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It was theorized that positive selection for shovel-shaped incisors over the spatulate incisors is more commonly found within cultures that used their teeth as tools due to a greater structural strength in increased shovel-shaped incisors. [2] In some instances, incisors can present a more pronounced version of this called double shovel-shaped.
The incisors occupy the front of the tooth row in both upper and lower jaws. They are normally flat, chisel-shaped teeth that meet in an edge-to-edge bite. Their function is cutting, slicing, or gnawing food into manageable pieces that fit into the mouth for further chewing. The canines are immediately behind the incisors.
This unreduced, or "complete" dentition is the origin of the family's name, which is Greek for "complete teeth". [3] [4] The incisors are closely packed but do not develop a distinct straight chopping surface. They range from chisel-shaped in some entelodonts (Archaeotherium) to massive and rounded in others .
In more derived forms like Lycorhinus and Heterodontosaurus, the teeth were chisel-shaped, with much higher crowns and no cingula, so that there was no difference in width between the crowns and the roots. [3] These derived cheek teeth were overlapping, so that their crowns formed a continuous surface on which food could be chewed.
The unerupted teeth are triangular in lateral view, which is the typical tooth morphology in basal ornithischians. The characteristic chisel-like shape of the fully erupted teeth therefore resulted from tooth-to-tooth contact between the dentition of the upper and lower jaws. [1] [2] [38]
The shape and size of the humeral process helps to identify the species. In S. robbianus, the humeral process is about 1 + 1 ⁄ 2 to 2 times as long as it is broad, rough, and with a ridge on the lower edge. [4] The fish has three pairs of barbels. The maxillary barbels are on located on the upper jaw, and two pairs of mandibular barbels are ...
Totaling 42 to 44 teeth, this dentition is closer to that of equids, which may differ by one less canine, than their other perissodactyl relatives, rhinoceroses. [ 27 ] [ 28 ] Their incisors are chisel-shaped, with the third large, conical upper incisor separated by a short gap from the considerably smaller canine.
Sinodonty is a particular pattern of teeth characterized by the following features: The upper first incisors and upper second incisors are shovel-shaped, and they are "not aligned with the other teeth". [11] The upper first premolar has one root, and the lower first molar in Sinodonts has three roots (3RM1). [11] [5]