Category: paleontology

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

Wonderful fossil dinosaur embryo shows birdlike “tucked” posture before hatching

December 24, 2021 • 11:00 am

This is one the most stunning fossils I’ve seen in a long time. It’s an almost perfectly preserved dinosaur embryo that somehow died in the egg during the Late Cretaceous (100 mya-66mya). It’s not just amazing for its preservation, but also for the posture of the unhatched embryo, which resembles the posture that modern bird embryos (an also early birds themselves) assume soon before hatching. The inference is that the behaviors that precede hatching in birds, and help them through the tough process of getting out of the egg, actually evolved from their reptilian ancestors—the theropod dinosaurs, of which this specimen is one.

The paper appears in iScience and is free; click on the screenshot below or get the pdf here.

I’ve really conveyed the gist of the paper in the first paragraph above, but you need to see this embryo! Click to enlarge; all the photos are high-resolution

(from paper): Figure 1. Oviraptorid embryo inside an elongatoolithid egg (YLSNHM01266) Abbreviations: cev, cervical vertebra; cv, caudal vertebra; dv, dorsal vertebra; f, femur; fi, fibula; II-1, pedal phalanx II-1; il, ilium; is, ischium; m, mandible; mt-I, metatarsal I; mt-III, metatarsal III; mx, maxilla; p, pubis; pm, premaxilla; r, radius; s, scapula; t, tibia; ul, ulna. Scale is 1 cm.

 

The specimen is given the number YLSNHM01266, and is described as a “new non-avian theropod dinosaur embryo. . . from the Late Cretaceous Hekou Formation of southern China.” No species name is given because without a fossil of an adult in the vicinity, we have no idea. We can tell, however, that it is a theropod dinosaur, and an “oviraptorid oviraptorosaur“.

Oviraptors constitute is a group of theropod dinosaurs of varying sizes, which lived in what is now North America and Asia. Fossils show that they had feathers, parrot-like beak mandibles, sometimes bony crests on the head, and walked on their hind legs. Paleontological analysis combined with phylogeny shows, as Wikipedia notes, that they are “close to the ancestry of birds.” (The ancestor of birds is thought by most but not all paleontologists to be theropod dinosaurs.)

Here’s a group of diverse ovoraptors from Wikipedia. You can see that their skeletons are more birdlike than those of other dinosaurs. Some scientists, indeed, group them with birds! Four species have been found with feather impressions, so it’s likely that the group (including the baby above) had feathers, but couldn’t fly. Maybe one of the species below is the adult that would have developed from the juvenile above!

Back to the fossil.  Here’s part of a later figure that helps you make sense of what’s what in the photos above. The air cell, also present in modern bird eggs, is to the right between the embryo and the shell.

If you want the technical description of the posture, here it is from the paper. I’ve bolded the important parts.

The articulated embryonic skeleton is preserved curled inside its egg (YLSNHM01266), with the skull positioned ventral to the body (Figure 1). The egg is elongate ovoid in shape with dimensions of 16.7 cm long by 7.6 cm wide, and has characteristics typical of the egg family Elongatoolithidae (see STAR Methods for eggshell analysis). The skeleton is almost complete, without much apparent postmortem disruption. The anterior surface of the skull faces toward the pointed pole and is situated about egg mid-length at the level of the ilium in-between the flexed hindlimbs, with a pes [foot] on either side. The anterior cervical vertebrae are in line with the long axis of the skull. The presacral vertebral column is strongly bent in an angular manner, so that the upper back of the embryo faces the blunt pole of the egg (similar flexion of the vertebral column is found in modern in ovo skeletons, e.g. Balanoff and Rowe, 2007: Figure 4, Day 18, and is not likely to be a taphonomic artifact). The skeleton is ∼23.5 cm in total length, measured from the anterior tip of the skull to the last preserved caudal vertebra, and occupies nearly the entire width of the egg and most of the length, with the exception of a ∼1.9 cm space between the dorsal vertebrae and the blunt pole of the egg. This space may represent the air cell, a space usually found between the back of the embryo and the blunt pole of bird eggs (e.g., Rahn et al., 1979). However, this inference is tentative and awaits further evidence. The posterodorsal, sacral and caudal vertebrae almost form a straight line along the long axis of the egg. Although the precise developmental stage of the embryo is unclear, it is likely to represent a late-stage embryo because the skeleton is well ossified and is large in size relative to the space inside the egg, as inferred in MPC 100/971 (Norell et al., 2001).

Note that the specimen is 23.5 cm, or a bit more than nine inches long: as long as a dollar bill and half of another one (American dollar bills are almost exactly 6 inches long, and can be used for emergency measurements).

When modern birds hatch, they assume this position as the first of three stages prior to hatching: “pre-tucking”, “tucking” and “posttucking” (we know this clearly because, sadly, many pre-hatched birds have been dissected from the egg). I won’t go through the complicated description of the changes in posture, but here’s how it happens in a chicken, with the fetal dinosaur placed between “pretucking” and “tucking”. “Membrane penetration” is when the bird uses its bill to get out of the membrane in which the embryo is enclosed, and “pipping” is when it begins to peck through the shell (often a long process).

Apparently birds always tuck their heads below their right wing, not their left, before pipping. How they know left from right (genetically) is beyond me; but somehow this asymmetry is coded in the DNA:

And here are three examples of embryonic oviraptors compared to a modern bird (chicken) at the assumed similar stages:

(from paper): Figure 3. In-ovo late-stage embryos of non-avian and avian dinosaurs (A) Oviraptorid specimens (MPC 100/971, YLSNHM01266 & IVPP V20183), which potentially correspond to various tucking stages. (B) Domestic fowl Gallus ontogenetic series (day 16-20) (modified from Rowe (2003)). Not to scale. Silhouettes modified from PhyloPic.

Now the authors are very careful not to overinterpret a single fossil, but I do think it’s likely that the oviraptor fossils show that their pre-hatching positions and behavior was passed on to birds, as oviraptors are phylogenetically close to the ancestor of birds (though we don’t know whether the ancestor of birds was an oviraptor).

The only question remaining is: do all dinosaur embryos—not just those closely related to the ancestor of modern birds—show similar embryonic behavior? The answer is, as usual, we just don’t know. There’s a severe shortage of well-preserved dinosaur embryos, as you might imagine One specimen of a sauropod, a distant relative, seems to show a different fetal posture than the ones above.

I hope we can find more fossil embryos, because, although behavior doesn’t fossilize, the correlates of behavior—represented by the posture of embryos—do. In that sense the way modern birds hatch might what some systematists call a synapomorphy: a character shared by two species (or groups) because it was present in an ancestor—in this case the common ancestor of the ovoraptors and modern birds. And it’s surely an adaptive synapomorphy, because birds that can’t get out of the shell don’t leave any genes behind.

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Xing, L. et al. 2021.  An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures.  iScience, in press.

Oldest evidence for animals found? New sponge-like fossil is 890 million years old, several hundred million years older than next oldest animal

July 29, 2021 • 9:15 am

First, we have to know what biologists mean by “animals”. In brief, they are multicellular organisms comprising eukaryotic cells (“true cells” with a nucleus and nuclear membrane, as well as organelles like mitochondria). Or, to be more specific, I’ll give the Wikipedia definition:

Animals (also called Metazoa) are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in which their body consists of a hollow sphere of cells, the blastula, during embryonic development.

Long before animals existed, living organisms existed, but these were cyanobacteria (“blue green algae”) and other microbes, not regarded as animals. The first cyanobacteria date back about 3.5 billion years, only a billion years after the Earth formed. The cyanobacteria are identified in fossil stromatolites—layered reef-like structures formed by the accretion of bacteria. Stromatolites are still forming in some places on Earth, like Shark Bay, Australia.

But when did the first metazoan, or “animal” appear? For that you can use either fossil or molecular evidence.

The earliest fossil scientists regard as an animal is Dickinsonia from the Ediacara fauna, dated about 540 million years ago.  Scientists think it’s an animal because its lipid biomarkers, which you can extract from fossils and the sediments above and below them, include cholesteroids, compounds found exclusively in animals. Dickinsonia is known only from imprints, like the one below, and its affinities are a mystery.

Dickinsonia

Molecular data, from which you can construct a phylogenetic tree of living animal groups and then extrapolate backwards, have shown that animals probably originated between 650 and 850 million years ago, but we have no animal fossils from that period. Those trees also show that perhaps the earliest animal was similar to sponges, for sponges seem to be the most “basal” animals—those that branched off the animal tree before other groups. This makes sponges the “sister group” of all other animals.

Now a new paper in Nature by Elizabeth C. Turner of Laurentian University in Canada has pushed the oldest animal fossil back a long way: several hundred million years—to 890 million years ago! And, in fact, the fossil shows features of early sponges, verifying the molecular conclusions.

Now not all paleobiologists agree that what Turner found is an animal—some say the structures observed may have a microbial origin—but Turner herself is pretty confident, as are some other paleontologists. So let’s take this conclusion as “likely, but not certain”. Surely further work will either strengthen or weaken Turner’s evidence.

You can access Turner’s paper by clicking on the screenshot below, or downloading the pdf here. The reference is at the bottom of this post.

Investigating the Little Dal Reef Formation in Northwestern Canada, itself a kind of stromatolite, Turner collected rocks between 1992 and 2018, and, in thin sections of those rocks, observed “vermiform” (worm-shaped) microstructures filled with calcite “spar”, or calcium carbonate crystals. These tube-like structures join and divide in a branching network, just like the tubules of modern sponges, some of which have a calcite skeleton. (The tubules of modern sponges allow them to circulate water through their bodies, getting food and oxygen.) These wormlike structures are surrounded in the fossils by a calcite “groundmass”, which may be the external body of the sponge.

Here’s what Turner says about these interconnecting tubules and why she regards them as early sponges:

The shape, size, branching style and polygonal meshworks of the Little Dal vermiform tubules closely resemble both spongin fibre networks of modern keratosan sponges (Fig. 2a–c) and vermiform microstructure either demonstrated or interpreted to be sponge-derived in diverse Phanerozoic microbial, reefal and non-reefal carbonate rocks. The compositional and textural homogeneity of the microspar groundmass supports an origin through permineralization of a pre-existing biological substance, rather than incremental accumulation of detrital sediment or microbial carbonate that passively incorporated complexly anastomosing tubular microfossils. Variable preservation and association with geopetal peloid accumulations are familiar aspects of Phanerozoic sponge taphonomy In previous work, detailed comparison of the three-dimensional characteristics of vermiform microstructure with branching cylindrical organism types yielded no convincing alternative to the sponge interpretation

Here are subfigures (a)-(b) of her Figure 2 showing the fossil network compared to that of a modern sponge (c), with the captions below (click photo to enlarge).

(From Fig. 2 of the paper): a, Well-preserved vermiform microstructure exhibits a polygonal meshwork of anastomosing, slightly curved, approximately 30-μm-diameter tubules embedded in calcite microspar (KEC25). Scale bar, 500 μm. b, Enlarged rectangle from a, showing branching tubules forming three-dimensional polygons intersected at various angles by the thin section; clear calcite crystals, about 10–20 μm in width, fill tubules in groundmass of more finely crystalline calcite (dark grey). Scale bar, 50 μm. c, Three-dimensional fragment of spongin skeleton from a modern keratosan sponge, illustrating its branching and anastomosing network of fibres (incident light). Scale bars, 100 μm (main panel), 20 μm (inset).

There are other pictures as well, but the first two are the heart of the matter. You may not think they look like much, but they do show the interconnecting, ramifying tubules with the light-colored calcite crystals typical of some groups of sponges. The area where these putative fossils are found is 890 million years old.  And these fossils are older than the next oldest and indisputable sponge fossils by 350 million years!

Turner hypothesizes that these early organisms couldn’t compete with the reef-building cyanobacteria, but were able to find “oxygen oases” to use the oxygen produced by the cyanobacteria. The association of these putative sponges with oxygen-producing bacteria may be one piece of evidence that these are indeed metazoans, which of course require oxygen.

As I said, some paleobiologists disagree about whether these are animals. You can hear a ten-minute Nature-sponsored discussion with Turner, some supporters, and some doubters here. I highly recommend that you listen to this short but lucid discussion.

One other point: these organisms must have survived at least one of the periods of extensive glaciation and freezing known as “Snowball Earth“, when the entire planet was either completely frozen or almost covered with ice except for some open water. (The most extensive was between 700 and 600 million years ago.)  In the linked article, author Laura Poppick says this about that period:

What did life on Earth look like at the time, and how did it change as a consequence of these events?

There were certainly bacteria and there were also algae and unicellular primitive animals, or protists.

There is also evidence that the first multicellular animals originated at this time, probably something like sponges.

Well, according to Turner, the first multicellular animals, probably something like sponges, originated nearly 200 million years earlier than this.

Stay tuned to see how the dispute about the nature of these fossils progresses. Are they animals or simply remnants of bacterial activity? As Turner says in the interview, “We are quite confident” that these are spongelike animals. “It’s almost,” she adds, “a no-brainer.”

And here’s Turner in the field:

(From source): Elizabeth C. Turner, geology professor at Laurentian University, conducting geological fieldwork on northern Baffin Island in 2012. (Supplied photo/Laurentian University)

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Turner, E.C. 2021. Possible poriferan body fossils in early Neoproterozoic microbial reefs. Nature (2021). https://doi.org/10.1038/s41586-021-03773-z

Neil Shubin to give prestigious lecture on “Your Inner Fish”

March 23, 2021 • 12:00 pm

The University has just announced that my colleague Neil Shubin, paleontologist, developmental biologist, and author, will be giving this year’s prestigious Ryerson Lecture. Click on the screenshot below for details:

You have to register in advance, and it’s online, but it’s free. Here are the details and the link:

A prestigious tradition celebrating the scholarly work of a UChicago faculty member, the Ryerson Lecture will take place virtually April 20 at 5 p.m CT. The lecture, entitled “Finding Your Inner Fish: Fossils, Genes and the History of Life,” is free and open to the public; registration is now open through this link.

The Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy, Shubin is known widely for his evolutionary work including the groundbreaking discovery of Tiktaalik roseae, the 375-million-year-old fossil considered a missing link between fish and all animals on land, including humans.

After you register (all that’s needed is your name, email address, and “do you plan to attend this lecture”—a weird question), you get a note that you’ll receive an email link to the talk on Monday, April 19—the day before.

Be there or be square!

Readers’ wildlife photos

January 21, 2021 • 8:00 am

These photos come from Robert Seidel, whose notes (and the Biblical quote) are indented. Click the photos to enlarge them.

“In my distress I called to the LORD; I called out to my God. From his temple he heard my voice, and my cry for help came to his ears. – 2 Samuel 22:7”

In that vein, allow me to offer you some wildlife images, mostly of fossilized wildlife. I saw your review of the movie Ammonite early last month [JAC: here], which by co-incidence was right before I spent a weekend at Lyme Regis on the Jurassic coast of South England, where Mary Anning used to live and work and the film is set. My photos and notes:

Sunset at Lyme Regis harbour. The breakwater you see features in several films, including I believe Ammonite, as well as Jane Austen’s Persuasion.

View from top of the breakwater out to sea. I like how the stones and waves blend together in this picture.

The cliffs to the East of Lyme Regis. These are not your perfect white chalk cliffs of the Dover type, but rather more messy, with alternating layers of tough limestone and soft siltstone.

The beach in front of the cliffs, looking quite prehistoric in my opinion. This is a tidal beach which is submerged under high water. If you go out towards the East, you should take to heart the frequently posted warnings about the danger of getting cut off by the tide!

A tidal pool on the beach. Sea snails like to burrow into the soft siltstone, making it look like swiss cheese.

To the West of Lyme Regis lies Monmouth Beach, named after the ill-fated Duke of Monmouth, who in 1685 landed at this point with an invasion force in an attempt to take the English throne (). Ammonites like this are ever present along that beach.

A very large ammonite, about a foot in diameter. Smaller ammonites got washed into the empty shell as it lay on the sea floor. At the nearby town of Charmouth, there is a small museum with some fantastic specimen of such “graveyards”.

The famous “ammonite pavement” of Monmouth Beach, just a few hundred meters walk from Lyme Regis. These should be Arietites bucklandii.

Bonus photo. There is an alternative feline theory about the origin of these structures. These are four out of five of my partner’s cats. From front to back: Simba, Bella, Tonto and Katie.