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An incipient frill is the principal evolutionary novelty of the __________.

A. Marginocephalia
B. Ankylosauria
C. Sauropoda
D. Theropoda

User Chrishomer
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Final answer:

The incipient frill is a distinctive feature of Marginocephalia, a dinosaur clade including Ceratopsians like Triceratops, which were known for their skull ornamentation.

Step-by-step explanation:

The incipient frill is the principal evolutionary novelty of the Marginocephalia. This group includes dinosaurs like the well-known Triceratops, characterized by a shelf of bone at the back of the skull, among other features. The Marginocephalia is divided into two subgroups: Pachycephalosauria, known for their thick-skulled members, and the Ceratopsia, known for their horns and frills.

The term 'incipient' suggests the initial development or an early stage of a trait. In Marginocephalia, the frill would have started as a simple feature in early members and evolved into a more elaborate structure in later genera. These frills served various functions such as display, temperature regulation, and species recognition.

User Nick Schmidt
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