a pygmy hippopotamus (Hexaprotodon liberiensis Morton 1844) (Mammalia, Hippopotamidae). Senckenbergiana biologica 88 (2): 345–348.
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