Overview of the Fossil Avian Fauna from the Sahabi Formation

Transcription

1 GARYOUNIS SCIENTIFIC BULLETIN, 2008, pp Special Issue, No. 5 Overview of the Fossil Avian Fauna from the Sahabi Formation DIMITRIOS MICHAILIDIS ABSTRACT Palaeontological field expeditions for the period 1978 to 1981 at the Sahabi Formation of Libya led to the collection of a variety of avian skeletal remains which indicate the presence of at least ten species. During the February-March 2007 field season of the E.L.N.R.P. in As Sahabi additional avian material was collected. This paper reports the preliminary evaluation of the new finds. In total 21 avian skeletal fragments were collected, with humeri being the most abundant. Appropriate measurements were made in an attempt to classify the material to the ordinal level. The current finds support the results of the analysis of the older As Sahabi avian material in that a mostly water-tied avifauna is represented, with a strong presence of Pelecaniiformes and Anseriformes. Future work will involve the use of comparative osteological collections as a means of attaining a more secure and detailed taxonomic allocation of the current fossil avian material. Dimitrios Michailidis, Department of Historical Geology and Palaeontology, Faculty of Geology and Geoenvironment, University of Athens, Athens, Greece, dmichailidis@geol.uoa.gr

2 MICHAILIDIS GARYOUNIS SCIENTIFIC BULLETIN INTRODUCTION The Sahabi Formation of Libya is significant among North African Mio- Pliocene fossiliferous sites in preserving a large and diverse palaeofauna (Boaz, 1996). The analysis of different elements of a palaeofauna can provide supplementary information concerning the palaeoecology and zoogeography of a fossil site. In particular, the As Sahabi fossil avian remains can be of some use in reconstructing the local Miocene palaeoenvironment. Walker and Dyke (2006) suggest that avian fossils are especially valuable for the reconstruction of the palaeoenvironment, because osteological differences between Miocene birds and their nearest recent relatives are minimal. On the other hand, the considerable environmental differences between the Miocene and the present time as well as the difficulty in assessing the significance of even minor osteological changes in organisms, make it hard to extract significant palaeoecological information from fragmentary remains without the additional use of geologic and taphonomic evidence (e.g. Vrba, 1980, Behrensmeyer, 1975). During five past field seasons (from 1978 to 1981) enough avian material was collected to allow the identification of 10 avian species (Ballmann, 1987). The resulting avifaunal list is as follows: AVES Ciconiiformes Ciconiidae Leptoptilos sp. Ciconiidarum gen. sp. Pelecaniformes Phalacrocoracidae Phalacrocorax sp. Anhingidae Anhinga sp. Pelecanidae Pelecanus sp. Falconiformes Accipitridae Accipitridarum gen. sp. Anseriformes Anatidae Anatidarum gen. sp. A Anatidarum gen. sp. B Anatidarum gen. sp. C Anatidarum gen. sp. D In this preliminary study the discovery of additional avian fossil material is reported. During the surface survey of the winter field season during February to March, 2007 of the East Libya Neogene Research Project at the Sahabi Formation of Libya, a number of identifiable avian skeletal elements were collected, from 11 different localities. Table 1 lists the different skeletal elements recovered. In total 21 skeletal fragments were collected. Four out of the 21 elements are unidentifiable. Humeri are the most abundant skeletal elements. METHODS The osteological nomenclature follows Baumel et al. (1993). The following abbreviations in describing the elements are used: dist.- distal; prox.-proximal; caud.- caudal; cran.- cranial; dors.- dorsal; ventr.- ventral; frag.- fragment; l- left; r- right; 120

3 Special Issue, 2008 FOSSIL AVES FROM AS SAHABI cor.- coracoid; hum.- humerus; tmttarsometatarsus; phal.- phalanx; uln.- ulna. Measurements were made with Mitutoyo dial callipers with an accuracy of 0.02 mm. The measurements are abbreviated as follows: L- greatest length; PW- proximal width; DW- distal width; PH- proximal height; DH- distal height. In the coracoid the following measurement is used: ALarticulation length (from the proximal end of processus acrocoracoideus to the distal end of processus procoracoideus). Humeri RESULTS AND DISCUSSION 4P204A, Proximal fragment of left humerus. Order: Pelecaniformes Measurements: PW: 20.54mm Some elements of the morphology of the proximal end of the humerus are preserved on 4P204A (Figure 1). In caudal view the area around the fossa pneumotricipitalis is badly worn, therefore, minimal information can be extracted. The overall shape of the caput humeri is apparent as well as a possibly shallow incisura capitis humeri. In cranial view, a deep sulcus transversus can be observed. Miller (1966) contrasts Phalacrocoracidae and Anhingidae by a series of characters one of which is the sulcus transversus on the proximal humerus. He states that in anhingas the sulcus transversus is short and deep only medially while in cormorants it is long and deep. It extends transversely to, but is narrowly separated from the impressio coracobrachialis (Miller, 1966, p. 315). In 4P204A the condition of the sulcus Figure 1. 4 P204A, Prox. frag. of l. hum. (Figure 1a, caudal view; Figure 1b, cranial view) 121

4 MICHAILIDIS GARYOUNIS SCIENTIFIC BULLETIN Table 1. Table of fossil avian material from the winter 2007 field season of the ELNRP at the Sahabi Formation. Fossil Avian material, Sahabi Formation. Winter 2007 ELNRP field season SpecNo. Locality Skeletal Element Position Side 26 P 14 A UNGUAL PHALANX 105 P 61 A UNGUAL PHALANX 11 P 103 A PHALANX 2 P 16 C FEMUR DISTAL - 11 P 37 A ULNA DISTAL LEFT 109 P 61 A ULNA RIGHT 7 P 99 B TARSOMETATARSUS PROXIMAL - 10 P 99 B BONE INDET-ULNA DISTAL - 14 P 204 A BONE INDET-SCAPULA - 83 P 60 A BONE INDET-CORACOID PROXIMAL - 25 P 14 A BONE INDET - 6 P 16 C CORACOID PROXIMAL RIGHT 27 P 62 A CORACOID PROXIMAL RIGHT 5 P 16 C HUMERUS DISTAL LEFT 71 P 24 A HUMERUS DISTAL LEFT 20 P 62 A HUMERUS RIGHT 9 P 99 B HUMERUS DISTAL LEFT 15 P 103 A HUMERUS PROXIMAL LEFT 5 P 201 A HUMERUS DISTAL RIGHT 4 P 204 A HUMERUS PROXIMAL LEFT 11 P 204 A HUMERUS DISTAL RIGHT 122

5 Special Issue, 2008 FOSSIL AVES FROM AS SAHABI transversus is similar to that observed by Miller (1966) for the anhingas. 20P62A, right humerus. Order: Pelecaniformes Measurements: L: mm, PW: 18.79mm, DW: 10.34mm. Elongate and slender humerus (Figure 2). In caudal view the elongate crista deltopectoralis is rotated over the cranial surface. The margo caudalis extends to the tuberculum dorsale. In cranial view, a short and medially deep sulcus transversus can be observed, a condition similar to that seen in 4P204A, a proximal fragment of left humerus. Figure 2. 20P62A, right humerus (Above, caudal view; Below, cranial view) 11 P204A, distal fragment of right humerus. Order: Pelecaniformes Measurements: DW: 17.17mm, DH: 12.12mm. This humeral fragment (Figure 3) is similar in size and morphology to 1P109A (hum., l., dist.) and 93 P16A (hum., r., dist.) identified as Anhinga sp. by Ballmann (1987). In cranial view the prominent thick condylus dorsalis, is almost parallel to the axis proximodistalis of the humerus. The small condylus ventralis is angled at about 50 degrees to the axis proximodistalis of the humerus. The tuberculum supracondylare ventrale is large. The fossa musculi brachialis is shallow and ovoid in shape. Laterally, it is more depressed, forming a 123

6 MICHAILIDIS GARYOUNIS SCIENTIFIC BULLETIN Figure 3. 11P204A, a distal fragment, right humerus (left, caudal view), and 1P109A, a distal fragment, left humerus (right, cranial view) Figure 4. Figure 4a, caudal view of 5P201A distal frag.ment right hum.erus, 5P16C distal frag.ment, left humerus, and 1P47A, a distal frag.ment, right humerus; Figure 4b, cranial view of 5P201A, distal fragment, r.ight humerus 124

7 Special Issue, 2008 FOSSIL AVES FROM AS SAHABI ridge on its border with the corpus humeri. In caudal view the fossa olecrani is broad and deeply excavated. The processus flexorius is strongly produced laterally. 5P201A, distal fragment of right humerus. Order: Anseriformes Measurements: DH: 17.61mm. Similar in size and overall morphology (Figure 4) to 1P47A (hum., r., dist.) identified by Ballmann (1987) as Anatidarum gen. sp. A. 5P16C, distal fragment of left humerus. Order: Anseriformes Measurements: DW: 32.79mm. This specimen (Figure 4) looks identical to 1P47A (hum., r., dist.) identified by Ballmann (1987) as Anatidarum gen. sp. A. Ulna 11P37A. Distal fragment of left ulna. Order: Pelecaniformes Measurements: DW: mm, DH: 6.38 mm. Similar in size and morphology (Figure 5) to 2P26A (ulna, r., dist.), identified by Ballmann (1987) as Anhinga sp. Coracoid 6P16C, right, proximal coracoid. Order: Anseriformes Measurements: AL: mm In dorsal view, the facies articularis humeralis faces dorso-laterally. The facies articularis humeralis is rounded and concave (Figure 6). Mayr and Weidig (2004) state that a cup-like facies articularis scapularis is seen in Anseriformes. There appear to be large pneumatic foramina penetrating the whole length of the processus Figure 5. 2 P26A dist. frag. r. uln. (left) and 11P37A dist. frag. l. uln. (Right) (Figure 5a, caudal view; Figure 5b, cranial view) 125

8 MICHAILIDIS GARYOUNIS SCIENTIFIC BULLETIN Figure 6. 6 P15C, prox. frag. r. cor. (Figure 6a, dorsal view, Figure 6b, ventral view). Figure 7. Figure 7a: 26P14A, phal. ungualis (left) and 105P61A phal. ungualis (right). Figures 7b and 7c: 11P103A, Pedal phalanx (Figure 7b, dorsal view; Figure 7c, plantar view). 126

9 Special Issue, 2008 FOSSIL AVES FROM AS SAHABI acrocoracoideus. Short (1969) argues that in Anseriformes there are pneumatic foramina under the brachial tuberosity, which are large in geese and small in swans. The sulcus m. supracoracoidei is excavated under the facies articularis humeralis and there appears to be no foramen nervi supracoracoidei. Phalanges 26P14A, Phalanx ungualis. Order: Falconiformes Measurements: L: mm, PW: 5.88 mm, PH: mm Ungual phalanx (Figure 7a) with a pair of canals lateral and medial to tuberculum flexorium. Absence of sulcus neurovascularis in the form of a groove. Mayr and Clarke (2003) state that Falconiiformes share a derived morphology of the pedal claws in that a sulcus neurovascularis is missing and in the presence of a pair of canals next to the tuberculum flexorium. 105P61A, Phalanx ungualis. Order: Strigiformes Measurements: PW: 5.51 mm, PH: mm Strongly curved ungual phalanx (Figure 7a) with a strong ball-shaped tuberculum flexorium. Its lateral side is excavated by a prominent groove (sulcus neurovascularis) that seems to extend throughout the osseous claw. 11 P103A, Pedal phalanx. Measurements: L: 20.36mm, PW: 8.30mm, PH: 7.74mm, DW: 6.56mm, DH: 6.58mm. This specimen is most likely the first pedal phalanx of the fourth toe of the left foot (Figure 7b and 7c). CONCLUSIONS This study has reported the discovery of additional fossil avian material from the Sahabi Formation and presented a preliminary analysis of the material. Future analysis of the material will focus on the use of comparative osteological collections as a means of attaining a more secure and detailed taxonomic allocation of the current fossil avian material. Ballmann (1987) reports the presence of a large Anatidarum gen sp. the size of modern swans with a mixture of morphological characteristics found in extant swans, geese, and Tadorninae. The importance of this find lies in that it is the only possibly European element of the avifauna which in general is most akin to the modern Ethiopian region (Ballmann, 1987). In the winter field season of February-March, 2007 at As Sahabi two distal humeri (5P201A and 5P16C) were discovered that are identical to the 1P47A distal humeral fragment identified as Anatidarum gen. sp. A. These finds reinforce the view of the presence of a European element in the As Sahabi palaeoavifauna. The current finds support the results of Ballmann s (1987) analysis of the As Sahabi avian material in that mostly water birds are represented, with a strong presence of Pelecaniiformes and Anseriformes. ACKNOWLEDGEMENTS I am indebted to Dr. Peter Ballmann for his suggestions and review of the current study, as well as for his advice concerning the study of avian evolution in general. I am grateful to Dr. Noel Boaz and all members of the ELNRP for giving me the opportunity to participate in the

10 MICHAILIDIS GARYOUNIS SCIENTIFIC BULLETIN field expedition and for allowing me to study the avian material from the Sahabi Formation. Also I would like to thank Dr. Parissis Pavlakis for his support and advice during the field season and during the preparation of this study. REFERENCES BALLMANN, P. (1987). A fossil bird fauna from the Pliocene Sahabi Formation of Libya. In: Neogene Paleontology and Geology of Sahabi (eds Boaz, N. T. et al.). New York, Liss, BAUMEL, J. J., KING, A. S., BREAZILE, J. E., EVANS H. E. and VANDEN BERGE, J. C. (eds.) (1993). Handbook of Avian Anatomy: Nomina Anatomica Avium, 2nd edition. Cambridge, Massachusetts, The Nuttall Ornithological Club, 23. BEHRENSMEYER, A.K. (1975). The taphonomy and paleoecology of Plio- Pleistocene vertebrate assemblages of Lake Rudolf, Kenya. Bulletin of the Museum of Comparative Zoology. 146 (10), MAYR, G. and WEIDIG, I. (2004). The Early Eocene bird Gallinuloides wyomingensis a stem group representative of Galliformes. Acta Palaeontologica Polonica 49 (2), MILLER, A. H. (1966). An evaluation of the fossil anhingas of Australia. The Condor 68 (4), SHORT, L.L. (1969). A new genus and species of gooselike swan from the Pliocene of Nebraska. American Museum Novitates 2369, 1-7. VRBA, E.S. (1980). The significance of bovid remains as indicators of environment and predation patterns. In: Fossils in the Making; Vertebrate Taphonomy and Paleoecology (eds A. K. Behrensmeyer and A. P. Hill). Chicago, University of Chicago Press, WALKER, C. A. and DYKE, G. (2006).New records of fossil birds of prey from the Miocene of Kenya. Historical Biology 18 (2), BOAZ, N.T. (1996). Vertebrate palaeontology and terrestrial palaeoecology of As Sahabi and Sirt Basin. In: Geology of Sirt Basin (eds M. J. Salem, A. J. Mouzughi and O. S. Hammuda), Amsterdam, Elsevier I, MAYR, G., and CLARKE, J. (2003). The deep divergences of neornithine birds: A phylogenetic analysis of morphological characters. Cladistics 19,