240 MYA: Messing Around in the Mid-Triassic

People tend to think of the dinosaurs filling the dominant terrestrial ecological niches during the entirety of the Mesozoic Era, from the Early Triassic all the way to the Late Cretaceous.  This is an oversimplification, however, as the dinosaurs didn't really evolve until the Mid or Late Triassic, and still up against competition from other groups of animals until the Early Jurassic.  Today, we are going to travel back in time 240 MY, back to the Middle Triassic Period.  This slice of time is approximately 10 MY after the mysterious Permian Extinction, and is about 10-15 MY before the first undisputed dinosaurs start showing up.  We are in a time when many of the animals that lived on the land and swam in the seas looked similar to life that is more familiar to us, but much of it was distinctly different.

All of the Earth's continents were united in the supercontinent Pangaea, surrounded by the super-ocean Panthalassa.  The Tethys Sea was nestled into what would one day become the somewhat smaller supercontinents Laurasia (North America, Europe, and Asia) and Gondwana (pretty much all the rest).  Warmer conditions prevailed, and the poles were ice free all year round.  Although the coasts seemed to be more hospitable to life, the center of Pangaea was not quite as welcoming, receiving little rain and remaining fairly arid.

There are several important sites around the world that preserve fossils from this time period.  Let's start in the ocean and work our way onto the land, starting with Monte San Giorgio.  This site along the border between Switzerland and Italy gives us insight into the ecosystem that flourished beneath the waves of the Tethys Sea.

Sauropterygian reptiles such as the ten-foot long Ceresiosaurus cruised around, likely hunting smaller sauropterygians such as Neusticosaurus.  These reptiles resembled the more famous Nothosaurus and the later plesiosaurs, with their four limbs greatly resembling paddles, all of approximately equal length.

The dolphin-like ichthyosaurs such as Mixosaurus and Besanosaurus would have zoomed around, feeding on faster prey such as squid and fish.  Mixosaurus was pretty much your stereotypical ichthyosaur, but Besanosaurus was a bit odd-looking, with all four fins/limbs being fairly close to equal in length, unlike the shortened hind flippers that is more commonly seen in ichthyosaurs.  Besanosaurus also seems to not have had a dorsal fin.

The giraffe-like protorosaur Tanystropheus also probably hunted fish and squid, using its extraordinarily long neck to ambush unwary prey items, sneaking up on them while the rest of the animal was still four or five feet away!

A drawing of the protorosaur Tanystropheus by the talented young artist Sam Lippincott!  Photo Credit: Sam Lippincott

The turtle-like placodonts like Paraplacodus and Cyamodus possessed large, flat teeth perfect for crushing the shells of molluscs and crustaceans.  The teeth of these placodonts are similar to the molars that you can see in the mouth of the walrus, a marine mammal that has a diet fairly close to the placodonts of 240 MYA.

Thalattosaurs like Askeptosaurus also probably fed on molluscs and crustaceans, and likely fish as well.  Askeptosaurus had a long snout, and superficially resembled animals like Ceresiosaurus and Nothosaurus.  In the picture below, the snout is tucked towards the animals left armpit, almost like it's trying to figure out whether Triassic animals can get B.O.

Several terrestrial reptiles have been discovered at Monte San Giorgio as well, such as the rauisuchian Ticinosuchus and another protorosaur like Tanystropehus (albeit one with a much shorter neck), Macrocnemus.  We'll talk more about the terrestrial ecosystems of the Mid-Triassic later, with more talk of animals like Rauisuchians!  Check back for our next post, featuring the French site Grès à Voltzia!

Lugano on Dwellable

Works Cited:



Bottjer, D. J. (2002). Exceptional Fossil Preservation: A Unique View on the Evolution of Marine Life. New York: Columbia University Press.

Braithwaite, C. J., & Zedef, V. Hydromagnesite Stromatolites and Sediments in an Alkaline Lake, Salda Golu, Turkey. Journal of Sedimentary Research, 66. Retrieved June 20, 2014, from http://jsedres.geoscienceworld.org/content/66/5/991.abstract

Carroll, R. L. (1988). Vertebrate paleontology and evolution. New York, N.Y.: W.H. Freeman and Company.

Fiorelli, Lucas E., Martín D. Ezcurra, E. Martín Hechenleitner, Eloisa Argañaraz, Jeremías R. A. Taborda, M. Jimena Trotteyn, M. Belén Von Baczko, and Julia B. Desojo. The oldest known communal latrines provide evidence of gregarism in Triassic megaherbivores. Scientific Reports. Retrieved June 21, 2014, from http://www.nature.com/srep/2013/131128/srep03348/full/srep03348.html#ref8

Hammer, WR., 1990: Thrinaxodon from Graphite Peak, central Transantarctic Mountains, Antarctica. Antarctic Journal of the United States, 255: 37-38

Lautenschlager, S., & Desojo, J. B. Reassessment of the Middle Triassic Rauisuchian Archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus. Paläontologische Zeitschrift. Retrieved June 20, 2014, from http://www.researchgate.net/publication/225706328_Reassessment_of_the_Middle_Triassic_rauisuchian_archosaurs_Ticinosuchus_ferox_and_Stagonosuchus_nyassicus

Mickelson, D. L. (2014, June 6). Triassic Tracks in the Moenkopi Formation. National Parks Service. Retrieved June 20, 2014, from http://www.nps.gov/care/naturescience/triassictrack.htm

Morales, M. Terrestrial Fauna and Flora from the Triassic Moenkopi Formation of the Southwestern United States. Journal of the Arizona-Nevada Academy of Science, 22. Retrieved June 20, 2014, from http://www.jstor.org/discover/10.2307/40024380?uid=3739568&uid=2&uid=4&uid=3739256&sid=21104182410797

Nesbitt, S. J. Arizonasaurus and Its Implications for Archosaur Divergence. Biological Sciences, 270. Retrieved June 20, 2014, from http://rspb.royalsocietypublishing.org/content/270/Suppl_2/S234.abstract

Nesbitt, S. J. Osteology of the Middle Triassic Pseudosuchian Archosaur Arizonasaurus babbitti. Historical Biology: An International Journal of Paleobiology, 17. Retrieved June 20, 2014, from http://www.tandfonline.com/doi/abs/10.1080/08912960500476499#.U6Ti2ZRdV1-

Nesbitt, S. J., Barrett, P. M., Werning, S., Sidor, C. A., & Charig, A. J. The Oldest Dinosaur? A Middle Triassic Dinosauriform from Tanzania. Biology Letters, 9. Retrieved June 20, 2014, from http://rsbl.royalsocietypublishing.org/content/9/1/20120949.abstract

Owen, D., & Pemberton, D. (2005). Tasmanian devil: a unique and threatened animal. Crows Nest, N.S.W.: Allen & Unwin.

Power, I. M., S. A. Wilson, G. M. Dipple, and G. Southam. Modern carbonate microbialites from an asbestos open pit pond, Yukon, Canada. Geobiology, 9. Retrieved June 21, 2014, from http://onlinelibrary.wiley.com/doi/10.1111/j.1472-4669.2010.00265.x/abstract

Reptiles. (n.d.). Monte San Giorgio. Retrieved June 21, 2014, from http://www.montesangiorgio.org/en/Monte-San-Giorgio/I-fossili/I-rettili.html

Switek, B. (2008, April 1). Heterodonty where you least expect it. Laelaps. Retrieved June 21, 2014, from http://scienceblogs.com/laelaps/2008/04/01/heterodont-archosaurs/