Fast Facts about Eurhinodelphids - The Long-Snouted Dolphins
Name: Xiphiacetus is a genus of eurhinodelphid dolphin. Many fossils now placed in Xiphiacetus were formerly called Eurhinodelphis, so both names are commonly encountered in older references and fossil collections.
Taxonomy: Eurhinodelphids, like all dolphins, are mammals. They are toothed whales in the order Cetacea, suborder Odontoceti. This page focuses on Xiphiacetus, especially X. bossi and X. cristatus.
Age: Miocene. Xiphiacetus lived roughly 23 to 5 million years ago.
Distribution: Fossils of Xiphiacetus and related eurhinodelphids are known from Miocene marine sediments in North America, Europe, Australia, and other regions. Xiphiacetus is one of the most common toothed whales in the Calvert Formation.
Body Size: About 6 to 9 feet (2 to 3 meters) long. The elongated snout made up a surprisingly large portion of the animal's total body length.
Teeth: Small, conical, and peg-like, broadly similar to the teeth of modern dolphins, but slightly more complex than those of many living odontocetes.
Diet: Probably small fish, squid, and other small marine prey. Its extremely long snout may have helped it disturb, probe for, or strike at prey, although the exact behavior remains uncertain.
Fun Fact: Eurhinodelphid dolphins had enormous snouts. In Xiphiacetus, the long beak may have accounted for nearly one-third of the body length.
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Xiphiacetus (Eurhinodelphis): The Details
Eurhinodelphids, the long-snouted dolphins, were common in ancient middle to late Miocene seas. The species Xiphiacetus bossi, which reached about 6 to 7 feet in length, is one of the most common cetaceans found in the Miocene Calvert Formation. Fossils of Xiphiacetus have been found on both sides of the ancient Atlantic, including Maryland, Virginia, France, and Belgium.
Like all dolphins, eurhinodelphids belong to the toothed whale group, Odontoceti. They are primitive dolphins traditionally placed in Eurhinodelphinidae, although the family has also been discussed under Rhabdosteidae in some references. Members of this group are known from Miocene deposits around the world, including North America, South America, Europe, and Australia.
Although Xiphiacetus was one of the more common Miocene dolphins, it was unlike any living dolphin today. It retained slightly complex teeth, meaning that the teeth varied somewhat depending on their position in the jaw. This is a primitive feature inherited from earlier mammalian ancestors, even though the teeth themselves were small and peg-shaped compared with many other fossil marine mammals.
Modern toothed dolphins and whales generally have simple peg-like teeth that look nearly identical throughout the jaw. Xiphiacetus teeth were still small and peg-like, but slightly more variable. This suggests a diet broadly similar to many modern dolphins: small fish, squid, and other small marine prey.
The extremely long snout is what makes Xiphiacetus so unusual. Although it may superficially resemble the long snouts of some modern river dolphins, eurhinodelphids are not the same lineage. The front of the snout appears to have been largely toothless. It may have been used to stir up prey from the sediment, probe along the sea floor, or strike at schooling fish. These behaviors are speculative, but they help explain why this extinct dolphin may have evolved such an exaggerated beak.
By the end of the Miocene, these strange long-snouted dolphins were disappearing and were eventually replaced by more modern dolphin groups.
Xiphiacetus Fossil Identification
Unfortunately, many eurhinodelphid fossils look similar to the dozens of other small- to medium-sized dolphin fossils found in Miocene marine deposits. The most common eurhinodelphid dolphin at the Calvert Cliffs is Xiphiacetus bossi, but isolated vertebrae and individual teeth are usually difficult to identify with confidence.
Jaw fragments are more useful. Eurhinodelphids had unmistakably long, slender jaws with small, closely spaced tooth sockets. A skull or diagnostic jaw material is usually needed before a fossil can be confidently assigned to Xiphiacetus.
For more images of a Xiphiacetus specimen, go to the Xiphiacetus Excavation Article.
Kellogg's Eurhinodelphis Plates
Kellogg described Eurhinodelphis specimens from the Calvert Cliffs region. Today, many of these fossils are discussed under Xiphiacetus. His publication includes identification plates for partial specimens. A few of those plates are shown below.
Kellogg, Remington. (1925). Description of a New Genus and Species of Whalebone Whale from the Calvert Cliffs, Maryland, and review of Miocene cetaceans.
References / Works Cited
Mchedlidze G.A.; Translated by Chakravarthy, R. (1984). General Features of the Paleobiological Evolution of Cetacea. New Delhi: Oxonian Press. Translated for Smithsonian Institution Libraries.
Recommended Books
Recommended Prehistoric Marine Mammals Books:
The Walking Whales: From Land to Water in Eight Million Years
J. G. M. Hans Thewissen, 2014
An excellent introduction to whale evolution, with firsthand fossil discoveries from Hans Thewissen, one of the world's leading whale paleontologists.
When the Whales Walked: And Other Incredible Evolutionary Journeys
Author: Dougal Dixon, 2018
An illustrated introduction to evolution for kids ages 5-9 (2nd-3rd grade), designed to spark curiosity through real science, where whales walk, snakes have legs, and dinosaurs take flight.
FAQs: Xiphiacetus (Eurhinodelphis) Fossils - Frequently Asked Questions
Quick answers about Xiphiacetus, the long-snouted Miocene dolphin formerly known as Eurhinodelphis, including its fossils, teeth, snout, and Calvert Cliffs occurrence.
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What is Xiphiacetus?
Xiphiacetus is a genus of extinct long-snouted dolphin from the Miocene. Many fossils formerly assigned to Eurhinodelphis are now placed in Xiphiacetus.
See: Fast Facts -
Is Eurhinodelphis the same as Xiphiacetus?
On this page, Eurhinodelphis refers to the older name commonly used for these long-snouted dolphins. Many specimens, including Xiphiacetus bossi, were historically discussed as Eurhinodelphis.
See: Xiphiacetus Details
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Where are Xiphiacetus fossils found?
Xiphiacetus fossils are found in Miocene marine deposits, including the Calvert Formation of Maryland and Virginia. Related eurhinodelphid fossils are also known from Europe, Australia, and other regions.
See: Xiphiacetus Details -
How big was Xiphiacetus?
Xiphiacetus was roughly dolphin-sized, about 6 to 9 feet long, with an extremely long snout that made up a large portion of the body length.
See: Fast Facts -
What did Xiphiacetus eat?
Xiphiacetus probably ate small fish, squid, and other small marine prey. Its long, toothless snout tip may have helped it disturb or stun prey, although the exact behavior is uncertain.
See: Xiphiacetus Details -
How can you identify Xiphiacetus fossils?
Isolated teeth and vertebrae are difficult to identify, but jaw fragments may be recognized by their long, narrow shape and small, closely spaced tooth sockets.
See: Fossil Identification -
Why did Eurhinodelphis have such a long snout?
The long snout may have been used to probe sediment, stir up prey, or strike at schooling fish, but the exact function is still uncertain.
See: Xiphiacetus Details -
Where can fossil collectors find Xiphiacetus material?
The Calvert Cliffs region is one of the best-known places for Miocene marine mammal fossils, including Xiphiacetus jaw fragments, teeth, ribs, and vertebrae.
See: Fossil Identification
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