Almost-Living Fossils Month #17 – Flowering Before It Was Cool

The Bennettitales were a group of seed-bearing plants found all around the world during the Mesozoic. They were an incredibly important part of ancient ecosystems, dominating the mid-level vegetation during the Jurassic and Early Cretaceous and making up over a third of the known plant species in some places. They came in two main varieties: the stocky cycad-like Cycadeoidaceae, mostly found in the northern continents; and the more slender branching tree-like Williamsoniaceae, which were more globally distributed. Most seem to have been around 2m tall (6′6″), but some may have reached much larger maximum sizes, perhaps as much as 15-25m (~49′-82′).

They date back to at least the Late Triassic (~230 mya), but they were already so diverse and numerous at that time that they probably originated much earlier – and very similar-looking leaves from the Permian and the Carboniferous hint that these plants may have actually first appeared at least 300 million years ago.

Their exact evolutionary relationships are still under dispute, with different paleobotanists classifying them as different types of seed-bearing plant. They’ve been traditionally placed close to the cycads due to their leaf shapes and growth patterns, but these similarities might be convergent since their complex flower-like reproductive structures and stomata instead suggest a possible evolutionary link to angiosperms or gnetophytes or “seed-ferns”.

The “flowers” of the bennettitaleans were round cup-like structures (sometimes resembling artichokes) which didn’t actually ever open up. While this would have made it very easy for them to self-pollinate, they may also have been some of the first plants to experiment with a mutualistic relationship with insects for pollination, possibly even partnering with early cupedid beetles in a similar manner to modern figs and their wasps.

Towards the end of the Cretaceous the rise of the true flowering plants seems to have started to send the bennettitaleans into decline, and the Cretaceous-Paleogene mass extinction at first appeared to have finished them off entirely. While there are a few Paleocene and Eocene-aged fossils that might be bennettitalean leaves, they’re not preserved in enough detail to tell for certain and they could actually be cycads.

But a few specimens from the Early Oligocene (~28 mya) of southeastern Australia and Tasmania have actually been identified as the leaves of a late-surviving species named Ptilophyllum muelleri. Since there were several other types of “relict” Mesozoic plants known to have still been present in the region around the same time (including horsetails and ginkgoes) it shouldn’t be much of a a surprise that the bennettitaleans had hung on there too – but sadly it’s not clear how much longer past this time they would have managed to survive. A drying and cooling climate towards the end of the Oligocene and into the Miocene, along with continuing competition from diversifying flowering plants, may have been enough to finally overwhelm these last few members of a once-impressive lineage.

Almost-Living Fossils Month #16 – Fancy Triangle Clams

Trigonia was a genus of bivalve mollusc that first appeared in the Middle Triassic, around 245 million years ago. Part of a much older lineage (the trigoniidans) that originated over 400 million years ago in the Late Silurian or Early Devonian, and distantly related to modern freshwater mussels, these bivalves have been found in marine deposits all around the world.

Their triangular shells had complex internal hinges, and often featured elaborate patterns of ribs and tubercules (which may have been adaptations to increase burrowing efficiency) that made them very visually distinctive. They lived mainly in shallow coastal environments, and in some places their fossils are so common that they must have been very numerous animals in their ecosystems.

Trigonia costata was a species living in Europe during the Early-to-Middle Jurassic (~174-166 mya), around the time when the trigoniidans were exploding in diversity. Usually around 5-7.5cm in length (2-3″), it was one of the longest-lasting individual species of Trigonia and one of the most common at the time.

Along with their other trigoniidan relatives, various Trigonia species continued to evolve throughout the entire rest of the Mesozoic, and while almost all of them went extinct at the end of the Cretaceous a few did manage to hang on into the Cenozoic.

The last record of an actual Trigonia comes from Argentina at the very end of the Paleocene, about 56 million years ago. After a nearly 200-million-year run, this long-lived genus finally disappeared – but although Trigonia itself was gone, that wasn’t quite the end of the trigoniidans altogether.

A single remaining lineage quietly continued on all the way into modern day, either descended from one of the Trigonia species or very closely related to the genus, living in waters off the coast of Australia and Tasmania. Known as Neotrigonia, they’re not quite as elaborately ornamented as some of their ancient relatives, but their complex shell hinges give them away as the only living trigoniidans – and their anatomy can give us some hints about what Trigonia’s soft tissue parts may have looked like, such as the presence of an unusual boot-shaped muscular foot that helps them burrow rapidly into the seafloor.

Almost-Living Fossils Month #15 – Digging Dryolestoids

First appearing in the mid-Jurassic, about 168 million years ago, a group of mammals called dryolestoids were some of the closest known relatives to the therians (the group that contains modern marsupials and placentals). They were found throughout North America, Eurasia, and North Africa up until the Early Cretaceous (~125 mya), but then mostly disappeared from the northern continents and instead migrated into South America – where they went on to flourish and became some of the most common mammals in the continent by the Late Cretaceous.

Although mostly known from only teeth and jaw fragments, the dryolestoids seem to have been a pretty diverse group of mammals during the Mesozoic, adapting to a variety of different diets and lifestyles ranging from small insectivores to relatively large herbivores.

Most of them died out in the end-Cretaceous mass extinction, except for the dog-sized herbivorous Peligrotherium which survived until 59 million years ago in the Early Paleocene… and one other known example from much much later into the Cenozoic.

Despite being absent from the fossil record for over 40 million years, the dryolestoids reappeared again in the Early Miocene of Patagonia (~21-17.5 mya) with a single late-surviving member: Necrolestes patagonensis.

The known Necrolestes fossils are surprisingly well-preserved compared to most other dryolestoids, with about a third of its skeleton represented. It was a small mole-like burrowing animal, about 10-15cm long (4-6″), with large canine teeth and an upturned snout. The cartilage in its nose was ossified into bone, strengthening it and probably supporting a pad of thick toughened skin – and also suggesting that it was a “head-lift digger”, using its snout like a shovel to dig through the soil.

While it superficially resembled the earlier mole-like dryolestoid Paurodon, it was actually much closer related to more generalist Mesozoic forms like the sabertoothed Cronopio.

After Necrolestes there’s no further evidence of dryolestoids living any closer to modern day. Much like the late-surviving gondwanatheres they lived alongside, these last dryolestoids may have specialized themselves so much that they couldn’t cope with sudden environmental changes, and the Middle Miocene extinction could have finished them off entirely.

Almost-Living Fossils Month #14 – Ancient Snakes

While the evolutionary origin of snakes is still rather poorly understood, one very early branch of their lineage – known as the madtsoiids – were a particularly long-lived group.

Originating back in the mid-Cretaceous (~100 mya), these “primitive” snakes were found mostly in the southern continents of Gondwana (known from South America, Africa, India, and Australia), but a few also spread into Europe. They were either some of the earliest true snakes or perhaps ophidians very closely related to them, and may have retained small hindlimbs that were slightly more well-developed than the vestigal ones of some modern snakes.

They ranged in length from under 1m (3′3″) to at least 7m (23′), with biggest of them rivaling some of the very largest living snakes in size.

They would have been similar to pythons, non-venomous and relying on constriction to kill their prey, although they had less flexible skulls than their modern relatives and couldn’t easily swallow animals much larger than their own heads. At least some of the Cretaceous species would have preyed on smaller dinosaurs, with one fossil even preserving a mid-sized madtsoiid in a sauropod nest alongside a hatchling.

Although the madtsoiids survived the end-Cretaceous extinction quite well and kept going throughout most of their range for the first half of the Cenozoic, most of them eventually disappeared in the Eocene-Oligocene extinction about 33 million years ago.

Aside from a single possible Late Olgiocene/Early Miocene record from South America (~29-21 mya), after that point the madtsoiids were found only in Australia, where they persisted almost into modern times.

Wonambi naracoortensis was one of the last of the Australian madtsoiids, living from the mid-Miocene (~11 mya) to at least the Late Pleistocene (~40,000 years ago). It was also one of the larger members of the group, 5-6m long (16′5″-19′8″), and seems to have been an ambush predator that lurked around waterholes to catch drinking animals.

The last madtsoiids went extinct at the same time as many of the other Australian megafauna, and it’s not clear exactly what caused them to die out. Humans had arrived in Australia about 20,000 years earlier, and hunting – either directly targeting the large snakes, or simply gradually reducing their available prey – combined with a changing climate may have been too much for them to handle.

Almost-Living Fossils Month #13 – Some Long Salamanders

A group of salamanders called batrachosauroidids first appeared in the fossil record at the very end of the Jurassic, about 145 million years ago, originating in Europe and quickly spreading to North America. Long snake-like bodies and reduced vestigial limbs gave these amphibians a very similar appearance to modern amphiumas or sirens, but they weren’t actually very closely related to each other – instead, the batrachosauroidids’ closest living relatives are thought to be mudpuppies and the blind cave-dwelling olm.

They were probably fully aquatic, living in wetlands with slow-moving currents, and the structure of their jaws suggest they were active predators that would have fed on other smaller animals in the water.

After surviving the end-Cretaceous mass extinction fairly well, with fossils of a couple of species known from both sides of the Cretaceous-Paleogene boundary, the batrachosauroidids continued on for most of the Cenozoic. They seem to have disappeared from Europe first, with the last known record in the mid-Eocene (~40 mya), but they persisted in North America for at least another 25 million years, well into the Miocene.

One of the last known members of the group was Batrachosauroides dissimulans from the mid-Miocene of Florida and Texas, USA (~16-13 mya). It was also one of the largest of the batrachosauroidids, similar in size to modern amphiumas at around 1m long (3′3″).

Past that point in time there’s no further evidence of batrachosauroidids, although due to the rather poor fossil record of salamanders it’s possible they may have survived for a while longer – but since amphiumas and sirens began to develop larger body sizes from the Late Miocene onwards, it’s likely that they were evolving to fill the ecological niches left vacant by the extinction of the last batrachosauroidids.

Almost-Living Fossils Month #12 – The Other Nautiluses

Nautiloids are represented today by just two living genera (Nautilus and Allonautilus), but they have a lengthy evolutionary history going back almost 500 million years.

The peak of their diversity was during the first half of the Paleozoic, with many different shapes of shells from coiled to straight, then they began to decline when their relatives the ammonites and coleoids appeared and began to compete for similar ecological niches. Although a few groups of nautiloids survived through the end-Permian mass extinction, most of them had disappeared by the end of the Triassic, leaving just one major remaining lineage known as the Nautilina (or Nautilaceae).

During the mid-to-late Jurassic (~165 mya) two new groups split away from the ancestors of the modern nautiluses – the cymatoceratids and the hercoglossids.

Cymatoceratids such as Cymatoceras sakalavum here had shells with a ribbed texture. Living during the Early Cretaceous, about 112-109 million years ago, this particular species is known from Japan and Madagascar and could reach a shell diameter of over 15cm (6″).

Hercoglossids, meanwhile, were much more smooth in appearance, but both groups also had more complex undulating sutures between their internal chambers than modern nautiluses do.

These nautiluses made it through the end-Cretaceous mass extinction and had a brief period of renewed success, filling the ecological roles left vacant by the extinct ammonites. But by the end of the Oligocene (~23 mya) both the cymatoceratids and hercoglossids vanished, possibly unable to deal with cooling oceans and the evolution of new predators.

Some of the hercoglossids’ Cenozoic descendants, the aturiids, managed to last a little longer into the Early Pliocene (~5 mya) before another period of cooling seems to have finished them off. Past that point, all that was left of the once-massive nautiloid lineage were their cousins the nautilids, who gave rise to today’s few living representatives.

(It’s also worth noting that the classification of the cymatoceratids seems to be in flux right now. Some paleontologists currently don’t consider Cymatoceras itself to actually be part of the group, instead being a nautilid much closer related to modern nautiluses. If this is the case then the cymatoceratids may not have actually survived past the Late Cretaceous – but the Cymatoceras genus alone still counts as an “almost-living” fossil since its various species ranged from the Late Jurassic to the Late Oligocene.)

Almost-Living Fossils Month #11 – The Lost Island Murderer

The modern solenodons, today found only on the Caribbean/Antillean islands of Cuba and Hispaniola, represent the last living survivors of a very ancient branch of placental mammals. Although they’re part of the eulipotyphlans – the lineage that also contains shrews, moles, and hedgehogs – their last common ancestor with the other members of that group dates back to over 70 million years ago.

And during their early evolutionary history, somewhere between the Late Cretaceous and mid-Eocene (~68-43 mya), the ancestors of the solenodons diverged into two different lineages: the solenodons themselves, and the nesophontids.

Known only from skulls and jumbled partial skeletal remains, nesophontids seem to have been fairly similar to their solenodon cousins. They would have been shrew-like in appearance, varying in total size from 5 to 20cm long (2-8″), with slender flexible snouts that they used to sniff out their small invertebrate prey. They also probably had a venomous bite like the solenodons, since their canine teeth had distinctive grooves for injecting toxic saliva.

Their remains have been found in various islands around the Caribbean, in Cuba, Hispaniola, Puerto Rico, the United States Virgin Islands, and the Cayman Islands. Between six and twelve different species are represented, all in a single genus called Nesophontes (meaning “island murderer”) – and all of the known specimens are actually subfossils from the Holocene, dating to less than 12,000 years old.

These relatively young ages mean that pieces of nesophontid DNA have been successfully recovered from bones within preserved owl pellets, which is how we could confirm their close relationship to solenodons and the dates of their ancestors’ probable divergence. But we have absolutely no idea about the rest of their family history during the entire Cenozoic, such as how and when they originally colonized the Caribbean or whether they had any other extinct relatives in the Americas.

(There is one possible partial specimen from a piece of Dominican amber, dating to the Oligocene or Early Miocene, 29-18 million years ago, but it’s not clear whether it’s a nesophontid, a solenodon, or something else entirely.)

Nesophontes edithae was the only species of nesophontid living in Puerto Rico and the United States Virgin Islands. It was the largest known member of the genus, at least 20cm long (8″), and may have been able to reach such a size due to the absence of competition from solenodons on those particular islands.

Along with its relatives around the Caribbean it seems to have survived frustratingly close to modern times, even existing alongside indigenous humans, with some remains only about 500 years old. But when the islands were colonized by Europeans from the 1490s onwards, the combination of the introduction of invasive Old World rats, new predators like domestic cats and dogs, and extensive deforestation probably killed off the nesophontids very quickly (along with all but two of the solenodon species).

Despite claims of fresh-looking remains in owl pellets and searches for surviving populations, there’s currently no convincing evidence for any living nesophontids, and radiocarbon dating has never found anything younger than 500-600 years old. 

Almost-Living Fossils Month #10 – Big Land Crocs

First appearing in the Middle Jurassic, about 167 million years ago, the sebecosuchians were a group of terrestrial crocodilians that are known from South America, Europe, North Africa, Madagascar, and India.

They were very closely related to (or possibly descended from) the diverse and often very weird notosuchian crocs. But while notosuchians were generally small and had specialized mammal-like heterodont teeth, the sebecosuchians were much larger (around 3-4m long / 9′10″-13′) and had blade-like serrated teeth convergently similar to those of some theropod dinosaurs. Their teeth were so incredibily dinosaur-like, in fact, that Cenozoic specimens have occasionally been mistaken for evidence of late-surviving non-avian dinos.

With deep narrow snouts, powerful jaws, and upright limbs, these crocs were clearly fast active predators, and must have been directly competing with similarly-sized theropods during the Mesozoic. They were obviously doing well enough to survive alongside their distant dinosaur relatives for many millions of years, right up until the end-Cretaceous extinction – but the surprising part is how the sebecosuchians seemed to survive the extinction just fine across most of their range, while the non-avian theropods obviously didn’t. Something about these particular large terrestrial predators allowed them to pull through relatively unscathed, although whether it was to do with their metabolisms or something else is still unknown.

By the end of the Eocene the sebecosuchians outside South America seem to have died off (coinciding with the rise of placental carnivorans), but the isolated South American forms continued their success for most of the rest of the Cenozoic.

One of the best-known species is Sebecus icaeorhinus from western South America, ranging from Colombia to Patagonia, with various fossils dating from the Early Paleocene all the way through to the mid-Miocene (~66-11 mya). About 3m long (9′10″), it was named after the ancient Egyptian crocodile god Sobek and was one the first sebecosuchians to be discovered, lending its name to the entire group.

The last definite fossils of Sebecus and its relatives come from the mid-Miocene, but they may possibly have survived up until at least the Miocene-Pliocene boundary about 5 million years ago. It’s not clear exactly why these big land crocs finally went extinct, but it was likely due to a combination of factors such as the influx of placental predators from North and Central America, along with climate changes from the continuing rise of the Andes mountains and the formation of the Isthmus of Panama.

Almost-Living Fossils Month #09 – Horned Sharks

All modern species of sharks and rays are part of a single lineage of cartilaginous fish known as neoselachians, and the closest evolutionary “cousins” to all of them were the hybodontiformes.

First appearing way back during the Devonian, about 400 million years ago, these early sharks were widespread around the world and incredibly successful as a group, living in both marine and freshwater environments.

Although due to their cartilaginous skeletons hybodontiformes are mostly known from fossilized teeth, there are still some complete specimens known that show us their overall body shape. They had two dorsal fins, each with a long spine in front, and an asymmetrically-shaped tail. Some of them also had small horn-like spines on their heads – this seems to be a sexually dimorphic trait, since the ones with “horns” also have claspers which show they were males – and they generally had powerful jaws with teeth specialized for crushing.

They were probably fairly slow swimmers most of the time, but would have still been capable of occasional bursts of higher speed, and various species were adapted to a wide range of food sources. Some had wider flatter teeth for cracking open hard-shelled seafloor invertebrates, and others were more opportunistic hunters that would have crunched on pretty much anything they could fit in their mouths.

Hybodontiformes were the dominant type of shark around the world before the end-Permian “Great Dying” mass extinction (~252 mya), and then went on to recover and flourish once again up until the mid-Jurassic.

Hybodus hauffianus was one of the Early Jurassic species, living around 183 million years ago in Europe. About 2m long (6′6″), it had two different types of teeth in its mouth – sharper ones in the front and flatter ones in the back – suggesting it was a generalist predator eating whatever it could catch. We do know its diet at least included the fast-swimming squid-like belemnites, since some fossils preserve clusters of their internal hard skeletons in Hybodus’ stomach region.

Towards the end of the Jurassic neoselachians began to diversify and take over most of the marine shark ecological niches, and the hybodontiformes became increasingly restricted to freshwater. During the Cretaceous they continued to do fairly well in those environments, but most of them still disappeared around the time of the end-Cretaceous extinction (~66 mya). Since most other sharks weren’t actually particularly affected by the extinction event, it’s not clear whether the hybodontiformes were more vulnerable for some reason or whether it was the ongoing competition from neoselachians that drove the majority of them extinct at that time.

Still, a few of them did seem to make it through to the Cenozoic, although they were absent from the fossil record until the Miocene. Freshwater deposits in Sri Lanka have evidence of a late-surviving member of the group living perhaps as recently as 5 million years ago – so they would have only gone completely extinct sometime after that, and we probably missed seeing them alive by only a few million years at most.

Almost-Living Fossils Month #08 – A Lot Of Lobsters

Hoploparia was a type of clawed lobster that first appeared in the fossil record in the Early Cretaceous about 140 million years ago. Many many different species within this genus have been found all over the world – over 100 of them have been described! – with quite a lot of anatomical diversity between them, showing that these lobsters were very good at adapting to a wide range of habitats and climates.

Although the vast majority of Hoploparia species lived just in the Cretaceous period, a small number of them did survive the end-Cretaceous mass extinction 66 million years ago. Hoploparia stokesi here was one of them, known from both the Late Cretaceous and Early Paleocene of Antarctica (~70-61 mya) – and was actually one of the first fossils ever described from the continent.

Specimens of this species are usually about 13cm long (5″), and show an evolutionary shift over time, developing much stronger claws and jaws, suggesting they were adapting their diet towards hard-shelled prey.

Various species of Hoploparia persisted on in North America, Europe, and Antarctica for the first half of the Cenozoic, but they never recovered to anywhere close to their Cretaceous levels of diversity. By the Early Miocene (~23-16 mya) there was just one known species left hanging on in Antarctica, and then they were gone.

(However, some modern lobster genera may in fact have originated from somewhere within the huge Hoploparia lineage back in the Cretaceous, so they might at least still have some close living relatives!)