Brachauchenius lucasi

Overview

Brachauchenius lucasi was a Cretaceous plesiosaur studied through material from its head, jaws, front part of the body and flipper-shaped limbs. Different specimens reveal different parts of its face and body. Following what survives in each fossil helps us understand the animal as a whole.^[1]

Key facts

USNM4989 preserves more than just a skull and lower jaw. Vertebrae extending from the neck into the front of the body, along with ribs, are also described. They provide important evidence for examining how the body connected behind the head.^[1]

Time and place

The type specimen is a Cretaceous fossil from near Delphos in Ottawa County, in the present-day US state of Kansas. The Cretaceous spans roughly 140–66 million years ago. A 2005 study reassessed its stratigraphic context by comparing old locality records with the rock surrounding the fossil.^[1][2]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The skull, lower jaw, axial skeleton of the neck and front part of the body, and ribs are described. Separate, incomplete limb material was assigned to this species through comparison with other specimens.^[1]

Brachauchenius lucasi was a marine reptile with a large head and short neck. A 2013 study estimated a body length of about 4–5 m for an adult with a skull about 1 m long. This reconstruction assumed that the head accounted for roughly one-quarter to one-fifth of total body length.^[3]

Habitat and reproduction

How might the flipper-shaped limbs have connected to the trunk? Researchers compare incomplete limb material with the same parts in other specimens. Bringing together information from the head, front of the body and limbs helps reveal the body configuration of a plesiosaur.^[1]

Fossil discovery

Historical records name John Potts as the collector of the type specimen. The National Museum is recorded as having purchased it from C. Sternberg in 1884. A 2005 study traced the fossil's background by reading old collecting records alongside the geology around its locality.^[1]

References

1. Schumacher·Everhart (2005) — A Brachauchenius specimen from Kansas
2. International Commission on Stratigraphy (2024) — Geological time chart
3. Schumacher·Carpenter·Everhart (2013) — Skull and body-size comparisons of Cretaceous pliosaurs

Research questions

How can an old formation name be related to a modern geological map? This specimen was recorded under a formation name that historically had a broad scope. Comparing nearby exposed rocks with the properties of the stone enclosing the fossil provides clues for reassessing its locality.^[1]

Observation

First follow the main axis from the head and jaws through the neck into the trunk. Then look separately at the limbs on either side and the outline toward the rear, considering how evidence from different specimens contributes to the reconstructed body.^[1]