HINDLIMB PROPORTIONS AND LOCOMOnON OF EMUARIUS GIDJU (PATTERSON & RICH, 1987) (AYES: CASUARIIDAE)
W ALTER E. BOLES
Boles, W .Eo 199706 30: Hindlimb proportions and locomotion of Emuarius gidju (Patterson & Rich, 1987) (Ayes: Casuariidae)o Memoirs of the Queensland Museum 41(2): 235-240. Brisbane. ISSN 0079-8835.
Using proximal and distal fragments, the length of the tarsometatarsus of Emuarius gidju is estimated and compared to that of other hindlimb elements. From these proportions and other hindlimb morphology, the inferred locomotory mode of E. gidju is compared with Recent casuariids. Emuarius gidju appears to have been more cursorially adapted than Casuarius and dwarf Dromaius, suggesting at least some open habitat in the Riversleigh palaeoenviron- ment. Using the relationship between weight and least circumference of the femur and tibiotarsus in Recent birds, the weight of E. gidju is suggested to have been 19-2Ikg. D Emuarius, Aves, hind[imb, [ocomotion.
Wa[ter E. Bo[es, Austra[ian Museum, 6 Co[[ege Street, Sydney NSW 2000, Austra[ia; received 4 November 1996.
Emus, Dromaius (Dromaiinae), form a promi- MATERIALS AND METHODS nent element of Australia's avifauna. The closely related cassowaries, Casuarius (Casuariinae), are Osteological tenninology follows Baumel & more restricted in distribution. These two groups Witmer (1993). Measurements were made with occupy very different modem habitats, and loco- vernier calipers accurate to 0.05mm and rounded motory adaptations correlated with these differ- to the nearest 0.1 mm. Institutional acronyms are ent habitats are obvious in the relative pro- AM (Australian Museum), QM (Queensland Mu- portions of the lower limb bones. Because of the seum) and SAM (South Australian Museum). relationship between habitat and limb propor- The type specimen of E. gidju (SAMP26779) tions, fossil emus and cassowariesare potentially is an associated distal tibiotarsal fragment, prox- good palaeoenvironmental indicators. Emus have imal tarsometatarsus including much most of the a better fossil record (Patterson & Rich, 1987), shaft, and complete set of pedal phalanges than cassowaries (Vickers-Rich, 1991). Patter- (Patterson & Rich, 1987) and numerous speci- son & Rich ( 1987) described lower limb elements mens of Emuarius are known from Riversleigh from the Miocene of central Australian as a small (Table 1). emu, Dromaius gidju. Boles ( 1991) erected To compare changes in relative proportions of Emuarius for this speciesand considered it closer the casuariid hindlimb, the following measures to emus than cassowaries, but nearer their dichot- were calculated for the bone lengths of the 3 omy than any other described taxon. extant species of Casuarius and the I living and The type material of Emuarius gidju is part of 2 recently extinct dwarf species of Dromaius: the Kutjamarpu Local Fauna, recovered from the TBTiFMR= Tibiotarsus x 100 Leaf Locality (UCMP V-6213) on the E shore of Femur Lake Ngapakaldi in the E Lake Eyre Sub-Basin, TMT4MR = Tarsometatarsus xI 00 South Australia. Much E. gidju material occurs Femur . at Riversleigh NW Queensland. Archer et al. TBT/rMT = Tibiotarsus xI 00 . (1989, 1994) considered the Riversleigh pal- Tarsometatarsus aeohabitat as rainforest, based on mammal re- Because the purpose was to find general, rather mains. than detailed, directions of change, measure- This paper is to 1) estimate the lower limb ments were taken from the literature (Table 2) and proportions of E. gidju; 2) compare these to mod- rounded to the nearest mm. Means were used em emus and cassowaries and, by implication, to where available. The sample sizes were often their style of locomotion; 3) make an initial esti- small, sometimes comprising single individuals. mate of the weight of E. gidju; and 4) interpret the Predicted body weight of Emuarius gidju was possible palaeohabitat at Riversleigh where E. calculated (Campbell & Marcus, 1991) from AM gidju occurs. f78585 (near complete femur) and QMFI6827 236 MEMOIRS OF THE QUEENSLAND MUSEUM
(distal tibiotarsal fragment). Tape was wrapped around the bones at their least circumferences, marked at the point of overlap, straightened and measured with calipers. These results were used in the equation loglo(weight)=a.loglo(circumfer- ence)+b, where the values of a (slope) and b (interecept) were those determined by Campbell & Marcus (1991) for all birds for the respective elements (femur: a=O.411, b=-0.065; tibiotarsus: a=2.424, b=O.O76).
RESULTS
Increased cursoriality in these birds is associ- ated with an increase in the lengths of the tibio- tarsus and tarsometatarsus relative to that of the femur (Howell, 1944). Relative proportions of the hind limb contributions of the long bones in Casuarius, Dromaius and Emuarius (Fig. 2) show that that of the tibiotarsus remains more or less consistent in all taxa; that of the femur de- creaseswith increased cursoriality, whereas that of the tarsometatarsusincreases. The relationship between these changes is consistent for Recent species: TBT/FMR = 0.45 [TMT/FMR] + 113; r=0.84. These changes appear independent of overall size when compared between genera, but within genera the smaller members have the greater TBT/TMT and smaller TMT/FMR. The TBT/FMR in Casuarius remains constant. It sug- gests from these figures that the smaller species in each genus are the least cursorial members. Using a tarsometatarsal length of 340mm and a The Kutjamarpu femur (AMF78585; Boles, femoral length of 198mm, gives a TMT/FMR of 1991) of E. gidju is 194mm long, which, because 172, greater than that of any Recent ca~uariid of abrasion, is a few mm less than its original except Dromaius novaehollandiae. Using these length, of about 198mm and very likely not values with the regression equation for the family 200mm. Complete tibiotarsi are unknown for E. (Fig. 4) gives a predicted TBT/FMR of 190, gidju (Table I ). Nevertheless, it is possible to which corresponds to a tibiotarsal length of predict the size and relative proportions of this 376mm. These 3 values give a combined length bone from other hind limb elements. Tar- of 916mm, virtually the same as the hindlimb of sometatarsi are represented by the holotypical Casuarius casuarius, although the proportional proximal end and shaft, and several distal frag- ments. An estimate of the tarsometatarsal length contribution of each bone to this length is differ- was made by using the proximal end and shaft and ent (Fig. 2). a distal fragment. The proximal tarsometatarsal This figure must be used with caution. The fragment is 276mm long; the longest edge of its fragments on which it is based represent different shaft is straight and shows no evidence of flaring individuals from different localities. As such, outward to trochlea metatarsi II. The distal piece there are several sourcesofpotentialIy significant is 64mm long; the small portion of shaft remain- variation between components. Geographical ing is just proximal to the flaring of trochlea variation may not have been of major importance; metatarsi II. Becausethere is little, if any, overlap living D. novaehollandiae exhibits little differen- between these two pieces, minimum length of the tiation across its range. There is much greater tarsometatarsusis 340mm (Fig. 3). size variation across this species' chronological HINDLIMB PROPORTIONS OF EMUAR1US G1DJU 237
than any known species of emu (illustrated in Patterson & Rich, 1987). In emus, phalanx ungualis of digit III is longer than that of digit 11, whereas in cassowaries it is reversed, with phalanx ungualis of digit II ex- tended into a long spike several times the length of phalanx un- gualis of digit III. Emuarius does not have phalanx ungualis of digit II developed into a spike, but it is still longer than that of digit III. Cassowaries have digits II and IV relatively long com- pared with digit III (ratios of 11:111and IV:111, respectively, without phalanges unguales 0.82, 0.76). Both are substan- FIG. I. Leaf Locality femur of Emuarius gidju compared with femora of tially reduced in relative length Recent casuariids, in cranial view. From left, Casuarills CasllarillS, C. in emus (ratios as above -0.55, bennettii, Emuarius gidju, Dromaius novaehollandiae and D. ater. 0.63). Both digits II and IV of Emuarius are comparatively range, with mainland fossils usually smaller than longer than those in emus (digit IV to a lesser modern birds. Patterson & Rich ( 1987) suggested degree ), but not to the extent seen in cassowaries that it 'may have been at anyone time in the (0.57, 0.68). Patterson & Rich ( 1987) suggested Pleistocene both larger or smaller than at that the reduction of digit IV and particularly of present'. Considerable intraspecific variation in digit II in E. gidju, compared with the highly living D. novaeho/landiae is probably related to cursorial v. novaehollandiae, appears to parallel age and sex, as well as individual differences similar reductions in other groups of terrestrial (Marchant & Higgins, 1990). For example, birds and mammals. among 22 modern specimens, Patterson & Rich In comparison with the pedal phalanges of cas- ( 1987) found a range in tarsometatarsal length of sowaries, those of emus are dorsoplantarly com- 332-422mm (mean 383mm; s.d. 18.0). pressed. Emuarius is somewhat intermediate, Miller ( 1963) described Dromaius ocypus from with its phalanges substantially more the middle to late Pliocene Palankarinna Local dorsoplantarly compressed than those of casso- Fauna from Lake Palankarinna, northern South waries, but less compressed than (but more sim- Australia. This species was intermediate in size ilar to) the condition in emus. between Emuarius gidju and living Dromaius Campbell & Marcus ( 1991) stated 'the least novaeho/landiae. The tarsometatarsus of D. OC- shaft circumference of either [femur or tibiotar- ypus is markedly shorter relative to its width than sus] can be a reliable indicator of the weight of a is that of D. novaeho/landiae, but less so than in fossil bird'. From their equation, and measure- Casuarius. Vickers-Rich ( 1991) interpreted this ments of E. gidju bones, predicted weights of this as suggesting a less cursorial lifestyle for D. species were 21 kg based on the femur and 19k9 ocypus than for D. novaeho/landiae. Because based on the tibiotarsus. The least circumference Patterson & Rich ( 1987) did not give comparative of the tibiotarsus is almost always at or distal to figures for relative widths, it is difficult to quan- the midpoint of the bone; in most birds it is in the titatively compare E. gidju with these species. distal third (Campbell & Marcus 1991 ). No tibio- Visually, Emuarius appears to be proportionally tarsal specimen of E. gidju is complete, although thinner for its length than is D. ocypus, but not to the length of that measured is about a third of the the degree of D. novaeho/landiae . predicted length for this bone. It is possible that Patterson & Rich ( 1987) pointed out that, al- the least circumference occurs on the missing though, the foot of E. gidju is more like that of section of tibotarsus, and the value given here emus than cassowaries, it is more cassowary-like would have to be adjusted. The predicted 238 MEMOIRS OF THE QUEENSLAND MUSEUM
TABLE 2. Measurements (mm) and measures of relallive proponions of watercourses. It was not until at hindlimb bones of Recent emus and cassowaries and of Emuariusgidju. least the middle Miocene (c. 15 For calculation of predicted measurements of E. gidju and of measuresof mya) that drying of the climate relative proportions, see text. -began and open habitats started
TBT/ITMT I TBT/ to appear on a large scale.
Species I FMR I TBT I TMT Source FMR VFMR TMT I There is no evidence of grass- lands before the end of the late Dromaius Patterson & 203 401 383 198 189 105 Miocene to Pliocene (Martin, novaehollandiae Rich, 1987 this volume). Dromaius Morgan& 164 293 234 125 The graviportal locomotion baudinianus Sutton,1928 1791143 of Casuarius is associated Morgan& Dromaius ater 178 331 274 121 with movement through the Sutton.1928 .1861.154 dense vegetation of the Aus- C.asuarius 236 388 306 IRichetal,,19881164 tralo-Papuan rainforests. In- unal>1Jendicularus 130 1127 creased cursoriality seems Casuarius 232 casuarius 384 300 IRichelal",19881166 128 correlated with the appearance 1291 of more open habitat, in which Casuariusbe.!!E!-!!iJ ?'1 365 I 229 !Richetal..19881165 I1041 li2J sustained running could take Emuariusgidju 198 I 376 I 340 I Thispaper , 1901172 1 1II I place. (While able to run if required, cassowaries have weights from the two bones are close enough to limited opportunities in such habitat to work up give an acceptable first estimate for E. gidju. and sustain a reasonable degree of speed because sufficiently open areas are restricted. ) Morpho- DISCUSSION logical correlates with cursoriality include pro- portional lengthening of the tibiotarsus and Throughout the early Tertiary, much of Aus- tarsometatarsus, and a reduction in the relative tralia was covered in closed forest, and the cli- size of digit II. Conditions between the extremes mate was considerably more humid than at of the states found in Casuarius and Dromaius present (Frakes et al., 1987). The dominant veg- are suggestive of levels of cursorial ability inter- etation type over much of the continent was mediate between theirs, although at what point rainforest. Nothofagus-dominated rainforest covered the Lachlan River valley during the late along the scale cannot be determined. This, in Eocene to late Oligocene-early Miocene (Martin, turn, suggests the possibility that the amount of 1987). Even where closed forests were not pres- open habitat might be also somewhere between ent, gallery rainforest probably occurred along that available to cassowaries and emus. TARSOMETATARSUS TIBIOTARSUS FEMUR Casuarius .IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII bennetti IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII ~
Casuarius casuarius
Emuarius gidiu
Dromaius aler
Dromaius novaehollandiae
FIG. 2. Comparative proportions of bones in the hindlimbs of Emuarius gidju, two species of Casuarius and t:-vo species of Dromaius. Note that while the tibiotarsal proportion remains relatively constant, the proportIon comprising the femur decreasesas that of the tarsometatarsus increases.
~ HINDLIMB PROPORTIONS OF EMUARIUS GIDJU 239
locomotion (Prange et al., 1979), more closely resembled Casuarius. There are alternative explanations that accom- modate both the cursorial hindlimb proportions of E. gidju and the absence of open spaces. One possibility is that the ground cover of the rain forests was sufficiently open for cursorial ani- mals to move rapidly without obstruction. For example, modern Nothofagus forests are fre- quently open below the canopy, without the dense understory of some other rain forest types (pers. obs.). Neville Pledge (pers. comm.) suggested that a situation may have existed similar to that which occurred on Kangaroo Island when the dwarf emu Dromaius baudinianus was extant. Much of the island's vegetation was very thick and would have prevented rapid passage of a large animal such as the emu. Large mammals, however , forced runways through the vegetation, permit- ting them to move with comparable, albeit re- stricted, ease. The emus apparently took advantage of these runways for their own prog- ress. Likewise, the large mammals known from FIG. 3. 'Combined' length of Leaf Locality proximal Riversleigh may have opened similar pathways tarsometatarsus and Riversleigh distal tarsometatar- through the thick undergrowth, which could have sus compared with tarsometatarsi of Recent been used by E. gidju. Nonetheless, D. casuariids, in cranial view. From left, Dromaius baudinianus was also noted for being very fast novaehollandiae,D. ater, Emuarius gidju, Casuarius and virtually uncapturable in open areas. casuarius and C. bennettii. A small Miocene dromaiid from Alcoota, NT, Casuarius has been considered more primitive is known from 2 phalanges and 3 unassociated than Dromaius on the basis of distribution, habi- trochleae (Patterson & Rich, 1987). These are of tat preferences and hindlimb. Schodde & Calaby comparable size with E. gidju. There are slight ( 1972) and Schodde ( 1982) cited the cassowaries differences in phalangeal morphology, and as elements of the Tumbunan avifauna, which Patterson & Rich ( 1987) retained these speci- represents the earliest lineages of extant Aus- mens as Dromaius sp. indet. until more complete tralo-Papua.n birds. The emus were placed by material is available. The Alcoota palaeohabitat Schodde (1982) in the autochthonous Eyrean has been interpreted as a lake, bordered by sedge fauna, which evolved in response to the opening or grassland, grading to woodland and gully for- of the Australian habitat. Boles ( 1991) consid- est (Murray & Megirian, 1992). This is a different ered Emuarius to be closer to the dichotomy of environment than that interpreted for the older cassowaries and emus than any other known Riversleigh deposits. Even if the Alcoota taxon, but too cursorially adapted and Dromaius- dromaiid proves to be E. gidju, it would have like to have been the common ancestor. II appears limited relevance to reconstructing the to mark in the Casuariidae a stage in the transition Riversleigh habitats because of the age differ- from a graviportal to a more cursorial locomo- encesof the deposits. It would, however. suggest tion. Although some characters of the hindlimb that E. gidju was preadapted for the more open of E. gidju are more similar to either Casuarius Alcoota environment. or Dromaius, many are intermediate between liv- Models of this species' locomotory mode de- ing members of these genera (Boles, 1991 ). Boles pend on extrapolations from living, non-conge- (1991) drew attention to the fact that the lower neric relatives. These are speculative, and must limb bones were more similar to those of be treated as such, while palaeoenvironmental Dromaius, whereas the femur, whose proportions reconstructions based on them require an even are more dependent on the bird's mass than its greater degree of caution. 240 MEMOIRS OF THE QUEENSLAND MUSEUM
y BOLES, W .E. 1991. Revision of Dromaius gidju Patter- son & Rich, 1987, with a reassessment of its generic position. Natural History Museum of Los Angeles County Science Series 36: 195-208. x / w O CAMPBELL, K.E., JR. & MARCUS, L. 1991. The ~ relationship of hindlimb bone dimensions to body -' .. weight in birds. Natural History Museum of Los m ~ Angeles County Science Series 36: 395-412. 0 ~ FRAKES, L.A., McGOWRAN, B. & BOWLER, J.M. 0 ~ w 1987. Evolution of Australian environments. pp. ... 1-16. In Dyne,G.R. & Walton, D.W. (eds), Fauna of Australia vol. 1A. General articles. (Australian Government Publishing Service: Canberra). HOWELL, A.B. 1944. Speed in animals. Their special- --"' "' .,' .,'- "' '0' ization for running and leaping. (University of FEMOROMETATARSALINDEX Chicago Press: Chicago). MARCHANT, S. & HIGGINS, P.J. (coordinators). FIG. 4. Relationship ofTMT/FMR and TBT/FMR of 1990. Handbook of Australian, New Zealand and Recent species of Casuarius (open circles} and .Antarctic birds, I. (OxforcPUniversity Press: Syd- Dromaius (closed circles}. Species numbered as fol- ney). lows: 1. Casuarius bennetti; 2, C. casuarius; 3. C. MARTIN, H.A. 1987. Cainozoic history of the vegeta- unappendiculatus; 4, D. baudinianus; 5, D. ater; 6, tion and climate of the Lachlan Ri ver Region, New D. novaehollandiae. Regression line is TBT/FMR = South Wales. Proceedings of the Linnean. Society 0.45 [TMT/FMR] + 113; r=O.84. The fine vertical line of New South Wales 19: 213-257. represents the intersection with this line of the TMT/FMR ( 172} for Emuarius gidju as calculated in MILLER, A.H. 1963. Fossil ratite birds of the late Tertiary of South Australia. Records of the South the text. Predicted TBT/FMR is 190. Australian Museum 14: 413-420. ACKNOWLEDGEMENTS MORGAN, A.M. & SUTTON, J. 1928. A critical de- scription of some recently discovered bones of the In addition to acknowledgements in Boles extinct Kangaroo Island Emu (Dromaius (1991) I thank Neville Pledge for discussion on diemenianus). Emu 28: 1-19. the Kangaroo Island habitat, Lynne Ho and Mau- MURRAY,P.&MEG.IRIAN,D.1992.Continuityand rice Ortega for figures, and Anna Gillespie for contrast in middle and late Miocene vertebrate communities from the Northern Territory. The information on E. gidju. The Riversleigh mate- Beagle 9: 915-218. rial was collected via an ARC Programme Grant PATTERSON, C. & P.V. RICH. 1987. The fossil his- to M. Archer; a grant from the Department of tory of the emus, Dromaius (Aves: Dromaiinae). Arts, Sport, the Environment, Tourism and Ter- Records of the South Australian Museum 21 : ritories to M. Archer, S. Hand and H. Godthelp; 85-117. support from the University of New South Wales; PRANGE,H.D.,ANDERSON,J.F.&RAHN,H.1979. a grant from the National Estate Programme Scaling of skeletal mass to body mass in birds and Grants Scheme to M. Archer and A. Bartholomai; mammals. American Naturalist 113: 103-122. and grants in aid to the Riversleigh Research SCHODDE, R. 1982. Origin, adaptation and evolution Project from Wang Australia Pty Ltd, ICI Aus- of birds in arid Australia. pp. 191-224. In Barker, tralia and the Australian Geographic Society. W.R. &Greenslade, P.J.M. (eds), Evolution of the flora and fauna of arid Australia. (Peacock Publi- REFERENCES cations: Frewville). SCHODDE, R. & CALABY, J.H. 1972. The biogeog- ARCHER. M.. HAND, S.1. & GODTHELP, H. 1994. raphy of the Australo-Papuan bird and mammal Riversleigh. 2nd ed. (Reed: Sydney). faunas in relation to Torres Strait. pp. 257-300. In ARCHER. M.. HAND. S.. GODTHELP. H. & D. Walker, D. (ed.), Bridge and barrier: the natural MEGIRIAN. 1989. Fossil mammals of and cultural heritage of Torres Strait. (Australian Riversleigh, northwestern Queensland: prelimi- National University Press: Canberra). nary overview of biostratigraphy, correlation and VICKERS-RICH, P. 1991. The Mesozoic and Tertiary environmental change. Australian Zoologist 25: history of birds on the Australian plate. pp. 721- 29-65. 808. In Vickers-Rich, P.V., Monaghan, J.M., BAUMEL, 1.1. & L.M. WITMER. 1993. Osteologia. Baird, R.F. & Rich, T.H. (eds), Vertebrate pal- Publications of the NuttaIl Ornithological Club aeontology of Australasia. (Pioneer Design stu- 23: 45-132. dio: Melbourne).