Topic: Dental batteries in ceratopsians, hadrosaurs and elephants
The dental batteries or 'pavements' of ceratopsians and hadrosaurs evolved independently, and yet the dentition of several more distantly related animals also converges on their highly adapted tooth form.
Ceratopsians and hadrosaurs were dominant plant-eating dinosaurs during the Late Cretaceous, and both independently evolved continuous batteries of serrated teeth that occluded at the back of the mouth to shear and slice vegetation.
Ceratopsians had two or three horns (e.g. in Zuniceratops and Triceratops respectively), an anterior beak, large skull, bony neck shield or ‘frill’ and a dense battery of shearing ‘cheek’ teeth. The upper maxillary and lower dentary bones housed a continuous array (‘battery’) of up to 40 teeth, each tooth the exposed member of a stacked column of 3-5 replacement teeth. Individual tooth cusps were serrated and occluded with teeth from the array on the opposite jaw, together forming a powerful shearing surface, capable of slicing fibrous plant material such as palm or cycad fronds. The large volume of tough vegetation that had to be consumed resulted in high wear and necessitated the capacity for rapid tooth replacement in these dinosaurs.
Hadrosaurs, or ‘duck-billed’ dinosaurs had a toothless, bony beak that was broad and long (somewhat like a duck’s bill), and arguably the most exceptional dentition of any herbivorous dinosaur. Edmontosaurus is a typical hadrosaur, and its bill was presumably used to clip leaves and twigs from tough plants such as gymnosperms, which were then crushed by a powerful battery of maxillary and dentary teeth. The dental battery comprised a continuous ‘pavement’ of tooth columns with up to five teeth stacked near-vertically at each position, and the exposed teeth of the upper and lower batteries interlocking upon jaw closure. The upper jaw was remarkably mobile, allowing effective use of the beak and powerful grinding and crushing within the dental battery. In an advanced adaptation to rapid tooth wear, the vertically stacked teeth of hadrosaurs supported continuous tooth replacement, enabling optimal processing of abrasive plant material.
Dental batteries in Elephantidae
The dental batteries or pavements of ceratopsians and hadrosaurs evolved independently within the dinosaurs, and yet the dentition of several distantly related animals also converges on their highly adapted tooth form. For example, mammals of the family Elephantidae (e.g. elephants, mammoths and stegodonts) have pre-molar and molar teeth specialized for herbivory (in addition to their characteristic incisors, modified to form tusks). The woolly mammoth (Mammuthus), African elephant (Elephas), Asian elephant (Loxodonta) and their close ancestors all have large ‘molars’ comprised of pseudo-vertical plates (individual tooth units) stacked against one another and bearing transverse enamel ridges. The broad field of transverse enamel ridges combined with horizontal anterior-posterior jaw movement provides powerful plant-shearing occlusion. Stegodonts independently evolved a similar, though slightly simpler dentition, comprised of large pre-molar and molar teeth with numerous roof-shaped parallel, transverse ridges that occlude for efficient grinding. Here then, we see remarkable convergent evolution of a long, broad pavement of shearing teeth in both elephantids and plant-eating dinosaurs, and furthermore, worn members are immediately replaced by already erupted and functional teeth in both of these distantly related herbivores.
Even further removed from dinosaurs is an unusual group of extinct fish called pycnodontids, and yet here we also find convergence on a pavement of molariform teeth as an adaptation to herbivory. In pycnodonts such as Stemmatodus, Pycnodus and Ceolodus, rows of wide oval-shaped molar-like teeth are present on the upper vomerine and lower pre-articular jaw bones, each with a flattened crown bearing a rim of tiny cusps. Vomerine teeth shear downwards and across the pre-articular molariforms, generating abrasion. As such, pycnodontid dentition may resemble less closely that of other specialized herbivores such as hadrosaurs and elephants, but convergence is evident regarding the evolution of a broad field or ‘pavement’ of teeth that are dedicated to shearing tough plant material.
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Map of Life - "Dental batteries in ceratopsians, hadrosaurs and elephants"
February 23, 2019