Banuptet

First contact between extraterrestrial life and man-made probes will not always go as hoped, as the Banuptet has demonstrated. Shortly after the Soviet Mars 3 lander descended in 1971 onto Terra Sirenum, its two primitive rovers encountered this duiker-sized critter, the first alien humanity made indirect contact with, as it was apparently grazing on the tundraic vegetation. After cautiously circling the probes, the specimen finally approached them and… attempted to chew on the rovers before losing interest and then defecated in front of the lander. Our guys at NASA at the time allegedly had a hearty laugh upon reading the Russian data.

Despite making such a bad first impression, the Banuptet is nonetheless a fascinating animal. It is an onychognath that spends most of its life nomadically. When it is winter in the south it spends most of the time around the equator and desert oases. Once the spring thaw arrives, it wanders south onto the blooming tundras to feed on the newly growing flora. To efficiently graze in bulk, the Banuptet has evolved a broad rake-like beak to raze off any loose vegetation.

As an endothermic animal, the Banuptet is covered in a unique form of insulation, which could be called “frilled scales”. Likely evolving from lizardine overlapping scales, these have developed frilled, filamentous brims, allowing them to function much more like feathers. Interestingly, the Banuptet cannot be called a true homeotherm, as its body-temperature can vary considerably throughout the year. In active phases of migration or the mating season, its physiology becomes warm-blooded in a mammalian sense, but during the winter-droughts its metabolism slows down and it becomes an ectotherm in order to conserve energy and brumate.  

Banuptets mate towards the end of southern summer. Impregnation between the hermaphrodites is determined by dominance displays using their dewlaps, which can be inflated with blood to turn red. After mating, the “mothers” carry out their young alone while wandering through the tundras and steppes. They give birth to live young, usually two or three at a time. The calves enter life fully developed and able to walk and run. As a consequence, parental care is rudimentary at best; the calves follow their parent for better protection, but the parent itself seems ambivalent as to their existence. As in ruminants on Earth, the young also follow the parent to feed on their droppings, a revolting but vital practice, as otherwise they would not develop the required gut flora to digest the tough plant life on Mars. Most calves do not survive their first autumn migration. 

Fig. 2: The Banuptet's size in comparison with the first man on Mars, Michael Collins.

The Banuptet is part of the wider cuneocephalian clade Deltadactylia, whose most conspicuous trait is that their limb count has been reduced to three: Two hindlegs and at the front a single so-called “great appendage” with four digits, which in some members serves as a third leg, in others as an arm. This is an extreme derivation from the ancestral condition, as even in basal cuneocephalians, the number of limbs was six. How this change happened is a complete mystery. All that is evident is that at some point in their evolution, the deltadactyls must have lost one limb segment, while having fused together the limbs of another. As embryological data is still lacking, we do not even know which of the ancestral segments were lost and fused; the great appendage could have evolved from either the frontmost or middle limb pair. In fact, the missing limbs have not even left behind vestigial bones and the breathing holes associated with them are also completely gone. This strongly implies that the limbs were not gradually reduced over time (like, say, the hindlimbs of whales) but, more drastically, that the arezoan equivalent of Hox-genes responsible for the development of a whole segment of the body has been deleted or suppressed.

Not helping with this is that the known fossil record of Mars is almost completely silent on the matter as well. Large, ungainly hexapods from both cuneocephalian and archaeocephalian stock, often grouped together into the polyphyletic group “Tagmasauria”, were once the dominant land animals during the Late Thermozoic Era (Sivgin 2345). Towards the middle of that era’s Cydonian period, the first deltadactylians suddenly appear with no known transitional forms. We have yet to find a cuneocephalian, both living and fossil, with an intermediate amount of limbs of just four or five. This strongly implies that this adaptation must have been so successful even in its incipient stages that selective forces acted fast enough towards its perfection that there was little time left for mosaic forms to leave a mark on the fossil record. A similar phenomenon is observed in the evolution of pterosaurs and bats on Earth, whose transitional forms are also unknown. But this opens up more questions than answers, for, unlike powered flight, there is no obvious advantage for tripedalism. As a general rule, the more legs an animal has, the faster it can run, so this would not have given deltadactylians an edge in the fight for survival against their earlier cousins. Their form of tripedalism, with only one front leg, is also extremely awkward and almost forces most of the lineage further down the line towards bipedalism. It also largely prevents the evolution of a sprawling gait, restricting them to an energetically consuming rectigrade posture. A betting man would not have put his money on this group surviving in the long run, but yet deltadactylians would go on to largely replace the “tagmasaurs” in the Late Cydonian period and the Hylozoic Era (though the rise of megafaunal periostracans may have been the bigger culprit there).

One attempt at an explanation has been that the great appendage evolved to cope with the lack of digits that onychognaths seem to struggle with (Budiman 2311). The whole phylum has ancestrally only had two fingers per hand and genetic quirks seem to prevent them from evolving more. The fusion of two limbs allowed the deltadactylians to have a hand with four digits, with which they could grasp objects. This explanation is not appealing for many reasons, however, as evolution does not work in such a goal-oriented way. The gaining of a grasping hand certainly was a neat byproduct of the fusion, but could not have been its initial cause.

At least when it comes to the loss of a limb pair, a more sensible suggestion has been put forward, which is that it has been lost due to being too energy-consuming. The extinction of large hexapods on Mars may not have been due to outcompetition by deltadactylians but rather because such large, multi-limbed bodies became increasingly harder to maintain with the changing of the atmosphere and the loss of much vegetation. The deltadactylian body plan definitely seems more efficient in that regard (even though a whole lung-segment has been lost) and is more than suited to outrun antitrematan predators, who have never been able to evolve more than three limbs. On that note, it is interesting that tripedalism never evolved on Earth but did at least three or four times independently on Mars. Possibly, the low gravity has an unforeseen effect on animal locomotion that makes this limb count more viable than we earthlings would expect.

References:

• Budiman, Daniel: Nothrotherium arabianum and the evolution of the deltadactylian (Cuneocephali, Onychognatha) hand, in: Current Astrobiology, 113, 2311, p. 45 – 67.
• Sivgin, T.K.: Life on a Dead Planet. The first 3 billion years of Evolution on Mars, Zürich 2345.