We
were hacking through a thicket when a team member fell into a
clearing; he had cut into a dirt path. Dirt paths were not a rare sight for us,
they were a necessity for anyone trying to explore the impenetrable jungles of
Yanhuo. Though they were usually indicated on our shared maps by whichever team
that made them, sometimes people forget or misplace their markers. However, we
were in the most southern reaches of the continentette, by the foot of the
Flaming Mountains, hundreds of kilometers away from any known site of
exploration.
My
first thought was that a different team, perhaps an early USSC operative before
my employment, had long beat us to it, but inspecting the trail quickly dispelled
that theory. It was at least two meters wide and wound in both directions for
about 50 meters before forking. USSC policy advised us to make straight and
narrow paths so we would not disturb the native fauna; whoever built this
certainly did not get the memo. Furthermore, the trail seemed to be frequently
and recently used, evident from its demarcation. Nothing grew on the path but a
few pitiful horsetails at the edges. We had been in close communication with
all the other Dome 4 teams since the Schoedsack incident. Not even one of them
had travelled anywhere near this part of the micro-continent in a few months.
We decided to walk the trail. After hours navigating junctions, we reached what seemed to be the end, a massive circular clearing filled with felled trees stacked on top of each other. On one of the stacks sat an enormous placoderm at least 1.5 meters in length, its azure shell glimmering in the midday sun. The mean hook on its chin, reminiscent of Changgu dromaeopods, suggested it could easily disembowel a human if it tried. None of us wanted to test that hypothesis. Luckily, it seemed to be asleep, so we retreated the way we came as fast as we could.
We
later discovered that the animal was a living specimen of Thylankoderma
saltentia, previously known only from a single coxa bone found
half-buried in a swamp. The holotype had been named after the goad-like spikes protruding
from the bone’s upper lobe, but if the discoverers had seen a thylankoderm in
the flesh, no doubt they would have named it after something more conspicuous.
These spikes are likely used as a defense against rammers by absorbing shock.
Combined with their graviportal frames, this makes thylankoderms exceptionally
hard to topple. Mantis storks and other tiehe find it just as difficult to penetrate
the thick skin of their hind bodies, not that they would risk losing a leg to a
thylankoderm’s formidable tail club.
The
function of thylankoderms’ vibrant shells immediately ignited debate. The first
and most obvious explanation was sexual selection, but this was overruled once
we realized males and females had the same color. We were left puzzled for
weeks until Ma He caught a small quadrupedal tieheforme trying to eat a piece
of blue tarp at our campsite. After some testing, he came to the realization
that the animal had mistaken the tarp for a piece of vegetation. Just like most
mammals on Earth, tieheformes possess dichromic vision, but unlike mammals
which lack cones sensitive to red light (protanopia), tieheformes have
anomalous cones sensitive to blue light (tritanomaly). This causes them to
perceive both green and blue as similar shades of cyan, the exact color of
thylankoderm carapaces. However, the question remains why thylankoderms would
use blue pigments for camouflage instead of the more conventional browns and
greens in other bipods. A recently proposed theory is that thylankoderms freely
acquire pigments through kleptoplasty, like the common lab animal, Elysia
chlorotica. The blue pigment of their shells would then be stolen
cyanobacteria from their helenophyte prey. However, this theory fails to
account for thylankoderm juveniles which do not have sophisticated enough
digestive tracks to consume helenophytes, but shine blue nevertheless. More
research is required before any conclusion can be made.
Thylankoderms shift niches as they age. Juvenile thylankoderms are far more predatory. Between the ages of 2 and 8, thylankoderms exploit their efficient gait to stalk pseudopods and jungle munchers which wear out far more quickly. During this stage of life, thylankoderms are disproportionately likely to attack USSC explorers, perhaps because human silhouettes somewhat resemble that of flesh-bearded tiehe, one of their chief food sources. When larger prey items are scarce, they will use their chin spike to gash logs, hoping to expose infaunal invertebrates, such as pauropods, isomites, and leafleeches.
As
thylankoderms age, they lose the ability to track prey across expanses of
jungle simply because of their bulk. Even just moving around often requires
them to topple trees. Adult thylankoderms graze by excavating helenophytes
with their protruding chins. Since bipods do not have necks, they pivot their
entire bodies to dig. Smaller helenophytes are finely chewed into a paste,
shell and all, before being swallowed. If a helenophyte is too large to fit
into the thylankoderm’s mouth, the animal will use its tail club to smash the
shell open before using its two tongues to extract the soft innards. These
animals, though far from docile, usually do not pose a threat unless
approached.
Thylankoderm
adults routinely create trails leading between particularly large helenophyte
gardens and sources of water. This allows them to cover a substantially wider
ranger and access far more resources than they would otherwise be able to; we
found that a tagged male walked nearly 170 km in just a month. Though this is
impressive, it still does not match the pace of the extinct Loxodonta
cyclotis, a species of Holocene elephant which made similar paths in the bygone Gabonese
rainforests. Just like elephants, thylankoderms are a
keystone species in the mosaic forests they inhabit. By creating inflammable
dirt paths as they travel, they make breaks that stop bushfires spreading into
the interior of jungles. Ironically, this makes the base of the Flaming
Mountains one of the few places in south-eastern Yanhuo where massive ancient
jungles can be found.
During
breeding season, male thylankoderms will create elaborate bower-nests out of
wood they fell as they travel. Though this might have started as a pure sexual
display, like that of the bowerbirds, these nests likely developed an important
role in child rearing later in their evolutionary histories. Stacked logs is a
great catalyst for xylophagous animals and small micropredators to start
congregating. Hapless baby thylankoderms then feed on these congregating
animals. This gives females which seek out males with the largest bowers a
selective advantage because it gives her offspring the most potential food.
Thylankoderm bower-nests give very young thylankoderms a safe feeding grounds
until their demand grows to a point where they can no longer sustainably eat
from the bower-nest. At this point, usually 6 or so months of age, they will
either leave the nest themselves, or for the case of stubborn youth, be driven
out by their mother. These younglings will usually still stay close to
thylankoderm trails, capturing small animals around fallen trees.
Thylankoderms
are far from the only species which walk their trails. Larger animals which
have a hard time travelling through jungles will often use them as a shortcut
to water sources. These animals attract their own predators, which hide in
trees on either side of the path. During breeding season, female thylankoderms guard
their nests to prevent predators from finding vulnerable juveniles. The
predator most ubiquitously associated with thylankoderm trails is the now
infamous mantis stork, which use it to amble between large bodies of water. If
one is caught away from water in a dry spell, it will start wandering until it
finds a trail and obsessively follow it to the end.
Despite
their basal appearance, the fossil record suggests thylankoderms to be a very
new lineage, diversifying after the mass extinction event 70 million years ago
that ended the reign of herbivorous cheiropods in southern Yanhuo. Both
morphologically and genetically, thylankoderms belong obviously to the plecclimorpha
order, including the armored rammers in Yanhuo and pleccles in Changgu. Despite
this, it remains frustratingly unclear where exactly thylankoderms fit within
plecclimoirpha, though with the discovery of some basal oddball pleccles on the
Naguo peninsula, I believe thylankoderms represent the most basal group in pleccloidea.
The first two illustrations, as well as the accompanying text, were a fan-submission by Spicybeast101 from our discord server. If you have similar fan-contributions in mind, you can send them to us and we might include them if we consider them fitting for the world.
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