Premolar evolution in Tenrec though Tursiops
Curious about those atypically monomorphic odontocete teeth
I added DGS colors to two odontocetes and several ancestors back to Tenrec. I was seeking dental patterns in their evolution from a basal mammal tooth morphology and tooth count (= incisors, canine, premolars and molars) to a derived supernumerary all-canine-like appearance.
Hyperdontia can occur in humans, too.
Here’s the hypothetical evolution of odontocete premolars (not to scale).
Starting with three premolars in Tenrec, then four, four, seven, eight and finally 17 in Tursiops. In each case 4 molars were retained. These premolars and molars all became canine-like in shape with a single root, not double-rooted (as in typical premolars) and not triple-rooted (as in typical molars).
‘Canine-like’ is ironic because
odontocetes and their ancestors lacked even one canine in the maxilla to start with. Much earlier the upper canine was phylogenetically lost following the marsupial Asioryctes in this placental 2 clade that included other canine-less members, including of xenarthrans and sengis.
Arrows in the diagram
point to the migrating narial openings in these odontocete ancestors.
Click this link and scroll down to view the chart of odontocete skulls.
This is a hypothesis of tooth evolution in odontocetes
and their ancestors. The changes here can only be seen by comparative anatomy, not in individual skulls. Competing hypotheses are welcome if they include the same taxon list.
In this case, tooth position is more important than tooth shape.
In other cases, tooth shape is more important in tooth identity.
In still other cases, it’s a mixture of the two: with premolar-like molars, molar-like premolars and canine-like premolars following vestigial canines.
This account of tooth number, shape and position
is only one reason why mammals continue to be difficult to score in phylogenetic analysis.
Odontocetes break the rules.
References
reptileevolution.com/orcinus.htm
https://pterosaurheresies.wordpress.com/2020/06/24/reversals-produce-whale-teeth-part-2/
Source: https://pterosaurheresies.wordpress.com/2026/03/02/premolar-evolution-in-tenrec-though-tursiops/
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