The Dinosaur Egg and Embryo Project
Paleo-Technician, Terry Manning

Acknowledgements

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

Introduction

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 long.

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

Dinosaurs:

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 eggs

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 weeks.

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.

Therizinosaur eggs

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 the embryos.

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.

Pond-tortoise embryos

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 preserved.

Scavengers

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.

Moldy eggs?

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.

Cretaceous Park

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!

Dinosaur classification

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 are plant-eaters.