The following terms with these definitions will be used on this page:
- Gavial
- Gavialoidea, the Tomistominae are considered gavials here
- Alligator
- Alligatorinae
- Caiman
- Caimaninae
- Basal alligator
- Non-alligatorid alligatoroid
- Crocodile
- Clade including Crocodylus + Mecistops + Osteolaemus
- Mekosuchian
- Mekosuchinae
- Sebecian
- Sebecia
Crocodylomorpha is one of the two surviving groups of archosaurs, along with birds, although represented today only by the Crocodilia. Most Crocodilia today live in places with hot, wet climate. That's the way for the Crocodilia of this timeline. But one other branch of crocodylomorphs survived in this timeline – the Sebecia. The Sebecia are one of the trio of coexisting predatory groups of South America, along with the fearsome birds of the Phorusrhacidae and the marsupial relatives known as the Sparassodonta. The Sebecia are entirely terrestrial, as common for many extinct pseudosuchians. On the contrary, the crocodilians have conquered the seas with the fully aquatic Carcharosuchia.
Classification[]
Today we are familiar with a simple set of crocodilians, and with the exception of the false gavial, without confusing relations. These are crocodiles, alligators, caimans, the gavial, and the false gavial. Although these have a complex evolutionary path, this cladogram will illustrate only living groups.
| Crocodilia |
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Note: Although this cladogram considers the possibility of the false gavial being in Crocodylidae, on this page it will be assumed to be in Gavialidae
Of course, it wasn't always this way. Taking extinct forms back to the Eocene into account, we add in mekosuchians and basal alligators, and there is strong evidence for crocodiles, alligators, and Tomistominae which escaped the fossil record. The evidence for a common ancestor of Gavialis and Gryposuchinae which escaped the fossil record and lived around this time is compelling; and Eogavialis, the sister taxon to this clade, was also clearly present at this time. The sebecians, not true crocodilians, also were present at this time. And in the warmer climate, the crocodylomorphs proliferated, becoming the most successful reptilian dynasty of this timeline.
Crocodilia[]
Gavialidae[]
By the point of divergence in this timeline, all non-gavialid gavials had long been extinct. Only the Gavialidae remained, represented by the basal gavialid Eogavialis; Progavialis, an ancestor of Gavialis and Gryposuchinae which escaped the fossil record; and the tomistomine Tenuidon, which also escaped the fossil record. Together, they represent the three branches of gavialid evolution at the time. All three would be successful, but one group in particular would evolve into the most successful group of crocodilians in the entire Cenozoic.
The following cladogram will be assumed for Gavialidae in this project.
| Gavialidae |
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Note: Eogavialinae is a hypothetical group, only known in our timeline from Eogavialis. Gavialinae includes more than just the direct ancestors of the modern Gavialis, being defined here as everything closer to Gavialis than to Eogavialis.
Eogavialinae[]
Eogavialis was an African gavialid, a piscivore which lived along the banks of rivers. Phylogenetically, it appears to be closer to the modern Gavialis than to the modern Tomistoma. Evolving in the late Eocene, Eogavialis survived until the late Pliocene on HE. Here, several branches of Eogavialis descendants evolved, all in the subfamily Eogavialinae. Eogavialis itself went "pseudo-extinct", evolving into other forms with the traditional Eogavialis surviving until the Miocene Thermal Maximum. But three tribes of Eogavialinae survived, each with a separate lifestyle.
The first of these tribes to evolve were more specialised African piscivores, the Afrogavialini. These evolved in the early Miocene in Kenya, the original land of Eogavialis. The first two genera of Afrogavialini were very specialised, Dipnophaga and Cichlophaga. The former fed almost entirely on lungfish, and went extinct during the Miocene Thermal Maximum; while the latter's diet consisted mostly of perciform fish, specifically cichlids, and also went extinct during the Miocene Thermal Maximum. However, the third of the five genera to evolve, Afrogavialis, evolved from a stock of Cichlophaga which converged with the modern Gavialis, evolving the very long and thin snout to catch fish. Afrogavialis lived mostly in eastern Africa, but by the Pliocene one population had moved to north Africa, and another to Europe. Despite the fact that the Sahara never formed, the area where it is today was still relatively dry. Xerogavialis evolved to withstand the dryness, the only gavial to live in a relatively dry climate in this timeline. The last of the Afrogavialini to evolve was Boreogavialis. It lived in southern Europe, migrating through the Middle East, but went extinct during a short period of relative cold during the Pleistocene. And thus, two genera of Afrogavialini survive to the present: the east African Afrogavialis and the north African Xerogavialis.
The second tribe of Eogavialinae to evolve were the Hemisuchini, although they evolved only just before the more conservative third tribe. They are the only gavials to hunt large game, like perissodactyls. The first two genera out of four to evolve were Scopulidontosuchus, a south African form with serrated teeth; and Hemisuchus, a "half crocodile" with a short snout and a robust build. The Miocene Thermal Maximum was nearly on par with the least of the "big five" mass extinctions, and Scopulidontosuchus was wiped out because of its competition with crocodiles, although not without a fight. A "standoff" of about 1000 Scopulidontosuchus, the strongest of the strong, kept a constant presence on the southern tip of Africa. Finally, when the Miocene Thermal Maximum reached its height, the heat-seeking crocodiles eventually drove the Scopulidontosuchus to extinction. However, the unique Hemisuchus survived, and gave rise to two more genera, appearing around the same time – Robustosuchus and Titanogavialis. Both of these genera were more adapted than Hemisuchus, and Hemisuchus went extinct in the middle Pleistocene after a gradual decline. Robustosuchus migrated from southern Africa to western Africa, the only gavial to do so, and evolved stronger jaws. Titanogavialis had an advantage in size, although its south African environment was filled with fish. Despite growing to a maximum size of 10 meters, Titanogavialis reverted to piscivory. With the crocodiles being more abundant in southern Africa, the first species of Titanogavialis, the carnivore Titanogavialis robustus went extinct, while the piscivore Titanogavialis piscivora survived.
Although similar to the Afrogavialini, the Isthmosuchini migrated to the Middle East, which in this timeline is little more than a strait due to the high sea levels. Due to heavy competition from the Gavialinae farther east, the one genus that migrated to the area around the modern Indus Valley soon went extinct. The first genus to evolve, Sinaisuchus lived on the Mediterranean, a usual piscivore which had migrated north after evolving from Eogavialis. Evolving in the early Miocene, Sinaisuchus managed to survive until the later Xerogavialis evolved and replaced it in the middle Pliocene, a time of warmth but also dryness, perfect for Xerogavialis. But Sinaisuchus didn't go extinct before evolving into two more genera – Isthmosuchus and Caspiosuchus. Isthmosuchus, which lived in Asia Minor, survived, once again evolving the snout of a modern gavial. Isthmosuchus survived, living the farthest east of any modern eogavialine. However, Caspiosuchus never evolved the long snout for catching fish, and also lived right in the middle of the territory of the Gavialinae, and went extinct in no more than 2 million years, dying out even before its ancestor, Sinaisuchus, right at the end of the Miocene. None of the Isthmosuchini went extinct in the Miocene Thermal Maximum because they evolved only 17 million years ago, with the Afrogavialini evolving 27 million years ago and Hemisuchini evolving 20 million years ago; so the then well adapted Sinaisuchus, the only of the Isthmosuchini to be around at the time, survived the thermal maximum.
Eogavialinae managed to grip nearly every piscivorous niche in Africa, and maintaining a presence in Asia Minor and for a short time even the Indian subcontinent. And two groups in this subfamily are unique to this timeline's Gavialidae: the land based Xerogavialis; and the robust Hemisuchus, Robustosuchus, and Titanogavialis robsustus. These robust gavials are in fact nothing like any crocodilian, best described as semiaquatic rauisuchians. But while much more diverse than in this timeline (in which they go extinct in the late Pliocene), with five living genera, there was one niche they didn't manage to exploit – the ocean. No, that would be left to the tomistomines.
Gavialinae[]
The critically endangered gavial
Gavials were represented by only three genera at the time of divergence, only one of which was common enough to be represented in the fossil record. Progavialis may not have been represented in the fossil record, but it surely was better adapted, being the only one of the original three genera to survive to the present. Still, its descendants fared worse than the original genus. Progavialis evolved just after than Eocene-Oligocene extinction, from a common ancestor with Eogavialis. Progavialis lived on the eastern coast of Asia, a piscivore nearly identical to the modern gavial. Progavialis was a success, one of the few crocodilians which lived at the point of divergence to survive to the present day. But isolated subpopulations gave rise to species which migrated to the Indian subcontinent, the Siamese peninsula, and the Middle East. At the height of their dominance, in the late Miocene, the Gavialinae rivaled the Eogavialinae, driving at least one of their rivals' genera to extinction.
The Gavialinae of this timeline are organised into two tribes, the first of which to evolve was the Asiaticonychini, which evolved from Progavialis in the early Miocene. Many members of this tribe live in the Siamese peninsula, not interfering much with the main stock of Progavialis. Their unique feature is a sort of claw on each of their front limbs, helping them spear fish. This works faster than using the jaws alone to catch fish, and so this tribe was a success. The first genus to evolve was Asiaticonychus, the type genus, nearly identical to Gavialis other than the claws on the front limbs. To more genera evolved from Asiaticonychus during the middle Miocene, Sinogavialis, a Chinese form with sharper teeth, which competed with Progavialis; and Assymetria, which had a claw on its right arm 4 centimeters longer than that of its left. Assymetria died out by the end of the Miocene, perhaps because the right claw was so long as to hinder swimming. However, Assymetria died out in an event which wiped out most Gavialinae, including its ancestor, Asiaticonychus, the cause of which is unknown. The only of the Asiaticonychini to survive was Sinosuchus, and Sinosuchus gave rise to the last of this tribe, Hastodon, with spear-like top teeth jutting out of the front of its mouth, almost straight forwards. Hastodon migrated from the Siamese peninsula to the area around the Bay of Bengal. Both Hastodon and Sinosuchus survived.
Some groups of animals proliferate very quickly, then go extinct suddenly, leaving an impression on the ecosystems they abandon. That's exactly the case with the Arabiogavialini. The first representative of the tribe, Nothogavialis, lived in India during the late Oligocene, a creature living in similar conditions to the modern gavial, and living on the rivers leading to the Bay of Bengal. One descendant of Nothogavialis lived on the southern tip of India, a relatively small (3 meter) piscivore called Dravidiosuchus. Nothogavialis stayed in its home territory, while Dravidiosuchus became a more aquatic creature, sometimes swimming freely along the coast from the near-sunken area which makes up the southern tip of India to the just as sunken area of the Siamese peninsula. Despite its aquatic nature, Dravidiosuchus never strayed far from the coast, preferring to swim in swamps and marshes. Then the Miocene Thermal Maximum hit. Nothogavialis was fine during this period, but Dravidiosuchus was in danger of living in a sinking area. This pushed the mainstream Dravidiosuchus farther into the Indian mainland, and certain subpopulations gave rise to Arabiogavialis, the namesake of the tribe, and the genus which displaced Caspiosuchus; as well as the less successful Persiogavialis, evidently living in Persia. The four genera lived well alongside each other, that is until the event that wiped out all but one genus of Gavialinae. All four genera were wiped out, beginning with Persiosuchus and ending with Arabiogavialis. These genera were wiped out alongside two genera of Asiaticonychini, and the best explanation seems to be a sort of infectious parasite only infecting members of this subfamily. And so, these ecosystems were devastated, and India would never see a gavial again.
So, no more than three genera of Gavialinae survive, saying that it was more luck than anything that Gavialis managed to survive to the present. Clearly, the Eogavialinae were destined to be successful, and Gavialinae to be no more than humble piscivores. But even the eight genera that make up the clade composed of Gavialinae and Eogavialinae were nothing compared to the low estimate of twenty genera of Carcharosuchia. No, none of these lived happily side by side. These were world conquerers.
Tomistominae[]
The modern false gavial, Tomistoma schlegelii
Tenuidon was, depending on how you think about it, a complete failure, or the most successful crocodilian of this timeline's Cenozoic. Apparently not adapted well enough, it evolved right before the absence of the Grande Coupure, and thus never had to deal with major changes in fauna and flora. The problem with Tenuidon was not its adaptations (although it was less derived than even the false gavial), but its range: it was stuck right in the middle of a sinking European continent. Tenuidon was wiped out 28 million years ago by lacking adaptations to its sinking habitat. Two genera, however, evolved from it, one being Anatopus, and the other Ruthenosuchus. Anatopus had webbed feet, and other than the unspecialised snout, was similar to Dravidiosuchus in anatomy. Meanwhile, the Russian Ruthenosuchus died out 25 million years ago due to the cool and dry climate of the late Oligocene, combined with its northern range. Anatopus survived until the Miocene Thermal Maximum, but its descendant taxon, Carcharogavialis, was the first of the carcharosuchian dynasty.
Carcharosuchia[]
All Linnaean ranks are obsolete in this situation. Carcharosuchia is nested within Tomistominae, and under Linnaean taxonomy, would be considered a tribe. But in truth, their diversity is the equivalent of a Linnaean superfamily, some might say even an order. After all, almost twice as many carcharosuchian species exist than crocodilians on HE. And so, we will treat this clade as neither a tribe or an order, but as an unranked clade which contains many nested clades within it. But how did this diversity come about? The story goes back to the first of their kind, Carcharogavialis.
Now, all groups with radical changes have to go through intermediate forms. That's exactly what Carcharogavialis was. It had a typical crocodilian tail, and webbed feet, living in the deeper parts of the Mediterranean Sea. Its limbs were longer than typical crocodilians; these would eventually give rise to flippers. Only coming onto land to lay eggs and mate, Carcharogavialis had nearly useless limbs, and with the sprawling crocodilian posture atypical of archosaurs, it was unable to walk well. A piscivore just like its relatives, this was no fearsome sea monster, but a true marine reptile nonetheless. Just before this time, a near salinity crisis in the Mediterranean due to the dry climate occurred, mostly trapping Carcharogavialis. But of course, there's nothing marine creatures prefer more than more ocean. And the Miocene Thermal Maximum was about to make that happen.
By the end of the thermal maximum, eight genera and fourteen species of Carcharosuchia existed. An event lasting just over 1 million years, the Miocene Thermal Maximum caused the extinction of certain competitors, but more importantly, the sea level rose fifty feet. Soon, Europe was just a collection of islands and straits, allowing for Cretaceous-like seaways. These eight genera were divided into two clades, Suchovenatores and Pterygiosuchia. At the time of the maximum, Suchovenatores had ten of the fourteen species, and five of the genera. They all lived throughout the straits of Europe, hunting medium-sized fish and small mammals. Their feet were a compromise between flippers and ambushing abilities. While they spent the majority of their life at sea, they needed strong limbs to get just a small bit onto land and take their prey by surprise. The majority of their diet was piscivorous, but at least the namesake of the group, Suchovenator, hunted small tylopods for some of its diet. The large game, however, was out of reach for the Suchovenatores, being overshadowed by the Choristodera.
A reconstruction of Pliosaurus, which has a close resemblance to some pterygiosuchians
Meanwhile, the Pterygiosuchia was a group with three genera, four species, and without any specialisations for large game. However, their great advantage was their limbs and pliosaur-like build. Although strong enough to get onto land and lay their eggs, their flippers were no longer webbed feet at all (the Suchovenatores having thalattosuchian-like limbs), and were expert swimmers. The original four species were made up of one species living off of western Europe (Plesiovenator minoris), a small game eating form reaching only four meters in length; and a west African group, the real world conquerers, eventually living in the entire Atlantic and Indian Oceans, and perhaps the only crocodilians of European origin to reach the Pacific.
| Animalia | |||||
|---|---|---|---|---|---|
| Mammalia | Eutheria | Laurasiatheria | Artiodactyla | Cetancodontamorpha • Dichobunoidea • Ruminantia • Tylopoda | |
| Ferae | Carnivora • Creodonta • Pholidota | ||||
| Meridiungulata | |||||
| Perissodactyla | Chalicotherioidea • Hippomorpha • Rhinocerotoidea • Tapiridae | ||||
| Euarchonta | Dermoptera • Haplorhini • Scandentia • Strepsirrhini | ||||
| Afrotheria • Leptictida • Xenarthra | |||||
| Metatheria | |||||
| Sauropsida | Aves | Neoaves | Passeriformes • Phorusrhacidae | ||
| Choristodera • Crocodylomorpha • Lepidosauria • Testudines | |||||
| Habitats | India • South America | ||||