Eastern coast of Utiwa

Close to the eastern coast of the continent of Utiwa, near the equator, there is a region that consists largely of grassland during the windy season, and savannah and temporary forests during the still season. Located near a seasonal ocean, the region can get much wetter in comparison to the deserts further to the northwest, especially during the torrential rain in the transitions from the windy season to the still season. This allows much more life to thrive than in the more inland regions, although the winds don’t allow plants to grow too tall. The dominant plant life in this region consists mostly of yellow grass-like organisms and bamboo trees.

Floriavis maximus

Size: 15 cm long from tail to head, 15 – 20 cm wingspan

Diet: nectar, seeds

Habitat: savannas, trees

Reproduction: All unfertilised ova develop into males, fertilised ova develop into females. Give birth to undeveloped young, which are stored in breathing slit.

Due to the existence of flower-like structures on many plants on Eurus, nectivores are fairly common on the planet, just as on Earth. One such group of nectivores are the florivorids. They belong to a broader group of flying animals called the saurorniths, which secondarily redeveloped flight using the wings ancestral to endosteans, previously used for other functions like temperature regulation, balance, and gliding.

To aid in their nectivorous lifestyle, florivorids have a number of adaptations such as their long, thin beaks and the ability to hover. Many saurorniths, florivorids included, have their wings fused together so all four can act as a single pair. And while this usually comes at the cost of not being able to hover as effectively, this isn’t the case for florivorids. To combat this, they’re capable of beating their wings at an extremely rapid rate, using elastic energy stored in their tendons and other connective tissues to help sustaining this beating once it’s started.

Unlike most other florivorids, who inhabit the wind shadow forests where flowering vegetation is more common, Floriavis maximus prefers more open spaces. It is larger than most of its relatives, unable to rely on its small size to hide from predators as effectively, and has developed a venom it can inject from its claws for defence. With less need for camouflage than other florivorids they instead have bright blue scales for display, with most individuals preferring to select mates for male exchange that have a brighter colouration. Their scale colour is due to a pigment they can’t produce naturally which they can only obtain from certain plants, so it’s a good indicator of fitness.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Tetraptera
Clade: Viviparitores
Class: Saurornithes
Order: Plaudaciformes
Family: Florivoridae
Genus: Floriavis
Species: F. maximus

Palapus litus

Size: 25 - 35 cm in length

Diet: Tiny basal insect-like holocelypheans

Habitat: Burrows in savannah and grasslands

Reproduction: Lay eggs. Offspring begin small and worm-like, living in their mother’s pouch after hatching. Females grow into their adult form in a cocoon.

With extremely strong winds half of the year, burrowing animals are very common on Eurus. The family Xenoaspalacidae contains species especially adapted to burrowing, allowing them to hide underground to shield themselves from the harsh winds, as well as protecting them from predators. Palapus litus is a typical Xenoaspalacid – or Eurus mole – with a short cylindrical body, short legs, and front limbs well adapted for digging with large, curved spade-like claws.

The existence of Xenoaspalacids is an example of convergent evolution. The Eurus mole has developed similar features to Earth moles due to them both occupying a similar niche, and as a result being subjugated to similar evolutionary pressures. This kind of convergent evolution is particularly common on Eurus, or at least easier to see. The large animals of the planet already have a similar body structure to Earth’s tetrapod vertebrates – they are therefore affected by similar environmental pressures in similar ways.

Palapus litus spends more time out on the surface than other related species, and as such has retained the capacity for sight, lost in many other Eurus moles. Its legs are also relatively longer than some other species, allowing easier movement on the surface, and it has larger eyes. They usually only come out during the still season, however, spending most of the windy season in the shelter their burrows provide, hibernating during the worst parts of it.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Clade: Ovata
Clade: Triodontes
Class: Marsupiata
Subclass: Pilata
Order: Brachypoda
Family: Xenoaspalacidae
Genus: Palapus
Species: P. litus

Platycastor orientalis

Size: 40 – 60 cm long (not including proboscis)

Diet: plants, Tmemichthid “fish”, tiny insect-like Holocelypheans

Habitat: coastal areas, retreat to pockets of saltwater on the seafloor plains during the windy season

Reproduction: Lay eggs. Offspring begin small and worm-like, living in their mother’s pouch after hatching. Females grow into their adult form in a cocoon.

Platycastor belongs to a group of animals called the Proboscates, characterised by the presence of a long flexible tubular proboscis at the front of their body, used for feeding. This proboscis is unsupported by bone, instead controlled and kept rigid by a series of strong muscular hydrostats. This proboscis developed from the lower tongue, rolled into a tube and fused at the top, but in many groups this is no longer apparent. In a large number of Proboscates, like Platycastor, the proboscis is seamlessly attached to the skin on the outside of the face and covered in hair, and can’t be retracted. More primitive Proboscate groups, in contrast, keep the tubular tongue rolled up in the mouth when not feeding. 

Winds on Eurus can easily become strong enough to carry small animals like Platycastor off the ground. While many small animals hide from the wind by burrowing, others solve this problem by developing a flat, squashed shape that allows the wind to just pass over them. Platycastor, with limbs ill suited for burrowing and a body poorly adapted to moving through tunnels, is one such animal. As a result, they face less competition from similarly sized animals during the windy season, many of which are dormant during this period. Platycastor, however, is able to remain active throughout the year.  

They tend to live near bodies of water, with Platycastor orientalis preferring coastal areas. They can swim, but are more comfortable on land, using their long proboscis to catch sea “fish” in addition to gathering algae and seaweed-like organisms. Platycastor will also eat “insects”, both those on land and in the water. During the windy season, when the oceans shrink, they retreat to the small lakes left over, feeding on the sea animals trapped there. Fish are often forced to cluster closer together at this time of year, at least those who don’t migrate further offshore or hibernate in the soil, so they’re easier to come by.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Clade: Ovata
Clade: Triodontes
Class: Marsupiata
Subclass: Pilata
Order: Proboscata
Family: Platycastoridae
Genus: Platycastor
Species: P. orientalis

 

Conorhamphus erythrus

Size: 35 – 45 cm in length, including tail, 80 – 100 cm wingspan

Diet: seeds, fruit, insect-like Holocelypheans

Habitat: savannahs and grassland  

Reproduction: All unfertilised ova develop into males, fertilised ova develop into females. Give birth to undeveloped young, which are stored in breathing slit.

Conorhamphus is a much more basal Saurornith than Floriavis, its four wings separate and with much longer legs. They belong to a group of granivores and fruit eaters known as Dianisodactyls. While most members of this group primarily inhabit rainshadow forests or the seasonally growing forests that appear during the still season, Conorhamphus prefers savannas, where it specialises in eating large seeds from bamboo trees. It’s able to use its four wings to hover near the tops of the trees where these seeds grow, staying relatively still as it feeds. In spite of the hovering ability their two pairs of wings gives them, they don’t have the energy to maintain hovering – or anything other than souring flight – for as long as Floriavis can.

Dianisodactyls are primarily characterised by the shape of their rear feet, with their opposing toes allowing them to grasp tree stems. Because of the shape of most bamboo trees, Dianisodactyls perch horizontally rather than vertically. Their feet have a locking mechanism that allows them to do this with relatively little energy, and they usually hold their bodies close to the tree so there’s less torque, using their front limbs for stability.

Another feature shared by most Dianisodactyls is the flexibility of their cartilaginous wing-supports; the series of “fingers” that run along the edge of wing-supporting limb. These supports aren’t homologous to digits, and have actually developed from hardened areas of the venation ancestrally present in Tetrapteran wings. While in many Saurornith groups they only provide support for the wing membrane, in the majority of Dianisodactyls they have a flexible joint at the base. This allows them to fold up their wings when they’re not in use. While most Saurorniths are able to hold their wings flat against their body, the ability to make them smaller like this is rarer in other taxa.

Conorhamphus can unfurl its wings further than most Dianisodactyls, allowing it to modify their aspect ratio. By unfurling its wings half way, they become much broader than when they’re folded by have the same length; most Dianisodactyls only open their wings slightly further than this. But past this point, the wings become narrower and longer, until it reaches a point where they have the same width as their folded state but are much longer. Conorhamphus usually lacks the flexibility to extend its wings any further than this, but this is much more than most of its relatives can extend their wings.

This ability to modify the aspect ratio of their wings allows them to change it to suit the situation. The wings are extended to their maximum extent during souring flight over longer distances, but to quickly escape from predators low aspect ratio wings are favoured, so their wings aren’t fully extended.

Other than this Cororhamphus and other Dianisodactyls are fairly typical Saurorniths when compared to more derived lineages like Florivorids. They have a beak, developed from the mandibles of their ancestors, which are homologous to the inner mandibles of Endosteans. This beak lacks the jointing of other Tetrapterans and has hardened and become more beak-like. They lack the ability to chew food with this structure, so food is ground up in a gizzard filled with chitinous plates. Unlike birds, their beaks open to the side, as opposed to opening vertically.

Most of the digestive organs have moved back to the “tail” of Saurorniths, actually an elongated and narrowed part of the torso, with the area in front dedicated to flight muscles and the respiratory system. In addition to their large, powerful flight muscles, which have a series of anchors and pivots inside the rib cage for them to push and pull against, there is a hydraulic pump providing these muscles with high pressure. Much like the birds of Earth, the actual lung itself is quite small, but a series of air sacs allows for the constant unidirectional flow of air both when breathing in and when breathing out. Unlike birds, however, Saurornith air sacs can serve as independently acting pumps.

Like many Tetrapterans, Saurorniths don’t lay eggs; they instead give birth to live young. Since this is quite energy intensive compared to egg laying for a flying species, and has the added disadvantage of weighing them down, pregnancy is short and the young they give birth to are very small and underdeveloped. Since many beak types don’t allow for the easy passage of larvae, in most species they burrow a hole through to the breathing slit and leave through there. The breathing slit also serves as a pouch for protecting their young as it grows, but they usually leave them behind in a nest or in their mate’s pouch if they need to leave for any extended period of time. Larvae are legless and beakless, and often blind.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Tetraptera
Clade: Viviparitores
Class: Saurornithes
Order: Dianisodactyliformes
Family: Conorhamphidae
Genus: Conorhamphus
Species: C. erythrus
 

Rhachioemys lambdanoton

Size: 15 – 35 cm

Diet: grass

Habitat: grasslands

Reproduction: egg-laying

This animal belongs to the order Acamptocormaria, which is characterised by a particularly thick and sturdy shell-like skeleton. The ribcage of Platysomes is already shell-like, lacking gaps between the rib plates, but in most lineages these plates overlap to allow bending. However, animals in this order have their ribs fused together so that the bones of their torso act as one solid unit, providing strength at the cost of mobility.

As small, slow moving herbivores, this serves them well, protecting them from predators. Their flattened body structure and stumpy legs prevents them from running effectively, so having at least some form of protection is essential to their survival. It is this adaptation that has allowed the group to become so successful, with members of this diverse order found throughout the planet.

Rhachioemys is a non-Marsupiate, belonging to a distinct class called Septoculida, so named for the presence of seven eyes; four major eyes and three smaller ocelli. While these ocelli have been lost in many groups, Marsupiates included, they are basal to Endosteans as a whole. Much more significant (but less immediately visible) distinctions between the two classes are that Septoculids are cold blooded, as well as the presence of chitinous serrations on their tongues. These serrations help in the processing of food, lacking the acid glands of Marsupiates, giving them an edge over other non-Marsupiates. Like Marsupiates they lay eggs, but most species do little to care for their young.

Most Septoculids have a covering of scales to protect them from the elements, since weather can get very extreme during the windy season and the rainy transition to the still season. As relatively inactive animals they will rarely attempt to seek cover, instead opting to endure these conditions. Their eggs, too, are protected from harsh conditions, with a much harder shell than those of Marsupiates, whose eggs don’t need strong shells well protected in their pouch.

Rhachioemys has a large, extendable and dextrous pair of tongues for obtaining food, allowing it to reach for vegetation without having to move its body. It will use its serrated tongues to grind up food before it even enters the animal’s mouth, at which point it will bring the loose pre-processed vegetation into its mouth for further chewing or just swallow it.  

The animal has numerous hair-like sensory organs near its mouth, characteristic of the order Acamptocormaria, which have developed from hydrostatic extensions of the muscular oral surface. These are able to move independently and are used to search for suitable food. Not only are they highly sensitive to touch, but these organs possess taste receptors. They are also able to extend their two frontmost eyes out of their head, raising them up on stalks, which is used to search for food. The two larger outer eyes are used for spotting predators.

The sensory organs at the front of the mouth can be used to detect incoming winds, and before the winds get too heavy they will usually crouch down so they’re closer to the ground, often tucking their limbs under their body. Although, with their stubby legs, this doesn’t do too much to change their overall height, it gives them a more aerodynamic shape allowing the wind to pass straight over them as if they were just a slight bump in the ground.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Clade: Ovata
Class: Septoculida
Order: Acamptocormaria
Family: Ptilemydidae
Genus: Rhachioemys 

Species: R. lambdanoton

Magnoros magnoros

Size: 2.5 to 3.5 meter high

Diet: grass, sometimes wood

Habitat: grassland

Reproduction: egg-laying, store their larvae in a pouch, build cocoons during metamorphosis

These large grazing herbivores come from the scaly, hairless group of Marsupiates characterised by their erect limb structure. Magnoridans, specifically, can be distinguished from other Marsupiates by their elongated heads, giving them a long proboscis supported by jointed skull bone. This allows the mouths of larger Magnoridans to easily reach grass or water without them having to bend their hefty bodies or, in some species, allows them to reach high leaves or seeds. Those belonging to the family Magnoridae, like the species Magnoros magnoros, have a series of hard chitinous teeth inside these elongated mouths, allowing them to use this large muscular organ to grind up hard fibrous plant matter.

Magnoros magnoros is among the most widespread and populous Magnorids, and is physically larger than species from related genera. Comparable to an elephant in size and weight, this is the largest animal found along the eastern coast, as well as many of the other areas its various different subspecies inhabit.

The mouth of Magnoros is very large and thick, giving plenty of room for the interior to be filled with thick crushing musculature for the chewing of food. A pattern of contractions and expansions of the muscles underneath the layer of skin covered in teeth takes place as the animal spends hours processing its food. Like most Marsupiates, their mouths have acidic glands, further aiding in mastication.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Class: Marsupiata
Subclass: Lepidodermata
Order: Magnora
Family: Magnoridae
Genus: Magnoros
Species: M. magnoros

Chenolarus utivensis

Size:  30 – 45 cm from shoulder to the tip of the tail, 50 – 80 cm wingspan

Diet: Tmemichthid “fish”, aquatic plantlife

Habitat: coasts, usually near equatorial grassland

Reproduction: Viviparous. Give birth to undeveloped young, which are stored in the breathing slit.

These relatives of Florivorids use their hovering ability to eat Tmemichthid “fish” rather than nectar, hovering over the water and catching fish in their beaks using their long necks. Their limbs are longer and they spend a great deal more time on the ground than their relatives, their heavier bodies unable to support a lifestyle almost permanently in the air. On land they can assume both a bipedal and quadrupedal stance, though aren’t as agile as they are in the air.  Their webbed limbs allow for a limited degree of swimming, and their light underside and darker back provides camouflage via countershading.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Tetraptera
Clade: Viviparitores
Class: Saurornithes
Order: Plaudaciformes
Family: Allochenidae
Genus: Chenolarus

Species: C. utivensis

Hadroglossus glaucos

Size: 1.3 – 1.8 meters in height, while stood with limbs erect

Diet: leaves, seeds, grass

Habitat: savannas

Reproduction: egg-laying, store their larvae in a pouch, build cocoons during metamorphosis

For most animals, there is a strong selective pressure towards a flat, curved body structure that allows wind to pass over the body. This can be at odds with certain life strategies, like for example browsing from trees. Euran bamboo trees, in particular, keep their seeds particularly high up, which can be a source of nutrition for many animals. This can be difficult to reach for animals that aren’t tall enough, but are too large to climb the relatively fragile bamboo trees. So in such animals, height and flatness are two competing evolutionary pressures.

One family, the cheiroglossids, have the best of both worlds. They stand tall, with long legs they’re able to hold erect below them, but the torso itself is relatively flat. This allows them to keep their body very close to the ground if they have to, just by crouching down during times of heavy wind. They can move around fairly easily even while they’re crouched in this position.

Since most bamboo trees will only grow during the still season, standing tall poses no problem during this time of year. During the windy season, with fewer trees, they have no need to stand as tall, and are relatively inactive during this time of year getting what little energy they can from grass.

One other adaptation common to cheiroglossids is the presence of an elongated tongue, used in feeding. The tips of these tongues have a pad adapted for grasping food.

Hadroglossus is stockier than other cheiroglossid genera, with a series of hard bony bumps on their back serving to protect them from predators. Sexual selection likely also played a role; although the males are small and worm-like, females do select other females to mate with. Or more accurately, to exchange males with.

Hadroglossus lives in large herds for protection against predators, and in-group competition is common, with individuals engaging in head-butting contests. They are highly intelligent animals, with singing ability affecting one’s position within the group as much as fighting. Hadroglossus uses the two breathing slits on either side of its head to produce these songs, which usually have a very low pitched humming quality to them, although they don’t engage in song as much as some other cheiroglossids.

Although Hadroglossus isn’t as swift a runner as other cheiroglossids, their size does offer a degree of protection.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Class: Marsupiata
Subclass: Pilata
Order: Ungulapedes
Family: Cheiroglossidae
Genus: Hadroglossus

Species: H. glaucos

Dolichorhis cursor

Size: 1.2 – 1.5 meters

Diet: grass, leaves, softer wood

Habitat: savannas, grassland

Reproduction: egg-laying, store their larvae in a pouch, build cocoons during metamorphosis

A much smaller and leanly build relative of Magnoros, the species Dolichorhis cursor shares the extended face characteristic of the order Magnorida. Unlike Magnoros, it lacks the chitinous teeth present along the oral lining of its relative, having instead developed teeth along its two tongues.

Dolichoris is a cursorial grazer, depending more on speed and the protection its herd offers than larger magnoridans do. Although not able to change direction quickly, they can gallop in a straight line at an impressively fast speed, and have a great deal of endurance. To facilitate their running, they stand only at the tips of their nails. These have developed into hooves, a feature that distinguishes them from most other magnoridans, the larger members of which have their hefty bodies supported by fleshy pads on the soles of their feet. These hooves have developed independently from those of the distantly related ungulapeds.

The rear eyes are larger than the frontal eyes, used primarily to watch out for predators.  Its position higher up on the body and away from the proboscis is ideal for this purpose. The smaller eye pair, meanwhile, is much closer to the mouth and is used to search for patches of vegetation on the ground nearby. They are mainly suited for short distance vision, and their ability to make out shapes at a distance of more than a couple meters is very poor. The rear pair, on the other hand, are much more adapted to long distance vision than close vision. 

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Class: Marsupiata
Subclass: Lepidodermata
Order: Magnora
Family: Dolichorinidae
Genus: Dolichoris

Species: D. cursor

Oxyodon aegialus

Size: 30 - 50 cm long

Diet: small animals

Habitat: coastal grasslands and savannah

Reproduction: egg-laying, store their larvae in a pouch, build cocoons during metamorphosis

Oxyodon is a small, long bodied carnivore that lives in burrows to escape winds and hide from larger predators. They tend to focus on small prey around the same size as themselves or smaller, such as Xenoaspalacids as well as Tmemichthid “fish”. They will also supplement their diet with whatever worm-like organisms they can find in their burrows.

There are a number of adaptations Oxyodon and other members of the order Oxyodontia have related to their carnivorous lifestyle. As well as a relatively short digestive tract common in carnivores, their mouths are well adapted for catching prey and piercing flesh, with a long, sharp beak and outer mandibles ending in very sharp teeth. The beak is visible even when the animal has its mouth closed. The beak and teeth are able to retain their sharpness by constant shedding, with a new, sharp tooth growing underneath. For this reason they have a habit of scratching their beaks against trees or rocks to maintain their sharpness.

A hole is also located at the front of the face to allow clear passage for sounds to reach their hearing organs. As nocturnal predators their hearing serves them well, and since true night only falls during the still season heavy winds don’t interfere with their hearing as much. The frontmost eyes are positioned close to the front of the head, giving them good binocular vision. With a second pair of eyes on the sides of their heads, they don’t sacrifice peripheral vision for this, allowing them to remain alert for predators.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Class: Marsupiata
Subclass: Pilata
Order: Oxyodontia
Family: Oxyodontidae
Genus: Oxyodon
Species: O. aegialus

Onychoglossus vitriolosus

Size: 1 meter tall

Diet: small to medium animals

Habitat: savannah, temporary bamboo tree forests

Reproduction: egg-laying, store their larvae in a pouch, build cocoons during metamorphosis

 

These large solitary ambush predators can be found throughout the more forested parts of the savannah, where trees provide them with plenty of cover to hide from their prey. Unlike most scaled Marsupiates, they’re more active during the still season when this cover exists, hibernating in caves during the windy season.

With their thick, sturdy bodies and short legs, they’re unable to affectively chase down prey, or even pounce for them from a concealed position, so they instead catch prey with their quick, lashing tongue. The upper tongue has a number of adaptations for this; in addition to its length and greater extendibility, the tip is covered in a number of chitinous spines capable of sheering flesh.

Because of their shells, the earlier researchers thought they were related to Magnorans at first, but they seemed to have developed this independently. Their shells and large builds protect them from predators like Pterodromids and Monocerodon, who they can’t effectively run from. All four eyes are positioned near the front of their body for good depth perception, and with their protective shells they don’t have as much need for peripheral vision to keep an eye out for predators.

They’re solitary and highly territorial, only coming together to mate, and tend to have large ranges. In-species fighting is accomplished with their tongues, and they often aim for the eyes to blind each other or attempt to damage each other’s tongue. Fighting is done to compete for territory, and an individual will usually give up before they get too injured.

The only times they exist in groups is after mating, where two females will occupy the same territory with the offspring they produced from each others’ male offspring. They work together to ensure the survival of their larvae, and protect them once the females enter their cocoons. They continue to look after their offspring for a short period after they emerge from their cocoons, until they’re able to fend for themselves. The mothers leave each other straight afterwards, but will keep the male offspring they produced with them in their pouch to trade the next time they mate.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Platysoma
Class: Marsupiata
Subclass: Lepidodermata
Order: Pyrocheles
Family: Onychoglossidae
Genus: Onychoglossus
Species: O. vitriolosus

Dihoplus savanna

Size: 1.5 meters high

Diet: meat, primarily large herbivores including ungulapedes and magnorans

Habitat: savanna, grassland

Reproduction: viviparous, young resemble miniature adults

These large cursorial predators belong to a group of carnivorous, bipedal Tetrapterans called Pterodromids. Their body plan is very different from the flying Saurorniths they’re distantly related to, and they’re much larger than them too. Unlike Saurorniths these animals are flightless, and use their wings for stability instead.

As they run, they hold their wings at such an angle that the air passing over them pushes them downwards, giving them more traction against the ground. Not only does this allow them to run faster, but being pressed securely on the ground this way keeps them from being blown away in the wind; a common problem for a lot of animals during the heavier parts of the windy season, even larger animals. While many adapt to this by having their bodies pressed against the ground, this doesn’t work as well for fast moving predators like Pterodromids.

While most Pterodromids are incapable of sustained flights, their wings are powerful enough that they can sometimes use them to provide a degree of forward thrust during running. This is used more often by smaller species than larger ones, although the fairly large Dihoplus does do this to an extent.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Superclass: Tetraptera
Class: Pterodromida
Order: Unguloraptores
Family: Dihoplidae
Genus: Dihoplus
Species: D. savanna

Monocerodon velox

Size: over a meter at the shoulder

Diet: medium to large-sized herbivores

Habitat: savannah and grassland

Reproduction: egg-laying, store their larvae in a pouch, build cocoons during metamorphosis

A much larger Oxyodont than Oxyodon aegialus, Monocerodon uses its conical, spear-like tooth to take down prey. Like other Oxyodonts it has a hole at the front of its head to allow for better hearing, but it is a pursuit predator that takes on much larger prey than most of its relatives, and has long limbs better adapted for running. Unlike most members of its order, whose limbs are spayed out to the side, Monocerodon holds its limbs in an erect posture directly under its body.

Monocerodon isn’t a pure pursuit predator and will also ambush prey if necessary, usually if the prey is larger than they are. Some species depend more on ambush tactics than others, with the tactics used depending largely on the environment and the amount of cover. Those who live in savannas and grassland like Monocerodon velox chase down most of their prey, whereas some wind shadow forest dwelling species are exclusively ambush predators.

After getting close enough during a chase, they leap onto their prey using their powerful hind legs, piercing down on them with their large, sharp tooth. If this doesn’t kill them instantly, the animal will die very shortly afterwards from the blood loss. Monocerodon is also able to use its front claws as a weapon, usually when hunting smaller prey.

These animals live in small groups consisting of a few related individuals. The dominant member of the group is typically the oldest. Monoceradon is most active during the still season, although they still do hunt during the windy season, mostly focusing on smaller animals. Individuals will fatten themselves up towards the end of the still season so they can last the windy season without as much food, and they’ll spend much of their time during the windy season huddled together for protection.

Taxonomy
Tree: Eurovitae
Domain: Euronucleata
Kingdom: Oxytrophia
Phylum: Holocelyphea
Subphylum: Endostea
Class: Marsupiata
Subclass: Pilata
Order: Oxyodontia
Family: Alloischidae
Genus: Monocerodon
Species: M. velox

Endosteans

Most large land animals on Eurus belong to the clade Endostea, characterised by the presence of an internal skeleton. It is this skeleton in addition to their circulatory and respiratory systems that have allowed them to reach their large sizes.

Evolution of Endosteans

The evidence that previous researchers on Eurus have gathered points towards Endosteans descending from a group of insect-like organisms called Holocelypheans. Going further back, Holocelypheans descended from shelled mollusc-like organisms. On the course of their evolution towards a more insect-like form, these “molluscs” developed numerous hydrostatic legs under their body, and eventually grew a jointed exoskeleton over their whole body for greater protection.

The group of Holocelypheans ancestral to Endosteans, the Arthropterans, had wings and was capable of powered flight, shown in the image below. These wings originally developed from the second and rear pair of limbs, which were used for swimming by their aquatic ancestors. These limbs developed numerous hairs on them to increase drag and function as fins. Although the exact details are unknown, not long after they moved to land, these fins developed into wings

The ancestral Arthropteran. This is the group the Endosteans arose from. Although they look like Earth flies, they’re more like flying spiders in a lot of ways

The aquatic ancestors of Arthropterans used their second and rear limb pairs for swimming. The front pair of these fins are primarily for guiding their movement and steering, whereas most of their thrust comes from the rear fins. The middle three pairs of limbs are used for walking, and the front pair are used in feeding

Arthropterans grew larger over time, but there a number of limitations to their size. One is the need to constantly shed their exoskeleton as they grow, leaving them weak and their weight relatively unsupported as their new cuticle hardens. One group of Arthropterans solved this by developing a layer of skin over their exoskeleton, which deposits new layers of skeleton over old ones as it grows. This is in stark contrast to their ancestors who grew their new exoskeletons underneath the last. Their old skeletons can be reabsorbed rather than shed. With this layer of flesh over it, their exoskeleton became an endoskeleton. This outer flesh consisted of not just skin but also fatty tissue, allowing the animal to hold as much fat as necessary without their skeleton restricting it.

Other adaptations included the development of a lung. This evolved from the tracheal system. In some species, the trachea can be expanded and contracted to allow for a kind of breathing, and it was this that allowed a lung-like organ to appear as the respiratory system further adapted to support a larger body. They also developed a closed circulatory system, rather than the open circulatory system of their ancestors.

These adaptations allowed the first Endosteans to reach a much larger size then the insect-like organisms they descended from, a previously untapped niche on Eurus for land animals. The earliest Endosteans looked something like the animal below, although keep in mind this is just a reconstruction. Although the first Endosteans were octopedal, in most modern groups one or more of these pairs of legs was either lost or repurposed.

The ancestral Endostean

Endosteans are split into two major groups; Platysomes and Tetrapterans. Platysomes tend to have flattened bodies to increase their ability to withstand strong winds, and they’ve lost all four wings. Their front legs have shrunk in size and came into use as jaws for feeding. In most lineages they are covered by a layer of skin that protects the mouth. Tetrapterans have retained their wings, and although many are incapable of flight they serve a function in temperature regulation and sometimes gliding. Tetrapterans have six legs, with the second to rear pair lost, although some groups have less limbs. Ancestrally they have two wing pairs, but in some groups one or both of these pairs have been lost.

In general, Platysomes have adapted to living out in open spaces in the wind, while Tetrapterans are more suited to enclosed environments like the planet’s “wind shadow forests”. However, both groups can be found in all environments.

Anatomy

Internal anatomy of an Endostean, showing the organs of the Platysome Monocerodon)

Monocerodon skeleton

Skeleton

The bones of Endosteans aren’t quite as strong as those of Earth vertebrates, but they’re far stronger than the chitinous exoskeletons of their ancestors. They’re made of a composite material consisting largely of calcium carbonate, but it’s mainly its honeycomb structure that gives Endostean bones their greater strength than that of their ancestors (many aquatic Holocelypheans already used calcium carbonate).

In terms of structure, the skeletons of Endosteans are very similar to that of their ancestors, apart from the fact it’s internal.

At the torso and head, the skeleton consists of a series of overlapping plates, completely covering the internal organs but allowing for movement. In Tetrapterans, however, there are gaps between these plates, except at the head (where more protection is needed), sacrificing defence for lightness.

The bones of the limbs consist of hollow cylinders, with elastic connective tissue at each joint connecting these bones. The muscles are situated on the inside of these cylinders, rather than the outside, a remnant of their ancestry from animals with exoskeletons. They typically have six legs, at the end of each are a pair of claws. The bone of these claws is typically quite flexible, often consisting more of chitin and connective tissue than calcium carbonate, and they’re hollow, with muscle inside. This muscle is able to bend the claws, although in some groups the claws have hardened and become less flexible.

Tetrapterans have wings similar in structure to the legs. Each wing is supported by a single jointed appendage, with hollow cylindrical bones and muscles on the inside.

Nervous system

The nervous system of endosteans is optic rather than electric. To transmit a signal, bioluminescent light is generated then carried along transparent “nerve” fibres that act as biological optical fibres. At the synapses, this light triggers the release of neurotransmitters, which in turn trigger the production of another bioluminescent signal. The nerves aren’t perfectly transparent and some light is lost, so these synapses are necessary for maintaining signal strength.

The central nervous system consists of a brain at the front of the animal, where most of the sensory organs are located, attached to a long spinal cord running along the underside of the body where it’s protected by bone.  

Muscles

Movement is achieved using tissues of variable elasticity. If elasticity is increased in one “muscle” and reduced in another, the muscle with reduced elasticity will contract in length and stretch its antagonist. This reversible change in elasticity is achieved by exposing the tissue to certain chemicals, released by glands found within the muscles. The activity of these glands is regulated by light, allowing the optical nerves to control muscles.

Muscles are located on the inside of the bones, and attach at their ends via connective tissue. Muscles consist of fibres aligned parallel to the long axis, as well as fibres arranged perpendicularly to the long axis, allowing them to both expand and contract, acting as a muscular hydrostat. This is probably a result of their ancestry from mollusc-like ancestors, whose entire bodies consisted of muscular hydrostats. This way, muscles control the animal’s movement by both pushing and pulling against bone. The insides of the bones have grove-like structures where the muscles attach to allow for this.

Circulatory and respiratory systems

Air is taken in and expelled through a pair of breathing slits at either side of the animal’s face or neck. Both slits have tracheae that lead to a single lung, surrounded in muscles that allow it to expand and contract to take air in and out. Usually, there are organs resembling vocal cords in either trachea. Unlike the tetrapods of Earth, this respiratory system isn’t connected to the digestive system in any way.

Two hearts are present along the back. The frontmost heart is the lung heart, or anterior heart, a two chambered heart responsible for pumping blood through the lung. Further back is the systemic heart, or posterior heart, which can have up to four chambers and pumps blood throughout the body and back to the lung heart.


The systemic heart carries both oxygenated and deoxygenated blood, with oxygenated blood directly from the lung going though the upper atrium and ventricles, and deoxygenated blood going through the lower atrium and ventricles. The lung heart, however, only pumps deoxygenated blood, pumping it through its single atrium and ventricle.

The blood of endosteans contains the copper-based oxygen carrying protein haemocyanin, giving it its blue colour. Deoxygenated blood, however, is colourless. Endosteans don’t have the equivalent of red blood cells, with the haemocyanin instead suspended directly in their blood plasma rather than carried by cells.

Haemocyanin is only about a quarter as efficient as the haemoglobin of Earth vertebrates. However, it’s more efficient in the low oxygen and low temperature conditions found in the deep sea where the endosteans’ distant mollusc-like, and later crustacean-like ancestors lived. In fact, the molluscs and crustaceans of Earth use the same protein. This protein was retained throughout the evolution of holocelypheans on land and as endosteans evolved; however, the specific form of haemocyanin changed over time, and in modern endosteans a more efficient haemocyanin is used which is unknown on Earth. This haemocyanin is over twice as efficient as the usual kind in the conditions found on the surface.

Digestive system

Endosteans have a U-shaped digestive tract, which they retained from their shelled mollusc-like ancestors. These molluscs’ shells forced their bodies to be shaped in such a way that their anus was just under their mouth, so both could leave the shell. This shape was retained even after the shell was reduced.

In platysomes, the digestive system begins at a mouth near the front of the body, which is protected by a layer of flesh just under the head forming a pouch. The inside of this pouch can be accessed through an external sphincter, where food is taken in. Inside the mouth there are two extendible tongues, one above the throat and one below the throat, as well as two different jaw pairs used to masticate food. The jaws consist of the inner mandibles, which are smaller, not attached to the skull and rarely ossified, as well as the larger outer mandibles. The inner mandibles are used to grind food, acting like molars. The outer mandibles developed from the front limbs and are used to cut food, acting as incisors, both coming into contact with a chitinous “beak” at the front of the roof of the mouth that it cuts against.

The mouths of tetrapterans have some differences. Tetrapterans lack outer mandibles, with the inner mandibles possessing attachments to the skull and are used for cutting rather than grinding. The mouth is positioned more to the front of the head, rather than underneath, and it lacks the protective pouch of platysomes with the mandibles exposed. The upper and lower tongues are both present, although they tend to be retracted inside the throat. The anus also ends inside the throat rather than just below it, with only one hole visible from the outside. Unlike the inner mandibles of platysomes, tetrapteran inner mandibles are usually fully ossified.

Once food enters the throat it travels through the oesophagus, through a series of muscle contractions, where it eventually reaches a stomach. In most tetrapterans, there is a gizzard before the stomach; this allows food to be ground up before reaching the stomach, since the mandibles of tetrapterans don’t chew. These gizzards are lined with numerous hard chitinous plates and surrounded by a thick layer of muscle. The stomach breaks down food chemically with enzymes and acid, but plays very little role in absorption. The lower lobe of the stomach functions as a crop, storing food, but can be greatly reduced in some species. Both tubes connect to the upper stomach; food is able to pass entirely through the stomach without entering the crop. The stomach also plays a role in detoxification.

After being processed in the stomach, food enters the posterior intestines, which play some role in food absorption but mainly absorb water and filter blood. After having nitrogenous waste added to it the stool travels around to the anterior intestines where the majority of nutrient absorption takes place. As it approaches the front of the body it passes through the rectum, and then an anus, located near the throat. In platysomes, it is inside the mouth pouch just below the opening to the throat. The waste is then expelled out of the mouth.

Senses

Endostean eye anatomy

Most major sensory organs are clustered near the front of the body. For vision, there are multiple paired eyes, usually between four and eight, as well as smaller ocelli in some groups. The major eyes are camera eyes able to resolve images, and although their general structure is comparable to that of the vertebrate eyes of Earth, on a closer look there are a number of differences.

Instead of a lens, the pupil consists of a small pin-hole that usually has a transparent protective membrane, with the light instead focused by a concave reflective structure called a speculum at the back of the eye. This focuses the image onto the retina, just behind the front of the eye, covered in photoreceptors that send signals down the optic nerve and to the brain. Images can be focused by changing the shape of the speculum, using muscles just beneath it pushing and contracting to modify its curvature as well as changing its position relative to the retina. The presence of the pupil in the middle of the retina creates a blind spot. There is also a second blind spot where the optic nerve passes through the retina.

The small ocelli developed much later, and are incapable of focusing or resolving a clear image. They likely appeared after the development of flight in holocelypheans, at least from the evidence I’ve been able to gather, and originated from photosensitive areas of the exoskeleton. They originally served a function in stabilising the flight of arthropterans, much like the ocelli of Earth insects do, but have come to assist the primary eyes in numerous other ways throughout endostean evolution. The ocelli are much harder than the primary eyes, consisting of a partially mineralised chitin lens with a retina at the back of the eye.

The hearing organs of endosteans are located near the front of the head inside the mouth. Each individual has a single “ear”, consisting of a loose bone able to respond to vibration. Hearing isn’t as good as in vertebrates; it’s likely that the windy nature of the planet meant that sensitivity to sound wasn’t as useful, since the wind often drowns it out. In fact, the endostean ear is more effective at picking up vibrations in the ground, as in platysomes who often have their mouths pressed against the ground. Unlike airborne sound, sound is able to travel effectively through the earth even in windy conditions.

Inside the mouth are a number of taste receptors, including receptors on the roof of the mouth as well as the tip of the tongue. There are scent receptors in the respiratory slits in some groups, although smell is rarely a strong sense.

In addition to these senses, there are also pressure receptors in the skin throughout the body, as well as temperature and pain receptors. There are three balance organs in the head just behind and under the brain (one rear and two front), able to sense orientation, and most muscles have stretch receptors.

Evolution of Endostean eyes

Reproduction

Endosteans have two sexes, although the males are much smaller and remain worm-like in form throughout their lives. The males mate by latching onto a female and slowly fusing to her, providing the female with a regular supply of sperm. Males tend to go inside the female's breathing slit; females probably originally had the sexual organ the males latch onto outside it, but it moved into the slit for protection.

In most species females "mate" by giving each other their male offspring. Some produce males asexually when their eggs haven't been fertilised, and females when their eggs have been fertalised; however, other Endostean groups will have to have mated before to birth any males.

Most Endosteans start out as worm-like larvae, metamorphosising as they mature, although some groups have fully-developed young. Larvae may or may not form a protective cocoon depending on the specific clade.

Young are grown in a uterus-like organ in the head, with a birth canal leading to the oesophagus. Eggs or live young go through the oesophagus and are expelled out of the mouth.

Bamboo trees

A bamboo tree

Other than desert, most of the planet’s dry surface is covered in grassland, because of the heavy winds. However, the still season provides an opportunity for taller tree-like organisms to grow, from the kingdom Erythroplasta. Since they only have a relatively short period of time to reach full height, these trees need to be very fast growers, helped by the high levels of ammonia and carbon dioxide in the atmosphere.

Their stems resemble those of the bamboo plants of Earth due to their similar means of growth, and their leaves are thin and needle-like to minimise surface area and increase wind tolerance (although their leaves can be fairly long). Bamboo trees reproduce by growing seeds near the top which, once the windy season begins, are blown away and spread by wind dispersal. The trees die shortly afterwards, leaving behind a grassy treeless landscape, and new trees won’t emerge until the next still season.

Major taxonomic kingdoms

Complex, multi-celled life on Eurus is grouped into five main kingdoms, as opposed to the three kingdoms of the eukaryotes of Earth. Of course, there are many divergent lineages that don’t fit into these, much like Earth’s protists, but these are the largest groupings.  

Erythroplasta

These organisms are similar to the plants of Earth, engaging in carbon dioxide photosynthesis and releasing oxygen into the atmosphere. They also use atmospheric ammonia as a source of nitrogen for protein production. This process releases hydrogen, contributing to the small amount of hydrogen present in the planet’s atmosphere, although it is eventually released out into space. They tend to use carotenoids as their photosynthetic pigment, rather than chlorophyll, giving them colours ranging between yellow, orange, and red.

Erythroplasts are more abundant near the equator where conditions are more stable throughout the year, although the taller species don’t grow as well during the windy season.

Cyanotriches

Cyanotrichs constitute another plant-like kingdom, with many distinctions that set them apart from erythroplasts. Their cells tend to be long and fibrous, and in addition to photosynthesis, they also engage in chemosynthesis. These plants are more fungus-like than erythroplasts, with many species acting as detrivores feeding off decaying matter. Some detrivores have even lost their ability to photosynthesise, becoming even more fungus-like.

Most species grow during the windy season when the seas retreat, growing on the dried-up sea beds and feeding off of the ample nutrients that are left behind. Since, near the equator, the sun is close to the horizon during this time of year, there is much less light available, so they’d be unable to sustain themselves on photosynthesis alone. This is where their ability to chemosynthesise and feed off of decaying matter give them an edge. They have various means of obtaining chemical energy, including the oxidation of atmospheric hydrogen, ammonia, and methane, as well as carbon dioxide reduction.

Because they grow close to the equator at a time of year when the sun is perpetually setting, most of the light available to them is red and orange. To absorb light from this part of the spectrum, they use the photosynthetic pigment phycocyanin, giving them their blue colouration.

Oxytrophia

These organisms engage in oxygen respiration, using oxygen to oxidise carbohydrates as a source of energy, similar to the animals of Earth. Some lineages are capable of movement, although more primitive groups aren’t. However, unlike Earth animals, oxytrophians with a nervous system have nerves that carry biogenic light rather than electric signals, with their nerves acting as optical fibres.

Methanotrophia

Methanotrophians mainly obtain energy by oxidising atmospheric methane, although they also oxidise hydrogen and ammonia. They tend to grow on the winter-side of the planet during the windy season, using chemical energy in the absence of light. They’re much rarer close to the equator.

Detrivora

Detrivorans feed off dead and decaying matter. They grow during the windy season close to the pole facing away from the suns, feeding off of the dead decaying organisms that grew during the still season and the summer. They are remarkable in their ability to withstand cold temperatures, lowering the freezing point of the water in their bodies by incorporating ammonia. During the summer, all detrivorans on the pole die, leaving behind dormant spores that will grow during the next winter.

Previous study of Eurus

For other planets I’ve studied, there has been no shortage of previous research for me to base my writings on. Amthalassa has an intelligent species whose zoological science and palaeontology has reached a similar level to our own, and Nemoros had a species settle on it that was even more advanced. However, on Eurus this wasn’t quite so simple.

The planet does have a sapient species, but their science hasn’t developed yet to the extent that they’ve comprehensively catalogued the life on their planet or studied their evolution. Luckily the planet was recently discovered by the wider interstellar community, and although few have taken interest in the planet there was a small group that worked to study the wildlife there.  

While they only spent two years or so on the planet, and the group of researchers was very small in size, they’ve been able to gather much more data than a larger group of humans would have been able to obtain in decades, thanks to their access to far more advanced technology. Thankfully I’ve been able to get access to this data, and have done a great deal of research myself.  As usual, most taxonomic names have been changed to ones easier for humans to pronounce, using Greek and Latin words.  

Equirectangular map of Eurus, showing continent names based off of those given by the previous researchers. The two shades of blue represent sea during the windy season and still season, with only the darker areas covered by water during the driest days of the windy season.