Talenkauen
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''Talenkauen'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of basal
iguanodont Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', '' Tenontosaurus'', and the hadrosaurids or "duck-bil ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
from the
Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...
or
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
age of the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
Cerro Fortaleza Formation The Cerro Fortaleza Formation, in older literature described as Pari Aike Formation, is a Late Cretaceous geologic formation of Campanian to Maastrichtian age (although it has formerly been reported to be Cenomanian to Santonian)Varela et al., 20 ...
, formerly known as the Pari Aike Formation of
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
n
Lake Viedma Viedma Lake ( es, Lago Viedma, ) is a Patagonian lake in the province of Santa Cruz, Argentina, situated near its border with Chile. Measuring approximately 50 miles (80 kilometers) in length, it is a major elongated trough lake formed from melt ...
, in the Austral Basin of Santa Cruz,
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. It is based on MPM-10001A, a partial articulated skeleton missing the rear part of the skull, the tail, and the hands. The type and only species is ''Talenkauen santacrucensis''.


Discovery and naming

One among a string of discoveries of ornithopods in South America, following taxa such as ''
Gasparinisaura ''Gasparinisaura'' (meaning "Gasparini's lizard") is a genus of herbivorous ornithopod dinosaur from the Late Cretaceous. The first fossils of ''Gasparinisaura'' were found in 1992 near Cinco Saltos in Río Negro Province, Argentina. The type sp ...
'' and ''
Anabisetia ''Anabisetia'' ( ) is a genus of ornithopod dinosaur from the Late Cretaceous Period of Patagonia, South America. It was a small bipedal herbivore, around long. Discovery Argentine paleontologists Rodolfo Coria and Jorge Orlando Calvo nam ...
'', the specimen that would become ''Talenkauen'' was collected in February 2000 and would later be described and named in a short 2004 paper by Fernando E. Novas and colleagues. It was discovered on Los Hornos Hill on the coast of
Viedma Lake Viedma Lake ( es, Lago Viedma, ) is a Patagonian lake in the province of Santa Cruz, Argentina, situated near its border with Chile. Measuring approximately 50 miles (80 kilometers) in length, it is a major elongated trough lake formed from melt ...
, in the Santa Cruz Province region of
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. Geologically, it hails from the
Cerro Fortaleza Formation The Cerro Fortaleza Formation, in older literature described as Pari Aike Formation, is a Late Cretaceous geologic formation of Campanian to Maastrichtian age (although it has formerly been reported to be Cenomanian to Santonian)Varela et al., 20 ...
. The
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
specimen is MPM–10001A, a relatively complete and articulated skeleton. The name ''Talenkauen'' is derived from the words "''Talenk'', meaning small, and ''kauen'', meaning skull, both from the Aonikenk language. The specific name ''santacrucensis'' refers to the province of
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
where it was found. Following its original, preliminary description, the taxon was described more thoroughly described in an unpublished PhD disseration in 2007 by Andrea V. Cambiaso. In 2020 an extensive description was published by Sebastián Rozadilla and colleagues. It has been recognized that, nestled amongst the rock matrix of the holotype specimen, are a collection of minuscule bone fragments and teeth. Identifiable as the teeth of some degree of ornithopod, and associated with the adult specimen, this is considered to be a neonatal, or recently hatched, baby specimen of ''Talenkauen''. It was described in a 2013 paper, which separated the specimen number MPM–10001 into MPM–10001A, for the adult specimen, and MPM–10001B, for the neonate. The specimen is one of only very few embryonic or hatchling ornithopod specimen, and was the very first discovered from the southern hemisphere. Wear on the tiny, 1.7mm wide tooth crowns indicate the individual had fed, meaning it was not an embryo and had hatched, but only recently before death. It was noted as possible that the adult had been practicing parental care due to the individuals being found together, but that more concrete evidence would be needed to confidently make such an assertion.


Description

''Talenkauen'' was rather like ''
Dryosaurus ''Dryosaurus'' ( , meaning 'tree lizard', Greek ' () meaning 'tree, oak' and () meaning 'lizard'; the name reflects the forested habitat, not a vague oak-leaf shape of its cheek teeth as is sometimes assumed) is a genus of an ornithopod dinosaur ...
'' in shape and build, but with a proportionally longer neck. The full length of the body is estimated at no more than . However, Gregory S. Paul gave a higher estimate of in length and in body mass. Unlike more
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
iguanodontians, it still had
teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
in the tip of the
beak 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 eating, preening, manipulating objects, killing prey, fighting, probing for food ...
(
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 mammal has b ...
ry teeth), and a first
toe Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plan ...
. More
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
iguanodonts lose this toe, retaining only the three middle toes. The
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
has reduced areas for muscle attachment, a featured shared with other
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
n ornithopods like '' Notohypsilophodon'' and ''
Anabisetia ''Anabisetia'' ( ) is a genus of ornithopod dinosaur from the Late Cretaceous Period of Patagonia, South America. It was a small bipedal herbivore, around long. Discovery Argentine paleontologists Rodolfo Coria and Jorge Orlando Calvo nam ...
''. This and other similarities to South American ornithopods suggests that there may have been a distinct Southern Hemisphere ornithopod group, but at the time the authors cautioned that such an interpretation was not entirely justified. In 2015, the describers of ''
Morrosaurus ''Morrosaurus'' is an extinct genus of herbivorous ornithopod dinosaur member of the Elasmaria, that lived in the late Cretaceous in the Antarctica. The only known species is the type ''Morrosaurus antarcticus''. Discovery In 2002 the Argent ...
'' found that such a clade did indeed exist. ''Talenkauen'' is most noted for a set of smooth,
ovoid An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or ...
plates found along the side of the
rib cage The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...
. These plates can be long (180 millimeters, or 7.1 in), but are very thin (only 3 millimeters thick .1 in. They were present with at least the first eight ribs, attaching along the middle portion of a rib and lying flat. Several other dinosaurs are known to have had similar plates, including ''
Hypsilophodon ''Hypsilophodon'' (; meaning "''Hypsilophus''-tooth") is a neornithischian dinosaur genus from the Early Cretaceous period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent research has put thi ...
'', ''
Nanosaurus ''Nanosaurus'' ("small or dwarf lizard") is the name given to a genus of neornithischian dinosaur that lived about 155 to 148 million years ago, during the Late Jurassic-age. Its fossils are known from the Morrison Formation of the south-weste ...
'', ''
Parksosaurus ''Parksosaurus'' (meaning " William Parks's lizard") is a genus of neornithischian dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton a ...
'', ''
Thescelosaurus ''Thescelosaurus'' ( ; ancient Greek - (''-'') meaning "godlike", "marvellous", or "wondrous" and (') "lizard") was a genus of small neornithischian dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was ...
'', and ''Macrogryphosaurus'' (also from Argentina, but from somewhat older rocks), which may have been related. Because of the fragility of the plates, and the fact that they may not have always turned to bone in the living animal, they may have been more widespread than currently known. Novas and colleagues suggested that the plates may be homologous to uncinate processes, strip-like bony projections found on the ribs of a variety of animals including the
tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...
,
crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
s,
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s, and some
maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...
n
theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
dinosaurs. In birds, uncinate processes help to ventilate the lungs, working with rib cage muscles, and Novas and colleagues proposed a similar function for the plates of ''Talenkauen''. This homology was rejected in a more recent study by Richard Butler and Peter Galton because of the plates'
form Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data ...
. The plates were too thin and limited in location to have been very useful as defensive devices.


Classification

Through
cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
analysis, it was found to be more basal than ''Dryosaurus'' and ''Anabisetia'', but more derived than ''
Tenontosaurus ''Tenontosaurus'' ( ; ) is a genus of medium- to large-sized ornithopod dinosaur. It was a relatively medium sized ornithopod, reaching in length and in body mass. It had an unusually long, broad tail, which like its back was stiffened with a n ...
'' and ''
Gasparinisaura ''Gasparinisaura'' (meaning "Gasparini's lizard") is a genus of herbivorous ornithopod dinosaur from the Late Cretaceous. The first fossils of ''Gasparinisaura'' were found in 1992 near Cinco Saltos in Río Negro Province, Argentina. The type sp ...
''. More recently, the describers of '' Macrogryphosaurus'' found their genus and ''Talenkauen'' to be related, and coined the
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
Elasmaria Elasmaria is a clade of ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia that contains many bipedal ornithopods that were previously considered "hypsilophodonts".Madzia, Daniel; Boyd, Clint A.; Mazuch, Marti ...
for the two genera. In 2015, several other Patagonian and Antarctic ornithopods were also found to be related. The simplified cladogram below results from analysis by Rozadilla ''et al.'', 2019, showing all members of
Elasmaria Elasmaria is a clade of ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia that contains many bipedal ornithopods that were previously considered "hypsilophodonts".Madzia, Daniel; Boyd, Clint A.; Mazuch, Marti ...
forming a
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 tr ...
.


Palaeoecology

''Talenkauen'', as a basal ornithopod, would have been a small,
bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
. Other dinosaurs from the Pari Aike Formation include the giant
titanosaurid Lithostrotia is a clade of derived titanosaur sauropods that lived during the Early Cretaceous and Late Cretaceous. The group was defined by Upchurch ''et al.'' in 2004 as the most recent common ancestor of '' Malawisaurus'' and '' Saltasaurus'' ...
''
Puertasaurus ''Puertasaurus'' is a genus of sauropod dinosaur that lived in South America during the Late Cretaceous Period. It is known from a single specimen recovered from sedimentary rocks of the Cerro Fortaleza Formation in southwestern Patagonia, Ar ...
'' and the large predatory theropod ''
Orkoraptor ''Orkoraptor'' is a genus of medium-sized megaraptoran theropod dinosaur from the late Cretaceous Period of Argentina. It is known from incomplete fossil remains including parts of the skull, teeth, tail vertebrae, and a partial tibia. The speci ...
''.


References


Notes


Citations


External links


National Geographic news release
on ''Talenkauen''; the National Geographic Society was one of the supporters of the research on this dinosaur. {{Taxonbar, from=Q220870 Ornithischian genera Cenomanian life Maastrichtian life Late Cretaceous dinosaurs of South America Cretaceous Argentina Fossils of Argentina Fossil taxa described in 2004 Taxa named by Fernando Novas