(Q017) Your classmate, whose part-time job entails reorganizing the paleoanthropology lab on campus, asks you to take a look at a skeleton that she thinks is that of a primate. After noting the absence of a postorbital bar, nails, and an opposable thumb, what would be a valid statement to make?

Question

BlackTom AI · Accepted Answer

We begin by restating the scenario and evaluating what the observed features imply about the specimen.
Option 1: 'She should label this skeleton a plesiadapiform rather than a primate.' The absence of a postorbital bar, nails instead of claws, and a non-opposable thumb are traits more consistent with plesiadapiforms, which are stem primates and not true crown primates. This statement aligns with paleoanthropological understanding that some early skeletal forms resemble primates superficially but lack key primate features. Thus this option correctly identifies that the specimen is not a typical primate.
Option 2: 'There is no way that the skull and the hands are from the same animal.' This claim introduces an unnecessary and unfounded doubt about taphonomic or labeling possibilities. In a classroom or lab setting, there is no evidence provided that would force a conclusion that the skull and hands cannot belong to the same individual, so this is an unwarranted assertion without supporting data.
Option 3: 'The skull is probably that of an Eocene euprimate.' Euprimates are true primates that typically exhibit derived features like a postorbital bar and other primate dental and skeletal traits. The explicit note of an absent postorbital bar contradicts the characterization as an euprimate, making this option inconsistent with the observed anatomy.
Option 4: 'The skeleton is that of an Old World monkey.' Old World monkeys are crown primates and would generally possess a postorbital bar, nails, and an opposable thumb. The described absence of these primate-specific features makes this option incompatible with what is known of Old World monkeys, so it is incorrect given the evidence.
In summary, option 1 coherently integrates the diagnostic traits—absence of a postorbital bar, nails, and non-opposable thumb—with the concept of plesiadapiforms as stem primates, while the other options rely on interpretations that conflict with the observed morphology or rely on incorrect assumptions about skull–limb correspondence or primate classification.

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