Prestigious feature in journal Science on the reproduction of prehistoric flying reptiles

Reblogged from http://www.lincoln.ac.uk/news/2017/12/1421.asp

For many years, palaeontologists have been uncovering the mysteries of reptiles, dinosaurs and other animals which roamed the earth more than 150 million years ago.

Now, in a fascinating feature for one of the world’s leading academic journals, Science, Dr Charles Deeming from the University of Lincoln, UK, shines a light on the reproductive biology of the pterosaurs – winged reptiles that flourished throughout the age of dinosaurs.

Dr Deeming, an avian and reptilian reproduction specialist in the School of Life Sciences at the University has studied pterosaur reproduction for 12 years. He has reviewed new research by an international team of research led by Xiaolin Wang which examined a find of more than 200 pterosaur eggs and associated embryos belonging to a pterosaur species known as Hamipterus tianshanensis.

The study by Wang et al, published in the same edition of the journal, also investigated lines of arrested growth in bone sections, enabling the age of the animal to be estimated.

Writing in the Perspectives section of Science today (1st December 2017), Dr Deeming explained: “The fact that these flying reptiles even laid eggs was only recently confirmed in 2004, with the report of two eggs from China, and one from Argentina that contained well-developed pterosaur embryos.

“We now know that pterosaur eggs had soft, parchment like shells comparable to those laid by modern-day lizards. Wang et al’s study supports this interpretation, as does a previous study of a smaller number of eggs from the same site. The fossilised eggs show little evidence of shell calcification, and many show a dimpling of the shell as seen in dead, dehydrated lizard eggs.

“Due to the nature of the shells, scientists believe that pterosaur eggs were buried, precluding any form of contact incubation by the parents. Adults may have attended or defended nests, which would explain the presence of adult skeletons in the specimen reported by Wang et al.

Wang et al suggests that pterosaurs nested in colonies, but Dr Deeming suggests that appropriate nesting sites might have been in short supply. Like modern-day sea turtles, female pterosaurs may have inadvertently dug up existing nests, revealing previously buried eggs, which could result in them drying out.

Dr Deeming added: “It is rare in studies of pterosaurs to find data which can provide such an insight into the development of an extinct species from the earliest stage to maturity, but care is needed when assessing the developmental stage of embryos from what remains a limited data set.

“We now have many questions to address: were the eggs buried in sand or covered in vegetation? Was clutch size limited to two (as suggested by previous fossil finds)? 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.”

Dr Deeming’s article is available to read in full online here: http://science.sciencemag.org/content/358/6367/1124

To access the research paper by Wang et al visit:
http://science.sciencemag.org/content/358/6367/1197

Prehistoric fossil sheds light on parenting in reptiles

A fossil specimen discovered by a farmer in China represents the oldest record of post-natal parental care, dating back to the Middle Jurassic.

The tendency for adults to care for their offspring beyond birth is a key feature of the reproductive biology of living archosaurs – birds and crocodilians – with the latter protecting their young from potential predators and birds, not only providing protection but also provision of food.

This behaviour seems to have evolved numerous times in vertebrates, with evidence of a long evolutionary history in diapsids – a group of amniotes which developed holes in each side of the skull about 300 million years ago and from which all existing lizards, snakes and birds are descended

However, unequivocal evidence of post-natal parental care is extremely rare in the fossil record and is only reported for two types of dinosaurs and varanopid ‘pelycosaurs’ – a reptile which resembled a monitor lizard.

A new study by the Institute of Geology, Chinese Academy of Geological Sciences, Beijing; the University of Lincoln, UK; and Hokkaido University, Japan, presents new evidence of post-natal parental care in Philydrosauras, a choristodere from the Yixian Formation of western Liaoning Province, China. Choristoderes are a group of relatively small aquatic and semi-aquatic diapsid reptiles which emerged in the Middle Jurassic Period more than 160 million years ago.

The team reviewed the fossil record of reproduction in this group using exceptionally preserved skeletons of the aquatic choristoderan Philydrosauras. The specimen was donated to the Jinzhou Paleontological Museum in Jinzhou City four years ago by a local farmer who discovered the skeleton.

The skeletons are of an apparent family group with an adult, surrounded by six juveniles of the same species. Given that the smaller individuals are of similar sizes, the group interpreted this as indicating an adult with its offspring, apparently from the same clutch.

Dr Charles Deeming, from the School of Life Sciences, University of Lincoln, UK, said: “That Philydrosauras shows parental care of the young after hatching suggests protection by the adult, presumably against predators. Their relatively small size would have meant that choristoderes were probably exposed to high predation pressure and strategies, such as live birth, and post-natal parental care may have improved survival of the offspring. This specimen represents the oldest record of post-natal parental care in diapsids to our knowledge and is the latest in an increasingly detailed collection of choristoderes exhibiting different levels of reproduction and parental care.”

A test of whether post-natal parental care is an ancestral behaviour that has persisted in the evolutionary development of amniotes will depend on future fossil discoveries.

The study is published in Geosciences Journal.

‘Post-natal parental care in a Cretaceous diapsid from northeastern China’ Geosciences Journal Junchang Lü, Yoshitsugu Kobayashi, D. Charles Deeming, Yongqing Liu DOI: 10.1007/s12303-014-0047-1

How the shape of eggs may explain evolutionary history of birds

The eggs of amniotes – mammals, reptiles and birds – come in a remarkable variety of shapes and sizes.

Evolutionary biologists have now addressed shape variety in terrestrial vertebrates’ eggs, pinpointing morphological differences between the eggs of birds and those of their extinct relatives, the theropod dinosaurs.

Researchers from the University of Lincoln, UK, examined eggshell geometry from the transition of theropods – a sub-order of the Saurischian dinosaurs – into birds, based on fossil records and studies of their living species.

The results suggest that the early birds from the Mesozoic (252 to 66 million years’ ago) laid eggs that had different shapes to those of modern birds. This may suggest that egg physiology and embryonic development was different in the earliest birds and so this may have implications for how some birds survived the Cretaceous-Palaeocene extinction event that wiped out the dinosaurs.

Their findings are published in the journal Royal Society Open Science.

Author Dr Charles Deeming, from Lincoln’s School of Life Sciences, explained: “These results indicate that egg shape can be used to distinguish between different types of egg-laying vertebrates. More importantly they suggest Mesozoic bird eggs differ significantly from modern day bird eggs, but more recently extinct Cenozoic birds do not. This suggests that the range of egg shapes in modern birds had already been attained in the Cenozoic.”

The origin of the amniotic egg (an egg which can survive out of water) is one of the key adaptations underpinning vertebrates’ transition from sea to land more than 300 million years ago. Modern amniotic eggs vary considerably in shape and size and it is believed this variety may reflect the different patterns of egg formation and development in these taxa.

Dr Deeming added: “From a biological perspective, it is self-evident that different egg shapes by birds, both past and present, might be associated with different nesting behaviours or incubation methods. However, hardly any research has been carried out on this topic and fossil data are insufficient to draw firm conclusions. We hope that future discoveries of associated fossil eggs and skeletons will help refine the general conclusions of this work.”

Dr Deeming and co-author Dr Marcello Ruta, also from the University of Lincoln, are now investigating how the highly variable amounts of yolk and albumen (egg white) in eggs of different species could be a possible determinant of bird egg shape.

D. Charles Deeming and Marcello Ruta ‘Egg shape changes at the theropod-bird transition, and a morphometric study of amniote eggs’ Royal Society Open Science
DOI: 10.1098/rsos.140311

 

Why Diplodocus did not put all her eggs in one basket

A team of scientists have suggested reasons why the largest dinosaurs ever to have walked the Earth produced smaller eggs than might be expected.

One of the defining characteristics of the dinosaurs was their vast size, and the sauropods – a suborder of dinosaurs which includes the famous Diplodocus – were the largest of all.

Yet scientists have been puzzled at the relatively small size of sauropod eggs. Both individual egg size and clutch size are smaller than might be expected for such enormous creatures, relative to modern egg-laying animals.

Researchers have now concluded that the substantial incubation time required for sauropod embryos to develop and hatch may have been an important constraint and that this could explain the small individual size of sauropod eggs.

The findings are published in the summer 2014 issue of the Paleontological Society’s journal, Paleobiology. The team, which included biologists from the University of Lincoln, UK, and George Mason University, Virginia, US, with lead researcher Professor Graeme Ruxton from the University of St Andrews, used data from modern birds and reptiles to investigate factors affecting clutch size in this group of dinosaurs.

They estimated that the time from laying to hatching of eggs, which were incubated in underground nests, was between 65 and 82 days. This long incubation time increases the risk of predation, which coupled with the relatively low temperatures expected in the nest, may have been a significant factor in limiting the egg and clutch size.

Having larger eggs than are in the fossil record may have been advantageous because of larger hatchling size but this may have been outweighed by the increased risk of predation during the egg stage.

Dr Charles Deeming, from the School of Life Sciences, University of Lincoln, UK, said: “We think that a long incubation period of sauropods is likely to have led to very high mortality through predation. We suggest that the females laid their eggs in small clutches, possibly in different nesting sites, as an adaptive strategy to mitigate the high predation risk associated with long time of exposure in the egg stage.”

Professor Ruxton, from the School of Biology at the University of St Andrews, added: “The living bird with the largest eggs, the ostrich, has to incubate its eggs for 42 days; during which time many eggs are lost to predators. An ostrich weighs about 100kg and lays a 1.5kg egg; a sauropod dinosaur might be 50 times heavier than an adult ostrich but its eggs were only a little heavier than an ostrich egg. Some people might find it a bit disappointing that giant dinosaurs didn’t lay equally giant eggs – but it’s very satisfying to think that we might finally understand why.”

There may also have been a finite limit to the period over which environmental temperatures are high enough for egg development.

The team believe their conclusions could be extended to other groups of dinosaurs.

Graeme D Ruxton, Geoffrey F Birchard, D Charles Deeming ‘Incubation time as an important influence on egg production and distribution into clutches for sauropod dinosaurs’ Paleobiology 40(3):323-330. 2014 DOI: http://dx.doi.org/10.1666/13028

 

Lincoln blue tits provide insight into climate change

Researchers believe that the size of birds’ nests created in response to changing weather patterns may be partly to blame for reproductive failures over the last two years.

An article in the April edition of The Biologist, the Society of Biology’s magazine, explains that birds produce different sized nests depending on the weather.

Written by Dr Charles Deeming, senior lecturer at the University of Lincoln and a Fellow of the Society of Biology, the article explains that nests are far more than just a way to hold eggs and chicks.

Dr Deeming said: “Over the past few years scientific interest in nests has increased, with studies ranging from nest composition, construction behaviour and thermal properties to the use of nests as potential signals to mates. We’ve realised that the factors affecting nest construction are far more complex than we had previously understood.”

Dr Deeming’s studies of great tits and blue tits breeding in nest boxes at the University’s Riseholme Park campus have shed light on how nests are built and how they function.

He found that individual birds can build extremely different nests each year. Cold weather on the days the bird was adding lining to the nest meant they built heavier nests than when the weather was warmer. This suggests that an important function of the nest is to keep the bird warm while it sits on the eggs. Once the nest is lined, the female will lay the first egg, which will be incubated for around two weeks. This means a larger, warmer nest will be important for keeping the bird warm if the weather is cold.

However, as climate change brings more unpredictable weather patterns the way birds construct nests will be affected. In both 2011 and 2012, for example, early spells of warm weather were followed by much lower temperatures.

At Riseholme, this seems to have had devastating effects on reproductive success. Birds building in these early warm periods are likely to construct a light, poorly insulated nest. If the weather subsequently turns cooler, having a poorly insulated nest may have an adverse effect on their reproductive success.

Birds use a wide range of materials in their nests, from moss to sheep’s wool, and their availability may also be altered by climate change. Certain plants may go extinct in local areas, so some species could lose a key nesting material.

Dr Mark Downs, chief executive of the Society of Biology, said: “Climate change will have a large effect on our ecosystems and our food production, and Dr Deeming’s is one of many studies demonstrating that the effects will be complex and difficult to predict. It is essential that we continue to study how organisms adapt to climate change and how we can best mitigate its effects.”

Dr Deeming concludes: “Much more research is needed to determine how local climate affects nest construction. Only then will we start to understand how climate change is likely to affect nest building, and hence reproductive success.”