Meet the plesiosaur: a gigantic aquatic reptile

There’s a common misconception that any kind of large prehistoric animal is a dinosaur – from a t-rex to the flying pterodactyl to the woolly mammoth.

When I first heard this, I couldn’t believe it. Did people really believe that a woolly mammoth qualified as a dinosaur? Obviously a woolly mammoth was covered in thick fur (hence the name), which makes it a mammal, even if you knew nothing else about it. They just aren’t reptilian like dinosaurs.

But flying prehistoric reptiles (like pterosaurs) and swimming prehistoric reptiles (like plesiosaurs) – those were just different types of dinosaurs, right?


Until recently, I didn’t realize that plesiosaurs and pterosaurs are not considered dinosaurs. I had mistakenly lumped them all together. True, they were all reptiles and they lived during the same geological time period (the Mesozoic Era), but they were sufficiently different from an evolutionary and biological perspective that they aren’t categorized as dinosaurs at all.

long necked plesiosaur underwater
meet the plesiosaur

Plesiosaurs were a group of long-necked marine reptiles that lived during the Mesozoic Era, from the late Triassic period, through the entire Jurassic period, to the late Cretaceous period (roughly 225 million to 80 million years ago). Some, but not all, types of plesiosaurs continued to exist until the end of the Cretaceous period, about 66 million years ago. This is approximately the same geologic time period as the dinosaurs.

While the name “dinosaur” means “terrible lizard,” the name “plesiosaur” means “close to lizard,” an appropriate name since they were admittedly similar in many ways to the dinosaurs.Β 

The world map looked extremely different hundreds of millions of years ago, but plesiosaurs were geographically distributed in many areas, throughout the Pacific Ocean and near what is now North America, Europe, Australia, and Asia.Β 

Early in their history, plesiosaurs split into two different lineages – pliosauroids and plesiosauroids. The latter had a longer neck that was very flexible. Interestingly, later on, plesiosaurs increased dramatically in size (up to 43 feet or so) and the neck reached extreme lengths. with half the total body length consisting of the neck and head. And the jaws had an estimated biting force of around 33,000 psi, possibly the largest known bite force of any animal!

plesiosaur skeleton

There is even some evidence that plesiosaurs may have been warm blooded and gave birth to live young, rather than laying eggs. Of course, there is significant debate about whether some dinosaurs were similarly warm blooded, but that is a topic for another post…

Further reading:


The Plesiosaur Directory



Which dinosaur had the longest neck?

When most people imagine a dinosaur, they might initially think of a large, menacing tyrannosaurus rex, or the slow and lumbering stegosaurus with huge plates along its back, or the three-horned triceratops with its massive frill or crest above its neck. But one of the most frequently recognized types of dinosaurs is a sauropod.

As mentioned in my last post, all dinosaurs are generally divided into two categories: saurischia (“lizard hips”) and ornithischia (“bird hips”). Within saurischia, it’s further broken down into theropods (bipedal carnivores like t-rex) and sauropods.

Sauropods were plant-eating dinosaurs that walked on all four legs and had extremely long necks, with relatively small heads. They grew to colossal sizes and were the largest animals to have ever walked the earth. Technically blue whales are larger, but they live in the ocean and don’t have to deal with the constraints of gravity, so it’s apples and oranges in terms of a comparison. Some of the most well known sauropods are brontosaurus (now known as apatosaurus, though this is a heated debate among some paleontologists) and brachiosaurus.

dark rendering of long-necked dinosaurs
mamenchisaurs (artwork by cheungchungtat)

It’s true that a lot of sauropods had very long necks – it seems to be one of their defining features. But the long neck is intriguing, and it raises several questions. Why is the neck so long? Structurally speaking, how was this possible? And which dinosaur had the longest neck?

It’s always hard to say anything with total certainty about animals that went extinct more than 66 million years ago. I had never heard of the “Mamenchisaurus” until recently, but it seems to be a strong contender for dinosaur with the longest neck, and in any pictures (whether skeletal or depictions of what it probably looked like in real life) it’s startling. The Mamenchisaurus was approximately 60 feet in total length, and a good 30 feet of that was just the neck. Relative to its body size, this animal had the longest neck of any known dinosaur.

The Mamenchisaurus lived in what is now China (though of course the map looked very different back then) and seems to have lived during the Middle and Late Jurassic, and possibly in the Early Cretaceous.

long-necked dinosaur
how’s the weather up there?

At first, I thought that the purpose of the long neck would have been to reach really tall vegetation and trees, like modern giraffes. But it seems more likely that the dinosaur used its neck more horizontally to reach medium height or lower level vegetation, and the benefit in neck length was instead to sweep across much larger areas. This way, it didn’t need to move its body much (if at all) while feeding. No doubt this saved a lot of energy considering the colossal size and weight of the body!

Further reading:

Meet Mamenchisaurus, American Museum of Natural History

Mamenchisaurus, Wikipedia

Mamenchisaurus, Natural History Museum, London, UK

Mamenchisaurus, Prehistoric Wildlife

Dinosaurs 101: Theropods and t-rex

Continuing the temporary non-rocketry theme from my last post –

I signed up for two classes beginning in early January: chemistry, which is an accelerated course that crams three months’ worth of material into four dense weeks, and a geology course all about dinosaurs, which takes place at a more reasonable pace. They’re both virtual classes, given the ongoing pandemic. Both have been really fascinating, and everyone loves dinosaurs, so I figured I’d post something about tyrannosaurus rex or a colossal, lumbering brontosaurus (or apatosaurus – more on that later).

Just as background, dinosaurs are generally divided into two major groups: saurischia and ornithischia. Within the saurischia group, it’s broken down even further into theropods and sauropods.

Theropods are a fascinating and really diverse group of dinosaurs, and at the risk of overgeneralizing a bit, theropods are meat-eating predators with very large and very sharp teeth. They had big heads and jaws, and they evolved to run at fast speeds on two legs, something that is obviously quite unusual among any animals, either back then or today. Their arms and hands were notoriously tiny (think t-rex arms), just because they weren’t that useful. Chasing down prey and catching it in your jaws requires powerful leg and jaw muscles, but not hands or arms, necessarily.

Speaking of tyrannosaurs, there have been some interesting recent discoveries about a baby t-rex.

baby t-rex, appears fluffy like baby chick

The background on the recent discoveries is that a tiny jaw fossil was found in Montana in 1983, and decades later, another tiny foot claw fossil was discovered in 2018 in Alberta, Canada. Both were roughly 71-75 million years old. Researchers didn’t know what they were looking at right away, but eventually realized that both fossils belonged to a baby t-rex. The jaw was extremely small, but it closely resembles other known t-rex jaws. 

What these fossils meant – for the rest of us non-paleontologists – is that a baby t-rex was extremely small compared to an adult t-rex. Babies, when they hatched, were about 3 feet long, compared to the adult that was up to 40 feet in length! 

What makes these discoveries so unusual is that there aren’t very many fossilized baby or young dinosaur skeletons in general, partly because the bones are so tiny and fragile. And while things like feathers don’t fossilize (as skeletal bones do), there’s indirect evidence that the baby t-rex would have hatched with feathers, looking kind of like a fluffy baby chicken – but much bigger and with a long tail, and presumably more menacing. 

The babies also had a different set of teeth, and it seems that they went through several sets as their diets changed as they grew older and larger. Dinosaurs are nothing if not chock full of interesting facts, and so I will leave you with one final impressive fact: once the babies grew into adults with their final set of teeth (and massive heads, jaws, and corresponding muscles), they could bite through anything, including bone, causing their prey to explode! This is very different from how a modern lion or tiger bites and kills its prey, which is more of a fatal bite that causes the prey to bleed out. Impressive for a creature that starts off life so small and looking like a fluffy chick.

Further reading:

American Museum of Natural History: What Did a Baby T. rex Look Like?

Baby tyrannosaurs dinosaurs were the ‘size of a Border Collie’

First tyrannosaur embryo fossils revealed