Investigating the diversity of sea-urchins

Research into sea-urchin fossils collected from Portugal has revealed that diversity of the taxa seems to be linked with the evolution of the sea basin.

Dr Marcello Ruta, from the School of Life Sciences, University of Lincoln, UK, was part of the team which investigated how echinoid (sea-urchin) diversity changed through the Mesozoic period – 252 to 66 million years ago.

They focussed on a comprehensive database of fossil specimens from the Lusitanian and Algarve basins in Portugal.

A long-standing debate in current paleobiological research concerns the significance of global diversity patterns retrieved from raw counts of fossils through time, and numerous quantitative studies of the quality of the fossil record have concluded that fossil diversity is biased by many factors.

In this study, researchers chose to focus on a regionally restricted, but well sampled series of echinoids from Portugal in order to control for certain biases.

The aim was to explore the nature of the Portuguese echinoid fossil record, by investigating the palaeodiversity signal and comparing it with the already documented echinoderm record from the same era from the UK.

The research revealed that the diversity pattern is far from having a defined trend, showing many fluctuations that appear to be linked with gaps in the geological record.

Dr Ruta concluded: “Echinoid diversity during the Mesozoic in the Lusitanian basin is far from having a general trend, differing from previous global studies in other taxonomic groups. Many of the variations in diversity seem to be linked to basinal discontinuities and, therefore, with the evolution of the basin. Furthermore, the temperature and sea level changes appear to have had very little influence on echinoid diversity.”

The study ‘Mesozoic echinoid diversity in Portugal: Investigating fossil record quality and environmental constraints on a regional scale’ is published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

The fossil sea-urchin Acrosalenia. Photo courtesy: Professor Andrew B. Smith, The Natural History Museum, London
The fossil sea-urchin Acrosalenia. Photo courtesy: Professor Andrew B. Smith, The Natural History Museum, London

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

Science and art reconstruct 300 million-year-old vertebrate

Paleontologists have provided a new cranial reconstruction of a long-extinct limbed vertebrate (tetrapod) from previously unrecognised specimens found in coal deposits from the Czech Republic.

The team of academics reviewed the cranial structural features of the Late Carboniferous Gephyrostegus bohemicus – a small animal of generally lizard-like build that lived 308 million years ago.

This early tetrapod could be the earliest example of a reptile and explain the origin of amniotes, all vertebrates that belong to reptiles, birds and mammals.

Experts from, Comenius University in Bratislava (Slovakia), University Museum of Zoology in Cambridge, The Natural History Museum in London, and the University of Lincoln, UK, have been able to study additional specimens unavailable in previous works.

Their aim was to provide an analysis of early tetrapod relationships incorporating their new observations of Gephyrostegus. Their analysis used skeletal traits across a sample of early tetrapod groups to identify the likely affinities of Gephyrostegus.

Their results are detailed in the Journal of Vertebrate Paleontology.

Dr Marcello Ruta, from the School of Life Sciences, University of Lincoln, UK, was one of the authors and produced a series of intricate hand-drawn recreations of the cranial structure of Gephyrostegus.

He explained: “Gephyrostegus has always been an elusive beast. Several researchers have long considered the possibility that the superficially reptile-like features of this animal might tell us something about amniote ancestry. But Gephyrostegus also shows some much generalised skeletal features that make the issue of its origin even more problematic. We conducted a new study that brings together data from a large number of early tetrapods. The study shows that Gephyrostegus is closely related to another group of Eurasiatic and North American tetrapods called seymouriamorphs, also involved in debates about amniote ancestry. We found some interesting new cranial features in Gephyrostegus that helped us establish this link.

“It was a privilege for me to work with an international team of world-leading authorities on early tetrapods. My co-authors have had a long and beneficial influence on my career and it was truly rewarding for me to team up with them. In addition, making detailed drawings of fossils has always been a key element of my scientific undertakings. Staring at specimens for a long time down a microscope and trying to make sense of their anatomy may be frustrating and tiring at times, but always immensely rewarding.”

Jozef Klembara, Jennifer A. Clack, Andrew R. Milner & Marcello Ruta. 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:4, 774-792 http://dx.doi.org/10.1080/02724634.2014.837055

 

New research on early tetrapod feeding habits

A study of the jaws of one of the earliest known limbed vertebrates shows the species still fed underwater, not on land.

Scientists from the University of Lincoln, UK, University of Zurich, Switzerland, University of Cambridge and University of Bristol, developed an innovative new method to infer the feeding mechanism of Acanthostega – one of the earliest and most primitive tetrapods.

Tetrapods – the four-legged limbed vertebrates – evolved from fish and include today’s amphibians, reptiles, birds and mammals.

Acanthostega is regarded as one of the best known early tetrapods, and has played a key role in debates about tetrapod origins since spectacular new specimens were discovered in Greenland in 1987. Dating back to some 360 million years ago (end of the Devonian period); it has often been seen as a near-perfect fish-tetrapod intermediate.

The UK and Swiss researchers employed advanced statistical methods from a range of disciplines to explore the anatomical, functional and ecological changes associated with the emergence of tetrapods.

They examined the movement and structure of the lower jaws of Acanthostega and several other early tetrapods and tetrapod-like fish. Their observations suggest the Acanthostega jaw was more geared towards feeding under water, indicating that this tetrapod retained a primarily aquatic lifestyle.

Dr Marcello Ruta, from the University of Lincoln’s School of Life Sciences, said: “The origin of tetrapod from fish is an iconic example of a major evolutionary transition. The fossils of Acanthostega continue to play an unsurpassed role in our understanding of the fish-tetrapod transition.

“Acanthostega retained many primitive and fish-like features while also displaying unquestionable tetrapod features such as fingers and toes. Its broad snout appears to be consistent with aquatic feeding habits (suction feeding), but its complex cranial joints appear to be similar to those of terrestrial vertebrates and would suggest direct biting on land environments as a means of prey capture. This paradox prompted our study.”

The team examined patterns of jaw shape variation to assess whether the Acanthostega jaw is overall more similar to the jaws of fish or those of tetrapods. They then used advanced engineering methods to simulate biting action.
Dr Ruta said: “The lower jaw of Acanthostega can be shown to be anatomically and functionally similar to the jaws of some early fish and contemporary fish-tetrapod intermediates.

“Its upturned anterior extremity and rearward-facing anterior fangs appear to be adaptations for a snapping action. All these observations imply that this type of jaw was capable of fast closure for efficient capture of fast prey, in support of a predominantly if not exclusively aquatic feeding action.”

Their results are published on Wednesday, 26th February in Proceedings of the Royal Society B.

Neenan JM, Ruta M, Clack JA, Rayfield EJ. 2014 Feeding biomechanics in Acanthostega and across the fish–tetrapod transition. Proc. R. Soc. B 20132689.
http://dx.doi.org/10.1098/rspb.2013.2689

Land animals kept fish-like jaws for millions of years

Research has confirmed how early land vertebrates, which evolved from fish, developed weight-bearing limbs and other adaptations long before their feeding systems adjusted to a vegetation-based diet.

Now, for the first time, fossil jaw measurements have demonstrated this gap in evolutionary development.

Scientists from the University of Lincoln (UK), the University of Massachusetts, Amherst, and the University of Oxford (UK), examined the lower jaws of 89 fossils of early tetrapods (four-footed animals) and their fish-like predecessors.

The fossils ranged in age from about 300 to 400 million years old and the team were interested in how the mechanical properties of the jaws of these animals differed through time.

They used 10 biomechanical metrics to describe jaw differences. One of these, called mechanical advantage, measured how much force an animal can transfer to its bite.

Dr Marcello Ruta, from the School of Life Sciences, University of Lincoln, said: Our study is the first of its kind to address changes in biomechanical properties of the lower jaw across the transition from fish to land vertebrates using a diverse range of extinct species. This work paves the way to in-depth analyses of the rates of evolutionary transformation in other anatomical structures during this major episode in vertebrate history. It also lays the foundations for integrative research that explores themes as diverse as the origin of the first terrestrial food webs, the impact of acquisition of new structures on the diversification of major animal groups, and patterns and processes of functional change.”

So it turns out that just moving into a new environment is not always enough to trigger functional adaptations.

The team discovered that the mechanical properties of tetrapod jaws did not show significant changes in patterns of terrestrial feeding until some 40 to 80 million years after the four-legged creatures initially came out of the water. Until then, tetrapod jaws were still very fish-like, even though their owners had weight-bearing limbs and the ability to walk on land.

In the paper, which has been published in an early online edition of the journal Integrative and Comparative Biology, the authors say the results may be explained by an earlier hypothesis: a shift from gilled to lung breathing in later four-footed animals was necessary before they could adapt their jaw structure to eating plants.

This finding suggests tetrapods may have shown a limited variety of feeding strategies in the early phases of their evolution on land.

Lead author Dr Phil Anderson, from the University of Massachusetts, said: “The basic result was that it took a while for these animals to adapt their jaws for a land-based diet. They stayed essentially fish-like for a long time.”

Dr Matt Friedman, lecturer in palaeobiology at the University of Oxford, said: “The thing that is really interesting is that the diversity of jaw function didn’t really take off until around the origin of amniotes – creatures that lay hard-shelled eggs on land rather than being tied to water for reproduction like fishes and amphibians. It is in amniotes and their closest relatives that we see the first evidence for dedicated herbivory – until that point tetrapods had basically been carnivores. So this means it took at least 50 million years of evolution after the origin of features like limbs, fingers and toes before tetrapods achieved dietary diversity that began to resemble what we see today.”

The statistical methods developed in this work could be used in future studies of more subtle biomechanical patterns in fossil animals that may not be initially clear.