DOI: 10.5061/dryad.1c59zw3vc
title: Eggs of extinct dwarf island emus retained large-size: Electronic supplementary material

description: Islands off southern Australia once harboured three subspecies of the
 mainland emu (Dromaius novaehollandiae), the smaller Tasmanian emu (D. n.
 diemenensis), and two dwarf emus, King Island emu (D. n. minor) and
 Kangaroo Island emu (D. n. baudinianus), which all became extinct rapidly
 after discovery by human settlers. Little was recorded about their life
 histories and only a few historical museum specimens exist, including a
 number of complete eggs from Tasmania and a unique egg from Kangaroo
 Island. Here we present a detailed analysis of eggs of dwarf emus,
 including a first record of an almost complete specimen from King Island.
 Our results show that despite the reduction in size of all island emus,
 especially the King Island emu that averaged 44% smaller than mainland
 birds, the egg remained similar-sized in linear measurements, but less in
 volume and mass, and had slightly thinner eggshell. We provide possible
 reasons why these phenomena occurred.
description: Samples     We used 38
 intact eggs of mainland emu <i>Dromaius n. novaehollandiae</i>
 in our analysis, including the subspecies, <i>D. n.
 woodwardi</i> of Northern Australia, a taxon no longer considered
 valid [1]. We used six intact eggs of Tasmanian emu <i>D. n.
 diemenensis,</i> two held at NHMUK and four at TMAG. A unique egg of
 Kangaroo Island emu and purchased by the NHMUK, was found hanging in a
 sealer’s hut prior to 1834 [2]. One of us (CR) excavated a unique, almost
 complete egg of King Island emu at Yellow Rock River, and found with an
 associated skeleton of King Island emu, plus other individual emu bones
 and eggshell. Modern eggshell measurements of <i>D .n.
 novaehollandiae</i> were obtained from recently broken eggs held at
 the NHMUK, whereas 19th century subfossil eggshell was collected in a dune
 deposit in central Australia. All subfossil eggshell came from sand dune
 deposits on King Island, as did Kangaroo Island eggshell, with the latter
 material showing slightly more signs of erosion. No Tasmanian eggshell was
 available for this study. Measurements
      For intact eggs, all measurements were
 taken using dial calipers and rounded to the nearest 0.1 mm. Total length
 of complete eggs was taken along the long axis, and greatest width along
 the short axis at the widest medial point. Egg volume from museum eggs,
 including extinct taxa, used scaled photographic images of the eggs, and
 measured using a code of a custom mathematical model of egg-shape based on
 an ellipse deformed with a distribution function, as described in [3].
 Eggshell thickness was measured using a micrometer rounded to the nearest
 0.1 mm, with recent museum and subfossil eggshell fragments measured away
 from eroded or broken edges. Eggshell thickness remains constant in museum
 specimens after collection and drying [4]; therefore, comparative eggshell
 thickness measurements of subfossil fragments and museum intact eggs are
 considered reliable. For intact egg thickness, a measurement was
 taken<i> </i>in the blowhole region of <i>D. n.
 novaehollandiae, D. n. diemenensis</i> and <i>D. baudinianus
 </i>eggs, with the technique described in [4]. Measurements proved
 difficult for the Kangaroo Island and Tasmanian eggs, because of the small
 size of the blowhole and fragile nature. 
 Statistics Mainland and
 dwarf island emu body masses estimates were calculated using algorithms
 that based on femora total length (mm) and mid-shaft width (mm) (table
 S3), based on [5-8]. Data for extant mainland emu taken from [8]; dwarf
 island emu from [8-9, this paper].  Measurement values are given as mean
 (minimum-maximum) values. x̄ = the calculated mass and estimate range for
 the mean.      A t-test was used to show any
 significance difference between mainland <i>Dromaius n.
 novaehollandiae </i>versus Tasmanian <i>D. n.
 diemenensis</i> for intact emu egg width, using a 2-tailed
 distribution and two-sampled unequal variance of total length, total width
 and volume of intact eggs. <i>D. n. diemenensis </i>showed
 only significant difference from <i>D. n. novaehollandiae</i>
 in volume (tables S4, S5, S6 and S7), which confirms our data. As unique
 specimens represent <i>D. n. baudinianus and D. n. minor</i>,
 they are not included in this statistical study, but the linear
 measurements show that <i>D. n. baudinianus </i>nestle within
 mainland emu size and <i>D. n. minor</i> is slightly smaller
 in all dimensions. T-test analysis of eggshell thickness showed no
 statistical difference with results significantly higher than the p-value
 0.05, so are not considered an evolutionary factor.