- The Dinosaur Egg and Embryo Project
- Paleo-Technician, Terry Manning
The Dinosaur Egg and Embryo Project owes a great debt of
gratitude to the following:
Paul Barrett, Sedgwick Museum, Cambridge; Richard Cole, Physics
Dept, Leicester; Erika Hegelburg, Biological Anthropology Dept,
Cambridge; Ed Jarzembowski, Maidstone Museum; Mike Lee, Zoology
Dept, Cambridge; Graham Legge, Booth Museum, Brighton; John Martin,
Leicestershire Museums Service; Konstantin Mikhailov, Palaeontological
Institute, Moscow; John Ockleford, Medical School, Leicester;
Dale Russell, Raleigh, North Carolina; Phil Small, X-Ray Dept,
Queen's Medical Centre, Nottingham; and last, but not least,
the staff of the University Museum of Zoology, Cambridge, namely
Yvonne Barnett, Ann Charlton, Monica Elsey and Ray Symonds.
Text written by Simon Cohen, Arthur Cruickshank, Ken Joysey,
Terry Manning and Paul Upchurch.
© 1995 the authors.
Published by Rock Art, 4 Gipsy Lane, Leicester LE4 6RB, UK
All rights reserved. No part of this publication may be reproduced,
stored in a retrieval system, or transmitted in any form or by
any means, mechanical, photocopying or otherwise, without the
prior permission of the authors.
THE EGG & EMBRYO EXHIBITION GUIDE
The specimens and photographs in this exhibition are largely
the work of Terry Manning of Leicester, a professional fossil
technician of twenty years experience. He has been working on
this project for several years, and has had to develop new techniques
to identify those fossil eggs which are most likely to contain
embryonic remains. Some of these rare fossils show extraordinary
detail of the embryonic soft tissues. This is the first time
that these spectacular fossils have been exhibited anywhere in
the World. They provide a mass of new information for scientists,
and as Dr Dale Russell, a World-famous Canadian dinosaur expert
has said ' they are the most wonderful dinosaurian remains that
I have had the privilege of viewing during my professional life.'
The fossil eggs show stages of dinosaur embryos from the period
when only soft tissues (such as cartilage) are present, to the
almost-hatched stage where bone and skin are preserved. Some
eggs show macabre evidence that insects have gained access to
unhatched eggs to eat the contents. The eggs forming the core
of the Exhibition are from the Cretaceous period of China (PRC).
There are four types of fossil egg with embryos in the exhibition
1)Therizinosaur (the more popular name, segnosaur is used
on the Exhibition labels), a long-necked bipedal, possible herbivore
that stood about 3 meters high and maybe was 4 meters long. These
eggs are oval in shape and about 90 mm long.
2)Perhaps ankylosaur, a quadrupedal, short-necked, armoured
herbivore that stood 2.5 meters high and was up to 10 meters
long when adult. These eggs are cylindrical and about 200 mm
3)An as yet unidentified dinosaur whose eggs are cylindrical
and at least half a meter long.
4)Tortoise. Previously the earliest fossil tortoise of this
modern type was about 40 million years old. This find pushes
their history back at least another 35 million years. These eggs
are spherical and 40 mm in diameter.
Dinosaurs and Eggs
The extinct reptiles commonly known as dinosaurs appeared
about 225 million years ago and became extinct about 65 million
years ago. Although some dinosaurs were gigantic, others were
relatively small, about the size of a chicken. It is believed
that birds evolved from one of these species of small dinosaur.
Reptile and bird eggs:
Dinosaurs laid eggs rather like those of living lizards,
crocodiles and turtles. Some reptile eggs are soft and leathery
whereas others have a hard shell, like that of birds' eggs. The
egg shells of large birds (such as the ostrich) and large dinosaurs
are quite robust, consisting of several layers of mineral material,
which lends itself to fossilization.
click here to view image (sorry under construction)
Eggs of various modern reptiles and birds:
Top row: crocodile and two different kinds of tortoise.
Lower row: ostrich, goldcrest and Aepyornis (the extinct
elephant bird of Madagascar).
All to same scale. The ostrich egg is 145mm long.
Dinosaur egg remains are not particularly rare; they are
known from over 220 localities world-wide. Dinosaur eggs have
been found in North America, France, Mongolia and China. It seems
likely that some species of dinosaur, like some living reptiles,
buried their eggs in the ground; this would make them more likely
to become fossilized. The 'Dinosaur Egg and Embryo Project' is
centered upon four different kinds of egg from the Nanchao Formation
(Upper Cretaceous; about 75-85 million years ago) of the Nanyang
Valley, Henan Province, PRC.
Embryonic bones within dinosaur eggs
This is not the first time that bones of developing dinosaurs
have been found within fossil eggs. Previous finds are summarized
in a book entitled 'Dinosaur Eggs and Babies', published by Cambridge
University Press in 1994. This book includes a description of
a remarkably good embryonic skull of Hypacrosaurus from Canada.
Others have subsequently described a partial embryonic skull
of an oviraptorid dinosaur from Mongolia. All four kinds of egg
studied in the present project have yielded embryonic bones and
two kinds have also yielded complete skulls.
Extraction of the embryos
Some of the eggs are infilled by silt (which could not have
happened unless they were cracked), some are infilled by calcite
crystals (calcium carbonate) and barites (barium sulphate) deposited
by percolating ground waters, and others by a mixture of silt
and calcite. Bones are composed partly of calcium phosphate.
Very dilute acetic acid will break down the calcareous matrix
of the silt and dissolve the calcite, but it does not attack
the bones so readily. At intervals the specimen is washed thoroughly
to remove salts and acid, dried in an oven, and any exposed bone
is impregnated with a plastic to prevent damage by further immersion
in acid. This process is repeated again and again, over many
Mode of preservation of the embryos
If an embryo died very young then its bones are less well
ossified than in an embryo which died at full-term. The position
of the bones within the egg also varies according to the stage
of development at which the embryo died. It seems that earlier
embryos are usually preserved around the center of the egg, perhaps
suspended on the dried surface of the yolk. Mid-stage embryos
are often stuck to the roof of the egg, perhaps having been buoyed
up by gas produced during decomposition, and subsequently sealed
in that position when the egg dried up. By contrast, the more
dense bones of late-stage embryos are usually spread over the
floor of the egg. Drying of the egg also seems to be an important
component in the preservation of unossified tissue such as cartilage.
The only sure way of identifying a dinosaur egg is to identify
an embryo within it. On this basis, one of the four kinds of
eggs available to us has been identified as a therizinosaur:
these are an enigmatic group of dinosaurs of uncertain affinity,
perhaps sauropodomorphs (big four-footed forms), perhaps herbivorous
theropods (normally meat-eaters), or perhaps they are a group
in their own right?
What is so outstanding about this particular find?
There are four special features:
1.the exceptional completeness of the embryonic skull; it
appears to be less damaged than any described previously.
2.the exquisite preservation of fine detail, such as the
claws, revealed by chemical preparation techniques.
3.the discovery of preserved soft-tissues, such as cartilage
and perhaps muscle and skin, in the therizinosaur eggs.
4.the recognition of various agencies which have contributed
to the partial preservation and to the partial destruction of
Preservation of soft tissues
Soft tissues may be preserved in fossils by several different
processes. Sometimes the actual tissue may be preserved intact
because it is embedded within mineralized tissue: for example,
collagens are relatively stable and have been extracted from
fossil bones. By contrast, other soft tissues may be preserved
by mineral replacement of the tissue, on a molecule by molecule
basis, producing replicas of muscle tissue such as those known
in some fossil fishes from the Santana Formation of Brazil. It
seems that both of these processes may have occurred within the
therizinosaur eggs, and produced some rather complicated results.
For example, some material which is not attacked by the acetic
acid has the characteristic appearance of cartilage, but chemical
analysis is essential to determine whether it is actually cartilage
or a mineral replica. Some thin layers appear to be composed
of mineral replicas of flattened (epithelial ?) cells; one sheet
of non-bony material is reminiscent of skin. Skin preservation
is already known from adult dinosaurs, especially where the skin
has been mummified by drying. This aspect of the therizinosaur
eggs is in urgent need of further research.
Four different kinds of eggs were available for study from
the Upper Cretaceous of China. All of these were originally thought
to be dinosaurian. But one of the small, nearly spherical eggs
has now been shown to contain the complete, largely articulated
skeleton of an embryonic pond-tortoise (emyid). The black preservation
of the bones is somewhat different from that of the therizinosaur.
Although this egg lacks the glamour of the dinosaurs, it is probably
the most perfectly preserved Upper Cretaceous embryo known. It
is up to 40 million years older than the previous earliest record
of this group of reptiles. In another disarticulated skeleton
one of the smallest bones of the body, the stapes, which conducts
vibrations from the ear-drum to the inner ear; is exquisitely
The majority of the embryonic remains found within dinosaur
eggs are not preserved as complete skeletons. Some eggs clearly
decomposed before they dried out, so scrambling the arrangement
of the bones. In other eggs the bones are actually broken up
and appear to be gnawed, and in several eggs the bones are reduced
to bone chips. There are clues regarding the identity of one
of the culprits. Several eggs contain large numbers of small
ovoid structures, rounded at one end and slightly pointed at
the other. They closely match the frass (faecal pellets of larvae)
of dermestid beetles which scavenge dried carcases. Differences
in the size of the fossil frass would indicate several different
larval stages. The frass does not dissolve in acetic acid, suggesting
that it contains a high proportion of powdered bone.
A rotten egg might be expected to be suitable for the growth
of molds. When the egg was subsequently infilled and mineralized
any molds present might be preserved as mineral replicas by the
same processes that were responsible for the preservation of
embryonic tissues. We suggest that this may account for some
structures resembling a tiny fungus, but this interpretation
needs to be investigated by further research.
It is well known that attempts are being made world-wide
to amplify traces of dinosaur DNA, so far without success. We
drilled a core from an egg known to contain both cartilage and
well-preserved bone. The core was subjected to the usual cleaning
techniques to reduce the possibility of contamination with DNA
from a modern source. It was then ground to powder and subjected
to the same techniques that have been used successfully to extract
residual DNA from less ancient fossil bones. We have so far failed
to detect any trace of DNA. Perhaps we should be relieved, bearing
in mind that we might have amplified the DNA of Upper Cretaceous
bacteria, fungi and dermestid beetles!
When paleontologists hear that a dinosaur egg has a baby
inside, the first thing they want to know is 'What kind of dinosaur
is it?' As you will have seen, at least some of these Chinese
eggs contain a dinosaur which has been identified as a 'therizinosaur'
- but what is a therizinosaur? Dinosaurs are divided into two
main groups. The Ornithischia (or 'birdhipped dinosaurs) include
many well-known forms such as the armored stegosaurs and the
horned ceratopsians, as well as Iguanodon. The second group is
called the Saurischia (or 'lizard-hipped' dinosaurs). This group
contains the sauropodomorphs and the theropods. The first includes
some very early dinosaur forms, known as prosauropods, and gigantic
sauropods (such as Diplodocus which were particularly abundant
towards the end of the Jurassic period (about 140 million years
ago). The theropods were carnivorous forms, and included Tyrannosaurus
and Velociraptor. Theropods are of particular interest because
they are thought to be the group which gave rise to birds. It
is very unclear where therizinosaurs fit into the classification
of the dinosaurs. Some paleontologists believe that therizinosaurs
are sauropodomorphs. More recently several researchers have found
evidence that suggests that they were unusual theropods.
The issue is still controversial and it may be that the baby
therizinosaurs in this exhibition will help settle this argument.
What sort of animals were therizinosaurs?
Therizinosaurs are bipedal dinosaurs which have been discovered
in the Middle and Late Cretaceous rocks of China (PRC) and Mongolia.
They were medium-sized forms, reaching lengths up to 4 meters.
Their skulls are rather unusual, possessing a well-developed
toothless beak at the front end of the jaws, and many small,
leaf-shaped, serrated teeth further back. The hands and feet
seem to have been equipped with very large and sharp claws. We
do not fully understand what therizinosaurs ate or how they lived,
although most other fossil and recent reptiles with similar teeth