Name Meaning: Yoke Root
Geologic Era: Late Eocene
Location Found: Florida
Estimated Range: Eastern North American coastline
Size: 6 meters long
Extinction: 34 million years ago
This jaw fragment probably comes from the most anterior part of the mandible, or lower jaw. In basilosaurid whales such as Zygorhiza, the teeth were longer and more pointed in front, and progressed to a more rough, spade shape toward the rear. Two of the three teeth are completely missing except for what is buried in the mandible, and the third tooth is partially exposed, if broken off.
As an early whale, Zygohiza retained some features of its land based ancestors. It’s body was not quite as streamlined as modern whales, and its front limb still had an elbow joint capable of flexing. In later forms of whales, this joint became completely immobile and fused. While Zygorhiza might have been capable of moving its elbow, that does not mean it was capable of land-based locomotion by any means. A flexible flipper would actually be something of a hindrance in fast swimming, as one broad, stiff surface works best to push water in one direction.
It is also unlikely that Zygorhiza would have been able to come on land to mate and bear young, as its overall body plan and lack of really functional forelimbs would have made this a difficult proposition at best. Zygorhiza more than likely lived its entire life in the water, including sleeping and reproducing.
Zygorhiza shared its environment with many different animals, ranging from sharks to much larger basilosaurid whales. In terms of where it stood on the food web, Zygorhiza probably stood where the previous smaller mosasaurs and marine crocodiles would have been. While Zygorhiza’s teeth indicate that it was a predator of smaller animals such as fish, Zygorhiza in turn would have been a target for some of the larger sharks of the time such as C. augustidens, a possible precursor to C. megalodon.
Even other whales could possibly have been a threat to Zygorhiza. The largest primitive whale of the time, Basilosaurus, also swam the oceans at the same time as Zygorhiza. Basilosaurus topped out at 18 meters long, which is approximately three times the length of Zygorhiza. This size difference could have easily made the smaller whale an appealing target for larger animals like Basilosaurus.
Skeleton: By Claire H. from New York City, USA – Early Whale Zygorhiza kochiiUploaded by FunkMonk, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=6992078
Life Reconstruction: http://spinops.blogspot.com/2012/06/zygorhiza-kochii.html?view=snapshot