He died on the spot after eating a dinosaur. Can he be called the "Crocodile God"?

How could the crocodiles living 100 million years ago eat the "dominant rulers of the earth" at that time - dinosaurs?

There really was a crocodile that not only ate a dinosaur, but also became a fossil along with it—and, about 100 million years later, it was discovered by paleontologists! This highly informative crocodile fossil actually contained several dinosaur bones in its abdomen.

This brave crocodile also earned its species a domineering yet childish scientific name, Confractosuchus sauroktonos, which literally means "Broken Crocodile God, Dinosaur Killer" in Chinese!

Scene reconstruction | Julius Csotonyi

Decryption layer by layer to restore the crime scene

This fossil was unearthed in the Winton Fossil Group in Australia and is from the Cenomanian stage of the late Cretaceous period. The skeletal fossils in the crocodile's abdomen indicate that its last dinner was most likely a dinosaur. What exactly happened at that time? Detective paleontologists try to reconstruct the scene from the clues in the fossils.

Protagonist 1: The main body of the fossil "Dinosaur Killer Crocodile"

This dinosaur killer has a similar head to today's crocodiles, but from the morphological characteristics, it cannot be classified into any known genus or species. It is a completely new species. Like the existing crocodiles, it belongs to the Eusuchia suborder and can be said to be a close relative of the existing crocodiles.

Although the lower body is almost completely shattered and cannot be restored, based on the proportions of the head, we can calculate that the crocodile's body length is about 2 to 2.5 meters. This size is not considered a very large crocodile, whether it is today or 100 million years ago.

A 3D reconstruction of the fossil found this time, with the red part showing the contents of the abdomen | White et al.

Protagonist 2: Dinosaur bone fossil in the belly

Based on a femur, paleontologists speculated that the unfortunate dinosaur in the crocodile's belly belonged to the ornithopod suborder. Ornithopod dinosaurs have a significant anatomical feature: a sharp protrusion on the upper side of their femur, scientifically known as the "4th trochanter." Based on the specific location, size and shape of the 4th trochanter, archaeologists have also ruled out the possibility that it was an ornithopod suborder such as Iguanodon.

Based on the diameter of the femur, scientists also estimated the weight of the dinosaur, which was only about 1 to 1.7 kilograms, not even as heavy as a chicken. With such a small size and an underdeveloped spine, paleontologists determined that this was a juvenile dinosaur.

Ornithopods, Iguanodon second from left｜John Conway

Modus operandi

The way the dinosaur's right femur was broken and the "V"-shaped concave tooth marks on the left femur indicate that the crocodile probably first pounced on the dinosaur, bit its hind legs to prevent it from escaping, and then tore the legs off and swallowed them - ambushing the prey and then dismembering and eating it, which is also the hunting method of modern crocodiles.

The dinosaur skeleton remains in the crocodile's abdomen, of which os is the left femur, tx is the right femur, and the depression on the femur in r is believed to be the tooth mark of the crocodile. | White et al.

Another possibility is that the crocodile may have swallowed and chewed the dinosaur directly after it died. In this case, the fracture in the femur may have been caused by chewing.

Due to the incomplete preservation of the fossils and the damage during excavation, the real cause of death of the dinosaur can only remain in doubt. However, this is not the only reason why this rare fossil excites paleontologists.

Catching the stomach of a crocodile to uncover an ancient recipe

Previously, most of the ancient crocodile fossils found by people had no residue in the abdominal cavity. We can only speculate the diet of crocodiles at that time by looking for teeth marks suspected to be crocodiles on other fossils or observing the shape of crocodile skulls. For example, the most famous crocodile in the Cretaceous period, Deinosuchus, is one of the largest crocodiles in history, with a body length of about 11 meters; scientists speculate that its food should be dinosaurs of similar size - but this is only a guess based on its body size, and there is no direct evidence.

Deinosuchus fossil | Daderot / Wikimedia Commons

Scientists analyzed that the fact that there were no food remains in crocodile fossils in the past may be a hint that crocodiles 100 million years ago may have had strong stomach acid like modern crocodiles. Therefore, few prey could remain intact in the crocodile's stomach until they were preserved by fossils.

However, if crocodiles 100 million years ago already had super strong stomach acid, why are there no traces of acid etching on the dinosaur remains in this fossil? Paleontologists further speculate that this dinosaur killer crocodile probably died soon after eating, and then quickly entered the fossilization stage, so the contents in its stomach were not corroded by strong acid.

Dinosaur killer crocodile skull fossil | White et al.

This unfortunate crocodile that died quickly after eating its last supper has excited paleontologists. Its appearance directly proves the existence of a food chain such as "crocodilian-ornithopod dinosaurs" in the late Cretaceous period. In other words, dinosaurs were indeed on the crocodile's menu at that time.

In fact, this dinosaur may be just one of their diverse diets. Many previous studies have found that the shape of crocodiles' skulls is related to their food choices. If you put the skull shape of the dinosaur killer crocodile into a known association graph, you will find that its skull shape is similar to that of omnivorous crocodiles. The "omnivorous" here does not mean that they can eat both herbivores and carnivores, but that their diet can include prey of different sizes, movements, etc.

The geometric morphology of crocodile skulls can help us infer their diet | White et al.

Crocodile: Evolving, please do not disturb

Whatever it ate before it died, the crocodile itself is worth studying. Its appearance reveals the history of crocodile evolution.

As a reptile adapted to amphibious life, modern crocodiles have a spine composed of procoelus vertebrae. This special spine can not only drive the crocodile to drag and turn on land without breaking due to friction between its heavy body and the ground, but also allow the crocodile to swing flexibly in water.

Vertebrae that are concave at the front and fit together provide more stability when the spine is bent than vertebrae that are flat at both ends | Fronimos, 2016

But it was not like this hundreds of millions of years ago. At that time, the ancestors of crocodiles did not have the special vertebrae they have today, but relied on the hard "exoskeleton" covering the outside of the spine - two rows of ossified epidermis to ensure mechanical support when turning. These two rows of "armor" greatly reduced their flexibility in the water, so the earliest crocodiles were more suitable for life on land.

Ossified epidermis from primitive form (top) to partially disintegrated (bottom) | Salisbury, 2001

Later, after billions of years of evolution, the long strips of ossified epidermis gradually disintegrated from both sides, becoming the keratin scales on the bodies of modern crocodiles, which support their flexibility in water.

Crocodiles now have patches of horny scales | Dewet / Wikimedia Commons

But which evolved first, the disintegration of the ossified epidermis or the appearance of specialized vertebrae? The emergence of the dinosaur-killing crocodile has helped paleontologists who have long been searching for the answer to this question to complete an important piece of the puzzle.

From the fossils, the ossified epidermis of the dinosaur killer crocodile has completely disintegrated, but only the vertebrae of the neck have evolved into a "front concave shape". This shows that at least the crocodiles on this evolutionary branch first abandoned the hard exoskeleton required for life on land and gave priority to flexibility in water. They "destroyed and then rebuilt", and then gradually acquired a strong spine that could bear the heavy body on land, and finally dominated the land again.

Why do the vertebrae start to strengthen from the neck? This may not be a coincidence. After all, eating is the most important thing. The strengthened neck can help them bite the prey, swing and tear, and their heads will not be torn off by the struggle of the prey. Back to the method of committing the crime in this case, the body structure of the dinosaur killer crocodile also proves that its ambush predation is feasible - it can swim from the water to ambush, and it can also tear smaller dinosaurs apart, and finally have a good meal (although it will die soon).

Excavation site｜White et al.

Behind the fossils, there are billions of years of history that we know nothing about. Just like this "case", paleontological research is full of uncertainty, and often requires working backwards from the results. We can only get a glimpse of the leopard, and perhaps one day a new fossil will be discovered that can easily overturn all previous theories.

The vastness of billions of years of evolutionary history makes people feel desperate, but also deeply attracted. Paleontologists can only use existing evidence to logically deduce the more likely truth, while at the same time being in awe of the limitations of this logical deduction. Perhaps this is the romance of paleontologists.

References

[1]Campione, NE, Evans, DC, Brown, CM & Carrano, MT (2014). Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions. Methods Ecol Evol, 5, 913-923.

[2] “Crocodile.” Wikipedia, Wikimedia Foundation, 21 Feb. 2022, https://en.wikipedia.org/wiki/Crocodile.

[3] “Crocodyliformes.” Wikipedia, Wikimedia Foundation, 27 Dec. 2021, https://en.wikipedia.org/wiki/Crocodyliformes.

[4] “Deinosuchus.” Wikipedia, Wikimedia Foundation, 3 Feb. 2022, https://en.wikipedia.org/wiki/Deinosuchus.

[5]Fronimos, JA (2016). Functional mechanics of concavo-convex articulations and neurocentral sutures in the vertebral column of sauropod dinosaurs (Unpublished doctoral dissertation). University of Michigan, Michigan, USA.

[6]Molnar, JL, Pierce, SE, Bhullar, BA, Turner, AH, & Hutchinson, JR (2015). Morphological and functional changes in the vertebral column with increasing aquatic adaptation in crocodylomorphs. Royal Society open science, 2(11), 150439.

[7]Salisbury, SW & Frey, EF (2001). A biomechanical transformation model for the evolution of semi-spheroidal articulations between adjoining vertebral bodies in crocodilians. In Crocodilian biology and evolution (eds GC Grigg, F Seebacher, CE Franklin), pp. 85–134. Chipping Norton, Australia: Surry Beatty and Sons.

[8]White, MA, Bell, PR, Campione, NE, Sansalone, G., Brougham, T., Bevitt, JJ, Molnar, RE, Cook, AG, Wroe, S., & Elliott, DA (2022). Abdominal contents reveal Cretaceous crocodyliforms ate dinosaurs. Gondwana Research, 106, 281-302.

Author: Yab

Editor: Maotun, Mai Mai

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