Elephant bird

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Elephant birds
Temporal range: Quaternary
↓
Aepyornis maximus
 skeleton and egg
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Infraclass: Palaeognathae
Clade: Novaeratitae
Order: †Aepyornithiformes
Newton, 1884[1]
Type species
†
Aepyornis maximus
, 1851
Genera

Elephant birds are extinct

convergently evolved
flightlessness from ancestors that dispersed more recently by flying.

Discovery

Elephant birds have been extinct since at least the 17th century. Étienne de Flacourt, a French governor of Madagascar during the 1640s and 1650s, mentioned an ostrich-like bird, said to inhabit unpopulated regions, although it is unclear whether he was repeating folk tales from generations earlier. In 1659, Flacourt wrote of the "vouropatra – a large bird which haunts the Ampatres and lays eggs like the ostriches; so that the people of these places may not take it, it seeks the most lonely places."[2][3] There has been speculation, especially popular in the latter half of the 19th century, that the legendary roc from the accounts of Marco Polo was ultimately based on elephant birds, but this is disputed.[4]

Between 1830 and 1840, European travelers in Madagascar saw giant eggs and eggshells.

Paris Academy of Sciences by Isidore Geoffroy Saint-Hilaire, based on bones and eggs recently obtained from the island, which resulted in wide coverage in the popular presses of the time, particularly due to their very large eggs.[4]

Two whole eggs have been found in dune deposits in southern

Genyornis newtoni, an extinct giant bird known from the Pleistocene of Australia. It is hypothesized that the eggs floated from Madagascar to Australia on the Antarctic Circumpolar Current. Evidence supporting this is the finding of two fresh penguin eggs that washed ashore on Western Australia but may have originated in the Kerguelen Islands, and an ostrich egg found floating in the Timor Sea in the early 1990s.[5]

Taxonomy and biogeography

Mullerornis modestus
Aepyornis maximus restoration

Like the ostrich, rhea, cassowary, emu, kiwi and extinct moa, elephant birds were ratites; they could not fly, and their breast bones had no keel. Because Madagascar and Africa separated before the ratite lineage arose,[6] elephant birds has been thought to have dispersed and become flightless and gigantic in situ.[7]

More recently, it has been deduced from DNA sequence comparisons that the closest living relatives of elephant birds are New Zealand kiwi,[8] though the split between the two groups is deep, with the two lineages being estimated to have diverged from each other around 54 million years ago.[9]

Placement of Elephant birds within Palaeognathae, after:[10][11]

Paleognathae

Struthionidae (ostriches)

Rheidae (rheas)

Tinamidae
(tinamou)

†

Dinornithiformes
(moa)

Apterygidae
(kiwis)

†Aepyornithiformes (elephant birds)

Casuariiformes (emu, cassowary)

The ancestors of elephant birds are thought to have arrived in Madagascar well after

vicariance. Gondwana broke apart in the Cretaceous and their phylogenetic tree does not match the process of continental drift. Madagascar has a notoriously poor Cenozoic terrestrial fossil record, with essentially no fossils between the end of the Cretaceous (Maevarano Formation) and the Late Pleistocene.[12] Complete mitochondrial genomes obtained from elephant birds eggshells suggest that Aepyornis and Mullerornis are significantly genetically divergent from each other, with a molecular clock analysis estimating the split around 27 million years ago.[9]

Species

Up to 10 or 11 species in the genus Aepyornis have been described,[13] but the validity of many have been disputed, with numerous authors treating them all in just one species, A. maximus. Up to three species have been described in Mullerornis.[14] Recent work has restricted the number of elephant bird species to three, with two in Aepyornis, one in Mullerornis.[15]

  • Order Aepyornithiformes Newton 1884 [Aepyornithes Newton 1884][13]
    • Genus Aepyornis Geoffroy Saint-Hilaire 1850[16] (Synonym: Vorombe Hansford & Turvey 2018)
      • Aepyornis hildebrandti Burckhardt, 1893 (Possibly divided into two subspecies[15])
      • Aepyornis maximus Hilaire, 1851
    • Genus Mullerornis Milne-Edwards & Grandidier 1894
      • Mullerornis modestus (Milne-Edwards & Grandidier 1869) Hansford & Turvey 2018

All elephant birds are usually placed in the single family Aepyornithidae, but some authors suggest Aepyornis and Mullerornis should be placed in separate families within the Aepyornithiformes, with the latter placed into Mullerornithidae.[15]

Description

Pachystruthio dmanisensis.[20][21] Females of A. maximus are suggested to have been larger than the males, as is observed in other ratites.[15]

Biology

Aepyornis skull

Examination of brain

crepuscular lifestyle. A. maximus had relatively larger olfactory bulbs than A. hildebrandti, suggesting that the former occupied forested habitats where the sense of smell is more useful while the latter occupied open habitats.[22]

Diet

Because there is no

Rhea americana, while the other species (A. maximus, Mullerornis modestus) were probably browsers.[24] It has been suggested that Aepyornis straightened its legs and brought its torso into an erect position in order to browse higher vegetation.[25]

Growth and reproduction

Elephant birds are suggested to have grown in periodic spurts rather than having continuous growth.

precocial.[18]

The eggs of Aepyornis are the largest known for any amniote, and have a volume of around 5.6–13 litres (12–27 US pt), a length of approximately 26–40 centimetres (10–16 in) and a width of 19–25 centimetres (7.5–9.8 in).[18] The largest Aepyornis eggs are on average 3.3 mm (1⁄8 in) thick, with an estimated weight of approximately 10.5 kilograms (23 lb).[15] Eggs of Mullerornis were much smaller, estimated to be only 1.1 mm (3⁄64 in) thick, with a weight of about 0.86 kilograms (1.9 lb).[15] The large size of elephant bird eggs means that they would have required substantial amounts of calcium, which is usually taken from a reservoir in the medullary bone in the femurs of female birds. Possible remnants of this tissue have been described from the femurs of A. maximus.[18]

  • Eggs of Aepyornis (top left) chicken (bottom left) moa (right) and ostrich (centre)
    Eggs of Aepyornis (top left) chicken (bottom left) moa (right) and ostrich (centre)
  • Elephant bird egg (far left, 1) in comparison to other eggs, including ostrich egg (centre, 3) and chicken egg (third from right, 6)
    Elephant bird egg (far left, 1) in comparison to other eggs, including ostrich egg (centre, 3) and chicken egg (third from right, 6)
  • Well preserved egg showing porous surface
    Well preserved egg showing porous surface
  • Egg of Aepyornis standing upright
    Egg of Aepyornis standing upright

Extinction

It is widely believed that the extinction of elephant birds was a result of human activity. The birds were initially widespread, occurring from the northern to the southern tip of

giant lemurs, the aardvark-like animal Plesiorycteropus, and the crocodile Voay.[25] Several elephant bird bones with incisions have been dated to approximately 10,000 BC which some authors suggest are cut marks, which have been proposed as evidence of a long history of coexistence between elephant birds and humans;[28] however, these conclusions conflict with more commonly accepted evidence of a much shorter history of human presence on the island and remain controversial. The oldest securely dated evidence for humans on Madagascar dates to the mid-first millennium AD.[29]

A 2021 study suggested that elephant birds, along with the Malagasy hippopotamus species, became extinct in the interval 800-1050 AD (1150–900 years

hyperdisease) have been proposed as a cause of extinction, but the plausibility for this is weakened due to the evidence of centuries of overlap between humans and elephant birds on Madagascar.[25]

See also

References

  1. ^ Brands, S. (2008)
  2. ^ Etienne de Flacourt (1658). Histoire de la grande isle Madagascar. chez Alexandre Lesselin. p. 165. Retrieved 21 May 2013.
  3. ^ a b c Ley, Willy (August 1966). "Scherazade's Island". For Your Information. Galaxy Science Fiction. pp. 45–55.
  4. ^
    S2CID 203423023
    .
  5. ^ Long, J. A.; Vickers-Rich, P.; Hirsch, K.; et al. (1998). "The Cervantes egg: an early Malagasy tourist to Australia". Records of the Western Australian Museum. 19 (Part 1): 39–46. Retrieved 24 April 2014.
  6. ^ Yoder, A. D. & Nowak, M. D. (2006)
  7. ^ van Tuinen, M. et al. (1998)
  8. S2CID 206555952
    .
  9. ^
    PMID 28089793
    .
  10. PMID 37227001
    .
  11. PMID 33287726
    .
  12. S2CID 59466434
    .
  13. ^ a b Brodkorb, Pierce (1963)
  14. ^ Davies, S. J. J. F. (2003)
  15. ^
    PMID 36854679
    .
  16. ISBN 978-1-4081-5861-6
    .
  17. ISBN 978-1-78548-136-9
    , retrieved 2 May 2023
  18. ^
    ISSN 0024-4066
    .
  19. ISBN 978-1-4081-5725-1
    .
  20. S2CID 88784039
    .
  21. S2CID 198384367
    .
  22. PMID 30381378
    .
  23. ^ Dransfield, J. & Beentje, H. (1995)
  24. PMID 35414222
    .
  25. ^
    doi:10.1016/j.quascirev.2006.02.001
    .
  26. S2CID 85920479
    .
  27. ^ Hawkins, A. F. A. & Goodman, S. M. (2003)
  28. PMID 30214938
    .
  29. S2CID 195555955
    .
  30. S2CID 236313083
    .

Further reading

External links
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