Ammit

The underground of Mars, sheltering its inhabitants from the harmful radiation and aridity on the surface, has become a refuge to many organisms. Some of which have no counterpart on the surface anymore, being relics of ages long past.

Ammit (Duatsuchus caecus) is one such relic, perhaps one of the oldest “living fossils” known from the planet. A relatively large carnivore at about one and a half metres long, it is assumed to be the last known member of a clade called Cancrisuchia, colloquially referred to as “crocstaceans”, archaic onychognaths that used their specialized raptorial arms for feeding. Some have compared them to Earth’s eurypterid “sea scorpions” in ecology and functional morphology.

In the fossil record, Cancrisuchia appears an unimaginably long time ago, in the Thermozoic Era, in the Argyrian, when Mars was still a semi-tropical ocean world and plant life was first starting to colonize the few strips of dry land. Cancrisuchians were among the earliest onychognaths to become amphibious, though unlike their later relatives, they mostly stayed at the boundary between water and land. Generally, they are thought to have been exclusively aquatic ambush predators, much as crocodylians and temnospondyl amphibians on Earth, and, once established in that role, dominated that niche for many millions of years. The key to their success lied, of course, in their raptorial arms. All archaeognaths lack teeth, their chelicere-like mouthparts functioning more like double-beaks. This limits their adaptability to carnivorous niches, especially compared to the toothed periostracans, which were at the same time taking over many marine niches. Cancrisuchians solved this problem by turning their first limb pair into another set of jaws, deriving from their shark-like scales projections which can for all intents and purposes be called teeth. Functionally these impressive “hands” can be settled somewhere between the claws of a lobster and the jaws of a crocodile, making for very effective weapons in grabbing and holding prey, possibly even further processing the food through careful manipulation by both hands.

Still, success does not last forever. The first major radiation of the Cancrisuchia, the Magnastracia, which included such impressive forms as the 7 metres long Deinoastacus, went extinct already in the Early Isidian, following climate changes. Their smaller cousins, the Microchelia, followed in their steps and over the course of the Thermozoic re-evolved comparably large sizes again. But these vanished too, at the end of the Cydonian, together with the large, reptilian thagmasaurs and various other lifeforms, in a massive extinction event whose cause(s) still remain mysterious. In the following Hylozoic, the role of aquatic ambush predator on Mars was largely filled by the so-called mangalasaurs, derived cuneocephalians unrelated to the cancrisuchians.

With that, it was long thought that Cancrisuchia is completely extinct. But the discovery of the ammit (made quite dramatically after it attacked a speleodrone) has seriously called that into question. While it is technically possible that it represents merely a case of convergent evolution from some unrelated lineage of archaeognath, the anatomical similarities between it and the fossils is too startling to accept that easily. If accepted as a genuine late-surviving microchelian cancrisuchian, on the other hand, it would open up the problem of there being a ghost lineage of these organisms that skipped the fossil record for two entire eras. Like in that old children’s story, it would be like finding a trilobite in your backyard today out of the blue.

One possible clue towards unravelling this conundrum is the fact that the ammit has (so far) only been found in flooded cave systems formed by the ancient lava tubes beneath Elysium Mons. If current palaeogeographical hypotheses are correct, then Elysium formed a slowly growing island continent throughout the Late Thermozoic and into the Hylozoic. We know for a fact (as far as facts go in astropalaeontology) that Elysium formed a refuge for other onychognath taxa during this time, such as the deltadactylians, which otherwise went extinct on the main southern continent. It could very well be then that some cancrisuchians could have survived on the former island as well. And perhaps these survivors adapted very early on to underground habitats, leaving little opportunity for them to fossilize.

Very little is known about the ammit in life, due to the inaccessibility of its habitat. Anatomically, its biggest difference compared to ancient cancrisuchians is the complete lack of eyes, attesting to a very long time adapting to the underground. Completely blind, its main sense organs are the long and specialized nasal and aural antennae. Like its ancestors, it probably is still an ambush predator, lying in wait beneath the surface of underground grottoes and lakes and waiting for prey, such as netchu, hekubus or medjed, to walk or swim by and be grasped by the raptorial hands. Any other behavioural or biological traits, including reproduction and activity, remain unknown.

Despite its fearsome appearance, due to a lack of resources underground, it must be leading an extremely slow, energy-efficient life, probably not moving for days, weeks or even months at a time and can probably go for years between feedings. A dim existence, living in darkness and a watery nothingness, unimaginable to the human mind. Though at the same time there must be some comfort, being all safe and cozy down there, unaware of the world slowly dying outside its shelter. Some may sympathize.

Does it even know that the oceans are gone?