An international team of researchers have published a ground-breaking study into bird evolution.  This research is part of an extensive four-stage project that aims to provide a better understanding of the avian genetic pool. The study is associated with the Bird 10,000 Genomes (B10K) Consortium which aims to sequence the genomes of every single species of bird. It should help scientists resolve puzzles about evolutionary relationships.

Studying Bird Evolution

Approximately sixty-six million years ago, Earth experienced a mass extinction event.  The impact of an extra-terrestrial bolide in what is now the Yucatan Peninsula (Mexico) caused ecosystems to collapse.  Scientists estimate that more than three-quarters of all known species became extinct.  The non-avian dinosaurs died out along with their pterosaur cousins.  This extinction event is referred to as the Cretaceous-Palaeogene (K-Pg) extinction event.  Fossil record data suggests that the vast majority of the world’s modern birds and mammals first appeared in the wake of that event, but further research was needed to clarify the origins of several clades.

The adaptability of many birds, such as their ability to consume seeds, a food resource that may have been relatively stable in the aftermath of the bolide impact, probably contributed to the survival of many lineages.

To read an article outlining research into avian survival: Seed-eating May Have Helped Some Birds Survive K-Pg Extinction Event.

Professor Peter Houde (New Mexico State University), is one of the fifty-two co-authors of this new study.  It was published in the academic journal “Natural” earlier this year. The paper outlines what the authors discovered about bird evolution and relationships and explains how the new analysis compares to previous research. General relationships between birds, and those between species within specific families, have been extensively studied. However, where exactly many groups of birds sit in relation to each other has been surprisingly difficult to figure out.

For example, it had been thought that diurnal raptors like eagles and buzzards (Accipitriformes), were not closely related to owls (Strigiformes). However, this new study demonstrates that owls are a sister lineage to the Accipitriformes.  That they are essentially nocturnal raptors.

Professor Peter Houde (New Mexico State University) highlighting the diversity of extant birds. He is one of fifty-two authors of a new study into the avian genome. Picture credit: New Mexico State University/Darren Phillips).

Picture credit: New Mexico State University/Darren Phillips

An Enormous Research Project

This new study represents phase two of the Bird 10,000 Genomes (B10K) project. Phase one, published in 2014, was ground-breaking both in its magnitude and in the data generated. The first part of the study sampled forty-eight species representing all orders of extant birds.  Phase two was more ambitious. It involved three hundred and sixty-three species from ninety-two percent of all bird families. Moreover, phase two analysed fifty times more DNA per species.  The dataset generated contained information on a hundred billion nucleotides.

Professor Houde explained:

“We’re only now beginning to understand how complex evolution is and to understand how biological processes work together to produce it.”

Complexity of bird evolution revealed by family-level genomes. The chart displays bird relationships and when groups diverged away from each other in deep geological time. Picture credit: Josefin Stiller, with paintings of birds by Jon Fjeldså.

Picture credit: Josefin Stiller and paintings of birds by Jon Fjeldså.

Scientists over the last two centuries inferred the relationships of birds and other organisms without the benefit of genetic data.

Professor Houde added:

“In the past, taxonomists who classified organisms were reliant on things like comparative anatomy and embryology and behaviour to infer relationships. It’s easy to see that a sparrow is close to a robin, but how might it be related to a duck? Are robins more closely related to ducks than they are to flamingos?”

Understanding Bird Evolution

Birds all ultimately descended from a single common ancestor.  However, taxonomists argue about the evolutionary relationships between different lineages.  Several competing and contrasting theories have been postulated.  The scientific consensus states that a species can have only one closest relative.  Yet, the conflicting hypotheses relating to taxonomy hinted otherwise. Is it possible that a species could be most closely related to two or more different lineages at the same time?

The “Proavis” model at the Grant Museum of Zoology (London).  A model depicting a hypothetical ancestor of birds.  Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Researchers had a difficult time understanding how birds could seem to have multiple relationships at the same time. This research explains how this could come about.  The genome is described as a “mosaic”.  The genome of an organism is made up of mosaic pieces that have different evolutionary histories.  It is likely that this pattern is related to biological processes that occurred early in bird evolution.

Birds are an extremely diverse group of animals. They can be found on every single continent, living in environments ranging from the driest desert to the ice and snow of the Poles. Within these habitats, they have further diversified to exploit a huge number of different niches. There are more species of birds known to science than species of mammals.

The research provides strong support for the idea that very few lineages of modern birds existed before and survived the K-Pg extinction event. The modern diversity of birds resulted from an explosive radiation of lineages immediately following it, as well as explosive population growth as birds expanded into vast newly uninhabited regions of the planet. This agrees with the fossil record but is contrasted by smaller studies.  It is likely that the Aves were able to exploit the niches in ecosystems vacated by the extinct dinosaurs.

The Rise of the Elementaves

The study has led to the placing of a seemingly diverse group of birds in one new group.  This group has been named the Elementaves as it includes specialists that are at home both in the water, on land and in the air. The Elementaves contains many species that you might expect to be closely related. For instance, penguins, albatrosses and pelicans. However, this group also includes other birds such as hummingbirds, swifts and the bizarre South American hoatzin. Therefore, the Elementaves contains the smallest and the largest volant birds.

Professor Houde opined:

“Furthermore, there are parts of the genome that are patently misrepresentative of what nearest relationships are. For example, you’ve got long-legged birds like storks, herons and cranes and so on and so forth.  They all like to wade in water, yet they’re not each other’s nearest relatives. There are certain genes that they have, that have over millions and millions of years, allowed these birds to adapt to be able to wade in water. But those genes will mislead you about how those birds are actually related to one another.”

The closest related living birds to the “Terror Birds” (phorusrhacids), the Cariamiformes, are placed in a group entitled the Australaves uniting them with parrots, falcons and the order Passeriformes (the perching birds, which includes more than fifty percent of all known bird species).  According to this research, they are far removed from other kinds of giant, flightless birds such as the ratites (ostrich, rhea, cassowary and emu).  The cassowary and the emu are covered in hair-like feathers.  It had been suggested that Cariamiformes such as Phorusrhacos longissimus may have possessed a hair-like integumentary covering.  However, they were probably feathered like other Australaves, and their large size and similarity is the result of convergent evolution.

The Kelenken in all its glory.  Cariamiformes were probably feathered unlike many large, flightless birds today that have a more bristle-like integumentary covering. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Wider Implications for Taxonomic Studies

Houde and his colleagues used mathematical and probabilistic models to describe genetic connections more accurately and evaluate bird evolution. Although many of the assumptions on which scientists had based their standard models of bird evolution turned out to be true, co-authors discovered others were not valid.  The Aves are an interesting group to study.  However, this research can be applied to other organisms.

Although the results are not yet definitive, the authors’ new approach and findings will provide opportunities to enhance future research in this area.

Everything Dinosaur acknowledges the assistance of a media release from New Mexico State University in the compilation of this article.

The scientific paper: “Complexity of avian evolution revealed by family-level genomes” by Josefin Stiller, Shaohong Feng, Al-Aabid Chowdhury, Iker Rivas-González, David A. Duchêne, Qi Fang, Yuan Deng, Alexey Kozlov, Alexandros Stamatakis, Santiago Claramunt, Jacqueline M. T. Nguyen, Simon Y. W. Ho, Brant C. Faircloth, Julia Haag, Peter Houde, Joel Cracraft, Metin Balaban, Uyen Mai, Guangji Chen, Rongsheng Gao, Chengran Zhou, Yulong Xie, Zijian Huang, Zhen Cao, Guojie Zhang et al published in Nature.

The award-winning Everything Dinosaur website: Dinosaur Toys and Models.

Dragonflies are amazing. Team members at Everything Dinosaur are lucky enough to spot the occasional dragonfly as they whizz around hunting and looking for mates. These ancient insects embody grace and agility. They are little changed from their Carboniferous antecedents. Stunning dragonfly fossils have provided palaeontologists with information on dragonfly evolution. Their fossils and living forms evoke a sense of wonder.

Occasionally, these beautiful insects alight and if we are quick, we can take a photograph. For example, we were able to take a photograph of a pair of dragonflies mating.

Dragonflies mating. These are likely to be Common Darter dragonflies.

Picture credit: Everything Dinosaur

The picture (above) shows a pair of Common Darter dragonflies (Sympetrum striolatum) – we think.  The female has curled the tip of her abdomen to connect with the male’s genitalia. This is referred to as the “wheel position”.  The two insects are resting on a limestone block.  The limestone is probably younger in age than the first, ancestral forms of flying insects that gave rise to the Order Odonata.  The Odonata comprises the dragonflies and their often smaller relatives damselflies. An easy way to differentiate between the two is that damselflies usually fold their wings when at rest.

Marvelling at Dragonfly Evolution

Some ancient forms were gigantic.  Wingspans in excess of sixty centimetres have been recorded in some genera.  It is thought that the during the Carboniferous, the absence of vertebrate aerial predators combined with high levels of atmospheric oxygen permitted early dragonflies to evolve into much larger forms than found in the Mesozoic and today.

To read: High Oxygen Levels and Super-sized Dragonflies.

In many cultures, dragonflies are viewed as a symbol of change and transformation.  This reflects their life cycle from aquatic nymphs to airborne aeronauts.  We find this ironic, as they have not changed greatly since their Carboniferous origins. Their presence often indicates a healthy ecosystem.  We are just happy to marvel at their beauty and grace.

Perhaps this female dragonfly will lay her eggs in our office pond.  Thus, we will have an opportunity to view the next generation of an amazingly beautiful creature that has endured through the ages.

Let’s hope so.

The Everything Dinosaur website: Prehistoric Animal Toys.

Size doesn’t matter for mammals with more complex brains, according to new research led by the University of Bath.  Mammals that have developed more sophisticated brains tend to have a smaller size difference between males and females of that species.  The research paper has been published in the academic journal “Nature Communications”.  The study can provide new insights into mammal evolution and the role of sexual selection.

In many mammal species, the males can be bigger than the females.  In some species, the females can be bigger on average than the males. This is a trait called sexual size dimorphism (SSD). For instance, male southern elephant seals (Mirounga leonina), are around three times larger than females. African elephants (Loxodonta) show SSD.  Males can weigh several thousand kilograms more than mature females.

A male African elephant (Loxodonta).  Male elephants tend to be much larger than the females.

In contrast, dolphins have no difference in sizes between the sexes. Humans are somewhere in between, with the average male being larger than the average female, but across the population there is an overlap.

Analysing the Genomes of 124 Species of Extant Mammal

The study involved researchers from the Universities of Bath and Sheffield, along with Cardiff University and UNAM (Mexico).  The team examined the genomes of 124 extant species of mammals. The genes were grouped into families of similar attributes and functions.  The size of these gene families was then calculated.  The researchers discovered that those species with a big difference in size between the sexes had bigger gene families linked to olfactory functions (sense of smell) and smaller gene families associated with brain development.

Therefore, this could also mean that those species with very little difference in sizes between males and females (termed monomorphic) had larger gene families associated with brain development. The authors suggest that in species with a large SSD, traits such as the sense of smell could be important for identifying mates and territories. In contrast, mammals with a smaller SSD are potentially investing in their brain development and tend to have more complex social structures. This means they compete for mates using other means than simply using size to select who to mate with.

Corresponding author for the research, Dr Benjamin Padilla-Morales (University of Bath), commented:

We were surprised to see such a strong statistical link between a large SSD and expanded gene families for olfactory function. Even more interestingly, the gene families under contraction were linked with brain development. This could mean that those species with a small SSD have bigger gene families associated with brain function and tend to show more complex behaviours such as biparental care and monogamous breeding systems.”

Size is Important in Some Mammal Species

The research team concluded that whilst body size in some mammal species is significant, for others it does not matter so much.  If size plays a role in sexual selection, then it leads on to considering how traits like SSD are shaping mammalian evolution.  Is SSD in some species influencing brain and genome development?

This new research helps to illustrate the complex interplay between sexual dimorphism, gene family size evolution, and their roles in mammalian brain development and function. It provides a valuable perspective in understanding mammalian genome evolution.

The research team hope to develop this line of enquiry further.  They want to investigate how testes size impacts the evolution of the mammalian genome.

Being small insectivores with fewer skull bones led to mammalian evolutionary success: Reduction in Skull Bones Led to Success for the Mammals.

The Implications for Mammalian Evolution

This research highlights the importance of considering the multifaceted nature of sexual selection and its diverse effects on different aspects of mammalian evolution and biology. The finding that body size plays a role in sexual selection for some species but not others suggests that the evolutionary pressures shaping sexual dimorphism can vary considerably across the mammalian lineage.

Understanding these nuanced relationships is crucial for piecing together the complex tapestry of mammalian evolution. Perhaps, a study of the fossilised remains of a particular group of mammals with descendants still living today could shed new light on when these relationships established. Could the Proboscidea Order (elephants and their relatives) provide a starting for this research? By examining the fossil records of such groups, scientists could gain a better understanding into the evolutionary processes that have given rise to the incredible adaptations found in the Mammalia.

A scale drawing of the Late Miocene prehistoric elephant Konobelodon atticus.  Could a study of ancient elephants provide a fresh perspective on the evolution of sexual size dimorphism (SSD).  Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Everything Dinosaur acknowledges the assistance of a media release from the University of Bath in the compilation of this article.

The scientific paper: “Sexual size dimorphism in mammals is associated with changes in the size of gene families related to brain development” by Benjamin Padilla-Morales, Alin P. Acuña-Alonzo, Huseyin Kilili, Atahualpa Castillo-Morales, Karina Díaz-Barba, Kathryn H. Maher, Laurie Fabian, Evangelos Mourkas, Tamás Székely, Martin-Alejandro Serrano-Meneses, Diego Cortez, Sergio Ancona and Araxi O. Urrutia published in the journal Nature Communications.

The award-winning Everything Dinosaur website: Prehistoric Animal Models and Toys.