Category: paleobiology

New findings about the Denisovans

July 5, 2024 • 11:45 am

We’ve known about the Denisovans for about 15 years, since part of a finger was found in a Russian cave (the “Denisova Cave“) in 2008 and wasw published two years later.  They were a hominin subspecies like Neanderthals. I consider these groups subspecies of H.sapiens because they both interbred with H. sapiens and left fertile offspring. Denisovans lived in Asia from about 300,000 to 25,000 years ago. (They may also have bred with Neanderthals.)  They are considered a sister taxon to Neanderthals, which means that these two groups shared a common ancestor that had already branched off from the ancestor of “modern” H. sapiens.

Wikipedia gives a useful table of all the known remains of Denisovans, which are judged as a distinct group from DNA sequencing. We have small bits of bone, including teeth, parietal bones, mandibles, and limb bones (and now, according to the Nature article below, a rib bone) from the three locations—all caves—shown below from the Wikipedia map shown below:

And here’s a picture of the Denisova Cave in Russia where it all started:

Xenochka, CC BY-SA 4.0, via Wikimedia Commons

Here’s a diagram of the route the Denisovans took as they colonized Siberia and SE Asia from the Middle East, as well as a “family tree” on the right showing the sister-group relationship of Neanderthals and Denisovans (the figure presumes that the common ancestor of the two was a different species, Homo heidelbergensis, which, confusingly. has been considered a subspecies of H. erectus or even H. sapiens.

John D. Croft at English Wikipedia, CC BY-SA 3.0, via Wikimedia Commons

Just as many Westerners have some Neanderthal DNA (I have a bit among my Ashkenazi genes), so some Asians and people from Oceania have Denisovan DNA.  This shows the hybridization I talked about above. And if two groups meet, mate, and produce fertile hybrids, they’re considered by evolutionary biologists to be subspecies, not species. Unless, that is, they’re hominins, for paleobiologists love to split names and create new species, a practice that produces more excitement and fame than simply saying “we found a new subspecies of Homo sapiens.”

Well, we’ve known about the Denisovans for a while, so what’s new? This news report from Nature (click to read) gives us a bit more information, like what kind of food they ate, as well as reporting on a new Denisovan rib bone found this year.

The results aren’t that thrilling to me, but many people thrive on human paleobiology, and so here are some extracts from the news:

When life got tough, the Denisovans got tougher. The enigmatic ancient humans hunted birds, rodents, even hyenas, helping them to thrive high on the Tibetan plateau for well over 100,000 years.

Those conclusions emerge from a study of thousands of mostly tiny animal bones that provide an insight into life at Baishiya Karst Cave in China1 — only the second archaeological site known to host Denisovans, after the Siberian cave that gave the group its name. Denisovans are a sister group to Neanderthals, and might have once lived across Asia.

Many of the cave remains could be identified only by their protein signatures. This included a rib bone that represents a new Denisovan individual, one of just a handful known.

“Denisovans are dealing with the full suite of animals they’re surrounded with in order to survive in this quite harsh landscape,” says Frido Welker, an archaeological scientist at the University of Copenhagen who co-led the study, published in Nature on 3 July. “It’s at high altitude. It’s cold. It’s not a nice place to be as a hominin.”

The article they’re discussing, a new one also in Nature, is below: click on the screenshot to read it:

And here’s the paper’s abstract, which discusses not only the discovery of a new rib bone from the cave in Tibet, but also some scratches on associated animal bones, indicating that they’d been processed for food, presumably by Denisovans:

Using zooarchaeology by mass spectrometry, we identify a new hominin rib specimen that dates to approximately 48–32 thousand years ago (layer 3). Shotgun proteomic analysis taxonomically assigns this specimen to the Denisovan lineage, extending their presence at Baishiya Karst Cave well into the Late Pleistocene. Throughout the stratigraphic sequence, the faunal assemblage is dominated by Caprinae, together with megaherbivores, carnivores, small mammals and birds. The high proportion of anthropogenic modifications on the bone surfaces suggests that Denisovans were the primary agent of faunal accumulation. The chaîne opératoire of carcass processing indicates that animal taxa were exploited for their meat, marrow and hides, while bone was also used as raw material for the production of tools. Our results shed light on the behaviour of Denisovans and their adaptations to the diverse and fluctuating environments of the late Middle and Late Pleistocene of eastern Eurasia.

Here, from the paper, is a human-cut bird wing bone showing the scratches, probably made when feathers were removed. This happens to be a golden eagle. How did they catch it?

(from the paper): Aquila chrysaetos right humerus (layer 4) with superficial and straight cut mark clusters, associated with the removal of feathers

And here from the paper is a photo of the rib bone from a Denisovan also found in the Tibetan cave, along with a phylogeny showing that the rib is closely related to a Denisovan mandible found in the same cave.  It’s not really earth-shaking that a Denisovan rib would be genetically similar to a Denisovan mandible found in a different level of the same cave, but it does add to the specimens we have. Note as well that Denisovans and Neanderthals are, again, placed by DNA analysis as sister groups: each other’s closest relatives.

(From paper): a, Photograph of the Xiahe 2 specimen. Scale bar, 1 cm. b, Phylogenetic tree for the Xiahe 2 specimen and reference proteomes. Support values at nodes are shown for the maximum likelihood and Bayesian analysis, respectively.

A summary from the News & Views piece of how scientists decided which species the animal bones came from (they used protein sequences from collagen rather than DNA to do this), and which animals they ate:

Proper excavations of the cave revealed more signs of occupation: dirt from the site dating to between 100,000 and 45,000 years ago contained DNA sequences from maternally inherited cell structures called mitochondria, matching those of the Denisova Cave remains. The dig, led by archaeologist Dongju Zhang at Lanzhou University in China, also uncovered thousands of mostly fragmentary animal bones.

To identify more than 2,000 of these remains, Zhang, Welker and their colleagues chemically analysed collagen protein signatures, which vary between animals. Especially common were caprines (the subfamily that includes goat and sheep) as well as wild yak, horses and gazelle. Carnivores, including wolves and foxes, also turned up in the mix.

Many of the bones from the cave, including those of hyena, caprines and golden eagles (Aquila chrysaetos), contained cut-marks and other signs of human predation. Even rodents and hare were probably hunted: a marmot (Marmota) leg bone was split open, potentially to harvest its marrow. Such small, speedy animals wouldn’t have been easy to catch, says Zhang, and bringing down carnivores such as hyenas would have taken moxie.

And here’s the Tibetan cave, Baishiya Karst Cave.  It’s no wonder they call these hominins “cavemen”. Where else could you get shelter from the rain and wind and a place to process your catch? And cook it, too, for there’s evidence that both the Denisovans and the Neanderthals could probably make fires.

What more do we know now? Well, we know what the Denisovans ate, which is really no surprise. Callaway tries to give his piece more oomph by saying that we now know the Denisovans’ “survival secrets”, but of course they had to eat something. But knowing what they ate is better than nothing. And we also have more bones, though as yet they haven’t yielded much new information. There’s more to come as excavations proceed, but the N&V ends rather lamely:

. . . . scientists’ picture of Denisovans is becoming less opaque thanks to information gleaned from dirt and shards of bone subjected to cutting-edge DNA and protein analysis, says Brown. “Denisovans are essentially, at the moment, a biomolecular population.”

The remains Zhang and her colleagues analysed are from pre-pandemic excavations of Baishiya Karst Cave. But the researchers are now back excavating the enormous cavern, hoping to find more insights into Denisovan life. “We haven’t reached the bottom,” says Zhang.

Perhaps I’ve gotten jaded, for the discovery of a new subspecies of humans in Eastern Asia, one that probably went extinct like the Neanderthals, truly is a surprise.

Fossilized behavior: termites trapped in tandem

April 9, 2024 • 10:00 am

Here’s a rare example of animal behavior being fossilized. In this case it’s in termites, whose modern representatives engage, as pairs, in a behavior called “tandem running”. This occurs after a group of reproductive termites  who have left their natal nest fly away, a behavior certainly evolved as a way of staring new colonies.  Unlike other social insects like bees, a termite colony contains both reproductive males and females, both of which have wings, eyes, and the capacity to mate and start new colonies (other workers lack wings and eyes). At mating time, a swarm of reproductive individuals fly away at random (they’re not good fliers), and then alight on the ground or, in the case at hand, on a tree trunk.  After dropping their wings, they form mating pairs, each of which can start a new colony. To find that colony, a male and a female engage in “tandem running,” with (in the species below) the female running around with the male close behind, his head contacting her abdomen. Apparently some species can have either a male or a female as the leader in the tandem run. I can’t find out whether mating occurs before the tandem run or after the pair burrow into the ground to found their new colony.

When the female finds a site she likes, the pair digs in (most termites nest underground), and, after mating, the female becomes the “queen”, and the male the “king”.  They remain monogamous, with the male continuing to fertilize the female throughout the life of the colony. This implies that all the termites in a colony are brothers and sisters. Since “kings” and “queens” can live for decades (25-50 years, according to one site, the colony can last a long time sending out reproductives to found new colonies.

At any rate, below you can see two examples of tandem running in reproductive alates (winged termites that have lost their wings). This is the behavior that appears to have been “fossilized”.

The YouTube notes:

When male and female termite alates (flying termites) pair up, they break off their wings and the male starts following the female around until she finds a suitable spot to start a new nest. This activity is called termite tandem running.

And so to the new paper in Proc. Nat. Acad. Sci. USA, which you can read by clicking on the title below or reading the pdf here.

The authors had a piece of 38-million-year-old Baltic amber, which is fossilized plant resin. (Baltic amber containing animal or plant inclusions like this can sell for a lot of money.) When resin or sap falls to the ground, it can, over long periods, be converted to amber by pressure and temperature of the sediments above. Eventually it becomes quite hard and can be mined.

In one pice of amber, the authors found two termites that looked as if they might have been tandem running when they got stuck in the sap and then preserved. Here’s a photo of their specimen, which is of the extinct species Electrotermis affinis.  The caption to the partial figure below is “E. affinis pair in Baltic amber. (A and B) The dorsal and ventral sides of the tandem, respectively, with (B) an arrow pointing to the 15-articles antenna of the tandem leader.”  The scale bars represent 0.5 mm.

This certainly looks like a tandem pair, but the problem is that they are not straight head-to-abdomen, but twisted a bit, so they are more side to side.  Because it’s hard to get a good look at specimens in amber, and you can’t cut the amber open (that destroys the specimen), the authors used  X-ray microtomography (a 3-D reconstruction using X rays) to show that the male is the one on the right in (A) and left in the ventral view (B); he’s smaller and the sexes can be told apart by the shape of the seventh “sternite”, or abdominal plate. They also saw that the female’s mouthparts were in contact with the tip of the male’s abdomen, which is what happens in tandem running.  So we have a male and female in the right contact position, buttressing the idea that this is a tandem pair.

The authors then hypothesized that this was indeed a pair that was doing tandem running (probably on a tree) when they got stuck in sap, and the side-by-side position resulted from the pair trying to get unstuck.  They failed, and eventually became part of a piece of amber.

To test this “position change” hypothesis, they put tandem-running termites of a living species, Coptotermes formosanus, in a sticky trap, a flat piece of cardboard covered with a sticky substance (I used them in the lab to catch cockroaches). This mimics a pair getting stuck in resin, and, as in resin, the pair could move around a bit after they got stuck.  Would the tandem runners move more side by side?

Indeed they did. The stickiness led to the tandem pair shifting their positions as they tried to free themselves. In fact, they assumed a more side by side position once stuck. (I have to say that I find this experiment disturbing, as it involves killing insects for the sake of science. However, I killed cockroaches to keep my lab free of organisms other than fruit flies.)

Here’s what they found in 17 termites that didn’t escape the trap:

The spatial orientation of the leader and the follower after entrapment was significantly different than in natural tandem runs. The distance between the body centroids of the leader and the follower was smaller in trapped pairs than in natural tandems (Fig. 2 D–G and SI Appendix, Fig. S2, Exact Wilcoxon rank sum test, W = 599, P < 0.001). This is because partners of trapped pairs were often positioned side-by-side, differing from the linear positioning of natural tandems (Fig. 2 D–G). The shorter inter-individual distance could result from the two individuals entering the sticky surface together and becoming stuck near each other without the ability to move away, rather than their active behavioral interactions to maintain proximity.

And a picture of a living tandem pair (female in front) that wound up stuck more side by side, like the fossilized ones above:

(From paper): The relative position of females and males forming mating pairs. (A–C) Mating pairs of the termite C. formosanus in (A) a natural tandem run and (B and C) on a sticky surface. Females are marked in red and males in blue. The convoluted lines indicate the trajectories of a female and a male during 30 min after the pair entered the sticky trap.

They also concluded, from a complicated logistic regression, that the probability was 74% that the following individual was a female.

Finally, here’s a reconstruction in the paper of the original event that led to the fossil. Note that the “fossilized behavior” term is a bit incorrect, as what gets fossilized is not their normal behavior, but what seems to be the behavior of a tandemly running pair that’s gotten stuck.  But given that there are individuals of both sexes in this pair, and that the antennae contact the abdomen, combined with what’s seen in the “resin mimicking” experiment, it’s seems likely that the authors are correct.

(from paper) Artistic reconstruction of E. affinis tandem pairs running freely on a tree bark and one tandem trapped by tree-resin.

What about other examples of fossilized behavior? I want to put in a paragraph about this from the paper, just for your delectation:

Some fossils preserve the “frozen” behavior of animals in actions at the moment of death (9, 10). However, our results demonstrate that animals on the sticky trap are not instantaneously immobilized and change their postures on the surface. These experiments imply that the spatial orientation of animals preserved in sticky matrices, such as in tree resin prior to fossilization into amber, is influenced by the process of entrapment. Therefore, the interpretation of fossilized behavior can be dramatically refined or even corrected by observing the behavior of living organisms under entrapment conditions. Some behaviors fossilized in amber may remain unaltered by the entrapment process. For example, the preservation of mating moths in copula (14) or hell ants grasping prey items (12) suggests that the inter-individual interactions of these behaviors are strong enough not to be disturbed by the movement on the sticky surface. However, entrapment in amber likely affects many other behaviors. For example, insects dispersing through phoresy [attachment to other insects as a way of moving around] can be preserved detached from the host insect, perhaps because the host struggled on the sticky surface before complete encasement (37). The consequence of different behavioral responses can be studied using extant relatives. Furthermore, animals have evolved behavioral responses to sticky objects. For example, recent studies have revealed that ants are not passively affected by sticky objects but actively modify them. Red imported fire ants cover sticky surfaces with soil particles to access food resources (38), and granivorous desert ants remove sticky spider webs from nestmates to rescue them (39). Scavenging insects can be attracted by large animals trapped on a sticky surface (11, 35), and the spatial distribution of these insects may have reflected their foraging behavior. Thus, future studies on behavioral responses to sticky objects by animals will increase our understanding of fossil records in amber, as well as shed light on the behavioral capacity of extant insects.

I found it really interesting that ants can get around the danger of sticky substrates by covering them with soil, and can even remove spider web stuck to other ants. Ants have brains about the size of a grain of sand, but this behavior is somehow coded in there (or else they learn to do this, which seems less likely).

********

Reference: K. Mizumoto et al, 2024.  Extinct and extant termites reveal the fidelity of behavior fossilization in amber.  Proc. Nat. Acad. Sci. USA. https://www.pnas.org/doi/10.1073/pnas.2308922121

 

Gene flow from Neanderthals and Denisovans to “modern” humans, and vice versa

February 26, 2024 • 10:45 am

Today I’ll try to summarize another paper that is difficult for one reason: figuring out how the authors (including Nobel laureate Svante Pääbo) sussed out which genes originated in Neanderthals and Denisovans (both lineages now extinct) and which in their sister lineage: the separate lineage leading to modern humans.  (All three lineages shared a common ancestor.) As we know, the modern human genome contains a lower percentage of genes that originated in Neanderthals, and this is also true for genes that originated in Denisovans (the latter are found more often in modern populations from Oceania, Asia, and in native North Americans).

As for the two extinct lineages, both derived from a single ancestor that, according to the paper below, left Africa for Eurasia about 600,000 years ago. That traveling lineage then split at an uncertain time to give rise to the Neanderthals, who went extinct about 35,000 years ago, and to the Denisovans (known from but a handful of teeth and bones), who went extinct around the same time as did Neanderthals. In the meantime, the lineage that gave rise to us—”modern” humans—stayed in East Africa, leaving for  Eurasia about 60,000 years ago, and some individuals in this group lived near the already-present Neanderthals and Denisovans.

Although human paleobiologists, who love to identify new species, call the Denisovans and Neanderthals species different from modern humans (i.e, different from “Homo sapiens“), I’m stubborn and consider all three groups members of the same biological species. That’s because there’s evidence of gene flow among all the groups: from Neanderthals and Denisovans to modern humans, from modern humans to Neanderthals, and even from Denisovans to Neanderthals and vice versa. Because these archaic genes persist in modern humans, the hybrids between the lineages must have been fertile to allow such backcrossing. Since we have populations who lived at least partly in the same area and produced fertile hybrids, they can be considered biological species, though perhaps biological species in statu nascendi.

Here’s a diagram of the three lineages from the paper whose title is below. The arrows show the direction of gene exchange and some examples of variants transferred by hybridization.

(from paper): Figure 1. Schematic illustration of the history of archaic and modern humans and DNA sequence evolution Derived mutations are highlighted. The occurrence of gene flow between groups is illustrated by arrows. The archaic groups contributed both derived and ancestral variants to modern humans. Note that the extent, number of gene flow events, and when they occurred are only partially known.

You can read the paper below by clicking on the title. The object of the paper is to answer this question:

Which genes were transferred between the lineages, and what effect did they have on the individuals who carried them?

Now, of course, the first question is “How do we know which genes actually originated in one of the three lineages after it split off from the others, and how do we know in which direction that gene was transferred to another lineage.”  This is not an easy question, and I asked my friend Phil Ward, an entomologist and systematist who works at UC Davis. I’ve put his explanation below the fold in case you want to know.

I trust the authors’ determinations of which genes originated where, and which ones were introduced into a given lineage by hybridization; after all, this is Pääbo and his group!  So I’ll just give a list of a few of genes transferred, which way they went, and what they appear to do in modern populations. Let me add two things. First, while it’s easy to find out what a gene does (it can be tested in cell culture or by inserting it in mice), it’s not so easy to determine what effect it has on the phenotype or reproduction of modern humans.

Second, the paper is quite “adaptationist”, with the authors suggesting reasons why a transfer might have been adaptive. (If it was really bad for the carrier, it would have disappeared from the population.) However, very few of the transferred genes are present in very high frequency in modern humans or Neanderthals, and so, if they had a really beneficial effect on reproduction or survival, one would expect that they would be “fixed” (present in every individual) or at least high frequency.  Since that’s not usually the case, the authors float hypotheses that transferred genes are good in some populations but not others. This seems to some extent like post facto rationalization based on a diehard adaptive viewpoint.

On to the genes! Indented sections are mine except for doubly-indented sections, which are excerpts from the paper:

Mutations in the Neanderthal lineage that got in modern humans via hybridization. 

Genes affecting fatty acid and lipid metabolism.  These genes appear to increase the risk of type 2 diabetes, so they’re not good for us.

Genes increasing sensitivity to pain (a sodium-channel gene in the nervous system). This gene appears to have a salubrious effect, because it’s associated with an increase in lifespan (genes that decrease pain sensitivity can allow you to suffer injuries and infections without noticing them, which is why sufferers from Hansen’s disease, lacking pain sensitivity, lose digits and other body parts). But if the gene is so good for us, why is it present in so few of us (0.4% of people in the UK)?

Genes affecting gestation. We received a progesterone receptor-variant that mutated in Neanderthals and that actually increases the frequency of premature births.  Here’s how the authors explain its persistence at high frequencies in both Neanderthals and modern human populations (some of the latter have a frequency of the gene of 20% or higher):

Since [this variant] is associated with an increased risk of premature births in present-day humans, it has been suggested to represent an evolutionary disadvantage to Neandertals, especially in the absence of modern medical care.  However, the Neandertal variants are also associated with an approximately 15% decreased risk for bleeding and miscarriages early in pregnancy as well as with having more siblings.  It is therefore tempting to speculate that it represents an evolutionary trade-off where the Neandertal variants rescues pregnancies that would otherwise have resulted in miscarriages, but the price paid is that some of these pregnancies result in premature births. Notably, two different versions of the Neandertal progesterone receptor gene have been contributed to modern humans, and both have risen in frequency, as shown by an increase in their occurrence in skeletal remains of individuals over the past 10,000 years.  Both Neandertal versions result in higher expression of the progesterone receptor and may thus mediate a higher progesterone effect during pregnancies. This is compatible with the finding that progesterone administration lowers miscarriage rates in women who previously experienced miscarriages  and suggests that increased progesterone effects mediated either by higher hormone levels or by higher receptor levels may protect at-risk pregnancies.

It’s okay to speculate, but perhaps there are other effects of the gene that we don’t know about, and are the bad effects of premature births overcome by the beneficial effects on bleeding and reduced early miscarriage? What we have here is a reflection of the author’s view that the transferred genes must in general have a net positive effect on reproduction, even if they can’t demonstrate it.

Genes affecting the immune system. Many of the genes we got from Neanderthals appear to interact with viruses and are at high frequencies in humans; the authors thus speculate that they spread to ward off infections and still do so in modern populations.  Also, some of the variants have big differences in frequency between populations, which the authors attribute to population-specific infections. Further, some of the variants may cause autoimmune disease (again, we know little about their effects on modern humans, which may be small.)  But they speculate that the existence of so many Neanderthal variants in modern humans strongly suggest that they spread in our lineage via selection for disease resistance.

Mutations in the Denisovan lineage that got in modern humans via hybridization. 

Genes affecting adaptation to high altitude. Here, taken from the paper, is the best example of a gene entering the modern human genome that is likely to have spread by natural selection. This example is pretty well known.

High altitude adaptation

One striking example of Denisovan influence on present-day populations is a 33-kb Denisovan DNA segment on chromosome 2 that occurs at an allele frequency of over 80% among Tibetans, while being absent or very rare in other Asian populations. It encodes EPAS1, a transcription factor induced by hypoxia that is involved in adaptation to low oxygen levels. Denisovans were present on the Tibetan high plateau; some of them may thus have been adapted to life at high altitudes and presumably contributed this genetic predisposition to modern humans as they arrived in the region.

We also received genes involved in producing adaptation to low temperature by “inducing brown fat”: these too seem to have spread in cold-climate populations by natural selection:

Cold adaptation and facial morphology:

Another example of a Denisovan genetic contribution is a 28-kb segment on chromosome 1, carrying the genes WARS and TBX15. It is present in almost 100% of Greenlandic Inuit and several other populations. The Denisovan variants affect the expression of genes that may influence adaptation to low temperatures, possibly by inducing brown fat.

At the end, the authors discuss genes that emerged in modern humans and found their way into Neanderthal lineages, including variants affecting purine (nucleotide) biosynthesis, preventing oxidative stress, gene splicing, and chromosome segregation.  The authors then present a “combinatorial view” of the modern human genome, noting that we’re likely to contain a variety of variants coming from our now-extinct ancestors, but different modern individuals have different combinations. Here’s that view from the paper’s abstract:

We propose that the genetic basis of what constitutes a modern human is best thought of as a combination of genetic features, where perhaps none of them is present in each and every present-day individual.

_________

Reference: Zeberg H, Jakobsson M, Pääbo S. The genetic changes that shaped Neandertals, Denisovans, and modern humans. Cell. 2024 Feb 14:S0092-8674(23)01403-4. doi: 10.1016/j.cell.2023.12.029. Epub ahead of print. PMID: 38367615.

Click “read more” to see the method for determining where a mutation originated and which way it was transferred:

Continue reading “Gene flow from Neanderthals and Denisovans to “modern” humans, and vice versa” →

Now the Pecksniffs want to change dinosaur names

February 22, 2024 • 10:30 am

Yes, it was inevitable. Now that birds and other animals are undergoing woke scrutiny to see which names are problematic (though scientific names cannot be changed), the Pecksniffs have begun to examine the names of dinosaurs, too. And according to this article from Nature (which contains a blatant misspelling), they have found some “bad” names, though not many. Click to read.

First, remember that the International Commission on Zoological Nomenclature has decreed that, for purposes of scientific communication, the Latin binomial names of animals (e.g., Anas platyrhynchos—the mallard) cannot be changed, though “mallard” could be changed. (The equivalent plant group hasn’t yet weighed in.) Thus what has been at issue is “problematic” common names, seen as being non-inclusive and fostering bigotry and racism (example Wallace’s owlet, named after the supposed miscreant Alfred Russel Wallace). See all my posts on this fracas here).

The problem with dinosaur names is that the common name and the scientific name are often similar, like Stegosaurus, a genus containing three recognized extinct species of dinosaurs. That one isn’t named after a person (the Latin name, based on its dorsal plates, means “roof lizard”), so it’s not problematic. But if it were, I suppose the woke could cancel the common name and call it something other than Stegosaurus.

In fact, dinosaur names can be problematic for reasons other than the person after whom they’re named (eponyms).  And, sure enough, the Perpetually Offended are trawling through dinosaur names to find the bad ones. Nature carries the article, even though this effort hasn’t been published in the scientific literature.  Below (indented) are some excerpts of this risible endeavor. Note the common error, due to ignorance, that I’ve put in bold. Of course you know that it’s “free rein”, referring to letting go of a horse’s reins. It has nothing to do with kings and the like.

It’s been 200 years since scientists named the first dinosaur: Megalosaurus. In the centuries since, hundreds of other dinosaur species have been discovered and catalogued — their names inspired by everything from their physical characteristics to the scientists who first described them. Now, some researchers are calling for the introduction of a more robust system, which they say would ensure species names are more inclusive and representative of where and how fossils are discovered.

Unlike in other scientific disciplines — such as chemistry, in which strict rules govern a molecule’s name — zoologists have a relatively free reign over the naming of new species. Usually, the scientist or group that first publishes work about an organism gets to pick its name, with few restrictions. There is a set of guidelines for species naming overseen by the International Commission on Zoological Nomenclature (ICZN). These include the requirements that the name is unique, that it is announced in a publication and that, for dinosaurs, it is linked to a single specimen.

Screenshot proof before the journal wises up:

But I digress, simply because this kind of stuff irks me.  Examples of “problematic names” are few, and in fact they don’t give a single one. The Pecksniffs simply decry the lack of dinosaurs named after indigenous people or the places where the bones were found. Further, if there were gendered names, most were male—as one expects when the field was dominated almost exclusively, as was the case a while back, by men.

To explore how dinosaur naming has changed over the past 200 years, Emma Dunne, a palaeobiologist at Friedrich-Alexander University in Erlangen–Nuremberg, Germany, and her colleagues analysed the names of all of the dinosaur fossils from the Mesozoic Era (251.9 million to 66 million years ago) that have been described, around 1,500 in total.

The authors wanted to know how much effort it would take to address what they saw as problematic names, which they describe as those “emanating racism, sexism, named under (neo)colonial contexts or after controversial figures”. They found several such names, equating to less than 3% of the dinosaurs they looked at.

Some of the names the team identified derive from the colonial names for lands where species have been discovered. Indigenous-language names of places or researchers are often not used or are mistranslated, the authors say.

For example, many of the dinosaurs discovered during a series of expeditions between 1908 and 1920 by German explorers in Tendaguru in Tanzania, which was then part of German East Africa, were named after German people rather than local expedition members, and the samples remain in Germany.

Now the ICZN says it’s not changing any of these names, though, disturbingly, its president says it could be open to “introducing different naming systems.”  But the article implies that this isn’t impending. And there aren’t that many dinosaurs that haven’t been found.

The main issue, of course, is whether changing 45 dinosaur names (3% of 1500) will make a substantial—or even a detectable—difference in the inclusivity of paleontology. Will people of color and women, previously repelled by the bigotry and patriarchy of dinosaur names, now come pouring into paleontology after 45 common names are changed?  If you believe that, I have some land in Florida to sell you. Regardless, the Pecksniffs think they’re doing a lot of good:

“The problem in terms of numbers is really insignificant. But it is significant in terms of importance,” says Evangelos Vlachos, a palaeontologist at the Museum of Paleontology Egidio Feruglio in Trelew, Chubut, Argentina, who also worked on the study. He wants future naming systems to be more rigorous. “We don’t say that tomorrow we need to change everything. But we need to critically revise what we have done, see what we have done well and what we have not done well, and try to correct it in the future.”

Besides the redundancy of “it is significant in terms of importance,” the fact is that changing 45 dinosaur names won’t accomplish anything except enable the re-namers to feel good about themselves. And this is the problem of all the biological renaming initiatives. They apply only to common names, which aren’t the same from country to country, and it’s ludicrous to expect that changing some of the “problematic” ones will actually make a field of science more inclusive.

This kind of effort would be much better spent tutoring or giving lectures to underprivileged kids. But that’s too much work.

h/t: Alex

Trilobite “horns” may have been used as weapons in male-male combat

January 19, 2023 • 9:15 am

Years ago I met Richard Fortey at the inaugural meeting of Spain’s new evolution society, and found him an affable and lovely guy. He’s a paleontologist and writer, and I had the pleasure of reading and giving a positive review to his first book, Life:  A Natural History of the first Four Billion Years on Earth, which is well worth reading (he’s written several other books, including Trilobite: Eyewitness to Evolution (also a good read).

And it’s four trilobite species that are the subject of Fortey’s new paper coauthored with Alan D. Gishlick, a geophysical sciences professor at Bloomsburg University, in PNAS, a paper you can read for free by clicking the title below (it’s free with the legal Unpaywall app., the pdf is here, the reference is at bottom, and judicious inquiry might yield a pdf if you can’t see the paper). Trilobites are common fossils, and were marine arthropods that went extinct without leaving descendants.

The upshot is that Gishlick and Fortey analyzed fossils of one species of trilobite found in Morocco, deriving from the Devonian (400 million years ago). This species, Walliserops trifurcatus, had a long trident attached to the front of their bodies, and tried to figure out what it was for. They also found one adult individual whose trident was a bit deformed (see below). Their conclusion is that these were weapons used by males to fight with other males, almost surely to compete for females. They are, posit the authors, the arthropod equivalent of reindeer horns. The other possible functions (feeding, digging, etc.) were largely ruled out.

Read on:

Here are four species of Walliserops, shown below. All specimens bear a rigid cephalic trident. W. trifurcatus has a slightly recurved trident that bends upwards, while the other species have tridents more flush with the surface of the sediment (all captions come from the paper):

Four recognized species of Walliserops: A. trifurcatus, UA 13447 (topotype); B. hammi, UA 13446 (holotype); C. tridens UA 13451 (holotype); D. lindoei ROMIP 56997. Images taken from photogrammetric models. (Scale bar, 10 mm.)

The obvious question is: what is this damn thing for?  And there are several hypotheses, all assuming that the structure was molded by natural selection (which includes sexual selection). The authors find evidence against all but one possible function. Here are the alternatives (of course, it could have been used for several things, but it’s likely that selection was wholly or largely on one function). Indented bits are quotes from the paper. The rest of the discussion concerns W. trifurcatus:

A.) Defense. Perhaps the structure could have been used to ward off predators, like the spines found on other trilobites.  Here’s how the authors rule this out:

However, such a function would have been difficult given the overall anatomy of the trident and the trilobite. The trident is rigidly attached and cannot be moved independently from the cephalon; it could only be flexed in a dorsal-ventral plane by the trilobite raising and lowering its cephalon. This would create further difficulties since the long genal spines limit how high the head could be angled without lifting the entire body. The trident, therefore, could not be employed in a versatile way, nor be presented as to defend from a predator attacking from above or behind. This morphology is not consistent with a defensive structure.

B.) A feeding structure.  Doesn’t seem likely:

A second possible function for the trident would be as an aid to feeding. Like all members of the Phacopida, Walliserops was probably a scavenger/predator, and it might be considered as a possibility that the trident was a comparatively sophisticated sensory device concerned with early detection of prey species—such as buried annelid worms—which could then be grasped by the endopods of the ventral limbs.

C.) Sensory detection of the environment.  This is also deemed unlikely from inspection of the structure:

However, examination of the trident in optical and scanning electron microscopy failed to find the arrays of cuticular pits or tubercles usually indicative of the presence of sensilla in fossil arthropods. Most groups of trilobites include species with exterior exoskeletal pitting that is preserved even if the intracuticular canals have been removed by calcite reorganization—and there is no evidence of such exterior pitting on the trident of Walliserops. The absence of evidence for specialized organs on the tines makes it unlikely that it was primarily a sensory apparatus.

D.) A spear to pierce prey:  Unlikely because the structure was inflexible, so the animal would have no way of accessing speared prey.

E.) An apparatus to dig, perhaps for prey.  The way it’s shaped and angled seems to preclude this (remember, it’s slightly recurved upward; see below):

Another possibility is that the trident may have been used to agitate sediment to disturb prey items, which could then be trapped by the limbs. It is difficult to conceive of W. trifurcatus digging into sediment because to engage sufficiently with the substrate the cephalon would have to tilt at an angle greater than would be allowed by movement on the posterior occipital margin. Equally, if the thorax was arched, the pygidial spines themselves would dig into the sediment.

F.) A combat device on males molded by sexual selection mediated by male-male competition for mates.  The authors consider this most likely, especially because the tridents resemble the structure of male dynastine (rhinoceros) beetles, which use them to fight for females.

Here’s a picture of three of those beetles which have similar projections as do the Walliserops trilobites (the one at the extreme right).

(From the Natural History Museum): An image comparing the different beetle morphologies as they relate to fighting mode compared to Walliserops. © Alan Gishlick

The authors did a complex morphometric analysis of body and horn shape of W. trifurcatus, comparing it with living rhinoceros beetles to see if the trident could have been used for shoveling/prying, grasping, or fencing—the three types of male-male combat seen in living beetles. The analysis puts the trilobite in the group of living rhinoceros beetles whose males fight by fencing/shoveling: jousting with the structure in front and then trying to shovel the opponent over onto its back. I won’t go into the gory statistical details, which involve principal-components analysis, but the recurved structure of the trilobite’s “trident” is similar to that of shoveling, prying, and fencing beetles (left column: observed means of fighting of living beetles; center: the cephalic structures used; right: the species name [trilobite at the bottom]).

Cephalic structures of taxa treated in this research in lateral view showing the nature of the curvature and orientation of the tip of the active weapon and how it relates to its employment in combat.

 

As you see, and as the statistical groupings show, W. trifurcatus is similar to the structures used in rhinoceros beetles for fencing, prying and shoveling. Here is Gishlick and Fortey’s scenario of how the males battled it out in the competition to pass on their genes:

We would hypothesize a fighting scenario in Walliserops similar to that of Trypoxylus. The trilobites would meet and at first spar with their forks, pushing and poking. At some point, they would shift to trying to slide the fork under the other, in an attempt to flip them over. Given the morphology of Walliserops, flipping would be a very effective combat technique. Although the appendages of Walliserops are unknown, it is likely that they were like those of other phacopids in not extending beyond the carapace. This is seen in the Devonian Chotecops, asteropygines Asteropyge, and Rhenops, and recently described in three-dimensional material from the Silurian Dalmanites. Once the trilobite was inverted, righting would not be a simple matter, especially if the dorsally directed spines had snagged in the sediment. An upended trilobite would probably be even more helpless than a beetle in this position and thus excluded from sexual competition.

It might also be dead!

Now the first thing that struck me when I saw this paper was the question that would have occurred to many of you: WHERE ARE THE BLOODY FEMALES??  One of the signs of male-male competition is that the structures used to compete are present in males but almost never in females, as they’re of no use in that sex—and detrimental to fitness if you don’t use them. Male deer have antlers, females do not. Body size, used for combat in elephant seals, is huge in the males, and much, much smaller in females.  So if these trilobite horns really were tools used for the “combat” form of sexual selection (the other form, as pointed out by Darwin, is female preference), the females should be around but lack the ornaments. Where are they?

Gislick and Fortey suggest that the females were indeed around, but because they lack the tridents they have not been identified as females of Walliserops trifurcata:

Since the diagnostic synapomorphy [JAC: shared derived trait] for Walliserops is the anterior trident, it would be likely that the female of the species has been classified in a different genus. That leaves two possibilities: either the females of the relevant species are at present unknown, or they are known but placed in another trilobite genus within Asteropyginae.

That mandates a search for trilobites that resemble the males but lack the horns.  The authors raise another possibility: the females weren’t preserved or were offstage, living elsewhere, but this seems less likely:

If we extend the beetle analogy further, it is possible that the females are not preserved if some trilobites, like many dynastines, engaged in sex-specific aggregations; in this case, the females were not always present in the same locations as the males, although it is difficult to explain why the latter were selectively caught up in obrution events. [JAC: “Obrution” is rapid burial in the sediments, the way these creatures must have died and been preserved.]

I favor the “females not yet found” hypothesis. There’s one more hypothesis, which is mine: both males and females have tridents.  I don’t know why this would be the case, although you could think that it’s used to take other individuals out of action in conspecific competition for food. But that makes little sense.

Finally, the authors found one example of W. trifurcatus with a deformed trident, having an extra spike (a “quadent”?). Here it is on the right. Note that the branching pattern can be asymmetrical in the normal three-pronged structure).

Examples of branching patterns for the middle tines in W. trifurcatus; A. left branching (HMNS 2020-001); B. right branching (HMNS PI 1810); C. teratological example (HMNS PI 1811) showing a secondary branching of the left-branching middle tine. Images taken from photogrammetric models. (Scale bar, 10 mm.)

Because the individual on the right was an adult, Gishlick and Fortey suggest that the deformed structure did not prevent the bearer from growing up and thriving, and thus was unlikely to be used for some vital function like feeding. This adds a little more weight to the sexual-selection hypothesis.

The Upshot:  The authors’ analyses and explanations seem plausible to me, though they’d be even stronger if they could find the females. That might be tough: in living species you could find them by looking at mating pairs or even seeing that the DNA was nearly identical, but this isn’t possible with fossilized trilobites, especially because in some living and sexually dimorphic species the females look very different from males.  If the authors are right, and I think they are, then this quote from the paper is correct:

Walliserops provides the earliest example in the fossil record of combat behavior, very likely ritualized in competition for mates. Although fossil life habits are difficult to prove, the consilience of morphology, teratology, and biometric data all point to the same interpretation, making it one of the more robust examples of paleoecological speculation.

h/t: Matthew

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Gishlick, A. D. and R. A. Fortey. 2023. Trilobite tridents demonstrate sexual combat 400 Mya. Proc. Nat. Acad. Sci. USA 120 (4) e2119970120 (in press).

Ancient ecosystem reconstructed using fossil DNA

December 9, 2022 • 10:30 am

The oldest DNA sequenced up to now was from a mammoth molar preserved in permafrost, and was dated about 1.2 million years ago. Now a group of scientists, excavating a 100-meter-thick layer of frozen soil in the “polar desert” of northern Greenland, not only found short stretches of DNA that identified the plants, animals, and algae present a long time ago, but also showed that that the time was at least two million years ago.

This is the oldest fossil DNA ever sequenced; it was preserved because it had been adsorbed to minerals in frozen soil. And although the stretches of DNA had degraded into short bits—about 50 base pairs long—they were sufficiently similar to modern taxa that they could identify the groups from which they came. In fact, they could reconstruct the whole ecosystem of that area 2 million years ago. It was much richer in flora and fauna than today’s polar desert, for at that time Greenland wasn’t covered with ice, it was much warmer (mean summer temperature about 10°C), and organisms could migrate to Greenland over land bridges. This might give us a hint of what kind of ecosystem could develop (minus the animals, which are largely gone) should global warming melt the ice presently in Greenland.

You can read the Nature paper for free by clicking on the screenshot below (the pdf is here, reference at the bottom). Below that is a clickable and short popular account of the findings, also published in Nature.

The News article for tyros (short; click to read):

Here’s the location of the area analyzed in northern Greenland, Kap København, where the layer of soil occurred (yellow star). The layer’s presence was already known, and some of the samples had been dug up in 2006 and had been sitting in a Copenhagen freezer for 16 years. Somebody had a bright idea to see if they could identify and sequence the DNA in that soil, and it worked!

(from the paper): a. Location of Kap København Formation in North Greenland at the entrance to the Independence Fjord (82° 24′ N 22° 12′ W) and locations of other Arctic Plio-Pleistocene fossil-bearing sites (red dots). b, Spatial distribution of the erosional remnants of the 100-m thick succession of shallow marine near-shore sediments between Mudderbugt and the low mountains towards the north (a + b refers to location 74a and 74b).

Small stretches of DNA were sequenced and compared to modern DNA as well as DNA inferred in ancestors of modern taxa. The DNA had of course degraded, but they found stretches about 50 base pairs long. Comparisons were mostly to mitochondrial DNA for animals and to conserved chloroplast or other plastid DNA from plants. (They also found ancient pollen that they used in conjunction with the DNA data.)

On the right you can see what animals were found, mostly identified to genus or family because there wasn’t enough DNA to do a finer analysis. I’ll put a list of what they found below this figure:

(from paper): Taxonomic profiles of the animal assemblage from units B1, B2 and B3. Taxa in bold are genera only found as DNA

Here’s what they found from the DNA; these were all organisms living roughly at the same time about 2 million years ago. And remember, that area now harbors very little life.

A mastodon! The figure below shows its placement on the phylogenetic tree of elephants.

70 genera of vascular plants, including sedges, horsetails, willows, hawthorns, spruce, poplars, yew, and birch. Some of these no longer grow in Greenland, but the mixture of plants includes those found in much warmer habitat. See the paper for a full list.

Algae, fungi, and liverworts

Marine phytoplankton and zooplankton

A hare

A caribou-like cervid (caribou are another name for reindeer). How did they get to Greenland? Presumably it wasn’t an island then, but we don’t know for sure.

A bird related to modern geese

A rodent related to modern lemmings

Reef-building coral

An ant

A flea

A horseshoe crab (identified as Limulus polyphemus, the modern horseshoe crab, regarded as a living fossil). These days Limulus doesn’t breed north of the Bay of Fundy (about 45° N), while the location of this site was 82° N. That shows how much warmer it was in Greenland then, though of course the crabs could have evolved in the last several million years to be acclimated to warmer waters.

There were no carnivores found; all the animals were herbivores. That doesn’t mean that there weren’t carnivores there, but I doubt it.

 

(From paper): b, Phylogenetic placement and pathPhynder62 results of mitochondrial reads uniquely classified to Elephantidae or lower (Source Data 1). Extinct species as identified by either macrofossils or phylogenetic placements are marked with a dagger.

The upshot: Well, we know how that DNA sequences can be preserved for twice as long as we thought, though it has to be under very special circumstances. More important, if you find areas (and they’ll have to be in cold regions) where you can extract even small sequences of fossil DNA, you might be able to reconstruct whole ecosystems. What we’ve found are animals and plants that weren’t expected to be there (reindeer, horseshoe crabs, hawthorns) and so on—species adapted to warmer habitats or now found in areas not in Greenland.

There are two explanations for this: the related today have lost their adaptations to cold habitats when they were forced out of Greenland as the ice caps formed, or the climate was simply warmer. (Of course, both could apply.) But know the latter is surely a contributing factor from independent evidence about climate. Still, there could have been some evolutionary change in thermal tolerance as well, something for which we can’t really get evidence.

But these different explanations aren’t that important: what is important is that we’re able to reconstruct entire ecosystems from fossil DNA—DNA twice as old as previously known. I’ll let the authors have the last word (from the paper):

No single modern plant community or habitat includes the range of taxa represented in many of the macrofossil and DNA samples from Kap København. The community assemblage represents a mixture of modern boreal and Arctic taxa, which has no analogue in modern vegetation. To some degree, this is expected, as the ecological amplitudes of modern members of these genera have been modified by evolution. Furthermore, the combination of the High Arctic photoperiod with warmer conditions and lower atmospheric CO2 concentrations made the Early Pleistocene climate of North Greenland very different from today. The mixed character of the terrestrial assemblage is also reflected in the marine record, where Arctic and more cosmopolitan SMAGs of Opistokonta and Stramenopila are found together with horseshoe crabs, corals and green microalgae (Archaeplastida), which today inhabit warmer waters at more southern latitudes.

. . . In summary, we show the power of ancient eDNA to add substantial detail to our knowledge of this unique, ancient open boreal forest community intermixed with Arctic species, a community composition that has no modern analogues and included mastodons and reindeer, among others. Similar detailed flora and vertebrate DNA records may survive at other localities. If recovered, these would advance our understanding of the variability of climate and biotic in

Will northern Greenland be like this again should global warming continue? I doubt it, for many of the species, like caribou, can no longer get there, and some, like mastodons, are simply extinct. But it’s enough to know what was there two million years ago.

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Kjær, K.H., Winther Pedersen, M., De Sanctis, B. et al. A 2-million-year-old ecosystem in Greenland uncovered by environmental DNA. Nature 612, 283–291 (2022). https://doi.org/10.1038/s41586-022-05453-y

First fossil evidence for brood care in insects, and a remarkable case of directional asymmetry

July 26, 2022 • 9:45 am

I’ll make this short and sweet.  A team of biologists from China have found, examining a fine-grained layer of fossils dated about 164 million years ago, a species of water boatman (“true bugs” in the order Hemiptera) that provide the oldest evidence for parental care in insects. The care is given by females, who attach their eggs to their second pair of legs. The curious thing is that in all the specimens examined, females attach the eggs to only their left middle leg: a rare example of “directional asymmetry”.

You can read about it by clicking below or downloading the pdf here.  The reference is at the bottom of the post.

 

Parental care is not that rare in today’s insects and other arthropods; you can see some examples in modern insects here. It’s also been seen in fossil insects, with the earliest cases described in the paper:

Among Mesozoic insects, the only two direct fossil evidence cases of brooding ethology are provided by the Early Cretaceous cockroach Piniblattella yixianensis with its oothecae enclosing eggs for protection and brood care; and the mid-Cretaceous scale insect Wathondara kotejai, which preserves eggs within a wax ovisac attached to the body of an adult female.

An ootheca is an egg mass, usually enclosed in a hardened shell, as in this modern cockroach (photo below). I assume the mother in the fossil species would stay with the mass, otherwise I can’t see this as an example of “brood care”:

Here’s a picture from Wikipedia labeled “cockroach (Periplaneta americana) with ootheca”:

An “ovisac” is similar: a capsule containing eggs. In the case of the scale insect above, that’s clearly brood care because the ovisac was attached to the body. The Cretaceous period lasted from 145 to 66 million years ago; and oldest of these two insects having brood care dates to about 126 million years ago.

Now, from the Haiffanggou Formation at the Xiayingzi quarry, a formation in NE China with lots of ancient mammals, dinosaurs, and insects, they’ve discovered the water boatman Krataviella popovi. Fu et al examined 157 specimens, 30 of which were females carrying eggs on the middle segment of their LEFT foreleg. Note the directionality of this asymmetry. If it were random, the chance that 30 specimens would all have eggs on the left side would be 9.3 X 10-10.

The age of this formation is 163.5 million years, so the brood care in these boatmen precedes the previous ‘record’ by about 38 million years. It’s not a unique phenomenon in insects, but it’s the earliest example of that phenomenon.

Here are two photos of females carrying eggs (red arrows), both from the paper and both on their left side. The preservation is remarkable, with some of the specimens prepared using only a sharp knife:

Figure 2 [excerpt]. Brooding in Karataviella popovi. (a) General habitus of egg-carrying specimen (NIGP177390). (b) Details of egg (NIGP177447). (c) General habitus of egg-carrying specimen (NIGP177445). Scale bars: 2 mm in (a,c,d); 1 mm in (f–h), 500 µm in (b,e)
Females and males can be identified independently of egg-carrying, so this is clearly a female trait.  Modern water boatmen often attach their eggs directly to the substrate with a kind of biological glue, and then leave, so there is no brood care. The authors hypothesize that the females in these fossil specimens were still using some kind of adhesive, but that it was used this way:

Since water boatmen eggs cannot adhere to new surfaces after being detached from their original place of deposition, this suggests that the females first secreted mucous substance and then laid eggs onto their own left mesotibia by specific bending movements of the abdomen, and then carried the brood until hatching. The unoccupied right mesotibia might have been used to maintain balance when swimming and feeding.

What seems unusual to me is the directionality of the trait: it’s only found on the left middle leg, never the right one.  This is called “directional asymmetry”. (If eggs were laid randomly on the left or right legs, it would be called “fluctuating asymmetry”.)

Directional asymmetry has fascinated me because, if it’s an evolved trait, it means that genes producing the directional trait “know” which side of the body they’re on. How can that be? If an ancestor already had biological or genetic gradients from top to bottom and front to back, it still means that a point on the right and left side with equal positions on these other two gradients would experience the same environment. So how do genes determine which side their cells are on so those genes can be activated differentially?  I’ve talked about this before, and you can read about it here, here, and here.  It’s a fascinating issue that’s not fully resolved. (Of course, once a genetic directional asymmetry is in place, it can be used as a developmental key for the evolution of further asymmetries. We ourselves have a fair number of such asymmetries.)

One solution, which just pushes the question back a bit, is to posit that the females have directionally asymmetrical ovipositors, and it’s simply easier to lay eggs on your left leg than on your right. But if the ovipositors and genitals are symmetrical (the authors don’t say), then it would probably be a directional behavioral asymmetry, with females behaviorally evolved to lay eggs on only one side. I don’t see the advantage of that, but of course behaviors can be directionally asymmetrical and conditioned by genes, like handedness in humans.  It’s still interesting to me that one of the earliest cases of directional asymmetry known isn’t discussed by the authors except to mention it. Their own big message is that this is the earliest case of brood care seen in insects, not that it’s directional.

Finally, what is the advantage of evolving this kind of brood care? I’m sure you can think of answers: having your eggs with you protects them from predators, and also aerates the eggs as the beetle moves through the water.  Or, as the authors note:

Karataviella adopted a strikingly similar brooding (egg-carrying) strategy to most marine and freshwater shrimps, lobsters and kin (Pleocyemata), where the females attach eggs to their pleopods using a sticky substance, allowing them to actively and intermittently adjust the position of the eggs in water or air, together with the movement during swimming that generates currents, to ensure ventilation and moistening of the eggs. Moreover, in K. popovi and some pleocyematans, a firm but elastic egg stalk is present and may contribute to the aeration of the eggs by facilitating regular shaking motion. Therefore, we speculate that the particular brooding behaviour of K. popovi effectively addresses the problems that large eggs experience relating to hypoxia, drowning and desiccation, resulting in enhanced offspring survival.

To close, here’s a drawing from the paper labeled “Ecological reconstruction of Karataviella popovi and anostracans in the Middle–Late Jurassic Daohugou biota.” What’s weird here is that all the egg masses are shown on the RIGHT mesotibia, and water boatmen do not swim upside down.  Go figure.

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Fu. Y. , P. Chen, and D. Huang. 2022.  The earliest known brood care in insects. Proc. R. Soc. B.2892022044720220447 http://doi.org/10.1098/rspb.2022.0447