Early origin of artiodactyls in South America

February 9, 2021

Bonaparte’s (1999) description of the Early Cretaceous sauropod Agustinia ligabuie was notable for its identification of nine bony fragments as representing dermal armour, which he classified into Types 1–4. Here are some examples:

Bonaparte 1999: figure 3. Agustinia ligabuei gen et sp. nov. Osteoderms. A, Type 1. B, Type 2. C, Type 3. Abbrev.: po, thick proximal ossification.

Consequently, Augustinia was for many years restored as uniquely spiky, a sort of “stegosaur sauropod”:

But Bellardini and Cerda (2017) showed that the so-called “osteoderms” are probably no such thing, but represent other, more normal, bony elements. Bonaparte’s types 1, 3 and 4 were all reinterpreted as complete or partial dorsal ribs, and type 2 as a portion of the iliac blade:

Bellardini and Cerda 2017: figure 6. Bony element type 2 (MCF-PVPH-110/08) of A. ligabuei, in medial (A1–2), and lateral views (B1–2) with interpretive line drawings. In this work we propose that MCF-PVPH-110/08 is a dorsal portion of the left iliac blade, centered above the acetabulum (C). Abbreviations: dmil dorsal margin of iliac blade, poap post-acetabular process, prap pre-acetabular process, sr sacral rib. Dashed lines indicate missing bone. Asterisks indicate the hypothetical position of morphological features.

However, careful re-examination of Bellardini and Cerda 2017: figure 6: part A1 shows clearly that the so-called type-2 osteoderm is in fact a sheep:

This is a significant finding, as the origin of Artiodactyla is generally held to have occurred in the early Eocene, with the earliest known representatives being from Europe, Asia, and North America (Rose 1996). The reidentification of the A. ligabuei type-2 osteoderm as a sheep pushes back the origin of artiodactyls by some 60 million years to the Aptian or Albian, and locates South America as the continent of origin.

References

  • Bellardini, Flavio, and Ignacio A. Cerda. 2017. Bone histology sheds light on the nature of the “dermal armor” of the enigmatic sauropod dinosaur Agustinia ligabuei Bonaparte, 1999. The Science of Nature 104(1):1-13. doi:10.1007/s00114-016-1423-7
  • Bonaparte, Jose F. 1999. An armoured sauropod from the Aptian of northern Patagonia, Argentina. pp. 1-12 in Y. Tomida, T. H. Rich and P. Vickers-Rich (eds.), Proceedings of the Second Gondwanan Dinosaur Symposium, Tokyo National Science Museum Monograph 15. Tokyo National Science Museum, Tokyo. x+296 pp.
  • Rose, Kenneth D. 1996. On the origin of Artiodactyla. Proceedings of the National Academy of Sciences 93(4):1705-9. doi:10.1073/pnas.93.4.1705

 

11 Responses to “Early origin of artiodactyls in South America”

  1. Brad Lichtenstein Says:

    That’s not a sheep! Nay! It’s an equid!

  2. Zach Miller Says:

    Next you’ll be telling us about Permian bears.

  3. llewelly Says:

    I think that’s a BAA-D interpretation of that bony element.

  4. Mike Taylor Says:

    Not bad, llewelly. Perhaps you think I was just determined to ram the artiodactyl origin back into the Cretaceous?

  5. Lars Dietz Says:

    So Ameghino was right when he said in the late 19th century that all major mammal groups originated in South America in the Cretaceous…
    Although much earlier artiodactyls have been described from Japan, all of them only a few mm in size:
    Okamura, C., 1987. New facts: Homo and all vertebrata were born simultaneously in the Former Paleozoic in Japan. Original Report of the Okamura Fossil Laboratory, 15, pp.347-573.

  6. Matt Wedel Says:

    The Bio library at UC Berkeley has the collected reports of the Okamura Fossil Laboratory. One of my few regrets from my time there is that I never got around to photocopying or scanning them. Maybe I can make a return pilgrimage one of these days and get that done.

  7. Brad McFeeters Says:

    Might be time to reevaluate the relationships of Carnotaurus.

  8. Nick Pharris Says:

    I get the feeling you’re pulling the wool over our eyes…

  9. Mike Taylor Says:

    I would never do that to ewe.

  10. Matt Wedel Says:

    You should both be lambasted for these puns.

  11. Mike Taylor Says:

    You know what Count Dracula would say to that? “Oh, Vine away!”


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