The Mekosuchinae Story: From Discovery to Extinction

The discovery of Mekosuchinae fossils dates back to the 19th century, with the first find in Queensland, Australia.

These ancient crocodile-like creatures were initially thought to be modern crocodiles, but further analysis revealed they were a distinct group.

The name Mekosuchinae comes from the Greek word "mekos", meaning long, and "souchos", meaning crocodile.

Mekosuchinae fossils have been found in various parts of Australia, including Queensland, New South Wales, and Victoria.

Mekosuchinae first appeared in the fossil record in the Eocene in Australia. This marks the beginning of the subfamily's existence.

They survived until the Pleistocene in Australia and until the arrival of humans in the Pacific islands of Fiji, New Caledonia, and Vanuatu. There is disagreement on whether Mekosuchinae is a subfamily within Crocodylidae or a distinct family, Mekosuchidae, on its own within the superfamily Crocodyloidea.

Mekosuchine crocodiles were a diverse group, with species like Trilophosuchus rackhami being nicknamed the 'drop croc' due to its short snout and large eyes.

The History of Discovery of Mekosuchinae is a fascinating story that spans over a century.

The first recorded discovery of a Mekosuchinae fossil was in 1887 by paleontologist Arthur Smith Woodward, who found a skull in a Queensland riverbed.

Fossils of this ancient group of crocodilians were initially thought to be extinct relatives of modern crocodiles.

But as more discoveries were made, it became clear that Mekosuchinae were a distinct group with unique characteristics.

One of the most significant discoveries was made by paleontologist Richard H. Tedford in 1966, who found a nearly complete skeleton in a New South Wales coal mine.

This find helped to shed light on the evolution and diversity of Mekosuchinae.

Further discoveries in the 1970s and 1980s revealed that Mekosuchinae were more widespread than initially thought, with fossils found in Western Australia and other parts of Australia.

In the 2000s and 2010s, researchers continued to study mekosuchines, describing two more Kambara species and two more Mekosuchus species.

The late 2010s and early 2020s saw a surge in research, with multiple papers published by Jorgo Ristevski, including a complete overhaul of the genus Pallimnarchus.

A new name, Paludirex, was coined to bring stability to the taxon, replacing Pallimnarchus. Jorgo Ristevski also conducted two studies on the cranium of Trilophosuchus.

In 2023, the previously unknown species Baru iylwenpeny was described, and in 2024, Ultrastenos was reinterpreted as being synonymous with Baru huberi.

Mekosuchinae first appear in the fossil record in the Eocene in Australia, marking the beginning of their evolutionary history.

Their existence spanned over 40 million years, with some species surviving until the Pleistocene in Australia and the arrival of humans in the Pacific islands of Fiji, New Caledonia, and Vanuatu.

A key turning point in their history was the arrival of crocodiles from the genus Crocodylus, specifically the Saltwater Crocodile, which led to the extinction of Mekosuchines in Australia.

Mekosuchines were a diverse group, with various species exhibiting unique characteristics, such as Trilophosuchus rackhami, a short-snouted, large-eyed species nicknamed the 'drop croc'.

Their diversity is evident in the different shapes and sizes of the species, making them a fascinating subject of study.

Some notable species include Mekosuchus, which island-hopped across the Coral Sea, and Harpacochampsa camfieldensis, which may have resembled a false gharial.

Mekosuchines became extinct in Vanuatu and New Caledonia after the arrival of people, who are presumed to have driven them to extinction.

Mekosuchines come in a wide range of sizes, with the smallest known genus Trilophosuchus measuring an estimated 70–90 cm (28–35 in) long.

Some of the smaller species include Mekosuchus whitehunterensis, estimated to reach lengths around 60 cm (24 in), and M. inexpectatus, which has been estimated to have grown to lengths of around 1 m (3 ft 3 in) by Holt and up to 2 m (6 ft 7 in) by Balouet.

The largest well understood mekosuchines belong to the genera Baru and Paludirex, reaching lengths of 4 m (13 ft) and 5 m (16 ft) respectively.

The human skull is a relatively long and narrow shape, with an average length of about 18 centimeters in adults.

This shape allows for a large brain-to-body mass ratio, which is thought to be an adaptation for intelligence and cognitive abilities.

The skull is also slightly curved, with a prominent occipital bone at the back.

The shape and size of the skull can vary significantly between individuals and populations.

In some populations, the skull shape can be more rounded or more elongated due to genetic and environmental factors.

The skull's shape and size can affect the way it fits together with the rest of the face and jaw.

Mekosuchines come in a wide range of sizes, from the tiny Trilophosuchus, estimated to be around 70-90 cm long, to the massive Paludirex, reaching lengths of 5 m.

Trilophosuchus is one of several small-bodied taxa, with other notable dwarf taxa including Mekosuchus whitehunterensis, estimated to reach lengths around 60 cm.

The largest well understood mekosuchines belong to the genera Baru and Paludirex, reaching lengths of 4 m and 5 m respectively.

Some medium-sized members of the family include Quinkana, with species estimated between 1.5 m and 3 m in length.

Ultrastenos possibly reached a length of around 1.5 m, and M. inexpectatus has been estimated to have grown to lengths of around 1 m by Holt and up to 2 m by Balouet.

Kambara reaches between 2.5-4 m depending on the species, making it one of the larger mekosuchines.

The false gharial has a very long, thin snout. Some species from the early Miocene epoch might have shared similar characteristics.

Harpacochampsa camfieldensis is an example of a species that might have looked a bit like a false gharial. It lived during the early Miocene epoch.

Mekosuchinae's origins are a topic of ongoing research and debate. The clade's early history is shrouded in mystery due to the poor fossil record from Australia.

The Mesozoic crocodylomorph record from the continent is limited to Confractosuchus and Isisfordia, which may be highly derived non-eusuchian members of Neosuchia or among the basalmost eusuchians.

The most common trees suggest that Mekosuchinae originated during the late Danian, approximately 66 million years ago. This would be around 10 million years before their first confirmed appearance in the fossil record through Kambara.

However, if Orientalosuchina is indeed a subclade of mekosuchines, this would push the origins of the clade back into the Cretaceous.

There are various hypotheses regarding the origin of Mekosuchinae in Australia. One possibility is that they arrived via long-distance swimming, possibly with some degree of salt tolerance.

Alternatively, mekosuchines could have hypothetically arrived via land if dispersing from Asia into Europe and then the Americas or directly from Asia into North America.

However, a key issue with this idea is the complete lack of mekosuchine fossil material from the Americas and Antarctica, rendering dispersal from Asia directly into Australia (or via India) the more likely of the two origins.

Here's a summary of the possible origins of Mekosuchinae:

The phylogenetic relationships of Mekosuchinae are also the subject of ongoing research and debate. The clade is traditionally thought to be closely related to true crocodiles, but some analyses suggest that they may be more distantly related.

In fact, two phylogenetic trees recovered by Ristevski and colleagues feature the clade Orientalosuchina, which is deeply nested within Mekosuchinae. This would shuffle how the group relates to other crocodilians, with mekosuchines as a whole being more distantly related to true crocodiles.

Mekosuchines were once a diverse group of crocodilians that thrived in Australia during the Eocene and Oligocene epochs.

Their range was still somewhat limited, but they rapidly diversified into various morphotypes, including semi-aquatic generalists, large prey specialists, and dwarf forms.

The ancestor of this radiation likely appeared no later than the middle Eocene, but the exact origin of this diversification remains unclear due to a 30 million year gap in fossil records.

Mekosuchines continued to evolve and adapt to their environment, but their diversity began to decline during the Miocene-Pliocene transition.

This period saw the disappearance of many established mekosuchine groups, including the large macropredatory Baru and dwarf forms like Ultrastenos, Trilophosuchus, and Mekosuchus.

Despite this decline, some mekosuchines, such as Quinkana and Paludirex, managed to survive and even give rise to new forms like Kalthifrons and Paludirex.

The mekosuchines, a group of ancient crocodilians, underwent a remarkable diversification during the Late Oligocene. Their range and diversity were still relatively restricted during the Eocene, but by the Late Oligocene, they had rapidly diversified into various morphotypes.

This diversification is thought to have originated from an ancestor that appeared no later than the middle Eocene. However, the exact origin of this radiation remains unclear due to a 30 million year gap in mekosuchine fossils between the Late Oligocene forms and the earlier Kambara.

Mekosuchines continued to evolve and diversify, with Miocene records primarily coming from localities in Queensland and the Northern Territory. Despite their enormous taxonomic diversity, their range was still somewhat limited during this time period.

The transition from the Miocene to the Pliocene saw a drop in diversity among mekosuchines, with the disappearance of both large macropredatory Baru and dwarf forms like Ultrastenos, Trilophosuchus, and Mekosuchus.

Mekosuchines, a group of ancient crocodilians, suffered greatly from the effects of global cooling and Australia's continuous drift north throughout the Pleistocene.

The gradual change in climate led to the disappearance of inland river systems, which had a devastating impact on semiaquatic mekosuchines like Paludirex.

The Lake Eyre Basin was among the first systems to rapidly deteriorate around 48,000 years ago, followed shortly by other systems in the next eight thousand years.

Rainfall fell to levels far below those of today, depriving the systems of their water supply, which didn't change until 30,000 years ago, when it was too late for the systems to recover.

Members of the genus Crocodylus could have potentially retreated to coastal waters due to their osmoregulation, but the more freshwater-dependent mekosuchines like Paludirex would have died out as their habitats dried up.

The aridification of Australia led to the collapse of the continent's rainforest systems around 50,000 years ago, and by 44,000 years ago, fires had begun to crop up more frequently than before.

Mainland mekosuchines died out during the Pleistocene, but isolated insular taxa continued to survive, possibly even into the Holocene.

The extinction of Mekosuchus is frequently linked to the arrival of the Lapita people in the South Pacific, supported by the association of M. kalpokasi remains with human tools at the Arapus archaeological site on Efate.

Mekosuchines were likely semi-aquatic predators, as evidenced by their robust build and short, broad snouts. They likely spent most of their time in or near water.

Their diet consisted of a variety of aquatic and terrestrial animals, including fish, turtles, and small mammals. They were likely apex predators in their ecosystems.

Some species of Mekosuchines had specialized dental structures, such as the "papillae" of the Sarcosuchus, which were likely used to grasp and hold onto their prey.

Terrestriality is a key aspect of animal behavior and ecology. It refers to the ability of an animal to live and thrive on land.

Some animals, like the sea turtle, have a strong instinct to nest on land, despite spending most of their lives in the ocean. This is crucial for their survival, as it allows them to lay their eggs in a safe and protected environment.

Terrestrial animals often have adaptations that help them navigate and survive on land, such as strong legs and sharp claws. For example, the gecko's ability to climb walls and ceilings is a result of its specialized feet and claws.

Many animals, including birds and mammals, have evolved to live in close proximity to water sources, such as rivers and lakes. This is often because water is essential for their survival, whether it's for drinking, bathing, or regulating their body temperature.

Some animals, like the desert-dwelling kangaroo rat, have even adapted to survive in environments with limited water availability.

In Australia's Pleistocene epoch, a mighty mekosuchine crocodile called Quinkana ruled the land as a true apex predator, sitting atop the food chain.

Quinkana was a formidable force, with its presence at the top of the food chain a testament to its power and adaptability.

The mekosuchines were known to spread to the Pacific Ocean islands by "island-hopping" across the Coral Sea, likely floating on logs or debris to reach new lands.

Greater Chesterfield Island and New Caledonia were among the first islands they colonized, paving the way for further expansion to other islands.

These ancient crocodiles were highly adaptable, able to thrive in various environments, from land to sea.

The fossil record of Mekosuchinae is a treasure trove of discoveries that have helped scientists understand the evolution of these ancient crocodilians. The first material recognized as belonging to this group was described in 1886 by Charles Walter De Vis.

The fossils discovered by De Vis in the Darling Downs in Queensland consisted of skull and postcranial fragments that he dubbed Pallimnarchus pollens. Later research showed that the material belonged to multiple individuals and different genera, including Paludirex and Quinkana.

In the 1970s and 1980s, scientists like Hecht, Archer, and Molnar published on crocodile fossil material, laying the groundwork for increased interest in Australasian crocodilians in the 1990s and early 2000s.

The earliest finds of mekosuchines date back to 1886, when English zoologist Charles Walter De Vis described fossil material from the Darling Downs in Queensland, Australia.

This material was initially dubbed Pallimnarchus pollens by De Vis, although he later admitted that he was unsure if it represented a distinct animal from other known taxa at the time.

The fossils consisted of skull and postcranial fragments, which were later found to belong to multiple individuals and even multiple different genera, including Paludirex and Quinkana.

The name Pallimnarchus eventually became widely used by other authors, despite De Vis' caution regarding the taxon.

In the 1970s and 1980s, a groundwork was laid for increased interest in Australasian crocodilians, which would eventually lead to the description of the subfamily Mekosuchinae in the 1990s.

The 1990s saw a surge in publications on crocodile fossil material, with authors like Paul Willis, Steven Salisbury, and Dirk Megirian becoming prolific in the study of mekosuchines.

These researchers proposed the concept of the Australian Tertiary crocodylian radiation, which initially included three mainland taxa: Baru, Quinkana, and Pallimnarchus.

The Middle Miocene-Pleistocene Sites are a treasure trove of fossil discoveries.

During this time period, many early human ancestors roamed the Earth, including the genus Australopithecus, which dates back to around 4-2 million years ago.

One notable site from this era is Laetoli in Tanzania, where ancient footprints were found preserved in volcanic ash.

These footprints, estimated to be around 3.6 million years old, provide valuable insights into the locomotion and behavior of early human ancestors.

The famous site of Olduvai Gorge in Tanzania, which spans from the Early Pleistocene to the Late Pleistocene, has yielded numerous significant fossil discoveries.

Some of the most notable finds from Olduvai Gorge include early human fossils, such as Homo habilis, and stone tools, which demonstrate the earliest stages of human tool use.

Figures play a crucial role in understanding the fossil record.

The figures in the article provide a visual representation of various species and their characteristics.

Figure 2 shows the position and orientation of the fossil, giving us a better understanding of its context.

Figure 5 displays a posterior fragment of the right fossil, specifically a Mekosuchinae, which is tentatively identified as Baru wickeni.

The fossil is from NTM P6372.

Baru wickeni is also depicted in Figure 6, which shows a posterior region of the left fossil.

The fossil is from NTM P2914-14.

The figures provide valuable information about the species and its characteristics.

Figure 9 shows the skull of Baru wickeni in dorsal view, giving us a clear look at its shape and structure.

The fossil is from NTM P91171-1.

This figure is particularly interesting as it provides a comprehensive view of the skull.

Baru wickeni is also shown in Figure 13, which displays its rostrum in dorsal view.

The fossil is from QM F16822, which is the holotype.

This figure is significant as it provides a detailed view of the rostrum.

Figure 17 shows Baru darrowi, which is a different species from Baru wickeni.

The fossil is from QM F30319.

This figure is interesting as it provides a comparison between the two species.

The geographic and stratigraphic distribution of Baru darrowi is shown in Figure 21.

This figure is particularly useful as it provides a broader context of the species' existence.

The world of Mekosuchinae is a fascinating one, and it's not just the named species that capture our attention. Unnamed forms of these crocodilians are just as intriguing, with several examples scattered across Australia and New Zealand.

The "Darling Downs taxon" is one such example, represented by multiple bone fragments that show some resemblance to Paludirex species, but are distinct from them. Unfortunately, the material is too fragmentary to be conclusively assigned to the genus or named as a new species.

In Australia's Mount Etna Caves National Park, ziphodont crocodilian teeth have been recovered, adding to the mystery of these unnamed forms. These teeth are similar to those of other ziphodont mekosuchines, but their exact affinities remain unclear.

The "OngevaQuinkana" from Alcoota is another unnamed species within the Quinkana genus, highlighting the complexity of these ancient creatures. As scientists continue to study these remains, we may uncover more about their place in the Mekosuchinae family tree.

The "Floraville taxon" may represent a separate genus of ziphodont mekosuchine, rather than just another Quinkana species, showing the diversity of these unnamed forms. This discovery is a reminder that there's still much to learn about the ancient world of crocodilians.