the report of two eggs from China (4, 5)
and one from Argentina (6) that contained
well-developed pterosaur embryos. These
eggs had thin shells free of the substantial
external layer of calcium carbonate that
is characteristic of hard-shelled eggs laid
by dinosaurs, crocodiles, and birds. Moreover, a skeleton of an adult female of the
Chinese pterosaur Darwinopterus was reported a few years ago with a parchment-shelled egg positioned between its legs (7).
A more recent report of the counter slab to
this specimen shows an imprint of a sec-
ond egg in the body cavity (8).
Pterosaur eggs thus had soft, parchment-
like shells comparable to those laid by
modern-day lizards (9). Wang et al.’s study
supports this interpretation (3), as does a
previous study of a smaller number of eggs
from the same site in China (10): The fossil-
ized eggs show little evidence of shell calci-
fication, and many have the characteristic
dimpling of dead, dehydrated lizard eggs.
Parchment-shelled eggs need to be bur-
ied in a moist substrate to ensure that they
do not dry out, thereby killing the embryo;
they rely on environmental sources of heat
for normal embryonic development. The
similarity of pterosaur eggs to lizard eggs
means that we can confidently assume
that pterosaur eggs were buried. This pre-
cludes any form of contact incubation by
the parents (as seen in
modern birds). However,
adults may have attended
or defended nests, which
would explain the pres-
ence of adult skeletons in
the specimen reported by
Wang et al. The relatively
low incubation tempera-
tures associated with en-
vironmental sources of
heat would have meant a long incubation
period, as is now suggested for dinosaurs
(11), and hatching of a relatively mature and
mobile offspring (as seen in modern rep-
tiles) (9). The accumulation of eggs in the
new specimen does not allow conclusions
about clutch size to be drawn, but the Dar-
winopterus find (7, 8) suggests that clutch
size was most likely only two eggs.
Wang et al. suggest that Hamipterus
nested in colonies. Appropriate nesting
environments may have been rare, forcing pterosaurs to adopt colonial nesting
through necessity—but it was not without
risk. Modern sea turtles nest colonially, but
while preparing their own nests, females
may inadvertently damage previously dug
nests and expose eggs to predators. Perhaps
the dimpled pterosaur eggs reported in (3)
indicate that Hamipterus also experienced
nest damage through intraspecific competition for limited nesting sites.
Unlike in their previous report (10), Wang
et al. (3) can confirm that the eggs include
pterosaur embryos and can provide details
of variation in egg and embryo size. They
also investigated potential rates of growth
of the posthatching animals found on the
same slab by documenting lines of arrested
growth in bone sections; this allows the age
of the animal to be estimated. Rare in stud-
ies of pterosaurs, such data provide insight
into posthatching ontogeny in extinct species
(12, 13), but care is needed when assessing the
ontogenetic stage of embryos (2). Although
the authors report on a range of embryonic
bones, they provide few replicates to allow as-
sessment of the range of size of the embryos
represented; only one bone of the hatchling
mentioned by the authors is illustrated.
The authors argue that some embryos
were close to hatching with poor bone os-
sification and no teeth; this would indicate
that the hatchlings were unable to feed
themselves. However, an alternative per-
spective is that the embryos were much
younger than estimated and not close to
hatching and that the lack of growth of
teeth is therefore unsurprising; in crocodil-
ians, teeth only arise in the later stages of
development (2). Therefore, although the
morphological data and observations are
better than what has been reported previ-
ously, it is important to be
cautious and not to infer
too many aspects of the
life history of Hamipterus
from what remains a lim-
ited data set.
Wang et al.’s study is remarkable for the number
of eggs in association with
adults and juvenile pterosaurs that it reports on.
This finding provides support for nest-site
fidelity, but as the authors suggest, this specimen does not represent the nest site itself,
and many questions remain unanswered.
Were the eggs buried in sand or covered in
vegetation? Was clutch size limited to two?
Why are so many of the eggs showing signs
of dehydration? Hopefully additional finds
of equally spectacular fossils will help us answer such questions for pterosaurs and allow
us to paint an increasingly complete picture
of reproduction in these extinct species. j
1. K.Carpenter, Eggs, Nests, and Baby Dinosaurs. A Look at
Dinosaur Reproduction (Indiana Univ. Press, 1999).
2. D. C. Deeming, D. M. Un win, in Reptilian Incubation , D. C.
Deeming, Ed. (Nottingham Univ. Press, 2004), pp. 1–14.
3. X. Wang et al., Science 358, 1197 (2017).
5. Q. Ji et al ., Nature 432, 572 (2004).
6. L. M. Chiappe, L. Codorniú, G. Grellet-Tinner, D. Rivarola,
Nature 432, 571 (2004).
7. J. Lü et al ., Science 331, 321 (2011).
8. X. Wang et al., An. Acad. Bras. Cienc. 87,1599(2015).
9. D. M. Un win, D. C. Deeming, Zitteliana B28, 199 (2008).
10. X. Wang et al ., Curr. Biol. 24, 1323 (2014).
11. G. M. Erickson, D. K. Zelenitsky, D. I. Kay, M. A. Norell, Proc.
Natl. Acad. Sci. U.S.A. 114, 540 (2017).
12. E. Prondvai, E. R. Bodor, A. Ősi, Paleobiology 40, 288
13. A.Chinsamy, L.Codorniú, L.Chiappe, Biol. Lett. 4,282
“…it is important…
not to infer too
many aspects of the
a limited data set.”
School of Life Sciences, University of Lincoln,
Joseph Banks Laboratories, Lincoln LN6 7DL, UK.
Little is known about how
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