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Revision of Dromaius gidju Patterson and Rich, 1987 from Riversleigh, northwestern Queensland, Australia, with a reassessment of its generic position

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Dromaius gidju Patterson and Rich 1987, from the Mio­ cene Kurjamarpu local fauna of central Ausrralia, was described on the basis of associated hindlimb elements. New hindlimb material from the type locality and from Oligocene/Miocene deposits in Riversleigh, northwestern Queensland, are referred ro this taxon. Tibiotarsal and tarsometatarsal remains of D. gidju are more similar ro those of emus than those of cassowaries, whereas the femora are more similar to femora of cassowaries. All hindlimb elements of D. gidju show some affinity ro both cassowaries and emus. The combination of hindlimb characters indicates an earlier stage in the development of increased cursoriality, so [ propose a new genus for this taxon, Emuarius, which is interpreted ro be nearer the mutual ancesror of the emu and cassowary lineages than any other described form.
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... No casuariiform fossils are known before the Late Oligocene [333], and thus far there is no indication that any other palaeognath lineage has ever been present in Australia (Figure 7, Table 6). One of these early fossil Casuariiformes, Emuarius gidju [337], had a temporal range spanning from approximately 24 Ma to 15 Ma and is known from a large number of specimens [341]. E. gidju was first described on the basis of a distal tibiotarsus, proximal tarsometatarsus and shaft, and a complete pes from the Lake Ngapakaldi Leaf Locality of the Wipajiri Formation in South Australia [336]. ...
... E. gidju was first described on the basis of a distal tibiotarsus, proximal tarsometatarsus and shaft, and a complete pes from the Lake Ngapakaldi Leaf Locality of the Wipajiri Formation in South Australia [336]. Two more specimens were found in late Miocene deposits in Alcoota, Northern Territory [336,356], and even more from formations spanning the late Oligocene to early late Miocene of Riversleigh, Queensland [337,340]. The genus Emuarius differs from Dromaius in its retention of a cassowary likefemur, while the tibiotarsus and tarsometatarsus have cursorial modifications and are emu-like [337,340]. ...
... Two more specimens were found in late Miocene deposits in Alcoota, Northern Territory [336,356], and even more from formations spanning the late Oligocene to early late Miocene of Riversleigh, Queensland [337,340]. The genus Emuarius differs from Dromaius in its retention of a cassowary likefemur, while the tibiotarsus and tarsometatarsus have cursorial modifications and are emu-like [337,340]. The pedal phalanges are of an intermediate morphology between the extant emu and cassowary, being more dorsoventrally compressed than those of cassowaries but less than those of emu [337,341]. ...
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The extant diversity of the avian clade Palaeognathae is composed of the iconic flightless ratites (ostriches, rheas, kiwi, emus, and cassowaries), and the volant tinamous of Central and South America. Palaeognaths were once considered a classic illustration of diversification driven by Gondwanan vicariance, but this paradigm has been rejected in light of molecular phylogenetic and divergence time results from the last two decades that indicate that palaeognaths underwent multiple relatively recent transitions to flightlessness and large body size, reinvigorating research into their evolutionary origins and historical biogeography. This revised perspective on palaeognath macroevolution has highlighted lingering gaps in our understanding of how, when, and where extant palaeognath diversity arose. Towards resolving those questions, we aim to comprehensively review the known fossil record of palaeognath skeletal remains, and to summarize the current state of knowledge of their evolutionary history. Total clade palaeognaths appear to be one of a small handful of crown bird lineages that crossed the Cretaceous-Paleogene (K-Pg) boundary, but gaps in their Paleogene fossil record and a lack of Cretaceous fossils preclude a detailed understanding of their multiple transitions to flightlessness and large body size, and recognizable members of extant subclades generally do not appear until the Neogene. Despite these knowledge gaps, we combine what is known from the fossil record of palaeognaths with plausible divergence time estimates, suggesting a relatively rapid pace of diversification and phenotypic evolution in the early Cenozoic. In line with some recent authors, we surmise that the most recent common ancestor of palaeognaths was likely a relatively small-bodied, ground-feeding bird, features that may have facilitated total-clade palaeognath survivorship through the K-Pg mass extinction, and which may bear on the ecological habits of the ancestral crown bird.
... The oldest known casuariid is Emuarius gidju (Patterson and Rich, 1987), a small species whose stratigraphic record extends from the late Oligocene (ca. 25 Ma) to the middle Miocene (15 Ma) from the Lake Eyre Basin of South Australia and the Riversleigh World Heritage Area in Queensland . Emuarius gidju was originally described as a species of Dromaius (Patterson and Rich, 1987), but Boles (1992) erected the genus Emuarius to emphasize its mosaic of emu-like and cassowary-like characters. Despite its intermediate morphology, Boles (1992) proposed that E. gidju was an early member of Dromaiinae rather than a member of the casuariid stem group. ...
... Emuarius gidju was originally described as a species of Dromaius (Patterson and Rich, 1987), but Boles (1992) erected the genus Emuarius to emphasize its mosaic of emu-like and cassowary-like characters. Despite its intermediate morphology, Boles (1992) proposed that E. gidju was an early member of Dromaiinae rather than a member of the casuariid stem group. Further material and a phylogenetic analysis have upheld the cassowary-like characters of E. gidju as plesiomorphic and its systematic position as an early dromaiine . ...
... observ. of unregistered NTM specimen). In NTM P6178, however, these two meet at a right angle, which is similar to, but slightly more extreme than, some E. gidju (e.g., Boles, 1992: fig. 4h) but not as marked as in Rhea (e.g., Cracraft, 1974:fig. ...
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A new, diminutive species of dromaiine casuariid, Dromaius arleyekweke, is described from dispersed skeletal elements from the late Miocene Waite Formation of the Northern Territory, Australia. Remains of D. arleyekweke, sp. nov., have been found from the Ongeva Local Fauna in the Alcoota Scientific Reserve, but most remains come from the stratigraphically lower Alcoota Local Fauna where they form part of a densely fossiliferous series of mingled bone beds. Previously, remains of the new species had been referred to the basal dromaiine genus, Emuarius, but phylogenetic appraisal of new specimens indicates that the species shared a more recent common ancestor with the extant Dromaius novaehollandiae than it did with the type species of Emuarius, E. gidju. Consequently, the new species is placed in the genus Dromaius as its oldest known member. Derived characters of D. arleyekweke that are shared with D. novaehollandiae to the exclusion of E. gidju include a distally flattened external condyle of the distal end of the tibiotarsus and a more elongate tarsometatarsus, with marked transverse compression of the midshaft and a weakly impressed median sulcus on trochlea metatarsi II. Casuariid evolution shows a trend of increasingly cursorial hind limb proportions on the emu lineage, but D. arleyekweke has a tarsometatarsus that is more elongate than that of D. novaehollandiae. This implies nonlinear evolution of cursoriality in dromaiines and that D. arleyekweke evolved extreme cursorial proportions independently of D. novaehollandiae, or that a high degree of cursoriality evolved early in Dromaius and was reversed in the Pliocene D. ocypus.
... Moreover, the absence of a supratendinal bridge is a derived feature that distinguishes MLP 10-X-20-1 from Dinornithiformes, and resembles in this aspect more derived ratites. Furthermore, the presence in MLP 10-X-20-1 of a cranially flat and caudally convex distal diaphysis is a trait shared with Casuariidae and Aepyornithidae (Andrews 1904, Boles 1992, whereas in other ratites, including rheids (e.g., Pterocnemia, Rhea) the diaphysis is elliptical in cross-section, with convex cranial and caudal surfaces. ...
... It is possible that environmental change might have contributed to the demise of several Ratitae clades. Available data suggest that the early palaeognaths were probably primarily forest dwellers, as in the case with basal tinamids (Cracraft 1974, Boles 1992, Bertelli & Chiappe 2005. During the Cretaceous and Paleogene in South America, open habitats and grasslands were scarce, and a warm-temperate or subtropical forest extended far into southern Argentina and Chile (Palazzesi & Barreda 2012, Palazzesi et al. 2014. ...
... In Australasia, the oldest ratite record is of Emuarius gidju and E. guljaruba from the late Oligocene-early Miocene of South Australia (Patterson & Rich 1987, Boles 1992. In New Zealand, the basal Apterygidae Proapteryx micromeros, and indeterminate Dinornithiformes were described from the early Neogene (Tennyson et al. 2010, Worthy et al. 2013. ...
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Agnolin, F.L., July 2016. Unexpected diversity of ratites (Aves, Palaeognathae) in the early Cenozoic of South America: palaeobiogeographical implications. Alcheringa 41, xxx–xxx. ISSN 0311-5518. Ratitae is represented in South America exclusively by Rheidae. Recently, the oldest purported fossil rheid, Diogenornis fragilis, was attributed by several authors to various other ratite clades. A new revision of museum fossil specimens from Argentina has resulted in the discovery of several ratite specimens that clearly do not belong to Rheidae, but resemble other clades. The newly identified specimens derive from Paleogene and Miocene strata. The great diversity of non-rheid Patagonian ratites ended via extinction of several groups by the late Miocene, probably owing to enhanced aridity that also favoured the dispersal of arid-adapted rheids. The new specimens described here reinforce the hypothesis that the traditional vicariant biogeographical model, which proposes ratite clades originated exclusively before the breakup of the Gondwana supercontinent, is questionable owing to the unexpected diversity of various ratite clades in South America, and also in Europe and Africa. This might indicate that the history of Ratitae was more complex than previously envisioned. Federico L. Agnolin* [[email protected]], Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Av. Ángel Gallardo, 470 (1405), Buenos Aires, Argentina. *Also affiliated with: Fundación de Historia Natural ‘Félix de Azara’, Departamento de Ciencias Naturales y Antropología, Universidad Maimónides, Hidalgo 775 (C1405BDB) Ciudad Autónoma de Buenos Aires, República Argentina.
... The Maximum Clade Credibility method implemented in TreeAnnotator forcefully prevents polytomies, but no signs of conflict were found in the resolution of any of the nodes of the tree. Results from the sampling of the prior differed from those from the main analyses, indicating that the recovered posterior (2004) 25 split Casuarius -Dromaius 23 Mya Boles (1992) probabilities are not just a product of the priors. The random clock analysis recovered a phylogeny where most of the nodes of the tree were younger than 1 Mya. ...
Article
Mitochondrial DNA (mtDNA) is a popular resource used for the study of evolutionary processes in birds, especially, to infer divergence times between lineages. In many cases due to the scarcity of fossils with which to constrain the age of nodes on a phylogenetic topology, dating relies on mtDNA substitution rates that, ideally specific to the taxa being studied. As such values are often unavailable, many studies use fixed‐rate values from other studies, like the ‘standard molecular clock’. The validity of this universal rate across all bird lineages and for the different mtDNA loci has been questioned by multiple authors. We here performed the most comprehensive calibration of the mtDNA molecular clock in birds, with the inclusion of complete mitochondrial genomes for 622 bird species and 25 reliable fossil calibrations. The results show variation in the rates among lineages and among markers, confirming the lack of universality of the standard molecular clock. Moreover, we provide specific rates for every mtDNA marker (except D‐loop) in each of the sampled avian orders, a valuable tool for molecular clock analyses in the absence of fossil calibrations.
... In the early Miocene the first ostriches originated in Africa, and by the middle to late Miocene, these large cursorial birds occupied the open landscapes across the continent, and had even dispersed into Eurasia (Bibi et al., 2006;Zelenkov et al., 2019). In Australia, giant cursorial gastornithiform and casuariform birds are known from the Miocene (Boles, 1992;Worthy et al., 2016). ...
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... In the early Miocene the first ostriches originated in Africa, and by the middle to late Miocene, these large cursorial birds occupied the open landscapes across the continent, and had even dispersed into Eurasia (Bibi et al., 2006;Zelenkov et al., 2019). In Australia, giant cursorial gastornithiform and casuariform birds are known from the Miocene (Boles, 1992;Worthy et al., 2016). ...
Article
Full-text available
The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval—the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analog for future climate scenarios, and for assessing the predictive accuracy of numerical climate models—the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re‐interpretation of proxies, which might mitigate the model‐data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here, we review the state‐of‐the‐art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modeling studies.
... representing non-ostrich palaeognaths (Notopalaeognathae) (Alvarenga 1983) with an offset value of 56Ma and a mean of 5.44. The second was based on the fossil Emuarius gidju representing the mutual ancestor of emus and cassowaries (Boles 1992) with an offset value of 25Ma and a mean of 3.33. We ran the BEAST analysis for 500 million iterations, sampling and recording the MCMC chain after every 50,000 generations. ...
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