Fossil Profiles: Forever in battle

 “Ever since we first landed on Eryobis, we noticed that dominant macrofauna on land consisted of two very different kinds of vertebrate. Unlike on Earth, where Tetrapods are the only dominant kind of terrestrial vertebrate, on Eryobis there are two: the sarcopterygian Anisospondyls and the actinopterygian Arachnopods.
Anisospondyls appear to have evolved from an aberrant lineage of Eryobean coelacanths colloquially known as Flattacanths while Arachnopods evolved from a group of Eryobean Holosteans known as octopodichthyian spiderfish.”

“For a long time, it remained a mystery how these two vastly different kinds of terrestrial vertebrates could’ve evolved in each other’s presence, considering they would often have to compete for resources.
Molecular data suggests that both of these clades arose around the same time in what is known as the early Phylloceous period, shortly after a sudden global warming event appears to have caused a major mass extinction, particularly in aquatic fauna.
But how this could’ve happened was still uncertain. That was, until we actually started discovering fossils from the early Phylloceous.
Unlike late Phylloceous fossil sites like the Gerritsen Formation, which show a plethora of both primitive Anisospondyls and basal Arachnopods, fossil sites from the early Phylloceous exhibit either exclusively Anisospondyls or Arachnopods as terrestrial vertebrates depending on the location.
This phenomenon brought forth the theory that Anisospondyls and Arachnopods evolved om different continents that were still separated in the early Phylloceous, but collided somewhere in the middle Phylloceous.”

“Over the years, as more fossils were discovered, the support for this theory grew ever more. The continents were given names for easier reference. The one where the Anisospondyls are thought to have come from was called Knoppira and the one where the Arachnopods originated was called Dallckia. Although has not yet been confirmed where exactly these ancient continents were (as tectonic movements over the eons appear to have completely broken them up and spread them across the modern continents), biodiversity in the fossil sites have confirmed that these continents collided in the late Trextian epoch of the early Phylloceous period. As all fossil sites younger than Trextian deposits feature both Anisospondyls and Arachnopods.”

“The collision of these paleocontinents caused an extinction event due to various flora and fauna suddenly competing with each other. But other than a drop in biodiversity in the early Schippelian, there was little evidence of direct interaction between early Anisospondyls and Arachnopods.
That was, until the discovery of a remarkable fossil found in a think layer of ash dated to the latest Trextian 205 million Eryobian years ago.
A nearly complete skeleton of the largest carnivore of ancient Dallckia, the Osteotariomorph Arachnopod Maxillolonchodon giganteus was discovered with broken bones, many bite marks and several teeth still embedded within its bones. But these teeth did not match the shape of Maxillolonchodon teeth. Instead, they matched other loose fossil teeth discovered in late Trextian deposits from ancient Knoppira. These teeth belonged to a great predator that had strangely left no fossils other than teeth. Until now.”

“Roughly 6 meters away from M. Giganteus laid another animal. It was an Anisospondyl, a big one too. It’s peculiarly shaped visendal spines indicated that it belonged to a group Dextrostelan Anisospondyls known as Aurispinidae.
These basal Anisospondyls had their lateral line organ on the visendal side zigzagging through the spines, thus making their entire sail a kind of ear. As an exquisitely well preserved fossil from the late Schippelian species Aurispinax jubatus shows, Aurispinids had a narrow mane of filaments running along their lateral line organ, presumably for amplifying sounds.
But unlike the other, later Aurispinids, the specimen found alongside M. Giganteus was not a herbivore it’s teeth were knife shaped and serrated, just like the teeth found stuck in the bones of M. Giganteus. This made it not only the oldest Aurispinid discovered so far, but also the only carnivorous species. For this reason it was called Protaurispinax carnifex, the absolute apex predator of late Trextian Knoppira.”

“But these fossils show what happened when the two largest terrestrial predators up until that point met each other. As P. Carnifex also had several teeth matching those of M. Giganteus embedded in its bones, it can be concluded that these two hyper-carnivores fought to the death upon running into each other.
As resources grew scarce after Dallckia and Knoppira collided, the large carnivores were forced to scavenge the coastline for washed up animals where they, unfortunately met each other at the foot of an ancient volcano.
It is presumed they both heavily wounded the other and though the evidence is circumstantial, the state of M. Giganteus suggest that P. Carnifex won the initial battle and later either bled out and died or was buried alive in ash from the nearby volcano.”

Rozenbed Formation

 “Tetrapods evolved their ears from the breathing spiracles of their primitive fish ancestors that lost their function once tetrapods switched to nose-breathing.
While a similar thing seems to have happened to the Arachnopods that turned their gills into sound-receptors once they could leave the water indefinitely,
for Anisospondyls something else happened.
Unlike Tetrapods and Arachnopods, the Anisospondyls never evolved choanae to inhale with. Instead repurposing their former gill openings to function as spiracles. This left them without any rudimentary head holes to be adapted into something else such as ears.
While advanced Anisospondyls seem to have found ways around not having ancestral ear holes, there seems to have been a time when they did have holes to hear with.”

“Anisospondyls being fish, their ancestors used to have a lateral line organ. Though it has been lost is all modern Anisospondyls, more basal Anisospondyls seem to still have retained it long after leaving the water.
Not only that, but some seem to have made it their primary auditory organ. Strange as this may sound, one must remember that the atmosphere on Eryobis is much denser and differently composed than Earth’s, making the lateral line organ much more efficient out of water than it would on Earth.
In most cases the organ seems to have been similar to those found in aquatic fish, flat and on the sides. This is proven by the fact that many basal Anisospondyls have been found with small holes in a single line of their heavy scales through the middle of the visendal and sometimes caecal sides of their bodies.”

“This was not an incredibly efficient way of perceiving sounds, as the organ was flat and could not be oriented to specific angles without the whole body having to turn. Hence is probably why no modern Anisospondyls still retain the lateral line organ.
Back in the Phylloceous period, basal Anisospondyls evolved a way to make their primitive method of hearing more effective: by raising the organ.
Surprisingly though, the evolution of such an ear-sail evolved not once, but twice. The method in which they evolved it, was however vastly different.”

“The first to evolve such an ear-sail was a family of Dextrotselan Anisospondyls called the Aurispinidae. The Aurispinidae, as is demonstrated by Protaurispinax, started out as carnivores and must’ve appeared in the early Trextian around 220 million Eryobian years ago. After the Trextian-Schippelian extinction however, almost all remaining Aurispinids were herbivorous.
What characterises Aurispinids are odd, asymmetrical protrusions located somewhere in the middle of the visendal spines, which were in reality just elongated osteoderms. These lumps were used to support the lateral line organ, which apparently zigzagged through the visendal spines. This give Aurispinids asymmetrical hearing and probably helped with determining where sounds came from.
As the beautifully preserved Aurispinax jubatus from the late Schippelian showed us, Aurispinids had a narrow mane of filaments, presumably derived scales, running along the lateral line organ on both sides of the sail. These filaments are thought to have made their ear-sail even more sensitive, making their hearing even more accurate.”

“But alongside Aurispinids in the middle and late Phylloceous, there was another, completely unrelated family of Anisospondyls which had raised their lateral line organ with with a sail.
This was a family of Katoptifylomorphs called the Syrinchotidae. The Syrinchotids are thought to have evolved in the late Trextian, but only first show up in middle and late Schippelian formations.
While Aurispinids had their lateral line organ zigzagging through their visendal spines, the Syrinchotids had theirs placed neatly on top of the spines. This is evidenced by the flat, satellite dish shaped tops of the spines. In real life, this probably made them look like they had Pan-flutes on their backs. The openings of the lateral line organ ran all over the sail, from the base of the head to halfway the tail. From the degree of curvature on the tips of the visendal spines, it can be concluded that the openings at the front of the animals were much larger than those at the back. This probably gave Syrinchotids a three dimensional hearing, with optimal security near their vulnerable heads.
To allow for an optimal placement of the organ however, Syrinchotids had to twist their shoulder (both pectoral and pelvic) girdles forwards. This makes them the very first Anisospondyls on record with asymmetrical shoulder girdles, an adaptation evolved independently later several times in unrelated groups.”

“Like the Aurispinids, they were herbivores. But unlike their hairy-sailed cousins, the Syrinchotids had perpetually downturned heads. This probably meant they fed on low growing vegetation while the Aurispinids were mainly browsers. This allowed for niche partitioning in the early years of coexistence. Later on in the Phylloceous however, the Syrinchotids appear to have outcompeted the Aurispinids in browsing niches.”

“The Rozenbed Formation dated to the late Schippelian from 195 million Eryobian years ago contains deposits of a seasonal swamp forest.
In this formation, a lot of animals of both Knoppiran and Dallckian origin were discovered.
The “megafaunal” herbivores found here were both of Knoppiran origin.
Found here were the roughly peccary sized Aurispinax jubatus and Syrinchotus reptans. Although small in comparison to their descendants in the Jelkeïan, these were the biggest land animals of the Schippelian.
It’s not known how these animals would have responded to meeting each other, but given that their diets were different enough, it’s speculated that such encounters would have been mostly peaceful.”

The Gerritsen Formation

 “Knowing what transpired in the past is crucial for understanding what is happening today. Though when you’re placed on a less than hospitable world where taking your breathing-mask off will end with you drowning in the air, and with very strict laws preventing large scale destruction of native habitat, getting to know what happened in this worlds past is not easy.”

“It is forbidden for us to do targeted fossil excavations in any place other than cliffs and deserts. Because of this, the fossil history of Eryobis largely eludes us. One of the only places where we can actually get a decent amount of fossils without destroying the environment are the coastal cliffs of northern Hatèmica. But these cliffs only show roughly a 5 million year window between 100 and 95 million years ago. Finding any easily accessible fossil sites older or younger is extremely difficult.”

“That is why we were absolutely thrilled when fossils were discovered in an area designated for urbanisation. While laying the foundations for buildings in the settlement that was to be called Gerritsen, they discovered gigantic petrified plant remains accompanied by some fossil arthropods.
It was then when excavation was started and the settlement of Gerritsen was permitted to expand in a different direction.”

“To this day, the Gerritsen Formation is the biggest fossil site on Eryobis. With over 70 identified genera of animals and an even greater amount of plants. This fossil site provides an excellent window of the middle-late Jelkeïan epoch of the Phylloceous period, 176-180 million years ago.
Determined to have been a subtropical forest, it is thought that the main site formed when a flash flood occurred which killed and buried most organisms instantly. This would explain the excellent state some fossils have been found in, with many showing soft tissue and a perplexing amount even preserving pigment.”

1. The largest animal of the fossil site is the Syrinchotid called Dixiphotocanthus brachycorythius. Named after its somewhat double edged sail and its close relationship to the genus Otocanthus, which it was at first thought to be a species of. Preserved with some soft tissue, the animal appears to have had thick, fleshy lips when it was alive and was covered with small, non overlapping scales. The amount of individuals found suggests Dixiphotocanthus lived in small herds and one even preserved pigment cells which revealed the animal was mostly brown in colouration with a number of both lighter and darker spots and stripes.

2. The biggest terrestrial carnivore of the formation, was the early Pulvinopod Gerritsenvenator ingens. With an oversized head and massive teeth, it is thought this animal could hunt both smaller and larger prey alike. Although it wouldn’t have been. Much of a threat to adult megafaunal herbivores like Dixiphotocanthus and Gewapansaurus. Like all Pulvinopods do, it is likely Gerritsenvenator also spent its early life in water and became terrestrial as it matured.

3. An early “modern” Pulvinopod, still needs formal description. Is thought to have been poisonous based on similar looking modern relatives.

4. The second largest terrestrial herbivore in the Gerritsen Formation was also a Syrinchotid. Dubbed Gewapansaurus proboscilabis, after an extraordinarily well preserved specimen showed that it had short, trunk like lips. But not only that, the specimen also preserved pigment. Mostly found to be reddish-brown in color, it had particular large patches of strangely shaped scales.. After being put under an electron microscope, it was discovered that these patches had a crystalline structure which in real life would’ve resulted in a blue color. As only one specimen has been discovered with pigment still “intact”, it is currently unknown if these blue spots were exclusively present in one sexe, or both.

5. Eokleisopneumis loricatus is the earliest known Kleisopneumoid Anisospondyl, the group with includes almost all modern Anisospondyls. It appears to have been an omnivore with sharp defensive osteoderms.

6. Another large herbivorous Anisospondyl was discovered in the Gerritsen Formation the Aurispinid Istiophorosaurus armatus. Istiophorosaurus is so far the youngest known Aurispinid and like it’s ancestors, had a mane of filaments covering the lateral line organ on its sail. While it also had large defensive spikes, their function is yet unknown for no predator of a size that warrants such defence has been discovered in the formation.

7. Present day Eryobis is no stranger to huge arthropods and this was no different in the past. A prime example of this is the huge cumacean discovered in the Gerritsen Formation dubbed Gigantolamprops terrestris. Due to its size and build, it’s thought Gigantolamprops was an omnivorous scavenger that fed on whatever it could find. It’s thick exoskeleton probably defended it against most potential threats in its environment, as it was not built for running away or fighting.

8. While largely in the shadow of the Anisospondyls, Arachnopods did not come without some giants 180 million years ago. Palaeophytodon grandis represents one of the first offshoots of the Osteotarian lineage and the earliest known herbivorous Osteotarian. Characterising for basal Osteotarians, it had a large mast like bone that bordered the not-yet-ossified pectoral fin, together forming pinnae used for hearing. Palaeophytodon had rather long horns, that were probably used for display.

9. Another early Osteotarian discovered here was Iridiotis pachyosteus. It was a medium sized omnivore. What’s most special about it, is that it was discovered with skin impressions which show it had an iridescent green throat, brow and ear pinnae that were used in display. As only one specimen has been uncovered, it’s unclear whether this was omnipresent in the species or just restricted to males.

10. A good number of Brachiostomatan Anisospondyls were discovered in the Gerritsen Formation. It’s thought Brachiostomes first appeared in the early Jelkeïan, about 20 million years before the Gerritsen deposits. They quickly spread and diversified due to the advantage their under-mouth caecal arms gave them in foraging. This one, while still unnamed, would’ve been a small carnivore when alive. It’s believed to be a early relative of the Brachiostomatan carnivores known from Bobossic deposits.

11, 62, 65, 66, 68 and 69 are some of the many basal, small Pulvinopod species discovered in the formation that are all yet to be described.

12. The third largest Brachiostome of the Gerritsen Formation is thought to have been an arboreal animal. Dendrokynichus elisus had long limbs with long fingers and a long tail that appears to have been prehensile. It was probably an omnivore with a preference for herbivory.

13. A small Dextrotselan Anisospondyl yet to be named. Thought to be a relatively close cousin to Aurispinids like Istiophorosaurus.

14. One of the biggest animals of the Gerritsen Formation was the Haligar species Jelkisuchichthys primivaeus. Jelkisuchichthys was previously only known from late Jelkeïan deposits, but J. Primivaeus shows the genus was already around in the middle Jelkeïan. As a Haligar, it was a close relative to the ancestors of all Anisospondyls. It is the biggest predator discovered in the Gerritsen Formation and would’ve hunted by laying in ambush near the water’s edge similar to a crocodile.

15. The discovery of Gerritsegyrinus remipus was quite interesting, for it appears to have been a secondarily aquatic Pulvinopod. As it’s limbs and pelvic girdle were incapable of supporting it on land. It would’ve been a hunter of smaller fish, arthropods and the larvae of other Pulvinopod species.

16. A large Rokanizid coelacanth species yet to be officially named. It’s big jaws would’ve been used to chew plant matter.

17. A yet unnamed Baculopterichthyan, it’s teeth show it was a carnivore.

18. Among the many Brachiostomatans found in the Gerritsen Formation was also an ancestor to the Corripiocetids that would dominate Eryobis’s oceans in the Bobossic. Like it’s later relatives, Gerritsecetus falcarostrum had a horizontally flattened tail and caecal limbs with long claws and spikes for seizing prey.

19. A yet unnamed species of primitive Bunnyfish.

20, 21, 22, 23, 24, 25, 26 and 27 are the largest among the countless basal Cyclopsflies found in the Gerritsen Formation and also the best preserved. These volant Kazacharthrans are yet to be described, but their morphology shows they had vastly different lifestyles.

28. The most common fish in the Formation was Gerritsenichthys pachytholus. This holostean had heavy jaws, with which it probably fed on arthropods and molluscs.

29. An animal with very uncertain affinities, Syncheognathus grandis is one of the most enigmatic animals found in the Gerritsen Formation. For while it has the fin rays of a spiderfish, it has the skull anatomy more reminiscent of an Arachnopod. Some researchers have proposed its a gigantic neotenous “flish”, but there is not enough evidence to back this theory. It was a large carnivore that would’ve hunted whatever could fit in its mouth.

30. Thought to be large primitive Flattacanth species, it is only known from fragmentary remains such as isolated fin bones and skull fragments. It is yet to be named.

31. A more complete Flattacanth found here was Lutambulus tortilis. A quite large fish, it would’ve been a bottom hunter, feeding on smaller animals that swam overhead. Because the vegetation in its habitat was red, it is thought that Lutambulus was reddish in coloration too.

32, 33, 34, 35, 37, 39 and 40 are a number of smaller, primitive Holosteans found in the Gerritsen Formation. Nut much is known about them and they are yet to all be described.

38. This particular Holostean has caught researchers’ eyes because it appears to be a close relative to spiderfish, as several of its pelvic fin rays were ossified. It is yet to be named.

36, 41, 42, 43, 44 and 45 are some true spiderfish found in the Gerritsen Formation. Their number of legs indicates they come a from a variety of lineages, but all are yet to be officially named.

46 and 47 are two relatively large freshwater Cumaceans, but are yet to be described despite occurring in large numbers.

48, 49, 50, 51 and 52 represent the Cyclid fossils found in the Gerritsen Formation. It is unknown whether the smaller specimens are separate species or just juveniles of the larger ones.

53. Probably the heaviest arthropod uncovered in the Gerritsen Formation was gigantic notostracan dubbed Titanopachyaspis gerritseni. This enormous crustacean was probably a scavenger or both animal and plant remains to sustain its huge size.

54. A relatively large, primitive aquatic Kazacharthran, it is yet to be named.

55, 56 and 57 some smaller, but still quite big Notostracans. They are yet to be formally described.

58. Gigantolamprops is not the only huge terrestrial cumacean discovered at the site. A whole different kind of land living cumaceans, that appear to have evolved independently, was also discovered here. Gerrixecaris wilsoni was one of these. It was roughly the size of a football and probably fed mostly on plant matter.

59. A large terrestrial Kazacharthran that is thought to be distantly related to the Cyclopsflies. Proscorpiocaris cyclops was the size of a small cat and, inferred from its mouthparts, was a carnivore. Although it is unknown whether it actively hunted or scavenged for food.

60 and 61 are two of the earliest Osteotarians that adapted for an arboreal lifestyle. Not much is known about them, as both are only known from fragmentary, crushed remains. But judging by their foot anatomy, it is thought they are basal members of, or perhaps are ancestral to the modern Osteotarian clade we call the Dactylourae.

63. A small and slender Anisospondyl. It is unknown what it’s affinities are and it yet to be named.

64. Found inside a huge petrified “tree” where the remains of another gigantic cumacean. A close relative of Gerrixecaris, it was called Dendroastacus xylophagus, as it is thought that the animal had hollowed out the “tree” it was found in itself. Overall, it’s the biggest arthropod of the Gerritsen Formation, but given its rather thin armor and slender legs, probably not the heaviest.

67. Another large Brachiostomatan, the carnivore dubbed Vellicovenator gracilis is thought to be a direct ancestor to the large predators that lived in the Bobossic based on the anatomy of its jaws and limbs. As the second largest terrestrial carnivore after Gerritsenvenator, Vellicovenator would not have taken on as large prey, but would’ve scavenged and was capable of climbing trees, thus likely having a greater array of prey.

70. A smaller relative of Gigantolamprops, it is yet to be described.

71. Based on the anatomy of its skull and spiracles, this Anisospondyl species, named Scoporhynchus vergus, has been determined to be Katoptifylan more derived than the Brachiostomes, but more basal than the Kleisopneumoids. It had relatively long legs and claws, which it probably used to climb and dig with. It is thought that it mainly fed on invertebrates with its slender beak.

72 and 73 are two yet unnamed “flish” of the “Pectoral-fin-first” variety.

74, 75 and 76 are three yet unnamed “flish” of the “Pelvic-fin-first” variety. They appear to have been quite diverse in their niches. The fossil of #76 had skin impressions which showed an intricate spiral pattern of spots on the lower side of the wings.