Evolution of Crocodiles: The Mystery of a Quarter of a Billion Years

Evolution of crocodiles: Saltwater crocodile walking on wide beach towards the troubled water, mountains in the background.

Assumption 2: In terms of life form, the Saltwater Crocodile and similar relatives have held the position at the absolute top of the food pyramid in the habitat of transition between land and water for longer than any other life form that emerged in biological evolution.

To examine assumption 2, it is necessary to draw mainly on the findings of the paleontological sciences on the evolution of crocodilians and relatives. Here, too, a stable verification with astonishing detail can be achieved. First, however, a clarification takes place again: the assertion that the Saltwater Crocodile itself or other modern crocodilian species have not changed over several dozen or even a hundred million years is probably not correct. However, there is, so to speak, a true core to this statement, which goes back much further and which will be at the centre of this verification.

If one first looks at the results of paleontology, which have been collected by fossils and genetic analysis in relation to the duration of the existence of today’s Saltwater Crocodile, these lie in a range of 4 – 4.5 million years [4]. The age of the species, as well as its ancestry, is rather murky because – as with most animal species – there are not enough fossil traces for such long-term empirical surveys.

It should be noted that in the taxonomic delimitation of real “species”, narrow margins are set in the biological systematics, the most important framework of which is the isolated reproductive community and very far-reaching similarities in anatomical details. The overall assessment made by scientists assumes that the species of today’s Saltwater Crocodile developed 6 to 12 million years ago [5][6].

Assumption 2 is not only about the species itself, but also the form of life with similar relatives, and thus a previously announced, even more interesting aspect emerges, which is not limited to “only” 4.5 or even 12 million years of evolution, but covers periods of up to a quarter of a billion years into the past. To this extent, fossils can be used to identify animals whose expert reconstruction produces forms very similar to today’s Saltwater crocodile. It can therefore be assumed that similar photos to those above and to the right could have been taken, hardly distinguishable to a layman, on a journey through time that would lead so far into the past that today’s continents would not even exist.

The land surface of the planet at that time consisted mainly of the giant continent Pangaea, which had just started to drift apart slightly. In the following explanations, I will assign all such reptiles emerged in evolution which strongly resemble today’s crocodilians to the “crocodile form” (note: this is independent of the taxonomic term cocodilforms). The purpose of this simplification is not a trick, to cheat the verification. Rather, it is about the amazing phenomenon of so-called “convergence” as a very important part of evolution. It will soon become clear what this is all about.

The unbelievably long Success Story of the Crocodile Form over a Quarter of a Billion Years of Evolution

The best known of those representatives of the crocodile form, which already existed well over 200 million years ago in the geological Triassic epoch (252.2 – 201.3 million years), belonged to the Phytosauria. Their numerous species, among them those of the genus Smilosuchus (living reconstruction see picture), were no direct ancestors of any of today’s crocodiles. A relationship exists only by a common line to the Crurotarsi, which numerous reptiles also belonged to, and which had no or very few similarities to the crocodile form.

However, such phytosaurs as Smilosuchus adamenensis are also attributed by expert scientists in almost every respect as having far-reaching similarities to today’s crocodiles [7] [8]. The only anatomical difference that was more striking was that the nasal openings of Smilosuchuchus and other phytosaurs were not at the tip of the snout, as in today’s crocodiles, but close to the eyes. The evolutionary purpose of this anatomy was, according to current scientific opinion, to be able to submerge the rest of the body at the surface of the water with a minimum of recognition , i.e. to remain as inconspicuous as possible.

Evolution of crocodilians: Drawing of a Smilosuchus adamanensis. Very similar to a modern crocodile.

The phytosaurs and their crocodile forms probably became extinct during the fourth great mass extinction in geological history, at the border between the Triassic and the Jurassic periods, about 201 million years ago. This event was probably caused by comet impact and volcanic eruption. Most previously existing large reptiles and, according to current expert opinion, up to 75 percent of all animal and plant species of the time did not survive this caesura. In the subsequent Jura (201.3 – 145 million years) and Cretaceous (145 – 66 million years) epochs. During the following evolution the ecological niches freed up in this way were occupied slowly, for example by the, initially, still rather small dinosaurs.

The crocodile form, on the other hand, reappeared quite shortly after the Triassic-Jura border in relation to the overall time frame. And again its evolution led to numerous semi-aquatic genera and species at the transition between land and water. It has been proven that the extensive Goniopholididae family existed from the beginning of the Jurassic period almost 200 million years ago until the late Cretaceous period. The oldest fossil evidence for this originates from the Calsoyasuchus valliceps species, and was dated at 196.5 million years [9]. The fossil traces show that during the evolution many crocodiles sometimes tended towards a more aquatic or more land-based anatomy, but on the whole “settled” on largely the same form, what I alternatively call the “crocodile form”.

Drawing of two Machimosaurus-species. The upper one is a M. hugii and very similar to a modern crocodile.

One example of a tendential deviation towards a more aquatic anatomy was the Machimosaurs (picture). They existed 160 to 130 million years ago, and probably spent most of their time in the sea, but still had legs. The largest known species, the Machimosaurus hugii, with a length of up to 12 meters, probably hunted for fish and turtles in the ocean as well as for large land animals on the shore, according to expert reconstructions, and its anatomy has far-reaching parallels with today’s Saltwater Crocodiles.

The extensive group of Pholidosauridae, whose species can be traced from the middle Jurassic to the late Cretaceous period (167.7 to 89.3 million years), moved predominantly in the anatomical centre of the crocodile form during evolution.

Evolution of crocodilians: Drawing of a Sarcosuchus. Very similar to a modern crocodile.

The largest of these, according to previous evidence, belonged to the genus Sarcosuchus (112.9 to 93.9 million years) with a body length of up to 11 meters and a weight of eight tons (picture). They lived around inland waters or brackish water zones, and probably hunted there as today’s crocodiles do. Sarcosuchians may be an example of crocodiles adapting their size during evolution, when dinosaurs on land developed increasingly large predatory forms from around the middle of the Cretaceous period.

Drawing of a Deinosuchus walking, again very similar to a modern crocodile.

Another suitable example are Deinosuchus, which, according to many experts, were superior to even the largest and strongest predatory dinosaurs, and perhaps even captured them as food. An empirical reconstruction of the biting power of this giant crocodile, up to 12 meters long and which lived about 70 or 80 million years ago, yielded a value of more than 100,000 N, which is far higher than that attributed to the species of the large Tyrannosaurus species [10], and even traces of bites on fossil bones of large predatory dinosaurs have been found to match fossil parts of Deinosuchus [11].

As in the Triassic period, numerous genera and species of the crocodile form existed during the 130 million year Jurassic and Cretaceous periods. Meanwhile, numerous other forms of large reptiles also appeared on the planet. Dinosaurs alone developed thousands of different species of land animals during their evolution, including small raptors and huge herbivores weighing over 80 tons. They also produced the largest known land predators, such as the well-known Tyrannosaurus Rex. In the air, the Pterosaurs were the largest animals capable of flight that probably ever existed. They, too, were carnivores: their wingspans reached well over ten meters and their weight more than half a ton. In the open ocean, other large reptiles existed at the top positions of the food pyramid, such as the species of Plesiosaurs and Mosaurs, with bodies weighing up to several tons and stretching to 20 meters long.

Almost all the large reptiles of the Jurassic and Cretaceous periods are no longer existent today. They disappeared, at the latest, during the fifth geological mass extinction about 66 million years ago, which was probably also caused by a comet impact and volcanic eruptions, and their possible remaining species did not develop back into their former positions afterwards. This also applies to all large dinosaurs. There are still the birds today which are direct descendants of dinosaurs, but they have become and remain relatively small creatures during evolution with many variations.

Only one form of the many large reptiles returned to their old position after the last geological catastrophe: Crocodiles. Most of their species probably died out 66 million years ago, and it could well be possible that the top position in the food pyramid at the transition between water and land was interrupted for some time. However, it can be stated with certainty that the crocodile form came back again in numerous genera and species, and that these showed a striking similarity to the species already existing a quarter of a billion years ago. And some still occupy their position at the top of the foodchain in the area between water and land today.

A steady Return through Convergence was more important to their long History than Survival

There is hardly anyone in paleontology who assumes that these recurring and far-reaching similarities are due to the common affiliation to the Crurotarsi branch . There are certainly some beneficial foundations in this regard for a steady return, but nearly 250 million years is an extremely long period of time, even on an evolutionary scale. Even over much shorter periods of time, biological evolution can produce many different living beings from a single parent form, whose recognizable characteristics are barely similar.

The real cause of the enormous similarity of Smilosuchus and the Saltwater Crocodile (as well as the species of the crocodile form that existed inbetween) is, also in the opinion of the expert paleontologists, “convergence”. This is about the fact that even life forms develop similar characteristics completely without relevant relationships to pure evolutionary adaptations in the same environmental conditions. Sometimes there are such strong similarities that practically unrelated species can hardly be distinguished, at least by a layman. Well-known examples are snakes and blindworms (Anguis fragilis), as well as swifts (Apus apus) and swallows (Hirundinidae).

The results of convergence sometimes extend to such precise details that it may be difficult to attribute these parallel developments to their mere adaptation to environmental conditions. On the other hand, in the reflective reconstruction of the respective developmental processes, even laypersons can quickly understand their evolutionary logic. Swifts and swallows have focused on the same food source of insects flying in the air. However, they did not only adapt to the mere snapping of the prey. Rather, through constant selection, they also aligned themselves as optimally as possible to the intersection of all the laws of nature which affect them during this activity. This ranges from such things as temperatures, thermals, humidity, gravity, centrifugal force, acceleration and everything that can be classified under the kinetics and dynamics. Since both swallows and swifts were affected by the same goal and same intersection of all the relevant laws of nature, two quite similar and small agile bodies with pointed wings emerged.

Power and Potential for Violence cannot have been the Recipe for Success of the Crocodile Form

The topic of the convergence of the “crocodile form” will be taken up later. Here, however, there are some further clarifications needed regarding frequent errors, which sometimes even reach into paleontological circles. One such error is the assumption that crocodiles were so persistent because they had such a great potential for physical violence. This is easy to refute, because the crocodile forms were demonstrably neither always defined by such physical size and extreme potential for violence as the Saltwater Crocodile or the Deinosuchus, nor were they dependent on such strong teeth as the latter examples possessed.

Since the Triassic period, many and much smaller species of the crocodile form have been found. There were large crocodiles both before and after the end of the Cretaceous period, which had a rather fragile muzzle, which did not fit at all to assumption number 1. The Ganges-Gharial, which still exists today, is up to six meters long, so it is hardly smaller than the Saltwater Crocodile and has a similar body. However, there is only one striking difference and it consists of a very narrow set of teeth, designed to catch smaller fish and ducks. The extreme potential for violence that can be seen in Saltwater Crocodiles is certainly a factor that affects their recurring position at the absolute top of the food pyramid. It cannot be, however, the most important and fundamental ingredient in their evolutionary recipe for success.

Saltwater crocodile between sharp rocks watching towards camera.

Other hypotheses about the extreme resistance of crocodiles, which are often discussed, quickly lose their substance upon closer inspection. Thus, often without knowing the overall history of the crocodile form, their stability is determined alone by the ”survival” of the violent geological and climatic faults at the end of the Cretaceous period, 66 million years ago. It is not uncommon for some supposedly decisive characteristics of crocodilians to be presented as a solution to the ”mystery” of this ”survival”, such as the fact that they were hematocryal and had a broad food spectrum.

In fact, however, there is no evidence that crocodiles survived the caesura 66 million years ago, in the sense that their species continued to exist under dark ash clouds and in icy cold temperatures. There is much to suggest that they largely disappeared. Out of the remains, which could quite likely have been small species without many similarities to the large Deinosuchus or the Saltwater Crocodile, the crocodile form came back through the evolutionary process with many species, including those at the absolute top of the food pyramid. This is – just like after the Triassic-Jurassic border – the crucial point. It must be about much more solid and fundamental factors of stability than the accidental survival of a single catastrophe.

The real mystery then lies in the questions of why this form was constantly reborn in the process of evolution, why it formed such striking similarities even over 250 million years, and why some of its species took the absolute top place in the food pyramid, at the transition between water and land again and again. If this mystery of biological evolution can be solved anywhere, there can be no better opportunity than to observe the strongest of all currently existing crocodiles. That has to be done where they themselves unfold, free and undisturbed, into their true nature.

In conclusion, it can be stated here that the proof of assumption 2 has also been provided in a stable manner. There is definitely no other proven form of life that has even come close to achieving such enormous stability at the top of the food pyramid, at the transition from water to land. There is no continuous line of corresponding species that leads from the Saltwater Crocodile, without interruption, up to 240 million years into the past. Already, however, the examples mentioned, which could be extended even further, are sufficient for the lack of any serious competition.

Continue to the Verification of the Assumption 3

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