A living fossil – A look into the past

Crocodilians have been portrayed in a poor light indefinitely. Rarely are complimentary words such as ‘majestic’ or ‘survivor’ used to describe them, and their case certainly has not been aided by those who in their day were prominent in the vertebrate zoology field. Indeed, George Cuvier once claimed that there was no difference between the mummified remains of a crocodile in Egypt and those crocodiles present at the time of his “observation”. Such was his belief in this that he used crocodiles to attempt to disprove evolution, and William Buchland also observed little difference in specimens over a period of time (1). These prominent views coupled with crocodilians well documented record for causing fear and deep-rooted cultural dislike, it is easy to see why these animals don’t seem to have the same pull at your heart strings as perhaps stereotypically a Panda may do.  Despite this, crocodilians exhibit levels of parental care not typical of reptilian behaviour and show remarkable intelligence, even demonstrating clear evidence of tool use (2). These animals are not only remarkable and crucial to the health of ecosystems, but they are also survivors brilliantly adapted to survive cataclysmic events destructive enough to end the reign of the dinosaurs. We need to appreciate these magnificent animals, as history shows they really are the epitome of true survivors.

The Tricky Triassic period… Dinosaur or crocodile?

Dr Steve Brusatte describes in his riveting book The Rise and Fall of the Dinosaurs: The Untold Story of the Lost World, that should you be fortunate enough or, maybe unfortunate enough, to be alive and kicking during the Triassic period, you would begin to become acquainted with many different species of reptiles. Some were small while others would have been roughly equivalent to a medium sized domestic dog and others would eclipse even them. Many of them were able to walk upright and were agile and effective predators. It would have made quite the spectacle.

The problem? Not only do many of these animals look the same, some belong to a different group of creatures entirely. Indeed, many species of early dinosaurs and crocodilians looked closely alike, and this incidence of convergent evolution has left many a palaeontologist baffled, in particular those working on remains found at the Hayden Quarry. As Brusatte describes, despite there being a split between the two main groups the avemetatarsalians (which gave rise to the dinosauromorphs and the dinosaurs) and the psuedosuchians (from which crocodiles originated) from their mutual starting point in life, the archosaurs (3).

Most likely the most famous find to illustrate the convergent evolution at play between crocodiles and dinosaurs however, had been several decades in the making and it came at the famous fossil site Ghost Ranch. During the late 1940’s this fossil site had become notorious for a huge number of fossilised remains of Coelophysis. As the popularity of the fossils began to fade and interest amongst experts began to diminish, a key mistake was made. A mistake that would not be noticed for over half a century until a PhD student by the name of Sterling Nesbit took a closer look at the specimen and noticed some key differences. While it no doubt closely resembled a dinosaur, the appearance of a beak replacing the sharp teeth that were trademarks of the specimens previously discovered at Ghost Ranch. Additional other differences were highlighted in very small arms and crucially the incredible similarity between the ankle of the specimen in front of him and those of crocodile ankles.  It became clear to him that this was no dinosaur and he was instead looking at the remains of a pseudosuchian displaying clear convergent characteristics of dinosaurs. His find would prompt high media attention and as is the right of the person who makes a discovery, he was able to choose the name for the specimen. It was named Effigia okeeffeae and is a landmark discovery in the evolution of early crocodilians (3).

Picture 1 Coelophysis: The dinosaur at the centre of the convergent evolution discovery. (Image credit: The Guardian)
Picture 1: Coelophysis: The dinosaur at the centre of the convergent evolution discovery. (Image credit: The Guardian)

It would seem however that even in these evolutionary stages the blueprint for today’s crocodiles was already beginning to take place. Many of the crocodiles living during the Triassic period were light weight, well adapted for running. In many ways quite different to the crocodiles frequenting our waters today.  Experts as a result of this have been led to theorise that these crocodiles may have led a warm-blooded existence and the anatomy of modern crocodiles supports this theory. Despite being cold-blooded, they are equipped with a four chambered heart which enables them to be able to regulate blood flow when diving. It is suspected that this sophisticated organ evolved from prehistoric crocodiles who lived on land and may well have had a much higher metabolism, a classic trait of a warm-blooded animal. As dinosaurs established their dominance and crocodiles took to the water more and more, the four chambered heart would have increased further still in importance ultimately becoming key to being able to dive to varying depths (4).

The Jurassic period diversity and adaptions

While the Triassic period really was the quiet before the storm as far as the dinosaurs were concerned, the Jurassic period really showed a huge shift in power as dinosaurs well and truly got a foot hold and stamped their authority on the world. As a result, crocodiles began to take to the water more and more with the land-based niches they once filled being taken over by dinosaurs. Despite this there were still plenty of opportunities for those ready to adapt to a more aquatic lifestyle and these adaptions really did take the form of the weird and wonderful.

Godzilla Croc and marine adaptions

Dakosaurus has bemused and intrigued scientists in equal measure. Boasting humungous jaws and teeth it earned itself the nickname of Godzilla. Metriorhynchus possessed a broad and flat head which would lead scientists to speculate this may be an adaption enabling them to move their heads sideways while keeping water resistance to a minimum. Based on what we know from the fossil record, it is speculated Metriorhynchus may have hunted in a similar way to modern day sharks, close to the surface and relying on short, sharp bursts of speed to overwhelm their quarry. Another adaption employed by crocs is the swallowing of stones to act as an aid with buoyancy, it is also thought that this enabled them to hunt at differing ocean layers (4).

Image 2 A Metriorhynchus (Image credit Wikipedia)
Image 2: A Metriorhynchus (Image credit Wikipedia)

Cretaceous

There is little doubt that during the Cretaceous period around most of the world dinosaur diversity had peaked with monstrous top predators such as the infamous Tyrannosaurus Rex engaging in titanic battles with a foe that shares similar celebrity status amongst dinosaurs the fearsomely armoured Triceratops. These were just some of the headline acts as an abundance of smaller carnivores lived in the shadows of the top predators and giant sauropods such as Argentinosaurus, that continued to rule the earth and so the dominance of the dinosaurs was almost unquestioned. The exception it seems is the south Americas, in particular Brazil. While the region still played host to some mighty impressive beasts such as the abelisaurids and the presence of sauropods was still felt, the diversity of species and the sizes they achieved are noticeably smaller.

Studies of the area have produced some truly astonishing finds. It seems the South Americas and of course the Southern Hemisphere still provided an opportunity for a diversity of crocodiles to fill the gaps in ecological niches which around the rest of the world had been taken care of by the dinosaurs. They thrived in and out of water, were able to dig and live in burrows and hunt prey down on all fours, this provides yet further evidence of the astonishing tenacious attitudes of these reptiles to find a way to adapt to their environment (3). Despite the dominance of the dinosaurs in almost all areas of the planet, there was still the opportunity for some true monsters of the crocodilian world to emerge and surely when one thinks of a monster crocodile, they must surely think of none other than the Super Croc itself Sarcosuchus .

This formidable animal appeared on the fossil discovery scene in the 1940’s however for over half a century it would be known only by small remains of armour and teeth, clearly this monster was reluctant to give up its secrets. In the year of the millennium Dr Paul Sereno stunned the scientific world by finding nearly half a skeleton of one of the biggest crocodiles to have lived.  Weighing in at anything up to ten tonnes and growing as long as a bus the waterways of North Africa would have been a treacherous place to visit even for dinosaurs, and with teeth perfectly adapted for grabbing prey there would surely have been little chance of escape once the prey was snared (4).

Image 3) Sarcosuchus to human scale comparison. (Image 3) Image credit Sarcosuchus to human scale - Prehistoric wildlife)
Image 3: Sarcosuchus to human scale comparison. Image credit: Sarcosuchus to human scale – Prehistoric wildlife

Humans and crocodiles a predator – prey relationship

The genus Crocodylus has been described by Dr Christopher Brochu as the most dangerous set of reptiles on the planet. It’s very difficult to argue with this when you consider the species listed within this genus include the Nile Crocodile and Salt Water Crocodile – both known to treat humans as a viable prey species. Fossil remains of early humans however suggest that this relationship between crocodiles and people may have been prominent for millions of years. Damage to the lower leg and ankle region of one unfortunate human matches the bite marks of Crocodylus anthropopohagus, a member of the giant horned crocodiles, that lurked within the waters of Tanzania some 1- 2 million years ago. As Dr Christopher Brochu acknowledges, this in itself does not provide conclusive proof that this was an act of predation but what cannot be disputed is at times our early ancestors were certainly bitten whether this may be through scavenging, attempted predation or indeed successful predation. These fossil finds present a rather unnerving fact, the largest potential threat our ancestors faced was one they may never have seen coming – until It was too late at least (1).

Present day

Despite the incredible diversity, the crocodilians have experienced varying factors that have conspired to reduce them now to just 23 species in the present day, of these some such as the Philippine Crocodile are hanging to their existence by the thinnest of threads. Humans have a lot to answer for. How can we allow an animal so perfectly adapted for the challenges of life it has survived for millions of years outliving an assortment of enormous prehistoric creatures to be subjected and exposed so harshly to the threats we as a species are responsible for, that some could be wiped of the face of the earth? How can we read stories such as the race to save a huge crocodile in Indonesia’s life because a car tyre has been wrapped around it and feel anything but shame and embarrassment? (5) This is our mess; we need to clean it up. We are all responsible for it, we can all do more. If we lose crocodiles we don’t just lose an iconic majestic animal, we lose a species crucial to the survival of ecosystems around the world.  It would be nothing short of criminal if the only way our children and grandchildren knew what a crocodile is through the same means they will know what a Tyrannosaurus Rex is. We have the power to stop this happening-lets make sure we do.

This article is based on research by experts and I DO NOT claim any of this information sourced in this article to come from myself. I have merely researched the subject and have listed and credited the sources below.

 

Further reading and information sources

1) The Giant Horned Crocodiles That Ate Our Ancestors – Christopher A. Brochu

2) Crocodilians use tools for hunting

Dinets, V., Brueggen, J. & Brueggen, J. (2013) Crocodilians use tools for hunting. Ethology Ecology & Evolution. 27 (1), pp. 74–78.

3) The Complete Illustrated Encyclopedia of Dinosaurs and Prehistoric Creatures Dr Dougal Dixon.

4) The Rise and Fall of the Dinosaurs. The Untold Story of a Lost World.  Dr Steve Brusatte.

5) Indonesia crocodile stuck in a tyre worries rescuers:  https://www.bbc.co.uk/news/av/world-asia-42661092/indonesia-crocodile-stuck-in-a-tyre-worries-rescuers

George Wykes
About George Wykes 2 Articles
George’s fondest memories as a young boy are being taught the difference between a green shank and a red shank while bird watching with his grandfather and later one Christmas being presented with his very own bird table. Since then, he has been fortunate that his passion for wildlife has seen him participate in conservation projects in unforgettable locations and have some once in a lifetime wildlife encounters, seeing a huge male jaguar feeding on a fresh green turtle kill will take some topping. George recently completed an MSc in Advanced Wildlife Conservation in Practice at UWE and his current interests include rewilding, spatial ecology, biodiversity surveying and reducing human – wildlife conflict.
Contact: Website

Be the first to comment

Leave a Reply

Your email address will not be published.


*


*