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mya
. Because of their antiquity—these are the oldest known dinosaur nests in the
world—thissitealsotellsusmuchabouttheearlyevolutionofnestingindinosaurs,
and is unparalleled for the sheer amount and quality of body- and trace-fossil good-
ness in a relatively small place. At this site are nest structures, eggshells, embry-
os, and juvenile footprints, all identifiable to the sauropodomorph
Massospondylus
.
(Sauropodomorpha is a clade that includes sauropods and their relatives, among
which were “prosauropods” like
Massospondylus
, lineages that only lived during
the Late Triassic through the Early Jurassic, about 230 to 180
mya
.)
Massospon-
dylus
wasnotamassivedinosaur,probablyweighingabout130to150kg(285-330
lbs);thismadeitmuchsmaller than
Maiasaura
orthenestingtitanosaurs, butabout
threetimesbiggerthan
Troodon
.Allinall,thesefossilsprovidedarareandintimate
look at dinosaur nesting from a time when this behavior might still have been relat-
ively new in dinosaurs. To put this in perspective, nearly all other nests interpreted
thus far, such as those of
Maiasaura
,
Troodon
, and titanosaurs, are from about 80
to 65
mya
, meaning the South African nests are more than twice as old as these.
Paleontologists had known about
Massospondylus
embryos and eggs since at
least the 1970s, but the exact source of these fossils had not been documented un-
til paleontologists followed up on a few clues much later, in 2006. The results of
this exploration and discovery, summarized in a report published by Robert Reisz
andfourotherpaleontologistsin2011,werespectacular.Thefirstembryosandeggs
were discovered at this site in 1976 in loose rocks on the ground, next to where a
highway crew had cut into the strata to allow better passage of a road in Golden
GateHighlandsNationalPark.(Suchexposures,whichgeologistsworldwiderevere
and covet nearly as much as easy access to beer, are known simply as road-cuts.)
Thismeantthatpeoplevisitingthisnationalpark—unawareofwhatworld-classpa-
leontological secrets resided there—had driven by the undiscovered nests, tracks,
and other fossils there for forty years before the rocks were scraped again.
The paleontologists working on this roadcut were elated to find that it held a
mother lode of mother-dinosaur data. Contained within a vertical span of siltstone
