In Sciuridae, the 2nd and 3rd incisors; and, above, the first two, below, the first three premolars are always absent. So, the dentition of adult is reduced to the formula 1023/1013
Among 28 skulls of
Sciurus lis collected from Nagano Pref., central Honshu, Japan, the author find three (10.7%) that lack the small peg-shaped upper premolar (P
3) . Of the three cases, one specimen lacked both sides of P
3, and the right was absent in two specimens.
The order of the eruption of the cheek teeth of
Sciurus lis was estimated as follows from five skulls of juveniles.
Upper jaw : p
3· p
4· M
1→M
2→M
3→P
3 · P
4Lower jaw : p
4 · M
1→M
2→M
3→P
4The replacements of the premolars occur during the developmental stage of 44 mm to 47mm in total skull length.
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