Epidexipteryx hui, Zhang & Zhou & Xu & Wang & Sullivan, 2008
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publication ID |
https://doi.org/ 10.1038/nature07447 |
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https://doi.org/10.5281/zenodo.6230241 |
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persistent identifier |
https://treatment.plazi.org/id/7670974E-8624-FFAD-FC6A-5340BC82D952 |
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Plazi |
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scientific name |
Epidexipteryx hui |
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gen. et sp. nov. |
Epidexipteryx hui gen. et sp. nov.
Etymology. Epidexi (Greek): display; pteryx (Greek): wing, feather; hui, in honour of the late young palaeontologist Yaoming Hu, who
contributed significantly to the study of Mesozoic mammals from China. Generic name pronounced ‘ep-id-ecks-IP-ter-icks’.
Holotype. A feathered pigeon-sized skeleton, preserved on part and counterpart slabs, and housed at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, collection number IVPP V15471 View Materials ( Fig. 1 View Figure 1 ; see Supplementary Information).
Locality and horizon. Daohugou, Ningcheng County, Inner Mongolia, north China. The age of the Daohugou sediments is contentious, with possible dates ranging from Middle Jurassic 7 to Early Cretaceous. However , published radioisotopic dating results span a narrower range from 152 to 168 Myr (Middle to Late Jurassic) 8 – 10.
Diagnosis. Medium-sized avialan with four elongate ribbon-like tail feathers (ETFs), highly procumbent and significantly enlarged anterior teeth, and a distally tapering pygostyle-like structure formed by ten unfused caudals at the end of the tail ( Figs 1 View Figure 1 and 2 View Figure 2 ; see Supplementary Information). Differs significantly from Epidendrosaurus , the only other known scansoriopterygid, in caudal morphology (tail 70% of trunk length in Epidexipteryx , compared with more than 300% in Epidendrosaurus ; 16 caudal vertebrae in Epidexipteryx , compared with more than 40 in Epidendrosaurus ; caudal prezygapophyses reduced in Epidexipteryx but significantly elongated in Epidendrosaurus ).
Description and comparisons. Epidexipteryx is estimated to be 164 g in body mass (see Supplementary Information), smaller than most other basal avialans 3,11. The holotype probably represents a subadult individual, because the ends of some of the long bones seem imperfectly ossified.
As in oviraptorosaurs 12, the skull is high in lateral view (height about 60% of length), the external naris is positioned high on the snout, and the parietal is proportionally long. The teeth of both the upper and lower jaws are highly procumbent, a feature previously known only in the ceratosaurian Masiakasaurus among theropods 13. Furthermore, the anterior teeth are much larger than the posterior ones, as in basal oviraptorosaurs 12, basal therizinosaurs 14 and probably Epidendrosaurus 4,5. There are probably 9 cervicals and 14 thoracic vertebrae, and the synsacrum is composed of 7 vertebrae. The caudal series is much shorter than in non-avian theropods or in other basal avialans. The anterior six caudal vertebrae are proportionally short and wide. The posterior ten caudals bear no transverse
processes. They form a structure similar to the elongated, incipient pygostyle in some basal birds 15,16 but are not fused to each other ( Figs 1a View Figure 1 and 2a View Figure 2 ; see Supplementary Information).
The partly preserved sternum is small and convex anteriorly, and seems to comprise two incompletely fused sternal plates, as in the primitive bird Jeholornis 17. The scapula is significantly shorter than the humerus, as in some derived maniraptorans, and the coracoid is sub-rectangular. The pelvis has an unexpected combination of features among theropods, as in Epidendrosaurus 4,5. The ilium is bird-like in having a long preacetabular process with a strongly convex anterior margin, but differs from the ilia of most non-avian theropods in having a small pubic peduncle. Unusually among theropods, the straight pubis is shorter than the ischium and is significantly shorter than the femur. It is anteroventrally oriented and lacks a pubic boot. The posteriorly curved ischium is laterally compressed, gradually widens towards the distal end, and lacks an obturator process. The humerus is about same length as the femur, proportionally longer than in most other basal avialans. The ulna is posteriorly bowed and the manus is significantly elongated (see Supplementary Information) as in birds and other derived theropods 18 – 22. The curvature of the manual claws falls within the range known for the pedal claws of ground-based foraging birds (see Supplementary Information). The femur is about 160% the length of the metatarsus, and 80% the length of the tibia ( Figs 1a View Figure 1 and 2a View Figure 2 ; see Supplementary Information).
Phylogeny and affinity. Phylogenetic analysis indicates that Epidexipteryx and Epidendrosaurus form a monophyletic Scansoriopterygidae (see Supplementary Information), representing a bizarre lineage at the base of the Avialae 6 ( Fig. 3 View Figure 3 ; see Supplementary Information).
Although possessing many derived features seen in birds, including a humerus as long as the femur, a long preacetabular process of the ilium with a strongly convex margin, and many other features, Epidexipteryx and Epidendrosaurus also show some striking similarities to oviraptorosaurs 12 and to a lesser degree therizinosauroids 14,21, including a short and high skull, an external naris positioned high on the snout, an anteriorly downturned and strongly dorsally convex mandible, a large external mandibular fenestra, and enlarged anterior teeth. Furthermore, some pelvic features, such as a proportionally very short pubis and a distally widening ischium, are not known in any other theropod. The bizarre appearance of scansoriopterygids indicates that morphological disparity among maniraptorans close to the origin of birds is higher than has previously been assumed, and underscores the importance of Jurassic theropods for understanding avian origins.
Integument. The integument bears feather-like structures of two types, ETFs and non-ETFs, which are roughly comparable to shafted and non-shafted feathers, respectively 23. The distal part of each non- ETF is composed of filamentous parallel barbs ( Fig. 2e, e View Figure 2 9, f), similar to the condition seen in the non-shafted feathers of other feathered dinosaurs and primitive birds 18,22–25. However, the free distal barbs of Epidexipteryx arise from the edge of a membranous structure ( Fig. 2b, c, d, d View Figure 2 9), an arrangement that has never previously been reported.
The four ETFs are tightly attached to the last ten caudal segments ( Figs 1a View Figure 1 and 2a View Figure 2 ). These feathers are incomplete distally, but the preserved part of each ETF is identical to the corresponding structure in some primitive birds 16,26–28, for example in having a similar central rachis and unbranched vanes ( Fig. 1a, d View Figure 1 and 2a, a View Figure 2 9; see Supplementary Information). Elongate tail feathers are a normal component of the ornamental plumage in extant birds. In contrast to other feather types, ornamental plumage is used to send visual signals that are essential to a wide range of avian behaviour patterns, particularly relating to courtship 29. For example, experiments have shown that, in some species, males with long tail plumage attract more mates than their short-tailed counterparts 30. It is highly probable that the ETFs of Epidexipteryx similarly had display as their primary function, rather than serving other purposes such as flight or insulation 29. Indeed, pennaceous feathers suitable for flight are not present in Epidexipteryx , even though the bones and integument are well preserved. Because pennaceous feathers are commonly encountered in other feathered maniraptorans 2,21,22,25, their absence constitutes another highly unusual feature of Epidexipteryx , as well as strongly implying that this taxon was non-volant. Epidexipteryx is the oldest and most phylogenetically basal theropod known to possess display feathers, indicating that basal avialans experimented with integumentary ornament as early as the Middle to Late Jurassic. Unless Epidexipteryx is interpreted as secondarily flightless, the absence of pennaceous limb feathers in this taxon suggests that display feathers appeared before airfoil feathers and flight ability in basal avialan evolution.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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