# A new method for estimating locomotion type in large ground birds

Delphine Angst, Eric Buffetaut, Christophe Lécuyer, Romain Amiot

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Delphine Angst, Eric Buffetaut, Christophe Lécuyer, Romain Amiot. A new method for estimating locomotion type in large ground birds. Palaeontology, 2016, 59 (2), pp.217-223. 10.1111/pala.12224. hal-02994723

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[Palaeontology, Vol. 59, Part 2, 2016, pp. 217–223]

# A NEW METHOD FOR ESTIMATING LOCOMOTION TYPE IN LARGE GROUND BIRDS

by DELPHINE ANGST<fnref n="1" />,<fnref n="2" />, ERIC BUFFETAUT<fnref n="3" />, CHRISTOPHE LECUYER<fnref n="1" />,<fnref n="4" /> and ROMAIN AMIOT<fnref n="1" />

Typescript received 4 October 2015; accepted in revised form 11 November 2015

**Abstract:** Estimating the locomotion type of fossil ground birds is necessary for a better understanding of their ecology. Until now, only one method has allowed us to estimate the locomotion of fossil ground birds, but its application is complicated in the majority of fossil cases because it requires data from the three bones from the same hindlimb of one individual. Here, we propose a new method using only the maximum length and minimum width of the tarsometatarsus to estimate the locomotion of these fossil birds. This method is easy to apply and better distinguishes the intermediate cases between graviportal (walking) and cursorial (running) birds. This

study shows that the species of large ground birds of the families Gastornithidae and Brontornithidae were all graviportal, probably because of their large body mass. More unexpectedly, it also shows that some Phorusrhacidae (e.g. *Paraphysornis*), usually described as cursorial birds, were in fact graviportal, probably because of their considerable body mass. All these new data about locomotion provide a better understanding of the ecology of fossil ground birds.

**Key words:** locomotion, fossil birds, ecology, Brontornithidae, Phorusrhacidae, Gastornithidae.

LOCOMOTION type is an important factor in the ecology of living organisms. It conditions not only food access, but also relationships between organisms in an ecosystem. Most often in the fossil record, the locomotion categories (terrestrial, aquatic, semi-aquatic, aerial) are usually determined relatively easily using limb anatomy. However, finer information about motion speed or endurance capacity is often difficult to obtain. To better frame the locomotion concepts in a continental context, two major types of terrestrial locomotion were defined, cursorial and graviportal, between which all intermediates are possible (Gregory 1912; Osborn 1934; Smith and Savage 1956; Coombs 1978; Stein and Casinos 1997; Carrano 1999; Murray and Vickers-Rich 2004). The cursorial locomotion type corresponds to a rapid and prolonged movement, as exemplified by horses, whereas the graviportal locomotion type characterizes terrestrial animals having a slow locomotion, with occasional running ability, as exemplified, for example, by elephants. Among the large terrestrial modern birds, we observe exactly the same division; ostriches represent cursorial birds, for example, but the case of graviportal birds is more problematic because no birds with this type of locomotion currently exist. How-

ever, among the sub-fossil birds that went extinct very recently, Aepyornithidae are considered to be graviportal (Amadon 1947; Rasmussen et al. 2001; Murray and Vickers-Rich 2004) and can therefore serve for comparison.

On this basis, the determination of the type of locomotion of terrestrial birds, especially fossil forms, has been attempted since the 1960s, mainly through the method proposed by Storer (1960). This method uses the ratio between the maximum lengths of the three hindlimb bones (femur, tibiotarsus and tarsometatarsus) of large ground birds. The type of locomotion can then be estimated from the relative proportions of the tarsometatarsus and the other two bones, cursorial birds having a proportionately longer tarsometatarsus than graviportal birds. This method, however, poses a serious practical problem because it requires a collection of the three bones of the same leg from the same individual. In the case of fossil birds, it is extremely rare to have sufficiently complete and articulated specimens to be able to apply this method. Here, we propose a new method for estimating the type of locomotion in large terrestrial birds that is based on the length-to-width ratio of the tarsometatarsus. Outputs of our model have also been compared with

<footnote n="1">¹UMR 5276, Laboratoire de Géologie de Lyon, Terre, Planètes et Environnement, Université Claude Bernard Lyon 1/CNRS/École Normale Supérieure de Lyon, 69622, Villeurbanne Cedex, France; e-mails: angst.delphine@gmail.com christophe.lecuyer@univyon1.fr; romain.amiot@univ-lyon1.fr</footnote>

<footnote n="2">²Current address: Biological Sciences Department, University of Cape Town, Private Bag X3, Rhodes Gift, Cape Town, 7701, South Africa</footnote>

<footnote n="3">³Laboratoire de Géologie de l'Ecole Normale Supérieure, UMR 8538, Centre National de la Recherche Scientifique, 75231, Paris Cedex 05, France; e-mail: eric.buffetaut@sfr.fr</footnote>

<footnote n="4">⁴Institut Universitaire de France, 103 Boulevard, Saint-Michel, Paris, 75005, France</footnote>
those obtained using Storer's method, and we show that this new method, using only one bone, is more easily applicable to the fossil record and provides a reliable alternative to Storer's method. Its application to fossil birds yields new information on the locomotion of different groups of fossil birds such as Gastornithidae, Brontornithidae and some Phorusrhacidae.

*Abbreviations*. AMNH, American Museum of Natural History, New York; DGM, Divisão de Geologia e Mineralogia do Departamento Nacional da Produção Mineral, Rio de Janeiro; FM, Field Museum of Natural History, Chicago; MACN, Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Buenos Aires; MLP, Museo de La Plata, La Plata; MMP, Museo Municipal de Mar del Plata, La Plata; MNHN, Muséum national d'Histoire naturelle, Paris; PUM, Princeton University Museum, New Jersey; UNSM, National Museum of Natural History, Smithsonian Institution, Washington DC; USGS, United States Geological Survey; YPM, Yale Peabody Museum, New Haven.

## MATERIAL AND METHOD

### *Material*

This study examined a wide range of modern and fossil large ground birds. Modern birds are represented by ratites, including ostriches, emus, rheas and cassowaries. Fossil birds include the main large groups of Cenozoic ground birds: Aepyornithidae, Dromornithidae, Dinornithiformes, Phorusrhacidae, Brontornithidae and Gastornithidae.

The moa (Dinornithiformes) bones used in this study are from the collections of the Muséum national d'Histoire naturelle (Paris) and the Musée des Confluences (Lyon). For most of them, no precise locality data or identifications are available. They have been referred to various species of Dinornithiformes using Worthy's key to the leg bones of moas (Worthy 1988) and the modern classification of moas provided by Worthy and Scofield (2012).

For each of these taxa, the maximum length of the three hindlimb bones and the minimum width of the tarsometatarsus were measured. The maximum lengths of the three hindlimb bones were used to apply Storer's method, and the maximum length and the minimum width of the tarsometatarsus were used to establish the new method proposed in this study. A total of 704 measurements were used, including 552 direct measurements and 152 taken from the literature (Angst et al. 2015). Storer's method model was tested with 22 different species, based on 531 length measurements. For comparison purposes, the proposed method was developed using the same species as Storer's model and includes 168 limb measurements for graviportal birds and 158 measure-

ments for cursorial birds, with a total of 326 measurements used to build the model.

### *Method*

The new method proposed here is based on the minimum width/maximum length ratio of the tarsometatarsus, which is the most sensitive bone to the mechanical constraints of locomotion and which was also used in Storer's (1960) method. The length is measured from the most prominent tip of the proximal end to the most prominent tip of the distal trochlea. The minimum width is measured in dorsal or ventral view at the narrowest level of the diaphysis (Fig. 1). All measurements were taken using callipers and are reported in millimetres. The length/width ratios are shown as a function of the width and the types of locomotion that are known for modern and sub-modern groups of birds.

In order to compare our new method to that of Storer, the lengths of the three lower limb bones were measured. For modern birds, the three bones of the same hindlimb from the same individual were measured and Storer's method was applied directly by comparing the proportions of these bones. In the case of fossil groups, for which only isolated bones are known, average bone lengths were calculated, and the proportions were calculated from these average values.

## RESULTS

### *Comparison of the methods*

Storer's method shows that birds with a tarsometatarsus maximum length of more than about 30% of the total hindlimb length are cursorial (Fig. 2, on the left of the vertical grey area), whereas graviportal birds have a shorter tarsometatarsus, corresponding to less than about 30% of the hindlimb length (Fig. 2, on the right side of the vertical grey area). Separation is most obvious for groups with a locomotion corresponding to the extreme cases, such as ostriches (*Struthio camelus*) or rheas (*Rhea americana*) for the cursorial birds or Dinornithiformes in the graviportal group (Fig. 2). Our observations of modern and sub-fossil birds have allowed us to define an area of uncertainty around this 30% marker (the vertical grey area on Fig. 2). It is bounded by the living cassowary (*Casuarius* sp.), which has the shortest tarsometatarsus of all cursorial birds (approximately 32% total limb length), and the sub-fossil *Aepyornis*, which clearly employed graviportal locomotion and has the longest tarsometatarsus of all known graviportal birds (approximately 28% total limb length).
<figure><img src="image_4.png" /><figcaption>**FIG. 1.** Measurements used in the new method. *Gastornis* tarsometatarsus from the Paleocene of Berru, France (Original fossil is in a private collection, but a cast is kept at the MNHN, collection number: L 3092.)</figcaption></figure>

The new method proposed here shows a well-marked, statistically significant difference between graviportal and cursorial birds (Kruskal–Wallis $p = 9.22 \times 10^{-28}$; Fig. 3). Cursorial birds have a length/width ratio greater than 12, while graviportal birds have a ratio lower than 12. These ratios correspond, respectively, to a very thin and slender tarsometatarsus and to a very massive and wide tarsometatarsus.

### Locomotion of fossil birds

*Phorusrhacidae.* Storer's method shows some uncertainties about the locomotion of some species of *Phorusrhacidae*, such as *Psilopterus bachmanni*, *Psilopterus lemoinei* or *Procariama simplex*, which are located in the intermediate

area (Fig. 2 grey zone). Using only Storer's method is insufficient to discriminate their locomotion, and it is not possible to clearly assign a cursorial locomotion to these species. Only the species *Mesembriornis milneedwardsi* is decidedly cursorial. In contrast, our new method places not only *Mesembriornis milneedwardsi* among the cursorial birds, but also all the intermediate species with a length/width ratio of the tarsometatarsus between 17 and 21, which is much higher than 12 (Fig. 3). An unexpected result is the case of *Paraphysornis brasiliensis*. Indeed, this species has a tarsometatarsus which is relatively short as compared with the two other bones of the hindlimb, so the application of Storer's method indicates that it was graviportal (Fig. 2). This bone is also very massive and wide with a length/width ratio of 6, well below 12 (Fig. 3), which is also a feature of graviportal birds.

*Brontornithidae.* Both methods used in this work show that *Brontornis* was a graviportal bird. Its tarsometatarsus is very short in comparison with its femur and tibiotarsus (<25%, Fig. 2), and it is very wide relative to its length, with a very small length/width ratio around 5–6 (Fig. 3).

*Gastornithidae.* In this case as well, both methods show that *Gastornis* was a graviportal bird. Storer's method shows a relatively short tarsometatarsus corresponding to about 25% of the hindlimb length (Fig. 2), and the new method provides a length/width ratio range between 5 and 8, which is much lower than 12 (Fig. 3).

## DISCUSSION

### Comparison of the methods

Storer's method permits a relatively good discrimination between the extreme locomotion groups (cursorial or graviportal). However, this method cannot clearly identify the locomotion mode of intermediate groups such as the Dromornithidae, some *Phorusrhacidae* and the casowaries, which correspond to a large part of our database. For these groups, the relative length of the tarsometatarsus falls within the uncertainty range separating cursorial from graviportal birds (Fig. 2, grey zone). This problem is probably amplified for the fossil groups by the lack of complete hindlimbs. In these cases, length measurements are taken for each bone separately, and in order to apply Storer's method, we had to use the mean values. Unfortunately, this has the effect of attenuating the signal, but no other solution is available so far to apply Storer's method to most fossil groups.

On the other hand, the proposed maximum-length-to-minimum-width ratio method permits discrimination
<figure><img src="image_5.png" /></figure>
<figure><img src="image_6.png" /><figcaption>**FIG. 3.** Estimated locomotion using the new method. Arrow shows the position of *Paraphysornis* because its marker is superposed on another one. Phorusrhacidae presented in the figure exclude *Paraphysornis*, which is represented separately for more convenient reading. Vertical dashed line represents the separation between the two groups: graviportal (length/width ratio <12) and cursorial (length/width ratio >12).</figcaption></figure>

between the locomotion types for all extreme cases, as well as the intermediate cases for which Storer's method fails to separate clearly. Therefore, this method not only allows a clear identification between the two locomotion types, but can also be conveniently applied to the fossil record, as it only requires two measurements (maximum length and minimum width) to be performed on only one bone type (tarsometatarsus).

### Locomotion of fossil birds

*Phorusrhacidae.* Phorusrhacidae are ground birds with a height ranging from around 80 cm to 3 m (Alvarenga and Höfling 2003). They are known from North and South America, North Africa and Europe during the Tertiary (Paleocene–Pliocene) and have been represented and described for decades as cursorial birds and predators preying on various mammals (Patterson and Kraglievich 1960; Tambussi *et al.* 1999; Noriega and Agnolín 2008). This study confirms with a quantitative approach that the majority of the Phorusrhacidae were cursorial, as previously proposed in the literature based on qualitative

evidence such as general anatomy; this could not be performed with Storer's method due to its greater uncertainty. However, among Phorusrhacidae, our results show clearly that *Paraphysornis brasiliensis* was a graviportal bird and thus the only currently known graviportal phorusrhacid. A possible explanation may be biomechanical constraints linked to the size and the body mass of this bird. Indeed, this bird is one of the largest known Phorusrhacidae, 2–3 m in height and weighing more than 100 kg (Alvarenga and Höfling 2003). These mechanical constraints linked to a heavy weight should have had an impact on the hindlimb bones of these terrestrial birds that may have implied a relatively slow graviportal locomotion. However, keeping in mind that the skull of *Paraphysornis* was clearly adapted to a carnivorous diet, this bird may have had a specific hunting method, either as an ambush predator or even as a scavenger, because, unlike other Phorusrhacidae, it was probably not able to pursue fast-running prey.

*Brontornithidae.* Brontornithidae are represented by only one genus and species, *Brontornis burmeisteri*, which has been known from the Miocene of Argentina since 1891

<caption>**FIG. 2.** Estimated locomotion of fossil and modern ground birds using Storer's method. Horizontal bars represent percentage of total hindlimb length represented by: femur (black); tibiotarsus (white); tarsometatarsus (grey). Vertical grey area corresponds to the intermediate length of the tarsometatarsus for which the locomotion is uncertain, bounded by observations of modern and sub-fossil birds with known locomotion traits: the cursorial modern cassowary (*Casuarius* sp.) and graviportal sub-fossil *Aepyornis* (see text for details). Average measurements for each limb bone were used, and numbers on bars indicate total number of measurements used. In the rare cases where it was possible to take all three measurements from one individual, those specimens are also illustrated separately.
* Graviportal birds; ** cursorial birds; ? birds for which the mode of locomotion is uncertain.</caption>
(Moreno and Mercerat 1891). It was initially included in the Phorusrhacidae, but its placement in this family was questioned on the basis of several anatomical criteria (Agnolin 2007; Tambussi 2011; Agnolin 2013; Tambussi and Degrange 2013; Buffetaut 2014). This study shows that *Brontornis* had a graviportal locomotion, which is another difference as compared with the majority of the Phorusrhacidae, and this condition was probably a consequence of its large body mass, as in the case of *Para-physornis*. This study thus provides new information about the ecology of this strange giant fossil ground bird, about which relatively little is known, despite the fact that it has been known since the nineteenth century.

*Gastornithidae.* Gastornithidae were herbivorous birds (Angst *et al.* 2014), known from the middle Paleocene (Selandian) to the middle Eocene (Lutetian) in Europe (Buffetaut and Angst 2014) and from the early Eocene (Ypresian) in North America and Asia (Andors 1988; Buffetaut 2013). This study points to a relatively slow graviportal locomotion. This type of locomotion had previously been proposed, using indirect evidence such as footprints attributed to these birds, which do not suggest a predator–prey relationship with the mammal footprints associated with them (Mustoe *et al.* 2012). Our new estimate of the locomotion mode of these birds challenges the traditional representation of the Gastornithidae which were generally depicted as fast-running predators (Witmer and Rose 1991), and this also has an impact on our understanding of the ecology of *Gastornis*. As pointed out by Buffetaut and Angst (2013), this misconception was partly based on the faulty reconstruction of the tarsometatarsus by Matthew and Granger (1917), which showed a long and relatively slender bone instead of the real short and robust element. In fact, this bird was herbivorous and did not need to move fast because its large size probably protected it from predators that were smaller than it. Moreover, it is interesting to note that all Gastornithidae had the same locomotion type regardless of their geographical origin (Europe or North America) or body mass (the American species was larger than the European ones).

## CONCLUSION

Storer's (1960) method is difficult to apply to fossil birds because it requires the utilization of the three bones of the same hindlimb from the same individual. Moreover, it does not allow the locomotion type of many bird groups having intermediate proportions to be estimated unambiguously. The new method proposed in this study, based on the maximum-length-to-minimum-width ratio, separates with greater precision the two locomotion types,

even for the intermediate cases. Terrestrial graviportal birds have a massive and wide tarsometatarsus, which corresponds to a maximum length/minimum width ratio lower than 12. Cursorial birds have a thin and slender tarsometatarsus corresponding to a ratio higher than 12. Moreover, this method requires only one bone, the tarsometatarsus, and involves only simple measurements (minimum width and maximum length), which can be easily applied to fossil birds. Contrary to what is commonly considered, we have shown that the Phorusrhacidae were not all fast-running birds, thus reflecting some ecological differences within this family of predators. The largest phorusrhacids must have had a distinct hunting method from that of the smaller members of their group because they were probably unable to run after their prey because of their large body mass. Furthermore, we show that the Gastornithidae were clearly graviportal birds, in agreement with their herbivorous diet.

*Acknowledgements.* We thank Ronan Allain, Christine Argot and Christine Lefèvre from the Muséum national d'Histoire naturelle (Paris), Didier Berthet from the Musée des Confluence (Lyon), Daniel L. Brinkman from the Yale Peabody Museum of Natural History (New Haven), Carl Mehling from the American Museum of Natural History (New York), Sandra D. Chapman from the Natural History Museum (London) for access to material in their care and also Trevor Worthy and Robert Kambric for their helpful comments on an earlier version of the manuscript.

## DATA ARCHIVING STATEMENT

Data for this study are available in the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.609j4

*Editor.* Roger Benson

## REFERENCES

AGNOLIN, F. 2007. *Brontornis burmeisteri* Moreno & Mercerat, un Anseriformes (Aves) gigante del Miocen Mdeio de Patagonia, Argentina. *Revista del Museo Argentino de Ciencias Naturales, 9*, 15-25.

— 2013. La posición sistemática de *Hermosiornis* (Aves, Phororhacoidea) y sus implicancias filogenéticas. *Revista del Museo Argentino de Ciencias Naturales, 15*, 39-60.

ALVARENGA, H. M. F. and HÖFLING, E. 2003. Systematic revision of the Phorusrhacidae (Aves: Ralliformes). *Papéis Avulsos de Zoologia, 43*, 55-91.

AMADON, D. 1947. An estimated weight of the largest known bird. *The Condor, 49*, 159-164.

ANDORS, A. V. 1988. Giant groundbirds of North America (Aves, Diatrymidae). Unpublished PhD thesis, Columbia University, New York, 577 pp.
ANGST, D., LÉCUYER, C., AMIOT, R., BUFFETAUT, E., FOUREL, F., MARTINEAU, F., LEGENDRE, S., ABOURACHID, A. and HERREL, A. 2014. Isotopic and anatomical evidence of an herbivorous diet in the Early Tertiary giant bird Gastornis. Implications for the structure of Paleocene terrestrial ecosystems. *Naturwissenschaften*, **101**, 313–322.

— BUFFETAUT, E., LECUYER, C. and AMIOT, R. 2015. Data from: A new method for estimating locomotion type in large ground birds. *Dryad Digital Repository*. doi:10.5061/dryad.609j4

BUFFETAUT, E. 2013. The giant bird *Gastornis* in Asia: a revision of *Zhongyuanus xichuanensis* Hou, 1980, from the Early Eocene of China. *Paleontological Journal*, **47**, 1302–1307.

— 2014. Tertiary ground birds from Patagonia (Argentina) in the Tournouër collection of the Muséum National d'Histoire Naturelle, Paris. *Bulletin de la Société Geologique de France*, **185**, 207–214.

— and ANGST, D. 2013. “Terror cranes” or peaceful plant-eaters: changing interpretations of the palaeobiology of gastornithid birds. *Revue de Paléobiologie*, **32**, 413–422.

— 2014. Stratigraphic distribution of large flightless birds in the Palaeogene of Europe and its palaeobiological and palaeogeographical implications. *Earth-Science Reviews*, **138**, 394–408.

CARRANO, M. T. 1999. What, if anything, is a cursor? Categories versus continua for determining locomotor habit in mammals and dinosaurs. *Journal of Zoology*, **247**, 29–42.

COOMBS, W. P. JR 1978. Theoretical aspects of cursorial adaptations in dinosaurs. *Quarterly Review of Biology*, **53**, 393–418.

GREGORY, W. K. 1912. Notes on the principles of quadrupedal locomotion and on the mechanism of the limbs in hoofed animals. *Annals of the New York Academy of Sciences*, **22**, 267–294.

MATTHEW, W. D. and GRANGER, W. 1917. The skeleton of *Diatryma*, a gigantic bird from the Lower Eocene of Wyoming. *Bulletin of the American Museum of Natural History*, **37**, 307–326.

MORENO, F. P. and MERCERAT, A. 1891. *Catálogo de los pájaros fósiles de la república Argentina conservados en el Museo de La Plata*. Taller de publicaciones del Museo, La Plata, 71 pp.

MURRAY, P. F. and VICKERS-RICH, P. 2004. *Magnificent Mihirungs: the colossal flightless birds of the Australian Dreamtime*. Life of the Past Series, Indiana University Press, 416 pp.

MUSTOE, G. E., TUCKER, D. S. and KEMPLIN, K. L. 2012. Giant Eocene bird footprints from northwest Washington, USA. *Palaeontology*, **55**, 1293–1305.

NORIEGA, J. I. and AGNOLÍN, F. L. 2008. El registro paleontológico de las Aves del 'Mesopotamiense'(Formación Ituzaingó; Mioceno tardío-Plioceno) de la provincia de Entre Ríos, Argentina. *INSUGEO, Miscelánea*, **17**, 271–290.

OSBORN, H. F. 1934. Aristogenesis, the creative principle in the origin of species. *American Naturalist*, **68**, 193–235.

PATTERSON, B. and KRAGLIEVICH, J. L. 1960. Sistemática y nomenclatura de las aves fororracoideas del Plioceno argentino. *Museo Municipal de Ciencas Naturales y Tradicional de Mar del Plata*, **1**, 3–49.

RASMUSSEN, D. T., SIMONS, E. L., HERTEL, P. and JUDD, A. 2001. Hindlimb of a giant terrestrial bird from the upper Eocene, Fayum, Egypt. *Palaeontology*, **44**, 325–337.

SMITH, J. M. and SAVAGE, R. J. G. 1956. Some locomotory adaptations in mammals. *Journal of the Linnean Society of London, Zoology*, **42**, 603–622.

STEIN, B. R. and CASINOS, A. 1997. What is a cursorial mammal? *Journal of Zoology*, **242**, 185–192.

STORER, R. 1960. Adaptive radiation in birds. 15–55. In MARSHALL, A. J. (ed.). *Biology and comparative physiology of birds*, Vol. 1. Academic Press.

TAMBUSSI, C. P. 2011. Palaeoenvironmental and faunal inferences based on the avian fossil record of Patagonia and Pampa: what works and what does not. *Biological Journal of the Linnean Society of London*, **103**, 458–474.

— and DEGRANGE, F. J. 2013. *South American and Antarctic continental Cenozoic birds: paleobiogeographic affinities and disparities*. Springer, Dordrecht, 113 pp.

TAMBUSSI, C., UBILLA, M. and PEREA, D. 1999. The youngest large carnassial bird (Phorusrhacidae, Phorusrhacinae) from South America (Pliocene–Early Pleistocene of Uruguay). *Journal of Vertebrate Paleontology*, **19**, 404–406.

WITMER, L. M. and ROSE, K. D. 1991. Biomechanics of the jaw apparatus of the gigantic Eocene bird Diatryma: implications for diet and mode of life. *Paleobiology*, **17**, 95–120.

WORTHY, T. H. 1988. *An illustrated key to the main leg bones of moas (Aves: Dinornithiformes)*. National Museum of New Zealand, 38 pp.

— and SCOFIELD, R. P. 2012. Twenty-first century advances in knowledge of the biology of moa (Aves: Dinornithiformes): a new morphological analysis and moa diagnoses revised. *New Zealand Journal of Zoology*, **39**, 87–153.