Niolamia
Niolamia is an extinct genus of South American meiolaniid turtle with a long and complex history. Like its relatives, Niolamia was a robust and heavily armored terrestrial turtle with large, horn like scales covering its head and a tail encased by rings of bone. This heavily armored build may have served the animal during intraspecific combat during courtship, though such encounters likely did not involve the horns and frill, which are thought to serve more of a display function. Scans of the skull reveal that Niolamia likely had a great sense of smell but only low frequency hearing, indicating that these animals communicated more through chemical signals and smells than through sound.
Niolamia is one of only two named meiolaniid turtles from South America, the other being Gaffneylania. Given that this family is primarily distributed throughout the Neogene and Quaternary of Australasia, this makes Niolamia an important piece in the evolutionary history and origin of this turtle family.
Remains attributed to Niolamia were seemingly first uncovered by Santiago Roth in 1889, with a well preserved skull found only shortly afterwards. The name Niolamia was however not coined by Roth or any of his contacts, but by Florentino Ameghino who briefly wrote about what was said to be another skull discovered by his brother. While Ameghino's name was retained for the animal, later publications were entirely based on Roth's material, as Ameghino neither diagnosed nor figured his fossil. The fact that Ameghino's material was never recovered after his initial communication has led some researchers to believe that the two specimens are one and the same.
History and naming
In 1898, British paleontologist Arthur Smith Woodward was sent a photograph of a meiolaniid tail ring by fossil collector Santiago Roth, who worked under Francisco Pascasio Moreno. Woodward writes that he was able to study the fossil itself in early 1899 after the material was sent from Argentina to London, allowing him to compare it to the remains of Meiolania platyceps, a turtle named by Richard Owen from Australia. According to Woodward, Moreno tasked Roth with a follow-up expedition, which recovered additional remains in the form of a carapace, skull and associated mandible.That same year Argentinian paleontologist Florentino Ameghino coined the name Niolamia argentina for a skull he claimed his brother Carlos discovered in the Guaranitic Formation. However, little information was given by Ameghino at the time, as the researcher didn't established a holotype, didn't diagnose the species or even figured the fossil material. The imprecise information was not an accident, but the result of the rivalry between Ameghino and Moreno. Their rivalry, similar to the Bone Wars between Edward Drinker Cope and Othniel Charles Marsh in America, saw the two intentionally hide records from one another, eventually leading to the complete loss of some information.
Around the same time Moreno authored a short communication describing the material Roth reportedly uncovered on his second expedition. Although various postcranial remains were also described, the skull was the only element that was figured. Two years later Arthur Smith Woodward published a more detailed paper, in which he illustrated the material more extensively and assigned it to the same species mentioned previously by Ameghino. However, rather than using the name Niolamia, Woodward created the combination Miolania argentina based on an accidental misspelling of Meiolania. Despite declaring Niolamia a junior synonym, Ameghino seemingly concurred with Woodward, using the combination himself in later publications. However, Sterli raises the possibility that rather than accepting synonymity, Ameghino never meant to call his material Niolamia in the first place and also misspelled Meiolania in his prior work.
The naming issue was somewhat resolved when George Gaylord Simpson and Coleman S. Williams established Roth's material as the neotype of Niolamia in 1938, reasoning that Ameghino's material was not described thoroughly enough to serve as the holotype. In the same paper the researchers also officially described additional meiolaniid remains from the Eocene parts of the Sarmiento Formation, which they named Crossochelys corniger. Although Simpson argued that the material of Crossochelys was not that of a juvenile, Eugene S. Gaffney reasoned for the contrary in his 1996 review of meiolaniids, declaring Crossochelys a junior synonym of Niolamia.
While meiolaniid research received a considerable boost under Gaffney, the fossils of Niolamia remained in storage and publications released during this time were primarily based on the work of Woodward, rather than first hand observation of the skull. The convoluted history and poor description of the early meiolaniid discoveries of South America eventually led to a full redescription of the neotype in 2011, authored by Juliana Sterli and Marcelo de la Fuente. Like Gaffney, they too argue that Crossochelys is simply a younger Niolamia individual, with the distinguishing features simply representing individual variation or traits that would change with age.
In a later publication, Sterli would further comment on the complex history of this taxon and the impact of the intense rivalry between Ameghino and Moreno on the history of Niolamia. According to Sterli, this competition may explain the whereabouts or rather the absence of Ameghino's fossil, which had seemingly disappeared from research history following the initial short description. No subsequent authors figured, described or even compared the Ameghino skull to the Roth skull. Juliana Sterli offers two possible explanations for this. It is possible that Ameghino's skull was simply lost, however it is likewise a possibility that the Ameghino and Roth skulls are the same specimen and that Ameghino misattributed the discovery to his brother. This would explain the improbability of two well preserved skulls being discovered in such quick succession by different teams and also explain why no researcher ever figured the Ameghino skull or compared it to the Roth material. Subsequently, Sterli refers to the neotype as the holotype in this publication.
Age and locality
The purposeful lack of information on the locality that the first Niolamia remains were found at and the general ambiguity around whether or not Ameghino's and Roth's skulls are distinct has led to a lot of confusion in subsequent years. Ameghino named the Guaranitic Formation in the Chubut Province as the place of origin of his fossils, claiming the material was collected near the Rio Sehuen and Rio Chubut. Woodward wrote that Roth's specimen meanwhile came from Cretaceous aged red sandstone, with the La Plata Museum specifying the Cañadón Blanco locality. However the mammal fauna of said locality is more in line with an Eocene to Oligocene age, which matches Ameghino's claim that Roth's material stems from Middle Eocene strata near Lake Musters and Lake Colhué Huapí. Analysis of the sediments present in the neotype's nasal cavity revealed it to be white tuff, very much unlike the sediments described by Woodward and similar to what is found in the Eocene to Miocene Sarmiento Formation. This is supported by the discovery of additional Niolamia fossils from the Sarmiento Formation. Subsequently, later research favors the hypothesis that these turtles lived during the Eocene.Description
Skull and horns
The best preserved fossil of Niolamia is a nearly completely preserved skull, which is the most diagnostic element in meiolaniid turtles. Like in its relatives, the skull is highly ankylosed, meaning the majority of sutures between the individual skull bones are fused and thus largely obscured. Only a few sutures are visible on the surface of the skull, primarily along the midline, however in ventral view the connections between the bones are more clearly visible. Niolamia possesses a single opening for the nares, lacking any divisions in its internal structure. This sets the genus apart from later taxa like Ninjemys and Meiolania, in which the internal nares are partially or fully divided by a bony septum. Above the nares, the nasal bone forms a small projection that extends beyond the end of the premaxillae, however this is nowhere near as well developed as in Ninjemys. The endocranium of Niolamia is dominated by the nasal cavity, which makes up approximately 60% of its volume. The vestibulum nasi is elongated, which today is only seen in turtles with snorkel like noses such as the mata mata, pig-nosed turtle and softshell turtles.Like other meiolaniids, the skull of Niolamia was covered in a multitude of horn or boss-like scales readily identifiable in the fossil material. These scales were described with varying nomenclature by different authors, with Woodward assigning them the numerals I - VII, while Simpson assigned letters to the individual scales. From Simpson's work, Gaffney refined and altered the nomenclature, which has since then become the standard nomenclature for the scale areas and horns of meiolaniid turtles. Most scales on the skull of Niolamia appear in pairs, the exception being scale A, X, Y and Z. Scale A in particular is part of the series of scales that form large horns and bosses along the back of the skull in all meiolaniids. While the region furthest back on the skull is covered by the A scale, which forms an "occipital crest". This crest appears as a large, upward directed frill with a deep notch along its middle. The B scales, which cover the horn cores formed by the squamosal bones, appear as large triangular elements directed to the side of the animal. These horns, which are similar to those of the Australian Ninjemys, are thought to have been even larger in life. The C scales sit before the B scales and are the smallest of the three elements, as is typical for turtles of this family. They extend outward and down, covering part of the skullroof and the side of the skull while overhanging the tympanic cavity. A striking feature that sets this turtle apart from its relatives is the size of the X scale. The X scale is a singular scale that is situated along the midline of the skull atop the skullroof. Typically, this is a rather small scale surrounded on all sides by the much larger D and G scales. In Niolamia however, this scale is among the largest, appearing as a rectangular element that takes up the entire skullroof between the D scales and thus preventing them from touching each other. It further stands out due to being concave, rather than bulging out like the D and G scales. However it is not clear if this actually represents how it appeared in life or if this was simply the result of distortion after the animals death. The E scales are small elements restricted to the side of the skull, just before the tympanic cavity. They are convex and form small, backward directed bosses. The H scales seen in derived meiolaniids appear to be missing in Niolamia. The F scales cover the region above the eye sockets, and the K and J scales the side of the skull from its back up to the beak region. The beak itself is covered by scale I, which can be divided into scale I1 and scale I2 in Niolamia. This region was likely covered by an extension of the rhamphotheca that covers the cutting surface turtles have in place of teeth. While the lower half of the snout tip is made up by the I scales, the top is covered by the unpaired scales Y and Z, extending from above the eyes to the elongated nasal bones.