By now, you're probably all aware of the new study published a few weeks ago in Science magazine about how male maniraptors brooded the eggs. It's old news, I know, but I'll lay out the basics for you anyway. Three dinosaurs have been found sitting atop nests: Citipati, Oviraptor, and Troodon. Everyone assumed they were females, but not so fast, kiddies! Now there's a way to tell. Remember way back when Horner and his colleagues sliced open a T.rex femur and found gold...I mean, medullary bone inside? Well, medullary bone has since been found in Allosaurus and Tenontosaurus. Finding medullary bone in dinosaurs isn't particularly surprising, as it's present in crocodilians and birds. For the uninformed, medullary bone is laid down in the long bones of archosaurs just before, during, and after a female becomes pregnant and provides the calcium needed to produce egg shells.
So if we assume that female archosaurs produce medullary tissue in their long bones in association with egg-laying (all signs point to "yes"), we can test those "nesting" theropod fossils to see if girls, but instead of lifting up their skirts, we're sawing their femurs in half. Anyway, it turns out that all three nesting dinosaurs, Citipati, Oviraptor, and Troodon, lack medullary bone, which means they're males. That means males brood the nest, a trait shared by modern paleognathine birds (ratites + tinamous), which most likely means that male brooding predates "modern" birds. Given the clutch sizes of the three dinosaurs, it also seems likely that, again like paleognathes, nests were filled by more than one female. So that's awesome--now we know a whole lot more about maniraptoran breeding behavior and physiology. We can probably assume that chicks were precocial and left the nest soon after hatching, although in some ratites, the chicks stay with the parent for several months to a year.
But wait--there's more! The authors of the paper perhaps did not realize that if maniraptors bred like paleognathine birds, there are implications for sexual dimorphism, too. In modern paleognathine birds, sexual dimorphism is limited to small size differences between the sexes. In the ostrich, plumage in males is more "flashy" than females. In general, however, paleognathine birds have fairly drab plumage. The cassowary is the most colorful ratite, but that's because its neck skin is bright blue! Bright plumage seems to be linked with mating dances and competition between males for females...however, with the flashy performances comes maternal brooding, biparental care and altricial young.
Another possibility is that the three nesting dinosaurs are males by coincidence, and that those species bred like raptorial birds. In raptors, both parents share brooding duties. The young are born extremely altricial but develop quickly. Like ratites, raptors don't show much sexual dimorphism aside from size differences. However, the clutch size of the fossil brooders argues against a modern raptor comparison. Raptors will often lay only two or three eggs in a single large nest. Paleognathine birds lay many more eggs, and oftentimes, multiple females will deposit their eggs in a shared nest, which the male then broods. So I think the paleognathine interpretation is the right one. Now, as for sexual dimorphism and coloration, I wonder if we could carry the ratite comparison over to non-avian maniraptors, too. Food for thought!