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a mixture of sediment and dung behind them and leaving distinctly visual “plugs.”
The burrows also varied considerably in size, from about a millimeter to 3 cm (1.2
in) wide, all of which were insect-sized and with circular outlines. This variation
implied that more than one species of insect made them.
Which insects made these burrows? First of all, they had to be ones that loved
tunnelingintodinosaurmanure.Thisnarroweddownlikelycandidatestotwomajor
groups, dung flies and dung beetles. Dung flies are relatively small and normally
just lay their eggs on feces; their larvae then hatch on this food supply and start
chowing down, which they continue doing until they pupate. In their life cycles,
dung flies do not dig wide and lengthy burrows into the dung, let alone backfill
them. But dung beetles do. Accordingly, Chin and Gill focused on these insects as
the most likely suspects for these trace fossils.
Direct observations of many modern dung-beetle species and their traces
served as guides for figuring out how these Cretaceous beetles' lives depended on
dinosaurwaste.Dungbeetlestodayemploythreedifferentstrategiesinhandlingfe-
ces: tunneling, dwelling, or rolling. Tunnelers burrow into and below a patty, mak-
ingandstoringabroodingchamberwithdungandeggs.Dwellersmakethemselves
at home in the patty itself, digging out brooding chambers so that the larvae emerge
inthedung-beetleequivalentofacandystore.Rollersscrapedungoffthesurfaceof
apile,shapeitintoabigball,andleavetheneighborhoodwiththeirprizes,evoking
Sisyphus as they roll dung balls larger than themselves. They later stuff these dung
ballsinburrowsdugelsewhere.Giventhethreechoices,ChinandGillfiguredthese
Cretaceous burrows were from tunnelers, which had burrowed into the dinosaur fe-
ces while it was still gooey, gathered some of this organic goodness, and placed it
into nearby burrows.
The most exciting conclusion drawn from this discovery was how
Maiasaura
interacted with and affected plants and insects in its surroundings, which in turn
provided a sketch of how a Late Cretaceous ecosystem might have functioned, and
with a dinosaur as a possible keystone species. As a large herbivore,
Maiasaura
