Niolamia
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''Niolamia'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
n 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 Courtship is the period wherein some couples get to know each other prior to a possible marriage or committed romantic, ''de facto'' relationship. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marri ...
, 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 The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...
and
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...
of
Australasia Australasia is a subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different context ...
, 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 Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino; September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especial ...
who briefly wrote about what was said to be another skull discovered by his
brother A brother (: brothers or brethren) is a man or boy who shares one or more parents with another; a male sibling. The female counterpart is a sister. Although the term typically refers to a family, familial relationship, it is sometimes used ende ...
. 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 Sir Arthur Smith Woodward, FRS (23 May 1864 – 2 September 1944) was an English palaeontologist, known as a world expert in fossil fish. He also described the Piltdown Man fossils, which were later determined to be fraudulent. He is not rel ...
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 Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
to
London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...
, allowing him to compare it to the remains of ''
Meiolania platyceps ''Meiolania'' is an extinct genus of Meiolaniidae, meiolaniid Stem-group, stem-turtle native to Australasia throughout much of the Cenozoic. ''Meiolania'' was a large turtle, with the shell alone ranging from in length. Four species are currently ...
'', a turtle named by
Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomy, comparative anatomist and paleontology, palaeontologist. Owen is generally considered to have been an outstanding naturalist with a remarkabl ...
from
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
. 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 Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino; September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especial ...
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 A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
, 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 The Bone Wars, also known as the Great Dinosaur Rush, was a period of intense and ruthlessly competitive fossil hunting and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope (of the Aca ...
between
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...
and
Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of paleontology. A prolific fossil collector, Marsh was one of the preeminent paleontologists of the nineteenth century. Among his legacies are the discovery or ...
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 (specimen MLP 26–40) 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 In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
, 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 George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...
and Coleman S. Williams established Roth's material as the
neotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...
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 The Sarmiento Formation (Spanish language, Spanish: ''Formación Sarmiento''), in older literature described as the Casamayor Formation, is a geological formation in Chubut Province, Argentina, in central Patagonia, which spans around 30 million y ...
(then named the Casamayor 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 In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...
as the
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
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 Chubut ( from Tehuelche language, Tehuelche 'transparent'; ) is a provinces of Argentina, province in southern Argentina, situated between the 42nd parallel south (the border with Río Negro Province), the 46th parallel south (bordering Santa ...
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 Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...
, 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 (initially described as ''Crossochelys'') 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 Ankylosis () is a stiffness of a joint due to abnormal adhesion and rigidity of the bones of the joint, which may be the result of injury or disease. The rigidity may be complete or partial and may be due to inflammation of the tendinous or mus ...
, 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 (from the bottom) 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 In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...
. Above the nares, the
nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...
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 The endocranium in comparative anatomy is a part of the skull base in vertebrates and it represents the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater in human anatomy. Structure Structurally, t ...
of ''Niolamia'' is dominated by the
nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...
, 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 Matamata () is a town in Waikato, New Zealand. It is located near the base of the Kaimai Ranges, and is a thriving farming area known for Thoroughbred horse breeding and training pursuits. It is part of the Matamata-Piako District, which tak ...
,
pig-nosed turtle The pig-nosed turtle (''Carettochelys insculpta''), also known as the Fly River turtle, the pitted-shelled turtle, and the Warrajan is a species of turtle which is native to northern Australia and southern New Guinea. It is the only living mem ...
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 bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral ...
s, 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 The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external audit ...
. 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 The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, grasping, and holding (in probing for food, eating, manipulating and ca ...
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.


Postcrania

In addition to the skull, ''Niolamia'' is also known from a variety of postcranial remains. Elements of both
shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...
s are described, as both the left and right preserve the elongated dorsal process of the
scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...
, which extends upwards in turtles. This process connects to the
acromion In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", : acromia) or summit of the shoulder is a bony process on the scapula (shoulder blade). Together with the coracoid process, it extends laterally over the sh ...
at an obtuse angle (greater than 90°), which resembles what is also seen in ''Meiolania platyceps'' and modern tortoises of the family
Testudinidae Tortoises ( ) are reptiles of the family Testudinidae of the order Testudines (Latin for "tortoise"). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like ot ...
. Overall, the anatomy of the shoulder blade has been taken to indicate a terrestrial lifestyle due to its similarity with modern tortoises. While no complete
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...
of ''Niolamia'' is known, researchers were nonetheless able to determine several aspects of its shape. Although the largest fossils of the shell are flattened, this is believed to have been caused by
taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek language, Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientis ...
, crushing the bone during preservation. Instead, it is suggested that ''Niolamia'' had a domed shell like modern tortoises, a hypothesis in part based on the angle between the dorsal process and the acromion of the shoulder blade, which resembles modern testudinids. The shell appears to be thickest towards the borders and thinnest towards the midline of the shell, reaching a maximum thickness of . Of the ten recovered shell remains, only four have their position on the shell known. The largest fragment was likely located at the back edge of the carapace, correlating with the 8th costal plate (which cover the shell between its spine and edge) and the 10th & 11th peripheral plates (the bony plates forming the edge of the bony shell). In this region the shell appears to possess backwards directed spikes. Rather than holding its shape towards the back of the shell, the carapace of ''Niolamia'' forms a ditch at its rear-most point, creating an embayment bordered by the final supracaudal scale. The recovered pattern of sutures and scale sulci is similar to that of modern tortoises, but could not be compared to the shell of ''Meiolania'', in which the number of scales is unknown. The carapace length of ''Niolamia'' has been estimated based on comparison between shell fragments and the general proportions of the related ''Meiolania'' as well as those of the stem-turtle ''
Proganochelys ''Proganochelys'' is a genus of extinct, primitive stem-turtle. ''Proganochelys'' was named by Georg Baur in 1887 as the oldest turtle in existence at the time. The name ''Proganochelys'' comes from the Greek language, Greek word ''ganos'' meani ...
''. The result yielded an estimated shell length of for ''Niolamia'', however this estimate is not a certain one due to the fact that only fragmentary shell remains were known. Subsequently, future discoveries could confirm or contradict these results. Like in other meiolaniids, the tail of ''Niolamia'' was covered in a series of protective bony rings that overlapped one another. These rings were roughly hexagonal in shape, with two pairs of spiky protrusions emerging. The top pair was more robust and directed upwards, while the smaller, lower pair was directed upwards and sideways. Unlike in ''Meiolania'', and more like in ''Ninjemys'', the tail rings of ''Niolamia'' were fully formed and lacked the opened underside seen in the more derived ''Meiolania''.


Phylogeny

Phylogenetic analysis consistently recover ''Niolamia'' in the same position relative to other meiolaniid turtles, which is as the basalmost member and sister to all Australasian taxa. This placement is consistent with both its appearance in time and its place of origins, as this genus is older than all named species from Australia and the western pacific islands. The bridge between ''Niolamia'' and the physically much different ''Meiolania'' is somewhat bridged by ''Ninjemys'', typically recovered as the basalmost of the Australasian forms, as it shares multiple traits including the laterally directed horns and large A scale area with ''Niolamia''. The later description of ''Gaffneylania'', also from the Neogene of Argentina, did not change this placement much. However, this is in part due to the fragmentary nature of the later, as its position within the family is uncertain, being placed either alongside the derived Australasian forms or in a basal
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...
with ''Niolamia''. The two phylogenetic trees below, after Gaffney, Archer & White and Sterli, de la Fuenta & Krause respectively, show the internal relationship of meiolaniids following the description of the two most recently named genera.


Paleobiogeography

''Niolamia'' provides important insight into the paleobiogeography of meiolaniid turtles due to its presence in Neogene South America. In contrast to ''Niolamia'', most other members of the family were endemic to Neogene to Quaternary Australasia, including ''Warkalania'', ''Ninjemys'', ''Meiolania'' and a variety of unnamed forms. For over 100 years ''Niolamia'' was the only form found outside this region until the discovery of ''Gaffneylania''. The presence of these two genera marks them as part of the Austral biogeogeographical kingdom, which includes southern
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
,
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
, south
Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
,
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
,
Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...
,
New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
and
New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...
. Animals of this biogeographical kingdom were heavily affected by the breakup of
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
in their distribution, with Antarctica in particular serving as a connective bridge between the fauna of South America and Australasia. Meiolaniids derive from the primarily Gondwanan Meiolaniformes, which at one point would have been found in both southern South America and Antarctica. Given the fact that South Tasmanian Sea formed between the Cretaceous and late Eocene, meiolaniids must have arrived in Australia by this time, as is confirmed by the fossil record. Antarctica and South America would remain connected until the opening of the
Drake Passage The Drake Passage is the body of water between South America's Cape Horn, Chile, Argentina, and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atlantic Ocean (Scotia Sea) with the southeastern part of the Pa ...
during the Eocene-Oligocene, by which point the South American meiolaniids had not only dispersed into Patagonia but already gone extinct. The cause of the extinction of ''Niolamia'' and other South American meiolaniids was likely the gradually cooling and drying climate of middle Eocene Patagonia.


Paleobiology


Lifestyle and senses

Few studies directly deal with the specifics of ''Niolamias lifestyle. One exception to this is a 2017 study dealing with the neuroanatomy of meiolaniids, which described the endocranial anatomy of ''Niolamia'', ''Gaffneylania'' and ''Meiolania''. Among the findings of the paper was that meiolaniids had an elongated vestibulum nasi. Although such a feature is associated with aquatic turtles today, correlating with a snorkel-like nose, it can also be interpreted as an adaptation for life in
desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...
s based on extant
lizards Lizard is the common name used for all squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The ...
. In these lizards the elongated vestibulum helps the animal to keep its nose free of sand, which may also occur during digging. However, the authors do not settle on a specific hypothesis and instead offer a variety of alternative ideas. These include an enhanced sense of smell,
thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
or even the production of sound. An enhanced sense of smell is also supported by the size of the nasal cavity (cavum nasi proprium). It is even greater than in extant terrestrial turtles, which in turn have a greater nasal cavity than aquatic species. Although the possibility that the dorsal region of the nasal cavity could have aided in vocalisation or thermoregulation, based on comparison to
ornithischian Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...
dinosaurs, is not dismissed outright, it is considered relatively unlikely given the much more simple structure in meiolaniids. Leaving aside the potential for additional uses, the enhanced sense of smell inferred by the large nasal cavity could have served several functions from foraging to intraspecific communication. Particular focus is placed on the later, with modern turtles displaying a wide variety of glands used to produce chemical secretions (musk glands, cloacal secretions and mental glands). While the presence of these glands cannot be observed in meiolaniid fossils, they may have been tied to the keen sense of smell inferred for them. Furthermore, chemical cues are associated with combat and aggression between modern turtles, especially during
courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage or committed romantic, ''de facto'' relationship. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marri ...
, which may entail various shell-based maneuvers. This is congruent with prior studies suggesting a combat function for the highly armored bodies of meiolaniid turtles, which feature differently shaped osteoderms and armored tails. The
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...
of ''Niolamia'' meanwhile is rather conservative and more in-line with what is seen in terrestrial turtles, which have a wide angle between the anterior and posterior
semicircular canals The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, ...
. In modern tortoises this angle is approximately 100°, in more aquatic turtles like geoemydids and plesiochelydids 80-95° and in meiolaniids up to 115°. In terrestrial species, this wide angle between the semicircular canals servers to improve the stability of the head while walking. Given the similarities to modern turtles however, it is assumed that they were sensitive to low frequency sounds and not especially vocal animals, relying more heavily on smell. However as significant changes in the inner ear anatomy may often be subtle, a larger sample size would be needed to make more concrete observations for ''Niolamia'' and other meiolaniids. Generally, both the enhanced sense of smell and the anatomy of the inner ear support the idea that ''Niolamia'' was a terrestrial animal like modern tortoises. This is the most commonly inferred lifestyle for meiolaniid turtles and generally favoured over the aquatic model, which is occasionally suggested but not widely accepted.


Function of the horns

The potential use of the horns and frill has been a frequently considered but rarely studied matter, with the primary study on the matter being published in 2024. The publication analyzed a variety of hypothetical combat behaviors performed with the head, including headbutting, locking of the horns and frill and sideways stabbing and the stresses such actions put on the skeleton. Generally, impacts with the snout, forehead and struggling using the notch between the frill and horns cause the least amount of stress, as opposed to caudal torsion of the frill and sideways stabs. Given the large amounts of stress caused by the latter two actions, such behavior was generally deemed unlikely. This means that although the frill would be large enough to protect the neck, it's unlikely to have been used that way given the stresses of caudal torsion that would affect the bone in such a scenario. Though impacts using the forehead are less stressfull and ''Niolamia'' does share the presence of trabecular bone with the pachycephalosaurids, headbutting is still considered an unlikely behavior. Part of the reasoning behind this is that in pachycephalosaurids the shock of impacts is in part observed by their enlarged dome-like head structures, which as such are not present in ''Niolamia''. The team further notes that the trabecular bone is more prominent in the horns and frills, yet these elements are positioned in a way that makes them unsuited for headbutting, with the frill in particular being angled so that would make direct contact with the frill of a rival impossible. Additional points against headbutting can be found in the absence of pathologies on the holotype of ''Niolamia'' and the fact that meiolaniids as a whole have highly ankylosed skulls, meaning the shock of an impact could not be absorbed by the sutures between bones. The team does however note that it is theoretically possible that such a function may have been instead filled by the scutes that covered the skull in life. The team, led by Federico J. Degrange, concludes that though the animal's sense of smell was likely significant during courtship, it is more likely that the horns and frill served as a display structure rather than being used in intraspecific combat. Such a display ritual may have incorporated different ritualized movements of the head based on the range of motion observed from the more recent ''Meiolania''. Nevertheless, this does not rule out other aggressive behavior that was speculated upon in prior studies, with Degrange and colleagues specifically highlighting the animal's ability to bite. Though a directly defensive function of the frill is also deemed unlikely, it may have still served as a visual deterrent when dealing with predators.


Ontogeny

Comparison between the neotype of ''Niolamia'' and AMNH 3161, formerly the holotype of ''Crossochelys'' and now considered to be a juvenile ''Niolamia'', makes it possible to identify several changes the animal underwent in the process of reaching adulthood. AMNH 3161 represents a very young individual, less than a fourth the size of the ''Niolamia'' neotype skull. Accordingly, the shape of the horns is also significantly downplayed compared to those of adult individuals. The large scales at the back of the skull for instance, Scales A, were initially interpreted as being separate in ''Crossochelys''. Following the synonymty, this interpretation is either wrong or the scales would combine into a single element in adults, as exemplified by the neotype. The X scale, which is the scale placed atop the midline of the skull, extends between the G scales in ''Crossochelys'', while no such split occurs in ''Niolamia''. The fact that the X scales in derived meiolaniids, such as ''Ninjemys'' and ''Warkalania'', forms an extension like that of ''Crossochelys'' suggests that this could be a paedomorphic trait in later members of the family. Among the features once considered to be diagnostic for ''Crossochelys'' was the presence of a "true
temporal fenestra Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (al ...
", however this is likely simply the result of the sutures not yet being closed in the juvenile.


References

{{Taxonbar, from=Q148454 Meiolaniformes Prehistoric turtle genera Eocene turtles Prehistoric turtles of South America Eocene reptiles of South America Divisaderan Mustersan Casamayoran Bartonian life Lutetian life Paleogene Argentina Fossils of Argentina Golfo San Jorge Basin Fossil taxa described in 1899 Taxa named by Florentino Ameghino Sarmiento Formation