A new songbird (Aves: Passeriformes) from the mid-Cenozoic of ...

A new songbird (Aves: Passeriformes) from the mid. Cenozoic of Riversleigh, northwestern Queensland WALTER E. BOLES BOLES, W.E., 2006. A new songbird (Aves: Passeriformes) from the mid-Cenozoic of Riversleigh, northwestern Queensland. Alcheringa Special Issue 1, 31-37. ISBN 0 9757 5 7. The new genus and species of songbird (Passeriformes) Corvitalusoides grandiculus is described from mid-Cenozoic deposits at Riversleigh, northwestern Queensland on the basis of a distal tibiotarsal fragment. The size of the bone indicates a bird larger than most passerines other than lyrebirds (Menuridae) and some ravens (Corvidae). It cannot be allocated with certainty to any passerine group, so is here regarded as family incertae sedis. This increases the number of named Australian Oligo-Miocene songbirds to four. Walter E. Boles [[email protected]], Terrestrial Zoology Section, Australian Museum, 6 College Street, Sydney, NSW 2010, and School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW 2052; submitted 3.8.2005, accepted 21.8.2006. Key words: Aves, Passeriformes, songbird, Riversleigh, Cenozoic.

SONGBIRDS OR PASSERINES (Order Passeriformes) comprise the most speciose order of living birds. Despite this, their fossil record is poor compared with that of many other groups of birds. Most named palaeospecies are PlioPleistocene, reflecting in part the paucity of passerine material from the Miocene and earlier, as well as the comparatively few studies that have been carried out on them. One of the most productive sites for pre-Pliocene passerines is the Riversleigh World Heritage Area, northwestern Queensland, which has sites ranging from late Oligocene to late Miocene. Many passerine bones have been recovered (Boles 1995a, 2000), representing four families thus far, with three named species: the lyrebird Menura tyawanoides Boles, 1995a (Menuridae); logrunner Orthonyx kaldowinyeri Boles, 1993 (Orthonychidae); and oriolid Longmornis robustirostrata Boles, 1999 (Oriolidae); see also Boles (2005) regarding indeterminate specimens of Meliphagidae. Described here is a fourth named species, based on a distal fragment of a tibiotarsus. This specimen is within the size range of species of Corvus Linnaeus, 1758 (ravens and ISBN 0 9757894 5 7/2006/7

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crows), thus matching or exceeding in size all living other Australian passerines except for species of Menura Latham, 1802 (lyrebirds).

Geology and geographic setting

The fossil described here was collected from the Riversleigh deposits, which are 5 km west of the Riversleigh homestead (19°02’ S, 138°45’ E), 200 km north of Mt Isa, northwestern Queensland, where they occur as an outcrop of Cenozoic limestone overlying the Cambrian Thorntonia Limestone. There are now over 200 named OligoMiocene sites at Riversleigh. An informal system of grouping has been used (Systems A-C). These systems are ‘regionally clustered sites that appear to be superpositionally-related (differing in age but not significantly in position) and/or space-related (spatially isolated but approximately contemporaneous)’ (Archer et al. 1989). The principal accumulations are thought to have occurred in several episodes involving large lakes, shallow pools and cave deposits. Current understanding of the age of these sites is taken from Creaser (1997); other birds represented at these sites are taken from Boles (1995a, 1997a, 2000). Dirks Tower Site is in the northern sections of the D-Site Plateau. The

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ages are still unclear, but may be System A (late Oligocene) or B (early Miocene). Other birds recovered from Dirk’s Towers Site are the small dromaiid Emuarius gidju (Patterson & Rich, 1987) and passerines.

Methods

The specimen (Fig. 1) described here was collected during fieldwork at Riversleigh directed by M. Archer, University of New South Wales, and is registered into the Palaeontology Collection of the Queensland Museum, Brisbane. Comparative specimens were measured in the collections of the Australian Museum, Sydney; Australian National Wildlife Collection, Canberra; Museum of Victoria, Melbourne; and South Australian Museum, Adelaide. Measurements follow the methods illustrated by Steadman (1980) and were made with digital calipers accurate to 0.01 mm and rounded to the nearest 0.1 mm. Additional measurements of Corvidae species were taken from Tomek & Bocheñski (2000). Terminology of bones largely follows Baumel & Witmer (1993).

Systematic palaeontology Order PASSERIFORMES Linnaeus, 1758 Ordinal identification is made by the following suite of characters (modified from Boles 1997b). The lateral and medial margins of the shaft (in anterior view) are parallel, curving neither laterally or medially, other than a slight flaring, usually on medial side, where they meet the condyli; both condyli are directed anteroposteriorly, are parallel with each other and with the midline of the shaft, and have their outer rims lateral and medial to the respective borders of the shaft (i.e. the shaft margins are not confluent with the outer borders of the condyli, instead meeting them at about their lateromedial midpoints). The incisura intercondylaris is centred between the condyli near the midline of the shaft and is of moderate depth and width; the pons supratendineus is moderately strong and more or less horizontal. A moderately

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prominent tuberositas retinaculi extensoris lateralis extends proximal to condylus lateralis and lateral to the pons supratendineus. The tuberculum retinaculi m. fibularis and tuberositas retinaculi extensoris medialis are well-marked protuberances on the lateral and medial shaft margins, respectively. The trochlea cartilaginis tibialis is of moderate depth. Family INCERTAE SEDIS At this time it is not possible to confidently allocate the fossil to a known family in the order. In size it is matched or exceeded only by members of the largest living passerines, species of Corvus (Corvidae: ravens and crows) and Menura (Menuridae: lyrebirds); both groups are represented in Australia. The fossil can be differentiated from these songbird taxa, as well as from the next largest Australian form Strepera Lesson, 1830 (Cracticidae: currawongs), which approaches the fossil in size. In Fig. 2, the sizes of the distal tibiotarsus of the fossil and representatives of these families are compared. Although living lyrebirds are larger, the specimen may be comparable in size to that of the fossil M. tyawanoides (the lack of common elements precludes a direct comparison); however, morphological differences between QMF36341 and living lyrebirds preclude their being confamilial. In Menura, the shaft broadens distally more markedly than in the fossil or other passerines, mostly on the medial side. Overall, the distal end is proportionally much broader than the fossil, caused by a wider incisura intercondylaris and the more medial position of the condylus medialis (although the condylus medialis is beyond the margin of the main shaft body by virtue of its distal flaring where the shaft margin meets the condylus at its midpoint). In Menura, the elongate tuberculum retinaculi m. fibularis is distally located, that is, less than its own length from the condylus lateralis; the tuberositas retinaculi extensoris medialis is low and rather weakly produced. The pons supratendineus is proportionally broader than in the fossil; the tuberositas retinaculi extensoris lateralis extends proximally, overlapping the

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NEW SONGBIRD FROM RIVERSLEIGH

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distal half of the tuberositas retinaculi extensoris morphology superficially resembles that of this medialis. The condylus lateralis is more genus. The corvids differ by having a rather low anteroposteriorly oblong (lateral view); the tuberculum retinaculi m. fibularis and the condylus medialis is half circular, rounded on its tuberositas retinaculi extensoris medialis low and distal margin, flattened on its proximal one (medial weakly produced. The latter structure is view). In anterior view, both condyli, particularly positioned relatively more proximally than in the the condylus medialis, project further distally fossil. The tuberositas retinaculi extensoris relative to the distal margin of the incisura lateralis extends only a very short distance intercondylaris than in the fossil. In anterior proximally. The condyli extend equal distances view, the profile of the distal margin of the incisura proximally and distally and are circular in side intercondylaris is asymmetrical, with the lateral views; the posterior rims project only slightly, half angling distolaterally from near the midpoint joining the shaft smoothly; the anterior rims to the distal end of the condylus lateralis and project a short distance, joining the shaft at 90°; the medial half excavated proximally. In these the condylus lateralis is thinner than in the fossil, characters, Menura differs from other passerine being about the same width as the condylus groups. medialis. The incisura intercondylaris New Riversleigh songbird Boles CAVEPS is The fossil tibiotarsus is similar in size to proportionally somewhat wider than in the fossil. that of the Australian Raven Corvus coronoides The Grey Currawong Strepera versicolor Figure Vigors1.& Horsfield, 1827, and its overall Latham, 1802, the largest member of this genus,

Fig. 1. Corvitalusoides grandiculus, QM F36341 (holotype), distal right tibiotarsus. A, anterior view; B, posterior view; C, lateral view; D, medial view; cl, condylus lateralis; cm, condylus medialis; trem, tuberositas retinaculi extensorius medialis; tlem, tuberositas retinaculi extensorius lateralis; trmf, tuberculum retinaculi m. fibularis. Bar equals 10 mm.

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has a tibiotarsus that approaches the fossil in size. The tibiotarsus of Strepera differs by having the end proportionally broader and squatter, a result of its proportionally shorter condyli. The tuberositas retinaculi extensoris medialis is situated more proximally relative to the condyli medialis than in the fossil. It and the tuberositas retinaculi extensoris lateralis are produced as small points; the tuberculum retinaculi m. fibularis low. The condyli lateralis and medialis (lateral and medial views, respectively) are half circular, rounded distally; the posterior rims project slightly (more so than in Corvus); the anterior rims project further, their proximal margins horizontal and flat, joining the shaft at 90°. The distal margin of the incisura intercondylaris (in anterior view) is uneven, with the medial half more excavated. Because the fossil can be distinguished from these other taxa, it is placed here in its own genus.

shaft at a distance from the condylus medialis about equal to the height of the condylus.

Corvitalusoides gen. nov.

Description. Measurements: length as preserved 27.5 mm (shaft ca. 20 mm), distal width ca. 9.4 mm, anteroposterior depth of condylus lateralis 9.4 mm. The sulcus extensorius occupies the lateral half of the anterior face such that its medial border is at about the proximodistal midline of the shaft; both it and the pons supratendineus canalis are centred over the lateral half of the incisura intercondylaris. The pons is horizontal and pinched at its midpoint. The tuberculum retinaculi m. fibularis is low; the tuberositas retinaculi extensoris medialis is well-developed as a medially directed flange that is flattened on its anterior face and rounded on its medial margin. The tuberositas retinaculi extensoris lateralis extends proximally along the lateral margin of the sulcus extensorius to about halfway between the tuberculum and tuberositas medialis. In anterior view, the condylus lateralis is 1.5-2 x broader than the condylus medialis and does not project as far distally. In lateral view, the condylus lateralis is circular on its posterior half and somewhat oblong on its anterior half with the distal margin angled anteroproximally; the distal and anterior rims are thickened and raised. In medial view, the condylus medialis is

Etymology. Derived from corvus, raven (L.), talus, ankle (L.) and oides, like or similar to (L.), in reference to the similarities of the fossil’s morphology to species to that of the genus Corvus. The name is masculine. Type species. Corvitalusoides grandiculus, only known member of genus. Diagnosis. Differs from other passerines of similar size by the following combination of characters of the distal tibiotarsus: the width of the distal end is approximately equal to the distal depth of the condylus lateralis; the condyli are unequal in width, with the condylus lateralis substantially broader than the condylus medialis; both join the anterior face of the shaft at about 90° angles; the condylus lateralis is anteriorly oblong and posteriorly circular (lateral view); the tuberositas retinaculi extensoris lateralis extends proximally to the midpoint between the tuberculum retinaculi m. fibularis and tuberositas retinaculi extensoris medialis; the tuberositas retinaculi extensoris medialis is produced as flattened flange and is located on the

Corvitalusoides grandiculus sp. nov. (Figs 1-2) Etymology. Grandiculus, rather large (L.), alluding to the size of the fossil relative to that of most Passeriformes. Holotype. QM F36341, distal right tibiotarsus, broken through the shaft and with the condylus medialis missing its anterior section and having its posterior rim slightly abraded. Type locality, local fauna and age. Dirk’s Towers Site (System A or B) , Riversleigh, northwestern Queensland, Australia; Dirks Towers Local Fauna; late Oligocene or early Miocene (ca. 25-15 mya). Diagnosis. As for genus, by monotypy.

New Riversleigh songbird

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Boles

CAVEPS


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Fig. 2. Size of holotype QM F36341 compared with distal tibiotarsi of large Australian passerine taxa and selected extralimital species based on width of distal end and depth of condylus lateralis (mm). Symbols used: species listed in approximate size sequence within respective genus from smallest to largest: X – QM F36341, Corvitalusoides grandiculus; circle – currawongs (Cracticidae: Strepera graculina, fuliginosa, versicolor); square – ravens and crows (Corvidae: Corvus frugilegus, brachyrhynchus, corone, orru, mellori, coronoides, cryptoleucos, corax); diamond – lyrebirds (Menuridae: Menura alberti, novaehollandiae).

rounded over the preserved posterior and distal margins. The distal margin of the incisura intercondylaris is more or less straight, angling slightly proximally towards the condylus medialis.

Discussion

The earliest reported Passeriformes are from the early Eocene of Murgon, Queensland, Australia (Boles 1995b, 1997b); no finer taxonomic resolution of the fragmentary specimens is possible. The order is represented in Europe by the early Oligocene (Mayr & Manegold 2004) and songbird fossils are not uncommon by the Miocene (Mourer-Chauviré et al. 1989; Cheneval 2000). These include taxa within the crown-group of Eupasseres (oscines plus suboscines), as well as others with a primitive morphology otherwise known only from the basal Acanthisittidae of New Zealand among living taxa; it is interpreted that these are outside the Eupasseres (Manegold

et al. 2004). Mayr & Manegold (2004) speculated that Passeriformes appeared in Europe, unrepresented there during the Eocene, around the Eocene/Oligocene transition, at the ‘Grande Coupure’, a major faunistic break apparently related to significant environmental changes, accompanied by a major isotopic excursion (Prothero 1994, Hooker et al. 2004). The Australian record of the Order from the late Oligocene onwards is plentiful but thus far all appear referrable to the Eupasseres and are dominated by the suborder Passeri (Oscines). Unfortunately, further interpretation of the history of the Passeriformes in Australia is impeded by the substantial gap in the fossil record between the early Eocene and the late Oligocene (Boles 2006). The named species and many fossils still awaiting detailed study demonstrate that Australia was a major site of songbird diversity 17 in the mid-Cenozoic. With the exception of

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Corvitalusoides grandiculus, the named passerines published to date have been allocated to living families and often extant genera. Corvitalusoides cannot be assigned to a modern family, but it indicates the presence of largebodied passerines other than those groups occurring in Australia today. With the revelation that the major lineages of oscine passerines (Corvida & Passerida sensu Sibley & Ahlquist 1990) originated in Australia (Barker et al. 2000, 2004; Ericson et al. 2000, 2003), either (or both) might be expected at Riversleigh. It is not possible a priori to predict to which group Corvitalusoides belongs. However, the Corvida (sensu Sibley & Ahlquist 1990) greatly outnumber the Passerida, particularly among endemic Australian or Australasian taxa and in the fossil songbirds thus far identified. In addition to adding to the number of known Cenozoic passerines in Australia, this study also demonstrates that, contrary to the commonly expressed maxim, there are sufficient osteological differences among songbird taxa to reward workers who look for them.

Acknowledgments

The Australian Museum for provided a venue in which to work and funds to support this research. The Riversleigh material was collected via various grants to M. Archer and the Riversleigh Research Project. The collection staff of the respective museums permitted me to measure specimens under their care. I thank the referees, Richard Holdaway and, particularly, Trevor Worthy for their useful criticisms and suggestions. References

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