| Talenkauen | |
|---|---|
 | |
| Holotype MPM-10001 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Clade: | †Elasmaria |
| Genus: | †Talenkauen Novaset al.2004 |
| Species: | †T. santacrucensis |
| Binomial name | |
| †Talenkauen santacrucensis Novaset al. 2004 | |
Talenkauen is agenus ofbasaliguanodontdinosaur from theCampanian orMaastrichtian age of theLate CretaceousCerro Fortaleza Formation, formerly known as the Pari Aike Formation ofPatagonianLake Viedma, in theAustral Basin ofSanta Cruz,Argentina.[1][2] It isbased onMPM-10001A, a partial articulated skeleton missing the rear part of the skull, the tail, and the hands. Thetype and only species isTalenkauen santacrucensis.[2]
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One among a string of discoveries of ornithopods in South America, following taxa such asGasparinisaura andAnabisetia, the specimen that would becomeTalenkauen 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 ofViedma Lake, in theSanta Cruz Province region ofArgentina.[2] Geologically, it hails from theCerro Fortaleza Formation.[1][3][a] Theholotype specimen is MPM–10001A, a relatively complete and articulated skeleton.[2] The nameTalenkauen is derived from the words "Talenk, meaning small, andkauen, meaning skull, both from theAonikenk language. The specific namesantacrucensis refers to the province ofArgentina where it was found.[2] Following its original, preliminary description, the taxon was described more thoroughly described in an unpublished PhD dissertation in 2007 by Andrea V. Cambiaso. In 2020 an extensive description was published by Sebastián Rozadilla and colleagues.[4]
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 ofTalenkauen. 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.[3]
Talenkauen was rather likeDryosaurus in shape and build, but with a proportionally longer neck. The full length of the body is estimated at no more than 4 meters (13 feet).[5] However, Gregory S. Paul gave a higher estimate of 4.7 m (15 ft) in length and 300 kg (660 lb) in body mass.[6] Unlike morederived iguanodontians, it still hadteeth in the tip of thebeak (premaxillary teeth), and a firsttoe. Morederived iguanodonts lose this toe, retaining only the three middle toes. Thehumerus has reduced areas for muscle attachment, a featured shared with otherSouth American ornithopods likeNotohypsilophodon andAnabisetia. This and other similarities to South American ornithopods suggests that there may have been a distinctSouthern Hemisphere ornithopod group, but at the time the authors cautioned that such an interpretation was not entirely justified. In 2015, the describers ofMorrosaurus found that such a clade did indeed exist.[5]
Talenkauen is most noted for a set of smooth,ovoid plates found along the side of therib cage. These plates can be long (180 millimeters, or 7.1 in), but are very thin (only 3 millimeters thick [0.1 in]). They were present with at least the first eightribs, attaching along the middle portion of a rib and lying flat.[2] Several other dinosaurs are known to have had similar plates, includingHypsilophodon,Nanosaurus,Parksosaurus,Thescelosaurus,[7] andMacrogryphosaurus (also from Argentina, but from somewhat older rocks), which may have been related.[8] Because of the fragility of the plates, and the fact that they may not have alwaysturned to bone in the living animal, they may have been more widespread than currently known. Novas and colleagues suggested that the plates may behomologous touncinate processes, strip-like bony projections found on the ribs of a variety of animals including thetuatara,crocodiles,birds, and somemaniraptorantheropod 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 ofTalenkauen.[2] This homology was rejected in a more recent study by Richard Butler and Peter Galton because of the plates'form.[7] The plates were too thin and limited in location to have been very useful as defensive devices.[2]
Throughcladistic analysis, it was found to be morebasal thanDryosaurus andAnabisetia, but more derived thanTenontosaurus andGasparinisaura.[2] More recently, the describers ofMacrogryphosaurus found their genus andTalenkauen to be related, and coined thecladeElasmaria for the two genera.[8] In 2015, several other Patagonian and Antarctic ornithopods were also found to be related.[5]
The simplified cladogram below results from analysis by Rozadillaet al., 2019, showing all members ofElasmaria forming apolytomy.[9]
Talenkauen, as a basal ornithopod, would have been a small,bipedalherbivore.[10] Other dinosaurs from the Pari Aike Formation include the gianttitanosauridPuertasaurus andDreadnoughtus[11] and the large predatory theropodOrkoraptor.[12]
