Kirby and Virtue

The tableau's unity and, consequently, its ability to signify univocally is always the result of intense objectivation and subordination of the elements within its confines. Diderot's rejection of contrast in both painting and theater as well as his repeated obsession with unity in both genres must be understood in this light. For the rejection of opposites and the desire for unity necessarily imply a leveling among elements and the existence of a certain self-censorship, which founds, according to Rousseau, the notion of the republic. (21) 

Thus, the "inner-democracy" of the tableau's elements underscores their subservience to deliver of the moral message. The constant association in the bourgeois aesthetic between tableau and virtue is not gratuitous; both exemplify the direct exercise of power over men and objects.

Likewise the tableau demands the subordination of the parts to the whole and forces them to assume a unity and coherence that are fundamentally unnatural; virtue necessitates the individual's self-sacrifice to an ideal (Family, Friendship, and Country). 

Both tableau and virtue are the sites of self-imposed inner violence; both stage, in the full sense of the term, the workings and tactics of a force and discipline (virtu) that originate not from outside, but from within. In this, the tableau and virtue are particularly bourgeois forms of power: all is natural. (22) 

Diderot's strategies of both "naturalization" and the delivery of a moral message are essential components in Diderot's idea of bourgeois happiness.

Bryson, Scott. "Strategies of happiness painting and stage in Diderot." French Forum 29, no. 1 (2004)

Actually, I can't push the parallels that far: Scott Bryson, in looking at Diderot's championing of the tableau in drama, suggests that it expresses the inner virtue of the human being. Identifying a conflict between bourgeois and aristocratic notions of 'happiness' in eighteenth century France (and claiming that there was a serious class war happening that was spilling over into the arts), Bryson argues that Diderot regarded the tableau as an expression of bourgeois values. Everything is in its right place, and the individual is determined in terms of social relationship - performing an act of self-sacrifice in order to take up their appropriate place in society.

I don't think Kirby is making that particular point in this splash page from Devil Dinosaur. In fact, I am pretty sure that Diderot would not be delighted by the fantastical subject matter. However, the splash page operates as a tableau, in which the relationship between the dramatis personae is defined by space and gesture. Notice how Moonboy is simply ignored by his captors.