Xiphactinus

## XiphactinusSword Ray

### Temporal Range

100.5 - 66 million years ago, Albian - Maastrichtian Stage, Middle - Late Cretaceous Period

## Characteristics

### Diet

Carnivore

**Top Speed** of 60 kilometers (38 miles) per hour

***“ Xiphactinus, known as 'X-fish'. A feeding opportunity soon attracts them in large numbers. At over 17 feet long, they are one of the largest and fastest fish in the ocean. ”***

― **David Attenborough**, *Oceans*
***Xiphactinus*** (Sword Ray), also known as the "***X-fish***" is a genus of giant predatory marine bony fish that lived in oceans all over the world 100.5 - 66 million years ago, from the Albian stage of the Middle Cretaceous Period to the Maastrichtian stage of the Late Cretaceous Period.

## Description

***“ With its huge mouth, Xiphactinus can scoop up several fish at once, and has even been known to swallow prey half its size whole. ”***

― **David Attenborough**, *Oceans*
*Xiphactinus* resembles a massive, fanged tarpon, reaching over 5.2 meters (17 feet) in length, with large mouths, fittingly large teeth, and large nostrils for easily detecting the scent of prey in the ocean. To pursue prey, it swims at a top speed of 60 kilometers (38 miles) per hour, at the cost of agility.

On Prehistoric Planet, *Xiphactinus* is shown to have a silvery body with black stripes across its back.

## Habitat

*Main: Western Interior Seaway*

Main: Western Interior Seaway

***“ By day, the prehistoric ocean provides opportunities for a very different type of hunter. In the warm, shallow seas of North America, fish numbers can almost match the nocturnal lantern fish shoal. ”***

― **David Attenborough**, *Oceans*
*Xiphactinus* is known from several areas all over the world, from Canada, the United States (most especially Late Cretaceous Formations along the East Coast), and Europe, all the way to Venezuela, Argentina, and even Australia.

Despite being one of the largest and fastest fish in the ocean, *Xiphactinus* is not the top predator, for it shares its known range with other, larger predators that can prey on it, like *Cretoxyrhina*, also known as the "Ginsu Shark", which grew as long as 7 - 8 meters (23 - 26 feet), as well as various mosasaurs, the biggest of which dominated their respective ecosystems as the apex predators. Even so, unlike *Cretoxyrhina* (which died out 73 million years ago due to the shrinking of the Western Interior Seaway and competition with mosasaurs), *Xiphactinus* survived, coexisting with the mosasaurs until the Cretaceous-Paleogene Extinction Event, a catastrophe that wiped out three-quarters of life on Earth 66 million years ago.

## Behavior

***“ But in the eyes of an X-fish, anything is on the menu... even their own kind. ”***

― **David Attenborough**, *Oceans*
*Xiphactinus* is known for its voracious appetite, with at least a dozen specimens preserved with large undigested or partially-digested prey within their stomachs. One of the most known of these finds is the "**Fish-Within-A-Fish**", showing a 4.2-meter (14-foot) *Xiphactinus* with a perfectly-preserved *Gillicus*, 1.9 meters (6 feet, 3 inches) long. The *Xiphactinus*, known for swallowing prey around half its size whole, likely died after its smaller relative struggled within its stomach and ruptured it in the process. In the show, this is referenced when, after the *Hesperornis* escaped, one *Xiphactinus* is shown carrying and chewing on a smaller *Xiphactinus*.

## Appearance

### Oceans

The second segment of Oceans, by the warm, shallow seas of North America, a massive shoal of fish attracts many *Hesperornis*, with the flightless seabirds catching several fish with their beaks full of needle-sharp teeth. This great gathering of fish also attracts several *Xiphactinus*, which swallow mouthfuls of fish whole.

***“ At first, there is plenty for everyone. But as fish numbers dwindle, the X-fish turn their attention elsewhere. Predator is about to become prey. ”***

― **David Attenborough**, *Oceans*
Suddenly, several *Hesperornis* are attacked by *Xiphactinus*, with some even being swallowed whole. The surviving *Hesperornis* frantically attempt to escape the predators with evasive maneuvers. While *Xiphactinus* is faster, *Hesperornis* is more agile, allowing some of the birds to repeatedly dodge their pursuers just a second before getting grabbed and devoured. Following this, one *Xiphactinus* is shown chewing on the body of a smaller X-fish, for their voracious appetites meant that any other living thing is on the menu. With the shoal of fish reduced to nothing, the banquet is over, and the predators move on.

## References

1. ↑ Note by Charles Sternberg, 1917
2. ↑ A small, exquisitely preserved specimen of *Mosasaurus missouriensis* (Squamata, Mosasauridae) from the upper Campanian of the Bearpaw Formation, western Canada, and the first stomach contents for the genus