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.
UPDATE: In light of new data and criticism of this paper, it has been retracted.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.
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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.
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Xing, L., O’Connor, J.K., Schmitz, L. et al. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature579, 245–249 (2020).
A new paper in Nature by Jean Vannier et al. reports the unusual finding of a parade of trilobites—a group of the ancient arthropods—apparently killed and fossilized while walking in tandem, like an invertebrate conga line. They’re 480 million years old, from the Lower Ordovician, and were found in Morocco. (The paper can be seen by clicking on the screenshot below, the pdf is here, and the reference is at the bottom.) This weird lineup of trilobites suggests some kind of collective behavior—the first such find documented by paleontologists. But what kind of behavior? The authors have two hypotheses, and I’ll discuss them briefly.
First, some photos of the species, Ampyx priscus, which had a hollow “glabellar spine” in front and two “librigenal spines” going backwards. The white scale line is 1 cm long, so these things were, including the front spine, about 6 cm (2.3 inches) long. The spines might have enabled the trilobites to sense each other and thus maintain contact while moving in line, much as spiny lobsters do when moving across the sea floor in line as I show below. (Any “communication” must have been tactile as these trilobites were blind.)
All captions are taken from the Nature paper. Here are the individuals at hand, with some close-ups of their spines:
General morphology and parameters of the raphiophorid trilobite Ampyx priscus Thoral, 1935, from the Lower Ordovician (Upper Tremadocian-Floian) Fezouata Shale of Morocco (Zagora area). (a–d) BOM 2481, overall morphology and details of genal spines. (e) Parameters used in measurements. (f,g) MGL 096718, genal spine showing internal mineralized infilling. (h) AA.OBZ2.OI.1, transverse thin section through right genal spine (see general view in Supplementary Fig. 8d). (i) MGL 096727, genal spine. (j) ROMIP 57013, external mould of glabellar and genal spine showing longitudinal ridge. a–d,f,g,i,j are light photographs.
Here are the fossils of the lined-up trilobites, which are remarkable, along with schematics showing the nature of the relief of the stone in which they were preserved.
Linear clusters of the raphiophorid trilobite Ampyx priscus Thoral, 193531, from the Lower Ordovician (upper Tremadocian-Floian) Fezouata Shale of Morocco (Zagora area). (a,b) AA.TER.OI.12 (see Supplementary Fig. 2a). (c) MGL 096727 (see Supplementary Fig. 5a). (d) AA.TER.OI.13 (see Supplementary Fig. 2b). (e) BOM 2461 (see Supplementary Fig. 2f). (a,e) are light photographs. Line drawings from photographs. Segmented blue lines in (b–d) join the central part of occipital rings of trilobites. Red arrows indicate the position of polished section in Fig. 3. Abbreviations are as follows: (x), Asaphellus aff. jujuanus (asaphid trilobite); (y), juvenile asaphid trilobite. Scale bars: 1 cm.
Here’s a video of spiny lobsters migrating in line, much like these trilobites:
So why were these ancient arthropods marching in line? The authors reject two hypotheses. First, that they were “mechanically accumulated along linear submarine reliefs (e.g. between ripple marks)”. This is the hypothesis that they were blown into grooves in the ocean floor and accumulated there, explaining the lines. That, however, doesn’t explain the consistent alignment rather than some being blown in backwards. The authors reject this because there is no indication from the fossil strata themselves that there were these reliefs.
They also reject the hypothesis that these trilobites were lined up in burrows underwater and then trapped and killed by sediments. Their rejection is based on the absence of “any colored outlines or disturbances in the sediments surrounding trilobites.” I’ll trust the authors on this since knowing how to detect ancient burrows is above my pay grade.
Rather, the authors proffer two hypotheses to explain the alignment. The first, shown on the left below, is that there were underwater storms or currents that made the trilobites orient in one direction, and then they “found” each other by tactile signals (or perhaps also by chemical signals), forming a line that served a protective function. As the authors say, “Such mechanical contacts [as in the lobsters above] appear to be essential for group cohesion and for optimal coordinated locomotion.” Marching in a line reduces drag, saves energy, and, say the authors, “reduces the probability of detection and attacks by predators by creating confusion in their [predators’] visual perception.”
The second hypothesis, shown on the right below, is that the trilobites emitted chemical signals like pheromones as a way of detecting each other and coming together for sexual reproduction, with the lines presumably indicating a migration toward spawning grounds. As the authors note, both explanations could be operating together.
Two non-exclusive hypotheses to explain the linear clusters of Ampyx priscus from the Lower Ordovician of Morocco. (a–c) Response to oriented environmental stress (e.g. storms); hydrodynamic signal (higher current velocity represented by white arrows) received by motion sensors triggers re-orientation of individuals; mechanical stimulation and/or possible chemical signals cause gathering, alignment and locomotion in group. (d–f) Seasonal reproductive behaviour; chemical signals (e.g. pheromones; see red circles and red arrows) cause attraction and gathering of sexually receptive individuals (males and females) and migration to spawning grounds. The alignment of individual may have been controlled by mechanical stimuli (as in a–c). Olfactive and mechanical sensors were probably located on the antennules (pink areas 4, 5), and genal and glabellar spines (green areas 1–3), respectively. The exact location of mechanoreceptors is uncertain (possibly on high-relief exoskeletal features such as the glabella).
As for how they were buried together, that’s a bit of a mystery since trilobites, when stressed, are supposed to have curled themselves into balls like modern isopods, and these didn’t do that, as you can see above. Here’s one scenario that explains the successive strata in which lines of trilobites were buried.
First, subject to periodic storms that disturbed the waters, the trilobites joined up in a Big March. (Or, as I noted above, they could be marching for mating!). Then, the storm quickly deposited sediment atop the marching trilobites, preserving them in situ. There could have been two other events that preserved them quickly: “water poisoning,” like the release of hydrogen sulfide gas or, more likely, the upward movement of oxygen-poor (“anoxic”) sediments, which killed the trilobites quickly from lack of oxygen as well as protecting the carcasses from scavengers.
You can see one instance of preservation in panels a-c below, and then another line of trilobites forming in panel “d”:
Scenario to explain the in situ preservation of the Ampyx linear clusters from the Lower Ordovician (Upper Tremadocian-Floian) of Morocco. (a) Deposition of a distal tempestite (event layer 1). (b) Epibenthic (e.g. trilobites) and shallow endobenthic (e.g. possible worms) organisms settle and generate bioturbation above red-ox boundary. (c) Second storm event layer entombs epibenthic fauna in situ; red-ox boundary moves upwards (white arrows). (d) New faunal recolonization. According to Vaucher et al.34, distal storm deposits are relatively thin (less than 5 cm) and consist of a waning (base) and waxing (top) phases (subdivision not represented in this diagram), and depositional environment is that of the distal lower shoreface with a possible water depth of approximately 30–70 m. Bioturbation is based on polished and thin sections (Fig. 3 and Supplementary Figs 8 and 9). Abbreviations are as follows: bt, bioturbation; tr, trilobite group (Ampyx); trc, trilobite carcasses (Ampyx); w, worm; wsi, water-sediment interface.
Now much of this is speculative, as it must be with limited information about what happened 500 million years ago. But it certainly looks as if, like spiny lobsters, these trilobites were marching in line, probably following each other using tactile cues. And so we get a rare window on invertebrate behavior from the distant past.
A new analysis of a remarkable hominin find in Ethiopia suggests that the species it represents, Australopithecus anamensis, may be one of the very earliest species in our lineage, and possibly the first hominin we know of that is undoubtedly part of our own genealogy. (“Hominins”, formerly called “hominids”, represent all fossils on our side of the family tree since we branched off from our common ancestor with the chimpanzees). The find has also has led to a revision of the idea that A. anamensis was the ancestor of the later A. afarensis, thought by many to be the ancestor of the genus Homo, and thus of modern Homo sapiens. (We love to know who our ancestors are, as witnessed by the popularity of companies like 23 & Me.)
A. anamensis lived from about 4.2 to 3.9 million years ago (mya) and A. afarensis from 3.9 to 3.0 mya. A. afarensis includes the famous skeleton of Lucy(about 3.2 mya), which is remarkably complete from the neck down but has only fragments of the skull. As the following diagram suggests (and this is typical), A. anamensis is the earliest known hominin to be part of our own lineage and is portrayed as the ancestor of A. afarensis:
That ancestry is presumed (as shown above) to have been a lineal transformation of A. anamensis into A. afarensis: that is, the former species was thought to have evolved over time, and as a unit, into A. afarensis.
This conclusion is what is cast into doubt by the recent find, documented in a new paper in Nature that you can access by clicking on the screenshot below (or see the pdf here). The new finds show that A. anamensis was in fact a contemporary of A. afarensis, so that the two species lived at the same time, at least for a while.
This doesn’t rule out, however, the possibility that A. afarensis evolved from one or more populations of A. anamensis while the latter species continued on, largely unchanged from other populations. (Some, however, would say that such a branching event would automatically change the name of A. anamensis; see below.) Thus both species could still have coexisted while A. afarensis could still be a descendant of A. anemensis.
The paper:
As you see, the new skull is 3.8 million years old, putting it at about the end of A. anamensis‘s tenure and about the time that A. afarensis appeared.
The new skull is remarkably complete: by far the most intact A. anamensis skull we have, and also has a number of features that tell us that it was a hominin and was not a member of A. afarensis. Since the earliest A. afarensis appears to have lived a bit earlier than this specimen (3.9 mya), it appears that A. afarensis cannot be a lineal descendant of A. anamensis. (But, as I said above, it could be a descendant of some A. anamensis populations.)
Here’s the skull, which has a tiny cranial capacity (365-370 cc compared to about 1200-1300 cc in modern humans), a sagittal crest, and brow ridges.
a, Anterior view. b, Posterior view. c, Superior view. d, Left lateral view. e, Right lateral view. f, Inferior view. The specimen is oriented in Frankfort horizontal plane. Scale bar, 1 cm.
You can see how small the skull is when compared to the head size of the paper’s first author:
Yohannes Haile-Selassie with the skull. Photograph: AFP/Getty Images
It appears to have been an adult male.
Why is it a hominin? Well, here’s the jargon that they use to show it’s a hominin and more primitive (that is, closer in appearance to the common ancestor) than is A. afarensis:
The specimen is readily identifiable as a hominin by the following morphological features: the canine is reduced in size compared to non-human apes and shows a strong lingual basal tubercle; the mastoids are inflated; the nuchal plane is more horizontal than in non-human apes; and the inion, which is coincident with the opisthocranion, lies near the level of the Frankfort horizontal plane. At the same time, the small cranial capacity, highly prognathic face, extensive pneumatization and other features discussed below indicate that MRD represents a hominin that is more primitive than A. afarensis.
Got that? Neither did I, but the paleoanthropologists do. At any rate, the dates put it earlier than most specimens of A. afarensis, and it has a longer upper canine, a smaller earhole, and a narrower palate. Here’s a comparison of the new specimen (MRD-VP-s/1, which we’ll call MRD) with Sahelanthropus tchadensis (a hominin that may be close to the common ancestor of the human and chimp lineages, and which lived about 7 mya), along with Australopithecus ramidus (a 4.4 mya hominin of unknown placement on the tree), and A. afarensis and the later A. africanus.
(All captions below are from the Nature paper): Red lines and arrows show the inclination of the frontal and the presence of a post-toral sulcus, respectively. Blue lines show the orientation of the mid and lower face, with an broken line indicating a segmented facial profile27. The green arrow marks the anterior projection of the zygomatic tubercle (relative to the anterior zygomatic root). Scale bar, 2 cm.
Here’s the back of the skull compared to a modern chimp and the two later australopithecines. Note the smaller braincase and more pronounced sagittal crest of MRD:
The transverse contour of the cranial base is convex in African apes, whereas A. afarensis shows an angular transition between the nuchal region and the greatly expanded mastoids (red dashed lines). In this regard, A. afarensis anticipates the morphology of robust australopiths, but A. africanus is less derived. MRD shows the primitive convex contour of the base, even though the mastoids are expanded. MRD is also primitive with regard to the great length of the nuchal plane (black arrows). However, it is similar to A. afarensis in the configuration of the compound temporal–nuchal crest (white dashed lines), the bare area (blue hatched triangle), and the overall ‘bell-shaped’ posterior outline (that is, the parietal walls are slightly convergent superiorly and the greatest width occurs basally across the enlarged mastoids).
A phylogenetic analysis of where the MRD skull fits on the hominin phylogeny. As you see, it appears before A. afarensis and sits on part of the phylogeny that gave rise to modern humans.
h, i, Cladograms from the K-combined and S&G-combined analyses (as in a and b), with apomorphies added to the cladograms to illustrate the implied pattern of evolutionary change. The character states reconstructed at nodes A and B provide the reference for identifying A. anamensis and A. afarensis apomorphies, which are shown here as rectangles containing their abbreviated character labels. Characters in red, orange, gold and green describe similar morphology and appear in both previously published studies27,33. See Supplementary Note 9 and Supplementary Table 1.
This species was sexually dimorphic, with males about five feet tall and weighing about 100 pounds (1.5 meters and 45 kilos), and females about 3.5 feet tall and weighing about 62 pounds (1.1 meter and 28 kilos). The skull size and features (tooth wear, etc.) suggest that it was an adult male. Here’s a reconstruction of the face from The Guardian:
The big findings: First, we now know what the cranium of a possible ancestor looked like, and crania are not easily preserved or found in the fossil record of hominins. This helps complete the picture of what A. amanensis looked like. Further, another major and unambiguous conclusion here—assuming the dating is correct—is that A. anamensis coexisted with A. afarensis for at least 100,000 years. A. afarensis is thought to be one of our ancestors, giving rise to the genus Homo as well as the extinct “robust” australopithecines. But this leaves one question:
Was A. anamensis an ancestor of A. afarensis? Just because the two species coexisted does not mean that the one who lived first wasn’t the ancestor of the one that appeared later. Consider that there were various populations of the earlier A. anamensis. Suppose one or more of these evolved into A. afarensis, but some other populations retained the appearance and traits of A. anamensis. Then we’d still have an ancestor/descendant relationship, though cladistic taxonomists would say that at the moment A. afarensis branched off, we’d have to change the name of A. amanensis. (This is part of the practice of cladistic classification, though it makes little sense to laypeople.)
Whether A. afarensis came into being this way or not, what’s clear is that two species of australopithecine lived at the same time, and one of them is thought by paleoanthrophologists, as the first diagram above shows, to have been the ancestor of several species of hominins, including us.
Reader Kevin called my attention to this new paper in Biology Letters about a giant fossil parrot found in New Zealand (click on screenshot for link, reference at bottom; pdf is here).
For eleven years a pair of large fossil bird bones (16-19 million years old)—two fragmentary “tibiotarsi”—languished in the Museum of New Zealand. Thought to belong to an eagle or duck (what duck, though, would have a partial tibiotarsus 7 inches long?), this paper’s re-examination shows that they are actually parrot bones. Here, by the way, is where the tibiotarsus is:
And to the left in the figure below are the two bones (dated between 16 and 19 million years old), with the scale bar being 2 cm: At the left are the bones of the ancient parrot. The two bones at the right are a comparison parrot, the extant Strigops habroptila, the famous flightless kakapo, also from New Zealand and weighing about 1.5-2 kg (3.3- 4.4 pounds). The kakapo is the world’s only flightless parrot, but the authors argue that H. inexpectatus was also flightless.
How they identified these bones as belonging to a parrot rather than another bird is above most of our pay grades, but I’ll just give a snippet to show how it went (this is an excerpt from more than a column of “comparisons”:
The named this ancient parrot Heracles inexpectatus. Here’s how they came up with the name:
Etymology: The nestorid Nelepsittacus from the St Bathans Fauna was named after Neleus. This much larger psittaciform is named after the Greek Heracles, who in Latin was known as Hercules, and who killed Neleus and his sons, except for Nestor. Genus gender masculine. The specific epithet denotes the unexpected nature of this find.
Let’s assume they’re right that it was a parrot, and I have no reason to think they’re not. What we have, then, is a giant parrot, singing in the choir invisible, inferred from the bones to be about a meter tall (39 inches and weighing about 7 kilograms—about 15.5 pounds. That’s about four times the weight of the kakapo, up to now the world’s heaviest known parrot. H. inexpectatus was a monster, and here’s a figure showing the size of this bird relative to a human, taken from a BBC article on the find (credit: PA media). (The bird to the left is unidentified, but looks to me like a magpie.)
Why do they think it was flightless? Well, it was huge, the bones are robust, and it lived on an island. Island birds are often flightless, evolving loss of flight due to an absence of mammalian predators, and New Zealand had no native mammals. (There was a giant predatory eagle that ate other birds.) Ergo the flightless kiwis evolved there, as well as the kakapo and a large variety of flightless moas, with one of the nine known species standing fully 12 feet tall with the neck extended, and weighing about 230 kg (510 lb).
Like many flightless birds, the moa went extinct, killed off for food by the native Maori. (The kakapo is also endangered, with all living individuals relocated to a predator-free island.) Just for grins, here’s a skeleton of that big moa that I photographed in Auckland in April of 2017:
What did it eat? There has been speculation that its size could enable it to prey on other birds, including parrots, and at least one parrot, the kea, is partly carnivorous, devouring the fat on the backs of sheep. And its beak would have been huge and formidable, capable of cracking just about any organic material. But, as the first author Trevor Worthy told the BBC, “It probably sat on the ground, walked around and ate seeds and nuts, mostly.”
We’re not sure if it could fly—probably not—but what we do know is that this is by far the largest parrot known to date, and the world’s only known giant parrot. Here’s one guess about what it looked like.
Reconstruction drawing: Brian Choo/Flinders University
There’s a new paper in Current Biology that details the finding of a very unusual bird in Burmese amber—a bird with one huge toe and weird bristles on its feet. You can read it with UnPaywall by clicking on the screenshot below (pdf here, reference at bottom).
The specimen, uncovered by amber miners five years ago, consists of a lower right leg and foot, as well as some feathers (both those attached to the leg and flight feathers free in the amber). It dates back about 99 million years, to the middle Cretaceous, when flying birds had already evolved from reptiles. Since it was a new species (the first ever described from amber), the authors gave it the binomial Elektorornis chenguangi, with the genus name meaning “amber bird”. Phylogenetic analysis places the species in the Enantiornithes, a bird family that went extinct without descendants at the K/T boundary—about 66 million years ago when the dinosaurs also began to die out. (All modern birds belong to the clade Neornithes, a group within the subclass Aves.)
Briefly, there are two remarkable features of this bird—features that may be connected.
The first is that the third digit on the foot is much longer than the second and fourth digits: about 41% longer. It’s also more curved than the other toes. That disproportionality is unique among all known birds, living or extinct. (The specimen was at first thought to belong to an extinct lizard, but it was immediately clear to experts that this was a bird.)
You can see the long claw in the Figure below, both to the left and in the drawing in the center. On the right you can see the second unusual feature: the scutellae scale filaments (SSFs), bristly feathers on the feet and legs.
(From paper) A) HPG-15-2 overview, with inset providing greater detail on foot, arrowheads marking different apices of unguals and ungual sheathes where visible, and red arrow marking base of mt III 4 shared with (D). (B and C) Osteological details. (D) Tuft of elongated SSFs near apex of mt III ph 3, with horizontal arrowhead marking edge of reticulae from digital pad, inclined arrowhead marking edge of scute, white arrow marking sloughed reticulae, and red arrow marking base of ungual in (A). (E) Detail of lowermost SSFs in (D), showing hollow cores (arrowheads) and mottled outer walls, presumably due to feather oils. Fe, femur; fi, fibula; lc, lateral condyle; mc, medial condyle; mt, metatarsal and corresponding digit; ph, phalanx; tb, tibia. Scale bars, 5 mm in (A); 1 mm in (A) inset; 0.5 mm in (D); and 0.25 mm in (E). See also Figures S1, S2, and S4.
The authors conclude that the configuration of the foot itself indicates that it was a perching (“arboreal”) bird. But what about that toe? When I first saw the figure, I thought the toe must have been for extracting prey (probably insects) from bark and tree holes, sort of like what the aye-aye (Daubentonia madagascariensis—a bizarre lemur with an elongated digit—does. And the possible sensory nature of the foot bristles would help with that task. Great minds think alike, for that is the authors’ own suggestion.
The figure below is of lesser interest to us; it shows some of the flight feathers from the wing that were also preserved in the amber. What is most important is that the feathers are asymmetrical, with the leading filaments (“vanes”) being less than half as long as the trailing filaments. That is an indication of flight, as shown in these modern bird feathers from Quora, which also explains the aerodynamic reason for the asymmetry.
Here’s a figure showing the feathers, which still bear brown pigmentation in the amber:
(From paper): (A) Overview of primary and secondary feather exposure at polished edge of amber piece, with inclined arrows marking primary rachises (P1 and P2 weakly distinguished from secondaries and marked in red); vertical arrows mark secondaries; horizontal arrows mark pale areas in wing; and lettered circles mark positions of (B) and (C). (B) Weakly pigmented reduced barbules from primary barbs in leading edge of wing. (C) Dark brown barbules from primary barbs in base of posterior vane of primary. Scale bars, 2 mm in (A); 0.25 mm in (B) and (C). See also Figures S1 and S2.
The authors are a bit waffle-y about this third toe, saying “the function of the elongated third toes is uncertain”. And indeed, it is uncertain. But in the abstract they are a bit more certain, saying “we suggest that the elongated third digit was employed in a unique foraging strategy,” i.e., extracting food (probably insects) from trees. And, given the presence of what are likely sensory bristles on the toes, similar to sensory bristles around the mouths in some New Zealand birds, including the kiwi, that makes sense. Here are the sensory bristles on a kiwi’s face, which undoubtedly help it forage and navigate at night, since the species are nocturnal:
Finally, here’s an aye-aye using its elongated finger to probe for insects. (That finger has a ball and socket joint and can swivel 360°.) I suspect that Elektorornis chenguangidid a similar thing.
Will we ever know? I don’t see how, but speculation is fun, and may lead to some testable predictions.
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.
Pterosaurs were the first vertebrates to attain powered flight, and lived between 228 and 66 million years ago. They aren’t on the line to modern birds, which evolved well after pterosaurs appeared, and they appear to have gone extinct without leaving descendants. Often called “pterodactyls” or “flying dinosaurs”, they weren’t really in the group that included dinosaurs.
As you almost certainly know, they looked like this: (from Wikipedia):
While learning about these creatures this morning, I found that some of them were huge—as big as giraffes when they stood upright! One of them, Quetzalcoatlus northropi, had a wingspan of up to 16 meters, or 52 feet! Here’s some diagrams of that creature (the first two are from Wikipedia):
It was a big as a small plane! Here’s a comparison of Q. northropi with a Cessna 172 light aircraft:
Ambling about on four limbs, they are estimated to have been about 3 meters (10 feet) high at the shoulder, and as big as a giraffe from top to bottom:
Members of this species were also heavy, of course: they weighed about 200–250 kg, or 440–550 pounds. No flying bird even gets close to that.
Now could these big puppies fly? Mark Witton, a paleontologist and artist, thinks they could have, and sets out the evidence at this post, which I’ll leave you to read since I want to emphasize a new paper instead. But can you imagine a giraffe-sized reptile flying? That would be something we’d all love to see.
On to the new results. It’s generally accepted that young pterosaurs (unlike most birds, including my ducks) came out of the egg fully ready to fly, even though they still could have hung around the nest and received parental care (there’s no evidence for such care). But not everyone agrees. A two-year-old story in the the Daily Beast describes research that suggested that, because their wing bones weren’t full ossified (turned into hard bone) when they hatched, they couldn’t fly until later:
If pterosaur parents stuck around, perhaps there wasn’t so much of an imperative for the little guys to take to skies immediately after hatching. And there’s evidence from one of the embryos, the authors argue, that they couldn’t if they tried. In a single individual, the researchers found that the thigh bone had mature features and shape (that is to say that it looked like an adult thigh bone, only smaller) while the wing bone had some features still missing or underdeveloped.
“We have made an important progress by showing that the same embryo had the humerus [one of the main bones of the wing] not well ossified, but had the femur very well developed,” Alexander Kellner of the Universidade Federal do Rio de Janeiro, one of the study authors, told The Daily Beast by email. He said the most likely explanation for this mismatched development is that hatchlings could run but not fly.
Well, a new paper in the Proceedings of the Royal Society B (click on screenshot below, reference at bottom), though it’s paywalled, suggests that newly hatched pterosaurs could fly after all, and were as precocious as their modern relatives, the crocodilians, which are born pretty much ready to go, looking like tiny adults but still requiring parental care. Judicious inquiry might yield you a pdf of the paper below:
Unwin and Deemng did extensive analysis of 37 eggs of one pterosaur, Hamipterus tiashanensis, ranging from very small eggs to eggs containing embryos and even a new hatchling. They also looked at 3 other pterosaur species, comprising 19 embryos in total. The analysis is complex, aging eggs by both their size and roundness (eggs get rounder as they develop, and absorb water through the semipermeable “shell”), and examining embryos and newly hatched pterosaurs.
What they concluded is that the flying parts of the pterosaur: the fore- and hindlimb leg bones (remember, the leg bones were part of the airfoil) were sufficiently ossified in very late embryos to be able to fly. Second, earlier studies claiming that the muscle attachments for flight couldn’t have been sufficient to power the wings, aren’t all that convincing. Here’s what the authors say. You can get the point through the jargon (I’ve omitted the references and put the key points in bold.)
Terminal stages of embryonic development, represented by MIC V246, IVPP V 13758, JZMP 03–03-2, and the humeri of a near-term embryo (no. 7) and a hatchling of Hamipterus , have multiple features that point towards flight ability in hatchlings. First, extensive ossification of all elongate structures contributing to the flight apparatus that are likely to have experienced significant loads in bending during flight. These include dorsal and sacral vertebrae, the limb girdles and diaphyses of long bones that form the wing spars. This stiffening of the skeletal components of the flight module is analogous to ossification sequences in Al. mississippiensis, the hatchlings of which are also highly precocial locomotors, but is in sharp contrast to most extant birds where, prior to hatching, only the central region of the diaphysis of long bones is ossified.
Second, inferences regarding the implied lack of development of key flight muscles, based on the absence or poor development of osteological features, are insecure for two reasons: (i) muscle attachment sites do not need to be ossified in order to function effectively. In tension, cartilage can accommodate loads comparable to those for bone ; consequently, it cannot be assumed, a priori, that an incomplete deltopectoral crest directly implies a relatively small m. pectoralis, the principal wing depressor; and (ii) the relative size and shape of the deltopectoral crest of embryos 7, 11–13 and the hatchling is smaller than that of adult Hamipterus, but it is directly comparable in terms of shape and relative size to the deltopectoral crest of other pterosaurs including individuals of Anurognathus and Aurorazhdarcho that are widely considered to have been flight capable
Third, the relative elongation of long bones contributing to the wing spars, their relative proportions to each other and the relative elongation of the fore limb of mid and late term embryos compare closely to the same indices for mature, flight capable individuals of ornithocheirids [JAC: this is a well-represented pterosaur]. This is in sharp contrast to most birds and all bats where fore limb proportions comparable to those of adults, and flight ability, are only achieved at a relatively late stage of postnatal development.
And here’s a diagram showing that late-stage embryos had well developed “flight bones”: similar to those of hatchlings and immature pterosaurs:
Figure 4. Fossil record of prenatal and early postnatal development in pterosaurs. Darwinopterus modularis (a) ZMNH M8802. Hamipterus tianshanensis (b1–3) outlines of egg shape illustrating changes in size and shape; (c) IVPP V18942 embryo 5; (d) IVPP V18941 embryo 11; (e) IVPP V18942 embryo 12; (f) IVPP V18943 humerus of embryo 13; (j) IVPP V18942 hatched? egg; (k) IVPP V18942 humerus. Ornithocheiridae genus et sp. indet. (g) IVPP V13758 embryo. Pterodaustro guinazui (h) MIC V246, embryo; (l) MIC V241 hatchling. Pterodactylus kochi (m) BSP 1967 I 276. Not to scale. (c–f,j,k) redrawn from [8], (g) redrawn from [2], (h) redrawn from [22], (l) redrawn from [28]; (m) redrawn from [21].
One last question: Did they have parental care, even if hatchlings could fly? The answer is simply, “we don’t know, as there’s a lack of evidence”. As the authors say, “such a behavior is difficult to demonstrate.” Indeed, I’m not sure what would count as evidence for parental care except for hatchlings that were unable to fly and thus unable to feed themselves. But these hatchlings may well have been able to fly.
At any rate, it’s interesting to contemplate a hatching nest of baby pterosaurs, with all of them taking off soon after leaving the egg.
