Reader Dom called my attention to today’s BBC Science in Action program, which contains several items of interest. You can hear the 35-minute show by clicking on the site below and clicking “listen now”:
There are four bits:
Start – 12:20. A discussion with Elizabeth Turner about her new evidence for 890-million-year-old animals (spongelike creatures), which I wrote about yesterday.
18:55-26:45: Prof Lesley Lyons from the University of Missouri discusses the similarity of the genome of cats to that of humans, and how that could be used for medical purposes in humans. I’m not keen on this because it implies that they’re going to experiment on cats. As she says, “they’re bigger than mice and cheaper than primates”.
26:45-end: A remembrance of Steven Weinberg, who died a week ago. There are extracts from two BBC interviews with Weinberg as well as discussions of his work by fellow scientists.
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.
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).
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.”
This article in Quillette caught my eye because it was about science—paleoanthropology—and its conflict with faith. The authors are a pair of anthropologists who have written a book about the topic, which is the perennial conflict between scientists on the one hand and Native Americans claiming ancient human remains that, they say, are their ancestors.
Click on the screenshot to read:
The title refers to a meeting of the SAA in April when Weiss gave a talk about the obstructionism of Native American creation myths as they affect paleoanthropology in North America. Although the talk is certainly germane, and provides food for thought (see below), it was in effect “erased” by the SAA, who refused to post it despite their pledge to do so. It was the only talk that wasn’t posted. The reason is clear: going up against the claims of Native Americans, even if those claims can’t be supported, is a no-win situation. As Weiss writes:
The new SAA president, Deborah Nichols, subsequently contacted me to let me know that the video of our live talk would not be posted by the SAA for others to view, due to reports of hurt feelings. (We had previously relied on the SAA’s emailed assurance to presenters that “sessions will be available for viewing on demand within 24–36 hours after their original broadcast, until July 17, 2021.”) Furthermore, we learned, the SAA would not even provide us with the video. (And so we re-recorded the talk, which you can find here.) Another SAA statement was then put out to inform readers that “the SAA board finds the presentation does not align with SAA’s values,” and mentioned that “the board categorically rejects the Weiss-Springer position.”
Here’s the 13-minute talk that Weiss re-recorded after the SAA refused to post it:
There was substantial other pushback on both professional and social media. Here’s an example of a reaction by an “indigenous archeologist” to Weiss’s abstract of the talk: archaeologist.”
Why was this abstract accepted @SAAorg? This is completely unacceptable and anti-Indigenous. This is why people are leaving your organization. Stop giving this type of work a platform. pic.twitter.com/L2zSXMjPyt
Well, we all know about these conflicts, and it’s conceivable that for some of them the Native Americans have a right to the bones and artifacts found by archaeologists, who of course lose the chance to study them. But in most cases that “right” is dubious, for the genetic connection between those claiming the bones and the person whose bones are claimed is tenuous at best. Often it rests solely on creation myths: many Native Americans claim that despite scientific evidence that the Americas were populated by “modern” H. sapiens who crossed the Bering Strait from Asia about 15,000 years ago, their ancestors have lived in America forever. Further, to establish that the bones belong to a specific tribe is almost impossible, because bones from people of multiple “tribes” have been found in one locality, and there was considerable migration within North and South America.
Genetic analysis could conceivably settle the question, but without the bones you don’t have the DNA, and even so it’s hard to narrow down ancient DNA to a specific existing group of Native Americans, who are fairly closely related to each other. It’s even worse because the U.S. government passed laws saying that establishing ancestral (i.e., genetic) affinity isn’t necessary: “cultural evidence”, like oral traditions and creation myths, is sufficient. That immediately puts science at loggerheads with superstitions, superstitions that can be demonstrably incorrect.
As an example, Weiss and Springer discuss the famous Kennewick Man, 8,400- year-old remains of a man found in 1996 in Kennewick, Washington. It’s one of the most complete ancient North American skeletons ever found (see photos at bottom), and dates pretty close to the time when Asians began populating the Americas. But the remains were claimed by several tribes of Native Americans, although, according to the authors “the oldest known American tribe, the Hopi, reliably dates its history to only about 2,000 years ago.”
This started a decade-long court case between Native Americans, scientists, and the U.S. Army Corps of Engineers. The case wasn’t resolved until 2004, and in favor of the scientists, though the remains have since been returned to a “coalition of Pacific Basin tribes” for reburial.
In the meantime, scientific studies of the skeleton, including use of DNA, showed that it was actually more closely related to “modern American Indian populations of Central and South America who are not ‘Native American'” by the U.S. government’s regulations. Using ancestry rather than creation myths, those other populations would have a stronger claim to the bones than would North American tribes.
In the meantime, scientists were able to find out a great deal of information from the skeleton. As the article states,
The greatly delayed scientific study was finally carried out, and the result was a magnificent peer-reviewed 2014 volume, edited by Jantz and Douglas Owsley of the Smithsonian Institution, titled: Kennewick Man: The Scientific Investigation of an Ancient American Skeleton. The studies revealed Kennewick Man’s age, sex, bone morphology, and bone chemistry, as well as modifications to the skeleton incurred during his life. This information, in turn, allowed inferences as to his food intake, food production, and other physical activities, and diseases and injuries he’d endured.
His affinities with other prehistoric and modern populations and individuals were also revealed by these studies. Kennewick Man’s dietary reconstruction from nitrogen isotopes (elements found in a variety of food sources that settle in bones and teeth, and which can be used to reconstruct eating and weaning patterns) revealed a diet composed mainly of marine foods. This differed from the previous view of Paleoindians as big game hunters. Kennewick Man also had bony growths in his ear canals called external auditory exostoses, which some have argued may have impacted his hearing and were related to chronic ear infections.
Kennewick Man had multiple injuries—including a projectile point (a spear head) in his pelvic bone. Chatters argued that this injury never healed properly and likely caused lifelong pain. Anthropologist Della Cook, on the other hand, suggested that the lack of reactive bone (which is evidence of bone healing from injury or infection) in the CT-scans suggests that Kennewick Man’s injury healed quickly. Interestingly, these two perspectives were both published in this 2014 book—an example of the open-minded manner in which science should be conducted and evaluated.
All of this information would have been lost had the repatriationists been successful. No other Paleoindian is as well studied as Kennewick Man, and many were reburied with just a simple osteological report. Such reports may include only the remains’ antiquity, sex, estimated age, and other basic information; and often are written up by undertrained students and marginal scholars who are not subject to peer review, and who do not report their findings in a way that contemporaries can validate. . .
Weiss and Springer describe other cases in which cultural tradition blocked scientific study, as well as scientific study that did succeed in finding out stuff about early Native Americans.
So what should the rule be? Of course, as a scientist who values scientific fact over creation myths or oral tradition, I’m biased in favor of empirical study. But if remains can be traced to a specific tribe or group of tribes, showing the bones to be more closely related to that group than to other tribes, one might consider tribal claims to be valid. Even so, perhaps there should be an allowed period of scientific study, say two years, before the remains are returned to present-day tribes for reburial or various rites. After all, it’s not as if these bones belong to a present family of Native Americans, like the remains of someone’s son recovered and returned after a battle.
But I don’t think that claims based only on “oral tradition” or “creation myths,” should be honored at all. In such a case, the remains should then be available to scientists. After all, if we honor such superstitious claims, we are also tacitly honoring the creation myths of anybody, including Christians, Scientologists, and Muslims, each of which has its own creation story. That is government entanglement with religion.
And it’s a double entanglement: one with the myths of Native American groups, and the other with the religion of Wokeism, which makes the SAA into an organization that renders decisions based not on empirical considerations, but on ideology and identity politics.
Well cut off my legs and call me Shorty (is that ableist?). A new report in the journal Nature Communications shows that some bacteria can remain dormant for over 100 million years in marine sediments—an unbelievable amount of time for an organism to remain “alive”—if you call it “alive.” I do: after all, the bacteria collected and revived by the researchers retained their ability to metabolize, take up labeled organic substances, and reproduce. Dormancy, to me, at least, is not the same thing as “death”.
Click the screenshot to read the paper (the pdf is here and the full reference is at the bottom).
The experiment was laborious yet the results are simple. If you want to know the gory details, the paper is there for your reading.
In short, the authors sampled clay sediments of different ages from the South Pacific Gyre, and did so in a way that, they aver, precluded contamination with modern bacteria. Supporting their claim that the bacteria they found in the inside of sea-floor cores were really bacteria in situ, they argue that the clays are almost impermeable to bacteria, with very low pore size, and there are thick impermeable layer above the sampled sediments. And there were strict precautions to prevent contamination.
To see if any bacteria in the sediments were capable of biological activity including reproduction, they tested for “anabolism” (the synthesis of molecules) by incubating the bacteria with oxygen (controls lacked oxygen) as well as radioactively labeled molecules that could be taken up and made into proteins and other molecules. The added molecules included 13C6-glucose, 13C2-acetate, 13C3-pyruvate, 13C-bicarbonate, 13C-15N-amino acids mix [mixture of 20 Amino Acids], and 15N-ammonium. Another control involved killing any bacteria with formaldehyde. The researchers could then visualize the bacteria and see, through fluorescence microscopy and radioactive visualization, if the precursor molecules had been taken up by bacteria.
Finally, the researchers could isolate bacteria at various times (the samples for activity, growth, and bacterial presence were taken at 3 weeks, 6 weeks, and 18 months) to see if the bacterial titer was increasing, i.e., they were dividing. Finally the authors isolated RNA (16S rRNA) from individual bacteria, amplified it, sequenced slow-evolving RNA, and saw what groups of living bacteria the ancient bacteria belonged to. (This assumes that we can still recognize the groups from modern sequences, but these molecules evolve very slowly).
1.) The aerobic bacteria (bacteria that require oxygen) were still viable, initiating metabolism and reproduction even in sediments as old as 101.5 million years. Anaerobic bacteria, which don’t require oxygen, didn’t do nearly as well, and the authors suggest that even low oxygen concentrations in the sediments over geological time simply kills anaerobic bacteria.
Here’s a figure from the paper showing photos of the bacteria, with the same bacteria then examined for uptake of added molecules. The caption is complicated, but you can see that, especially with added amino acids (and oxygen), the cells glow furiously (d and h are electron-microscope images of the same bacteria shown fluorescing in the rows).
2.) The bacteria divided, as measured by the increase in numbers over time in the samples.
3.) Anaerobic bacteria were much harder to find metabolizing than aerobic bacteria. The former were effectively defunct.
4.) The lineages of bacteria identified as persisting in the sediments, judged from sequencing them and comparing the 16S rRNA to modern samples, include Actinobacteria, Bacteroidetes, Firmicutes, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria, and cyanobacteria (“blue-green algae”). It would be interesting to compare the sequences of these early species with their modern relatives to see exactly how much and what kind of evolution has gone on.
5.) How did they survive? One thought was that they formed dormant spores, which can last a long time in bacteria. But this suggestion is ruled out because none of the bacteria identified were from spore-forming lineages. It seems the bacteria simply became dormant, surviving without any—or hardly any—detectable metabolism, and without reproduction.
This raises the question: were these things really alive for 101.5 million years? I can’t see why not, unless you think that something that becomes dormant is dead, and then, Lazarus-like, revives when the dormancy is broken. If you take the authors’ word that sufficient precautions were taken to prevent contamination with modern bacteria, then what we have here are the oldest living organisms on Earth.
Note: The classification of “dinosaur” above isn’t totally accurate, for the creature discussed below is an archosaur, a member of the group that gave rise to dinosaurs, pterosaurs, and crocodilians. But we might as well call it a dinosaur, as few people know what an “archosaur” is.
The ancestors of the dinosaurs could not have been big, for they evolved from amphibians, and amphibians, for a number of reasons, are limited in size. But this new paper in PNAS shows that some of the earliest ancestors of dinos were very small—not just small, but tiny. The new species described below, which falls into a group that later diverged into pterosaurs (flying reptiles) and the dinosaurs, was only 10 cm tall, the distance between my index fingers in the photo below:
Click on screenshot to read the paper; the pdf is here, and reference at bottom of post.
The partial skeleton of this tiny creature, whose dentition suggests it ate insects, was discovered in 1998 in Southwestern Madagascar. Although the age of the specimen is a bit uncertain, a good estimate is about 237 million years.
Here are some drawings of the parts of the skeleton they recovered, including leg bones, a forearm bone, and the jaws (interpreted as coming from single individual), and a figure showing where they fit into the body (figure F). The size, estimated from the bones, which clearly put the species in the ancestral group Ornithodira (also known as Avemetatarsalia), show that the creature was only about 10 cm tall. It must have been really cute: a pet-sized reptile. Note that the length of the scale bar on the left, showing the femurs, is one centimeter (about 4/10 of an inch), while on the right the scale bar for the jaws is only about 40 mm (1.6 inches):
The authors named the fossil Kongonaphon kely, meaning “tiny bug slayer”. They explain the etymology:
. . . derived from kongona (Malagasy, “bug”) and φον (variant of ancient Greek φονεύς, “slayer”), referring to the probable diet of this animal; kely (Malagasy, “small”), referring to the diminutive size of this specimen.
The teeth, as you can see in the drawing above, were simple ones: conical and without serrations. That suggests that the creature lived on insects (I used “bug” in the title as a generic word for insects, though technically, bugs are in the order Hemiptera). The estimated size of 10 cm comes from the size of the preserved femur, which is only about 1.6 inches long. The specimen wasn’t a juvenile, as the authors saw signs of arrested growth in the fossil bones. The bones also indicate strongly that K. kely was bipedal, like T. rex and the theropods.
To place this individual in the phylogeny of dinosaurs and their ancestors, the authors did a computer analysis of 422 characters derived from these bones, and K. kely fell out in group B of the phylogeny below, which includes the dinosaurs and the pterosaurs (the relative size of this tiny species is shown to the right). I’ve put a box around K. kely.
B is the base of the Ornithodira, the group that gave rise to all dinosaurs and pterosaurs, and you see that K. kely is an early (“basal”) member of this group
Here’s a reconstruction of K. kely, eyeing a beetle, from Science Alert;(artist’s impression by Alex Boersma):
Now the diminutive size of this creature doesn’t mean that the common ancestor of all dinos and peterosaurs was this small. But it does imply that the ancestor of those groups, which falls out in a “reconstruct-the-size” analysis, was smaller than we thought. K. kely itself could have been the result of a “miniaturization event” in which a somewhat larger ancestor produced some tiny descendants. The estimated size of ancestral Ornithodiran is estimated fo be about 13.3 cm, or about 5.3 inches tall, and the ancestral species of the Dinosauromorphs, which includes dinos and birds but not pterosaurs, is even smaller, about 6.5 cm (2.5 inches)!
What are the implications of this beyond showing that the ancestral dino and ancestral dino/pterosaur were likely a lot smaller than we thought? Well, first of all, we have no idea why these early creatures were so small. My own guess is that since insects had already evolved, there was an “open niche” to specialize in eating them, and if you want to make a living as a terrestrial reptile eating insects, you can’t be the size of a T. rex.
The authors note that the small size of this species (and probably its close relatives) accounts for the absence of ornithodirans in Early and Middle Triassic faunas, for small creatures have tiny, fragile bones that aren’t easily preserved. In fact, our best knowledge of early Ornithodirans previously came from sediments in Argentina whose nature allowed for the preservation of small animals.
Finally, the authors speculate that these small species would have a problem with heat retention, since they were ectothermic (“cold blooded”). Small creatures have a higher surface area/volume ratio than larger ones, which means more heat lost by radiation. Thus, suggest the authors, the filaments covering the bodies of some dinos and pterosaurs—which might have been homologous to feathers that eventually covered the theropods—would have been useful as insulation. This sounds good, but of course there are plenty of extant small insect-eating reptiles, like geckos and anoles, that make a fine living without feathers. But it would still be useful to look at these early, small species to see if there is any evidence for filamentous body cover.
This new paper in Nature (click on screenshot, pdf here, reference at bottom) has the potential to be the big human-paleobiology story of the last several years. It reports finding human occupancy of a high-altitude cave in Mexico during the last glacial maximum (LGM): about 26,000 years ago. And that, say the authors, implies that humans have been in the New World since more than 30,000 years ago—more than doubling the time we thought they’d been here. Previously, the best guess was that humans crossed the Bering Strait from Siberia about 15,000 years ago, and then spread through the Americas.
Click on the screenshot below to get the paper (free through the legal app Unpaywall, or you can make a judicious inquiry).
Before we accept these results as overturning the received wisdom about humans in the New World, though, there has been some criticism of the paper, as you can see in a precis in Science by Andrew Curry.
The cave where the finds were made sits atoop a remote mountain in the Mexican state of Zacatecas, about 2,740 m high, and has been studied since 2012. Although dry and barren now, it was thought to be verdant during the LGM, with water, plants, and plenty of edible animals nearby. Researchers worked there for a month at a time, camping in the cave and hauling water and food by donkey from the nearest town.
What made the researchers suppose that the cave was occupied by humans were several things, most prominently 2000 specimens of what looked like sculpted tools. Here’s a figure showing some of these putatively manufactured objects:
Now I would have thought that by now paleoanthropologists would be able to distinguish non-human rock artifacts from real, chipped tools, but apparently that’s not the case. As one critic says in the Science writeup:
Critics point out that the tools are simple and don’t resemble other toolkits from the Americas, raising the possibility they’re the product of natural breakage. “They look like they could be artifacts, but why aren’t they found anywhere else in the landscape?” wonders David Meltzer, an archaeologist at Southern Methodist University. The tools’ consistency is also remarkable, he says. “If these tools are real, why are they only found—so far at least—in this one spot over a 10,000-year period? Humans adapt and adopt new technology.”
The tool-making conclusion, at least, must remain tentative. There was also burned wood that was radiocarbon dated, implying human campfires, but the critics again say that this could derive be from “wind-blown” wildfires. The researchers also used OSL dating of quartz from the sediments, which tells you when the mineral was last exposed to light, ergo when it was laid down.
Finally, the researchers trawled the cave for DNA, which they could sequence to see what kind of animals and plants were there. The fauna included bats, mice and other rodents, marmots, goats, and sheep, as well as birds, though this could have come from more recent occupancy. Plant DNA included forest species like spruce, pines, grasses, and palms. The disappearance of cold-adapted species and forest trees that gave way later to Joshua trees and grasses suggests that the sediments in the cave did go through the late Glacial Maximum, which was followed by a period of dryness.
Notably, no human or humanoid DNA was found in the cave, which would have gotten people much more excited about this find.
How strong is the evidence for human presence in the Americas beginning 30,000 years ago? The 30,000 years is a guess by the authors, derived from guessing how long it would take humans to get to a 26,000-year-old cave residence in Mexico after crossing from Siberia. In terms of the age of the cave itself, that seems reasonable, but the evidence for human occupation is largely the “tools”, and their provenance is doubtful. And if humans inhabited the cave continuously for millennia, as the authors suppose, then why wasn’t human DNA found there? My judgment, and I’m a tyro here, is that the evidence is intriguing but not terribly strong. A lot hinges on whether the “tool-like” stone artifacts really were chipped by hominin hands.
On the other hand, the Science article says that there is a cave in the Yukon that’s yielded dates as old as the Mexican cave (about 24,000 years), but although it contains thousands of animal bones, there are “few stone tools or cut marks.” But other researchers are beginning to think that people came to America earlier than we thought, and could have spread quickly by traveling along the West coast by boat, avoiding the largely frozen interior. Here’s a tweet (h/t: Matthew) showing sites where there could have been earlier habitations:
News & Views: Two studies in Nature report evidence that the initial human settlement of the Americas happened earlier than is widely accepted. Some of the evidence suggests settlement began at least 10,000 years earlier than was generally suspected. https://t.co/OBuIQzBI7v
How good are the dating methods? From what I read, they seem fairly reasonable, and they used at least two methods that give about the same dates. The question is not how old the cave is, but whether humans lived there and made the tools and charcoal.
What happened to the people? Part of the reason we think humans have been in the New World for only 15,000 years is not just evidence from habitation, but from DNA of Native Americans (note: there are some older estimates). If that’s the case, why doesn’t the DNA give a consistent age of 30,000 years from when Native Americans branches off from East Asians? One possibility is that the early arrivers went extinct without leaving descendants, so we wouldn’t find a genetic signature of their existence. Given that some paleoanthropologists see evidence of an early arrival from other sites, like that in the Yukon, the possibility of extinction seems unlikely.
All in all, this is an exciting finding, and may well be right, but we’ll have to let the experts fight it out.
Excavating in the cave, a photo from the Science precis:
Do send in your wildlife photos, as the tank continues to empty. Today’s batch, from Robie Mason-Gamer, is unusual because it comprises fossils. Robie’s notes are indented:
This message stretches the definition of “wildlife” somewhat, back to a swampy Carboniferous community that existed over 300 million years ago. I hope the text is not overly long.
The Mazon Creek Formation in northeastern Illinois is a special place: a Carboniferous fossil site with unusual abundance and preservation, known as a lagerstätte. The fossils, estimated to be about 309 million years old, are extraordinarily well-preserved inside ironstone nodules called concretions.
I visited Mazon Creek in 2007, on a field trip associated with a botanical conference in Chicago. I recovered about 10 nodules of varying sizes and shapes, but none that I cracked open had anything interesting inside. It was disappointing, like opening a present and finding it empty. I still have a few unopened nodules; I guess I get more enjoyment from what might be in them than what is probably actually there.
However, I did end up with a few decent fossils. Field trip participants each received some de-accessioned Field Museum specimens, complete with ID labels. My other source was more unexpected. I used to hang out in a little local bar (since closed) with a group of friends. There was a semi-regular customer whom I came to recognize by sight, but did not otherwise know. One day, from across the bar, I saw him pull a Mazon Creek fossil out of his pocket and examine it. This startled me out of my usual reticence: “Hey! That looks like a Mazon Creek fossil!” He was interested in talking about it, and after a conversation, he went out to his car and came back with a box of 10 opened nodules, and gave them to me.
There are many seed ferns (Pteridospermatophyta) at Mazon Creek. Seed ferns comprise multiple extinct lineages of plants with fern-like leaves, but they reproduce through seeds (rather than spores, like true ferns). Many of them were large trees. This one is labeled as Alethopteris serli; here are the positive and negative halves of the nodule, and a closer look at the leaf surface. (Length 3 in/8 cm):
This fossil, labeled Macroneuropteris scheuchzeri, is a single leaflet from the large frond of an arborescent seed fern. (Length 4.25 in/10.75 cm)
Fossil horsetails are also common at Mazon Creek. All extant horsetails are herbaceous, but some extinct lineages included large trees. The top specimen is labeled Annularia stellata; the bottom one (unlabeled) is either that or some other Annularia. (One confusing thing about plant fossils is that—because different plant parts are often separated during fossilization—paleobotanists apply different taxonomic names to fossils of different plant parts, none of which need be the name of the actual organism. Annularia is an example of a “form genus”—it’s the name of this particular form of fossil leaf whorl, which likely came from a tree-horsetail in the genus Calamites.) (Width 1.5 in/3.25 cm)
Last, here is a true fern. The top left specimen (with closeup on the right) is labeled as Pecopteris unita. Again, this is the “form” name of the leaf fossil; the organism itself was likely a large tree fern of the extinct genus Psaronius. The lower left specimen (unlabeled) might or might not be the same thing; there are lots of Mazon Creek fern and seed-fern leaves that look alike to me. (Length 4.5 in/11 cm):
One of the big mysteries of paleobiology is where complex life (i.e., animals) came from, and what the earliest animals looked like. The first traces of life that we have go back about 3.7 billion years ago, but those are cyanobacteria (the so-called “blue green algae”). The first “true cells”—unicellular eukaryotes, go back to about 1.8 billion years. But then there’s a huge gap of 1.2 billion years before we have the first traces of more complex multicellular life (putative sponges, jellyfish, and ctenophores) near the beginning of the Ediacaran period (571-541 million years ago). That fauna contained a number of bizarre and enigmatic forms.
Many of those forms went extinct without issue at the beginning of the Cambrian (about 545 million years ago). But since there was not a separate and later creation that led to modern animals (we know this from molecular data), some of the earlier fauna alive during the Edicarcan period must surely have been the ancestors of modern animals. Today’s paper involves a search for the earliest representatives of the Bilateria, a group that includes all but the simplest animals. I’ll let Wikipedia tell you what the Bilateria are:
The bilateria/ˌbaɪləˈtɪəriə/ or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and a back (ventral-dorsal axis). Nearly all are bilaterally symmetrical as adults as well; the most notable exception is the echinoderms, which achieve secondary pentaradial symmetry as adults, but are bilaterally symmetrical during embryonic development.
Most animals are bilaterians, excluding sponges, ctenophores, placozoans and cnidarians. For the most part, bilateral embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm. Except for a few phyla (i.e. flatworms and gnathostomulids), bilaterians have complete digestive tracts with a separate mouth and anus. Some bilaterians lack body cavities (acoelomates, i.e. Platyhelminthes, Gastrotricha and Gnathostomulida), while others display primary body cavities (deriving from the blastocoel, as pseudocoeloms) or secondary cavities (that appear de novo, for example the coelom).
So, in the fossil record, paleobiologists have been looking for animals that are bilaterally rather than radially symmetrical, with a front and back (ergo a head and anus with a gut between them), and with evidence of a coelom (body cavity). Kimberella, found in both Russia and Australia (see fossil below), is a putative bilaterian, but people still argue about whether it may be a coelenterate (jellyfish relative), animals that aren’t bilaterians. (There are also “scratch marks” associated with it, suggesting that it had a radula and may have been a kind of mollusc, which are bilaterians:
Now, however, in a new paper in the Proceedings of the National Academy of Sciences (USA), four researchers have found what seems to be an unambigous fossil of a bilaterian, as well as the burrow that it was probably making as it tunneled underneath the shallow-sea sand, feasting on microbial mats of bacteria. You can access the paper free by clicking on the screenshot below, or get the pdf here (reference at bottom).
Several of these creatures, named Ikaria wariootia, are found near “trace fossils”: tracks or burrows that were given the name Helminthoidichnites (traces of animals, like their paths, were given scientific names in the absence of the animal who made them). They are dated—using igneous material like ash, near the sedimentary layer)—to about 560-551 million years ago (dating done by correlating strata with dated similar strata in Russia).
The fossils, both animal and its tracks, are in fine sandstone from the Nilpena beds in South Australia, where fantastic Ediacaran forms have been found. And what they show are small bilaterian-looking animals ranging in size from 2-7 mm (0.1-0.3 inches): about the size of a grain of rice. Moreover, at least one of them was associated with a trace burrow of about the size that would be made by such a creature. That one’s in the photo below. (The animal shown below was probably displaced from the burrow by movement of the substrate.) The scale bar to the right is 1 mm. Note that the burrow shows lateral “zig zags”, as if some animal was humping itself along right beneath the sand.
And there are many specimens of the creature visualized by laser scanning. They show a creature with a broad end (presumably the front) and a narrower end (presumably the rear), with all of them showing relatively similar ratios of length/width, suggesting this is not some geological artifact but a real animal. Note the broad front end (burrowers are larger in front than the rear when there’s asymmetry), as well as the bilateral symmetry:
I’m not a paleontologist, but these data and photos are pretty convincing that here we do indeed have a very early bilaterian, perhaps one close to the “common ancestor” of all animals save the few taxa listed above. (We cannot know, of course, whether this is the “common ancestor” of bilateral animals, even though the hyperventilating media suggests otherwise. But it’s certainly something that is close to what that common ancestor might have looked like.)
The evidence of bilateral symmetry is manifest in the fossils. The nature of the furrows in the sediment probably made by this creatures suggest to the authors that it has a coelom (body cavity) and musculature, while the “V-shaped transverse ridges” in the burrows suggest that it had “peristaltic locomotion” like earthworms:
Peristaltic locomotion is a common locomotor pattern in elongated, soft-bodied invertebrates, particularly in segmented worms, such as earthworms. It involves the alternation of circular- and longitudinal-muscle-contraction waves. Forward movement is produced by contraction of the circular muscles, which extends or elongates the body; contraction of the longitudinal muscles shortens and anchors the body.
That is, the movement isn’t smooth but is jerky, which would produce the ridges. To the authors, this implies a “potentially modular body construction” with the necessary muscles. The authors also suggest that “sediment displacement and scavenging reveal that Ikaria likely had a coelom, mouth, anus, and through-gut” (all traits of Bilateria).
I’ve checked with one early-life paleontologist, who says that yes, this is pretty good evidence for an early bilaterian, and the only good evidence in which a putative early bilaterian is associated with its tracks in the sediments. The authors of the paper provide a reconstruction of Ikaria and its track in the paper, which, with the color added, makes it look a bit penis-like:
This is a pretty important discovery, I think, as it gives us a glimpse of what may be the ancestor of all bilaterally symmetrical animals, including, of course, us.
Sadly, as I noted above, some news organizations say it is the common ancestor, and we have no way of knowing that. Here’s one of the miscreant organizations (Phys.org), which gets most of the stuff right but has a very misleading headline (click on screenshot). And you can blame the news site of the University of California at Riverside, which provided the article that Phys.org copied word for word.
Always be wary when you see in the news that a “common ancestor” or “missing link” has been identified. In this case, the very university that was home to the first author Scott Evans badly screwed up the significance of the finding. We have no fricking idea whether I. wariootia is the “ancestor of all animals”, a claim that is flat wrong in two senses. First, sponges, coelenterates, and other radially symmetrical fauna are “animals”, but not descendants of this wormy creature. Second, we have no idea whether I. wariootia is even the ancestor of “all bilaterians.”
Now the authors themselves don’t make this claim; the blame rests on the media and on the UCR publicists, but one would think that the UC Riverside publicity department would run the headline past the researchers.
Well, never mind; it’s still an important finding and a really lovely one.
On March 12, I wrote about the new Nature paper describing the fossil of Oculudentavis khaungraa, identified as a tiny (2-gram) dinosaur/bird found in Burmese amber. But the very next day I had to hedge the results after reading Darren Naish’s Tetrapod Zoology post, not only on humanitarian grounds (the amber used in the study may be “blood amber”, used to fund the military), but, most important for the science, because other paleontologists started doubting that this fossil was indeed that of a theropod. As Darren notes,
“. . . a number of experts whose opinions I respect have expressed doubts about the claimed theropod status of the fossil discussed below and have argued that it is more likely a non-dinosaurian reptile, perhaps a drepanosaur or lepidosaur (and maybe even a lizard).”
The article below, translated from the Italian by Google (click on screenshot), was called by my attention by reader Gerdian de Jong who wrote this to me:, “The respected paleontologist Andrea Cau writes in his blog Theropoda.blogspot why Oculudentavis is not a bird or theropod and that wider analysis points to stem-Gekkota.”
A to-scale reconstruction by Darren. Note that the ruler is in centimeters, not inches (2.54 cm/inch, so the 10-cm ruler is only about four inches long.
I’ll call attention to other articles/critiques about this specimen as they come to my attention. At any rate, right now it’s unwise to regard this as a theropod dinosaur that was also avian.
Click on the screenshot to read in Italian or get a translation. I’ll provide a summary of the translation (indented) below.
After reading the study, and observing in detail the navigable 3D model of the skull, produced by the authors, I believe that the interpretation proposed by Xing et al. (2020) is very problematic. Oculudentavis in fact has numerous anomalous characteristics for a bird and even for a dinosaur. And this makes me doubt that it is classifiable within Dinosauria (and Avialae).
Absence of anti-orbital fenestra.
Quadrate [bones] with large lateral concavity.
The maxillary and posterior teeth of the maxillary extend extensively below the orbit.
Dentition with pleurodon or acrodont implant.
Very large post-temporal fenestra.
Spoon-shaped sclerotic plaques.
Coronoid process that describes a posterodorsal concavity of the jaw.
Very small size.
Oculudentavis is much smaller than any other Mesozoic avian discovered so far. Its dimensions are comparable to those of the skulls of many small squamata found in Burmese amber.
In conclusion, there are too many “lizard” characters in Oculudentavis not to raise the suspicion that this fossil is not a bird at all, let alone a dinosaur, but another type of diapsid, perhaps a scaled lepidosaur, if not possibly a specimen very immature than some other Mesozoic group (for example, a coristodero).
If I had to bet money between the hypothesis that it is a very small bird with unusual “lizard” convergences and the hypothesis that it is a very immature skull of a non-dinosaurian reptile, I will point the second.
To read more about why the traits in bold are more indicative of a lepidosaur than a dinosaur, read the original article.
But what are lepidosaurs? They are a monophyletic group of reptiles that contains the extant snakes, lizards, tuataras and worm lizards (“legless” lizards). “Monophyletic” means that the group contains all descendants, living or extinct, from a common ancestor. Lepidosaurs do not include dinosaurs. Here’s a family tree from Quora, which shows that dinos aren’t within the Lepidoauria, as the latter group is over on the right.
Now the fact that this fossil may not have been a theropod dinosaur but a lepidosaur, like a lizard, doesn’t make the original results uninteresting. In fact, to me it makes them more interesting. First, it shows that there could have been convergent (independent) evolution to birdlike forms in both dinosaurs and lepidosaurs (perhaps from a lizard-like ancestor). That would be stunning.
Further, it shows that regardless of whether the species in amber was a theropod or a lepidosaur, there may have been a whole radiation of miniature, bird-like creatures from an entirely different group of reptiles. Whether that was true depends on finding more specimens. Since these are small and fragile, it’s unlikely that they’d be found in anything other than amber. We shall see.
In the meantime, I hope the mainstream press, which touted this specimen as a form of dinosaur, at least gives a clarification. While the messy details of anatomy are unlikely to interest the public, at least they’ll know that science is an ongoing process, and what is regarded as “true” is provisional, only becoming less provisional when more data are gathered. Right now we have but a single specimen of this type.
Yesterday I wrote about the discovery, published in Nature, of a very small theropod dinosaur that appeared to be part of the radiation of early birdlike dinos. It was tiny and had features so unusual that it couldn’t really be placed in a phylogeny. The creature was named Oculudentavis khaungraae and was remarkably well preserved (well, just the head) in Burmese amber dated at 99 million years ago.
I’d like to issue an addendum after reading Daren Naish‘s post on his well -known website Tetrapod Zoology (h/t Dom). As Naish is a vertebrate paleontologist, he knows a ton more than I about this stuff, and in fact is able to evaluate its phylogenetic position. You can read his post by clicking on the screenshot below:
There are two issues raised by Daren. The first is whether this really is a feathered, avian-like theropod. The second is the ethicality of using specimens from Burmese amber. We’ll take the science first, with quotes from Naish’s piece indented.
After consulting with various experts in the field, Naish says this:
. . . . a number of experts whose opinions I respect have expressed doubts about the claimed theropod status of the fossil discussed below and have argued that it is more likely a non-dinosaurian reptile, perhaps a drepanosaur or lepidosaur (and maybe even a lizard).
That might explain why some of the fossil’s features, like the bulging of the eyes from the head, are more lizard-like than theropod like. Here’s one reconstruction of the creature by Mette Aumala, reproduced by Nash (I’ve also obtained permission to use it):
The Tetrapod Zoology piece has several drawings and reconstructions of the creature by Naish, and you can see them there.
Naish adds this:
At the time of writing, this proposed non-dinosaurian status looks likely and a team of Chinese authors, led by Wang Wei, have just released an article arguing for non-dinosaurian status. I don’t know what’s going to happen next, but let’s see.
If it’s not a theropod, and not a feathered relative of early birds, this would markedly change its evolutionary significance. It wouldn’t make the fossil insignificant, but would divert us onto a track about the possibility of a bunch of miniature reptiles (and maybe amphibians) that we don’t know about because they’re too small and fragile to be preserved.
If it is a theropod, Naish is excited by the possibility that many early birds may have been as tiny as this creature (Naish estimates it as about 9 cm long, or about 3.5 inches). Finally, if it was a theropod/bird, Naish speculates, following the authors, that it could have foraged for invertebrates on the forest floor, or even on “tiny vertebrates, like a dinosaurian shrew.”
At any rate, after reading Naish’s article we need to step back and not decide, prematurely, that this was an early avian creature or even a descendant of theropod dinosaurs. The mainstream press, unwilling to investigate as deeply as Naish, missed the possibility that this may be not a theropod but possibly even a non-dinosaurian reptile.
Second, there’s the issue of the amber. Naish gives three links to articles about why studying specimens from Burmese amber might be illegal (one of the links goes to a paywalled New Scientist article, but the other two are below). The issues are these:
1.) Much of the recent informative, specimen-containing amber has been smuggled out of Myanmar illegally into China, depriving Myanmar of its paleontological heritage.
2.) The Burmese military and paramilitary could derive funds from these sales, so the money could be use to fund their wars against ethnic minorities like the Rohingya or Kachin.
3.) The workers aren’t treated particularly well (for example, if there’s an accident, they have to pay for their own healthcare).
4.) The fossils may remain in private hands, like those of Chinese collectors, and thus aren’t available for other scientists to study. Some journals won’t public analyses of specimens that aren’t available to other scientists (see video below).
5.) Finally, not an ethical issue but a scientific one. Many of these specimens simply can’t be accurately dated because they’re dug out of the ground in areas off limits to those who could provide dates. The specimen used in the Nature paper was dated at 99 million years old, but that’s based on locality information, not on dating the amber itself or the surrounding strata. And the locality information may be dubious as well. Accurate dating is of course essential to place the fossil in its evolutionary context.
Here are two links about the ethicality of describing specimens from Burmese amber; they are given by Daren, and I give two short extracts and the links:
But much of the fossil-rich amber is mined in Myanmar, a country recently ordered by the United Nations International Court of Justice to protect its Rohingya Muslim minority against genocidal acts. The mining and sale of the amber may also be a source of profit for the country’s military. A report published last year in Science Magazine detailed how the amber is mined in a state where Myanmar’s military has long fought another ethnic minority, the Kachin, and how amber gets smuggled into China, where it can fetch high prices, potentially fueling that conflict.
These concerns are leading more scientists, especially in Western countries, to shun the use of this amber in paleontological research.
“Ever since the Rohingya crisis, I’ve boycotted the purchase of Burmese amber, and have urged amber colleagues to do the same,” said David Grimaldi, a paleontologist and the curator of amber specimens at the American Museum of Natural History in New York.
From Science:(article noted above; long and worth reading):
But as much as Burmese amber is a scientist’s dream, it’s also an ethical minefield. The fossils come from conflict-ridden Kachin state in Myanmar, where scientists can’t inspect the geology for clues to the fossils’ age and environment. In Kachin, rival political factions compete for the profit yielded by amber and other natural resources. “These commodities are fueling the conflict,” says Paul Donowitz, the Washington, D.C.–based campaign leader for Myanmar at Global Witness, a nongovernmental organization. “They are providing revenue for arms and conflict actors, and the government is launching attacks and killing people and committing human rights abuses to cut off those resources.”
Here’s a really nice Science video from last May on the general issue of specimens in amber, what knowledge we’ve derived from them, and the ethical problems of studying Burmese amber.