Dinosaurs: What did their size really mean?

Dinosaur skeletons at Melbourne Museum :: Photo by: S. Barker

Is big always better? Is big normal? What can body size tell us about an animal?

These are some of the questions explored in a recent paper about the distribution of body size in dinosaurs. It also looked at whether the huge sizes some reached were common in nature. 

Why should you care whether dinosaurs were bigger more often than other animals? 

There are 3 key points:

1. It can demonstrate how big animals fit into their ecosystem, 
2. what might drive animals to get really big and 
3. what being big means at time of global change.

The researchers trawled through vast amounts of information to collect as many records of body size as possible. As well as dinosaurs, they collected body size information of:

• Birds
• Reptiles
• Amphibians
• Fish
• Terrestrial mammals
• Extinct Cenozoic (65Ma-now) terrestrial mammals
• Extinct pterosaurs

The first 5 were all extant (currently living) species. The two groups of extinct animals were included to make sure there was no bias in the fossil record, just in case we only dig up big bones!

As well as comparing all the various animals, they compared the 3 main types of dinosaurs: 

• Ornithiscian: For example plant eating duckbills, stegosaurs & Triceratops; 
• Sauropodomorphs: The long necked plant eating dinosaurs, for example brachiosaurs, apatosaurs, diplodicus; and 
• Therapoda: Meat eaters, which ultimately evolved into birds, for example T. rex and velociraptors.

Frequency distribution of species body 
size for eight different animal groups: 
(a) extinct dinosaurs; (b) extant birds; (c) extant reptiles; 
(d) extant amphibians; (e) extant fish; (f) extant mammals; 
(g) extinct pterosaurs; and (h) Cenozoic mammals.  O'Gorman & Hone

The scientists also compared dinosaurs found in 2 prolific dinosaur fossil formations, the Morrison formation and Dinosaur Park, and across time periods of the Age of Dinosaurs, the Mesozoic. These comparisons were to make absolutely sure that there were no biases in the results.

All the non-dinosaurian animals showed a higher, or normal, frequency of smaller body size, and so did the Theropods. The herbivorous Ornithischians and Sauropodomorphs however, showed a uniquely high frequency of large size.

The other interesting result was that the dinosaurs got larger more often towards the end of each time period. The Late Triassic, Late Jurassic and Late Cretaceous all see a higher frequency of these massive animals. From this we can speculate that:

1. Times of stability can allow animals to evolve into ginormous size.
2. Being big is not so good when things start to change in your environment. 

So why were the big plant eating dinosaurs so darn big? It appears to be a combination of factors. The first being escape from predators: once you get really big, not much can hurt you. The other factor has to do with processing food. These dinosaurs were eating very tough, nutrient poor, plant material that took a lot of breaking down. As they got bigger, their gastric tract also increased and allowed for more efficient processing of food.

This paper shows that when it comes to size, the dinosaurs were truly unrivaled. No other group of animals has such a high frequency of gigantic size. The large size of the herbivorous dinosaurs was a double edged sword. While it helped them avoid predation and made them fantastic plant processing machines, it left them vulnerable to changes in their environment so that they suffered greatly at each major extinction event they faced. 

It also raises the question: was it the preference for smaller size, that lead to the survival of Therapods in the form of birds?

What do you think? Could the smaller size of Therapods be part of the reason they continue to live successfully today?

Reference: 

O’Gorman EJ, Hone DWE (2012) Body Size Distribution of the Dinosaurs. PLoS ONE 7(12): e51925. doi:10.1371/journal.pone.0051925

Follow up: Did T. rex have feathers?

Sue the T. rex
The largest and one of the most complete T. rex skeletons ever found.
Image Source: Wikipedia

Dear readers, you will never guess what happened!

After I published the previous post 'Did T. rex have feathers?' and posted the link on Twitter I got a response that I hadn't expected.

A tweet from the BBC Earth's Walking With Dinosaurs @walkwithdinos:

"@barkersaur It's *quite* the talking point amongst our Facebook fans... Here's our take though, by Steve Brusatte: http://ow.ly/i3rv7"

If you follow the link you will notice immediately that both our articles begin with... the same picture! Which is amusing, and also a pleasant discovery.

A quick background on Steve Brusatte:

Steve is a vertebrate palaeontologist from Columbia University and the American Museum of Natural History. He is particularly interested in theropod dinosaurs. He has authored many papers and three books. One of which I own, Dinosaur Palaeobiology, edited by the eminent Professor Michael J. Benton. It is the text book on Dinosaurs if you want to get into the nitty gritty details.

Steve's article 'Did T. rex have feathers?' (yes, we chose the same titles too) is well worth reading as it discusses:

• Why fossils with feathers are precious and unique
• Another fossil relative of T. rex that had feathers (Dilong)
• Other dinosaurs that had feathers
• Where T. rex may have had its feathers

I enjoy the way he finishes his article with a hopeful thought:

"Maybe someday we can test this hypothesis by finding a rare fossil of T. rex that was fossilised in that set of perfect conditions for preserving feathers."

Wouldn't that be wonderful? I am not certain if the rock we normally find T. rex fossils in is likely to preserve feathers, but we can dream.

If you put  'feathered t rex' into google images you will enjoy the varied and amazing artistic interpretations!

One of the many interpretations of how T. rex might have looked
Image Source: Deviant Art

How do you picture T. rex? Are feathers too hard to imagine? What colours should T. rex be?

Did T. rex have feathers?

Can you imagine Tyrannosaurus rex with feathers? Because that’s what research suggests may be the case.

(Image Source IFLS )

In my last post ’Why Palaeontology?’ I stated one of the most significant findings of Palaeontology in the last 50 years was confirmation that birds are descended from therapod (meat eating, three toed) dinosaurs.

There are many similarities between therapod dinosaurs and birds.  Most of these similarities are anatomical, including:

• a wishbone (fused collar bones)
• three toed foot
• three fingered hand
• a half moon shaped wrist bone
• hollow bones
• and feathers.

Feathers are the most spectacular similarity that dinosaurs share with birds. The first time they were seen together was with the discovery of Archaeopteryx. It wasn't until the 1990's that more feathered fossils were found, in China. Hundreds more.

The Tyrannosaur family tree - Yutyrannus huali is the
largest of these found with feathers
(Image source Xing Xu et al.)

Some of the Chinese feathered dinosaurs knocked Archaeopteryx off its perch as the oldest feathered dinosaur. A study in 2012 looked closely at dating some of China’s earliest feathered dinosaur fossils. It concluded that many were present 161 million years ago, which is around 10-20 million years older than Archaeopteryx.

Feathered dinosaurs are usually small. Archaeopteryx was about the size of a crow. In 2012, however, a paper was published by Nature that described a huge feathered dinosaur, a distant ancestor of the iconic Tyrannosaurus rex, Yutyrannus huali.

Yutyrannus huali was over 9m long and roughly the same weight as a medium sized car. Yutyrannus huali had feathers when it was an adult. This is strong evidence that the infamous Tyrannosaurus rex may have also sported feathers as an adult. Over 6000kg of feathered killing machine. 

Despite this evidence artistic depictions and toys of T. rex seem slow to adopt the new feathery covering. I quite enjoy the idea of the giant meat-eater being covered in feathers, how about you?



Science Ruined Dinosaurs cartoon pictured can also be purchased as a T-shirt.

For further reading and images try the Wired Science article Giant Feathered Tyrannosaur From China.

Why Palaeontology?

What if you understood all the changes in the natural world, just because you looked at rocks and unlocked their secrets?

Last year I decided to change careers and become a Palaeontologist. My father has a PhD in Geology, and was an avid fossil collector in his youth, so some of his passion for rocks may have rubbed off!

Since the early 60’s, when Dad was studying, there have been some dramatic changes in Palaeontology, inlcuding:

• A name change to ‘Palaeobiology’
• 100's of  feathered fossils discovered in China in the 1990's
• The confirmation that Birds are descended from Dinosaurs (Willis)
• Proteins have been removed from fossils (Lester, 2007)
• A protein responsible for colour was found in fossil feathers (Zhang et al. 2010)
• The discovery that DNA will only last about 6.8 Million years (Barras, 2012)
• The sex of some fossils has been confirmed (Chinsamy et al. 2012)
• 65 Million years ago an asteroid wiped out the Dinosaurs, quickly. (Klotz, 2013)

It took over 100 years before scientists confirmed
that birds were dinosaur decendents (image source)

These changes and discoveries mean we are better equipped to reconstruct, and understand, ancient organisms and their environments. Although, I know some of you deplore the thought of a ‘fluffy’, feathered, T. rex!

If you study Palaeobiology you will be familiar with being asked, “Why are you studying that?” in a somewhat sceptical tone. Palaeobiology PhD student Sarah Werning recently explored this in her article ‘Why Palaeontology is Relevant’.

No doubt you recognise, several of what Sarah refers to as ‘public-friendly’ responses:

• “Paleontologists teach anatomy at many medical schools.”
• “Fossils play an important role in oil discovery.”
• “Paleontology is a good ‘gateway drug’ to the other sciences.”
• “Paleontology is a good way to teach critical thinking skills.”
• “Paleontology is inherently interesting; it doesn’t need further justification.”  (Werning, 2013)

Unfortunately, none of these reasons explain why Palaeontology is important. Reading Sarah’s article I realised my responses have changed over time. Instead of using one of the ‘public-friendly’ reasons, I now talk about Palaeobiology in terms of understanding ancient life so we can better understand life today. For example:

• “Knowing what happened to living things when it got hotter or colder in the past, we can understand the effects of climate change today.”
• “We can gain greater insights into how evolution works.”
• “The current rate of extinction can be calculated after studying past mass extinctions.”

The extinction of non-avian Dinosaurs had a big impact 
on the evolution of mammals, including humans. (image source)

Palaeobiology is not limited to a science that lists everything that came before us, it puts those organisms into context. It is the context that is important.

Palaeontology is becoming increasingly relevant. The key to the future of life and the earth is locked up in the rocks, all we need to do is decode it. Like most sciences, it is constantly evolving and being built upon. The changes and discoveries,  since the 1960’s, mean we can understand our past and present better than ever before.

What other ways do you think Palaeontology has changed, or is relevant?

You can read Sarah Werning's article at Plos Blogs http://blogs.plos.org/paleo/2013/02/19/why-paleontology-is-relevant/

Other references:

Willis, P. abc.net.au, Dinosaurs and Birds The Story

Chinsamy et al. 2012. Nature Communications 4: 1381

Lester, B. 2007. Cosmos Online, Protein extracted from T. rex fossil

Zhang et al. 2010. Nature 463: 1075-1078

Barras, C. 2012. New Scientist: Life, DNA's half-life identified using fossil bone

Klotz, I. 2013. Reuters, Asteroid may have klled dinosaurs quicker than scientists thought