A new species of hominin hits the news. What is it and what does it mean?

September 10, 2015 • 10:00 am

“Hominins” (formerly “hominids”), comprise all species, extinct and living (the latter is only H. sapiens), that fell on the side of the lineage that produced modern humans after the divergence of that lineage from the lineage leading to modern chimpanzees (our closest living relatives). Not all hominins fall in the genus Homo, of course: we have Australopithecus, Sahelanthropus, Paranthropus, and several other genera whose members went extinct without issue. Further, not all members of the genus Homo need have been our ancestors: several species might have lived—and probably did live— at the same time, as the chart below indicates. And some of these species probably went extinct without issue, and so aren’t our ancestors:

We are in fact not sure what earlier species evolved into Homo sapiens. Homo erectus, with a fairly big brain and widspread geographic distribution, might be a candidate, but we’re not even sure about that. Fossils are generally scarce, their characteristics overlap with fossils from other places, and we’re often unable to distinguish different species from simple variation among geographic localities within a single species—the brand of variation that is sometimes called “racial variation”.

This has led to a tendency to name every new fossil as a separate species (who wants to just describe yet another specimen of H. habilis?), which in turns leads to acrimonious debate about what species is what, and that then leads to the Big Debate about “what species was on the lineage leading to modern humans?”

Unfortunately, we can’t yet answer that last question, nor one closely connected with it: “When did we become human?” That question is nonsensical, I think, for it depends on exactly what you mean by “human”. If it involves purely physical traits, then we can at least in principle pinpoint such a time, though which traits you choose will themselves be arbitrary. If it’s mental traits or behavior, that’s even harder, for such things don’t fossilize. Sometimes, however, we might find instances of ritualized behavior, as in the burial of Neanderthal bodies and the anointing of skeletons with ochre. Did that make us human? Or was it speech, something notoriously difficult to discern from fossils? Or was it the complexity of cogitation or the development of the “intentional stance,” something almost impossible to discern from skeletons?

At any rate, a new species of hominin, H. naledi, has been described in a new paper (reference at bottom, free access) in eLife. It was written by Lee Berger et al. (the “et al.” are about 60 authors!), and describes a collection of 15 skeletons discovered together in a cave in South Africa. This is a remarkably complete collection of skeletons, and the gist of the paper is described at both the BBC and the New York Times. What I put below is distilled largely from these secondary sources, though I’ve had a look at the paper as well.

First, what’s notable is that there are so many skeletons, which—unlike many hominin fossils, found as partial skulls or other bones—allowed the authors to piece together a complete view of the species’ skeletal traits. Here are some of the remains in a photo by John Hawks from the BBC site:

Now why is this considered a new species of hominin? Well, it’s a mosaic of primitive and advanced traits, as the paper itself says:

H. naledi presents yet a different combination of traits. This species combines a humanlike body size and stature with an australopith-sized brain; features of the shoulder and hand apparently well-suited for climbing with humanlike hand and wrist adaptations for manipulation; australopith-like hip mechanics with humanlike terrestrial adaptations of the foot and lower limb; small dentition with primitive dental proportions.

How old is this species? We don’t know. The cave can be dated, and could be as old as 3 million years, and the authors say likewise that these fossils could be three million years old, antedating the earliest described species of Homo—H. habilis—by nearly a million years. But that’s the age of the cave, not of the fossils. The fossils could be two million, one million, or even 500,000 years old. (H. floresiensis, the “hobbit,” which was about three feet tall with a tiny brain and totally non-modern skeleton, lived as recently as 12,000 years ago!)

Like australopithecines, H. naledi had a very small skull but a largely modern postcranial skeleton. Why isn’t it an australopithecine? Largely because its brain is bigger (by about 25%), its molars are very small (australopithecines had big molars) and there are skull characteristics that lump it with species like H. erectus. But many of the traits still fall within the range of australopithecines. Here are some additional drawings from the BBC showing “modern” traits mixed with primitive ones:

The curved fingers may imply that this species was partly arboreal, i.e., that it still climbed trees:

The shape of the foot suggests, though, that the species was at least largely bipedal, a modern trait. (Australopithecines were also bipedal, as we know from the Laetoli footprints).

So let’s get to the three big questions. Two of them are answered erroneously in the title of the New York Times piece: “New species of human ancestor is found in a South African cave.” This is bad journalism on two counts: we have no idea whether H. naledi was on the lineage leading to H. sapiens. That means that we can’t say with any assurance that it was one of our ancestors. All we can say is that it was related to our ancestors. Second, we don’t know for sure if it’s a new species, for that’s a judgment call. But let’s look in a bit more depth.

Is H. naledi a new species? Evolutionary biologists define a “species” as a group of individuals or populations separated from other such groups by reproductive isolating barriers that prevent them from successfully exchanging genes. Since we don’t know this from fossil hominins (though we do for Neanderthals vs. H. sapiens, which clearly did exchange genes and thus belong in the same species), we usually make such judgments solely on morphological grounds: does this species look different from other described hominin species? The authors’ judgment, based on the many skeletons and fragments they have, is that it does, and so they give it a new name.

That, however, doesn’t convince me fully, for the differences are small, and, as the authors note, many of the feature resemble those of H. habilis or early H. erectus. That there may be diagnostic differences in some traits doesn’t convince me that this is a new species, for this could simply be a localized geographic variant—perhaps even a genetically related band—of a species already described. So I think it’s a bit premature to give it a new name. But I’m not particularly concerned about that. What’s more important is to get an accurate date for this fossil, for if it really is 3 million years old, that would certainly push back the origin of the genus Homo by a long period.

Is H. naledi our ancestor? As I said above, we don’t have the slightest idea. No journalist should state that this group is on the lineage leading to modern humans.

Did H. naledi practice ritual burial? This seems more likely, as all the skeletons are piled up together, though I don’t see any sign that there was any superstition involved in this practice. Perhaps they were sequestering the dead people away from others to avoid the stench. And even if they were putting the dead together (these dead involved hominins of all ages, by the way), this says little about the mentality of this species beyond the fact that they recognized the dead as different from the living. Again, it’s way premature to say that these things were “human,” as if they had a mentation or a spirituality resembling that of modern humans. This statement by Lee Berger, then, which appeared in the BBC report, seems to me largely meaningless, for “what it is to be human” depends completely on what you mean by “human”:

Prof Berger believes that the discovery of a creature that has such a mix of modern and primitive features should make scientists rethink the definition of what it is to be human – so much so that he himself is reluctant to describe naledi as human.

I don’t even know if scientists have a consensus view of “what it is to be human”!

Now I don’t mean to be highly critical of the paper, as the description of the trove of skeletons is remarkable, and the analysis and description of differences from existing species is very good. I suppose what I’m criticizing here is largely the press coverage of this find, but also the willingness of the investigators to give this group a new species name when its age isn’t even known, and when it could simply be a geographical variant of an existing species—something that would be clearer if we had dates! And I am not an expert in human evolution, so I could be missing something, or have erred in my opinion. As usual, I’m willing to be corrected. But for the moment, caveat lector.

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Berger, L. R. et al. 2015. Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. eLife: 2015;4:e09560, DOI http://dx.doi.org/10.7554/eLife.09560.

Readers’ wildlife photos (including paleobiology!)

August 28, 2015 • 7:10 am

I’m pleased to feature some paleontology today from reader John Scanlon. In case you didn’t know, stromatolites are layered accretions of microorganisms, usually cyanobacteria (“blue-green algae”), and they represent some of the oldest fossils on earth: about 3.5 billion years old—only about a billion years after the Earth was formed. But these accretions are still formed today by living bacteria, and exist in a few spots on the planet that have extremely salty water, including Australia, Brazil, and Mexico.

Shark Bay, Australia, which John mentions below, is one of these places, and I’ll put a photo of living stromatolites below his photos. His notes:

My phone generally doesn’t do justice to actual fauna, but might do for some nice palaeobiology on a recent working trip in the Hamersley Range (Pilbara, Western Australia). The area’s well known for its banded ironstone formations (BIF; formed as the dissolved iron in the oceans rusted out, keeping the level of toxic oxygen low for a while), but also has extensive basalt flows (also dikes and sills) and outcropping granite/greenstone basement, ranging from Archaean into Proterozoic. The tectonic stability of the area is shown by the fact that most of the stratified rocks are still nearly horizontal , though there are also some very attractively folded BIFs around the edges.

The attached photos show something I haven’t often seen in the Pilbara: really well preserved stromatolites (in the Carawine Dolomite). They have the same range of sizes and shapes as the ones forming today in Hamelin Pool at Shark Bay, not very far away. The stromatolitic carbonates formed in shallow parts of the basin at the same time as the BIFs were accumulating in the deeper areas. The vertical and horizontal jointing and differential etching of the rock make them outstandingly clear examples, and also full of crevices so I had good reason to spend time looking at the rock while searching for animals. In one pic, wave ripples on a horizontal surface have been polished by Euro (JAC: waleroos, a marsupial: Macropus robustus) using the overhang as a sleeping shelter.

Ref: Rasmussen et al. (2005, doi: 10.1130/G21616.1) date these rocks to about 2.63 Ga. [JAC: 2.6 billion years old!]

The remnants of ancient life:

Wave ripples polished by sleeping wallaroos!:

Here are some living stromatolites being formed today in Shark Bay, Western Australia (picture from Wikipedia). They look just like their fossil forebears.

Here’s a cross-section of a living stromatolite, showing its similarity to the ancient ones (source here):

Putative amphibian fossil shows “broken” bone; said to be first indication of terrestriality

May 26, 2015 • 10:00 am

Now this paper is way above my pay grade, as it involves all kinds of complicated scanning, computer, and mathematical analysis of a “fishapod” fossil. The conclusion, from a new paper in PLoS ONE by Peter Bishop et al., is that the fossil, Ossinodus sp., shows a callus on its radius (one of the two lower forelimb bones), and that this callosity may represent partial but not complete healing following a fracture (there are suggestions of an infection, and the beast may have died before healing was complete). The analysis suggests in turn that the animal fell nearly a meter onto its leg, breaking the bone. Because such falls presumably cant occur in water, the authors conclude that this creature fell on land.

From this they say that Ossinodus, which dates to 333 million years ago, was a tetrapod—a proto-amphibian living at least partly on land—and that this is the earliest tetrapod known, since before this the oldest indisputable tetrapods come from 327-331 mya. If this report and its conclusions are correct, then, this pushes the earliest invasion of the land back between 2 and 5 million years earlier than previously known.

Here’s the beast, which looks a lot like the famous Tiktaalik, itself likely a transitional form (or something related to one) between fish and amphibians. Also shown is the callus on the foreleg and the caption from the paper:

Through CT (computer tomographic) scanning, they were able to visualize through the callus to the bone, and suggest that there was a crack (fracture) indicating that the animal had fallen on its foreleg. Here’s a reconstruction of the fracture; the arrows indicate five different models of weight loading that the authors used to see what might have caused the fracture:

After making these models, calculating the putative weight of the animal (10-25 kg), and making a few other assumptions, they conclude that this fracture must have resulted from a fall of between 0.85 to 1.1 meters, or about three feet. They say this could not have happened in the water, and, ruling out other explanations, argue that this shows pretty clearly that the animal was terrestrial. In their view, the invasion of land had begun. From the paper:

As all of the estimations and assumptions underpinning the above calculations have been made on the conservative side (e.g., the purposeful overestimation of body mass), we are confident that the force required for the radius to fracture in the manner it did was very large, and that a fall on land is entirely possible from a mechanical perspective. Consistent with a fall hypothesis, the mode of displacement along the fracture (Fig 7a) is very similar to that of proximal radius fractures in humans which result from a fall onto an outstretched arm, where the humerus impacts upon the radial head [33,34]. Since the force required for fracture in the FEA was a distributed load, this excludes the possibility that it resulted from a bite (predatory or otherwise), where an impacting tooth would produce a spatially concentrated load. We therefore conclude that the most plausible explanation for the fracture in the radius of Ossinodus was that the animal was living on land and sustained a fall.

And they claim, with confidence, that the species antedates the next oldest terrestrial vertebrate by several million years:

Ossinodus is the oldest biomechanically demonstrable, terrestrially adapted tetrapod, being at least two million years older than Casineria kiddi, and at least five million years older than the East Kirkton tetrapod assemblage. These small (generally less than 40 cm long), Scottish tetrapods have previously been widely regarded as the oldest known terrestriality adapted vertebrates.

The confidence here is stronger than the indication in the previous paragraph that a land fall is “entirely possible.” For “entirely possible” is not the same as “very probable”!

This is an intriguing finding, and the authors did a huge amount of work. It’s possible that they are indeed correct, but I have some questions about the assurance of the authors’ conclusion. Some of these caveats may reflect my ignorance of the analysis, for it’s indeed complicated, and readers with biomechanical interests should read the paper, which is available free at the link below.

1. Was the creature terrestrial? We don’t know. The fossil was of course found in sedimentary rock, i.e., it was buried underwater. Ossinodus could have been semi-aquatic, like early amphibians must have been, but it could have been fully aquatic. There is no independent evidence, beyond the broken radius, that it was partly or fully terrestrial.

2. Does the pathology unequivocally demonstrate a fall-induced fracture? I’m sure there are other explanations for this dysplasia, or even the crack (if it was indeed a fracture that occurred during life), including developmental anomalies. Can we rule out all other causes (including bites) with enough confidence to conclude this was a fall on land? Is there any evidence that fish break bones in the same way?

3. The sample size is small. We have a single individual with a single broken forelimb bone. Is that sufficient to lead to such sweeping conclusions? It would be nice to either have samples with other broken bones, or some other indication of terrestriality.

In sum, we have an intriguing finding here, and the authors may well be correct, but I’m not sufficiently convinced by the data—and the complicated analysis—to conclude that we have an animal that was unequivocally terrestrial or amphibious. Were I the authors, I would hedge my bets a bit more than they did when claiming they’d found a “biomechanically demonstrable” terrestrial tetrapod.

I also wonder why they published the article in PLoS ONE, a journal which has a less rigorous review process than journals which vet things not just for the soundness of the analysis, but for the novelty of the findings. If I had unequivocal evidence of the earliest land animal, as the authors say they do, I would have sent it to Nature or Science.

As I said, some of my questioning may reflect my naivité about the methods and analyses, but the earliest known tetrapod really deserves publication in a more visible journal.

h/t: Steve

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Bishop, P. J., Walmsley C. W., Phillips M. J., Quayle M. R. , Boisvert C. A., and McHenry C. R.. 2015. Oldest pathology in a tetrapod gone illuminates the origin of terrestrial vertebrates. PLoS ONE 10(5): e0125723. doi:10.1371/journal.pone.0125723

New fossils: the world’s earliest known bird

May 8, 2015 • 11:15 am

Here’s a short scientific report (yesterday’s didn’t inspire much enthusiasm)—short because much of the paleontology is beyond my expertise, as the paper consists largely of describing features I’m not familiar with. But this new paper in Nature by Min Wang et al. (link and reference below) is quite important, for it describes what appears to be the earliest true bird: two specimens of a species found in China in the early Cretaceous (130.7 million year old). And it pushes the origin of the ancestor of modern birds back at least five million years.

Based on its features, this bird, named Archaeornithura meemannae, falls within the group “Ornithuromorpha,” which includes all modern birds and their common ancestor, as well as all the extinct descendants of that ancestor. It can thus be regarded as a “bird,” and its well-preserved plumage suggests that it not only could fly, but was close to the appearance of modern birds.

I’m going to let the readers, some of whom really know this stuff, apprise us all of its further significance, as well as correct any errors I make.

Here is one of the two fossils, showing the plumage and wings. It was about the size of a sparrow. The main slab is to the left, the counter slab to the right (these are the two halves of a “compression fossil” found in sedimentary rock, obtained when you split the rock to get the fossil itself):

Oldest-Ancestor-of-Modern-Birds — (From paper): Figure 1 | Holotype of Archaeornithura meemannae gen. et sp. nov., STM7-145. (a) Main slab; (b) counter slab. Anatomical abbreviations: al, alular digit; ba, basicranium; co, coracoid; cv, cervical vertebrae; d I–IV, pedal digit I–IV; fe, femur; fi, fibula; fu, furcula; hu, humerus; ma, major digit; mi, minor digit; pr, primary remiges; pu, pubis; ra, radius; re, rectrices; sc, scapula; st, sternum; ti, tibiotarsus; tm, tarsometatarsus; ul, ulna. Scale bars, 10 mm.

Below are the wingbones of the same specimen (aren’t they cool?), and its very birdlike feet:

Screen Shot 2015-05-08 at 10.30.30 AM — (From paper) Figure 3 | Detail anatomy of Archaeornithura meemannae gen. et sp. nov. (a) Photograph and (b) line drawing of the left wing, STM7-145, counter slab; (c) line drawing of hands of other hongshanornithids (not scaled; from left): Hongshanornis longicresta, Longicrusavis houi, Tianyuornis cheni, Parahongshanornis chaoyangensis; (d) STM7-163, counter slab; (e) STM7-163, main slab; (f) feet, STM7-163, main slab. Anatomical abbreviations: al, alular digit; am, alular metacarpal; ca, caudal vertebrae (six vertebrae counted); del, deltopectoral crest; d I–IV, pedal digit I–IV; hu, humerus; is, ischium; ma, major digit; mam, major metacarpal; mi, minor digit; mim, minor metacarpal; mt I, metatarsal I; pb, pubic boot; pu, pubis; py, pygostyle; ra, radius; sp, supracondylar process; ti, tibiotarsus; tm, tarsometatarsus; ul, ulna. Scale bars, 10 mm (a,f), 5 mm (d,e).

Finally, the plumage and feet of the second specimen. The preservation is quite amazing:

Screen Shot 2015-05-08 at 10.32.40 AM — (From paper): Figure 4 | Plumage of Archaeornithura meemannae gen. et sp. nov. (a) Left wing, STM-7-145, main slab; (b) right wing, STM-7-145, main slab; (c) covert feathers over the skull and neck, STM 7-163, counter slab; (d) alular feathers on the left alular digit, STM7-163, main slab. Abbreviations: af, alular feather; dc, dorsal coverts; pr, primary remiges; re, rectrices. Scale bars, 10 mm (a–c), 5 mm (d).

A few points. First, the “flight” feathers are symmetrical. That used to be a sign that the bird couldn’t fly, as asymmetrical feathers (with the leading edge about half the width of the trailing edge) are present in modern flying birds. But apparently asymmetry is no longer seen as a sign of flightlessness.

Second the bird had a head crest (see reconstruction below).

Third, it had two other features suggesting it could fly. The first is “fan-shaped retrices”, or tail feathers. This shape helps provide lift to a flying bird. It also had an “alula“, also called a “bastard wing”: a group of feathers associated with the mobile first digit of the bird, and present in some modern birds, where it can help the flying animal slow down without stalling.

Here’s a graphic of an alula (in red), and a photo of it extended in action, helping an eagle land (both from Wikipedia). I believe the alula in the eagle picture is the clump of four feathers sticking up on the far wing.

As the authors note:

Archaeornithura preserves fairly advanced plumage including a well-developed alula and fan-shaped rectrices (Figs 1 and 4. . ). Both the alula (bastard wing) and a fan- shaped tail are aerodynamically important for living birds during slow flight and increases manoeuvrability.

Finally, here’s a reconstruction of A. meemannae from the Cosmos site. That’s a damn bird!

Screen+Shot+2015-05-06+at+3.47.03+pm — [Credit: Zongda Zhang]

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Wang, N. et al., 2015. The oldest record of ornithuromorpha from the early cretaceous of China. Nature Communications 6, Article number:6987doi:10.1038/ncomms7987

More on the dino-bat Yi qi

May 4, 2015 • 2:00 pm

Five days ago I wrote about the new Nature paper revealing the “dino-bat” fossil Yi qi, a bizarre species of theropod that had feathers but also membranous wings like a bat—and a special new bone, evolved from the wrist, that supported its wing. It isn’t clear whether this creature could fly, but it surely could at least glide. At any rate, Nature has put out a two-minute video about the beast, and here it is. (If you didn’t read the post, this can serve as a precis.)

I don’t like the slur on pigeons at the end, for, in parts of the world, pigeons are the most common dinosaurs.

h/t: Heather Hastie

Dinosaur feathers found in amber

April 21, 2015 • 10:00 am

UPDATE: I’m a real dummy; I failed to check the dates of any of these items and a eagle-eyed reader noted that they’re all from 2011! I should have seen that from the dates on the Science paper, if not the links. Oh well, it’s still interesting stuff.

*******

A paper in Science by Ryan McKellar et al. (reference and link below; no access to full paper without $$!) reports the amazing discovery of feathers preserved in amber from the late Cretaceous (around 65-90 million years ago). The amber (fossilized plant resin) was discovered in deposits at Grassy Lake, Alberta, Canada. There’s also a nice piece in The Atlantic which summarizes the importance of the findings and a series of photos at io9.com with explanations of what each photo shows. The striking finding is that there are all stages of feather evolution seen in the amber, from simple filaments to very complex feathers.

Now we’re not sure what creatures these feathers belong to, so I’m jumping the gun a bit with the title. Our uncertainty is because there are no fossils of anything in the layer where these feathers were found. But the authors justify the conclusion that these are dinosaur feathers because they’re in layers near those containing near dino remains:

Although neither avian nor dinosaurian skeletal material has been found in direct association with amber at the Grassy Lake locality, fossils of both groups are present in adjacent stratigraphic units. Hadrosaur footprints are found in close association with the amber, and younger (late Campanian and Maastrichtian) strata of western Canada contain diverse nonavian dinosaur and avian remains. There is currently no way to refer the feathers in amber with certainty to either birds or the rare small theropods from the area. However, the discovery of end- members of the evolutionary-developmental spec- trum in this time interval, and the overlap with structures found only in nonavian dinosaur com- pression fossils, strongly suggests that the proto-feathers described here are from dinosaurs and not birds.

Since we already have all kinds of fossil dinosaurs showing imprints of feathers, and those feathers seem to range from simple filaments to more complex feathers similar to those of modern birds, what does this finding add to what we already know? The answer is that these are 3-dimensional feathers that aren’t compressed, and give us a much better look at what early feathers were like. And that view supports a previously-suggested scenario of where bird feathers came from.

That scenario, as sketched in the paper, is diagrammed below. It begins with single filaments (I) that branch out to form a tuft of filaments (II), and some of these either coalesce to form a central shaft, or “rachis” (IIIb), or develop secondary branches (IIIa), with the next step the development of “tertiary” branches (IIIa + b).

Then those tertiary bits can either develop hooks (“distal barbules”: “d.b.” in the middle figure) or unhooked “proximal barbules” (“p.b.”). At this point, stage IV below, we pretty much have a modern feather with a central shaft and side filaments that hook together to make the feather into a unit (essential for flying). In stage V, other specializations develop. Remember, this figure represents a hypothesis about how feathers evolved before the amber feathers were found.

What the authors found was that basically every stage of feather development could be seen in the eleven specimens of amber analyzed in the paper. This, then, supports the scenario given above. I’ll show some photos from io9, but let me first add four things.

First this scenario for feather development suggests that feathers evolved, as I and many others long suspected, for thermoregulation. The filaments are, according to the authors, present in densities that would help thermoregulation and “protection” (I’m not sure what they’d protect), militating against any use in gliding (filaments don’t help you glide) and perhaps against ornamentation as their sole function (though they could also have served to ornament the bird).

Second, some of the feathers are so well developed that, according to the authors, they would have enabled the dinosaurs bearing them to fly. I’m not an expert on this, so I’ll take their word for it.

Third, some of the feathers are pigmented, and in ways similar to those of modern birds. Further, some of the filaments are coiled at their base, a feature that modern birds like grebes still have, and use to trap water to ferry to their young. Apparently the coiling of a straight filament enables the groove in the middle to trap water through capillary action.

Finally, all of these stages of feather evolution were found in roughly the same time period (same deposit), implying that there were all sorts of dinos coexisting with different degrees of feather evolution. Certainly not all of them gave rise to modern birds; most surely went extinct along with the rest of the dinosaurs. In fact, it’s likely that none of these specimens are from a species that was ancestral to modern birds.

Now to the feathers; all indented captions are from io9:

An isolated barb from a vaned feather, trapped within a tangled mass of spider’s web in Late Cretaceous Canadian amber. Pigment distribution within this feather fragment suggests that the barb may have been gray or black. Image via Science/AAAS

This is one of the later stages of feather evolution.

Below is an earlier stage when there were just filaments. Notice that there are many all together, which supports the notion that they could have been involved in thermoregulation.

Numerous individual filaments in Late Cretaceous Canadian amber. These filaments are morphologically similar to the protofeathers that have been found as compression fossils associated with some dinosaur skeletons. Pigment distributions within these filaments range from translucent (unpigmented) to near-black (heavily pigmented). Image via Science/AAAS

Here are the water-retaining feathers with filaments coiled at their base:

Cross-section through a feather with basally-coiled barbules, accompanied by a microphysid plant bug. The helical coiling observed within these barbules is most obvious in isolated barbules within the image, and is directly comparable to coils found in modern bird feathers specialized for water uptake. The high number of coils in the amber-entombed feather is suggestive of diving behavior, but similar structures are also used by some modern birds to transport water to the nest. Image via Science/AAAS

Pigmented feathers!

Series of six feather barbs in Late Cretaceous Canadian amber. Localized pigmentation creates a beaded appearance within each barbule: This has implications for the structural interpretation of fossil feathers exhibiting this general morphology. Pigment distribution within the specimen suggests that the feather would have originally been medium- or dark-brown in color. Image via Science/AAAS

More colored feathers.

A feather barb within Late Cretaceous Canadian amber that shows some indication of original coloration. The oblong brown masses within the dark-field photomicrograph are concentrated regions of pigmentation within the barbules. In this specimen, the overall feather color appears to have been medium- or dark-brown. Image via Science/AAAS

And more complex feathers.

Overview of 16 clumped feather barbs in Canadian Late Cretaceous amber. Image via Science/AAAS

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McKellar, R. C., B. D. E. Chatterton, A. P. Wolfe, and P. J. Currie. 2011 A diverse assemblage of late Cretaceous dinosaur and bird feathers from Canadian amber. Science 333:1619-1622

A new phylum of very weird sea creatures

September 7, 2014 • 6:57 am

Read some biology today; it’s good for you!

It’s not often that a new animal phylum has been described, but a new paper in PLoS ONE apparently does just that, basing the phylum on two enigmatic species, dredged up from the deep sea, that can’t be placed in any existing phylum. This may add one more to the 35 phyla that already exist (see the list here, and please look. It’s nice to review the major divisions of life.)

The paper is by Jean Just et al. (all authors are from the Natural History Museum of Denmark at the University of Copenhagen), and the reference and pdf, which is free, are below.

What we have is something that looks like a cnidarian (jellyfish, corals, and sea anemones) or a ctenophore, but with a stalk. (Some cnidaria do have a stalk). But it has features that keep it from being placed in the phyla Cnidaria or Ctenophora. Its placement on the tree of life is further complicated by two things: we don’t really know where some major groups fit on the tree of life already (see below), and we don’t have any DNA or molecular data from this group to see what it’s most closely related to, or whether it’s an outgroup (a more distant ancestor) to all metazoans (multicellular animals).

The problem is that these creatures, which I’ll show shortly, were dredged up off of Victoria, Australia in 1986 from 400-1000 meters down. They were then fixed in formalin and later transferred to 80% ethanol. I’m no molecular biologist, but I think that would pretty much destroy the DNA, preventing any molecular analysis. And the samples are now old, shrunken a bit and degraded, and so some features may be effaced.

What we have are two species placed in a new genus, Dendrogramma, which the authors consider members of a new phylum as well, though they didn’t formally name one in this paper—probably because the placement of these creatures is uncertain. Two species were named. Here’s the first, Dendrogramma enigmatica:

Like the other speciers, it has a flattened disc with a notch in it, a stalk (so it was attached to the substrate), and a mouth-like opening that leads into an “gastrovascular” canal in the stalk that also feeds into the radiating canals in the disc. The tissue types were not examined, so we can’t draw homologies between the types of layers and those of other metazoans. Here’s the other species, Dendrogramma discoides:

And both species together. You can see from the scale (1 mm) that they were very small (10 mm = 1 cm, and there are 2.54 cm per inch).

Because of the stalk and the inflexible disc, these things were probably unable to swim but attached to rocks or the sea floor. Given their mouthlike opening, the authors suggest that “they fed on microorganisms, perhaps trapped by mucus from the specialized lobes surrounding the mouth opening.”

Why aren’t they members of existing phyla like cnidarians and ctenophores? Because they lack features found in those phyla. As the authors say (my emphasis):

Dendrogramma shares a number of similarities in general body organisation with the two phyla, Ctenophora and Cnidaria, but cannot be placed inside any of these as they are recognised currently. We can state with considerable certainty that the organisms do not possess cnidocytes, tentacles, marginal pore openings for the radiating canals, ring canal, sense organs in the form of e.g., statocysts or the rhopalia of Scyphozoa and Cubozoa, or colloblasts, ctenes, or an apical organ as seen in Ctenophora. No cilia have been located. We have not found evidence that the specimens may represent torn-off parts of colonial Siphonophora (e.g., gastrozooids). Neither have we observed any traces of gonads, which may indicate immaturity or seasonal changes. No biological information on Dendrogramma is available.

Given the absence of DNA data or complex characters that might help us decide where these things fit in the tree of life, the authors can only speculate. One big problem is that we don’t really know where the major phyla of multicellular animals fit on the tree. For example, some biologists claim, based on both molecular and morphological data, that the “outgroup” (the most unrelated phylum) to all metazoa is the Porifera (sponges). Others (and the authors of this paper take this position) claim that the outgroup is really Ctenophora (which, based on morphology alone, I would have thought were more closely related to the cnidarians, as biologists once thought [they’re really distantly related groups, though]). So here’s the phylogeny presented in the paper, showing cetophores as the outgroup to other metazoans (including the Bilateria, the group of phyla that includes all bilaterally symmetrical animals, including us:

To hedge their bets, the authors have also included ctenophores within other groups, as its placement is uncertain. They’ve put Dendrogramma as either an outgroup to all other phyla, or perhaps more closely related to the ctenophores or cnidarians. We just don’t know yet.

Molecular evidence could potentially resolve the placement of all these groups, and, frankly, I’m surprised that we haven’t settled the issue. For Dendrogramma we clearly need fresh material to get DNA (the authors plead for someone to get more specimens), but we could get plenty of DNA from the other species. Either that hasn’t been done (which I strongly doubt), or the lineages diverged so long ago that DNA evidence is inadequate to settle the question of, say, whether sponges or ctenophores are the outgroup. Perhaps some reader can explain to us why this major issue remains unsettled.

I noticed that the discs of these species resemble some creatures described from the Ediacaran fauna (also called the “Vendian fauna”), a group that lived from about 580 million years ago to about 545 million years ago, when the “Cambrian explosion” occurred and Ediacaran animals (if they were animals!) disappeared. (For pictures of various weird Ediacaran creatures, see here.)

My friend Latha Menon, who is not only the trade science editor at Oxford University Press (and editor of the British edition of WEIT) but also a Ph.D. candidate at Oxford’s Department of Earth Sciences, would know more about this, as she works on discs that strongly resemble these, but lived hundreds of millions of years ago. I therefore asked her to relate the new finding to the old group, as they could be related. Her answer is below, along with references. As you can see, she’s a very good writer, and I’m grateful for her input on this issue.

by Latha Menon

The discovery of Dendrogramma from the deep sea off Australia has undoubtedly caused a frisson of excitement among researchers on early life. A living fossil? An Ediacaran that has been surviving quietly in bathyal regions for several hundred million years? Let’s not get carried away, but it is an intriguing find.

When Reginald Sprigg discovered, in the 1940s, a set of strange impressions, many of discoidal forms, preserved on surfaces of the sandstone and quartzite of the Ediacara Hills, South Australia, he called them “medusoids”. Further work by Martin Glaessner and Mary Wade in the late ’60s continued to describe the various discoidal forms as medusoids, while frondose forms such as Rangea were considered to be Pennatulaceans (sea pens), and Dickinsonia was thought to be an annelid. Since then, Ediacaran macrofossils have been found all over the world, including spectacular fossil assemblages from the White Sea coast in Russia, the Nama Group, Namibia, Lantian and Miaohe Formations in South China, and the remarkable “E surface” at Mistaken Point, Newfoundland (see e.g. Fedonkin et al., 2007). The biota gave its name to the Ediacaran Period (635-541 Ma) ratified in 2004, and the fossils themselves appear from about 579 Ma (perhaps earlier), soon after the Gaskiers glaciation, the last of several widespread glaciations, and stretch up to the Cambrian boundary. Close to the boundary, the earliest biomineralized forms, the “small shelly fossils” appear, along with intense burrowing activity (bioturbation), and the Ediacarans, as far as we know, disappear, perhaps in an extinction. So what were the Ediacarans?

Nearly 70 years after Sprigg’s discovery, with many more fossil impressions, the affinities of the Ediacaran biota remain uncertain. Remember, that’s all we have – impressions (and in some cases, carbonaceous compressions) in the rocks. No skeletons; no biomineralized parts; and certainly no DNA. Molecular clocks provide little help so far back in time; results are notoriously varied and unreliable. Fossils really matter. And in spite of the limitations, a great deal of work has been done to glean information from the often exquisitely detailed impressions and the sedimentology of the surrounding rock, which indicates the setting in which they lived and died. As more evidence accumulated concerning morphology and sedimentary context, the early interpretations of medusoids, pennatulaceans, and annelids was increasingly questioned. Some may reach 30 cm and more in size, but were they necessarily early animals? The late Dolf Seilacher proposed that these enigmatic forms represented a “failed experiment”.

Discoidal forms are particularly hard to interpret. Some simple forms may be pseudofossils formed by physical processes; others have been persuasively explained as microbial colonies (Grazhdankin and Gerdes, 2007). Still, some possible affinities with familiar taxa have been suggested, with evidence put forward for bilaterian traces from about 555 Ma, and the claim that Kimberella may have been an early mollusc (Fedonkin & Waggoner, 1997). Our own group has found evidence in the early Ediacaran Avalon assemblage of Newfoundland for horizontal and vertical motion associated with a discoidal form (Liu et al., 2010; Menon et al., 2013), suggesting that some of these discs may indeed have been simple polyp-like forms. Two weeks ago, we published a paper describing Haootia quadriformis n. gen. n. sp. (Liu et al., 2014: – an extraordinary fossil impression that appears to indicate muscle bands, and bears a striking similarity to modern stalked jellyfish (Staurozoa). The idea that some of the Ediacaran discoidal forms may have been stem-group medusoids has made a big come-back.

And then we hear of Dendrogramma. The authors have referred it to Metazoa incertae sedis [“of unknown placement”]. The organism resembles cnidarians and ctenophores, but lacks the characters to establish a certain affinity with either group, though molecular analysis of further individuals might yet show that it belongs to one of these lineages (the existing specimens were damaged in preparation and not suitable for DNA analysis). Whether or not Dendrogramma turns out to represent a new phylum, it does seem to be a relatively primitive form, lacking cnidocytes, colloblasts, and other more sophisticated characters. From the discription, Dendrogramma appears to be a simple diploblastic animal with a disc showing a distinct pattern of gastrovascular branches and, in the case of one of the two species, D. discoides, a stalk with a possibly trilobed mouth-field. Various Ediacaran discoidal forms, particularly those from the diverse assemblages of South Australia and the White Sea, Russia, have trilobed structures within the disc, most obviously Tribrachidium. The authors point out the similarity of D. discoides with Albumares brunsae, and Anfesta stankovskii, as well as the less obviously trilobed Rugoconites from South Australia. There does appear to be a morphological similarity, particularly with the former two forms, both in the trilobed structure and in the pattern of radial ridges compared with the gastrovascular branching on the disc of Dendrogramma.

So can we conclude that Dendrogramma is a living Ediacaran? That’s almost certainly going too far. But it does seem quite possible that some of the trilobed Ediacaran discs may represent stem-group forms of such a lineage, lacking in such modern armoury as cnidocytes (for what would they sting?) and possessing a simple small mouth with no surrounding tentacles. As for all the other kinds of Ediacaran forms, even the many other discoidal forms, well, the work goes on.

Latha’s References:

Fedonkin, M.A., et al. (eds), 2007, The rise of animals: Evolution and diversification of the Kingdom Animalia: Baltimore, Maryland, Johns Hopkins University Press

Fedonkin, M.A., and Waggoner, B.M., 1997, The late Precambrian fossil Kimberella is a mollusc-like bilaterian organism: Nature, v. 388, p. 868–871

Glaessner, M.F., 1959, Precambrian Coelenterata from Australia, Africa and England: Nature, v. 183, p. 1472–1473

Glaessner, M.F., and Wade, M., 1966, The late Precambrian fossils from Ediacara, South Australia: Palaeontology, Vol 9 (4), pp. 599-628

Liu, A.G., McIlroy, D., and Brasier, M.D., 2010, First evidence for locomotion in the Ediacara biota from the 565 Ma Mistaken Point Formation, Newfoundland: Geology, v. 38, p. 123–126

Menon, L.R., McIlroy, D., and Brasier, M.D., 2013, Evidence for Cnidaria-like behaviour in ca. 560 Ma EdiacaranAspidella, Geology, v. 41, p. 895–898

Sprigg RC. 1947. Early Cambrian (?) jellyfishes from the Flinders ranges, South Australia: Trans. R. Soc. S. Aust. 71(Pt. 2):212–24

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REFERENCE TO THE NEW PAPER: Just, J., R. M. Kristensen, and J. Olesen. 2014. Dendrogramma, New Genus, with Two New Non-Bilaterian Species from the Marine Bathyal of Southeastern Australia (Animalia, Metazoa incertae sedis) – with Similarities to Some Medusoids from the Precambrian Ediacara. PLOS One DOI: 10.1371/journal.pone.0102976

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