Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
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):
(from paper): Anatomy of the femur and maxilla of Kongonaphon kely gen. et sp. nov. (UA 10618). (A) Right femur in anterolateral, (B) posteromedial, and (C) proximal views. (D) Right maxilla in right lateral and (E) palatal views. (F) Preserved elements in the holotype, UA 10618, presented in a silhouette of Kongonaphon. aof, antorbital fenestra; at, anterior trochanter; fht, tip of femoral head; fp mx, facial process of maxilla; ft, fourth trochanter; mx f, maxillary foramen; pf, palatine fossa; pmt, posterior medial tubercle; t, maxillary tooth. Illustrations credit: American Museum of Natural History/Frank Ippolito.
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
(from paper): Body size of early avemetatarsalian (bird line) archosaurs mapped onto a consensus supertree, based on the current phylogenetic analysis (SI Appendix) and recent analyses (22). Silhouettes are scaled to estimated femoral lengths for the labeled nodes (SI Appendix, Table S1): A, base of Avemetatarsalia (represented by Teleocrater); B, base of Ornithodira (represented by Ixalerpeton); C, base of Dracohors (Silesauridae + Dinosauria) (represented by Silesaurus); and D, base of Saurischia (represented by Herrerasaurus). Silhouettes credit: Phylopic/Scott Hartman/Mathew Wedel, which is licensed under CC BY 3.0. Silhouette of Kongonaphon to the right of the taxon label is to scale.
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:
(from paper): a, Core. b–e, Flakes; inlay in b emphasizes an isolated platform. f–j, Blades. k–o, Points. Scale bar, 3 cm. Most items are from component SC-B; d and m belong to SC-C. One Pseudotsuga sp. (Douglas fir) charcoal fragment closely associated with the bifacial preform shown in m in stratum 1223 was dated to 27,929 ± 82 uncalibrated radiocarbon years BP (PRI-5414). More lithic finds are shown in Extended Data Figs. 5, 6.
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.
THE UPSHOT
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:
(from precis): Researchers dug nearly 3 meters deep in Chiquihuite Cave and found almost 2000 stone tools. DEVLIN A. GANDY
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.
All of my Mazon Creek fossils are plants, but a diverse ancient fauna is represented there as well, including the Illinois State Fossil, the enigmatic Tully Monster (Tullimonstrum gregarium). The site represents an entire ecosystem, preserved in incredible detail. Here is a recent review of the site.
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:
Kimberalla quadrata. Arkhangelsk Regional Museum Author: Aleksey Nagovitsyn (User:Alnagov)
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.
(from PNAS): Photograph. . . (of I. wariootia. (A) Specimen (white arrow) associated with Helminthoidchnites [JAC: the burrow]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:
(from PNAS): Type specimen of I. wariootia from Nilpena, including (A) photograph; and (B–D) 3D laser scans. Notice distinct bilateral symmetry (wider end identified by white star in C and deeper end by black star in D). P57685. (Scale bars, 1 mm.)
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:
(From paper): Reconstruction of Ikaria in life position forming a Helminthoidichnites-type trail.
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.”
Speculative life reconstruction of Oculudentavis, its feathering and other details inspired by Jeholornis and other archaic members of Avialae. I’ve depicted it on the forest floor but am not necessarily saying that this is where it spent all of its time. Image: Darren Naish.
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.
A very rough, semi-schematic skeletal reconstruction of Oculudentavis which I produced in order to gain a rough idea of possible size. As you can see, it would have been tiny. The overall form of the skeleton is based on that of jeholornithiform birds; read on. Image: Darren Naish.
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.
UPDATE: In light of new data and criticism of this paper, it has been retracted. The “dinosaur” is in all likelihood a lizard or other non-dinosaurian reptile . For more information see the Nature report here.
_____________
Yes, we have a novel fossil, just described in Nature, that’s neither fowl nor reptile. And it’s TINY—roughly two grams. How small is it? Well, it’s about the size of the world’s smallest bird: the bee hummingbird of Cuba (Mellisuga helenae), which is this size:
The intermediacy of this fossil, which is part of the radiation that led to the evolution of modern birds from dinosaurs, is instantiated by the title and content of the paper below (it’s not free, but judicious inquiry will get you a copy).
The fossil, found in 99-million-year-old amber from Myanmar (Burma), is called a dinosaur above, but in the fourth paragraph of the paper it says (my emphasis), “Diagnosis: Very small bird with the following autapomorphies [a derived trait found only in one species or group]”. Is it a bird or is it a dinosaur?
Well, it’s both: it’s a transitional form: both the smallest dinosaur ever found as well as the smallest extinct bird. (As I said, it’s about the size of the smallest living bird: the bee hummingbird. Both weigh about 2 grams, or 1/15th of an ounce!) The transitional nature of the creature is shown by its reptilian features, including teeth, as well as birdlike features including a well-defined eye socket and a dome-shaped skull (see below). But it also has unique features, like a massive “scleral ring” (a circle of heavy bones around the eye); many teeth (over 100 in total) that extend the length of the jaw; the fact that the teeth are not, like those of dinosaurs, embedded in sockets but attached to the jaw by their sides; and the shape of the eyes, which suggests that they may have bulged out of its head like a lizard’s. These features are not known in either dinosaurs or early or modern birds.
Because the creature was found in amber, it was well preserved compared to early birds, which have fragile bones that are easily crushed. (The Chinese specimens that gave us much insight into bird evolution come from very fine sediments that preserved and mineralized the bones, but nothing this small has been found—only one-sixth the size of the next largest early bird.) The species has been named Oculudentavis khaungraa (“Eye-tooth-bird” with the name khaungraae coming from the donor, Khaun Ra).
Here are some photos and drawings from the paper; I’ve put below the CT scan of the skull as well as a larger picture of the amber. Note that the scale bar at the top, to the right of “b”, is only 5 mm, or about 1/5 of an inch.
The CT scan is below. Look at that bony ring (“sclerites”) around the eye! The fact that the eye opening is small suggested to the authors that this creature was diurnal (active during the day).
Further, the numerous teeth, which, as you can see from above, go all the way from the tip of the jaw to behind the eye, as well as the shape of the tongue, suggested to the authors that this was a predator. Unlike the smallest birds like hummingbirds, which sip nectar, this thing probably ate small arthropods and other invertebrates.
Here’s an enlargement of the amber in which it was found:
Because of the many unusual and unique features of Oculudentavis khaungraa, it’s hard to place it in a phylogeny of birds and dino-birds. The authors have tentatively placed it where the red arrow is in the phylogeny below, near the famous Archaeopteryx. But the authors also suggest that “the taxon falls outside Ornithuromorpha” (also called Euornithes), the group that includes all modern birds. The fact is that it’s such a weird creature means that they can’t really place it anywhere with any accuracy.
The authors suggest that the weird features of the creature are a byproduct of its miniaturization, which can, they say, cause the reappearance of ancestral traits. And while they and the media—which has covered this widely—say that O. khaungraa can shed light on early bird evolution, it’s hard to see what light that is.
Since there’s only one specimen, and only the head, it’s hard to tell what it means. It may be a one-off group, a weird branch in the early radiation of avian-like theropod dinosaurs that went extinct. It may show us that the ecology of early feathered dinos, which probably now includes diurnal predators on invertebrates, is wider than previously thought. The interest in this creature probably stems mostly from its intermediacy, its size, its excellent preservation, and its combination of features hitherto unknown in the radiation of feathered theropods. (We don’t know if O. khaungraa had feathers, as the paper gives no information, but it seems likely).
Here’s a very good 3.5-minute Nature video that summarizes the discovery in detail.
_________________
Xing, L., O’Connor, J.K., Schmitz, L. et al. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature579, 245–249 (2020).
The conventional wisdom about the migration of Homo out of Africa, where the genus originated, involves the spread of Homo erectus about 2 million years ago across Eurasia, with that species appearing to have gone extinct without issue.
After that, the Neanderthals, which split from the lineage producing “modern” (i.e., living) H. sapiens about 800,000 years ago, moved to Europe some time between then and 600,000 years ago. (For convenience, I’ll call Neanderthals “Neanderthals” and “modern H. sapiens” as sapiens, though I think they’re both subspecies of H. sapiens.)
Then, it was thought, sapiens moved into Europe and then Asia beginning about 60,000 years ago, with Neanderthals becoming extinct around 40,000 years ago, though having left a genetic legacy within sapiens. (That ability to produce fertile hybrids between H. sapiens sapiens and H. sapiens neanderthalensis is why I consider both lineages to be subspecies of the same biological species).
There was, however, tantalizing evidence—as summarized in a Nature News & Views article (free with UnPaywall) about the paper discussed today—that two skulls found in Israel, dated between 500,000 and 200,000 years ago, might also been close to the “modern H. sapiens” lineage, but the evidence is fragmentary and these could actually be Neanderthals.
The figure below, from the News & Views piece, summarizes fossil finds of Homo from the Eastern hemisphere (see key at bottom of figure for species designation, and note the Neanderthals and Denisovans):
Figure 1 | Some key early fossils of Homo sapiens and related species in Africa and Eurasia. Harvati et al.5 present their analyses of two fossil skulls from Apidima Cave in Greece. They report that the fossil Apidima 1 is an H. sapiens specimen that is at least 210,000 years old, from a time when Neanderthals occupied many European sites. It is the earliest known example of H. sapiens in Europe, and is at least 160,000 years older than the next oldest H. sapiens fossils found in Europe (not shown). Harvati and colleagues confirm that, as previously reported, Apidima 2 is a Neanderthal specimen, and they estimate that it is at least 170,000 years old. The authors’ findings, along with other discoveries of which a selection is shown here, shed light on the timing and locations of early successful and failed dispersals out of Africa of hominins (modern humans and other human relatives, such as Neanderthals and Denisovans). kyr, thousand years old.
The Israeli fossil provided weak evidence that sapiens may have left Europe well before the conventional date of about 60,000 years, though these forays into Eurasia, at least judging from genetic evidence, didn’t give rise to humans living today.
Now a new article in Nature by Katerina Harvati et al. (click on screenshot below for free UnPaywall access, with pdf here and reference at bottom), suggests much more strongly that sapiens did indeed leave Africa for Eurasia much earlier than we thought: in fact, way earlier—about 210,000 years ago. That more than triples the time length of time since the first sapiens left Africa. Note, though, that the new find, even if it is sapiens (and there are doubts), is not ancestral to living modern humans; the population seems to have vanished without issue.
The paper is based on two skulls originally found in 1978 in a cave in Apidima in southern Greece, but were only now dated and thoroughly analyzed morphologically.
There were two skulls in the same place and piece of sedimentary rock, one dated at about 170,000 years ago (“Apidma 2”) and the other a bit older at 210,000 years (“Apidima 1”). Apidima 2 is represented by a pretty complete cranium, minus the jaw, while Apidima 1 is only the rear of the skull. The fossils are shown below, with Apidima 2 at top. Both are pretty badly banged up.
(All figure captions are from the Nature paper).
a–c, Apidima 2. a, Frontal view. b, Right lateral view. c, Left lateral view. d–f, Apidima 1. d, Posterior view. e, Lateral view. f, Superior view. Scale bar, 5 cm.
Because the skulls were so incomplete, their shapes had to be determined through reconstruction by computed tomography; and for Apidima 1, which has no face at all, the rear of the skull was reconstructed by making a mirror image of the better-preserved half. This fragmentary nature of Apidima 1 has to be kept in mind when assessing what it was.
The take-home lesson from the paper is that the dating and structural studies (done through uranium series analysis) shows that Apidima 2 falls well within Neanderthal types, but Apidima 1 shows features that lead the authors to conclude that it is indeed sapiens. These sapiens features include a more rounded rear of the cranium as well as the lack of a characteristic Neanderthal trait, a bulge at the back of the skull like a bony hair bun. As the authors say, using morphological argot that you can skip (I’ve eliminated references in the paragraph below):
By contrast, Apidima 1 does not have Neanderthal features; its linear measurements fall mainly in the region of overlap between taxa. It lacks a Neanderthal-like rounded en bombe profile in posterior view. The widest part of the cranium is relatively low on the parietal; the parietal walls are nearly parallel and converge only slightly upwards, a plesiomorphic morphology that is common in Middle Pleistocene Homo. It does not show the occipital plane convexity and lambdoid flattening associated with Neanderthal occipital ‘chignons’. Rather, its midsagittal outline is rounded in lateral view, a feature that is considered derived for modern humans . The superior nuchal lines are weak with no external occipital protuberance. In contrast to some Middle Pleistocene specimens, the occipital bone is not steeply angled and lacks a thick occipital torus. A small, very faint, depression is found above the inion Although suprainiac fossae are considered derived for Neanderthals, similar depressions occur among modern humans and in some African early H. sapiens. The Apidima 1 depression does not present the typical Neanderthal combination of features. It is far smaller and less marked even than the ‘incipient’ suprainiac fossae of MPE specimens from Swanscombe and Sima de los Huesos, and is closest in size to the small supranuchal depression of the Eliye Springs cranium, a Middle Pleistocene African (MPA). Apidima 1 therefore lacks derived Neanderthal morphology, and instead shows a combination of ancestral and derived modern human features.
The placement of Apidima 1 with sapiens and Apidima 2 with Neanderthals is shown in the following two graphs, where known fossils are grouped and identified with dots of various shapes. In the following, “modern” sapiens are blue triangles, Neanderthals are red stars, Middle Pleistocene Eurasians are yellow squares, and Middle Pleistocene Africans (presumably sapiens) are purple squares. The two axes represent various “principal components” that capture combinations of shapes and measurements that help distinguish specimens.
“Rec 1-4” are the reconstructions of Apidima 2. As you see, they fit pretty nicely within Neanderthals, or are closer to them than they are to sapiens (blue polygons). This is why Apidima 2 is considered a Neanderthal skull.
a, Analysis 1. PCA of Procrustes-superimposed facial landmarks, PC1 compared to PC2. H. sapiens, blue triangles (n = 19); Neanderthals, red stars (n = 6); MPE, yellow squares (n = 3); MPA, purple squares (n = 3). b, Analysis 2. PCA of Procrustes-superimposed neurocranial landmarks and semilandmarks, PC1 compared to PC2. H. sapiens (n = 25), Neanderthals (n = 8), MPE (n = 3), MPA (n = 5); Apidima reconstructions, black polygons, Apidima reconstruction mean configuration, black star. Wireframes below the plots illustrate facial and neurocranial shape changes along the PC1 of each analysis, respectively. Specimen abbreviations can be found in Supplementary Table 9. See Methods for detailed descriptions of analyses 1 and 2.
Here is Apidima 1, which is labeled as a diamond symbol in both left and right. As you see, it falls within the sapiens parameters and isn’t near the shape of Neanderthal skulls (red stars).
a, Analysis 3. PCA of Procrustes-superimposed neurocranial landmarks and semilandmarks, PC1 compared to PC2. H. sapiens (n = 23), Neanderthals (n = 6), MPE (n = 4), MPA (n = 5). b, Analysis 4. PCA of Procrustes-superimposed midsagittal landmarks and semilandmarks, PC1 compared to PC2. H. sapiens (n = 27), Neanderthals (n = 10), MPE (n = 5), MPA (n = 6).Wireframes below and next to the plots illustrate neurocranial and midsagittal shape changes along PC1 (analyses 3 and 4), and PC2 (analysis 4). c, Neurocranial shape index (analysis 3). Violins show the minimum–maximum range, boxes show the 25–75% quartiles and lines indicate the median. Modern Africans, green dots (n = 15); all other samples and symbols as in a and Fig. 2. See Methods for detailed descriptions of analyses 3 and 4.
Finally, here’s a different analysis that places both Apidima 1 (black triangle) and reconstructions of Apidima 2 (“Rec 1-4”) on one plot. Apidima 1 is close to “modern sapiens” (blue polygon(, but falls between it and early H. sapiens from Africa (purple polygon), demonstrating that, while sapiens-like, it wasn’t fully “modern” in its morphology.
Apidima 2 falls squarely within the ambit of Neanderthal skulls (red stars).
Analysis 5. PCA of Procrustes-superimposed neurocranial landmarks and semilandmarks shared between Apidima 1 and Apidima 2, PC1 compared to PC2. H. sapiens (n = 23), Neanderthals (n = 6), MPE (n = 4), MPA (n = 5). Wireframes below and next to the plot illustrate shape changes along PC1 and PC2. Symbols as in Fig. 2.
So there you have it: decent but not wholly convincing evidence that sapiens had already left Africa 210,000 years ago, and lived in the same period and place as Neanderthals. That’s a long time before we thought, and constitutes a dramatic revision of how we thought humans moved about in the last few thousand years.
A couple of questions remain:
How reliable is this conclusion? Well, I’m not a paleontologist, so I won’t put a definitive imprimatur on this diagnosis. In his News & Views piece, Eric Delsen notes that “Given that the Apidima 1 fossil and those from Misliya and Zuttiyeh (latter from Israel) are only partial skulls, some might argue that the specimens are too incomplete for their status as H. sapiens [JAC: they mean “modern H. sapiens”] to be certain. Delsen suggests that “paoleoproteomics”—sequence analysis of ancient proteins from the skulls—might help resolve this issue, even if DNA isn’t available.
Chris Stringer, one of the paper’s authors, issued a tweet that Matthew retweeted, praising it for its rigor and scrupulous honesty (Stringer says the reaction should be “a healthy skepticism”):
Now this take from Chris Stringer is rigorous and scrupulously honest. Oh, and fascinating! If true, this puts humans in Europe 150,000 years earlier than we thought. Here’s the paper: https://t.co/2tTKMa8wLAhttps://t.co/VDe4T2Hzk3
Did these early-emerging sapiens have contact with Neanderthals? Perhaps, though the dates of the two skulls are 40,000 years apart. But there is evidence for a long persistence of Neanderthals in Greece, so it’s likely that the two subspecies did coexist in the same general area. But if they mated with each other, there are no traces of that Neanderthal DNA in modern humans, which helps answer the next question:
If this fossil is indeed sapiens, what happened to the population? The authors suggest that the sapiens population simply died out without issue, and that’s supported by genetic data suggesting that all modern humans descend from an egress from Africa about 60,000 years ago. The Greek population may have simply gone extinct by attrition, or may have been wiped out by Neanderthals. Who knows? But if they died out without issue, as is likely, they are not our direct ancestors.
As Steve Gould used to say, when he taught human evolution every year he simply dumped his previous year’s teaching notes in the trash and wrote an entirely new lecture. That may have been an exaggeration, but shows how rapid the pace of understanding human evolution was. And still is! Given the paucity of finds in the genus Homo, there are many surprises to come.
