Senckenbergiana lethaea 88 (2) 195 – 198 1 text-fig. Frankfurt am Main, 30.12.2008
The peculiar scapula of the late Eocene Elaphrocnemus phasianus Milne-Edwards, 1892 (Aves, Cariamae)
With 1 Text-figure
Gerald Mayr & Cécile Mourer-Chauviré
Abstract
The Eocene bird Elaphrocnemus phasianus is a stem lineage representative of the Cariamidae (seriemas) and among the most abundant medium-sized avian species in the Quercy fissure fillings in France. We describe the previously unknown scapula of this species, which exhibits a highly unusual morphology. Most notably, the acromion is greatly elongated and there is a concave facies articularis coracoidei rather than a tuberculum coracoideum as in most other birds. These features also distinguishElaphrocnemus from other representatives of the Cariamae. The long acromion probably serves to strengthen the canalis trios- seus, which in other Cariamae is achieved by a bony bridge connecting the processus procoracoideus and acrocoracoideus of the coracoid. The peculiarities of the pectoral girdle and wing of Elaphrocnemus may indicate that this taxon had better flight capabilities than other Cariamae.
Key words: fossil birds, Paleogene, Elaphrocnemus, Quercy
eschweizerbartxxx sng- Zusammenfassung
Die eozäne Vogelart Elaphrocnemus phasianus ist ein Stammgruppenvertreter der Cariamidae (Seriemas) und eine der häufigsten mittelgroßen Vogelarten in den Spaltenfüllungen von Quercy in Frankreich. Wir beschreiben die bisher unbekannte Scapula dieses Vogels, die eine höchst ungewöhnliche Morpholo- gie aufweist. Insbesondere ist das Acromion stark verlängert und es gibt eine konkave Facies articularis coracoidei statt eines Tuberculum coracoideum wie bei den meisten anderen Vögeln. Diese Merkmale unterscheiden Elaphrocnemus auch von anderen Vertretern der Cariamae. Das lange Acromion diente vermutlich dazu, den Canalis triosseus zu verstärken, was in anderen Cariamae durch eine knöcherne Brücke erzielt wird, welche die Processus procoracoideus und acrocoracoideus des Coracoids verbindet. Die Eigenheiten des Brustgürtels und Flügels von Elaphrocnemus weisen darauf hin, daß dieses Taxon vermutlich eine bessere Flugfähigkeit als andere Cariamae hatte.
Schlüsselworte: fossile Vögel, Paläogen, Elaphrocnemus, Quercy
Introduction E. phasianus Milne-Edwards, 1892, E. crex Milne-Edwards, 1892, and E. brodkorbi Mourer-Chauviré, 1983. Mourer- Elaphrocnemus is one of the most abundant medium-sized avi- Chauviré (1983) also recognized that the wing bones assigned an taxa in the 19th century collections from the middle Eocene to the taxon “Filholornis” actually belong to Elaphrocnemus, to late Oligocene age Quercy fissure fillings in France. Three and Mayr & Mourer-Chauviré (2006) assigned an almost species were distinguished by Mourer-Chauviré (1983), i.e. complete skull and other cranial remains to E. phasianus. The
Dr Gerald Mayr (Corresponding author
© E. Schweizerbart’sche Verlagsbuchhandlung (Nägele u. Obermiller), 2008, ISSN 0037-2110 196 The peculiar scapula of the late EoceneElaphrocnemus phasianus Milne-Edwards, 1892 (Aves, Cariamae) exact age of the specimens from the old collections is unknown, to the fact that the facies articularis scapularis of the coracoid but new excavations have shown that Elaphrocnemus phasianus of E. phasianus is convex and not flat or concave as in other occurs in late Eocene deposits and E. crex in Oligocene sites birds (Text-fig. 1G). (Mourer-Chauviré 1983). The scapula of Idiornis gallicus (Milne-Edwards, 1892) Elaphrocnemus was assigned to the Idiornithidae by differs from that of E. phasianus in that there is a tuberculum Mourer-Chauviré (1983) and earlier authors (e.g. Cra- coracoideum (Mourer-Chauviré 1983: 101), which corre- craft 1973), which also includes the middle Eocene to late sponds to the fact that the coracoid of Idiornis has a concave Oligocene Idiornis Milne-Edwards, 1892 and three further, cotyla scapularis. The acromion of the scapulae of the bathor- less well-known taxa from the Quercy fissure fillings. Togeth- nithid (see Olson 1985) Bathornis grallator (Wetmore, 1944) er with the Phorusrhacidae (Paleocene to Pliocene of South and the Phorusrhacidae is very short (Sinclair & Farr 1932, America, Pleistocene of North America) and Bathornithidae Wetmore 1944: fig. 8). The acromion of the only known (late Eocene and Oligocene of North America), these birds scapula of bathornithid Paracrax wetmorei is broken, and there are stem group representatives of the Cariamidae (seriemas), is a large pneumatic foramen caudal to the facies articularis whose two extant species have a South American distribution. humeralis (Cracraft 1968). The scapulae of other fossil Car- The taxon including extant Cariamidae and their fossil stem iamae are unknown. lineage representatives is usually termed Cariamae. Elaphrocnemus distinctly differs from Idiornis and extant Cariamidae in several osteological features, and may be outside Discussion a clade including Idiornis, Phorusrhacidae, and Cariamidae (Mayr 2002). In the present note we describe the previously Both scapulae articulate well with the coracoid of E. phasianus unknown scapula of Elaphrocnemus phasianus, which exhibits (NMB Q.D.242) (Text-fig. 1H). The presence of a concave a very unusual morphology without counterpart among other facies articularis coracoidei allows an unambiguous assignment birds. to Elaphrocnemus, which is the only avian taxon of matching Anatomical terminology follows Baumel & Witmer (1993) size known from the Quercy fissure fillings with a convex fa- and Vanden Berge & Zweers (1993). The fossil specimens are cies articularis scapularis of the coracoid. This identification is deposited in the collections of the Naturhistorisches Museum also supported by the fact that, although scapulae are rather Basel, Switzerland (NMB) and the Université des Sciences et rare among the 19th century material of the Quercy fissure fill- Techniques du Languedoc, Montpellier, France (USTL). ings, two specimens are present in the collection of NMB, in which bones of E. phasianus are the most abundant remains of medium-sized birds from the Quercy deposits. Mourer-Chauviré (1983) assigned a different type of Systematic Paleontology scapula to the larger species E. crex, which has an only slightly elongated acromion. This bone (USTL ITD 527; Text-fig. 1I) Aves Linnaeus, 1758 eschweizerbartxxx sng- was associated with remains of E. crex in the Quercy locality Cariamae (sensu Mourer-Chauviré 1983) Itardies. Given the great similarity of the coracoids, it is how- ever unlikely that the scapulae of E. phasianus and E. crex are Elaphrocnemus phasianus Milne-Edwards, 1892 so different. Because USTL ITD 527 further lacks a concave facies articularis coracoidei, we conclude that this specimen Referred specimens: NMB Q.D.378, NMB Q.D.293 has been erroneously referred to Elaphrocnemus. (left scapulae lacking the caudal ends, Text-fig. 1). The coracoid of Elaphrocnemus differs from that of other Locality and horizon: Unknown locality and horizon of the Cariamae in that the processus procoracoideus is greatly re- Quercy fissure fillings in France; probably late Eocene (see In- duced. In Idiornis and extant Cariamidae this process fuses troduction). with the processus acrocoracoideus to form a closed canalis Measurements (in mm): NMB Q.D.378: maximum length triosseus which guides the tendon of musculus supracoracoi- as preserved, 41.7; maximum diameter of facies articularis hu- deus (Text-fig. 1J). In Elaphrocnemus, by contrast, closure of meralis, 4.7. NMB Q.D.293: maximum length as preserved, the canalis triosseus is accomplished by the very long acromion 32.6; maximum diameter of facies articularis humeralis, 5.3. of the scapula (Text-fig. 1H). Also with regard to the morphology of the wing bones, Description and comparison: The most unusual feature Elaphrocnemus distinctly differs from other representatives of of the two scapulae is the greatly elongated acromion, which the Cariamae. Most notably, the humerus exhibits a strongly exceeds that of most extant birds, including the Cariamidae, in protruding, triangular crista deltopectoralis, which resembles relative length (only in Pelecanidae [pelicans] is there a simi- that of extant Columbidae (pigeons and doves) and Psittaci- larly elongated acromion). The acromion of the scapula of E. dae (parrots) in its shape (Mourer-Chauviré 1983: pl. 1). phasianus is further characterized and distinguished from that The functional significance of the large crista deltopectoralis of the Cariamidae by its square tip which forms a small medial of the Columbidae and Psittacidae has been detailed by Steg- hook, the rugose and irregular surface of its medial margin, mann (1964), who noted that in these taxa the furcula is very and the presence of a ridge along the margo dorsalis (Text-figs weak owing to the presence of a large crop. One of the major 1A-F). As in extant Cariamidae the facies articularis coracoidei functions of the avian furcula is to serve as an insertion site forms an angle with the comparatively small facies articularis for the cranial portion of the musculus pectoralis. The cranial humeralis. In contrast to the former, however, the facies articu- curvature of the scapi clavicularum of the normally developed laris coracoidei of E. phasianus is concave, which corresponds furcula results in a cranial position of a portion of this muscle The peculiar scapula of the late EoceneElaphrocnemus phasianus Milne-Edwards, 1892 (Aves, Cariamae) 197
eschweizerbartxxx sng-
Text-fig. 1. Incomplete left scapulae (A-F) and left coracoid (G) ofElaphrocnemus phasianus Milne-Edwards, 1892 from an unknown horizon of the Quercy fissure fillings; (H) coracoid (NMB Q.D.242) and scapula (NMB Q.D.293) in articulation; (I) the extremitas cranialis of a scapula (USTL ITD 527) which was assigned to Elaphrocnemus crex Milne-Edwards, 1892 by Mourer-Chauviré (1983), and the scapula and coracoid of the extant Cariama cristata (K, J; right side, reversed to facilitate comparisons). (A, C, E) NMB Q.D.293 in medial, ventrolateral, and ventral view; (B, D, F) NMB Q.D.378 in medial, ventrolateral, and ventral view; (G) NMB Q.D.242 in dorsal view; (H) specimens NMB Q.D.242 and NMB Q.D.293 in articulation. Abbreviation: acr - acromion, fac - facies articularis coracoidei, fah - facies articularis humeralis. Scale bars equal 5 mm (same scale bar for all figures except H). 198 The peculiar scapula of the late EoceneElaphrocnemus phasianus Milne-Edwards, 1892 (Aves, Cariamae) relative to the humerus, which enables the bird to draw the Cracraft, J. (1973): Systematics and evolution of the Gruiformes wings forward. In birds with a weakly developed furcula with- (Class Aves). 3. Phylogeny of the suborder Grues. – Bulletin of out cranial curvature, however, the musculus pectoralis cannot the American Museum of Natural History, 151: 1 – 127. perform this function, which is taken over by the unusually Mayr, G. (2002): A new specimen of Salmila robusta (Aves: Grui- well-developed musculus coracobrachialis cranialis (“anterior”) formes: Salmilidae n. fam.) from the Middle Eocene of Messel. – in Psittacidae and Columbidae. This muscle originates on the Paläontologische Zeitschrift, 76: 305 – 316. processus acrocoracoideus of the coracoid and inserts on the Mayr, G. & Mourer-Chauviré, C. (2006): Three-dimensionally pre- planum intertuberculare of the humerus (Vanden Berge & served cranial remains of Elaphrocnemus (Aves, Cariamae) from Zweers 1993). Its large development in Columbidae and Psit- the Paleogene Quercy fissure fillings in France. – Neues Jahrbuch tacidae is correlated with the reduction of the proximal por- für Geologie und Paläontologie, Monatshefte, 2006 (1): 15 – 27. tion of the crista deltopectoralis, which thus has a pointed, Milne-Edwards, A. (1892): Sur les oiseaux fossiles des dépots éocènes triangular shape. de phosphate de chaux du Sud de la France. – Comptes Rendus We assume that the same considerations also apply in du Second Congrès Ornithologique International: 60 – 80. the case of Elaphrocnemus. Like Phorusrhacidae and extant Mourer- Chauviré, C. (1983): Les Gruiformes (Aves) des Phospho- Cariamidae, this taxon probably also had a very weak furcula rites du Quercy (France). 1. Sous-ordre Cariamae (Cariamidae et (which may or may not have been correlated with presence of Phorusrhacidae). Systématique et biostratigraphie. – Palaeoverte- a large crop). However, and as indicated by the well-developed brata, 13: 83 – 143. crista deltopectoralis, Elaphrocnemus seems to have had bet- Olson, S. L. (1985): The fossil record of birds. – In: D. S. Farner, J. ter flight capabilities than other Cariamae. This corresponds R. King & K. C. Parkes [Eds], Avian Biology, 8: 79 – 238. to the fact that it also has a proportionally shorter tarsometa- tarsus than Idiornis and extant Cariamidae (Mourer-Chau- Sinclair, W. J. & Farr, M. S. (1932): Aves of the Santa Cruz Beds. – Reports of the Princeton University Expedition to Patagonia, viré 1983) and thus appears to have been less cursorial. The 1896 – 1899, 7 (2): 157 – 191. long acromion of Elaphrocnemus may serve to strengthen the processus acrocoracoideus, on which the musculus coracobra- Stegmann, B. (1964): Die funktionelle Bedeutung des Schlüssel- 105 chialis cranialis inserts. Just because of their uniqueness, the beines bei den Vögeln. Journal für Ornithologie, : 450 – 463. latter feature and the peculiar shape of the articulation facets Vanden Berge, J. C. & Zweers, G. A. (1993): Myologia. – In: J. J. between coracoid and scapula are likely to be apomorphic fea- Baumel, A. S. King, J. E. Breazile, H. E. Evans & J. C. Vanden tures of Elaphrocnemus. Berge [Eds]: Handbook of avian anatomy: Nomina anatomica Because the Cariamae had a wide distribution in the Paleo- avium. – Publications of the Nuttall Ornithological Club, 23: 189 – 247. gene, a better knowledge of their phylogenetic interrelation- ships would be of great interest from a biogeographic point Wetmore, A. (1944): A new terrestrial vulture from the Upper Eo- of view. By outgroup comparison with other birds outside the cene deposits of Wyoming. – Annals of the Carnegie Museum, Cariamae, the differences of the carpometacarpus (absence of 30: 57 – 69. a tubercle on the ventral margin of the os metacarpaleeschweizerbartxxx sng- minor) and hypotarsus (which is not block-like as in Idiornis, Pho- Manuscript received: 14 March 2008 rusrhacidae, and Cariamidae) seem to be plesiomorphic and Reviewed manuscript accepted: 17 July 2008 support a position of Elaphrocnemus outside a clade including Idiornis and extant Cariamidae, as assumed by Mayr (2002). Certainly, however, this hypothesis still needs to be evaluated in a more comprehensive analysis, which also includes rep- resentatives of the Bathornithidae, and which is beyond the scope of the present note.
Acknowledgements
We thank B. Thüring (NMB) for the loan of the fossil speci- mens, S. Tränkner (SMF) for taking the photographs, and Z. M. Bochenski and E. Bourdon for reviewing the manu- script.
References
Baumel, J. J. & Witmer, L. M. (1993): Osteologia. – In: J. J. Baumel, A. S. King, J. E. Breazile, H. E. Evans & J. C. Vanden Berge [Eds]: Handbook of avian anatomy: Nomina anatomica avium. – Publications of the Nuttall Ornithological Club, 23: 45 – 132. Cracraft, J. (1968): A Review of the Bathornithidae (Aves, Grui- formes), with Remarks on the Relationships of the Suborder Cari- amae. – American Museum Novitates, 2326: 1 – 46.