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Zygorhiza mandible issues

Wednesday, November 23, 2016 11:51
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(Before It's News)

Zygorhiza kochiii (Late Eocene, 36mya; 5.2m; Kellogg 1936) is a dorundontine odontocete, smaller than Zeuglodon (Basiliosaurus), but larger than Maiacetus. Like its tenrec ancestors, Zygorhiza had long, slender toothy jaws.

Figure 1. (above) Zygorhiza kochi from George Mason University website, likely captured from Kellogg 1936.

Figure 1. (above) Zygorhiza kochi from George Mason University website, likely captured from Kellogg 1936. To make the jaws fit and teeth occlude the mandible had to be reduced and the cranium had to tilted down posteriorly.

Today’s problem involves the jaws
which were presented, apparently, in a scale that did not permit the teeth to occlude properly when reattached to the skull. By reducing the mandible and lowering the rear of the skull all the parts mesh and match. Not sure what the fossil looks like, but this is what happens when you test the restoration and create a reconstruction.

Perhaps
the mandible and skull come from two different specimens. It’s also worth noting how this odontocete whale’s teeth appear to be evolving back to primitive shapes, that is, cusps aligned all in a row, rather than W -shaped in occlusal view. And, of course, extant odontocete teeth have no distinct cusps, but have all reverted to a complete arcade of canine-like pegs largely made up of former premolars.

References
Kellogg R 1936. A review of the Archaeoceti. Washington: Carnegie Institution of Washington. pp. 100–177.

wiki/Zygorhiza

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