Xiphactinus

Name Meaning: Sword Ray

Location Found: Niobrara Chalk, KS

Geologic Era: Cretaceous

Size: Up to 6 meters long

Estimated Range: Worldwide

Extinction: 66 million years ago

Here are a few vertebrae from a large, tarpon-like fish that swam the sea that covered the middle part of the United States during the Cretaceous period. Several of the vertebrae are glued together, while one is loose. None of the vertebrae would have come from a full sized individual, but I would estimate the attached vertebrae to have come from fish 3 meters long, while the single bone came from a fish about 4 meters long.

The Western Interior Seaway was home to many creatures, and Xiphactinus was far from the largest. While its appearance may mirror the modern tarpon fish, they were not closely related. However, the physical similarities could easily indicate a similar manner of feeding. Xiphactinus would have approached its prey from underneath, and used its impressive fangs to snare prey and ensure that it would not escape. In addition to Xiphactinus, the Seaway was inhabited by sharks much larger than Xiphactinus, elasmosaurs, and mosasaurs such as Tylosaurus that could reach sizes in excess of 15 meters in length. In short, an attempt at fishing in these waters would rank up there with ‘invading Russia in the winter’ on the scale of horrible ideas. Xiphactinus itself was documented prey of large sharks such as Cretoxyrina, as well as larger mosasaurs.

Shown above is a mid-sized Xiphactinus, with the Assistant Curator for scale. A look at the interior of the specimen shows another fish, a related animal called Gillicus. As the picture shows, the specimen is called “Fish-Within-A-Fish,” and was found by George F. Sternberg (currently on display in the Sternberg Museum of Natural History in Hays, Kansas). Gillicus was related to Xiphactinus, and had a similar (if scaled down) body plan. In this case, the Xiphactinus was a victim of its prey. The degree of preservation on the Gillicus show that it did not have time to be digested, and so it follows that the Xiphactinus died very shortly after swallowing the smaller fish. Most likely what happened was that the spines of the Gillicus ruptured a vital organ in Xiphactinus, possibly the heart or liver. Another possibility is that the Gillicus was large enough to internally obstruct the gills of the Xiphactinus, though the fact that the fish is in the abdominal cavity makes this less likely.

Image Credits:

Life Restoration: By ДиБгд at Russian Wikipedia – Transferred from ru.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2460152