Zygorhiza
Name: Zygorhiza
(Yoke root).
Phonetic: Zie-go-rye-za.
Named By: Genus created by Frederick W. True in
1908. Type species of Z. kochii named by
Remington Kellogg in 1936.
Synonyms: Zeuglodon brachyspondylus minor,
Zeuglodon hydrarchos, Zeuglodon hydrarchus, Zygorhiza brachyspondylus,
Zygorhiza brachyspondylus minor, Zygorhiza minor.
Classification: Chordata, Mammalia, Cetacea,
Archaeoceti, Basilosauridae.
Species: Z. kochii (type)
Diet: Carnivore.
Size: Body between 5 and 6 meters long, Skull
1 meter
long.
Known locations: Especially well known from the
Eastern United States, but likely had a broader distribution in life.
Time period: Late Eocene.
Fossil representation: Multiple specimens.
Zygorhiza
belongs to the same group of primitive prehistoric whales
as Dorudon
and both of these whales are more distantly related to the massive
Basilosaurus
which was quite possibly a predator of both of these
whales. Although similar in form to Basilosaurus,
Zygorhiza had a
much smaller body that was actually more in proportion to modern whales
with the total body length being six times greater than the length of
the skull.
The
front limbs of Zygorhiza are actually very
primitive in form because
the elbow was still capable of being flexed. In later more modern
forms the joints of the front limbs would become completely fused to
form rigid paddles for better control in the water. The retention of
this joint has led to the suggestion that Zygorhiza
left the water to
mate and give birth on land just like a pinniped (seals, walruses,
etc.), however this is just a theory. Even with jointed front
limbs, Zygorhiza was still much better adapted to
an aquatic life and
at six metres long it was even bigger than a bull elephant seal. It’s
just as probable that this elbow joint was merely a trait of its more
terrestrial ancestors like Ambulocetus
that would later become lost as
habitat conditions favoured a more rigid fore limb construction.
Like
with all known ancient whales from its time, Zygorhiza
was a predator
of other marine animals, hunting either fish, smaller marine
mammals or even sea birds when able. The robust teeth and relatively
long narrow jaws resembled those of earlier marine reptiles like
Mosasaurus,
and it’s quite probably that whales like Zygorhiza
evolved to fill a similar predatory niche as them. However the early
members of the cetacea were not alone in these waters, and equally
large if not bigger sharks
like C.
angustidens were already
patrolling the world’s oceans, giving the smaller whales like
Zygorhiza something else to worry about.
Further reading
- A review of the Archaeoceti. - Washington: Carnegie Institution of
Washington. pp. 100–177. - R. Kellogg - 1936.
-
An archaeocete whale (Cetacea: Archaeoceti) from the Eocene Waihao
Greensand, New Zealand. - Journal of Vertebrate Paleontology. 17 (3):
574–583. - Richard K�hler & Ewan R. Fordyce - 1997.
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