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17/02/2022

11/01/2022

Starfish: rare fossil helps answer the mystery of how they evolved arms
A chance discovery of a beautifully preserved fossil in the desert landscape of Morocco has solved one of the great mysteries of biology and palaeontology: how starfish evolved their arms.

Starfish are one of the most recognisable animals on our planet. Most people probably associate them with trips to the beach, walking in rock pools or swimming in the sea. They might appear simple creatures, but the way these animals’ distinctive biology evolved was, until recently, unknown.

Our new study, published in the journal Biology Letters, sheds light on how the starfish developed its distinctive shape.

The mystery of starfish
Starfish, and their close relatives the brittle stars, belong to a group called the echinoderms. These are animals with spiny skins, including sea urchins, sea lilies and sea cucumbers, with bizarre biological traits. They have no head or a brain, and have a unique circulatory system called a water vascular system, which uses seawater instead of blood. They even possess the power to regenerate over 75% of their body mass if it is lost.

Starfish have almost always had the same five-armed body shape. This has not changed for almost 480 million years, throughout the five great mass extinctions they survived.

Other echinoderms use their arms to filter feed or catch food from the water and, unlike starfish, face upwards with their arms spreading outward to feed. But starfish do not, and their distinctive body shape appeared in the fossil record fully formed. So for years scientists have been perplexed by how it evolved and how starfish are related to their close relatives, the brittle stars.

The Pompeii of palaeontology
The Fezouata formations are sedimentary rock deposits in Morocco dating back to the early Ordovician period, a critical stage in the evolution of life, which ended around 460 million years ago. Palaeontologists think life rapidly diversified during this time, in an episode call the great Ordovician biodiversification event, when animals we might recognise today first appeared.

The Fezouata formations are a bit like the Pompeii of palaeontology. The conditions on the seabed meant even soft tissue, which would normally be destroyed over time, could be preserved. Because of this, the formations provide a window into what happened at a key moment in the history of life on Earth.

The Fezouata Formations.
The Pompeii of palaeontology. Aaron Hunter, Author provided
Although starfish might appear very robust animals, they are typically made up of lots of hard parts attached by ligaments and soft tissue which, upon death, quickly degrade. This means we rely on places like the Fezouata formations to provide snapshots of their evolution.

The starfish fossil record is patchy, especially at the critical time when many of these animal groups first appeared. Sorting out how each of the various types of ancient starfish relate to each other is like putting a puzzle together when many of the parts are missing.

The oldest starfish
Cantabrigiaster is the most primitive starfish-like animal to be discovered in the fossil record. It was discovered in 2003, but it has taken over 17 years to work out its true significance.

What makes Cantabrigiaster unique is that it lacks almost all the characteristics we find in brittle stars and starfish.

Starfish and brittle stars belong to the family Asterozoa. Their ancestors, the Somasteroids were especially fragile - before Cantabrigiaster we only had a handful of specimens. The celebrated Moroccan palaeontologist Mohamed Ben Moula and his local team was instrumental in discovering these amazing fossils near the town of Zagora, in Morocco.

The breakthrough
Our breakthrough moment came when I compared the arms of Cantabrigiaster with those of modern sea lilles, filter feeders with long feathery arms that tend to be attached to the sea floor by a stem or stalk.

The striking similarity between these modern filter feeders and the ancient starfish led our team from the University of Cambridge and Harvard University to create a new analysis. We applied a biological model to the features of all the current early Asterozoa fossils in existence, along with a sample of their closest relatives.

A photo of two Cantabrigiaster fossils.
Cantabrigiaster is the most primitive starfish-like animal to be discovered in the fossil record. Aaron Hunter, Author provided
Our results demonstrate Cantabrigiaster is the most primitive of all the Asterozoa, and most likely evolved from ancient animals called crinoids that lived 250 million years before dinosaurs. The five arms of starfish are a relic left over from these ancestors. In the case of Cantabrigiaster, and its starfish descendants, it evolved by flipping upside-down so its arms are face down on the sediment to feed.

Although we sampled a relatively small numbers of those ancestors, one of the unexpected outcomes was it provided an idea of how they could be related to each other. Palaeontologists studying echinoderms are often lost in detail as all the different groups are so radically different from each other, so it is hard to tell which evolved first.

11/01/2022

Conservation hope: Many wildlife species can recover if given a chance
There is real and justified concern about the state of our world’s ecosystems. Satellite imagery reveals few places left untouched by humanity. As the global human population and our overall consumption continue to grow in concert with the upheaval of our climate systems, the outlook for non-human species seems grim.

In response, scientists have tried to measure the state of global biodiversity. One of the biggest impact efforts has been the Living Planet Index (LPI), an ambitious project that compiles population trends for more than 4,000 vertebrate species around the world.

According to the LPI, the average population has declined by more than 50 per cent since 1970. The most common and intuitive interpretation of this is that the average animal population is less than half the size it was 50 years ago — and so it has been widely reported in the media. A number of other global studies concur that the situation is dire.

So it may come as some surprise that a growing number of influential studies, at both the continental and global scales, find that there is no average change to the local abundance of animal species. This has fuelled a heated debate about how to reconcile contrasting claims of the magnitude of the threat to biodiversity.

The answer to this debate is important for our understanding of how humans are reshaping the world’s biodiversity. Several of us wondered whether the conflicting results were because of methodology. In our investigation, we focused on the LPI, which calculates the aggregated change for all wildlife populations that have data in a given year based on the mean of the population trends. Unfortunately, means are notoriously sensitive to extreme data points. Importantly, some populations have been monitored many times since the 1970s, but many have only been surveyed two or three times.

Measurement matters
And indeed, methods do matter, a lot. When one removes the most extreme 354 collapsing populations from the near 14,700 populations analyzed (so, dropping a measly 2.4 per cent), an average 56 per cent decline since 1970 changed to about a zero per cent decline.

There is a small set of populations that seem to be doing extraordinarily badly. For the rest of the vertebrate populations in the database, roughly half are increasing, often from past lows, like humpback whales in the North Pacific. Half are decreasing, even from past lows, like right whales in the North Atlantic.

The more-than-50-per-cent global decline statistic widely reported in the media is driven by very few, but very extreme, populations.

Importantly, the extreme trends driving the mean tended to be those with less data. And this may go some way to resolving the debate: several of the influential papers reporting less extreme overall changes intentionally left out populations with few observations, because they were felt to be unreliable.

An underwater photograph of a humpback whale
A humpback whale calf. Humpback whale populations are increasing in the North Pacific. (Shutterstock)
A detailed global picture
Of course, trying to summarize the state of the world’s vertebrate biodiversity with a single number entirely masks the complicated picture of how different species and regions are faring. Entire groups of related species are in significant decline in some broad regions, such as land birds in the Indo-Pacific. Other groups may be improving, such as land birds in Asia and Europe. In total, 17 per cent of the species groups examined could be undergoing broad declines.

And even in regions that are demonstrably improving on average, a sizeable fraction of populations are still in decline. Entire groups of species indeed have poor prospects in an era of human ecological dominance, but others seem to be stabilizing or recovering from historic lows.

Unfortunately, it’s still hard to predict which species will thrive and which won’t. Though our data sets are better than ever, even wealthy countries often only have good data for a limited set of species. Tellingly, most of those extreme, data-poor time trends that had outsized influence on the LPI came from poorly studied, biodiverse regions like the tropics.

The sad reality is that we don’t fully know how the Earth’s biological diversity is faring, because we have not invested enough in understanding this question.

Accuracy and prevention
And so, precaution is prudent. Logically, most species on Earth will not fare well when their habitat is destroyed, filled with ecologically novel predators and pathogens or over-harvested, but our results suggest to us that many can recover if given a chance.

Many species are happy to live cheek-to-jowl with us: think of the many birds that may visit your backyard feeder or the opportunistic mammals that can thrive in urban environments like skunks, raccoons and coyotes. The apparent balance in population trends suggests that we need to better identify where species are managing to thrive alongside humans, and why, so that we can direct our resources to replicate this success everywhere.

11/01/2022

Southern African hunters may have used symbolism in choosing bones to craft arrows
Animals have long played an important symbolic role in human societies. They feature prominently in myths and folklore throughout the world. In some cases animals are used metaphorically: they express clan identity and are used to illustrate concepts of leadership, healing and protection.

In a newly published study, scholars in South Africa and the United Kingdom – myself among them – have discovered a possible link between the animal bones people used to make tools, like arrowheads, and the symbolic importance that people attached to those animals in the past.

The study focused on what is today the Tugela River catchment area of South Africa’s KwaZulu-Natal province. Here, about 1,200 years ago, immigrant Nguni farmers came into contact with Bushman hunter-gatherers. Ethno-historical records show that animals played an important role in both cultural groups as symbols and metaphors to express ideas. Early interactions between these two groups, as happened in our study area, resulted in the dynamic exchange and assimilation of ideas and symbols.

We wanted to know whether the symbolic importance of certain animals translated into the technological domain at this time and place. That is, whether people were selecting the bones of specific animals and not others to use as raw material for their tools. And, if so, we wanted to know which animals they were selecting.

In several other parts of the world, such as Canada and Russia, people used the bones of animals that were important within their respective cultures to make tools. Nothing like this has been documented in southern Africa and we wanted to find out whether this was because this practice was not followed in the region or whether it was simply undocumented.

To find out, we used a method known as ZooMS. This analyses the collagen proteins found in animal bones. Collagen proteins are unique to different groups of animals. So, we could “fingerprint” samples from modern animals and then recognise them in archaeological samples of unknown origin.

The study found that there was selective targeting of animals for tool manufacture at some sites, with a narrowing of the range of selected species after about AD 1,000. Certain groups of antelopes appear to have been deliberately avoided. This suggests bones weren’t used just because they happened to be available. We hypothesise that distinctive animal behaviours, such as that of the rhebok, were appropriated by people to serve as metaphors through which to understand human society. And we believe this symbolism was expressed through people’s tools as a means of harnessing the “power” of the animal.

Animal symbolism
The Bushmen (or San) believed that animals such as the eland, rhebok and hartebeest possessed supernatural powers. These could be harnessed by shamans during certain ceremonies to bring about rain or influence the movement of game. In some cases, items of clothing made from these animals would be worn during healing and rain-making ceremonies.

Animals were also frequently depicted in San rock art. A clear emphasis was placed on those species believed to be particularly powerful, such as eland, rhebok and roan.

Among the Nguni, spirits of the ancestors were commonly ascribed the behavioural traits of certain wild animals, among them elephants, rhinoceros, lions and baboons.

Forty-three species are known to have been divinatory animals among the Nguni: some of these species’ bones regularly formed part of diviners’ kits because they were believed to confer those animals’ “powers” to the diviners.

The archaeology of KwaZulu-Natal
The Tugela River catchment area was first occupied by hunter-gatherers from about 7,000 years ago. Once farming communities began settling the area in the fifth century AD, hunter-gatherers started moving out of the mountainous areas to live nearer the farmer settlements. There, they benefited from trade in pottery and agricultural produce in exchange for wild animal skins and services rendered.

When farmers and hunter-gatherers came into contact, they adopted parts of each other’s material culture as well certain words and concepts linked to divinatory animals. The Nguni regarded the Bushmen as spiritual mediators, able to intercede with the supernatural world to bring about rain and other boons.

Even the caves the Bushmen occupied were seen by the Nguni as places of power. On the other hand, the new domestic animals introduced by the Nguni farmers were quickly assimilated into hunter-gatherer cosmology. They replaced eland and other antelopes as a favoured rock art motif.

Technology for answers

Using technology to analyse which animals’ bones were used in hunting tools, the researchers were able to draw several conclusions. Dr Justin Bradfield
We extracted small amounts of collagen from 84 bone arrowheads excavated from 11 archaeological sites spanning a 6,000-year period in the Tugela River catchment region. We then identified the taxonomic tribe of animal represented in the bone arrowheads.

Antelope species belonging to the Alcelaphini tribe (including hartebeest, wildebeest and bontebok) were the most abundantly represented source of bone arrowheads. Certain species of antelopes, including impala, gazelle, springbok and duiker, were not represented in any of the bone arrowheads. This is despite the fact that these species are abundantly represented in the unmodified food waste at the sites: they account for 66% of the meat consumed.

We also found that at some sites bone points were made from animals – including giraffe and buffalo – that were not represented at all in the unmodified fauna food waste.

This suggests deliberate targeting and avoidance of certain species. We think those animals that were deliberately targeted to make tools represent animals that people considered culturally or symbolically important. Our findings also suggest that the range of species targeted by hunter-gatherers to make their tools narrowed after farmers moved into the area.

We ruled out mechanical properties (that the bones used for tool manufacture were mechanically the best suited to their role as arrowheads) and trade as the reasons for the pattern of raw material selection we identified.

Symbolic significance emerged as the most likely reason for certain animal bones being used in tools to the exclusion of other, readily available animals. For instance rhebok, hartebeest and eland were all well represented in our sample; each is a symbolically important animal in 19th century Bushman folklore. These animals were associated with rain, and the power to influence game during a hunt. So, it’s possible their bones would be used in hunting tools, to imbue the tools with powers to aid in the hunt.

Future research will aim to test our hypothesis by analysing larger numbers of bone tools from the region.

11/01/2022

11/01/2022