Newly published research led by scientists at the University of Bristol has shed light on the remarkable evolution of the jaws of snakes and lizards.  These animals are part of the order Squamata which in turn, is part of the Superorder Lepidosauria. The Lepidosauria includes the Squamata and also the Rhynchocephalia. The Rhynchocephalia is today, only represented by one living species the Tuatara (Sphenodon punctatus). However, the fossil record demonstrates that the Rhynchocephalia were once extremely widespread and diverse.

The study focused on the evolution of remarkably varied jaw shapes within the Lepidosauria which drove their extraordinary success.  For example, the snakes and lizards represent the most diverse and speciose of all tetrapods.  Around twelve thousand species have been described.

A team of evolutionary biologists led the research, and it provides a new understanding of the intricate factors influencing the evolution of lower jaw morphology in the lepidosaurs.  The paper has been published in the Proceedings of the Royal Society B.

An image of an anole (a species of “false chameleon”) crushing a snail with its jaws. Picture credit: Professor Anthony Herrel (co-author in the study).

Picture credit: Anthony Herrel (co-author of the study)

To read a related blog post about the discovery of a remarkable fossil in Germany that highlights the evolutionary links between the Squamata and the Rhynchocephalia: Tiny Fossil Sheds Light on Reptile Evolution.

The Jaw Shape of Snakes and Lizards

The scientists discovered that jaw shape evolution in lepidosaurs is influenced by a complex interplay of factors beyond ecology, including phylogeny (evolutionary relatedness) and allometry (the scaling of shape with size). The study demonstrated that at least in terms of jaw shape, snakes are outliers. Snakes exhibit a unique jaw morphology.  This is most likely due to their highly flexible skulls and their ability swallow prey many times larger than the width of their head.

Corresponding author for the study, Dr Antonio Ballell Mayoral (School of Earth Sciences at the University of Bristol), commented:

“Interestingly, we found that jaw shape evolves particularly fast in ecologically specialised groups, such as in burrowing and aquatic species, and in herbivorous lizards, suggesting that evolutionary innovation in the lower jaw was key to achieve these unique ecologies. Our study shows how lizards and snakes evolved their disparate jaw shapes which adapted to their wide range of ecologies, diets, and habitats, driving their extraordinary diversity.”

Diagram showing rates of evolution of lower jaw shape across the ‘family tree’ of lepidosaurs. Picture credit: Dr Antonio Ballell Mayoral and colleagues.

Picture credit: Dr Antonio Ballell Mayoral and colleagues

The Lower Jaw is a Key Element in Ecological Adaptation

This research work underlines the critical role of morphological innovation in promoting the diversification of extremely biodiverse groups like the lepidosaurs.  The lower jaw is a vital component of the vertebrate feeding apparatus, the researchers conclude it is a key element in driving ecological experimentation and adaptation.

As for any future research, the scientists would like to examine the morphology of the entire lepidosaur skull.

Dr Ballell Mayoral explained:

“Lower jaws are important, but they work together with the jaw closing muscles to support essential functions like feeding and defence. We are exploring the relationship between skull shape and the arrangement of the jaw closing musculature through evolution, and how it has impacted the diversification of feeding mechanics and habits.”

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

The scientific paper: “Ecological drivers of jaw morphological evolution in lepidosaurs” by Antonio Ballell, Hugo Dutel, Matteo Fabbri, Elizabeth Martin-Silverstone, Aleksandra Kersley, Chrissy L. Hammond, Anthony Herrel and Emily J. Rayfield published in the Proceedings of the Royal Society B.

Visit the award-winning Everything Dinosaur website: Dinosaur Toys and Models.

Scientists have discovered new species of ghost shark that lives exclusively in the deep waters of Australia and New Zealand. It is a type of Australasian Narrow-nosed Spookfish and has been named Harriotta avia.  The new fish species has been scientifically described by Dr Brit Finucci of New Zealand’s National Institute of Water and Atmospheric Research (NIWA).

It was previously thought to be part of a single globally distributed species, until research revealed it is genetically and morphologically different from other ghost fish.

Harriotta avia – A New Species of Ghost Shark

Dr Finucci named the new species in memory of her grandmother.

Dr Finucci explained:

“Avia means grandmother in Latin; I wanted to give this nod to her because she proudly supported me through my career as a scientist. Chimaeras are also rather ancient relatives – the grandmas and grandpas – of fish and I thought the name was well suited.”

A new species of ghost fish has been described. Named Harriotta avia it lives exclusively in the deep waters of Australia and New Zealand. Picture credit: NIWA.

Picture credit: NIWA

An Ancient Order of Cartilaginous Fish

Chimaeriformes certainly are an ancient order of cartilaginous fish (Chondrichthyes).  They probably evolved in the Devonian. Most extant species are found at depths greater than two hundred metres, and they live on the seafloor.  Harriotta avia feeds on crustaceans, however in the Palaeozoic these types of fish evolved to fill a variety of niches.  For example, in 2023, research was published that identified suction feeding in Carboniferous Chimaeriformes.

To read about this research: Carboniferous Chimaeras were Suction Feeders.

Most fossil and extant chimaeras are small, very few specimens exceed one metre in length. However, other prehistoric, cartilaginous fish that were distantly related to the newly described H. avia grew much larger. For example, the Permian genus Helicoprion with its bizarre tooth-whorl jaw, has been estimated to have grown to around eight metres in length.

PNSO Haylee the Helicoprion replica. The stunning emerald eye on the model is reminiscent of the eye of a chimaera such as the deep-water Rabbit Fish (Chimaera monstrosa) to which Helicoprion is distantly related.

The picture above shows a model of the prehistoric fish Helicoprion.  This Permian predator is distantly related to extant ghost sharks.  The Helicoprion model is from the mid-size model range produced by PNSO.

To view the PNSO models and figures in stock: PNSO Models and Figures.

Chimaeriformes

Ghost sharks (Chimaeriformes) are a group of cartilaginous fish closely related to rays and sharks. These mysterious creatures are also known as rabbitfish, ratfish and elephant fish.

They have a smooth skin, free of scales.  Most feed on crustaceans such as shrimp and molluscs with their distinctive beak-like teeth.

Dr Finucci added:

“Harriotta avia is unique due to its elongated, narrow and depressed snout; long, slender trunk; large eyes; and very long, broad pectoral fins. It is a lovely chocolate brown colour.”

Ghost sharks are mainly found in the depths of the ocean.  Some are thought to live at depths of up to 2,600 metres.  This makes them hard to monitor and study.  Marine biologists know very little about their habits, reproduction or their conservation status.

A spokesperson from Everything Dinosaur commented:

“This is an exciting development.  It is likely that the deep ocean holds many more secrets.”

The specimens were collected in the Chatham Rise off New Zealand’s coast during research surveys for Fisheries New Zealand.

Everything Dinosaur acknowledges the assistance of a media release from the National Institute of Water and Atmospheric Research in the compilation of this article.

A team of international scientists have been collaborating on a genetic study of extant bird species.  This programme sets out to provide a better understanding of the phylogeny of Aves.  It has been operating for a decade and is split into four phases.  A report outlining the conclusions of phase two was published in the spring (2024).  This immense study of bird genomes has highlighted some important characteristics of bird evolution.  For example, it has confirmed the phylogeny of the extinct phorusrhacids within the Aves order.

The complex nature of avian evolutionary relationships has been highlighted by this research.  The study, conducted by the Bird 10,000 Genomes (B10K) Consortium has enabled a comprehensive bird family tree to be constructed.  This research provides strong support for the hypothesis that very few lineages of modern birds existed before the K-Pg extinction event.

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.

To read Everything Dinosaur’s blog post about this research: New Analysis Re-Writes Bird Evolution.

The Relationship Between Phorusrhacids and Extant Flightless Birds

One of the conclusions of the study is that the Cariamiformes order is far removed genetically from the Palaeognathae.  This infraclass of birds (Palaeognathae) consists of the flightless ratites and one lineage of volant birds (Tinamous).  Life reconstructions of extinct members of the phorusrhacid family vary.  For example, Phorusrhacos longissimus, a phorusrhacid known from the Miocene, has been depicted with plumage like its living relative the Seriema, whilst other depictions give it a bristle-like integumentary covering reminiscent of an Emu or a Cassowary which are both ratites.

For instance, the CollectA Deluxe Kelenken figure, gives this phorusrhacid a coat of bristle-like feathers on the neck and the body.  The feathers on this scale model resemble those of an Emu or a Cassowary.

The CollectA Deluxe Kelenken figure has an integumentary covering on the neck and body which resembles the bristle-like feathers of a ratite such as a Cassowary. Picture credit: Everything Dinosaur.

Picture credit; Everything Dinosaur

To view the CollectA Deluxe range of figures in stock: CollectA Deluxe Prehistoric Animal Models.

The complexity of avian evolution is being revealed by a genetic analysis at the species level. Cariamiformes such as the “terror birds” Phorusrhacos and Kelenken are far removed from the ratites. Members of the Phorusrhacidae may not have had bristle-like feathers as found on Emus and their relatives but plumage reminiscent of more closely related birds such as falcons and parrots.  Perhaps model makers will utilise some of the findings from this extensive research programme in their prehistoric bird figures.

Convergent Evolution

Evolving into large flightless birds, descended from a common ancestor is a trait shared by both the ratites and the phorusrhacids.  However, this is not because these two types of bird are closely related.  It is more likely to represent an example of convergent evolution.  From a model making perspective, it is difficult to find extant animal references.  After all, nothing like the “terror birds” exists today (fortunately).

Visit the Everything Dinosaur website: Prehistoric Animal Figures.

Over the weekend, we took advantage of the warm autumn weather to clean and tidy up the office pond.  To our surprise we discovered a single tadpole.  This September tadpole had not metamorphosed into a frog but had remained in its juvenile state.  We have seen this phenomenon before, and there could be several reasons for this particular tadpole not developing.  For example, it could have a genetic abnormality that prevents this tadpole from changing.  It could remain a tadpole for the remainder of its life.

A tadpole spotted in the office pond on a warm September day (2024).  It can be seen in the bottom left corner of the image. Picture credit: Everything Dinosaur,

Picture credit: Everything Dinosaur

A September Tadpole

The cool and wet weather in June could have prevented the tadpole from developing properly.  Tadpoles feed on algae, perhaps there was a shortage of food or too much competition and this tadpole, plus others we did not spot, have had their growth stunted.

We certainly had a lot of frogspawn in the office pond this year.  In total we counted thirteen batches of spawn.  The frogspawn is being laid earlier in the year.  For example, this year’s spawning started in the middle of February.

To read our blog post about the first frogspawn spotted this year: Frogspawn Spotted in the Office Pond (2024).

Whilst the vast majority of the tadpoles turn into frogs in a single year, some seem to take longer. This might be a strategy to ensure more of the progeny survive.  For example, the conditions in the summer might not be ideal for the survival of the froglets as they emerge from the water.  So, if some of the tadpoles remain in the pond until the following spring, the conditions might have improved thus permitting them a greater chance of survival.

At least one tadpole from the office pond is likely to overwinter. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

We have taken out some of the weed but left plenty of oxygenating plants.  We have tidied up the waterlilies too.

Waterlilies belong to the family Nymphaeaceae.  These plants have a fossil record dating back to the Cretaceous.

We shall keep checking on the tadpole and the other pond life over the autumn and winter months.

Visit the award-winning Everything Dinosaur website: Dinosaur Toys and Gifts.

One of the most enigmatic members of the Aves is the Phorusrhacos “terror bird”.  Phorusrhacos (P. longissimus) was scientifically described in 1887 by the Argentinian palaeontologist Florentino Ameghino. The genus name is pronounced four-rus-rak-cus.

Recently, Everything Dinosaur published an article summarising the results of the latest phase in the Bird 10,000 Genomes (B10K) project. This programme involves the most extensive and ambitious research into the genetics of the Aves. Phase two of the study revealed some fascinating insights into the phylogeny of our feathered friends.  For example, it was confirmed that owls are a sister lineage to the Accipitriformes.  Accipitriformes consist of most of the diurnal birds of prey.  Birds such as hawks, eagles, kites and buzzards.

Intriguingly, falcons although similar to other birds of prey, are not Accipitriformes.  Falcons are not closely related to other birds of prey. They are grouped into a clade that also contains the songbirds, parrots and the enigmatic Cariamiformes. The clade is known as the Australaves.  Giant, predatory flightless birds such as the Phorusrhacos “terror bird” are members of the Cariamiformes order.

This means that falcons are related to “Terror Birds”…

A close-up view of a Phorusrhacos terror bird. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

To read Everything Dinosaur’s article about the latest findings from the Bird 10,000 Genomes (B10K) Consortium: New Analysis Re-Writes Bird Evolution.

The Phorusrhacos “Terror Bird”

The holotype material (MLP 20-122) consists of an incomplete mandible. Ameghino mistakenly believed that these fossils represented a toothless mammal. The avian nature of Phorusrhacos was first proposed in 1891, based on a comparison with fossil remains of a related species Patagornis marshi which had just been described (Moreno and Mercerat).  These enigmatic creatures, with their huge skulls and powerful beaks have inspired numerous artists.  Both Charles R. Knight and Zdeněk Burian produced illustrations of Phorusrhacos.

Stunning “terror bird” artwork by Burian. A pair of Phorusrhacos squabble over a recent kill.

Picture credit: Zdeněk Burian

The phorusrhacids were the dominant terrestrial predators on the isolated continent of South America for millions of years. Some phorusrhacids dispersed into Central America and the southern United States during the Great American Biotic Interchange when North America became united with South America in the Pliocene.

Mike from Everything Dinosaur commented:

“These large, cursorial hunters were the apex predators in many Cenozoic ecosystems.  There is nothing like them alive today.  The only extant members of the Cariamiformes are the two species of Seriema, both of which are native to South America just like the giant Phorusrhacos longissimus.  It is perhaps because there is nothing like these creatures living today that Phorusrhacos evokes a fierce majesty of a lost world.”

The “terror birds” were the last apex theropod dinosaur predators.  With their passing, most of the top predatory niches in terrestrial food webs were the domain of the Mammalia.

The Everything Dinosaur website: Prehistoric Animal Models and Figures.

Visiting the Liverpool World Museum is always a delight. Amongst the exhibits there is a small section that highlights the evolution of tetrapods. There is a stunning coelacanth specimen on display. Coelacanths are sometimes referred to as “living fossils”. They are lobed-finned fishes (Sarcopterygii) in the class Actinistia. Their fossil record dates back to the Devonian. The last of their kind was thought to have become extinct at the end of the Cretaceous. That was, until December 1938, when a coelacanth was caught by a fisherman off the east coast of South Africa close to the Chalumna River estuary.

A stunning coelacanth specimen on display at Liverpool World Museum. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Significance of the Coelacanth Specimen

The coelacanth display is part of a larger exhibit that highlights the evolutionary transition of vertebrates onto the land. As these fish have fleshy, lobe-like fins it had been thought that the coelacanth might be the youngest diverging non-tetrapod sarcopterygian. However, the genome of this fish was sequenced in 2013, and it was discovered that lungfish are more closely related to tetrapods.

To read about the sequencing of the coelacanth genome: The Coelacanth Gets Its Genome Unravelled.

A scale drawing of a coelacanth (Latimeria). Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Liverpool World Museum is a great place to visit. If you go, please take a look at the coelacanth display. It is a wonderful way to connect with a group of creatures that have been around since the Devonian.

Several models of coelacanths have been produced.  For example, both the Mojo Fun and Safari Ltd ranges include coelacanth figures.

For prehistoric animal models visit the Everything Dinosaur website: Prehistoric Animal Models.

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.

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