Category: fossils

A transitional fauna shows that the “Cambrian explosion” was happening before the Cambrian

April 5, 2026 • 8:30 am

The Cambrian Period, beginning at 538.8 Ma (million years ago) and lasting about 52 million years, is famous for marking the transition from simple and largely unicellular animals to, beginning at the period’s inception, representatives of modern groups.  This apparently rapid onset of modern forms of multicellular animals constitutes the famous “Cambrian Explosion.”

The Cambrian was preceded by the 96-million-year-long Ediacaran period, extending from 635 million years ago to the beginning of the Cambrian. The Ediacaran fauna, consisting of some multicellular animals of unknown affinity and things looking like members of some modern groups like cnidarians (represented today by jellyfish, corals and anemone). But most of the Ediacaran groups appeared to have died out at the end of the Ediacaran, and for unknown reasons.

The boundary between the Ediacran and the Cambrian thus marks a major transition in animal life.   Many of the “modern” groups that first arose during the Cambrian don’t have apparent ancestors in the Ediacaran, and so those modern groups were thought to have evolved almost instantaneously (in geological time!). But surely modern groups had ancestors during the Ediacaran: unless you’re a Biblical fundamentalist, you realize that ancestors of modern groups had to have existed well before the Cambrian explosion.

Now a paper in Science, based on a fossil group called the Jiangchuan Biota that spans the period from 559-534 million years ago, shows that representatives of “modern” groups seen in the Cambrian explosion were indeed present in the late Ediacaran, pushing back the time of origin of modern phyla 4-5 million years.  This conclusion was possible because of the remarkable preservation of the animals (and some algae), all present as carbonaceous films on rocks—the same kind of films (presumably due to rapid burial) that enabled us to see the remarkable Burgess Shale fauna of the middle Cambrian. The new find was in the province of Yunnan in Southwestern China.

You can see the paper by clicking the screenshot below, reading the pdf here, or reading the shorter blurb at an Oxford University sit. at the bottom. All photos below are taken from the paper.

I won’t go into all the terminology involved in identifying the groups but will show a few fossils from the paper strongly suggesting that some “modern” groups arose in the late Ediacaran.

First, an anomalous animal that appears to be some kind of worm, but one with a “holdfast” disc on its butt. We don’t know what this one is, but it has oral projections or tentacles. The disc is very clear:

Another wormlike animal (note that these are small: a few millimeters) having a clear oral region. Again, we’re not sure what this is, but the preservation as a carbon film is remarkable:

A deuterostome (animals where the first opening in the embryo becomes the anus rather than the mouth), a group thought to have appeared in the Cambrian but here seen in the Ediacaran: this one resembles  Herpetogaster, known from the early Cambrian which, according to Wikipedia, “possessed a pair of branching tentacles and a tough but flexible body that curved helically to the right like a ram’s horn and was divided into at least 13 segments”. This one, like Herpetogaster, has tentacles (at leat four) and a stalk.  It’s interpreted as a relative of acorn worms, relatives of modern echinoderms which are hemichordates, the closest living group to modern chordates (animals with notochords and a dorsal nerve chord, which include all vertebrates).

The one below,described in the paper as “Margaretia-like animal now known as a dwelling tube for an enteropneust hemichordate worm”. It’s also described as having “regular, oval-shaped holes running along its length”. Again, we see what is likely an early hemichordate, showing that the relatives of modern chordates seem to have been present several million years before the Cambrian explosion began.

The one below is identified as a ctenophore, or comb jelly, a phylum of early animals previously known only from the mid-Cambrian. “OS” stands for “oral skirt”, described as “a specialized, often scalloped, muscular, or rigid structure surrounding the mouth, primarily found in Cambrian-era fossil comb jellies such as Ctenorhabdotus and Thalassostaphylos. Unlike modern ctenophores, these ancient species used the skirt for feeding, potentially to engulf large prey.”

Finally, this animal is thought to be an early cnidarian with tentacles and a holdfast (HF). Although one form identified as a cnidarian had already been recognized from the Ediacaran, here we have another that’s different, showing a radiation of cnidarians before the Cambrian.

These fossil data support already-existing molecular data suggesting that animal groups had already evolved and diversified before the Cambrian, though until now no fossils, or only a few suggestive fossils, were known.

The authors’ summary below, though written in scient-ese, basically says that a major radiation of animal phyla had already begun before the Ediacran/Cambrian boundary, but we did not know about it because the conditions for forming this kind of trace fossil, requiring rapid burial in marine sediment (and subsequent finding by investigators!) were infrequent:

The new Jiangchuan animal fossils, dominated by bilaterians of apparently diverse affinities, with rarer fossils more typical of late Ediacaran deposits, could be described as a “Cambrian-type” assemblage from the late Ediacaran. A dominantly bilaterian assemblage from the late Ediacaran may not have been discovered until now as a result of the paucity of carbonaceous compressions from this time, hinting at a broader taphonomic bias (51).

If you want a short, readable summary of the importance of this fine, click below to read a shorter summary from Oxford University.

My Boston Globe op-ed about the fallacies of “de-extinction”

May 1, 2025 • 9:40 am

Yes, we’ve all heard that three white dire wolves are running around at some secret location, and we’ve heard about Colossal Biosciences, a Dallas-based firm that, it says, is going to fix the “colossal problem” of extinction. The main way they propose to do it—and the bit that’s gained all the attention—is to “de-extinct” animals by finding fossil DNA of extinct species, sequencing some bits that presumptively code for a few of their traits, and then, using CRISPR, put those bits into the fertilized eggs of a living species that’s a close living relative. That way you get a hybrid animal, which is by necessity genetically about 99.9% or more of the living species but with a few traits of the extinct species. Then–voilà–you can say you have “de-extincted” the species. The misleading hype involved in that verb is obvious.

For example, dire wolf genes were extracted from fossil specimens, and 15 of those bits were edited into 14 genes in the fertilized egg of a grey wolf (they actually put in 20 bits, but 5 of those involved mutations existing in dogs and wolves.  Since the grey wolf genome has 2.4 billion bases, you can see that only a tiny bit of dire wolf genome went into the wolf genome. The edited wolf egg was then transferred into surrogate dog mothers, and the mostly-grey-wolf hybrids were extracted by caesarian section (the dogs weren’t killed).  Voilà: they got three largish white wolves that they called dire wolves.  (The white color, by the way, did not come from the dire wolf DNA bnt from dog or coyote mutations. They edited whiteness into the hybrid because dire wolves were white when they featured, much larger, in the t.v. show Game of Thrones. We don’t know what color the dire wolves really were, but I doubt it was snow white. They did not live in snowy areas.)

The Big Project of Colossal, however, is the “de-extincting” of the woolly mammoth, a project I’ve discussed on this site before. (The dodo and thylacine are also on tap to be edited back to life.) Colossal promises that we’ll have faux mammoths—which paleobiologist and mammoth expert Tori Herridge denigrated as “elephants in a fur coat” because a few of the changes will involve hairiness—by 2028. Good luck with that!

There are many problems with the “de-extinction” scenarios that have nevertheless raked in $435 million for Colossal thanks to donors like Paris Hilton and Tiger Woods. And although other scientists like Tori and Adam Rutherford have described some of these problems, I decided to summarize them all in one place for American readers.  Thus my op-ed in today’s Boston Globe, which you can find here, though it may be paywalled. Clicking on the headline below, however will take you to a non-paywalled archived version of the text.

The article summarizes four major problems with “de-extinction”, which you can read in the article.  The Globe had a special piece of art made to illustrate my article, and I absolutely love it (see below, and notice the hook).  The illustration is the creation of Patric Sandri, a Swiss artist. Thanks to the artist and especially to my editor, who was perhaps the most amiable and easiest op-ed editor I’ve ever worked with.

Enjoy (unless you work for Colossal)!

Illustration by Patric Sandri for the Boston Globe

Readers’ wildlife photos

July 3, 2024 • 8:15 am

Today we have a large batch of photos from neuroscientist Mayaan Levy, who documented her travels to the isle of Skye. Her captions are indented, and you can enlarge the photos by clicking on them.

“Over the sea to Skye”

Skye makes you believe in Faeries. You may find yourself gazing at the clouds and storms come and go at the whim of the Cailleach. You might avoid stepping into the swamps by Loch Coruisk worrying the Kelpie will snatch you. The Isle takes you back in time to when folks believed in magic, and for the duration of your stay, you’re allowed to give in, throw any logic or contemporary science to the bitter island wind, and indulge in this quaint fantasy.

We visited in late May 2023. I’ve been a low-key Scotophile for a while before, drawing on Hume, Robert Louie Stevenson, Braveheart, the Hogwarts express, and more recently Outlander (which is my guilty pleasure. Guilty as charged). After Skye, my Scotophilia worsened and is now considered incurable.

Skye (“The Island of the Clouds”, was connected to the Scottish mainland only in 1995 with the construction of the bridge. The only way on or off before, was by sea. The photos are from our north-bound hike on the Skye trail, spanning 80 miles, plus a Loch Coruisk circuit, totaling at about 100 miles. We took 6 days, but I wish we have had double, or even triple that time.

The ocean meets the mountains and the clouds. Taken right before Torrin.

Skye has way more sheep than people. A fun pastime while hiking was to try to guess by how much, and upon getting signal we have discovered that both of us grossly underestimated. The answer is 10-fold more sheep than people! In the 21st century! Some sheep are marked in different colors (for different owners), and they graze / sit on / sleep on the tall and steep cliffs. Throughout the Island you can see old stone walls the crofters have erected ages ago.

Elgol is famous today due to its role in politics back in the 18th century, and this role was just to be a clandestine location, in the middle of nowhere and difficult to approach. The site in question is Bonnie Prince Charlie’s cave, where he hid from British government forces after the defeat of the Jacobite army in Culloden (1745).

Elgol Beach – it took scaling some class 3 sea cliffs to get here:

Beadlet Anemones (Actinia equina) – if I wasn’t in Neuroscience I would be a Marine Biologist. These creatures have 192 tentacles (so cool!), and they are sort of immortal (please weigh in on this) or at least have extremely long lives:

Elgol beach is rich in fossils. I have no clue what left this impression fossil:

One of my favorite areas was hidden Loch Coruisk and the Black Cuillin – a semi-circle of pitch black, ominous mountains. Multiple legends and myths surround the Cuillin, and I’m afraid I can’t do them justice. If you’re interested, some can be found here.

A view southwest of Loch Coruisk and the sea:

The peaks of the Black Cuillin tower in the distance over Sligachan 19th century bridge:

Our next stop was Portree (probably from “Port of the king” port + re as in many Latin languages), the capital of Skye, where there are more people than sheep but fewer residents than tourists. We were hungry, and luckily Portree is the place to get authentic fish and chips. Now, by fish I don’t mean small mackerels in newspaper, I mean a foot long, deep fried haddock. Chips are similar to what Americans call fries, except the Scottish ones tend to be very soggy as opposed to crispy. To each their own (ugh).

Is it a phone booth? Is it a library? (on the outskirts of Portree):

Portree harbor:

Fish farming just north of Portree. Perhaps this was home to our lunch not so long ago:

From Portree we hit the woods. There aren’t many trees on Skye, and it’s not clear to me exactly why. The island is at the mercy of the elements, with strong winds even in the summer which naturally will strip the land. But it may also be the case that humans deforested the isle to raise livestock.

I told you Faeries live here:

Small emperor moth (Saturnia pavonia) – common throughout Europe but is actually the only one from this family to inhabit the British Isles:

Now we start climbing for an epic stretch starting at the Storr, walking on the cliff edges of the Trotternish ridge. The ridge, including the Old man of Storr, was created when lava erupted from beneath, causing the softer rock to slide down about 60 million years ago. Skye’s geological origins are partially volcanic; Land that was to become the British Isles was once upon a time landlocked in pretty much the middle of Pangea. When the super-continent split and multiple fault lines were created, heat generated beneath led to a series of mini volcanic eruptions. Indeed, these events were part of a period of increased volcanic activity all over Earth, which some hypothesize might have been the true cause of the K-Pg extinction (aka the Deccan Traps theory). Disclaimer: not my field, and I have no skin in this game, but the so called “Dinosaur wars” have been fascinating from a history and sociology of Science perspective.

I can’t go to Skye and not have a photo of this landmark: Ladies and Gentlemen, the Old man of Storr. On the right side of the photo is the Storr itself – the tallest formation on the ridge. On the left side of the photo you can see that there are several steps or levels of cliffs until the final drop to the ocean:

The north-most point of the Trotternish ridge, looking south:

Volcanic sea cliffs:

Setting up camp for the final night on Skye. We’ll be back:

Readers’ wildlife photos

June 18, 2024 • 8:15 am

Neuroscientist Mayaan Levy has sent in a second batch of photos, which are below. I’ve indented her captions and IDs, and you can enlarge the photos by clicking on them.

Come on, feel the Illinoise!

During my years in Chicago I traveled out-of-state often. I longed for the mountains: the Rockies, the Cascades, the Sierra Nevadas, the Smokies, the Whites (NH) and the Catskills. On busy weekends or when we ran out of money, as it tends to happen to grad students, we would stay home in flat yet wondrous Illinois. Blasting jazz or Sufjan Stevens in my then-boyfriend’s (now-husband) ’99 Chevy Lumina with magenta velvet seats, we’d hope to get somewhere where we would see some nature. Only when we left Chicago I realized how much I miss Illinois woods. This is a small, nostalgic tribute.

Our favorite destination was probably Shawnee national forest, which was quite a stretch for the Chevy. Here are some Shawnee turtles:

Box turtle (unsure whether Terrapene carolina or Terrapene ornata, I believe the latter is considered threatened):

Midland painted turtle (Chrysemys picta marginata) – Illinois State reptile!:

 Common Snapping Turtle (Chelydra serpentina) hanging out on trail:

What I find fascinating about turtles is their brumation: I get it that metabolism slows down considerably like in hibernation, but how do they deal with the anoxia underwater?

Shawnee also has world-class mushroom forging. The place is a mycologist’s paradise. As amateurs, we were always after choice edibles – fry them in butter, add them to risotto, throw them into Chicago style stuffed deep-dish. Despite eating nuts, seeds, fruit and eggs, I find it quite weird sometimes that when we eat mushrooms we actually eat their reproductive organs.

Black morels (Morchella elata). Spotted in early April, they are among the first mushrooms to pop up, and boy, are they tasty. If you’ll be nice in the comments maybe I’ll disclose the exact location. While I’ve been told to never eat morels with booze (you’re welcome to weigh in on this if you know more), I’ve seen many moonshiners and rednecks with beers in hand forage for them:

Pear-shaped puffballs (Apioperdon pyriforme). Edible as well, but when mature the puffballs burst and spray spores right into your face:

We think these are a type of honey mushrooms (Armillaria mellea), but we’re not sure. Please let me know in the comments if you can identify:

An epic chanterelle (Cantharellus cibarius) haul from Shawnee in early July 2020. They are my favorites but they are not fun to clean. Unfortunately, this trip was cut short upon discovering scores of deer ticks on our clothes;

Moving west, the Hennepin canal, nowadays an awesome biking trip, started as an ambitious project to link the Mississippi and Illinois rivers to ship goods. It’s a really interesting piece of history, so here’s the Wikipedia page about it

As for wildlife, if you camp you’d be serenaded by frogs and toads, water birds live around, and mosquitos are unfortunately a problem.

One of the locks on the canal (it has about 30, some of them are still functioning!):

Dusk, right after rain, on the Hennepin canal:

The closest destination, and therefore holds a warm spot in my heart is Busse woods. It has a mini-lake / swamp, and I’ve often seen people there taking photos of birds. As usual, we’re after the food: mulberries, black walnuts, and:

Huge Chicken-of-the-woods spiral (Laetiporus sulphureus), a summer mushroom:

Kankakee river state park is where we’d go to put our feet in the water, look at some pretty conic shells and pretend to be pirates on an epic adventure for an afternoon. Several years ago a new pedestrian bridge was built across the river, resulting in a large pile of debris which is overlooked by most. However, rocks in this pile are rich in fossils. I’m unsure from what period exactly, but I (amateur naturalist) would guess Cambrian / Ordovician when aquatic life flourished and before the first big mass extinction. If you know more about the geology of the Illinois basin, but please share your knowledge.

Some sort of crinoid impression fossil:

Trilobite?:

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.

__________________

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

Photographs of readers

June 7, 2020 • 2:30 pm

Today’s reader photos come from Bruce Thiel, whom I met at a talk I gave in Portland, Oregon. And there he gave me one of his fantastic preparations of fossil crabs, which I cherish and keep on my mantelpiece. You can see his preparations in his “reader’s photos” here. They are fantastic.  Bruce’s words are indented.

Here I am removing matrix from a Cretaceous Avitelmessus crab from North Carolina, using a pneumatic air chisel.  After 120 hours of work, the crab is still unfinished –including 40 hours work by two previous owners.  The two crabs on the right (#13) were given to the Smithsonian Natural History Museum and on display in the “Deep Time” Exhibit which reopened last summer after a five-year remodel.  A third crab also on display is not pictured.

What started out as a retirement hobby turned into an obsession to search for crab-bearing concretions in the 30-50 million year old ocean sediments in the Pacific NW.  Refining my technique led to the challenge of seeing if I could free the claws from the rock to create more sculptural poses.  However crabs are prepared exactly as they fossilize with no “rearrangement” of claws for aesthetics.

The top second-to-the-left crab in the second picture is noteworthy in that it hosts several 33-35 MYO tube worms. Two other tube-worm infested crabs were sent to Kent State where they were studied, published and donated to the Rice NW Museum of Rocks & Minerals here in Oregon.

While hunting for fossil crabs, I stumbled upon three concretions containing bones of a large penguin-like flightless bird, a Plotopterid, that turned out to be a new genus and species, published and named Olympidytes thieli, given to the Senckenberg Museum, in Frankfort, Germany.
See more crabs and info about the prep process at: https://whyevolutionistrue.com/2014/09/21/readers-wildlife-photos-100/