Category: fossils

Wonderful fossil dinosaur embryo shows birdlike “tucked” posture before hatching

December 24, 2021 • 11:00 am

This is one the most stunning fossils I’ve seen in a long time. It’s an almost perfectly preserved dinosaur embryo that somehow died in the egg during the Late Cretaceous (100 mya-66mya). It’s not just amazing for its preservation, but also for the posture of the unhatched embryo, which resembles the posture that modern bird embryos (an also early birds themselves) assume soon before hatching. The inference is that the behaviors that precede hatching in birds, and help them through the tough process of getting out of the egg, actually evolved from their reptilian ancestors—the theropod dinosaurs, of which this specimen is one.

The paper appears in iScience and is free; click on the screenshot below or get the pdf here.

I’ve really conveyed the gist of the paper in the first paragraph above, but you need to see this embryo! Click to enlarge; all the photos are high-resolution

(from paper): Figure 1. Oviraptorid embryo inside an elongatoolithid egg (YLSNHM01266) Abbreviations: cev, cervical vertebra; cv, caudal vertebra; dv, dorsal vertebra; f, femur; fi, fibula; II-1, pedal phalanx II-1; il, ilium; is, ischium; m, mandible; mt-I, metatarsal I; mt-III, metatarsal III; mx, maxilla; p, pubis; pm, premaxilla; r, radius; s, scapula; t, tibia; ul, ulna. Scale is 1 cm.

 

The specimen is given the number YLSNHM01266, and is described as a “new non-avian theropod dinosaur embryo. . . from the Late Cretaceous Hekou Formation of southern China.” No species name is given because without a fossil of an adult in the vicinity, we have no idea. We can tell, however, that it is a theropod dinosaur, and an “oviraptorid oviraptorosaur“.

Oviraptors constitute is a group of theropod dinosaurs of varying sizes, which lived in what is now North America and Asia. Fossils show that they had feathers, parrot-like beak mandibles, sometimes bony crests on the head, and walked on their hind legs. Paleontological analysis combined with phylogeny shows, as Wikipedia notes, that they are “close to the ancestry of birds.” (The ancestor of birds is thought by most but not all paleontologists to be theropod dinosaurs.)

Here’s a group of diverse ovoraptors from Wikipedia. You can see that their skeletons are more birdlike than those of other dinosaurs. Some scientists, indeed, group them with birds! Four species have been found with feather impressions, so it’s likely that the group (including the baby above) had feathers, but couldn’t fly. Maybe one of the species below is the adult that would have developed from the juvenile above!

Back to the fossil.  Here’s part of a later figure that helps you make sense of what’s what in the photos above. The air cell, also present in modern bird eggs, is to the right between the embryo and the shell.

If you want the technical description of the posture, here it is from the paper. I’ve bolded the important parts.

The articulated embryonic skeleton is preserved curled inside its egg (YLSNHM01266), with the skull positioned ventral to the body (Figure 1). The egg is elongate ovoid in shape with dimensions of 16.7 cm long by 7.6 cm wide, and has characteristics typical of the egg family Elongatoolithidae (see STAR Methods for eggshell analysis). The skeleton is almost complete, without much apparent postmortem disruption. The anterior surface of the skull faces toward the pointed pole and is situated about egg mid-length at the level of the ilium in-between the flexed hindlimbs, with a pes [foot] on either side. The anterior cervical vertebrae are in line with the long axis of the skull. The presacral vertebral column is strongly bent in an angular manner, so that the upper back of the embryo faces the blunt pole of the egg (similar flexion of the vertebral column is found in modern in ovo skeletons, e.g. Balanoff and Rowe, 2007: Figure 4, Day 18, and is not likely to be a taphonomic artifact). The skeleton is ∼23.5 cm in total length, measured from the anterior tip of the skull to the last preserved caudal vertebra, and occupies nearly the entire width of the egg and most of the length, with the exception of a ∼1.9 cm space between the dorsal vertebrae and the blunt pole of the egg. This space may represent the air cell, a space usually found between the back of the embryo and the blunt pole of bird eggs (e.g., Rahn et al., 1979). However, this inference is tentative and awaits further evidence. The posterodorsal, sacral and caudal vertebrae almost form a straight line along the long axis of the egg. Although the precise developmental stage of the embryo is unclear, it is likely to represent a late-stage embryo because the skeleton is well ossified and is large in size relative to the space inside the egg, as inferred in MPC 100/971 (Norell et al., 2001).

Note that the specimen is 23.5 cm, or a bit more than nine inches long: as long as a dollar bill and half of another one (American dollar bills are almost exactly 6 inches long, and can be used for emergency measurements).

When modern birds hatch, they assume this position as the first of three stages prior to hatching: “pre-tucking”, “tucking” and “posttucking” (we know this clearly because, sadly, many pre-hatched birds have been dissected from the egg). I won’t go through the complicated description of the changes in posture, but here’s how it happens in a chicken, with the fetal dinosaur placed between “pretucking” and “tucking”. “Membrane penetration” is when the bird uses its bill to get out of the membrane in which the embryo is enclosed, and “pipping” is when it begins to peck through the shell (often a long process).

Apparently birds always tuck their heads below their right wing, not their left, before pipping. How they know left from right (genetically) is beyond me; but somehow this asymmetry is coded in the DNA:

And here are three examples of embryonic oviraptors compared to a modern bird (chicken) at the assumed similar stages:

(from paper): Figure 3. In-ovo late-stage embryos of non-avian and avian dinosaurs (A) Oviraptorid specimens (MPC 100/971, YLSNHM01266 & IVPP V20183), which potentially correspond to various tucking stages. (B) Domestic fowl Gallus ontogenetic series (day 16-20) (modified from Rowe (2003)). Not to scale. Silhouettes modified from PhyloPic.

Now the authors are very careful not to overinterpret a single fossil, but I do think it’s likely that the oviraptor fossils show that their pre-hatching positions and behavior was passed on to birds, as oviraptors are phylogenetically close to the ancestor of birds (though we don’t know whether the ancestor of birds was an oviraptor).

The only question remaining is: do all dinosaur embryos—not just those closely related to the ancestor of modern birds—show similar embryonic behavior? The answer is, as usual, we just don’t know. There’s a severe shortage of well-preserved dinosaur embryos, as you might imagine One specimen of a sauropod, a distant relative, seems to show a different fetal posture than the ones above.

I hope we can find more fossil embryos, because, although behavior doesn’t fossilize, the correlates of behavior—represented by the posture of embryos—do. In that sense the way modern birds hatch might what some systematists call a synapomorphy: a character shared by two species (or groups) because it was present in an ancestor—in this case the common ancestor of the ovoraptors and modern birds. And it’s surely an adaptive synapomorphy, because birds that can’t get out of the shell don’t leave any genes behind.

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Xing, L. et al. 2021.  An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures.  iScience, in press.

Oldest evidence for animals found? New sponge-like fossil is 890 million years old, several hundred million years older than next oldest animal

July 29, 2021 • 9:15 am

First, we have to know what biologists mean by “animals”. In brief, they are multicellular organisms comprising eukaryotic cells (“true cells” with a nucleus and nuclear membrane, as well as organelles like mitochondria). Or, to be more specific, I’ll give the Wikipedia definition:

Animals (also called Metazoa) are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in which their body consists of a hollow sphere of cells, the blastula, during embryonic development.

Long before animals existed, living organisms existed, but these were cyanobacteria (“blue green algae”) and other microbes, not regarded as animals. The first cyanobacteria date back about 3.5 billion years, only a billion years after the Earth formed. The cyanobacteria are identified in fossil stromatolites—layered reef-like structures formed by the accretion of bacteria. Stromatolites are still forming in some places on Earth, like Shark Bay, Australia.

But when did the first metazoan, or “animal” appear? For that you can use either fossil or molecular evidence.

The earliest fossil scientists regard as an animal is Dickinsonia from the Ediacara fauna, dated about 540 million years ago.  Scientists think it’s an animal because its lipid biomarkers, which you can extract from fossils and the sediments above and below them, include cholesteroids, compounds found exclusively in animals. Dickinsonia is known only from imprints, like the one below, and its affinities are a mystery.

Dickinsonia

Molecular data, from which you can construct a phylogenetic tree of living animal groups and then extrapolate backwards, have shown that animals probably originated between 650 and 850 million years ago, but we have no animal fossils from that period. Those trees also show that perhaps the earliest animal was similar to sponges, for sponges seem to be the most “basal” animals—those that branched off the animal tree before other groups. This makes sponges the “sister group” of all other animals.

Now a new paper in Nature by Elizabeth C. Turner of Laurentian University in Canada has pushed the oldest animal fossil back a long way: several hundred million years—to 890 million years ago! And, in fact, the fossil shows features of early sponges, verifying the molecular conclusions.

Now not all paleobiologists agree that what Turner found is an animal—some say the structures observed may have a microbial origin—but Turner herself is pretty confident, as are some other paleontologists. So let’s take this conclusion as “likely, but not certain”. Surely further work will either strengthen or weaken Turner’s evidence.

You can access Turner’s paper by clicking on the screenshot below, or downloading the pdf here. The reference is at the bottom of this post.

Investigating the Little Dal Reef Formation in Northwestern Canada, itself a kind of stromatolite, Turner collected rocks between 1992 and 2018, and, in thin sections of those rocks, observed “vermiform” (worm-shaped) microstructures filled with calcite “spar”, or calcium carbonate crystals. These tube-like structures join and divide in a branching network, just like the tubules of modern sponges, some of which have a calcite skeleton. (The tubules of modern sponges allow them to circulate water through their bodies, getting food and oxygen.) These wormlike structures are surrounded in the fossils by a calcite “groundmass”, which may be the external body of the sponge.

Here’s what Turner says about these interconnecting tubules and why she regards them as early sponges:

The shape, size, branching style and polygonal meshworks of the Little Dal vermiform tubules closely resemble both spongin fibre networks of modern keratosan sponges (Fig. 2a–c) and vermiform microstructure either demonstrated or interpreted to be sponge-derived in diverse Phanerozoic microbial, reefal and non-reefal carbonate rocks. The compositional and textural homogeneity of the microspar groundmass supports an origin through permineralization of a pre-existing biological substance, rather than incremental accumulation of detrital sediment or microbial carbonate that passively incorporated complexly anastomosing tubular microfossils. Variable preservation and association with geopetal peloid accumulations are familiar aspects of Phanerozoic sponge taphonomy In previous work, detailed comparison of the three-dimensional characteristics of vermiform microstructure with branching cylindrical organism types yielded no convincing alternative to the sponge interpretation

Here are subfigures (a)-(b) of her Figure 2 showing the fossil network compared to that of a modern sponge (c), with the captions below (click photo to enlarge).

(From Fig. 2 of the paper): a, Well-preserved vermiform microstructure exhibits a polygonal meshwork of anastomosing, slightly curved, approximately 30-μm-diameter tubules embedded in calcite microspar (KEC25). Scale bar, 500 μm. b, Enlarged rectangle from a, showing branching tubules forming three-dimensional polygons intersected at various angles by the thin section; clear calcite crystals, about 10–20 μm in width, fill tubules in groundmass of more finely crystalline calcite (dark grey). Scale bar, 50 μm. c, Three-dimensional fragment of spongin skeleton from a modern keratosan sponge, illustrating its branching and anastomosing network of fibres (incident light). Scale bars, 100 μm (main panel), 20 μm (inset).

There are other pictures as well, but the first two are the heart of the matter. You may not think they look like much, but they do show the interconnecting, ramifying tubules with the light-colored calcite crystals typical of some groups of sponges. The area where these putative fossils are found is 890 million years old.  And these fossils are older than the next oldest and indisputable sponge fossils by 350 million years!

Turner hypothesizes that these early organisms couldn’t compete with the reef-building cyanobacteria, but were able to find “oxygen oases” to use the oxygen produced by the cyanobacteria. The association of these putative sponges with oxygen-producing bacteria may be one piece of evidence that these are indeed metazoans, which of course require oxygen.

As I said, some paleobiologists disagree about whether these are animals. You can hear a ten-minute Nature-sponsored discussion with Turner, some supporters, and some doubters here. I highly recommend that you listen to this short but lucid discussion.

One other point: these organisms must have survived at least one of the periods of extensive glaciation and freezing known as “Snowball Earth“, when the entire planet was either completely frozen or almost covered with ice except for some open water. (The most extensive was between 700 and 600 million years ago.)  In the linked article, author Laura Poppick says this about that period:

What did life on Earth look like at the time, and how did it change as a consequence of these events?

There were certainly bacteria and there were also algae and unicellular primitive animals, or protists.

There is also evidence that the first multicellular animals originated at this time, probably something like sponges.

Well, according to Turner, the first multicellular animals, probably something like sponges, originated nearly 200 million years earlier than this.

Stay tuned to see how the dispute about the nature of these fossils progresses. Are they animals or simply remnants of bacterial activity? As Turner says in the interview, “We are quite confident” that these are spongelike animals. “It’s almost,” she adds, “a no-brainer.”

And here’s Turner in the field:

(From source): Elizabeth C. Turner, geology professor at Laurentian University, conducting geological fieldwork on northern Baffin Island in 2012. (Supplied photo/Laurentian University)

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Turner, E.C. 2021. Possible poriferan body fossils in early Neoproterozoic microbial reefs. Nature (2021). https://doi.org/10.1038/s41586-021-03773-z

Photographs of readers

June 7, 2020 • 2:30 pm

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

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

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

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

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

Sue’s new digs

December 31, 2018 • 12:30 pm

by Greg Mayer

Sue, the remarkably complete Tyrannosaurus rex discovered by (and named for) Sue Hendrickson, and excavated by Pete Larson and the Black Hills Institute of Geological Research, has long graced Stanley Field Hall at Chicago’s Field Museum of Natural History. Last year, the Museum announced that Sue would be moved upstairs, into the “regular” dinosaur hall, and that her place would be taken by a model of Patagotitan, a very large sauropod dinosaur. We’ve been following Sue’s progress here at WEIT, and earlier this month the new arrangements were completed and opened to the public.

Let’s start with what’s taken Sue’s place in Stanley Field Hall.

Stanley Field Hall, December 28, 2018.

Standing more or less where Sue once stood is Patagotitan. Unlike Sue, who is 90% actual fossil by volume, Patagotitan is a cast. (Note the elephants and people for scale.)  Swooping over the elephants is a life reconstruction of Quetzalcoatlus, the largest known pterosaur, who shares etymological roots with Jerry’s favorite beuatiful bird. Several smaller, long-tailed pterosaurs– Rhamphorhynchus, I think– can be seen over the Patagotitan. Hanging from the ceiling are several large planters, which resemble the “floating islands” from Avatar.

Hanging planters in Stanley Field Hall.

There were many small lights attached to each planter. I could not discern how the plants were watered.

From the second floor we could look down upon Patagotitan,

Stanley Field Hall.

and look Quetzalcoatlus in the eye.

Quetzalcoatlus in Stanley Field Hall.

Sue is now housed in a special section of the longstanding exhibit, Evolving Planet, which is organized as a walk through time, from the pre-Cambrian to the Cenozoic. Another life reconstruction of Quetzalcoatlus, this one in standing posture, has been placed at the entrance. They were big!

Quetzalcoatlus at entrance to Evolving Planet.

The new Sue hall is located in Evolving Planet in the appropriate spatial and chronological location– the end of the Cretaceous.

Note that the signage is bilingual, in English and, in a smaller font, Spanish. The Field has adopted this convention for all it’s new exhibits.

So here’s the old girl herself!

Sue, the Tyrannosaurus rex.

(Sue’s sex is actually unknown, so, properly, it’s “itself”.) Here’s a video overview of all of her.

In the video, you may have noticed that, compared to her previous mounting, Sue now has a second set of “ribs”, the gastralia, or “abdominal ribs”. These were part of the original excavation, but not included before. The true ribs have also had their distal ends extended a bit laterally, giving Sue a more barrel-chested appearance.

The new, barrel-chested Sue.

This is also a life reconstruction mural in the exhibit. I believe it is a new reconstruction; it is not the one by John Gurche that was found in the old second floor exhibit.

The new, barrel-chested Sue, as she might have appeared in life.

The revisions in the mounting are explained in this ‘science makeover‘ explainer on the Field’s website. Sue’s skull is still housed in a case separate from the mount, and the other Sue materials (most notably bronze models of various bones) from the old second floor overlook have been moved in to the new exhibit.

An engineer friend who I showed some of these pictures to thought that Sue was depicted as too front-end heavy, and that she would topple over forward. The current view is that the tail was massive and muscular, and provided a counterweight, but I, too, thought that, especially with the new barrel chest, she did look a bit over-extended, the heavy front end held too horizontal to readily balance over the hind legs.

A number of associated fossils from the late Cretaceous are also in Sue’s part of the hall, most notably this Triceratops skull.

As some readers may know, Sue came to the Field Museum by a roundabout and unsavory process, involving civil and criminal legal battles, and major financial intervention by McDonald’s (the burger chain) and Disney. The Field Museum’s part in this was largely, if not wholly, salutary, but nonetheless, as in the last exhibit, there is little or no mention of these circumstances in the new exhibit, other than a prominent nod to Sue Hendrickson. Some of the Black Hills Institute’s photos and field notes figure in the exhibit, and are subtly, but properly, acknowledged.

What were the first animals?

October 31, 2018 • 11:45 am

by Matthew Cobb

I’ve just finished making a BBC World Service radio programme about the first animals. Anyone, anywhere in the world, can listen to it (it’s only 28 minutes long!) – you just have to register with the BBC (free, rapid and cost- and spam-free). Click on the pic to go to the BBC website:

The programme deals with two different ways that researchers are studying this question – by looking at fossils, and at DNA. In both cases I interview researchers and – in the case of the Ediacara – get to handle some fossils. I also ate some 600 million year embryos at Bristol University (to see what they tasted like, obviously), but we didn’t include that in the programme. . .

The fossil data relate to what are called the Ediacaran biota – strange fossils from before the Cambrian, around 570 million years ago. The fossils are very hard to interpret – they don’t look like much alive today – but an amazing technique for analysing cholesterol molecules in the rock, so organic molecules preserved for all that time, has confirmed that Dickinsonia, the thing in the picture above, was an animal. Other techniques involve looking at large numbers of Ediacaran fossils and seeing how their distribution relates to those of modern animals. All the data suggest that some of the Ediacaran weirdos were indeed animals, although we cannot know if they are the ancestors of any animal alive today.

The DNA data focuses on a different question, which DNA can answer – which of the groups of animals alive today was the first to branch off the tree of life? Traditionally there has been a straightforward answer to this: sponges, which are nerveless and tissueless. But 10 years ago comparative genomic studies dropped a bombshell – they suggested that the first group to branch off were the ctenophores or comb jellies. This has caused a huge row because it would mean either that nerves evolved twice – once in the ctenophores, and once in our ancestors, after the nerveless sponges branched off – or that the huge sponge group somehow lost the genes for producing nerves.

Many biologists (myself included) don’t like either of these options, and prefer the sponges as the first model, but the data are persistent. Or are they? I spoke to experts on both sides of this argument, which has caused quite a hoo-haa in the zoological community for the past decade.

Anyway, go ahead and have a listen – download it and listen to it on public transport or while you are exercising. NB: I made the programme with ace producer Andrew Luck-Baker.

If you are a teacher, especially if you teach animal evolution, please get your students to listen to it.

Sue update

March 2, 2018 • 10:15 am

by Greg Mayer

She’s gone. I was at the Field Museum on Wednesday for the first time since the previous month, and the removal of Sue the Tyrannosaurus rex has been completed.

Stanley Field Hall, where Sue used to be.

Viewed from the balcony above, visitors walk through Stanley Field Hall, seemingly unaware of the ghostly white outline of Sue’s now departed plinth.

Where Sue used to be, from above.

A sign explained where Sue will eventually show up.

Sue’s actually not gone away entirely, for the second floor balcony display, featuring Sue’s real skull, remains in place. [JAC: the skull was always up there as it was too heavy to mount on the skeleton downstairs.]

The second floor display also includes touchable, life-size, bronze models of various parts of Sue, including the (relatively) tiny forearm. Devotees of the concept of unity of type, and Neil Shubin‘s Your Inner Fish in particular, will recognize the “one bone, two bones, many bones” pattern found throughout the tetrapod vertebrates and their piscine forebears.

A bronze model of Sue’s forearm.

A closeup of the digits; the two distalmost phalanges of the outer (lower, in this photo) digit were among the few bones missing from Sue’s skeleton, and the ones in the model are based on Albertosaurus, a related theropod dinosaur.

Sue’s fingers.

From up on the balcony, I could also get a better look at the model of Pteranodon longiceps hanging from the ceiling.

Pteranodon longiceps in the Field Museum.

And zooming in a bit.

Does the position of this model mean that Pteranodon is Ceiling Reptile?

So long, Sue…. see you upstairs!

February 20, 2018 • 7:45 am

by Greg Mayer

Sue, the iconic Tyrannosaurus rex that has inhabited the Field Museum of Natural History‘s Stanley Field Hall since 2000, is coming down. But, shortly after she comes down, she’ll be going up– upstairs that is.  The Museum announced plans last year to replace Sue in Stanley Field Hall with a model of Patagotitan mayorum, a much larger dinosaur than Tyrannosaurus rex. At the same time, they’ll be adding plants and pterosaurs to the Hall. Bill Simpson (who for some reason appears to be being assisted by Ricky Gervais) explains what’s going to happen to her in this video. (And continue watching the next video, also featuring Bill, that comes up after the first finishes.)

A similar model of Patagotitan has been on display at the American Museum of Natural History in New York for a couple of years now. It doesn’t even fit in the dinosaur hall there, and its head and neck poke out into the hall way to greet visitors arriving by elevator! Sue will be moving upstairs to the Field’s second floor, whose balconies overlook the Hall, where she’ll join the rest of the dinosaurs in the Evolving Planet exhibit. Sue is a theropod, and though in the same order of dinosaurs as Patagotitan, which was a sauropod, Sue and her kin ate creatures like Patagotitan and its kin.

I had gotten to see Sue up close during the study and preparation phases prior to her being placed on exhibit, and wanted to say farewell (for a little while), so I went down to see her before the deconstruction. These are pictures from a visit in late December.

Sue towers over her human prey admirers in Stanley Field Hall.
Getting closer to Sue’s business end.
The better to eat you with.
The somewhat old-fashioned painted reconstruction on the second floor, overlooking Sue down below. Sue’s skull, which is too heavy to be supported on the body of the mounted skeleton in Stanley Field Hall, has always resided in a separate display case on the second floor balcony, just below this painting.
One of the pterosaurs is already in position.

I went down again last month, and took a few more pictures, mostly closer shots of interesting parts of her anatomy.

A closer view of her teeth.
Her reduced, two-fingered, forelimbs. The functional significance of this feature is much speculated on, but unknown.
Her strong, 4-toed (3 forward, 1 back) hind foot. These provided a powerful mode of locomotion.
Au revoir, Sue!

The tale of how Sue got from South Dakota to the Field Museum is a long and tortuous one, and not very edifying; but that’s a story for another post.

Here’s the organism (well, sort of. . . .)!

December 8, 2017 • 12:00 pm

Did you guess what organism made the pattern below, found on a recent dive around the hydrothermal vents off Tonga?

Here’s the answer in the second tweet:

How big is that thing? The laser beam images are 10 cm (about 4 inches apart): The paper from which this comes (below) adds, “Note the shield-shaped elevation, marginal elevated rim and mote, and color (pale pink) of the area of the pattern compared with the surrounding veneer of gray calcareous lutite (image courtesy The Stephen Low Company).” You can find thousands of these things on the wall of the mid-Atlantic Ridge.

The pattern is similar to that described in a 2009 paper in Deep Sea Research (click on screenshot to go there):

It’s called a “living fossil” because the patterns are nearly identical to those found in ocean sediment cores from about 50 million years ago. That doesn’t mean, of course, that the organism that made (or left) this pattern is the same as the ancient one, for it may be not a fossil but a burrow.

But what IS the organism involved? The paper above doesn’t say, because they haven’t recovered an organism from whatever makes this pattern. DNA sequencing of material recovered from the holes shows genetic material from foraminiferans, protists that probably settled in the holes rather than making them.

When the holes are injected with resin underwater, and then the cast recovered, it looks like this (caption from paper):

Fig. 8. Photo of plasticine reconstruction (3-D) of the modern P. nodosum pattern based on observation of the hexagonal pattern of holes at the sediment–water interface and vertical shafts connecting with an underlying horizontal hexagonal network of tunnels or tubes (model and photo by Hans Luginsland).

The raised nature of the pattern as well as the rim can, according to the authors’ models, enhance water flow over the openings, suggesting that either this is a burrow of some sort or the 3-D remains of an organism that filtered microbes out of the water.  The authors suggest this could be a remnant of one of two types of organisms:

1.) Xenophyophores: Giant single-celled foraminifera that have multiple nuclei and form a “test”, a hard skeleton made from minerals extracted from seawater.

2.) The remains of a sponge. As the authors say:

Alternatively, the modern form is the compressed body of a hexactinellid sponge adapted to an unconsolidated sedimentary substrate (Rona and Merrill, 1978). If this interpretation is correct, then the fossil form is a body rather than trace fossil.

These sponges have hard parts as they contain spicules (small bits of the body) made of silicon.

Alternatively, it could be something else. The authors don’t consider that it might be burrows of a worm, but this site suggests that:

The short answer is, “We have no fricking idea.” There are many mysteries on the ocean floor.