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Details on Jibeinia II

This was written up for my website, though it's not uploaded yet.

Jibeinia Hou, 2000
= "Jibeinia" Hou, 1997
J. luanhera Hou, 2000
= "Jibeinia luanhera" Hou, 1997
Early Aptian, Early Cretaceous
Dawangzhangzi Beds of Yixian Formation, Hebei, China
Holotype- (IVPP collection; lost) (juvenile) partial skull, mandible (22 mm), six cervical vertebrae (~2.4 mm), five dorsal vertebrae (~2.9 m), dorsal ribs, gastralia, sacrum, six caudal vertebrae, pygostyle (13 mm), scapula (20 mm), coracoids (11.5 mm), incomplete furcula, sternum (17 mm), humerus (23.3 mm), radius (24.2 mm), ulna (24 mm), semilunate carpal, ulnare, metacarpal I (2 mm), phalanx I-1 (4 mm), manual ungual I (2.5 mm), metacarpal II (9.3 mm), phalanx II-1 (6 mm), phalanx II-2 (3.7 mm), manual ungual II (2.1 mm), metacarpal III (8.3 mm), phalanx III-1 (1.5 mm), phalanx III-2 (2.9 mm), manual ungual III (1 mm), partial ilium, pubis (21 mm), partial ischium, femora (22.2 mm), tibiae (28 mm), astragali, calcanea, distal tarsal, metatarsal I, phalanx I-1, pedal ungual I, metatarsal II, phalanx II-1, phalanx II-2, pedal ungual II, metatarsal III (16.3 mm), phalanx III-1, phalanx III-2, proximal phalanx III-3, pedal ungual III, metatarsal IV, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, feather impressions
Diagnosis- narrow furcular branches; metacarpal II does not extend past metacarpal II (?); three phalanges on manual digit III (?); trochlea of metatarsal II not wider than that of metatarsal III (?).
Comments- The name "Jibeinia luanhera" was first used in Hou (1997), but only in the captions of three illustrations. In the text, it was merely called Ji Bei bird (this is untrue in the English translation). Because the scientific name was not given in the text itself, "Jibeinia" was a nomen nudum. Later, Hou (2000) used the scientific name in the text of his semipopular Picture Book of Chinese Fossil Birds, with accompanying illustrations and disgnosis. This counts as the first official use of the name. Unfortunately, neither work contains trustworthy descriptions or accurate illustrations. The illustrations in Hou (1997) are hopelessly schematic, while the skeletal reconstructions in Hou (2000) aren't respresentative of bird anatomy, let alone that of Jibeinia itself. Hou's (1997) descriptions contain features not known in birds (e.g. septomaxillae, presternae) as well as numerous characters which clash with those described in more recent and better illustrated papers (e.g. Confuciusornis in Chiappe et al., 1999). In addition, the holotype is presently lost (Hou pers. comm., 2001 to Zhang et al., 2004) and existing casts are of low quality. Thus all morphological details of Jibeinia are suspect, except the few which can be gleaned from published photographs.
Based on comparison with undoubted juvenile enantiornithines (Dalingheornis, Liaoxiornis, GMV 2158, GMV 2159, etc.), Jibeinia is near certainly a juvenile as well. Characters supporting this conclusion include- unfused sacrum; sternal keel absent; high interclavicular angle; humeral head not concave proximally; humeral distal condyles undeveloped, which in turn causes the ventral condyle to not project distally; carpometacarpus fusion absent; pelvic fusion absent; cnemial crest absent; tibiotarsal, proximal tarsal and distal tarsal fusion absent. Some of these characters are seen in most of the taxa described by Hou (1997), so may be due to the schematic illustration quality or incorrect description instead. Of the diagnostic characters listed by Hou (1997), most are symplesiomorphic for enantiornithines (numerous unserrated maxillary teeth; large, broad sternum; reduced manual digit III; fused pubic symphysis; metatarsals partially fused proximally and unfused distally; metatarsal II shorter than metatarsal III or IV) or ambiguous (extremely concave cervical centra; unexpanded distal pubes). The narrow posteromedian sternal process is present in almost all enantiornithines as derived as Longipteryx, while the final character (poorly developed posterolateral sternal processes) is problematic. The distal end of the right process is covered by another element, while the right process has a broader base which may be the remains of a large distal expansion. If the right side is more accurate, it would resemble Hebeiornis, while the left side could resemble Eoenantiornis. Another possibility is that the sternum is similar to Sinornis in possessing a small anterolateral process on the right side, with most of the posterolateral process broken off. Interestingly, if manual phalanx III-1 is actually a broken piece of metacarpal III, both the apparently short metacarpal III and presence of three phalanges on that digit would be resolved and the manus would resemble those of other enantiornithines. Hou previously claims Confuciusornis has five phalanges on manual digit III in the same book (again probably due to a broken element), so such a mistake by him would not be unheard of. It would still have two phalanges on the digit however, which would be like basal enantiornithines but unlike avisaurids.
Jibeinia exhibits several primitive characters for an ornithothoracine. It supposedly lacks a sternal keel, has three phalanges on manual digit III, and a metacarpal I which is unfused to the carpometacarpus. In addition, the unfused carpometacarpus and pelvis, absent cnemial crest and unfused tibiotarsus and tarsus are all near certainly juvenile characters, being more primitive than more basal avebrevicaudans like Sapeornis and Confuciusornis. However, Jibeinia exhibits a narrower interclavicular angle (~66 degrees) and less phalanges on manual digit III than confuciusornithids and most more basal maniraptorans. Because Jibeinia is probably a juvenile, it is unclear if some characters it possesses are due to being juvenile or being basal. The posteromedian sternal process is narrow as in enantiornithines, but the ventral humeral condyle doesn't appear to be distally projected, if the illustration can be trusted. The latter is the juvenile condition for enantiornithines, however. Metatarsal IV is reduced in width as in enantiornithines as derived as Lectavis. As in Protopteryx and more derived enantiornithines, the medial edge of metacarpal I appears to be convex, though metatarsal II's trochlea appears to be smaller in size than that of metatarsal III and metacarpal III ends far proximally to metacarpal II. The latter two characters are more primitive than Protopteryx and do not vary with age, though the trochlear size may be due to inaccurate illustration. The maxillary teeth and short ulna distinguish Jibeinia from protopterygids, even though the posteromedial sternal processes and possibly narrow metatarsal II trochlea are like Cuspirostrisornis, while the large interclavicular angle, unfused carpometacarpus and unfused distal tarsals are like Protopteryx. The latter three characters may be caused by ontogeny on Jibeinia or both taxa however. The presence of eight sacral vertebrae, and the absence of lateral coracoid processes and metatarsal V are similar to taxa as derived as Iberomesornis. Euenantiornithine characters include the narrow posteromedian sternal process and pneumotricipital fossa (unknown in more basal enantiornithines except Wyleyia), though the humeral head is apparently not concave proximally (if the illustration is accurate). The latter is true of juvenile euenantiornithines too though. The posteromedial sternal processes and short manual phalanx II-2 are shared with the Longipteryx+Enantiornis clade. The short rostrum and toothed maxilla are unlike longipterygids, though Jibeinia does share some characters with each longipterygid genus- a wide interclavicular angle and incompletely fused carpometacarpus with Longipteryx (both possibly ontogenetic in Jibeinia or both taxa), and elongate posteromedial sternal processes and a short manus with Longirostravis. The short manual digit I is like Dalingheornis and more derived taxa, while the convex lateral coracoid margin and very short manual phalanx II-2 are like Eocathayornis and more derived taxa. The short ulna is unlike Eocathayornis+Otogornis, and the multiple phalanges on manual digit III are unlike avisaurids, but the short manus is similar to the latter clade. Elongate posteromedial sternal processes are like cathayornithids, but the unenlarged pedal ungual I is unlike the Concornis+Neuquenornis subclade. Liaoningornithid synapomorphies are almost entirely lacking (Jibeinia has a short sternum with posterolateral and posteromedial processes, an unexpanded posteromedian process, distally unfused metatarsus and metatarsal IV reduced in width), except for the possibly unenlarged metatarsal II trochlea. Finally, the premaxillary teeth are unlike the Boluochia+Gobipteryx subclade.
When summed up, Jibeinia is most likely to be a basal cathayornithid of Eoenantiornis-Sinornis grade. The discordant characters are almost all potentially ontogenetic and due to Jibeinia's juvenile age. Not only are more basal positions less parsimonious, but the discordant characters are not those that could be explained by ontogeny, making such positions even more unlikely. For instance, a position sister to Protopteryx (as has been suggested by Zhou and Zhang, 2005) is at least 7 steps longer, even if the probably shared juvenile characters of Jibeinia and Protopteryx are counted as true synapomorphies.
Besides those characters listed in the diagnosis, probably non-ontogenetic differences from Eoenantiornis include the apparently more tapered rostrum, medial articular process, shorter manual digit I, broader penultimate manual phalanges, less curved manual unguals, and longer metatarsal IV. Differences from Sinornis include the more shallow anterior dentary, supposedly amphicoelous cervical vertebrae, narrow ventral tubercle of humerus, longer manual digit I, wider manual phalanx I-1, less reduced phalanx III-1/2, larger manual unguals, and apparently absent femoral neck. Yet even taxa with semiheterocoelous cervicals (e.g. Confuciusornis) are described as amphicoelous by Hou (1997), and central morphology varies with position in other enantiornithines.
Zhang et al. (2004) suggested Jibeinia may be a senior synonym of Hebeiornis (described by those authors as Vescornis), which they described from the same formation. This was based on their identical size and numerous similar characteristics. Indeed, it only takes one more step to place Jibeinia as a basal gobipterygid related to Hebeiornis. Besides those characters listed in the diagnosis, Jibeinia differs from Hebeiornis in- more shallow anterior dentary; elongate posteromedial sternal processes; narrow ventral tubercle of humerus; larger manual ungual I. Jibeinia supposedly has amphicoelous cervicals and dorsals, while Hebeiornis has heterocoelous cervicals and an opisthocoelous dorsal (but note the comment above regarding enantiornithine central articulations). Besides the numerous juvenile characters listed above (some of which Hebeiornis shows as well- unfused sacrum, metacarpal I unfused to carpometacarpus, proximal tarsals unfused to tibia), Jibeinia is younger based on supposed foramina between neural arches in the pygostyle, and its undeveloped distal femoral condyles. Based on comparison to Hebeiornis, the proximal coracoid of Jibeinia may be broken off, though Hou does describe it as having a rounded head. If it is complete, it is shorter than in Hebeiornis.
References- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Hou, 2000. Picture Book of Chinese Fossil Birds. Yunnan Science and Technology Press, Kunming, China.
Zhang, Ericson and Zhou, 2004. Description of a new enantiornithine bird from the Early Cretaceous of Hebei, northern China. Canadian Journal of Earth Sciences. 41(9), 1097-1107.