2023-10-05 10:55:48
This research used skulls in museums to investigate the biology of teeth and chewing in hippos. – MICHELLE AIMÉE OESCH, CC-BY 4.0
MADRID, 5 Oct. (EUROPA PRESS) –
Hippos have the widest mouth of all mammals, but their chewing is very inefficient, limiting the amount they can eat. The reason is that they need their jaws to fight.
This is the conclusion of a study by Annika Avedik and Marcus Clauss, from the University of Zurich (Switzerland), published in the open access journal ‘PLOS ONE’which suggests that this animal could have lost the ancestral movement of the jaw from side to side.
To investigate, the researchers observed chewing in common hippopotamuses (Hippopotamus amphibius) and pygmy hippos (Choeropsis liberiensis) using video footage of zoo animals.
They also measured the size and arrangement of teeth in the skulls of museum specimens of 86 common hippos and 21 pygmy hippos.and looked for signs of wear that would indicate how the animals chewed their food.
In both species there was little difference in the width of the upper and lower jaw teeth or cheeks, suggesting a primarily vertical chewing movement.
The size and position of the canines do not prevent side-to-side chewing, but the long lower canines limit the extent of grinding. More importantly, common hippos have interlocking upper and lower front teeth that almost completely prevent side-to-side movement.
Video recordings and wear analysis confirm that pygmy hippos use a slight side-to-side grinding motion when chewing, while common hippos rely almost exclusively on vertical jaw movements.
The slight side-to-side chewing movements used by living hippos suggest that the ancestors of both modern species relied more on jaw-crushing movements.
It is not yet known why modern hippos lost this ability, but chewing efficiency may have been compromised in favor of the evolution of a rigid jaw and wide jaw opening, which is an advantage during fights with other hippos. According to the authors, the inefficiency of chewing could have limited common hippos to a semi-aquatic lifestyle.
The authors add that “most herbivores grind their food by moving their jaw laterally. Hippos have given up this because they need a rigid jaw to fight,” they explain.
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