A 72 to 66-million-year-old embryo found inside a fossilized dinosaur egg
sheds new light on the link between the behavior of modern birds and
dinosaurs, according to a new study.
The embryo, dubbed ‘Baby Yingliang’, was discovered in the Late Cretaceous
rocks of Ganzhou, southern China, and belongs to a toothless theropod
dinosaur, or oviraptorosaur. Among the most complete dinosaur embryos ever
found, the fossil suggests that these dinosaurs developed bird-like postures
close to hatching.
Scientists found the posture of ‘Baby Yingliang’ unique among known dinosaur
embryos — its head lies below the body, with the feet on either side and the
back curled along the blunt end of the egg. Previously unrecognized in
dinosaurs, this posture is similar to that of modern bird embryos.
In modern birds, such postures are related to ‘tucking’ — a behavior
controlled by the central nervous system and critical for hatching success.
After studying egg and embryo, researchers believe that such pre-hatching
behavior, previously considered unique to birds, may have originated among
non-avian theropods.
Led by scientists from the University of Birmingham and China University of
Geosciences (Beijing), the research team from institutions in China, UK, and
Canada today published its findings in iScience.
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| Photo of the oviraptorosaur embryo “Baby Yingliang.” Credit: Xing et al./iScience |
The embryo is articulated in its life position without much disruption from
fossilization. Estimated to be 27 cm long from head to tail, the creature
lies inside a 17-cm-long elongatoolithid egg. The specimen is housed in
Yingliang Stone Nature History Museum.
Fion Waisum Ma, joint first author and PhD researcher at the University of
Birmingham, said: “Dinosaur embryos are some of the rarest fossils and most
of them are incomplete with the bones dislocated. We are very excited about
the discovery of ‘Baby Yingliang’ — it is preserved in a great condition and
helps us answer a lot of questions about dinosaur growth and reproduction
with it.
“It is interesting to see this dinosaur embryo and a chicken embryo pose in
a similar way inside the egg, which possibly indicates similar prehatching
behaviors.”
‘Baby Yingliang’ was identified as an oviraptorosaur based on its deep,
toothless skull. Oviraptorosaurs are a group of feathered theropod
dinosaurs, closely related to modern-day birds, known from the Cretaceous of
Asia and North America. Their variable beak shapes and body sizes are likely
to have allowed them to adopt a wide range of diets, including herbivory,
omnivory, and carnivory.
Birds are known to develop a series of tucking postures, in which they bend
their body and bring their head under their wing, soon before hatching.
Embryos that fail to attain such postures have a higher chance of death due
to unsuccessful hatching.
By comparing ‘Baby Yingliang’ with the embryos of other theropods,
long-necked sauropod dinosaurs and birds, the team proposed that tucking
behavior, which was considered unique to birds, first evolved in theropod
dinosaurs many tens or hundreds of millions of years ago. Additional
discoveries of embryo fossils would be invaluable to further test this
hypothesis.
Professor Lida Xing from China University of Geosciences (Beijing), joint
first author of the study, said: “This dinosaur embryo was acquired by the
director of Yingliang Group, Mr. Liang Liu, as suspected egg fossils around
the 2000. During the construction of Yingliang Stone Nature History Museum
in 2010s, museum staff sorted through the storage and discovered the
specimens.
“These specimens were identified as dinosaur egg fossils. Fossil preparation
was conducted and eventually unveiled the embryo hidden inside the egg. This
is how ‘Baby Yingliang’ was brought to light.”
Professor Steve Brusatte from the University of Edinburgh, part of the
research team, said: “This dinosaur embryo inside its egg is one of the most
beautiful fossils I have ever seen. This little prenatal dinosaur looks just
like a baby bird curled in its egg, which is yet more evidence that many
features characteristic of today’s birds first evolved in their dinosaur
ancestors.”
Reference:
An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on
avian-like prehatching postures” by Lida Xing, Kecheng Niu, Waisum Ma, Darla
K. Zelenitsky, Tzu-Ruei Yang and Stephen L. Brusatte, 21 December 2021,
iScience.
DOI: 10.1016/j.isci.2021.103516