The Siren

Of all mythological creatures, none are so ubiquitous in modern culture; they appear in artwork, stories, and advertising. But the image and lore surrounding both sirens and mermaids has evolved in modernity, and the line between what were once two very distinct creatures has become blurred to the point of erasure.
How this occurred is a subject for another time, so suffice it to say, the following presentation maintains the distinction held by the ancients. As unbelievable as it sounds, both sirens and mermaids are real, and other than being largely aquatic, the two species have very little in common.
The focus of this presentation is the siren, a deadly and fearsome creature known for luring unwitting humans to their doom. And so, my dear reader, I humbly ask that for the duration of this presentation, you set aside any preconceived notions influenced by popular media and let your mind open to a biology that seems, admittedly, to have little precedent in the natural world.
Rest assured that the wonders of nature are not bound by our imaginations, and sometimes reality is even more disturbing than fiction.

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In the 8th century BCE, Homer wrote of Odysseus, a hero whose 10-year journey homeward was fraught with countless challenges and perils. In brief, along this journey, it is said that Odysseus sailed near a chain of islands upon which lived the dangerous sirens.
Legends of these creatures held that their song was so enchanting that no sailor could resist it. Longing to hear it more clearly, they would run aground, and the sirens consumed the poor sailors by the shipload.
Odysseus had been forewarned, however, and he instructed his crew to stuff their ears with wax and to tie him to the mast. The sirens did indeed call to Odysseus and his crew, but unlike so many before, they were unable to lure them to their deaths.
This is a story you've probably already heard, perhaps many times. What you may not know is that in the original story, Homer provided no visual descriptions of the sirens themselves. It wasn't until roughly 500 years later that Apollonius of Rhodes would describe these creatures as part woman and part bird, a description that would persist in Greek artwork for the next few centuries before the more familiar image of a part human, part fish being would overtake it.
The stories of sirens and mermaids echo through my own childhood memories, and I grew up fascinated by these creatures' otherworldly allure. And so, as a young man eager for adventure and at the risk of sounding pretentious, I set out on a quest of my own.
Thinking no investigation could begin without visiting the legend's alleged habitat, I landed in Italy, prepared to document the history of these creatures or perhaps even speak with an eyewitness. I never expected to see a specimen for myself, much less to have the opportunity to examine it in anatomical detail.
Once again, the tale of how this came to be is too lengthy for this brief presentation, but I suspect the time to unveil these mysteries is soon to come. And so, though historical accounts of the siren are inconsistent, to say the least, there exists a grain of truth in nearly every myth.
Indeed, there are several attributes described by numerous historians and writers that are, by my own observations, rooted in reality. These can be broken down as follows:
First, luring human prey through vocalization. As Pliny the Elder said, "They charm men by their song, and, having first lulled them to sleep, tear them to pieces."
Second, the apparent amalgamation of human and beast. As I will prove, this is arguably the most disturbing aspect of these creatures' physiology.
Third, a population in the Mediterranean Sea, or perhaps more specifically, the Tyrrhenian Sea. Both siren and mermaid sightings have been reported worldwide, but they appear to have originated in this part of the world.
Though I realize it sounds fantastic, I ask you to suspend your disbelief for our time together. The truth is that Sirenus horridus, as I have dubbed this disturbing creature, is almost nothing like what I had in mind before that fateful trip to the Mediterranean. And biologically speaking, it is one of the greatest examples of environmental adaptation to have ever existed.

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Throughout history, the siren entered humanity's awareness through extraordinarily narrow windows - glimpses of a tail beneath the water's surface, a haunting call in the distance, a human-like hand reaching up from the depths. And still, this species took up residence in humanity's subconscious, and its legend took on a life of its own, as evidenced by modern artwork, media, and countless stories. The image of the siren refuses to fade.
But now, my valued reader, I present to you the true image of this creature. Do not let its disturbing visage distract you. As I mentioned previously, Sirenus horridus is a wonder of nature and, as I will show, a distorted reflection of ourselves.
It is my belief that Sirenus horridus was once relatively common throughout the Mediterranean, its range stretching from the Alboran Sea to the Levantine and north to the Tyrrhenian and Aegean. Relatively isolated from the rest of the Atlantic by the Strait of Gibraltar, the deep waters of the Mediterranean Basin provided adequate resources for this species to thrive.
Specifically, ancient sightings of sirens placed them on the Sirenum Scopuli, a chain of three small, rocky islands. English essayist Joseph Addison described these islands as "about a stone's throw from the south side of the island of Capri," but others indicate that they were located in the Tyrrhenian Sea instead.
In any case, the ocean's depth, up to 17,280 feet in the Calypso Deep, allows the siren to escape human view when necessary, and individuals may go their entire life without being detected by a human - at least by ones that survived to tell the tale.
I hypothesize that this species spends most of its time within the mesopelagic zone, typically ascending the water column only to hunt. This not only allows the siren to remain undetected, but it also reduces competition from a similar, though completely unrelated creature: the Mermaid, which spends most of its time in the epipelagic zone. Note that the abyssal mermaid is found in a different part of the world, and this poses no competition to this species.
Additionally, the sea's high salinity and warm average temperatures facilitated the sirens' growth. Indeed, adults can reach lengths of up to seven feet and weigh upwards of 200 pounds. Though we will explore this biology further, in short, it is my recommendation that Sirenus horridus be classified in the clade Sarcopterygii, a taxon that includes lobe-finned fish such as coelacanths, lungfish, and under a strictly cladistic view, also includes tetrapods, including humans.

Origins

The reason for this classification is that sirens appear to have inherited a number of traits shared with other bony fishes. Their entire body is covered in scaloid scales composed of bone and cosmine and covered in keratin, though compared to their relatives, these scales are small and very thin, making them appear almost smooth, especially from a distance.
The posterior of their bodies terminates in a powerful diphycercal caudal fin, supported by a surprising amount of highly vascularized red muscle, making it capable of extraordinary bursts of speed, especially when hunting in the depths.
Of course, sirens are able to breathe underwater, utilizing gills located at the base of their necks and just anterior of the pectoral girdle. But they also possess rudimentary lungs, as seen in the order Dipnoi, a point to which we will return in due time.
Like their ancestors, sirens appear to be ectothermic, relying on their environment to maintain their body temperature. However, I have observed that the gill arches contain a dense network of blood vessels, likely capable of producing heat and allowing the siren to withstand a greater range of colder temperatures than their less derived relatives.
Even still, the lack of true endothermy has restricted their impressive speed to short bursts and has not bestowed the siren lineage with great intelligence. Indeed, this species appears to act on instinct and mimicry rather than true cunning or planning. Depending on your perspective, this is either a relief or even more terrifying.
My own observations were limited to a single female specimen, so I cannot say whether the species exhibits notable sexual dimorphism. But given the lack of obvious external primary or secondary sexual characteristics, I believe that genders will prove very similar in overall appearance.
But besides the anatomy of these creatures, perhaps the most unnerving aspect of their biology has to do with their diet. Though they are opportunistic omnivores, feeding on a mix of smaller fish, crustaceans, snails, and more, with sharp, backward-facing dentition, powerful jaw muscles, grasping limbs, and features specifically designed to lure hominids, in the modern era, Sirenus horridus' preferred prey items are humans.

In eons past, our sea-dwelling ancestors turned their collective gaze to the land. As evidenced by creatures like Tiktaalik, fin became limb, and primitive pectoral bones became the shoulder girdle.
Since that time, formerly land-based lineages have even returned to the water, such was the case for Ambulocetus, the semi-aquatic creature whose very name translates to "walking whale." Indeed, history is filled with examples of creatures of many different varieties moving from water to land and from land to water, usually due to specific environmental pressures.
It is my hypothesis that something - perhaps a lack of resources, a climate imbalance, or even competition from a similar creature in its niche - forced the ancestors of Sirenus horridus to venture out of the deep waters of the Mediterranean and into the shallows of the coastline.
It was here that this lineage found a new home. Resources were abundant, and over vast stretches of time, much like present-day mudskippers, numerous adaptations allowed them to prop themselves up, crawling over dry rocks and even onto the shore itself for short periods of time.
Long-standing scientific studies indicate that at some point in the distant past, a basal bony fish, perhaps a species similar to the Silurian era Guiyu oneiros, gave rise to ray-finned fishes, lobe-finned fishes, and eventually Tetrapoda, the ancestors of the siren, likely underwent a similar trajectory, venturing out of the sea and onto coastlines throughout the Mediterranean.

Anatomy and Physiology

Besides its head, a point to which we'll return shortly, what sets Sirenus horridus apart from other fish are its distinctly human-like forelimbs. And indeed, rather than lobed fins, these appendages are very similar to those belonging to land-dwelling tetrapods.
Sarcopterygians are the perfect lineage to produce such a surprising body plan, and for numerous reasons. Fossils from genera such as Panderichthys and Tiktaalik, both of which are descended from more basal lobe-finned fishes, exhibit well-developed limbs.
Specifically, in Panderichthys, we see limbs placed more forward and located at a right angle to the body, as opposed to being more oriented toward the posterior. Muscles adapted as well, allowing for a greater range of motion and eventually affecting further development of crucial bones within.
For example, the humerus of both Panderichthys and Tiktaalik are considered transitional because they are almost L-shaped, a feature which early tetrapods would refine further. They also exhibit a low latissimus dorsi process, a low entepicondyle, and an intermediate ectepicondylar canal.
In short, due to the orientation of the forefin toward the posterior region, the muscles were able to act at a right angle to the body, giving Panderichthys the ability to very effectively prop itself up. Similar adaptations have granted Sirenus horridus the ability to pull itself onto the shore, but this highly adaptable lineage has taken it multiple steps further.
First, there is the robust ribcage, a key trait of land-living creatures. This helps support the trunk and has allowed Sirenus to develop somewhat advanced lungs, but we will return to that point in a moment.
Second are the presence of greatly elongated fin rays, very similar to the digits of human hands. There are no opposable digits, however, and articulation capability is likely limited to swimming and sweeping, grabbing gestures, and of course, pulling its heavy posterior region across the rocky land.

The bones of the upper limbs could be compared to the ulnare and intermedium of true tetrapods, with a robust shoulder including expanded scapular and coracoid elements. The distal joints also appear to be highly mobile, able to flex, move, and likely fully support the weight of the upper body.
Third, and perhaps most notably, much like Tiktaalik, the ancestors of Sirenus horridus lost the bony plates in the gill area that would have restricted lateral head movement. As a result, modern sirens have a kind of neck separating the pectoral girdle from the skull and giving these creatures a mighty advantage when hunting on land.
Of course, as the sirens' ancestors moved into the shallow, intertidal zones, there came an increasing need for a more specialized respiratory system. The adaptations that would solve this problem also facilitated these creatures' most notorious trait: their song.

At some point in the early Devonian, a progenitor of the siren found itself stranded in a shallow, likely intertidal pool, with oxygenated water slowly depleting. Fortunately for this individual, it possessed a genetic mutation that had produced a hole in the gill membrane, which led into the swim bladder through the mouth.
The swim bladder itself was thin enough to allow oxygen to diffuse through it, and in effect, it acted as a primitive lung. Because of this mutation, this individual survived and eventually, through a series of other changes, and at the risk of sounding reductive, the siren was born.
This has happened in other areas of nature, and specifically for what I suspect to be a not too distantly related lineage. All extant lungfish also exhibit extraordinarily unique respiratory systems. Indeed, not only do they possess lungs derived from specialized subdivided gas bladders, but some also retain the gills that allow them to breathe in water.
The same is true of Sirenus. Eventually, in order to prevent drowning upon returning to the water, a valve appeared in the throat which guarded the entrance to that pulmonary outgrowth. This valve would eventually become the larynx, a structure that essentially sits within the windpipe, closing it off when necessary.
In many animals, these flaps of flesh can vibrate when air is passed through them, creating sound. Of course, in many animals, these are also called vocal cords. But first-hand observations via dissection indicate that sirens possess a startlingly advanced vocal apparatus and can produce vocalizations beyond those of which even humans are capable.

In fact, the entire apparatus, which I hesitate to call a larynx at all, extends distally to the base of the trachea, at the point where it forks into the two pulmonary branches. Here, the structure appears strikingly similar to the membrana tympaniformis and pessulus of the avian syrinx.
Though the specimen I observed in detail was expired, it seems likely that as the lungs contract, unique throat muscles modulate the sound shape by changing the tension of the membranes and the bronchial openings in a manner bizarrely similar to birds.
In short, this advanced vocal anatomy allows the siren to produce a multitude of sounds. In fact, the lower part of this voice structure's position between the two pulmonary branches may allow it to produce two sounds at once.
Not only could this ability account for the siren's legendary song, but it may also explain the ancient association of the siren with the body of a bird. In any case, certain sustained vocalizations could undoubtedly be alluring and, biologically speaking, that is precisely the point.
I present to you now, for the first time, a fragment of Sirenus horridus' terrible vocalizations, personally recorded one dark night as I rode a small boat seaward from the coast of Italy. Be warned, however; though this sound serves a purpose, it is deeply unnerving.

This, dear reader, is a form of mimicry designed to elicit an empathetic response in humans. Had I not known what was truly producing the sound, even I may have been taken in by the entirely irrational assumption that a child was stranded on a spit of land somewhere in the endless ocean.
Indeed, Sirenus horridus is a master of mimicry. Throughout history, there is little doubt that it would mimic the sound of a call for help or perhaps even a chorus picked up from passing sailors. Intrigued by the sound, sailors would turn from their course, close enough to land to allow the sirens to hunt and drag their victims onto the shoreline for further consumption.
But a vocalization alone would likely not be enough to fool every sailor, especially when they drew close enough to see the creature for themselves. However, as previously mentioned, these creatures are masters of mimicry in more ways than one.
When the ancestors of Sirenus horridus made the transition from the deeper sea to the shallows, they not only set the stage for their descendants to enter an elaborate mythos, but at the shoreline, they encountered another creature.
Just as they were carving out a niche in the intertidal zone, the sirens' progenitors began to face competition from both the sea and the land. And once again, they were forced to adapt.
Allow me, if you will, a slight digression. You see, as fellow scientist and marine biologist Alister Hardy posited more than a decade ago, it seems very possible that certain "ape stock," as he puts it, were forced out of the trees, perhaps due to competition, and took to life in and near shallow coastal waters.
While this notion is not without controversy, certain aspects of Hardy's observations are worth considering. And indeed, the human body does exhibit several features that strongly suggest adaptations to a semi-aquatic lifestyle.
Once again, an in-depth discussion of this so-called "aquatic ape hypothesis" is beyond the scope of this presentation. In summary, however, our lack of body hair, similar to whales or hippopotamuses, our layer of subcutaneous fat, the location of our trachea, and even bipedalism itself could be direct evidence of a water-dwelling lineage of apes.
I hypothesize that a group of these shore-dwelling apes intersected with the lineage of Sirenus at some point in the distant past. And in competing with each other for these resources, the lineage that would become sirens developed two forms of mimicry nearly in tandem.
The already-discussed vocalizations allowed them to lure these apes into the water where their newly elongated limbs could pull them beneath the waves. Then, ever so slowly, the head and face of the siren lineage began to change.
Random dermal markings that could have been mistaken for eyes or perhaps a nose, or both, increased certain individuals' likelihood of attracting their simian prey. Eventually, these markings became consistent across generations, forming an entirely false face designed to lull their victims into a false sense of security.
The front of the skull flattened, the orbital sockets migrated closer to the top of the skull, and the mouth fully concealed the siren's full set of vicious teeth. Even the dorsal fin extended anteriorly, appearing to have split along the median plane and now hangs from the supraoccipital crest at the rear of the skull, eerily reminiscent of human hair.

Now, at a distance or in the hazy oceanic fog, modern sirens, having pulled themselves to a rocky outcropping or perhaps peering upward from beneath the water's surface, are easily mistaken for human. Add to this their unique arrangement of dorsal fins and elongated grasping forelimbs, and it is little wonder why so many have fallen victim to their deadly allure.
In fact, it is my hypothesis that the culmination of these adaptations are a stunning example of what is known as aggressive mimicry, a phenomenon easily observable in the bioluminescent lure of the anglerfish or in the arachnogenous Myrmarachne.
The latter is especially notable, as its elongated cephalothorax and relatively long calyces project forward to very closely resemble the ants they hunt. They have even been observed to wave their front legs in a manner that simulates antennae. Needless to say, many ants are immediately fooled by these ant-mimicking spiders, a mistake that often costs them their lives.

But while similar traits do have precedent in nature, Sirenus horridus is arguably the most impressive example known and likely the first to persist with its aggressive mimicry despite currently occupying an entirely different environment than the prey it evolved to imitate.
Over the millennia, the extraordinarily adaptable siren lineage has been forced to adapt even further. A combination of factors has led to what I suspect is a gradual decline in population, and its once readily available prey has moved beyond the siren's reach.
Sirens are still out there. If you travel to the region where Odysseus once sailed, you too may spot the silhouette of a beautiful woman calling out from a distant island. As you draw near, you may realize that what you thought to be a human is but a mere reflection frozen on the face of deep time.
If that happens to you, my valued reader, it may already be too late.

Watch the video here:

Scientific Name

Sirenus horridus

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You may notice that the artwork in this article is different than that in the YouTube video. That's because I wanted to slightly redesign the creature for two reasons. First, I didn't think the quality of the original artwork was quite up to my standards. Second, and more importantly, I believe that this design borrowed too heavily from other sources.
Still, for Patrons of 'Sack of Potatoes' and higher, the original artwork will display below: