Did dinosaurs have high blood pressure?

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.

sauropods chatting it up

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

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?

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.

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. 

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!

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:


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

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


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

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
fluffy


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?

https://www.amnh.org/explore/videos/exhibits/growing-up-tyrannosaurus-rex


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

https://www.bbc.com/news/uk-scotland-edinburgh-east-fife-55796799


First tyrannosaur embryo fossils revealed

https://www.nationalgeographic.com/science/2020/10/first-tyrannosaur-embryo-fossils-revealed/

Off to the races in 2021: new year, new baby

Wow! It’s been a while since my last post, so I feel obligated to provide some sort of explanation. It’s been a busy start to the new year. My wife and I had our first baby, Ava, near the end of January, and there was a tremendous amount do in preparation for her winter arrival. And of course there’s been even more to do ever since she joined us nearly four weeks ago! As you might expect, the past month has been a complete blur. We’re a bit overwhelmed but are managing to adapt to life with a newborn. We’re extremely fortunate that everything went well, and we have a happy and healthy baby.

newborn baby swaddled with eyes open
Welcome Ava!

Improbable Ventures is meant to be primarily about rockets, from theoretical rocket science to my practical misadventures in high power rocketry (much more to come on this topic soon). But it is also meant to be broader, encompassing related projects and ventures, and it’s impossible to completely separate it from my own personal life as well – which is why you might see me writing the occasional article about a class I’m taking, or a recent trip or hike I took, or a new baby.

As a sleep-deprived new father, I’m not sure that I have anything particularly profound to say about parenthood that hasn’t been said much more eloquently by other people, many times before. It’s exciting and exhausting. I thought it would be a lot of work, but it turned out to be more than I’d imagined. It’s not particularly complicated; it’s just that virtually nonstop, around the clock care is required.

More interesting than any perspective I can provide is the baby’s point of view. What a dramatic difference to go from being in the womb – totally dark, almost like a sensory deprivation chamber except for hearing mom’s heartbeat and her voice on a regular basis – to suddenly (unwillingly) being born. It must be total sensory overload, except you have no words for anything, no way to describe your experience even within your own mind, and no way to understand anything that’s happening or what might come next. The baby has never had to use her lungs and breathe on her own before, or feel hunger, do things like drink and swallow milk, and suddenly she is forced to figure all of this out – and fast.

While it’s true that babies basically just eat, sleep, and cry (there’s no shortage of crying) all day and all night, it’s remarkable that they learn as rapidly as they do!