One big Triassic land predator: Erythrosuchus africanus

Reconstruction of Erythrosuchus africanus. CZJ posing as scale.

When it comes to ferocious prehistoric land carnivores, there is one group that never did get much attention outside paleontological circles and it is likely that you never heard of them: the erythrosuchids. This is a pity because, as far as we know, Erythrosuchus africanus was the largest land predator in South Africa during the Middle Triassic period. At an estimated total body length of 5 meters, it possessed a massive one meter long skull  equipped with numerous sharp conical teeth, superficially resembling that of big meat eating dinosaurs such as Tyrannosaurus rex. The head was thus disproportionately large with respect to the rest of the body. Unlike T-rex however,  Erythrosuchus was quadrupedal, stalking preys on its rather short limbs. The limbs had a semi-erect posture, making it a more efficient runner than most of its contemporaries. Early representations of Erythrosuchus show it with a deep tall snout but modern reconstructions based on the discovery of a complete skull, indicate that it had a more tapered face similar to other erythrosuchids.

The creature has been first described by Scottish paleontologist Robert Broom in 1905 from fragmentary and poorly preserved remains (on a side note, Broom became famous for his later discoveries of early hominid fossils including Paranthropus robustus). Erythrosuchus (the name means “Red crocodile”)  is today known from a number of specimens all relatively incomplete but enough to provide a good picture on what the animal may have looked like in real life. All the fossils were unearthed from the upper layers of the so called “Cynognathus assemblage zone”, Upper Beaufort Series, of the Karoo basin of South Africa and date from the Early Middle (Anisian) Triassic period  (~245 MYA). Erythrosuchus was therefore contemporary with the cynodonts Cynognathus, Diademodon and Trirachodon and the large plant-eating dicynodont Kannemeyeria, the latter representing its main meal in all probabilities. Other representatives of the Cynognathus assemblage zone fauna are the small theriodont Bauria, the agile archosauriforme Euparkeria, the early rhynchosaurs Howesia and Mesosuchus and the big capitosauroid amphibians such as Watsonisuchus.

The erythrosuchids represent the first radiation of large terrestrial carnivores within the Archosauriformes. They were not quite archosaurs (the higher clade that includes crocs, dinosaurs and birds) but very close relatives. Erythrosuchids appeared in the late Early Triassic period and survived to the end of the Middle Triassic period and had likely a worldwide distribution. Erythrosuchus was the largest among them. The most primitive erythrosuchid is the medium-sized long snouted Fugusuchus hejiapensis from the Heshankou formation (Olenekian) of the Shanxi province of China. Others representatives include Garjainia prima from the Yarenskian horizon (Olenekian) of the Orenburg region of Russia, Vjushkovia triplicostata and Uralosaurus magnus both from the Donguz Formation (Anisian) of the Orenburg region of Russia,   Shansisuchus shansisuchus and Guchengosuchus shiguaiensis, both from the upper Ermaying Formation (Anisian) of the Shanxi Province of China. Chalishevia cotburnata from the Bukobay Formation (Ladinian) of the Orenburg region of Russia, is the last known member of the group. It is conjectured that the erythrosuchids went extinct because they were outcompeted in their ecological niche by more efficient archosaurian predators such as the Rauisuchians.

References:

Cruickshank, A. R. I. (1978). The pes of Erythrosuchus africanus Broom. Zoological Journal of the Linnean Society, 62(2), 161-177.

Gower, D. J. (1997). The braincase of the early archosaurian reptile Erythrosuchus africanus. Journal of Zoology, 242(3), 557-576.

Gower, D. J. (2001). Possible postcranial pneumaticity in the last common ancestor of birds and crocodilians: evidence from Erythrosuchus and other Mesozoic archosaurs. Naturwissenschaften, 88(3), 119-122.

Parrish, J. M. (1992). Phylogeny of the Erythrosuchidae (Reptilia: Archosauriformes). Journal of Vertebrate Paleontology, 12(1), 93-102.

Were dinosaurs responsible for their own demise by initiating a runaway climate change?

Many scenarios have been put forward to explain the sudden disappearance in the fossil record of all non-avian dinosaurs, along with many other group of animals such as plesiosaurs, mosasaurs, ammonites and pterosaurs, at the very end of the Cretaceous period, 65 million years ago. Explanations such as starvation due to the rise of flowering plants that their stomach could not process, epidemic diseases of planetary proportion or loss of genetic diversity have long been discarded by scientific evidences. Today, most scientists adhere to the idea of a catastrophic event that caused global devastation of such magnitude many group of animals were unable to cope with. A large crater off the Yucatan peninsula (the Chicxulub crater) is believed to be the site of a massive asteroid/comet impact that wiped out the dinosaurs and 75% of life on Earth (Hildebrand et al., 1991). More recently, the Deccan traps theory, volcanic activity of unprecedented scale on the Indian subcontinent, gained ground when precise dating of the event shows it happened just before the so called K-Pg (Cretaceous-Paleogene) boundary (Schoene et al., 2015). A more exotic theory proposed dark matter in our galaxy as the prime culprit for the deed (Rampino, 2015).

However, in a new study that has just been published in the Journal of Supernatural Geological Studies, Dr. A. Zierste and co-workers came up with another plausible explanation (Zierste et al., 2015). It is well known that the Earth went through an episode of extreme “global warming” with high level of greenhouse gases during the Paleocene and Eocene periods of the Tertiary that followed the Cretaceous. The famous “Messel pit” in Germany with its exceptionally well preserved fossils of a rich tropical and subtropical fauna and flora is a vivid testimony of what the climate was at this high latitude. Zierste wondered about the mechanism that caused this greenhouse effect. Using a Tunable laser Spectrometer (TLS) similar to the one employed by the Mars Curiosity Mission (Webster et al., 2015), her team measured with high precision the isotopic ratio of light elements such as carbon and oxygen contained in sedimentary rocks from the end of the Cretaceous period to the beginning of the Eocene period. The data indicate a gradual increase in methane and carbon dioxide levels in the atmosphere that peaked right at the K-Pg boundary. But what is the origin of the high level of greenhouse gases? Zierste has a surprising answer to it: dinosaurs! These beasts were reaching gigantic proportions by the end of the Jurassic. The long-necked sauropods in particular were truly titanic, with some individuals attaining an estimated weight of 100 tons. To sustain their body mass, they have to eat tremendous amount of plants. Their stomachs were formidable fermentation chambers, producing colossal amount of methane gas that were naturally released in the Mesozoic atmosphere through gastric emanations. Methane is actually 20 times better at trapping heat than carbon dioxide. A 2006 United Nations' Food and Agricultural Organization report (http://www.fao.org/ag/magazine/0612sp1.htm ) has shown that the some 1.5 billion cows bred for milk and meat by the human population on Earth today have a non-negligible contribution to the current climate change, generating 18% more greenhouse gas than transport, in CO2 equivalent unit. Now imagine the amount of methane gas that dinosaurs could have produced. Bone histology studies have shown that the biggest dinosaurs lived to very old age, maybe 100 years and their population were most probably quite large, as they were social animals living in herds. It is difficult to estimate the total population of dinosaurs that lived on Earth at any moment of time during the Mesozoic but Zierste and her colleagues using a conservative number of about 1 billion sauropods and hadrosaurs calculated that they would have generated a staggering 20 billion metric tons of methane per year, enough to provoke a fast climate change and rapid rise of the Earth atmospheric temperature. In other words, dinosaurs perished because they induced a runaway global warming triggered by their own flatulence. Without the asteroid impact, that put an end to the continuous rise in temperature by provoking a global cooling, it is likely that the remaining 25% species of animals and plants would also have vanished and we would not be around to tell the tale.

References:

Avril Z., Peter S. G., Robert T. B., Ines L. P., Lambert J. B., Stewart M.T., Fernando E. N., Oviedo T. F., Oscar J., Lewis C. C. (2015)  Geochronological correlation of NH4 level with global atmospheric temperature at the Cretaceous/Paleogene boundary. J. of Supernatural Geological Studies, 90., 1-12.

Hildebrand, A. R., Penfield, G. T., Kring, D. A., Pilkington, M., Camargo, A., Jacobsen, S. B., & Boynton, W. V. (1991). Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico. Geology, 19(9), 867-871.

Rampino, M. R. (2015). Disc dark matter in the Galaxy and potential cycles of extraterrestrial impacts, mass extinctions and geological events. Monthly Notices of the Royal Astronomical Society, 448(2), 1816-1820.

Schoene, B., Samperton, K. M., Eddy, M. P., Keller, G., Adatte, T., Bowring, S. A., ... & Gertsch, B. (2015). U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science, 347(6218), 182-184.

Webster, C. R., Mahaffy, P. R., Atreya, S. K., Flesch, G. J., Mischna, M. A., Meslin, P. Y., ... & Lemmon, M. T. (2015). Mars methane detection and variability at Gale crater. Science, 347(6220), 415-417.