| Hulsanpes | |
|---|---|
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| Skeletal diagram of ZPAL MgD-I/173 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Dromaeosauridae |
| Subfamily: | †Halszkaraptorinae |
| Genus: | †Hulsanpes Osmólska,1982 |
| Type species | |
| †Hulsanpes perlei Osmólska, 1982 | |
Hulsanpes (meaning "Khulsan foot") is agenus ofhalszkaraptorinetheropoddinosaurs that lived during the LateCretaceous in what is now theBarun Goyot Formation ofMongolia, about 75-72 million years ago. The remains were found in 1970 and formally described in 1982 by Halszka Osmólska, who noted that the genus is represented by an immature individual.Hulsanpes represents the first record of the basaldromaeosauridsubfamilyHalszkaraptorinae.
The firstfossil remains ofHulsanpes were discovered in 1970 during the third Polish-Mongolian expedition at Khulsan in theGobi Desert. Twelve years later, thetype species,Hulsanpes perlei, was named and described by thePolishpalaeontologistHalszka Osmólska in1982.Hulsanpes is based on theholotype fossilspecimenZPAL MgD-I/173, uncovered in a sandstone layer of theBarun Goyot Formation, dating from the LateCampanian (roughly 72million years ago). It consists of a partialbraincase fragment and the rightmetatarsus composed by the second, third and fourthmetatarsals and three pedalphalanges from an apparently immature individual. Osmólska mentioned the braincase as preserved in the holotype but this element was never described. Based on the unusual morphology of the metatarsus and second phalanges she concluded thatHulsanpes represented adeinonychosaur taxon, but due to the lack of more material, she tentatively classified the genus as a dromaeosaurid taxon. In an etymological aspect, thegeneric name,Hulsanpes, can be translated as "Khulsan pes" and is derived from theLatinized name of the type locality Khulsan and the Latinpēs meaning "foot" (Hulsan +pēs). Thespecific name,perlei, is in honour to the veteran Mongolian paleontologistAltangerel Perle.[1]
The holotype specimen is represented by a very small immature individual and therefore all the available data is somewhat limited. The roughly textured bones are indicators of an early stage of life, probably a post-hatchling chick. The genus itself can be distinguished in having the contact area of metatarsal III and IV straight in a frontal view and the lower end of metatarsal IV projected to the lower lateral side.[2]
Overall, the preserved rightmetatarsus is a gracile and compact element with the three main metatarsals only lacking the first one, in all metatarsals the upper end is slightlyeroded. Although compact, the third metatarsal is not pinched at the upper end, indicating that the metatarsus was not arctometatarsalian. Metatarsals II, III and IV are similar in length (3.4 cm (34 mm), 3.9 cm (39 mm) and 3.6 cm (36 mm) respectively), although the third one is the longest. There are three pedalphalanges preserved but only one being complete. The first phalanx of metatarsal III is very eroded missing most of its lower part but preserving the upper one; it remains articulated to the metatarsal. The first phalanx of metatarsal II is complete but the second one is severely damaged, lacking most of the lower region, however, it is articulated to the first phalanx.[1][2]
The partialbraincase is a small element, measuring just 1 cm (10 mm) in length, it is embedded in a small portion of the sandstone layer. In general, the morphology is very complex and has an irregular shape. Based on comparisons with othermaniraptorans, the preserved portion can be identified as the right inner side of theprootic-opisthotic bones in the braincase.[2]
When first described in 1982, Osmólska tentatively placedHulsanpes within theDromaeosauridae. Several features of the specimen were, according to Osmólska, too "primitive" for it to be a genuine bird taxon such as the lack of fusion of the metatarsals except in the lower region but this might partly be due to the young age of the individual specimen.[1] Although its juvenile nature is reminiscent of a miniature individual ofVelociraptor, and though these traits areplesiomorphic, it might still belong to another, non-avian,maniraptoran lineage besides Dromaeosauridae.[3] A 2004 phylogeny of Dromaeosauridae recoveredHulsanpes as a dromaeosaurid (due to a coding error forSinovenator),[4] but Agnolin and Novas in 2013 assigned it toAveraptoraincertae sedis based on the fact that the extremely gracile metatarsals are similar to Avialae and metatarsal III interpreted to be pinched at the upper region.[5] This latter statement has been proven to be incorrect though.[2]
After several inconsistencies surrounding the placement of the genus, in2017 during the description ofHalszkaraptor a new clade, theHalszkaraptorinae, was coined by Cau and colleagues, containing the new genusHalszkaraptor and its close relatives which were identified as being the long enigmaticHulsanpes andMahakala. The analysis showed that the Halszkaraptorinae was the most primitive known dromaeosaurid group, slightly related tounenlagiines.Hulsanpes occupied a derived position within the Halszkaraptorinae as thesister species ofMahakala. The cladogram below is based on the results obtained in the phylogenetic analysis performed during the description using updated data from the Theropod Working Group:[6]
| Dromaeosauridae |
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Hulsanpes has been re-classified as a halszkaraptorine taxon, updating various aspects about the life-style of these animals.Hulsanpes had a similar life-style to those of the modern-daysawbills orwaterfowls, spending most of their time in aquatic environments (such as rivers) using fore and hindlimb-assistedswimming. But like all dinosaurs, they come up onto land toreproduce and laid eggs in terrestrialnests.[6][7] However, it appears to be thatHulsanpes may have been more terrestrial based on the holotype metatarsus, which features adaptations for a moresubcursorial life-style, supporting the diversification within this subfamily.[2]
The holotype specimen was recovered from theBarun Goyot Formation at the type location of the formation, the Khulsan locality. This formation is interpreted to date back to the Middle-Late Campanian stage of the Late Cretaceous period, about 72 million to 75 million years ago. Most of the environments present consisted of largerivers with otherwater bodies, and prominentdune-like terrains. Here,Hulsanpes shared their habitat with diverse dinosaurs such asBagaceratops,Gobipteryx,Parvicursor,Saichania,Tarchia andTylocephale.[8][9] The locomotory specializations ofHulsanpes may suggest a reducedsource competition with other species in the formation.[2]
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