Niolamia

Credit: Armin Reindl on the Wikimedia Commons.

*Niolamia* is an extinct genus of meiolaniid turtle that lived in Argentina during the Middle Eocene.

## History

Arthur Smith Woodward (1898) received a photo of a tail ring from collector Santiago Roth of a meiolaniid. Early in the next year, Woodward writes that he was able to directly examine the specimen after being sent from Argentina to London. He compared them with *Meiolania*, with Woodward recalling that Roth was tasked by Francisco Pascasio Moreno, the man he worked under, to conduct a follow-up, which in time would recover a carapace with cranium and mandible that were associated. In the same year, Florentino Ameghino coined the genus name from a skull that his brother Carlos supposedly found in the Guaranitic Formation. Ameghino failed to provide a holotype, coin a species or figure the material due to a long-standing rivalry with Moreno, similar to the Bone Wars. Near this time, Moreno wrote a short communication describing what Roth found during the second expedition, leaving MLP 26–40 (the cranium) as the only unfigured element. Woodward authored a more detailed description with extensive illustrations two years later, using the name *Miolania* (a misspelling) in an attempt to sink the genus name Ameghino coined into *Meiolania*. Ameghino himself later, seemingly, agreed through his use of the new combination. Sterli hypothesizes that Ameghino intended to assign his material to *Meiolania*. and that *Niolamia* may have been a misspelling. This had been somewhat resolved by the time Simpson and Williams (1938) concluded that Roth's material should be a neotype. They suggested that Ameghino's material was not adequately described to claim holotypic status. The same publication also named *Crossochelys*, a junior synonym. *Niolamia* remain in storage for much time and publications on the genus relied on Woodward's writings rather than new examination. A full redescription of the neotype was published by Sterli and de la Fuente (2011) due to such poor data and convoluted history. Sterli would comment later that the history of these taxa reflects the rivalry between Ameghino and Moreno, as well as why Ameghino's fossil had seemingly disappeared following description. As well, no later figures, descriptions or comparisons were made of this skull. Sterli suggests that it was either lost before any comparisons could be made or that it was the same fossil as the Roth skull and misattributed to his brother's finding. This would explain why two well-preserved crania were found in quick succession by two teams and why it was never figured, described or compared. Sterli, in the same publication, refers to the neotype as the holotype.

## Description

The most diagnostic element in turtles is the head, complimenting what is known of this genus. Like other meiolaniids, the skull is very ankylosed. Only select sutures can be viewed on the cranial surface, most on the midline. The ventral view sports a denser concentration of sutures. A single narial opening is seen lacking any internal sutures, This is unlike *Ninjemys* and *Meiolania*, where there are many interior separations. The nasal is a small projection that reaches over the termination of the premaxillae, but is not as developed as *Ninjemys*. The endocranium consists mostly, ~60%, of the nasal cavity. An elongate vestibulum nasi is only seen in turtles possessing snorkel-like noses and present in *Niolamia*. As common for the group, many horns and boss-like scales are found, but are given different nomenclature by different authors. Woodward calls them numerlas I-VII and Simpson identifies them through lettering. Gaffney later took Simpson's scheme and adapted it to be the basis for all meiolaniids. Most are identified in pairs, except for A. X. Y and Z. A is a series for the horns and bosses along the rear (called the occipital crest). This is a large upwards frill with a defined notch at the middle. B covers the horn cores by the squamosals, being large and triangular. In *Niolamia*, they are like *Ninjemys* but larger. C is before B and consists of the smallest, reaching out and down to cover part of the roof and the side of the cranium while simultaneously overhanging the tympanic cavity. The X scale (which in this genus is, abnormally, a large concave rectangular scale that separates the D and G scales through its massive size and occupation of the entire roof) is typically a single bulging scale atop the cranial roof that is typically smaller than D and G. It is not sure if X appeared as this in life or is taphonomic distortion. E are small and convex backwards-reaching bosses that sit on the side just before the tympanic cavity. H are only found in derived forms and is not seen in this one. F are over the orbits, and K and J reach from the back to the beak, which itself is covered by I (deriving into the I1 and I2 types in this genus). The beak was probably covered by an extended beak that covered the "dental" (cutting surface in turtles) region. The lower snout tip is covered by I, and the upper by Y and Z that reach from the orbital tops to the nasals.

Material from both shoulder girdles are known, preserving the elongate dorsal scapular process and connecting to the acromion to form an obtuse angle. This is similar to *Meiolania platyceps* and Testudinidae and suggests terrestrial behaviour. No complete carapace is known, but it may be determined to have been domed like tortoises (obscured by taphonomic crushing). It is thickest to the borders (maximum 1.5 centimeters (0.59 inches)) and thinnest at the midline. Ten shells of this taxon are known and only four have their position known" the largest fragment was probably situated to the rear and correlating with the 8th costal plate and the 10th-11th peripheral plates (occupying the back edge and rim of the shell). This area may have had backward-reaching spikes. A depression forms at the most rear point of the shell, forming a recess that borders the last supracaudal scale. The suture patterning and sulci placement are like tortoises and were not comparable to *Meiolania* because this region was not available in fossils. Comparison of fragments with related taxa (*Meiolania*, *Proganochelys*) suggested that the shell may have been around 1.2 meters (3 feet 11 inches) long, though this estimate is not certain. The tail, like other meiolaniids, had many overlapping hexagonal bony rings bearing paired spike-like knobs. The uppermost pair, more robust and upward-reaching, and lowermost, the smallest and reaching up and to the side, were fully formed and the open underside (an apomorphic character) is not present, unlike *Meiolania* and *Ninjemys*.

## Classification

When included in phylogenies, it is consistently considered one of the basalmost memebers and sister to the Australasian branch. This is confirmed by anatomical details and place of origin, as it is older than all named taxa from Australia and the western pacific islands. *Ninjemys* somewhat bridges this taxon and *Meiolania*, the last two being very very far apart, morphologically speaking. The foremost is the youngest known of the Australasians, sharing laterally-reaching horns and a large A scale area. Description of *Gaffneylania* did not much change its position, probably because this new taxon was fragmentary and forms a basal polytomy with *Niolamia*. Gaffney, Archer and White recover:

Sterli, de la Fuenta and Krause after describing new taxa:

## Paleobiology

A 2017 study of meiolaniid neuroanatomy describes this taxon and others, finding an elongate vestibulum nasi as common to the group. This is commonly seen in aquatic turtles with snorkel noses, or in lizards with desert adaptations that stop sand from entering the nose, especially during digging. The authors do not select a hypothesis and offer a variety of ideas, such as enhanced smell, thermoregulation or sound production. The nasal cavity supports the sense of smell hypothesis, but the ability to create sound or regulate temperature in the dorsal region of the cavity is not entirely disproved through comparison with ornithischian dinosaurs (though it is considered unlikely due to the simplified structure of meiolaniids). Enhanced smell, if true, may have aided in foraging and/or communication. The latter is emphasized, and modern turtles have many chemical-secreting glands (musk, cloacal, mental) that, while unable to confirm from bones alone, may be tied to scent. Chemicals may correlate with combat and aggression, mostly during courtship. Their displays include many shell-based motions, which is consistent with the horns, osteoderms and tail armour which have previously been tied to combat by authors. The inner ear is like that of terrestrial turtles (having a wide angle of the anterior and posterior semicircular canals). Modern tortoises have ~100°, aquatic-leaning geoemydids/plesiochelydids with 80-95° and meiolanids reaching 115°, A wide-angle aids in stability of the head during movement. Similarities with modern turtles suggest, however, that meiolaniids were sensitive to low-frequency sounds and were not very vocal, instead preferring smell. To judge this in meiolaniids, a smaller sample would be required because large changes in anatomy may be hard to identify. It was likely terrestrial like a tortoise due to enhanced smell and inner ear morphology. This is most often accepted over the aquatic model, as sometimes offered but not always taken.

## Paleoecology

Assuming the two known skulls are the same specimen, locality data is confused by the fact that Ameghino mentioned the Guaranitic Formation (near the Rio Sehuen and Rio Chubut) and Roth mentioned Cretaceous-aged red sandstone (the La Plata Museum lists Cañadón Blanco). However, this locality has a mammal fauna more like the Eocene-Oligocene, backing Ameghino. White tuff was found in the nasal cavity of the neotype, much unlike what Woodward claimed and similar to the Eocene-Miocene Sarmiento Formation. "*Crossochelys*" from this formation support this assessment. Other research favours the conclusion that it is of Eocene age. Additionally, over 100 years since discovery saw *Niolamia* as the only meiolaniid in the region until the naming of *Gaffneylania*. These two taxa are part of the Austral biogeographical kingdom (southernmost South America, Antarctica, southern Africa and Australia/New Zealand/New Guinea. This group is thought to have been very affected by the separation of Gondwana, distributing them variously. Meiolaniids were once part of a Gondwanan Meiolaniformes that broke into distinct lineages before the South Tasmanian Sea had formed between the Cretaceous and late Eocene, suggesting arrival in Australia before this event. They would have moved into Patagonia and gone extinct before the Drake Passage formed and severed the connection between Antarctica and South America. *Niolamia* and related forms probably went extinct through gradual cooling/drying in Patagonia during the middle Eocene.

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 https://en.wikipedia.org/wiki/Niolamia
2. ↑ https://bioone.org/journals/bulletin-of-the-peabody-museum-of-natural-history/volume-56/issue-1/014.056.0102/A-Review-of-the-Fossil-Record-of-Gondwanan-Turtles-of/10.3374/014.056.0102.short?tab=ArticleLink