I recently took a class all about dinosaurs, and one topic was whether dinosaurs were cold-blooded, which has traditionally been the conventional view, or in fact warm-blooded. The evidence, it turns out, is mixed, and just learning about the different types of evidence is really interesting. One of the pieces of evidence listed stood out to me in particular: dinosaur blood pressure. I thought I would do a little research on this topic to find out more.

Basically, a warm-blooded (endothermic) metabolism requires high blood pressure to rapidly circulate the blood throughout the body. Endotherms have higher blood pressure than cold-blooded animals (ectotherms). So did dinosaurs have high or low blood pressure? 

At first glance, this doesn’t seem particularly helpful. If we don’t know whether dinosaurs were cold or warm blooded, how would we know their blood pressure levels either? Fascinatingly, it is (somewhat) possible to answer this question!

Since one of the most critical functions of the heart is to pump blood to the brain, we can estimate dinosaur blood pressure based on the vertical distance between the dinosaur’s heart and brain. And we do have lots of fossils where we can measure this distance directly. Considering the extremely long necks of certain gigantic sauropods, this distance could be enormous. If we extrapolate blood pressures in dinosaurs from current animals, the pressures in sauropods would be so high that it is questionable how this was even possible without something rupturing or exploding.

However, the picture is further complicated by a separate but related debate about dinosaur posture. What did sauropods do with their enormously long necks? Did they keep them relatively low to the ground and horizontal when walking and feeding, or did they hold them much higher (closer to vertical) in order, for example, to reach higher vegetation on trees? The answer to this makes a huge difference when estimating blood pressure because it takes a much higher pressure to move blood up a vertical neck, against gravity, than sideways when the neck is kept low. The answer to this is we don’t know for sure, but there seems to be a lot of evidence in favor of the more vertical neck/ posture (from the structure of the bones in the neck), which leaves open the question of how exactly their bodies could pump blood with such high pressure to the brain.

One possibility is a gigantic heart to pump with more power, literally weighing several tons. This would probably be very inefficient, and the problem of such explosive high blood pressure would remain. Another alternative some have proposed are multiple smaller hearts in the neck to assist the primary heart. This isn’t physically impossible, but there doesn’t seem to be any evidence for this either. One other possibility would be using some sort of valves or muscle contractions in the neck, like living giraffes, to transport blood to the brain (although a sauropod neck is much, much longer than a giraffe’s neck).

Paleontologists like Robert Bakker in the 1970s and more recently Michael Habib argue something along these lines. Bakker suggested sauropods use neck muscle contractions to pump blood up the neck. Habib agrees and points to large neck bones called cervical ribs that are actually a very flexible form of bone, and can act as springs. This could have allowed a sauropod with a very long neck to move the blood without an impossibly high blood pressure.

This idea makes sense to me. These sauropod necks that were 30 or 40 feet long must have had extremely powerful muscles. From an evolutionary standpoint, why not co-opt these muscles into more than one function, and use them to assist the heart with pumping blood? Of course like many hypotheses and arguments with dinosaurs, this idea is also not without criticism.

There are other interesting related questions involving blood pressure that would never have occurred to me. For example, no matter what the mechanism to pump blood with such high force to the brain (whether a gigantic heart or assistance from neck muscles), when a sauropod did lower its head to the ground (e.g. to drink water), how did it prevent a huge rush of blood to its head? Modern day giraffes have evolved a web of little arteries that solves this problem, but it’s not clear whether dinosaurs had something similar.

There is a lot of speculation and unanswered questions about dinosaurs’ circulatory system. Unlike the skeleton, it didn’t fossilize and there’s no direct evidence of things like the size of the heart or the structure of arteries. But it’s an interesting area with vigorous debate because these were real problems that had to be addressed, and sauropods managed to address them one way or another!

Further reading:

How Long-Necked Dinosaurs Pumped Blood to Their Brains

https://www.smithsonianmag.com/science-nature/how-long-necked-dinosaurs-pumped-blood-their-brains-180957011/

The Evidence for Endothermy in Dinosaurs

https://ucmp.berkeley.edu/diapsids/endothermy.html

Of Barosaurus and Blood Pressure

https://www.nationalgeographic.com/science/article/of-barosaurus-and-blood-pressure

Bakker, Dinosaur feeding behaviour and the origin of flowering plants, Nature

https://www.nature.com/articles/274661a0.epdf

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?

Wrong.

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.

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. 

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. 

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!

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:

Britannica

https://www.britannica.com/animal/plesiosaur

The Plesiosaur Directory

https://plesiosauria.com/

Wikipedia

https://en.wikipedia.org/wiki/Plesiosauria

ThoughtCohttps://www.thoughtco.com/plesiosaurus-1091520

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.

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.

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

https://www.amnh.org/exhibitions/sauropods-worlds-largest-dinosaurs/meet-mamenchisaurus

Mamenchisaurus, Wikipedia

https://en.wikipedia.org/wiki/Mamenchisaurus

Mamenchisaurus, Natural History Museum, London, UK

https://www.nhm.ac.uk/discover/dino-directory/mamenchisaurus.html

Mamenchisaurus, Prehistoric Wildlife

http://www.prehistoric-wildlife.com/species/m/mamenchisaurus.html