Hrypidex Rannu

Nothornitha are a clade of the Periostraca, characterised by using their limbs to bipedally walk upright with a gait comparable to that of birds (hence the name). Modern nothornithes are traditionally differentiated into two separate groups: the bennus and the rannus. Whereas the bennus have fur covering their bodies and often a reduced tunicine tail, rannus represent the likely more ancestral condition of having a naked periostracum and a more elongated tail used for counterbalance. This goes hand-in-hand with metabolic differences as well, with bennus being endothermic, while the body-temperatures of rannus are more often influenced by the surrounding environment. Various skeletal details have also been identified in the skull, foot and carapace that supposedly set the two apart (more on that later).

The hrypidex is one of many different rannu species, though it is among the better-known ones. It is commonly found around the desert edges and oases of the great northern dustbowl desert. Its curved foot-claws, raised orbital bulge and secodont scolecodonts easily mark it as a scavenging and predatory animal, mostly feeding on smaller creatures such as archaeocephalians or dust slugs. It also frequently enters into squaffles with thecocerates such as the cecrops, though this has been characterized as less of a predatory behaviour and more of a rivalry between two predators competing for the same resources. Rannus usually come out on top during such conflicts, as their tooth-derived beaks are not only more formidable weapons than the keratinous beaks of the thecocerates, but they are on average also just much heavier than the lightly built onychognaths (the internal skeleton of periostracans essentially being a tortoise on two legs, only able to walk thanks to Mars' lower gravity). Cecrops can usually only retaliate by raiding the nests of rannus, but that is itself quite risky. Although not as sharp or active as their more derived bennu-cousins, rannus can make for excellent parents, closely guarding their nests until the young are old enough to feed themselves. Many rannus raise their young in pairs, but the hrypidex usually nests alone. The parent is usually determined through a mating ritual, where the distinctive crest of the pseudoskull is shown off in a nodding motion.

Returning to rannus in general, it is probably wrong to separate the Nothornitha simply into rannus and bennus. Most likely, rannus are a paraphyletic grade out of which monophyletic bennus (whose clade would be called either Eunothornitha or Avidonta in this model) arose (Sivgin 2345). Archaic rannu-like creatures, referred to as “Barocrania”, were the dominant animal group on land during the Hylozoic Era, their fossil members usually being split into the clades Carnornitha, Segnornitha and Rhynchornitha, whose members could sometimes reach sizes that exceeded those of Earth’s dinosaurs. Avidonts (or at least organisms appearing to be avidonts) do not appear in the fossil record until the Early Kaseiic, the last period of that era, descending either from small carnornithes (Hermann 2201) or the segnornithes (Krätschmer 2213), depending on what researcher is asked. Extant rannus are largely seen as still-living archaic carnornithes, though some researchers assert that a few could also be surviving segnornithes (the placodont, shield-skulled rhynchornithes seem to have gone extinct with no descendants).

This classic paraphyletic model has also been called into question, however, as we largely lack genetic data to potentially affirm or falsify it. Trace fossils and controversial body-imprints of Kaseiic barocranians possibly show that these had already developed a fuzzy periostracum long before the appearance of Avidonta, meaning that the insulating fur of bennus is not a derived but an ancient trait. Many extant forms also freely mix rannu- and bennu-like traits, such as combining a long tail with fur or the other way around, while also showing a mosaic of cranial and pedal characteristics from both groups. Samuel Leidy has thus recently proposed the quite radical hypothesis that classic “barocranians” have gone completely extinct at the end of the Hylozoic and that the bennu-type avidonts are the only surviving nothornithe lineage. In this model, the rannu-type animals we see today are actually derived bennus that secondarily (and perhaps even independently of each other) lost many traits associated with endothermy, possibly as an adaptation to the worsening habitability of Mars. Leidy’s modest proposal has been met with criticism by fellow astropaleontologists, though the results from recent molecular studies have been interpreted by some as potentially supporting this model. Only further research may clarify how these organisms are linked to their past.

References

• Hermann, David: Dental and pedal anatomy of Syntarsornis kasaiensis (Ceratornitha, Carnornitha) and the origin of bennus, in: Journal of Astropaleontology, 112, 2201, p. 34 – 67.
• Krätschmer, Daniel: Avidontomorph cranial anatomy in Micrornis gracilis, in: Journal of Astropaleontology, 123, 2213, p. 61 – 66.
• Sivgin, T.K.: Life on a Dead Planet. The first 3 billion years of Evolution on Mars, Zürich 2345.