| Issi | |
|---|---|
 | |
| Skulls of theholotype and paratype | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Family: | †Plateosauridae |
| Genus: | †Issi Beccariet al., 2021 |
| Species: | †I. saaneq |
| Binomial name | |
| †Issi saaneq Beccariet al., 2021 | |
Issi (meaning "cold" inGreenlandic) is aplateosaurid dinosaur from theLate TriassicFleming Fjord Formation ofGreenland. It contains one species,Issi saaneq; the fullbinomial name means "cold bone". Fossils ofIssi were previously assigned to the speciesPlateosaurus trossingensis, but new finds allowed for a reassessment of that material that showed that it possessed features thought to be exclusive toBrazilian sauropodomorphs such asUnaysaurus andMacrocollum. This ultimately led to the designation ofIssi as a distinct genus in2021.[1] This taxon is the first non-avian dinosaur described from Greenland.
On 27 July 1991, at the east coast of Greenland, onJameson Land, in the Iron Cake site on the northern slope of the MacKnight Bjerg near the Flemingfjord, by William W. Amaral, William R. Downs, Stephen M. Gatesy, Neil H. Shubin and Niels Bonde, members of a team fromHarvard University headed byFarish Jenkins, a skull was uncovered of a basal sauropodomorph. In 1994, the find was reported in the scientific literature and referred toPlateosaurus engelhardti.[2] In 2018, the correctness of this assignment was doubted.[3] In 1995, a skull was discovered of a smaller juvenile animal. In 2012, an additional three skeletons were excavated. After aCAT-scan by Marco Marzola, Filippo Rotatori and Alexandra Fernandes of the first two finds, followed by a digital deformation, it was concluded in amaster's thesis by Victor Beccari that they represented ataxon new to science.[4]
In 2021, thetype speciesIssi saaneq was named and described by Victor Beccari Dieguez Campo,Octávio Mateus, Oliver Wings, Jesper Milàn andLars Bjørn Clemmensen. The generic name means "cold" and thespecific name "bone", both inKalaallisut, a reference to the fact that it was the most northern basal sauropodomorph ever discovered.[1]
Theholotype, NHMD 164741, was found in a layer of the Malmros Klint Formation of theFleming Fjord Group, dating from the middleNorian. It consists of a relatively complete skull with lower jaws and teeth. It is the exemplar found in 1994. It mainly lacks parts of the right side and the rear side of the right lower side. The skull is partly articulated. It represents a later stage juvenile or subadult individual.[1]
Theparatype is specimen NHMD 164758, found in 1995 in the same layer. It consists of a skull with lower jaws, more complete than the holotype. It only lacks the rear right corner of the skull roof. It represents a medium stage juvenile, about a third shorter than the holotype. Both types are part of the collection of theNatural History Museum of Denmark. The three skeletons discovered in 2012, specimens NHMD 164734, GM.V 2013‐683 and NHMD 164775, were in 2021 not formally referred or described; the latter skeleton had even not been fully prepared yet. This limited the description to the head.[1]
The skull of the holotype ofIssi has a preserved length of 243.7 millimetres.[1]
The describing authors in 2021 indicated some distinguishing traits. Four of these areautapomorphies, unique derived characters. The base of the main body of the premaxilla is pierced by a small foramen. Thesquamosal bone has a rear branch that is long horizontally. Thequadrate bone is rather tall relative to the height of the snout. Thearticular bone has a well-developed process at the rear upper side, with a rectangular profile in side view.[1]
Furthermore, a unique combination is present of six traits in themselves not unique. The depression around the bony nostril is weakly developed. The foramen below the nostril is small. The front edge of the nostril is positioned in front of the horizontal midpoint of the premaxilla. The horizontal length of theantorbital fenestra is less than the length of the eye socket. The depression around the antorbital fenestra ends in front of the descending branch of thelacrimal bone. The ectopterygoid the branch connecting to thejugal bone is strongly curved.[1]
The holotype and paratype, NHMD 164741 and NHMD 164758, were initially considered to represent some species ofPlateosaurus, likelyP. engelhardti orP. trossingensis. However, in 2021 they were reinterpreted as belonging to a distinct genus, thesister species ofPlateosaurus. The results of the describers'phylogenetic analyses are shown in thecladogram below:[1]
