Illuminating the Evolution of Animal Life – Humbling Thoughts

Recently two scientific papers have been published that delve deep into the origins of life on Earth.  In one paper, published in the “Proceedings of the National Academy of Sciences USA”,  the origins of animal body plans (Animalia) were explored, analysing the anatomical designs of animals, looking at how animal life half a billion years ago evolved and changed over time to bring us the biodiversity we see today and that which is preserved in the fossil record.

Tracing the Origins of the Animalia

This study mapped shared characteristics and one of the conclusions drawn from the research was that all those weird and wonderful Cambrian creatures, as preserved in the Burgess Shales of British Columbia or in the Sirius Passet Lagerstätte of Greenland, are actually less weird than the butterflies and birds that you might see in your own garden.

The Body Plans of Bizarre Cambrian Creatures Such as Hallucigenia are not that Bizarre According to a New Study

Picture credit: Royal Ontario Museum/Dr Jean Bernard Caron with additional annotation by Everything Dinosaur

In the second scientific paper, which shares a number of authors with the first publication and was published last month in the journal “Nature: Ecology & Evolution”, researchers examined the evolution of all life as a whole, conducting research using a new molecular clock analysis to plot a unified timescale for the early evolution of life on our planet.

What is the Molecular Clock?

The idea of a molecular clock is based on the idea that evolutionary changes occur at regular time intervals, that the rate of genetic change (mutation), has remained constant over time.  The molecular clock uses this premise, it plots the number of differences in the genomes of two living species (for example a human and a bacterium) and these changes are proportional to the time since they shared a common ancestor.

Using this methodology, the scientists, from the universities of Bath and Bristol were able to avoid putting too much reliance on a very fragmentary and often highly controversial early life fossil record. 

This research team concluded that the last universal common ancestor of cellular life existed more than 3.9 billion years ago and that the crown clades of two primary divisions of life – Eubacteria and Archaebacteria emerged less than 3.4 billion years ago.  Furthermore, the scientists concluded that modern eukaryotes (organisms whose cells have a nucleus enclosed within membranes – animals, protists, plants and fungi), don’t constitute a primary lineage of life and emerged relatively late during life on Earth’s evolutionary history (around <1.84 billion years ago).

Eukaryote Cell Compared to the Prokaryote Cell Typical of Eubacteria and Archaebacteria

Picture credit: Everything Dinosaur

Did Animal Body Plans Emerge Over Deep Time or Come About in Response to Sudden Changes?

This was the question that the researchers set out to answer in the paper published the “Proceedings of the National Academy of Sciences USA”.  It is agreed that complex animal life evolved from single celled eukaryotes and that multi-cellular animals diversified into thirty or forty distinct anatomical body plans, but when and how did these body plans emerge?  Were the majority of these different body plans already in existence after the Cambrian explosion, some 500 million years ago?

To answer these questions the research team, consisting of scientists from Bristol University, Dartmouth College in New Hampshire and the University of West Georgia, looked at features from living groups of animals and cross-referenced those characteristics against what can be identified from the fossil record.

Professor Philip Donoghue (Bristol University) a co-author of both scientific papers explained:

“This allowed us to create a ‘shape space’ for animal body plans, quantifying their similarities and differences.  Our results show that fundamental evolutionary change was not limited to an early burst of evolutionary experimentation.  Animal designs have continued to evolve to the present day, not gradually as Darwin predicted, but in fits and starts, episodically through their evolutionary history.”

Mapping the Evolution of Different Types of Animal Body Plan

Picture credit: Bristol University

The research team propose that major expansions in the type of animal following the Cambrian explosion aligns with other major ecological transitions such as the conquest of terrestrial environments.

Bradley Deline (University of West Georgia) added:

“Our results are important in that they highlight the patterns and pathways in which animal body plans evolved.  Many of the animals we are familiar with today are objectively bizarre compared with the Cambrian weird wonders.  Frankly, butterflies and birds are stranger than anything swimming in the ancient sea.”

Trying to Fit Extinct Animals into the Study

Contributors to both scientific papers, James Clark (Bristol University) and Mark Puttick (Milner Centre for Evolution, University of Bath), looked at how fossils could be incorporated into this research.

Dr Puttick stated:

“One of the problems we had is that our study is mostly based on living species and we needed to include fossils.  We solved the problem through a combination of analysing the fossils and using computer models of evolution.”

James Clark added:

“The fossils plot intermediate of their living relatives in shape space.  This means that the distinctiveness of living groups is a consequence of the extinction of their evolutionary intermediates. Therefore, animals appear different because of their history rather than unpreserved jumps in anatomy.”

Studying the Genomes of Different Animals (Animalia)

Jenny Greenwood, also from the University of Bristol’s School of Earth Sciences, wanted to explore how this study might be reflected in the genomes of different organisms.  She wanted to work out which of the many proposed genetic mechanisms drove the evolution of animal body plans.

Jenny commented:

“We did this by collecting data on the different genomes, proteins, and regulatory genes, that living animal groups possess.  The differences in anatomical designs correlate with regulatory gene sets, but not the type or diversity of proteins.  This indicates that it is the evolution of genetic regulation of embryology that precipitated the evolution of animal biodiversity.”

These researchers have concluded that animal evolution has been permitted or driven by gene regulatory evolution.

Two Papers Helping to Improve our Understanding of the Evolution of Life on Earth

Picture credit: Everything Dinosaur

Everything Dinosaur acknowledges the help of a press release from Bristol University in the compilation of this article.

The two scientific papers:

“Integrated Genomic and Fossil Evidence Illuminates Life’s Early Evolution and Eukaryote Origin” by Holly C. Betts, Mark N. Puttick, James W. Clark, Tom A. Williams, Philip C.J. Donoghue and Davide Pisani published in the journal Nature: Ecology & Evolution.

“Evolution of Metazoan Morphological Disparity” by B. Deline, J. Greenwood, J. Clark, M. Puttick, K. Peterson and P. Donoghue  published in the Proceedings of the National Academy of Sciences USA.

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Scientists find Kayentatherium wellesi Fossil Along with Young

The Order Mammalia has a number of distinguishing characteristics when compared to the other vertebrates.  For example, mammals tend to have bigger brains and tend to produce some of the smallest numbers of offspring per litter.  Mammals evolved from reptiles and at some point in their evolutionary history, larger brains developed and smaller broods became the norm.  Scientists writing in the academic journal “Nature”, have published details of the discovery of the fossilised remains of a Jurassic stem mammal, one that was found in association with thirty-eight babies.

The fossilised specimens might help palaeontologists to work out how mammals developed a different approach to reproduction when compared to their reptilian ancestors.

A Skeletal Reconstruction of the Probable Mother (Kayentatherium wellesi) and Offspring

Picture credit: Eva Hoffman/The University of Texas at Austin

Jurassic Stem Mammal Kayentatherium wellesi

The fossils represent Kayentatherium wellesi, a cynodont, it was only as the specimen was being prepared that the researchers realised that this was an exceptional fossil.  The find of a 185-million-year-old K. wellesi with offspring are the only known fossils of baby stem mammals with what is believed to the mother.

The presence of so many offspring, probably only recently hatched from their eggs when they died, indicates that these types of stem mammal had litters more than twice the size of any living member of the Mammalia.  The size of the brood is akin to the breeding strategy of extant reptiles

Lead author of the study, Eva Hoffman (who studied the fossils whilst a graduate student at the University of Texas at Austin), commented:

“These babies are from a really important point in the evolutionary tree.  They had a lot of features similar to modern mammals, features that are relevant in understanding mammalian evolution.”

The Kayenta Formation of Arizona

Hoffman co-authored the study with her graduate adviser, Jackson School Professor Timothy Rowe, who collected the specimen during fieldwork exploring the Early Jurassic sediments of the Kayenta Formation in Arizona, more than eighteen years ago.

Computerised tomography was used to reveal the bones inside the matrix back in 2011.  However, advances in CT-scanning finally permitted researchers at the University of Texas at Austin to reveal the babies, including complete skulls and partial postcranial material.

Advances in Computerised Technology Over the Last Seven Years Permitted the Fine Details of the Babies to be Discerned

Picture credit: Eva Hoffman/The University of Texas at Austin

The Skulls of the Babies – The Same as the Adult’s Only Smaller

The highly detailed computer-generated images permitted the researchers to verify that the tiny bones were Kayentatherium wellesi, the same as the adult.  The analysis revealed that the skulls were scaled-down replicas of the adult, only ten percent the size of an adult skull, but otherwise proportional.  This contrasts with extant mammals, as their babies are born with shortened faces and large skulls to accommodate a big brain.  The brain of mammals is a very energy demanding organ, for example, in humans the brain needs more energy than any other organ of the body.

It has been estimated that the brains of human beings require around 20% of the total energy needed by our bodies each day.  Breeding and producing offspring also requires a lot of energy.  The discovery that Kayentatherium, a stem mammal, had a tiny brain and many babies, despite otherwise having much in common with extant mammals, suggests that a critical step in the evolution of the Mammalia was trading large litters for large brains.  This evolutionary change is therefore likely to have taken place more recently than 185 million-years-ago.

Professor Rowe explained:

“Just a few million years later, in mammals, they unquestionably had big brains and they unquestionably had a small litter size.”

Where does the Jurassic Stem Mammal Kayentatherium Sit on the Mammalian Evolutionary Tree?

Kayentatherium was very probably endothermic (warm-blooded) and the skeleton shows a number of anatomical traits associated with modern mammals.

The Place of Kayentatherium on the Mammalian Family Tree

Picture credit: Eva Hoffman/The University of Texas at Austin

The mammalian approach to reproduction directly relates to our own species development (Homo sapiens), including the development of our own brains.  By looking back at our early mammalian ancestors, we can learn more about the evolutionary process that helped shaped the development of humans.

Professor Rowe added:

“There are additional deep stories on the evolution of development and the evolution of mammalian intelligence and behaviour and physiology that can be squeezed out of a remarkable fossil like this now that we have the technology to study it.”

The scientific paper: “Jurassic Stem Mammal Perinates and the Origin of Mammalian Reproduction and Growth” by Eva A. Hoffman and Timothy B. Rowe published in Nature.

Everything Dinosaur acknowledges the assistance of a press release from the University of Texas at Austin in the compilation of this article.

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Kapes bentoni Saved by a Scan

The fossilised remains of a little reptile that roamed the land we now know as Devon has helped make links with the prehistoric vertebrate fauna of the Middle Triassic of Russia.  Thanks to the use of computerised tomography (CT) scans, palaeontologists have had the rare opportunity to study the skull and postcranial elements of a procolophonid reptile.  The fossil was found by co-author of the scientific paper, Dr Rob Coram of Swanage in November 2014, from a foreshore exposure of the Pennington Point Member of the Otter Sandstone Formation located close to the town of Sidmouth on the south Devon coast.

The Triassic sandstone deposits in these cliffs, which ironically form part of the famous UNESCO World Heritage site the “Jurassic Coast” contain vertebrate remains, but they are quite rare and often show signs of extensive weathering and transportation prior to burial and fossilisation.

The Fossil Specimen (BRSUG 29950-13) and Two Computer Generated Images

Picture credit: Bristol University/Papers in Palaeontology

Procolophonid Reptiles (Procolophonidae)

The reptile has been identified as an example of Kapes bentoni, several species are included in this genus, all of which, including the type species K. amaenus, which was named in 1975, come from Russia.  Procolophonids looked superficially like lizards, but they are not closely related to the Squamata.  They are parareptiles, which evolved in the Permian and had a wide distribution during the Triassic, before becoming extinct shortly before the Triassic came to an end.  When Dr Coram tried to clean and prepare the fossil, he found that the fossil material was too fragile and conventional preparation techniques would have resulted in permanent damage to the fossil bones.

Dr Coram commented:

“I tried everything I could.  I have had a lot of experience of removing rock from fossils using a fine needle and working under the microscope, but this was a nightmare.  When I touched it with a needle, small pieces of bone fell off.”

CT Scanning the Devon Fossil

In order to allow the fossil to be studied, Dr Coram contacted colleagues at Bristol University and a CT scan of the small fossil was organised.  The job of interpreting the scans and the resulting computer generated images was given to PhD student Marta Zaher, who was at the Bristol University for a few months, normally she is based in Zagreb (Croatia).  The three-dimensional scans of the skull and postcranial material turned out to be far better than the scientists had hoped.  Even wear facets on the tiny teeth of the Kapes specimen could be discerned and studied.

Once all the scans had been compiled the researchers could examine the procolophonid fossil in great detail.  Most of the procolophonid fossils from England are highly fragmentary, but the scans revealed the presence of a skull, cervical vertebrae, the shoulder girdle, forelimbs and the front half of the torso.

An Illustration of the Skeleton of Kapes bentoni (Lateral and Dorsal Views)

Picture credit: Bristol University/Papers in Palaeontology

Spectacular CT Scans of a Triassic Specimen

Student Marta explained:

“The scans are amazing.  They show every detail of the tiny, five-centimetre (two inch) long skull.  You can see each tooth, and even the wear patterns.  Almost all the tiny bones of the palate and braincase are there.”

She added:

“This identifies the animal without question as a procolophonid.  These lived worldwide at the time, and they were important plant-eaters, with broad teeth fused to their jaws, and which wore down under grinding from the tough plant food.”

Several years ago, less complete specimens of the procolophonid had been found in the Devon rocks, and two academics then at the University of Bristol, Patrick Spencer and Glenn Storrs, had suggested the Devon animal was the same as Kapes from central Russia.

A spokesperson from Everything Dinosaur commented:

“Thanks to the use of computerised tomography, the researchers were able to get an unprecedented insight into the anatomy of an anapsid.  This non-destructive technique has helped scientists to identify that this Devon specimen is very closely related to other reptiles, fossils of which come from the terrestrial red beds of Russia.”

A Diagram of the Skull Produced from the CT Scan Data

Picture credit: Bristol University/Papers in Palaeontology

Co-author of the scientific paper published in “Papers in Palaeontology”, Professor Mike Benton (Bristol University) stated:

“The new study confirms that the two animals are very close relatives, two species of the genus Kapes.  This is most unusual, to have evidence of a biogeographic connection over thousands of kilometres.  In the Middle Triassic, there was dry land in the UK and in Russia, but the area in between was filled with the Muschelkalk Sea, covering Germany and much of central Europe.”

Kapes bentoni

Many of the early procolophonids were insectivorous, however, Kapes bentoni was a plant-eater.  This idea is reinforced by the heavy wear on the teeth as observed in the CT scans from this study.  K. bentoni had a short, stocky body and it may have been fossorial (lived in a burrow).  The spines on the skull have provided the scientists with a bit of a puzzle.  It has been suggested that these spines had a defensive function, making the reptile seem bigger and more intimidating to a potential predator.  The spines would also have obstructed any predator attempting to swallow Kapes head-first.

A Life Reconstruction of the Procolophonid Kapes bentoni

Picture credit: Marta Zaher

The scientific paper: “The Middle Triassic Procolophonid Kapes bentoni: Computed Tomography of the Skull and Skeleton” by Marta Zaher, Robert A. Coram and Michael J. Benton published by Papers in Palaeontology.

Everything Dinosaur acknowledges the assistance of a press release from Bristol University in the compilation of this article.

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