Worthy Trevor H, Hand Suzanne J, Archer Michael
School of Biological, Earth and Environmental Sciences, University of New South Wales, New South Wales, Australia.
School of Earth and Environmental Sciences, University of Adelaide, North Terrace, Adelaide, South Australia, Australia.
Integr Zool. 2014 Mar;9(2):148-166. doi: 10.1111/1749-4877.12050.
In Australia, ratites (Aves: Palaeognathae) are represented in the extant fauna by the family Casuariidae with 1 species of emu Dromaius novaehollandiae and 1 cassowary Casuarius casuarius. The Australian fossil record reveals no other extinct ratite families but there are a number of other casuariid species. Most significant of these, due to its Oligo-Miocene age and because it is known from abundant material, is Emuarius gidju. Here, we describe additional material and confirm that the taxon had a temporal range of Late Oligocene to Middle Miocene (approximately 24-15 Ma). We reveal new morphological details, including notably that the species had relatively much smaller eyes than D. novaehollandiae, in addition to a less well-developed cursorial ability, as inferred from its pelvic limb. In these respects, Emuarius is similar to Casuarius and suggest that it was adapted to denser vegetation than the open woodlands and grasslands that characterise much of Australia today and to which D. novaehollandiae, with its large eyes and enhanced cursorial ability, is strongly adapted. Emuarius was compared to and found to be distinct from the poorly provenanced Australian fossil species C. lydekkeri. We conducted a phylogenetic analysis of morphological data that robustly shows that E. gidju is the sister taxon of Dromaius and together these taxa form a clade that is sister to Casuarius. This indicates that the evolution towards enhanced cursorality that characterises Dromaius took place after the divergence of the emu-cassowary lineages and was likely not the driving mechanism of this divergence. Comparisons between D. novaehollandiae and D. baudinianus revealed no qualitative skeletal differences and we suggest that the latter taxon is best considered to be an island dwarf that should be taxonomically recognized at a subspecific level only.
在澳大利亚，平胸鸟（鸟纲：古颚总目）在现存动物群中以鹤鸵科为代表，有1种鸸鹋（鸸鹋属）和1种食火鸡（食火鸡属）。澳大利亚的化石记录显示没有其他已灭绝的平胸鸟科，但有许多其他鹤鸵科物种。其中最重要的是中新世-渐新世时期的Emuarius gidju，因其时代以及丰富的化石材料而闻名。在此，我们描述了更多材料，并确认该分类单元的时间范围为晚渐新世至中中新世（约2400-1500万年前）。我们揭示了新的形态细节，尤其值得注意的是，该物种的眼睛比鸸鹋小得多，此外，从其下肢推断，其奔跑能力也不太发达。在这些方面，Emuarius与食火鸡相似，表明它适应的植被比当今澳大利亚大部分地区以开阔林地和草原为特征的植被更茂密，而鸸鹋因其大眼睛和更强的奔跑能力，非常适应开阔林地和草原。Emuarius与来源不明的澳大利亚化石物种莱氏食火鸡进行了比较，发现两者不同。我们对形态数据进行了系统发育分析，有力地表明E. gidju是鸸鹋属的姐妹分类单元，这些分类单元共同形成了一个与食火鸡属为姐妹的进化枝。这表明，鸸鹋所具有的增强奔跑能力的进化发生在鸸鹋-食火鸡谱系分化之后，可能不是这种分化的驱动机制。鸸鹋和巴氏鸸鹋之间的比较没有发现骨骼上的定性差异，我们认为后一个分类单元最好被视为一个岛屿侏儒种，仅应在亚种水平上进行分类识别。
