Following up on a comment I made over at Updates from the Vertebrate Paleontology Lab, I here bring you pictures of an unusual sirenian chevron from the Late Oligocene of Puerto Rico.
These fossils were collected as part of a partial articulated postcranium which I mentioned here. Chevrons, also known as hemal arches, are (normally) V-shaped* bones, consisting of two rami that meet ventrally, hence the shape. They protect blood vessels.
Chevrons, also known as hemal arches, are (normally) V-shaped* bones, consisting of two rami that meet ventrally, hence the shape. They protect blood vessels.
*More like Y-shaped due to the length of the symphysis in some specimens.
In the picture above you can see left lateral views of two of the chevrons I collected with that specimen. The chevron on the left seems to represent fused chevron 2 + 3 (missing part of its ventral edge), and the other one is chevron 4, which is normal.
Here is a posterior view, again, the one on the left likely represents fused chevron 2 + 3, and on the right is chevron 4, which is missing the right ramus.
To me this seems to have been a developmental anomaly rather than occurring due to an injury. Apparently, this is a first, at least for Sirenia! As I mentioned above these are part of an articulated partial postcranium, belonging to a new dugongine taxon from the Late Oligocene of northern Puerto Rico (you can see the skull here).So, leave a comment, let me know what you think about this unusual bone!