| Epidexipteryx | |
|---|---|
 | |
| Holotype fossil,Paleozoological Museum of China | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Scansoriopterygidae |
| Genus: | †Epidexipteryx Zhanget al.,2008 |
| Species: | †E. hui |
| Binomial name | |
| †Epidexipteryx hui Zhanget al., 2008 | |
Epidexipteryx is agenus of smallmaniraptoran dinosaurs, known from one fossil specimen in the collection of theInstitute of Vertebrate Paleontology and Paleoanthropology inBeijing.Epidexipteryx represents the earliest known example of ornamental feathers in the fossil record.[1]
Thetype specimen, belonging to a subadult individual, is catalog number IVPP V 15471.[2] The specific name,Epidexipteryx hui ("Hu's display feather"), and its Chinese nameHúshì Yàolóng ("Hu Yaoming's display dragon") were coined in memory of paleomammologistHu Yaoming.[3]
Due to a pre-publication error,[4] a manuscript of theEpidexipteryx hui description first appeared on a preprint Web portal in late September 2008. The paper was officially published in the October 23, 2008 issue of the journalNature.[2]
E. hui is known from a well-preserved partial skeleton that includes four long feathers on the tail, composed of a centralrachis and vanes. However, unlike in modern-stylerectrices (tail feathers), the vanes were not branched into individual filaments but made up of a single ribbon-like sheet.Epidexipteryx also preserved a covering of simpler body feathers, composed of parallel barbs as in more primitive feathered dinosaurs. However, the body feathers ofEpidexipteryx are unique in that some appear to arise from a "membranous structure"[2] at the base of each feather. It has been suggested that this may represent a stage in the evolution of the feather.[5]
In all, the skeleton ofEpidexipteryx hui measures 25 cm (9.8 in) in length (44.5 cm (17.5 in) including the incomplete tail feathers),[6] and the authors estimated a weight of 164 grams, smaller than most other basal avialans.[2] Gregory S. Paul presented a length estimate of 30 cm (12 in) and body mass estimate of 220 g (0.49 lb).[7]
The skull ofEpidexipteryx is also unique in a number of features, and bears an overall similarity to the skull ofSapeornis,oviraptorosaurs and, to a lesser extent,therizinosauroids. It had teeth only in the front of the jaws, with unusually long front teeth angled forward, a feature only seen inMasiakasaurus among other theropods. The rest of the skeleton bore an overall similarity to the possibly closely relatedScansoriopteryx, including a hip configuration unusual among other dinosaurs: thepubis was shorter than theischium, and the ischium itself was expanded towards the tip. The tail ofEpidexipteryx also bore unusual vertebrae towards the tip which resembled the feather-anchoringpygostyle of modern birds and some oviraptorosaurs.[2]
The exact phylogenetic position ofEpidexipteryx within Paraves is uncertain. The phylogenetic analysis conducted by the authors of its description recovered it as a member of the familyScansoriopterygidae and as a basal member of the cladeAvialae;[2] this was confirmed by the subsequent analysis conducted by Huet al. (2009).[8] A later analysis conducted by Agnolín and Novas (2011) confirmed it to be a scansoriopterygid, but recovered a different phylogenetic position of this family: Scansoriopterygidae was recovered inpolytomy with the familyAlvarezsauridae and the clade Eumaniraptora (containing the clades Avialae andDeinonychosauria).[9] Turner, Makovicky and Norell (2012) includedEpidexipteryx but notScansoriopteryx/Epidendrosaurus in their primary phylogenetic analysis, as a full-grown specimen is known only of the former taxon; regardingScansoriopteryx/Epidendrosaurus, the authors were worried that including it in the primary analysis would be problematic, because it is only known from juvenile specimens, which "do not necessarily preserve all the adult morphology needed to accurately place a taxon phylogenetically" (Turner, Makovicky and Norell 2012, p. 89).Epidexipteryx was recovered as basal paravian that didn't belong to Eumaniraptora. The authors did note that its phylogenetic position is unstable; constrainingEpidexipteryx hui as a basal avialan required two additional steps compared to the most parsimonious solution, while constraining it as a basal member ofOviraptorosauria required only one additional step.
Cau (2024) cast doubt on the validity ofEpidexipteryx, considering it ajunior synonym of the contemporaryEpidendrosaurus due to the diagnosis being based on incomplete tail remains within the holotype, the length of the presacral series, which is not fully known inEpidendrosaurus, and the co-ossification of the 10 distalmost cervical centra, which is interpreted as an ontologically variable trait. As such, theEpidexipteryx holotype would represent a more mature individual ofEpidendrosaurus.[10]
A separate exploratory analysis includedScansoriopteryx/Epidendrosaurus, which was recovered as a basal member of Avialae; the authors noted that it did not clade withEpidexipteryx, which stayed outside Eumaniraptora. Constraining the monophyly of Scansoriopterygidae required four additional steps and movedEpidexipteryx into Avialae.[11] A monophyletic Scansoriopterygidae was recovered by Godefroitet al. (2013); the authors found scansoriopterygids to be basalmost members of Paraves and the sister group to the clade containing Avialae and Deinonychosauria.[12] Agnolín and Novas (2013) recovered monophyletic Scansoriopterygidae as well, but found them to be non-paravian maniraptorans and the sister group to Oviraptorosauria.[13]
An abbreviated version of Zhanget al.'s 2008cladogram is presented below.
| Maniraptora |
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Epidexipteryx appears to have lackedremiges (wing feathers), though based on the relatedYi, it may have possessed some sort of membrane wing to allow gliding.[2][14]
Epidexipteryx is known from theMiddle Jurassic orUpper Jurassic ageDaohugou Beds ofInner Mongolia,China (about 160 or 154mya).[2]
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