Extinct Animals of the Cambrian to the Cretaceous!

This will be a limited edition 11x17 print exclusively for sale at spx​ this year!

I love extinct animals, especially lesser-known and non-dinosaur ones. So here are some critters from the Paleozoic through the Mesozoic. Don’t take the period designations too literally, it’s more of a “pretty much around this time” thing, since I couldn’t fit all of them exactly where they should be, scientifically. I’d love to do a sister-image to this with the Cenozoic era!

Here’s a list of the creatures featured!
Cambrian Period






Early Triassic

Middle Triassic

Late Triassic

Early Jurassic

Late Jurassic

Early Cretaceous

Late Cretaceous


Drawing by Mick Ellison of the American Museum of Natural History, NYC. 

When: Early Cretaceous (~125 million years) 

Where: Liaoning, China

What: Mei is a paravian dinosaur. Paraves is the clade comprised of birds and two families of non-avian dinsaurs; Troodontidae and Dromaeosauridae. As Mei is a fairly basal member of the troodontids, it is not very far removed from the common ancestor of all paravians. Its bird-like heritage can be easily seen in this extraordinary articulated fossil shown above. This specimen was found in a sleeping pose, which is very much like the resting posture of many modern birds, with the legs folded underneath the body and the head folded back and resting on the shoulder.  It is this pose that gives the taxon its full name:  Mei long, which translates to ‘sleeping dragon’. This animal is a sub-adult, determined via the ends of its bones not yet being fused, and would be roughly 21 inches (~53 cm) long, if it was not curled up as it is.  

 The find of a basal troodontid in this pose gives us far more information than just when the sleeping posture was adapted by this clade. It has been determined that modern birds commonly sleep like this to preserve their body heat, covering up the areas that are most prone to radiating heat. If Mei long  and its kin were not ‘warm blooded’ than there would be no benefit to sleeping in this pose. Thus, this provides another compelling bit of evidence that the ‘warm bloodedness’ of modern birds was present in their mesozoic non-avian relatives. 


Quetzalcoatlus - the largest pterosaur 

Reconstructions by Mark Witton. 

When: Late Cretaceous (68-65 million years ago)

Where: North America

What: Quetzalcoatlus is a gigantic pterosaur. Just how gigantic it was has been the subject of some debate, as no 100% complete specimen has been found. While the first estimates put its wingspan at up to 50 feet (16 meters) this has been reduced to 36 feet (11 meters) in the latest studies. The reason for this disparity is due to allometry - the physical properties of bones require that as an animal gets larger its skeletal structure is not just that of a smaller animal made larger. Thus the wing bones of Quetzalcoatlus were relatively thicker than that of a smaller species, and while this was taken into account in the first estimates, it took a better understanding of pterosaur evolution in general for a refined estimate to be generated. 

This large size brings with it another debate: could Quetzalcoatlus fly? The answer is yes, this pterosaur sailed over prehistoric Texas. A big mystery was how Quetzalcoatlus could take off, and recent work by functional morphologists has provided a solution to this puzzle. Pterosaurs differed from all other flying vertebrates in that they retained the majority of the digits on their hand outside of the wing itself; this not only allowed these fingers to be used to manipulate their environment, but was critical for terrestrial locomotion. Quetzalcoatlus was quadrupedal on the ground, like all other pterosaurs, but it had a specially developed system of ligaments and tendons in its wrist joint that allowed it to ‘spring’ up and take flight.  This can be seen in this video.  

Another, more minor, debate is what did Quetzalcoatlus eat? Most pterosaurs are closely associated with large bodies of water and have a fish based diet - but all Quetzalcoatlus remains have been found hundres of miles from ancient shorelines. This, combined with morphology of the skull, has lead to the conclusion that these giants instead fed on smaller vertebrate that they would capture with their large beaks, such as the baby sauropod not having a good day in one of the reconstructions above. 


Les Ptérodactyles, reptiles volants; Les Diplodocus, reptiles terrestres; Les Ichthyosaures, reptiles marins, Mathurin Méheut, 1940s (murals from the Geological Institute of Rennes)

Coiled in stone, bones once sheathed in muscles testify vivid moments now lost. Sinews and skin, fins and wings, membranes and tendons enveloped them—once parts of breathing things that fed and swam and flew and sang songs I will never hear.

Now the skeletons lie flattened, pressed between eons of geologic layers—sediments made of silt and years, piling like mattresses made to hide a princess’ pea, a bed made of rock with sandstone blankets and sheets of shale hiding fish-lizards, pterodactyls, and the Diplodocus.

Here’s a slightly older illustration that I never put on Tumblr, and my blog is full of feathers and dinosaurs, so how about some pterosaurs and pycnofibers for a change instead?

This is a trio of Pteranodon longiceps, two males and a female. It’s a modification/cropping of a larger illustration, a dromaeosaurid digging scenario. 



Mounted specimen on display at Harvard Museum of Natural History

Reconstruction by Jaime Chirinos

When: Cretaceous (~ 125 - 99 million years ago)

Where: Australia

What: Kronosaurus is an australian plesiosaur. Yes, it is a plesiosaur even though it lacks the long neck that many people associated with the group. Plesiosauria is roughly divided into two groups;  Plesiosauroidea - the long necked forms and Pliosauroidea - the short necked forms. Kronosaurus is an example of the latter clade, and shows many of the defining features of this group - such as an enormous head with massive jaws, a short neck, and a relatively short tail- the opposite in many ways of their cousins the plesiosauroids. This australian sea monster was one of the largest of its clade, with estimates of up to 33 feet long (~10 meters). Its teeth reach almost 5 inches (~12 cm ) long in crown length - the part above the gumline. The total tooth would have been over double in size. The large size of its teeth, combined with distinct shape and the lack of clear cutting surfaces also  for their easy identification if they are found as isolated material. 

The Kronosaurus specimen seen above was found in on private property in central Queensland, Australia in the 1920s. A crew from Harvard was shown where the specimen was weathering out, and set about excavating the fossil. After years of work, the specimen was boxed up into over 80 crates, weighing in at over 6 tons and shipped to the states, where it was mounted at the Harvard museum. Decades later the original discoverer of the material finally got the see the results of the preparation and mounting of what he termed ‘his dinosaur’ at the age of 93. In life Kronosaurus was a top predator; there are fossils of Elasmosauridae plesiosaurs that show bite wounds that could have come from Kronosaurus! No fish for this animal, it was after much bigger prey, leading to amazing plesiosaur vs plesiosaur encounters. Or so I like to imagine!



The Largest Aquatic Reptile of Mesozoic Era 

Species: M.‭ ‬hoffmannii‭ (‬type‭)‬,‭ ‬M.‭ ‬beaugei,‭ ‬M.‭ ‬conodon,‭ ‬M.‭ ‬lemonnieri,‭ ‬M.‭ ‬missouriensis.

Discovery,‭ ‬classification and naming

       Like‭ ‬with the dinosaur Megalosaurus,‭ ‬the official naming date for Mosasaurus actually belies its history of study.‭ ‬The first fragmentary skull material was found in the Netherlands in‭ ‬1764,‭ ‬with subsequent study by Martinus van Marum concluding that the remains were those of a fish‭ (‬To be fair to him no one at the time knew of the prior existence of giant marine reptiles‭)‬.‭ ‬In the early‭ ‬1770‭‘‬s a canon named Theodorus Joannes Godding found a second incomplete skull.‭
       It was a retired army physician named Johann Leonard Hoffmann however that would raise the profile of the creature with his discovery of further remains‭ ‬and correspondence with scientists about them.‭ ‬The true nature of the creature still remained elusive however as Hoffman thought he had the remains of a crocodile,‭ ‬and even the Dutch professor Petrus Camper also misidentified them as an ancient sperm whale in‭ ‬1786.‭ ‬Still it is quite easy to understand where Camper was coming from as even today these remains can be taken as bearing a superficial resemblance to toothed whales like Acrophyseter.‭
       The fossils also form a part of French revolutionary history in that French forces seized them from the Fortress of Maastricht in the Netherlands where they were then transported to France.‭ ‬An additional bit of trivia:‭ ‬the Maastrichtian age of the Cretaceous‭ (‬which Mosasaurus is known from‭) ‬is named after the Maastricht region.‭ ‬The story of how the remains were captured and the resulting legal challenges in the later years of the eighteenth century is often mentioned but exact details are hard to verify,‭ ‬and‭ ‬the story‭ ‬seems to have developed through a combination of ideas about what happened coming together to form a sequence of events that may not have happened exactly as told.
       When the fossils were in France they were studied by Barthélemy Faujas de Saint-Fond,‭ ‬who also thought the earlier crocodile identification was the correct one.‭ ‬Study of them continued elsewhere however when Petrus Camper’s son,‭ ‬Adriaan Gilles Camper reviewed his father’s original notes.‭ ‬Adriaan Camper disagreed with both the crocodile and whale hypothesis and thought the remains were those of a giant monitor lizard.‭ ‬Although not quite on the mark,‭ ‬he was still pretty close as monitor lizards are members of the diapsid group of reptiles,‭ ‬the earliest members of which are thought to be the ancestors of the marine reptiles that included the later mosasaurs.‭ ‬Other later finds such as the‭ ‬2005‭ ‬discovery of Dallasaurus lend further weight to the idea that mosasaurs evolved from monitor lizards.‭
       Confirmation for this idea came in‭ ‬1808‭ ‬when Georges Cuvier,‭ ‬a leading naturalist who used comparative anatomy to identify unknown bones also agreed with the analysis.‭ ‬William Daniel Conybeare formerly named the creature Mosasaurus in‭ ‬1822‭ ‬with the second skull‭ ‬used for‭ ‬the holotype.‭ ‬However Conybeare only came up with the genus name,‭ ‬something that happened surprisingly often in the early years of palaeontology.‭ ‬Mosasaurus did not get a specific type species name until‭ ‬1829‭ ‬when Gideon Mantell provided one‭ (‬something that he also had to do for the first known dinosaur Megalosaurus‭)‬.‭ ‬Despite the advancement in its identification,‭ ‬the suggestion‭ ‬thatMosasaurus was an aquatic creature did not happen until‭ ‬1854‭ ‬when Hermann Schlegel proposed that the limbs of Mosasaurus where flippers,‭ ‬not feet.

Mosasaurus the marine reptile
       Although‭ ‬probably‭ ‬not‭ ‬quite‭ ‬as long as some of the larger mosasaurs,‭ ‬Mosasaurus seems to have been one of the more heavily built.‭ ‬In fact Mosasaurus was so robust that a skull discovered in‭ ‬1998‭ ‬was mistakenly classed as belonging to Prognathodon,‭ ‬a mosasaur that specialised in eating armoured prey.‭ ‬Being such a large creature with a heavy build suggests that Mosasaurus had a preference for larger slower prey,‭ ‬quite probably other marine reptiles.‭ ‬Further support for this specialisation and behaviour comes from the side wards facing eyes that meantMosasaurus had poor stereoscopic vision.‭ ‬A lack of this ability strongly suggests that Mosasaurus did not rely heavily upon gauging distances between itself and prey and as such probably did not rely upon speed to chase down prey over distance.
       While some would envision Mosasaurus as a scavenger the fossil evidence also contradicts this as the olfactory bulb‭ (‬the part that processes smells‭) ‬is one of the most poorly developed areas.‭ ‬While many oceanic predators use smell to detect injured prey for an easy meal,‭ ‬Mosasaurus would have been at a disadvantage to most of these.‭ ‬Perhaps the most likely scenario for Mosasaurus hunting behaviour is one that saw it hanging around the upper ocean and waiting for other marine reptiles to surface for air.‭ ‬At this time they would be at their most vulnerable as they would be in the most lit portion of the water‭ (‬and silhouetted against the light ifMosasaurus was looking up from below‭)‬,‭ ‬and unable to dive back down‭ ‬as‭ ‬they would drown without‭ ‬a‭ ‬fresh supply of air in their body.‭ ‬Using its tail to provide a quick burst of speed Mosasaurus could launch a sudden attack that if it did not kill the prey,‭ ‬would at least injure it so that Mosasaurus could follow and hound it until it tired.
       By being a predator of the upper ocean Mosasaurus probably did not have much cause to dive deep.‭ ‬However the optimum angle of approach for an ocean predator is from below as not only does this make prey easier to spot against the surface light,‭ ‬the murk of the deeper water can conceal some if not all of the body of the hunter until it is ready to strike.‭ ‬This does not mean descending into the abyssal zone‭ (‬the part of the ocean so deep sunlight can’t penetrate‭) ‬as the effect of an animal beginning to disappear into the depths can be seen after just a few meters down.‭ ‬Mosasaurus probably never had to go further than the maximum depth that its prey commonly frequented which realistically was probably near the surface as well as this provides the greatest abundance of large scale prey species like fish.‭ ‬It also should be remembered that Mosasaurus is best associated with Europe,‭ ‬much of which was submerged under a shallow sea during the Cretaceous.‭ ‬Such a marine environment would have made permanent deep water living physically impossible as the depth was just not there.
       Mosasaurus has suffered from the wastebasket taxon effect which is where any remains that remotely resemble it automatically get included into the genus.‭ ‬Over the years a long list of species names has grown as a result,‭ ‬although modern analysis of the remains only recognises the four species above.‭ ‬Other long held species names are now considered dubious and probably synonymous with other older species.