72. The Old World primates (apes and monkeys) have a dental formula of

Question

72. The Old World primates  (apes and monkeys) have a dental formula of

BlackTom AI · Accepted Answer

Old World primates (Catarrhini) possess the dental formula 2.1.2.3 because they have two incisors, one canine, two premolars and three molars in each quadrant of the jaws.

1. Relevant knowledge points and concepts
- A dental formula lists teeth per quadrant in the order: incisors.canines.premolars.molars.
- It describes one quadrant (upper or lower); total teeth = sum per quadrant × 4.
- Primate groups differ: Catarrhini (Old World monkeys and apes, including humans) characteristically have 2.1.2.3; Platyrrhini (most New World monkeys) often have 2.1.3.3.

2. Complete reasoning process step by step
- Identify the tooth counts per quadrant for Old World primates: incisors = 2, canines = 1, premolars = 2, molars = 3.
- Assemble these into the dental formula format: 2.1.2.3.

3. Calculations with intermediate steps
- Sum per quadrant: 2 (incisors) + 1 (canine) + 2 (premolars) + 3 (molars) = 8 teeth per quadrant.
- Total number of teeth = 8 × 4 quadrants = 32 teeth, matching the human dentition typical of Old World primates.

4. Why the correct answer is correct
- The 2.1.2.3 pattern is a diagnostic trait for Catarrhini; it reflects the presence of two premolars (rather than three) and three molars, and matches observed dentitions in apes, Old World monkeys, and humans.

5. Why the other options are incorrect
- 2.1.2.2 would give only 7 teeth per quadrant (28 total) and lacks the third molar characteristic of Catarrhini.
- 2.1.1.1 yields 5 per quadrant (20 total), which is not characteristic of these primates.
- 2.1.3.3 gives 9 per quadrant (36 total) and corresponds to many New World monkeys (Platyrrhini), not Old World apes and monkeys.

6. Conclusion confirming the answer
- Therefore the correct dental formula for Old World primates (apes and monkeys) is 2.1.2.3, which matches the provided answer.

72. The Old World primates (apes and monkeys) have a dental formula of 单项选择题

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