Counillonia
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''Counillonia'' 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
dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...
therapsid from the area of
Luang Prabang Luang Prabang (Lao language, Lao: wikt:ຫຼວງພະບາງ, ຫຼວງພະບາງ, pronounced ), historically known as Xieng Thong (ຊຽງທອງ) and alternatively spelled Luang Phabang or Louangphabang, is the capital of Lu ...
in
Laos Laos, officially the Lao People's Democratic Republic (LPDR), is the only landlocked country in Southeast Asia. It is bordered by Myanmar and China to the northwest, Vietnam to the east, Cambodia to the southeast, and Thailand to the west and ...
,
Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...
that lived at around the time of the
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
-
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
boundary and possibly dates to the earliest
Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.9 Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which ...
. Its
type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...
and only known species is ''C. superoculis''. ''Counillonia'' was related to the Triassic dicynodonts such as ''
Lystrosaurus ''Lystrosaurus'' (; 'shovel lizard'; proper Ancient Greek is ''lístron'' ‘tool for leveling or smoothing, shovel, spade, hoe’) is an extinct genus of herbivorous dicynodont therapsids from the late Permian and Early Triassic epochs (arou ...
'' and the
Kannemeyeriiformes Kannemeyeriiformes is a group of large-bodied Triassic dicynodonts. As a clade, Kannemeyeriiformes has been defined to include the species '' Kannemeyeria simocephalus'' and all dicynodonts more closely related to it than to the species '' Lystro ...
that survived the
Permian mass extinction The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the sixth and last period o ...
, but it was more closely related to the Permian genus ''
Dicynodon ''Dicynodon'' (from Ancient Greek '' δίς'' "two" and '' κυνόδους'' "canine teeth", often translated to "two canine-teeth" or "two dog-teeth") is a genus of dicynodont therapsid that lived in southern and eastern Africa during the Lat ...
'' than to either of these lineages. ''Counillonia'' may then possibly represent another line of dicynodonts that survived the Permian mass extinction into the Triassic period, depending on its age. The discovery of ''Counillonia'' in Laos and its unexpected evolutionary relationships hint at the less well understood geographies of dicynodont diversity across the Permo-Triassic boundary outside of well explored regions like the
Karoo Basin The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a per ...
in
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
.


Description

''Counillonia'' was a medium-sized dicynodont (skull length of ) currently known only from a single skull that's missing the lower jaws. However, it likely resembled other closely related dicynodonts, particularly ''Dicynodon'' itself, and so was probably a squat, sprawling quadruped with a short tail and a large head with nearly toothless jaws and a
tortoise 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 o ...
-like beak, sporting a pair of prominent tusks.


Skull

The skull of ''Counillonia'' is short and relatively slender in construction, with the typically broad
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 ...
of most dicynodonts at the back (although they are relatively reduced for a dicynodont) and a short, narrow snout that comes to a squared-off beak tip. The caniniform process of the
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
is short and directed anteriorly so that the tusks point somewhat forward as well as down, and sits entirely in front of the eyes. The upper jaw is completely toothless apart from these two tusks. The interorbital region between the eyes is narrow, and so the large
orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...
are characteristically directed upwards. The nostrils are large, occupying approximately 1/3 of the snout's surface, and sit low at the front of the snout above the short and fused
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
e. 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 ...
s near the front of the snout sport a single well-developed boss that sits almost right above the nostrils and the premaxilla. This boss is bordered on each side by wide, elongate depressions that extend up on to the
frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...
s behind the nasals. The boss has a roughened, rugose texture, but the surface of the rest of the snout is too weathered to determine if they were similarly rugose. Contacts between the bones are difficult to discern, and sutures are hardly visible on the surface of the skull, mostly between the contacts of the frontals and the surrounding bones. The
pineal foramen A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production ...
(the opening for the "third eye") is oval and lies across the
parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...
s just behind the preparietal and is positioned relatively far back in the last quarter of the skull. The
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...
and rear of the skull is somewhat weathered, but they appear similarly constructed to those of other dicynodonts. The
secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves med ...
formed by the premaxilla is unusually short and reduced, and their contact with the
palatine bone In anatomy, the palatine bones (; derived from the Latin ''palatum'') are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxilla, they comprise the hard palate. Stru ...
s is not visible. The palatines themselves preserve expanded, roughly textured pads that indicate the front of the roof of the mouth was covered in
keratinous Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. It is the key structural material making up Scale (anatomy), scales, hair, Nail (anatomy), nails, feathers, horn (anatomy), horns, claws, Hoof, hoove ...
horn like the beak.


History of discovery

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 ...
and only specimen of ''Counillonia'' was discovered in the
Purple Claystone Formation Purple is a color similar in appearance to violet light. In the RYB color model historically used in the arts, purple is a secondary color created by combining red and blue pigments. In the CMYK color model used in modern printing, purple is m ...
of the Luang Prabang Basin in northern Laos. This sedimentary unit mostly consists of purple
silty Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...
-
claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than and are too small to ...
s mixed with layers of conglomerates and
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
, as well as
volcaniclastic Volcaniclastics are geologic materials composed of broken fragments (clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...
sediments. Estimated dates for the age of the formation have ranged from the
Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...
to the
Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...
or even the earliest
Jurassic period The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. The Jurassic constitutes the second and m ...
. More recently,
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...
using U—Pb geochronology from detrital zircon has yielded a maximum age for deposition of 251.0 ± 1.4 Ma. It has been further suggested that mixing and reworking of the sediments implies that the actual depositional age of the formation is possibly even younger than this date, and so likely placing it in the Early Triassic. However, the reliability of this date was contested by Jun Liu in 2020, who argued that based on
biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...
the Purple Claystone Formation should instead be regarded as Late Permian in age, comparing ''Counillonia'' to dicynodonts found in the 255-253 million year old ''Daptocephalus'' Assemblage Zone of South Africa. Furthermore, Liu argued that the conditions of the Permian mass extinction in equatorial regions between the
palaeolatitude Paleomagnetism (occasionally palaeomagnetism) is the study of prehistoric Earth's magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.'' Certain ...
s where Laos was situated (such as high temperatures over 40 °C) would have been inhospitable for dicynodonts, and concluded that ''Counillonia'' instead likely pre-dates the extinction event for these reasons. The first dicynodont remains to be discovered in the Purple Claystone Formation was a single, poorly preserved partial skull discussed by
French French may refer to: * Something of, from, or related to France ** French language, which originated in France ** French people, a nation and ethnic group ** French cuisine, cooking traditions and practices Arts and media * The French (band), ...
geologist A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...
Jean-Baptiste-Henri Counillon in 1896. This skull was described in 1923 by another French geologist, Joseph Répelin, who named it as a new species of ''Dicynodon'', "''Dicynodon incisivum''". The incomplete and damaged nature of the skull made identification difficult, and it has been variously attributed to ''Dicynodon'' and ''Lystrosaurus'' due to a supposed resemblance to the latter. The specimen has since been lost, and the poor quality of the remaining illustrations of the skull are unsuitable for supporting the validity of the species, and "''D. incisivum''" has since been considered a ''
nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...
''. As such, its relationships to other Purple Claystone dicynodonts like ''Counillonia'' remain unknown, despite the similarities the lost skull of "''D. incisivum''" and the type of ''Counillonia'' share with ''Dicynodon''. More dicynodont remains were recovered by a Franco-Laotian expedition between 1993 and 2003 led by
palaeontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
Philippe Taquet Philippe Taquet (born 25 April 1940 Saint-Quentin, Aisne) is a French paleontologist who specializes in dinosaur systematics of finds primarily in northern Africa. He is a member of the French Academy of Sciences since 30 November 2004, president ...
. Three skulls in particular were studied and briefly described in 2009 and were assigned to ''Dicynodon'', tentatively as a new species, although this relationship was not tested and remained uncertain. In 2019, the three skulls were more described in full detail and were recognised as representing two distinct new
taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
, one of which, specimen LPB 1993–3, is the holotype for ''Counillonia''. The other two skulls were assigned to another new genus, ''
Repelinosaurus ''Repelinosaurus'' is an extinct genus of dicynodont from the Purple Claystone Formation of Luang Prabang in Laos, Southeast Asia that lived at around the time of the Permian-Triassic boundary and possibly dates to the earliest Early Triassic. It ...
''. The holotype was temporarily stored, prepared and studied at the
Muséum National d'Histoire Naturelle The French National Museum of Natural History ( ; abbr. MNHN) is the national natural history museum of France and a of higher education part of Sorbonne University. The main museum, with four galleries, is located in Paris, France, within the Ja ...
in
Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...
, and is permanently housed at the Savannakhet Dinosaur Museum in Laos. LPB 1993-3 is relatively complete, although the left portion of the orbit is damaged and it is missing the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other tetrapods which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the f ...
and
quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids ( reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms up ...
s, as well as poorly preserving the preparietal, prootic and epipterygoid bones. The top surfaces of the snout and head are also partly weathered and eroded. The genus was named in honour of the geologist Jean-Baptiste-Henri Conillon as the first person to recognise the presence of dicynodonts in Laos, while the species is from the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''super'' (upward) and ''oculis'' (eyes) in reference to its upward-facing orbits.


Classification

Preliminary studies of specimen LPB 1993-3 found it to be closely comparable to ''Dicynodon'' based on comparative anatomy. A
phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
was later performed when ''Counillonia'' was officially described, utilising the dataset of Angielcyzk & Kammerer (2017), where ''Counillonia'' was found to be a "''Dicynodon''"-grade
dicynodontoid Dicynodontoidea is an infraorder of dicynodont therapsids that includes the famous dicynodont '' Dicynodon'', '' Lystrosaurus'' and the Triassic Kannemeyeriiformes, as well as numerous other closely related species. The name was coined by Ameri ...
forming a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
with ''Dicynodon'' and various other ''Dicynodon''-like species. Amongst these similar species, ''Counillonia'' could be distinguished by three unique
autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...
(derived traits): a relatively large median pterygoid plate, and a braincase with no intertuberal ridge on the basioccipital and distinct backwards-facing processes on the opisthotics. The
occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the Atlas (anatomy), atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape ...
that connects the skull with the
spinal column The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmen ...
is also unfused, a feature it only shares with '' Delectosaurus'' among the "''Dicynodon''"-grade taxa (in which they are otherwise fused). ''Counillonia'' also differs from its nearest phylogenetic and geographic relatives in various other combinations of features on the skull that further distinguish it from these other genera. Furthermore, despite not being found as particularly closely related to the existing valid species of ''Dicynodon'', many of the genera within the "''Dicynodon''"-grade were formerly assigned to ''Dicynodon'', and so the results of the phylogenetic analysis corroborate the initial identification. A simplified
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
, an excerpt from the full analysis by Olivier and colleagues focused on the relationships of the "''Dicynodon''"-grade dicynodontoids, is shown below: Unusually, their analysis recovered ''Counillonia'' and the other "''Dicynodon''"-grade taxa united as a clade
sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...
to the Kannemeyeriiformes, and not as a
grade Grade most commonly refers to: * Grading in education, a measurement of a student's performance by educational assessment (e.g. A, pass, etc.) * A designation for students, classes and curricula indicating the number of the year a student has reach ...
of taxa leading up to Lystrosauridae and Kannemeyeriiformes, which are usually recovered as each other's sister taxa. In this analysis, ''Counillonia'' shares four
synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...
with all the other members of this clade, and they all together share another two with the Kannemeyeriiformes. Another analysis performed in 2020 by Jun Liu found ''Counillonia'' to be the sister taxon to the contemporary Laotian dicynodont ''Repelinosaurus'', together forming a clade with the newly described Chinese dicynodont '' Taoheodon''. Liu identified a 'core-''Dicynodon clade containing these taxa, ''Dicynodon'' itself, and the
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
n genera '' Delectosaurus'' and ''
Vivaxosaurus ''Vivaxosaurus'' is a genus of dicynodont from Late Permian (Changhsingian) of Russia. It has been found at Sokolki on the Northern Dvina River near Kotlas in Arkhangelsk Oblast, Russia. It lived during the latest Permian, and was a contempora ...
''. A simplified excerpt of the cladogram produced by Liu (2020) is shown below:


Palaeoecology

In the Purple Clay Formation, ''Counillonia'' is currently only known to have co-existed with the basal kannemeyeriiform dicynodont ''Repelinosaurus'' and the semi-aquatic
chroniosuchia Chroniosuchia is a group of tetrapods that lived from the Middle Permian to Late Triassic in what is now Kyrgyzstan, China and Germany, Eastern Europe. Chroniosuchians are often thought to be reptiliomorphs, but some recent phylogenetic analyses ...
n
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
''
Laosuchus ''Laosuchus'' is an extinct genus of chroniosuchian known from the Permian-Triassic boundary of Asia. Two species have been named. Discovery ''L. naga'' was found in the Luang Prabang Basin of Northern Laos, part of the Indochina block. The s ...
''. The only direct evidence of plants in the formation are preserved root traces in palaeosols, but a locality underlying the Purple Claystone Formation and above late
Changhsingian In the geologic time scale, the Changhsingian or Changxingian is the latest age or uppermost stage of the Permian. It is also the upper or latest of two subdivisions of the Lopingian Epoch or Series. The Changhsingian lasted from to 251.9 Ma a ...
(Late Permian) deposits preserves a rich and diverse palaeoflora. The sediments preserved indicate that the Purple Clay Formation was deposited in a
braided river A braided river (also called braided channel or braided stream) consists of a network of river channel (geography), channels separated by small, often temporary, islands called ''braid bars'' or, in British English usage, ''aits'' or ''eyots''. ...
environment that gradually transitioned to an
alluvial plain An alluvial plain is a plain (an essentially flat landform) created by the deposition of sediment over a long period by one or more rivers coming from highland regions, from which alluvial soil forms. A ''floodplain'' is part of the process, bei ...
with ponds. The region was volcanically active, as evidenced by the volcaniclastic rocks mixed in with the sediments of the formation. This appears to be associated with a
volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...
that was formed as the then isolated
Indochina Block The Sunda plate is a minor tectonic plate straddling the equator in the Eastern Hemisphere on which the majority of Southeast Asia is located. The Sunda plate was formerly considered a part of the Eurasian plate, but the GPS measurements ha ...
where Laos was located approached the rest of the supercontinent
Pangaea Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous period approximately 335 mi ...
.


Palaeobiogeography

The presence of typical Permian fauna like ''Counillonia'' at a time close to the Permian mass extinction may suggest that the Indochina Block, including the Laos region, may have acted as a refugium for Permian life across the Permo-Triassic boundary (similarly, plant diversities in nearby South China appear to have been relatively stable across the Permo-Triassic boundary). This could also be supported by the absence of "''Dicynodon''"-grade dicynodonts like ''Counillonia'' in other parts of the world, such as in the Karoo Basin of South Africa where they appear to have disappeared entirely. This could reflect a potential bias in the geographic sampling of Permo-Triassic dicynodonts that may hinder our understanding of how they evolved, such as potential Triassic aged "''Dicynodon''"-grade dicynodonts like ''Counillonia''. Alternatively, if ''Counillonia'' is Late Permian in age, its presence in Laos would indicate that the Indochina Block was connected to the Southern and Northern China Blocks by this time. This is in contrast with previously inferred dates suggesting that these landmasses did not collide and connect with each other until the Triassic period.


References

{{Taxonbar, from=Q65065333 Bidentalia Lopingian synapsids of Asia Early Triassic synapsids of Asia Early Triassic genus extinctions Fossils of Laos Fossil taxa described in 2019