Unsolved Paleo Mysteries Month #20 – Dubious Diskagma

Only around 0.3-1.8mm long (0.01-0.7″), Diskagma buttonii is known from the Paleoproterozoic of South Africa, dating to a whopping 2.2 billion years ago. These tiny urn-shaped structures were connected into bunches, and were found in rocks that were once ancient soils – hinting that there may have been some form of (relatively) complex life present on dry land much earlier than previously thought, as far back as the early stages of the Great Oxygenation Event.

But what these things actually were is a mystery. Their size and complexity resemble some sort of eukaryote, which would make them one of the oldest known representatives. They also have some similarities to the older fossil Thucomyces lichenoides, the younger fossil Horodyskia, and a modern fungus with internal symbiotic cyanobacteria.

Or they could be a very early “experimental” branch of life with no close living relatives. For now, we just don’t know.

Unsolved Paleo Mysteries Month #19 – Mesozoic Maritime Mammal Molars

Icthyoconodon jaworowskorum was a member of the volaticotherians, a group of eutriconodonts most famous for featuring the earliest known gliding mammal. Living during the Early Cretaceous of Morocco (~145-140 mya), it’s known only from a few isolated teeth.

Based on the measurements of the teeth it was probably one of the larger eutriconodonts, close in size to Jugulator. I can’t find any body size estimates, but it may have have a total length of around 50-60cm (20-24″).

Plenty of fossil mammals are known solely from teeth, but what’s most interesting about this one is that its remains were found in coastal marine deposits without any signs of degradation or transport damage by water currents. This indicates the animal probably died at sea very close to the location where it was preserved.

A few other eutriconodonts are now known to have been semi-aquatic, so Ichthyocondon might have been adapted to a similar lifestyle, making it one of the earliest known marine mammals. Another potential explanation is that it was a Volaticotherium-like glider that got blown out to sea.

As with many of this month’s paleontological mysteries, we need some more substantial fossil remains to know for sure. I’ve reconstructed it here as both main possibilities, as an otter-like semi-aquatic animal and as a patagium-bearing glider.

Unsolved Paleo Mysteries Month #18 – The Biggest Beefy Boys

In 1878, during the Bone Wars of American paleontology, Edward Drinker Cope published a description of a partial sauropod vertebra and femur from the Late Jurassic of Colorado (~150 mya). He classified it as a new species of the diplodocoid genus Amphicoelias (which he had named earlier that same year), designating it as Amphicoelias fragillimus in reference to the bone’s poor condition and incredibly fragile structure.

But what set this fragmentary find apart was its sheer size. The partial back vertebra measured around 1.5m tall (5′), with estimates of its full height anywhere up to 2.7m (8′10″) – twice the size of the same bone in Diplodocus, and far larger than anything else known.

Obviously its very difficult to accurately estimate the full body size of an animal from a single broken bone, but plenty of attempts have been made anyway, producing lengths of up to 60m (197′). For comparison, the largest living animal the blue whale reaches lengths of around 33m (108′).

Around the time of Cope’s death in 1897, his massive fossil collection was sent to the American Museum of Natural History, and the A. fragillimus vertebra was entered into their catalog–

Only to vanish, never to be seen again.

Multiple searches through the collection have found no trace of it, and there’s speculation that at some point the fragile bone may have crumbled entirely into pieces and been thrown away. No other material of A. fragillimus has ever been found in the ~140 years since its description, despite searches of the area where it was originally discovered, leading to claims of the entire specimen being a hoax – suggestions that Cope exaggerated or typoed his measurements in his rush to outdo his rival Othniel Charles Marsh.

Without that paleontological holy grail of finding the lost fossil or a new specimen, we just don’t know how big that bone truly was, or whether A. fragillimus was a living kaiju or a much more “normal-sized” sauropod. There’s even been some speculation of it being proportioned more like a rebbachisaur, with tall “sailback” vertebrae.

Except…

In a surprise plot twist, there is another.

An absolutely enormous neck vertebra hints at the existence of other gigantic mega-sauropods. We still don’t have enough remains to know what the heck was going on with these animals – how did they even manage to get so huge? were they rare individuals who lived long enough to grow into “super-adults”? – but the prospect of perhaps one day finally validating A. fragillimus’ enormous size is exciting.

My version of Amphicoelias fragillimus here works out to about 50m long (164′), although it might be closer to 60m long with a more horizontal neck posture. Its proportions are mainly based on a mixture of Diplodocus, Supersaurus, and Barosaurus, with slightly taller neural spines raising its back profile a bit and some big fat deposits thickening up its tail.

Unsolved Paleo Mysteries Month #17 – Enigmatic Ediacarans

Although Precambrian fossils have been known since the mid-1800s, the overwhelming belief among 19th and early 20th century scientists that complex life couldn’t have originated that early meant such discoveries either weren’t taken seriously or were forcibly assigned to a Cambrian age. It wasn’t until the discovery of Charnia in the 1950s that views began to change.

(Or, rather, the second discovery of Charnia, since the schoolgirl who first found it wasn’t taken seriously either.)

Since then, a wide variety of strange soft-bodied fossils have been identified from over 30 different localities around the world, on every continent except Antarctica, dating to ages from over 600 to 542 million years ago. They’re now known as the Ediacaran biota, after the Ediacara Hills in Australia where some of the most famous examples have been found.

A few show possible similarities to known groups, but we still don’t know what sort of lifeforms most of them they actually were. Animals, fungi, algae, foraminifera, microbial colonies, or lichens have all been proposed – but they might also belong to a completely unique kingdom or phylum, a “failed experiment” in multicellular life with no living descendants.

And they’re gradually turning out to be not nearly as “simple” as once thought, showing evidence of their own thriving ecosystems and evolutionary specializations – which makes their sudden disappearance at the end of the Ediacaran Period all the more mysterious.

Tribrachidium has been found in Australia, Ukraine, and Russia (558-555 mya), grew up to 5cm in diameter (2″), and shows unusual tri-radial symmetry. Affinities to both cnidarians and echinoderms have been suggested, but no classification has really stuck. Recent 3D modelling and fluid dynamic studies reveal its shape was adapted to direct water currents into the nooks between its “arms”, allowing it to feed on suspended organic particles.

Yorgia is known from Australia and Russia (~555 mya), and appears to be a transitional form between two other ediacarans, Dickinsonia and Spriggina. It has what appears to be a “head” end with an asymmetrical lobe, and a segmented body in a glide reflection pattern, growing up to 25cm long (10″). Trace fossils from its feeding strategy have also been found – chains of imprints over seafloor microbial mats, where it moved from spot to spot and “grazed” with the entire underside of its body.

Fractofusus is somewhat older (575-560 mya) and perhaps even stranger. Discovered in Canada in 1967, it was known only as “the spindle organism” for 40 years before being finally named in 2007. Its 40cm long form (16″) shows fractal self-similarity, made up of frond-like elements that branch even further again and again and again, creating a large surface area relative to its internal volume that may have been used to directly absorb nutrients from the surrounding seawater. It also seems to have been capable of reproducing in two different ways – producing both water-borne offspring and stolon-like clones of itself.

Unsolved Paleo Mysteries Month #16 – Strange Snoots 2: Oddball Ornithischians

Those extinct horses weren’t the only ancient creatures with unexplained noses. Some dinosaurs had equally weird things going on with their snouts – and while hadrosaurs’ big honkin’ snoots are fairly well-known, there were other ornithischians with their own bizarre nasal anatomy.

An illustration of the skull of an extinct horned dinosaur, showing the unusually large nasal cavity. Below is a reconstruction of the dinosaur's head in life.
Triceratops horridus skull and head reconstruction

Many ceratopsids had an enormous nasal opening forming a giant bony “window” through their snout, with the chasmosaurines like the famous Triceratops having additional bony projections and hollowed regions within these holes. They probably supported some huge elaborate cartilage structures in life, but what they were for is still a mystery. They may have helped with heat dissipation or moisture conservation, aided sound production, provided a highly sensitive sense of smell, housed a vomeronasal organ, held part of an air-filled pneumatic system… or, getting more speculative, possibly even some sort of inflatable nasal display structure.

An illustration of the skull of an extinct armored dinosaur, showing the multiple holes inside the nasal cavity. Below is a reconstruction of the dinosaur's head in life.
Minotaurasaurus ramachandrani skull and head reconstruction

Some ankylosaurids, meanwhile, went with multiple holes instead. Minotaurasaurus here had two additional openings around its nostrils, and Pinacosaurus could have up to five – the purpose of which is unknown. Many ankylosaurs also had forward-facing nostrils (a rare trait in archosaurs) and incredibly complex looping airways through their skulls. These may have allowed for mammal-like “air conditioning”, regulating the heat and moisture content of each breath, or perhaps enhanced their sense of smell or served some sort of resonance chamber function. Or, again, maybe even nose balloons.

Also floofy ankylosaur because I can.

Unsolved Paleo Mysteries Month #14 – The Mystery Mega Mammal

During a 1923 expedition by the American Museum of Natural History to Inner Mongolia, China, a huge mammal skull was discovered dating to the Middle Eocene (~48-37 mya). About 83cm long (2′8″), with small low-set eyes, it was named Andrewsarchus mongoliensis in honor of expedition member Roy Chapman Andrews.

Almost a century later that one skull is still all we have. And despite this animal’s popularity among paleo-fans, we actually know very little about it.

It was originally classified as a mesonychian, leading to the many many depictions of it as a sort of “big bad wolf”. But more recent studies have placed it in the even-toed ungulates instead, with some suggestions that it might be most closely related to entelodonts, hippos, and whales.

Although it was certainly a big animal, it may not have been the giant “super predator” it’s often depicted as – its teeth aren’t particularly specialized and resemble those of entelodonts, suggesting it may have been more of an opportunistic omnivore than a dedicated carnivore.

Without more material we just don’t know for certain. So, frustratingly, the rest of Andrewsarchus’ body remains a mystery.

I’ve reconstructed it here based on one of its more obscure possible relatives: the anthracotheres, a group which may have been closely related to modern hippos. Scaling its body proportions to these animals produces rough measurements of about 1.45m tall at the shoulder (4′9″) and 3m long (9′10″), or about the same size as some of the big entelodonts or large modern bears.

Unsolved Paleo Mysteries Month #14 – Thousands of Tiny Butts

Gluteus minimus are small fossils, sometimes referred to as “horse collars”, up to 11mm across (0.4″). Always slightly asymmetrical in the same direction, with growth lines on one surface and a solid internal structure, they’ve been found in large numbers from the Late Devonian of Iowa, USA (~385 mya).

Although they were first discovered in 1902, they weren’t formally described until 1975 – and ended up being named after a butt muscle.

What sort of creature they represent, however, is completely unknown. They’ve been suggested to be fish scales, fish teeth, parts of various molluscs, or brachiopods. And, more recently, to perhaps be otoliths.

They still can’t be confidently placed in any one phylum.

(Due to scarce reference images of G. minimus, this post’s illustration is directly based on the figure of the holotype specimen in the original description paper.)

Unsolved Paleo Mysteries Month #13 – The Case of the Absent Archaeopteryx

One of the most famous of all fossil organisms, and a classic example of a transitional form, Archaeopteryx is currently known from 12 body fossil specimens.

Except one of them is missing.

The Maxberg specimen was part of the private collection of Eduard Opitsch, the owner of the Bavarian quarry where it was originally discovered in 1956. Despite being partially disintegrated, and missing its head and tail, it was still an immensely important discovery – at the time, it was only the third recognized Archaeopteryx ever found.

After briefly attempting to sell the new Archaeopteryx, Opitsch eventually allowed it to be held at the local Maxberg Museum. In 1974 he permitted casts to be made from it – but then suddenly removed it from public display and refused all further requests to access or study it.

(This may have been a reaction to the 1973 announcement of the more complete Eichstätt specimen. Opitsch, who was described as having “a difficult personality”, became increasingly defensive about the fossil, seeming to feel this new discovery was getting more attention and was deliberately devaluing his own.)

From then on the Maxberg specimen was lost to science.

When Opitsch died in 1991 his heir attempted to locate the fossil – it was rumored to be kept under his bed – but it was nowhere to be found. There’s some speculation that he was buried with it, literally taking his prized Archaeopteryx to the grave as a final act of spite. Another possibility is that it was stolen and sold in secret, perhaps to this day hidden away in a wealthy owner’s private collection.

It’s been missing for over 25 years, but there’s still lingering hope that the missing Maxberg specimen will one day resurface.

For now, though, all we have left are a few casts, photographs, and x-rays.

Unsolved Paleo Mysteries Month #12 – Muddled Mosasaurs

Numerous groups of reptiles have “returned to the water” and become aquatic over the last three hundred million years, but tracing their direct ancestry can be surprisingly difficult. Highly modified and specialized anatomy, lack of transitional forms, and similar features convergently evolving multiple times can all obscure relationships, making it hard to properly classify them.

We’re only just starting to figure out the true origin of turtles (they’re probably archosauromorphs), and they’re a marine reptile group with living members.

Some of the completely extinct ones are even more uncertain. For example: mosasaurs. (Represented here by the eponymous Mosasaurus.)

While some semi-aquatic early mosasaurs are known, and they seem to be closely related to aigialosaurs and dolichosaurs, their exact placement within the squamates is a lot less clear. Traditionally they were regarded as the sister group to snakes, but some studies have found them to be closer to monitor lizards instead, and others have even placed them as much more basal scleroglossans. Their classification in phylogenetic analyses is “highly unstable”, changing depending on what other reptile groups are included, so there’s no real current consensus.

(And even if they are most closely related to snakes, that doesn’t necessarily help much – the exact origin and evolution of snakes is still very poorly known, too!)

Unsolved Paleo Mysteries Month #11 – Strange Snoots: Equid Edition

Horse evolution is often represented as a simple progression from Eohippus* to modern Equus, but it was actually a lot more complicated than that – and some ancient horses had some very odd things going with their snouts…

(* For a long time Eohippus was considered synonymous with Hyracotherium, but more recently has been split back off as its own genus again.)

An illustration of the skull of an extinct horse, showing the unusually large holes in the bones in front of the eye sockets. Below is a reconstruction of the horse's head in life.
Pliohippus sp. skull and head reconstruction

Pliohippus, from the Middle Miocene of North America (~15-12 mya), and several of its other close relatives had especially large, deep recesses in their skulls, usually referred to as “preorbital fossae”.

And the purpose of these holes is still unknown. Although superficially similar depressions are seen in various other perissodactyl groups, they vary in position and structure and probably weren’t all homologous.

Ideas have included resonating chambers, some sort of glands, inflatable sacs, or attachment sites for complex lip musculature.

An illustration of the skull of an extinct horse, showing the unusually large nasal cavity. Below is a reconstruction of the horse's head in life.
Hippidion sp. skull and head reconstruction

Meanwhile Hippidion from the Pleistocene of South America (2 million – 10,000 years ago) had especially long and domed nasal bones. This must have supported an enormous nasal area – possibly giving it a saiga-like air-conditioning system, a highly sensitive sense of smell, or perhaps even some sort of prehensile proboscis-like snout.

Unless we find some exceptional soft-tissue preservation, the facial anatomy of these equids is going to remain enigmatic.