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:

When Is A Turtle Not A Turtle?

When it's a placodont!  All right, so they're technically not turtles.  Instead, they are a classic example of the fascinating phenomenon known as "convergent evolution," as we shall soon see!

Placodonts were a fascinating group of marine reptiles that lived during the Triassic Period in the Mesozoic Era, between around 235 and 200 million years ago (MYA), and thought to have a common ancestor with the long-necked plesiosaurs and the long-necked nothosaurs, all of which are in the large group called the saruopterygians.  As a group, the placodonts are sometimes referred to as "walrus turtles," due to their diet of molluscs and other shelled invertebrates and, of course, their general appearance.

Like the turtles and tortoises of today, the placodonts would not have been all that quick and nimble.  Their weight would have made them negatively buoyant, akin to the manatees and sea cows of today, meaning that they would have had no trouble swimming along the bottom of the ocean, snapping up molluscs and other shelled invertebrates, and using their large, flattened cheek and palatal teeth to crush them down.  It's also possible that they scraped algae off of marine rocks and swallowed it whole, letting it slowly digest in their massive guts!  Like modern sea turtles, the placodonts are thought to have been amphibious, spending most of  their time (sleeping, chillaxing, and other activities) on land, but dipping into the water to feed, akin to the extant marine iguana of the Galápagos Islands.

Although younger placodonts would have been especially vulnerable to predation from many different types of animals, many paleontologists puzzle over why the ponderous adult placodonts would have needed this armor, as there don't seem to be any marine predators capable of making a meal out of them that lived at the same time.  Of course, as we mentioned before, they probably spent much of their time on land and, as we also mentioned before, their awkward build would have left them particularly vulnerable to attack.  So to counter this, some of the placodonts started to evolve in a very turtle-like appearance. 

Placodus, the animal whose name is lent to the entire group, displays a single row of dermal ossifications above its neural spines down its back.  This dermal armor (a fancy way of saying "skin armor," in which the skin hardens into an armor like structure, as seen in the armadillo) would have helped to protect the animal from attack.  Earlier, more primitive genera, such as Paraplacodus, lack this dermal ossification.  However, other, more derived placodonts take this ossification of the dermals to a whole new level.

Remember Henodus, the first picture in this post? Henodus is one of those dermal armorers (I don't think that's actually a word) that took the ossification of the dermals to a whole new level.  Outwardly similar to the turtle shell, the placodont armor was composed of a number of polygonal ossicles, while the shells of turtles are composed of large plates.  Two other placodonts that were extremely well armored include Cyamodus, as well as the VERY turtle-looking creature, Placochelys. 

Like many other animals, the placodonts became extinct at the end of the Triassic Period.  Many groups did survive, however, and one of those groups that survived through to the Jurassic Period was actually the turtles!  220 MYA, the placodonts were sharing the seas with what would one day become the hard-shelled reptiles adored by so many people! 

This is the birthday post of Darlene Neher!  Happy birthday, Auntie Dar!  If you like what you are reading, please feel free to follow us here or via Facebook!  And remember, if you have a birthday coming up, just email me the date at cuyvaldar123946@gmail.com with the date and your favorite animal, and I will do my best to get a post in!