Saturday, February 9, 2013

New ‘chid on the block

Azhdarchids are just plain weird animals. Theories on the lifestyles of these bizarre pterosaurs have ranged from depicting them as giant vultures, big shorebirds probing in sand and mud, and even as skimmers dragging their jaws along the water to catch fish. It wasn’t till 2008 that a reevaluation of the fossil evidence was conducted, and in a groundbreaking paper by Mark Witton and Darren Naish, it was determined that the azhdarchids had lifestyles similar to storks or ground-hornbills: they stalked their prey on dry land, walking and possibly even trotting or running along, using their huge heads and bills to subdue anything from amphibians to small dinosaurs. (Witton & Naish, 2008)
The newly-discovered azhdarchid, Eurazhdarcho. Reconstruction by yours truly.
This week, news of a new species of azdarchid from Romania was published. Eurazhdarcho langendorfensis had a wingspan of 3m (~10ft), and while it wasn’t the largest species (in fact, it is ranked among the smallest), it still would have been a sight to behold in the flesh. The discovery of any new species from this bizarre family of reptiles is significant, as most fossilized azhdarchids are known from very fragmentary remains. E. langendorensis, in fact, is one of the most complete specimens, yet it is only known from 15 individual bones.

Even more interesting than the (relative) completeness of E. langendorfensis is the environment in which it lived. At the time when Eurazhdarcho lived, Romania was an island in the Tethys Sea. As part of a great archipelago, it was one of numerous scattered islands which would one day form Europe. On this island, which was then covered in dry forests and seasonally swamped with monsoonal rain, Eurazhdarcho lived alongside a variety of dinosaurs. This was a continental, terrestrial environment rather than a coastal or oceanic one, further enforcing the hypothesis that azhdarchids were the “terrestrial stalkers” that Witton and Naish had proposed.(Vremir et. al, 2013) However, Eurazhdarcho wasn’t the only stalker on the island. There was something far, far bigger.
The monstrous Hatzegopteryx. Reconstruction by Mark Witton.
Hatzegopteryx thambema was a tremendous animal: as tall as a bull giraffe, it weighed up to 250kg (~550lb) and sported a 12m (~40ft) wingspan. Four times as large as Eurazhdarcho, H. thambema was likely the dominant predator of the island; with a massive, toothless beak, it likely ate just about everything it could swallow, from amphibians to small dinosaurs to foliage. Yet, while H. thambema grew to epic proportions which far dwarfed Eurazhdarcho, the two species were able to coexist.

Sympatry is when closely-related species, which differ in size, overlap in range but not in niche. This is a common occurrence in the modern world, and it comes as no surprise that it happened in the Mesozoic Era, but fossil evidence of this is uncommon. The fact that H. thambema and Eurazhdarcho overlap in range indicates an instance of prehistoric sympatry. The two avoided competition by simply feeding on different diets; the larger of the two species was adapted for a larger menu, while the smaller could exploit resources which the larger may overlook. This eliminates competition and allows the two species, no matter how different in size or similar in genetics, to both survive in the same habitat.
Evidence for sympatry in azhdarchids has been found in both North America and Europe. Image from Vremir et. al, 2013.
The remains of small azhdarchids are commonly found in the same formations as giants are. Perhaps, like herons or egrets, several species of azhdarchid inhabited the same environment and used the same generalist feeding strategy, separated only by size. Fossils not only have the ability of individual animals and species, they give us a clear picture of how these species interacted with one another. Each discovery we make, the Mesozoic world becomes a much more complex and beautiful one.


Vremir M, Kellner AWA, Naish D, Dyke GJ (2013) A New Azhdarchid Pterosaur from the Late Cretaceous of the Transylvanian Basin, Romania: Implications for Azhdarchid Diversity and Distribution. PLoS ONE 8(1): e54268. doi:10.1371/journal.pone.0054268

Witton MP, Naish D (2008) A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. PLoS ONE 3(5): e2271. doi:10.1371/journal.pone.0002271

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