Long ago, during the Late Cretaceous Period, much of the American Midwest was covered by a shallow sea. Scientists today call it the Western Interior Seaway. Different kinds of magnificent monsters lurked in the murky waters of this North American seaway. One of them was a sharp-toothed predator fish that would have dwarfed famous marine predators today, such as the Great White.
The fish’s name translates as “sword-ray” in Latin. High among the largest fish to have lived in the Cretaceous, it had a ferocious appetite. Several fossils of this fish have been found in association with fossils of other aquatic creatures it either preyed on or was a prey to itself.
What Did Xiphactinus Look Like?
Sharks are kings in today’s aquatic ecosystem. But back in the Cretaceous, these sharp-toothed predators weren’t as high up in the food chain as they currently are. The title of the “big dog” of the Cretaceous would go to other marine monsters like the Xiphactinus.
Xiphactinus was a giant fish with smooth-pointed teeth that gave it an undoubtedly menacing appearance. The big-dog title fits even more because it literally had the face of a bulldog courtesy of its big, sharp, fang-like teeth. In terms of size, it was an average of 16.7 feet long, although experts think it might have grown up to 20 feet. Male great white sharks are about 11 to 13 feet on average, while the larger females often peak at about 15 to 16 feet. That provides some context into how large this fish probably was.
In addition to being massive, Xiphactinus had a fear-inducing appearance. Like all predators, the sharp-toothed monster brandished massive teeth in its huge jaws. Each needle-sharp teeth were several inches long and were quite noticeable on its huge head. Interestingly, the fish’s body was notably slim rather than robust.
The slender body would have favored mobility, allowing the animal to move faster in its marine home. Calculated estimates reveal that the fish species could reach an amazing top speed of 37 miles per hour (60 kilometers per hour). It also had a dorsal fin that faced backward, a pelvic fin that faced downwards, and very smooth scales that further aided quick motion.
What Did Xiphactinus Eat?
Xiphactinus was a formidable predator, and its interesting feeding habits have been the major talking point in studies relating to this animal. The massive size and unique dentition of this fish suggest that it could have been able to feed on almost every animal smaller than itself. Xiphactinus was the largest bony fish that lived during the Cretaceous. Its jaw was massive enough to swallow a six-foot-long fish. Fossils of partially digested fish of this size have been found inside the bowels of this predator, providing insights into its feeding habits.
Some of these discoveries suggest that the Xiphactinus attempted to eat prey larger than it could feed into its stomach and may have choked to death on its food. It’s not every day you find a fish-within-fish situation, and this case was one of the most interesting ones. Scientists found the remains of a six-foot prehistoric shark (Gillicus arcuatus) in the belly of a Xiphactinus. Experts believe the prey struggled for freedom and possibly damaged a vital organ of the Xiphactinus in the process, possibly causing the death of this particular voracious Xiphactinus.
The marine predator’s diet would have included any unlucky fish, smaller marine reptiles, and even seabirds (such as Hesperornis). A streamlined body would have made it easy for the Xiphactinus to catch up with prey without much fuss. The animal also had a unique adaptation that favored predators. It could generate heat and maintain a temperature higher than its immediate environment (i.e., endothermic). This phenomenon is seen in present-day predator fish species like the bluefin tuna, swordfish, and the great white shark. With this strategy, Xiphactinus could produce the needed energy to swim faster than its prey.
Where Did Xiphactinus Live?
This sharp-toothed predator lived in an ancient Cretaceous sea known as the Western Interior Seaway. This was during the later years of the Cretaceous Period (about 90 to 65 million years ago). The water body had covered an extensive area that would have included much of present-day North America. The ancient sea contained early plankton, mollusks, fish, and marine reptiles. Flying reptiles (pterosaurs) and ancient birds would have constantly been flying over the water body.
Xiphactinus remains have been discovered in different Cretaceous formations on the east coast of the United States, Europe, Australia, Argentina, and Canada. Some include the Kanguk Formation, Ashville Formation, La Luna Formation, and Salamanca Formation. Fossil evidence also suggests that this fish was widely distributed in the Northern Hemisphere. However, only one specimen has been recovered from the Southern Hemisphere.
Threats and Predators
This giant sharp-toothed predator was not completely invisible. Even though it was big by modern standards, it was not the only massive predator in the Western Interior Seaway. Squalicorax (popularly known as the crow shark) and Cretoxyrhina (another prehistoric shark from the Cretaceous) were two likely predators of the Xiphactinus.
A fossil of Xiphactinus audax was found with a shark tooth in its vertebrae. The tooth has been discovered to belong to a Cretoxyrhina. The most plausible story behind that specimen is that the shark tried to attack the Xiphactinus and lost its tooth while at it. While we do not know if this attack was successful, the best guess is that Cretoxyrhina emerged victorious in their encounters a few times. This shows that the two species cohabited within the same period and were not friends.
Xiphactinus remains one of the fiercest sea monsters known to man. Although it was only slightly bigger than the great white, there is a difference in how they consume prey. Xiphactinus had smooth teeth and would have swallowed its prey as a whole. The great white, on the other hand, has a zig-zag dentition. With evolution on its side, the latter can fiercely attack larger prey more easily. Unlike Xiphactinus, it can cut its captured prey into smaller pieces and swallow the chunks at once. Considering this, a battle between Xiphactinus and a great white would have been epic.
The Extinction of the Predator Fish
Xiphactinus lived during the Cretaceous Period from about 112 million years ago. Experts think the fish was alive until the end of the Cretaceous some 65 million years ago. The period ended with a mass extinction event. This disastrous event led to the disappearance of up to 70% of species on the planet.
This event is known as the K/T extinction event. Although dinosaurs were the most famous casualties of the extinction event, the Cretaceous marine life was also affected. A large amount of sulfur was released into the atmosphere after a massive asteroid hit the planet. This resulted in sulfuric rain that increased the acidity of the prehistoric water body. As a result, many plankton and algae (the primary marine food source) died out. Gradually, the marine ecosystem started to collapse once the foundation organisms disappeared. Xiphactinus most likely also died due to this domino effect of organism loss.
It’s hard to imagine a planet with giant, sharp-toothed predators like this still swimming in the world’s oceans. But we have marine predators like the great white shark to point to as examples of what the food chain in the Cretaceous might have looked like. They may not be quite as intimidating as the fish with the bulldog face, but they definitely rule the water world today.
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The photo featured at the top of this post is © Danny Ye/Shutterstock.com
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- Prehistoric Otter, Available here: https://prehistoricotter.co.uk/2021/01/29/xiphactinus-the-beautiful-bull-of-the-sea/
- Wikipedia, Available here: https://en.wikipedia.org/wiki/Xiphactinus
- National Geographic, Available here: https://www.nationalgeographic.com/animals/facts/xiphactinus