Antediluvian Salad: 2012-07-15

Friday, July 20, 2012

Mountaineering Moa: Coproecology of the Upland Moa (Megalapteryx didinus)

Much like the Mammoth family, Moa birds (Dinornithiformes), are tantalizingly alluring because they only very recently went extinct (13th century A.D.). Like the Woolly Mammoth we don't just have fossils of these avian giants but also mummified bodies, eggs, midden remains and feces. Because of their recent extinction, quality of remains, and the fact that their vegetative habitat still exists in New Zealand allows perhaps better precision in reconstructing their ecology than any other group of extinct mega-herbivores.

A recent paper in PLoS ONE analyzes the preserved coprolites of the Upland Moa (Megalapteryx didinus). 35 coprolites from a remote sub-alpine cave reveal pollen, macrofossil traces, and DNA representing 67 plant species. Included is the first evidence of Moa feeding on the nectar rich flowers of New Zealand flax (phormium) and tree fuchsia (Fuchsia excorticata).

Common in cultivation around world New Zealand Flax Phormium cookianum

The pattern of pollen in the coprolite suggests the Upland Moa made periodic foraging trips up to the sub-alpine zone in the summer but retreated to lower elevations in the winter- perhaps making it vulnerable to newly arrived human hunters. The breadth of plants consumed suggests a generalist herbivore that did not feed at one level or in one type of habitat. The amount of seeds discovered suggested to the researchers that the Upland Moa, and perhaps other Moa species, were important dispersers of seeds in New Zealand vegetative communities. Furthermore, the authors suggest, modern day New Zealand plant communities may yet show further changes in distribution since the loss of these native herbivores is so recent and introduced mammalian herbivores have appeared.

Illustration by Author. Upland Moa (Megalapteryx didinus) enjoying some Phormium cookianum flowers in rocky terrain.

Large extinct megaherbivore, fragile island ecology, introduced mammalian herbivores....hmmm hopefully some of you are connecting the dots between this article and my last article. A quote from the paper:

"The coprolites provide some evidence for recent changes in plant abundance and distribution since human settlement. Fuchsia and wineberry (Aristotelia) were identified from the coprolites using both DNA and pollen, yet were not recorded from the Garibaldi Range by Druce et al. [38]. Both taxa are highly palatable to introduced herbivores [69], [72] and can suffer severe local declines due to over-browsing [73]. Further evidence that the herbivory pressure exerted by introduced mammals on Garibaldi Plateau is greater than that exerted under the prehuman avian-dominated regime comes from the large number of plant taxa in the coprolites (34.3%) that are now largely restricted to trench and sinkhole walls (Fig. 5). Rather than reflecting a tendency for upland moa to feed around these holes, it is more likely that these sites are now refuges to a range of palatable plants, which once may have been more widespread in subalpine herbfields but are now heavily browsed by introduced mammalian herbivores."

Those troublesome ungulates- once again we see that our hoofed friends put undue browsing pressure on a system that previously easily sustained 250 kg 12 foot tall herbivorous birds. In This Island Earth II you will remember I contrasted some of the characteristics that allowed Pygmy Mammoths to thrive with the native vegetation but not feral pigs. Did Moa birds share some of these characteristics? Let's see.

Reproduction. Moa are known for laying small clutches (Holdaway & Jacombs 2001). This makes the Moa reproductively more like the mammoth than the pig. In exceptionally good years they will not overrun their habitat in a single season.

Movement. Based on the pollen evidence the Upland Moa seems to have exploited both upper and lower elevations. Many Moa species show range overlap so perhaps they had some sort of resource partitioning going on. Again, more like the mammoth in utilizing different habitats effectively. Not any one habitat would feel the brunt of Moa browsing.

Food Choices. Again, like the mammoth, the Upland Moa shows a diversity in food choices. Does not put stress on any one type of vegetation. Unlike the pig and say, acorns.

Feet. What do you know, the Moa has relatively soft feet (if not pretty) compared to hoofed mammals. The sharp claws on the Upland Moa foot pictured below were, I postulate, adaptations to negotiate rocky terrain

Again, we can't assume that the size of a herbivore is proportionate to the amount of stress it places on the vegetation!!!

Pertinencia

No Moa: Modeling an Extinction. http://www.archaeology.org/online/features/moa/

Wood JR, Wilmshurst JM, Wagstaff SJ, Worthy TH, Rawlence NJ, et al. (2012) High-Resolution Coproecology: Using Coprolites to Reconstruct the Habits and Habitats of New Zealand’s Extinct Upland Moa (Megalapteryx didinus). PLoS ONE 7(6): e40025. doi:10.1371/journal.pone.0040025

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0040025

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Wednesday, July 18, 2012

Paleo-Myth Number 8: Crocodilians Are An Ancient, Unchanged Family

Archosaur on Archosaur violence

Few archosaurs invoke the title "ruling reptiles" more so than crocodiles. Popular and iconic crocodiles never seem completely satisfied as mere aquatic predators. Never content playing second fiddle to anything in their respective environment- these macropredators challenge, and often win, the dominant mammals around them. And the extent to which crocodiles venture onto land in order to hunt or procure carrion is little appreciated. This reptilian insubordinance hints at a rich and varied ecological history for the group.

While many appreciate that the crocodile lineage is old- it most certainly was not ecologically conservative nor are the extant living species particularly old or "living fossils". A commonly heard mantra on pop-nature programs is that such and such species of crocodile is hundreds of millions of years old or a "living dinosaur". But in reality modern crocodile species arose in the Late Miocene (Brochu, 2001) and are thus at most 5-7 million years ago. The Nile Crocodile for instance is only 2.5-3.5 million years old (Trutnau & Summerlad 2006). The reason for this persistent belief is both cultural and anatomical. From Brochu, 2001:

Crocodylian skulls have been phylogenetically plastic. But the morphospatial region within which they have varied is rather narrow; a limited number of anatomical solutions may exist for a given ecological problem, and because crocodylians tend to interact with their surroundings with their snouts, similar snout morphologies seem to have arisen multiple times in disparate lineages. This may be partially responsible for the widespread view that crocodylians (and crocodyliforms generally) are “living fossils” that have changed little since the Mesozoic. When the group as a whole (living and extinct) is viewed in a phylogenetic context, they no longer look so static.

Five basic Croc snouts in Tertiary. A. Leidyosuchus canadensis, a “generalized” alligatoroid from the Late Cretaceous of North America. B. Thoracosaurus macrorhynchus, a slender-snouted gavialoid from the Paleocene of Europe. C.Alligator mcgrewi, a blunt-snouted alligatorid from the Miocene of North America (drawing adapted from Schmidt, 1941). D. Mourasuchus, a duck-faced caiman from the Miocene and Pliocene of South America (drawing adapted from Price, 1964 and Langston, 1965). E. Pristichampsus vorax, a ziphodont crocodylian from the Eocene of North America (drawing adapted from Langston, 1975). Drawings not to scale; A through D in dorsal view, E in right lateral view

So the crux of the matter is that differing crocodile lineages, constrained by ecological design, come up with remarkably consistent solutions to fit their given morpho-eco space. In this manner crocodiles appear relatively little unchanged since the Mesozoic but in truth we have multiple lineages adapting to the unchanging constraints of living as an amphibious predator repeatedly throughout their geological history.

One of the revelations in recent years has been the unexpected diversity of crocs in the Mesozoic.

L-R. Stomatosuchid, Sebecosuchian, Metriorynchid, Spenosuchian. from Tetrapod Zoology

Indeed the variety of crocodiles in this time period borders on the comical- and ultimately suggests that they were aggressive competitors with dinosaurs, marine reptiles, and mammals for an astonishing variety of niches.

Giving theropods a run for their money and perhaps grabbing the top terrestrial predator throne in parts of Cretaceous Gondwanaland were the Sebecosuchids.

Growing up to 4 meters long, these were not insignificant predators and if alive today would no doubt be considered large predators. How and to what extent they interacted with theropods has been of great interest and conjecture. They were most likely ambush rather than pursuit predators and possibly tried to give a devastating first blow to the prey to mortally wound it.

Sebecosuchian attacking an indeterminate ornithopod. Illustration by Author.

But there were also smaller more gracile guys like the Spenosuchians.

Illustration by Author. Spenosuchian.

Indeed this veritable racehorse of a croc so characterized early crocodilians as terrestrial runners that the four chambered heart of modern crocodiles is most parsimoniously explained as an anatomical anachronism leftover from when crocodiles were actually endothermic (warm blooded). As crocodiles expanded into freshwater niches as ambush predators a slower metabolism was evolved that more suited that lifestyle.

There were also burrowing herbivorous crocs, duck billed crocs, and armadillo like crocs- but you can go interwebbing for those if you choose to...

Well, this post is not meant to be exhaustive- I just wanted to dispel the myth of modern crocs as "evolutionary holdovers from the distant past". This topic has been blogged about extensively by Darren Naish, check out the links below.

Cheers!!