Wikisource:WikiProject Open Access/Programmatic import from PubMed Central/Identification Classification and Growth of Moa Chicks (Aves Dinornithiformes) from the Genus Euryapteryx

by Leon Huynen; Brian J. Gill; Anthony Doyle; Craig D. Millar; David M. Lambert

Abstract

Background

The analysis of growth in extinct organisms is difficult. The general lack of skeletal material from a range of developmental states precludes determination of growth characteristics. For New Zealand's extinct moa we have available to us a selection of rare femora at different developmental stages that have allowed a preliminary determination of the early growth of this giant flightless bird. We use a combination of femora morphometrics, ancient DNA, and isotope analysis to provide information on the identification, classification, and growth of extinct moa from the genus Euryapteryx.

Results

Using ancient DNA, we identify a number of moa chick bones for the species Euryapteryx curtus, Dinornis novaezealandiae, and Anomalopteryx didiformis, and the first chick bone for Pachyornis geranoides. Isotope analysis shows that ∂¹⁵N levels vary between the two known size classes of Euryapteryx, with the larger size class having reduced levels of ∂¹⁵N. A growth series for femora of the two size classes of Euryapteryx shows that early femora growth characteristics for both classes are almost identical. Morphometric, isotopic, and radiographic analysis of the smallest Euryapteryx bones suggests that one of these femora is from a freshly hatched moa at a very early stage of development.

Conclusion

Using morphometric, isotopic, and ancient DNA analyses have allowed the determination of a number of characteristics of rare moa chick femora. For Euryapteryx the analyses suggest that the smaller sized class II Euryapteryx is identical in size and growth to the extant Darwin's rhea.

Background

In depth analysis of growth in ancient animals is often limited due to the scarcity and degraded nature of skeletal material or tissues of different ages. Similarly, the rare occurrence of different aged bones for New Zealand's extinct ratite moa (Aves: Dinornithiformes) has made any analysis of moa growth difficult ^[1], ^[2], ^[3].

Adult moa ranged in size from less than 20 kg for the small coastal moa Euryapteryx curtus curtus to over 200 kg for the South Island giant moa Dinornis robustus^[2]. The identification of species within the Euryapteryx genus has been particularly difficult. Latest data suggest the existence of a small subspecies (E. curtus curtus) limited to New Zealand's North Island, and a larger subspecies (E. curtus gravis) found only in New Zealand's South Island ^[4].

How moa grew is largely unknown with most published work comparing moa to the growth characteristics of their extant relatives ^[2], ^[3]. Relatively recent work analysing cortical growth marks in moa limb bones suggest that, unlike their modern relatives, moa had a particularly long pre-adult growth period ^[5].

We analyse moa growth using a number of rare moa chick femora, currently housed at New Zealand's Auckland Museum and kindly made available to us. The museum houses a significant number of samples of moa chick bones from sand-dune sites in New Zealand's upper North Island, especially from the Karikari Peninsula/Doubtless Bay area, including Tokerau Beach. Adult bones from these sites have been attributed to three moa species with most being derived from E. curtus curtus^[2], ^[6], ^[7].

To date, only one embryonic moa has been identified to species, where bones associated with an egg were shown to belong to the heavy-footed moa Pachyornis elephantopus^[2], ^[8]. As bones of developing chicks, which often lack identifying characters, are particularly difficult to identify ^[1], ^[2] we use a minimally destructive technique to genetically assign differently sized immature moa femora to the species level. We then use bone morphometrics to present a growth series of chick femora for Euryapteryx. In addition, we present isotope and radiographic data for the smallest moa femora to determine whether these may have derived from unhatched eggs. The isotope data has also allowed us to further explore the status of two subspecies proposed for moa from the genus Euryapteryx^[9].

Results

We successfully amplified a relatively short (∼70 bp) hypervariable mitochondrial DNA fragment from 29 of 32 immature bones sampled from various locations in New Zealand (Tables 1,2; Figures 1,2). Femur LB6261c was identified as belonging to Dinornis novaezealandiae and is 72 mm long (Table 2, Figure 2). Bones of a late-term embryonic moa (identified as Pachyornis elephantopus) were recovered from inside an egg in 1866 ^[2], ^[8]. The egg was 226 mm long and 155 mm wide with the embryonic femur being approximately 48 mm long (with ends restored). An egg found at Kaikoura and attributed to Dinornis was shown to be 240 mm long, and by proportion, its embryo (if at the same stage as the Pachyornis egg) would have had a femur approximately 51 mm long. Therefore the size of LB6261c suggests it was from a recent hatchling. Further evidence for the extreme immaturity of this femur is the lack of caudal tuberosities on the femur shaft, a feature of the femur that separates Dinornis from the emeid moas ^[1], ^[2]. Turvey and Holdaway (2005) ^[3] described ‘postnatal’ bones of Dinornis and showed that femora at growth-stage 1 began at 156 mm in length with their youngest stage 1 individual having an estimated weight of 15.8 kg. Thus their sample included only well-grown chicks and did not include hatchlings. The single Pachyornis geranoides femur: At 82 mm long, LB7976 (Table 2) is likely to be from a well-developed chick, since this moa species is relatively small. Although difficult to determine due to erosion, an excavation at the proximal end of the bone may be the pneumatic fossa that characterises this species ^[1], ^[2]. LB7976 is the only known chick bone of this species. Four Anomalopteryx didiformis femora were identified; AIM LB6666c, AIM LB6261a-b, and AIM LB6285a (Table 2), all derive from Doubtless Bay, and are the first chick bones to be identified (by DNA) for this species, as well as being the first record of this species from Doubtless Bay. For Euryapteryx curtus 22 femora specimens were identified by DNA, and include the 11 smallest femora (see Figure 2). These form the first large sample of chick bones attributable with certainty to this species, and were used for detailed morphological, radiographic, and isotopic analyses. The sequence targeted allows discrimination of all moa species and identifies two distinct genetic haplotypes for Euryapteryx. The haplotypes can be separated by a single SNP that associates class I Euryapteryx with thick eggshells (0.98 mm - 1.60 mm) and class II Euryapteryx with thin eggshells (0.74 mm–0.98 mm) ^[6]. The distribution of the two Euryapteryx classes (I and II) closely mimics the distribution proposed for subspecies E. curtus gravis and E. curtus curtus respectively ^[4].

Moa sample locations.The locations of moa samples used in this work are shown.

Examples of moa chick femora.From left to right: LB5990, LB8295, LB6070, LB6261d, LB6284, LB6261c, LB12961, LB6285b, LB6657, LB6071, LB6069. All are left femora except the two at far right. DNA analysis suggests all are from Euryapteryx except for LB6261c which was identified as Dinornis. Gridlines are at 10 mm intervals.

Table 1

"Moa sequences.(10.1371/journal.pone.0099929.t001)"

File:Pone.0099929.t001

Mt hpt.	Sequence
E1