Guardian of the Forest

Evolutionary biology is rife with great sound bites that have, usually for worse, been appropriated for social means- nature red in tooth and claw, survival of the fittest- and the unfortunate, bastardized corollaries of Social/Free Market Darwinism. Too often we are drawn into looking at the natural world through the lens of the hyper-competitive, exclusionary, kill or be killed, survival of the fittest paradigm. And no doubt these struggles exist, are readily observable, and play a role in the saga of life. But what often gets tossed aside, ignored, or simply ramrodded is the extent to which commensal relationships shape and motivate the interplay of species in a particularly nuanced fashion. And of particular importance to me in terms of both extinct and extant species is the concept of keystone species. For it is the presence of particular keystone species that most ameliorates the conditions for the maximum diversity and abundance of a multitude of other species.

Now I have shouted from the top of my little mountain in this small little corner of the interwebz that we need to pay attention to keystone species, past and present. My sister blog, southland beaver, is essentially a tribute to one of the most magnanimous keystone species of all time- Castor canadiensis- and how reintroduction of this rodent into Californian watersheds can, relatively economically, assist in everything from steelhead salmon restoration to flood control. And if keystone species are important in contemporary ecosystems, I do not think I am overstepping the bounds of rational thought to suggest keystone species in the past and particularly in dinosaur dominated ecosystems were also important. I have been critical at the lack of paleoecological studies that take into account commensal/keystone species concepts. Many of the more interesting topics in dinosaur ecology have to do with how do so many large animals coexist ecologically? The Kem-Kem of Africa, with its abundant theropods or Laramidia with its never ending diversity of large ornithischians are great examples. These ecosystems have perplexed people and most studies have focused on niche pertitioning as a way to reduce competition. But this is looking at these ecosystems through the guise of competition. Although less readily apparent, and some may argue impossible to tell from the fossil record, invoking commensal relationships and particularly keystone species concepts addresses these problems more succinctly I believe. For Laramidia, as I have argued here, ceratopsids were the keystone species due to their ability to fell and clear forested areas lowering the browse height for other dinos and turning over nutrients quickly. In the Kem-Kem I argued here that spinosaurids, due to their superior fishing abilities, opened up opportunities for other theropods through klepto-parasitism, scavenging, and as prey.

But in this post I want to talk about not an animal but a plant that acts as a keystone species, Dicranopteris linearis- the Old-World Forked Fern or Uluhe. And I also want to muse a bit about how this plant,  or uluhe- may offer insight into Mesozoic ecosystems as the fern family it belongs to, Gleicheniaceae, was particularly abundant and widespread through the Mesozoic.

Dicranopteris linearis. Forest & Kim Starr. Wiki Commons

For this post I am pulling most of the info from this paper The ecology of climbing fern Dicranopteris linearis on windward Mauna Loa, Hawaii. It's free go read it. But let me give you the quick and dirty summary.

Ulehe is a little unusual for a fern because it requires full sun, if it is too completely shaded by high canopy it will diminish and die. As such it grows in newly cleared/disturbed areas such as roadsides, forest clearing, landslides, fire damaged areas and even lave fields. While spore germination is likely the primary method of colonizing newly disturbed areas, once the fern is established it quickly spreads through rhizomatous growth and aggressive shoot growth. These shoots, which can reach 6 meters in length, grow long initially to cover as great an amount of area as possible and the secondary fiddleheads emerge from side growths along the length of the shoot. This habit of growth also allows the fern an ability as a climber as well. All together this rapid colonization and monopolization of forest clearings is akin to a vegetative "blitzkrieg" forming immense fern thickets up to 3 meters thick. Not only that but after establishment the leaves and stems quickly die but are slow to decompose, even in wet and hot Hawaii. A dense mat of slowly decomposing dead fern substrate/forest detritus prevails allowing the ferns own rhizomes and roots to spread through it. The fern has also been suggested to have some allelopathic characteristics, preventing the germination of seedlings within its fern thicket network.

Ok, so we what we have here is basically an ecological pioneer species in forest succession. A lot of competition/exclusion going on here- how does this plant serve the forest community as a whole? How is it a keystone species?

Well the key role that the fern serves, remember it only grows in full sun, is that by monopolizing recently cleared areas it serves to prevent pioneer exotic species of plants from getting a toehold in these   pivotal areas. This notion if corroborated by the observation that where the fern has been eliminated, invasives have made inroads into the larger native forest ecosystem.

But the Hawaiian islands are the most remote landmasses on earth, the only reason invasives are a problem is because of man. And I am not just talking western man, Polynesians brought their own grab bag of non-native flora and fauna to Hawaii. True, but this gets into a larger debate on is man part of the natural world or separate? Well I tend towards the belief that man, although often psychologically removed from the natural world, is still part of it. And if you step back into the larger scope of geologic time, if you go back in the paleoecological history of all species- at one time or another in their lineage they were an invasive species at some time/place. Following from this, the invasives of today- spread by man or not- will be the natives of tomorrow somewhere in the geological future.

But the point to remember here is that the unique and diverse flora of Hawaiian tropical forests- once established- has been maintained by the uluhe fern.

So what does this man for Mesozoic times? Well as mentioned earlier Gleicheniacean ferns were particularly abundant and diverse during the Mesozoic. If they had similar adaptations to modern forms, which is a good probability, then it stands to reason that they may have served similar functions. Perhaps in addition to colonizing talus slopes, they colonized land cleared by particularly rambunctious herds of titanosaurs or iguanodonts? And that these fern thickets served as particularly useful hiding/ambush sites for even very large dinosaurs? Recall that uluhe forms thickets 3 meters tall, with detrital substrates up to 1 meter thick. Now I have always been particularly outspoken on the tendency of paleoartists to conveniently place dinosaurs on exposed plains for maximum visual framing. I get it, people want to see the dino in full visual glory, except that once you start looking at how often this style is repeated- it starts to provide a bit of a disservice as to how modern animals use and move through vegetation.

Indian One Horned Rhino. Kaziranga Park India. Wiki Satish Krishnamurthy

When I think of dinos moving through gleicheniacean fern thickets I am reminded of large mammals moving through elephant grass in places like Kaziranga park in India. Fully grown rhino, elephants, and water buffalo can disappear seamlessly into the 3-4 meter tall elephant grass. Large dinosaurs would have behaved much the same in Mesozoic fern thickets. While large herbivores likely foraged and hid in these thickets, theropods-especially large ones- may have found them particularly useful as ambush sites.

I recall a documentary I saw on cassowaries once, don't recall name of it presently, and the one scene that leapt out at me was one of a cassowary scrambling up a near vertical, highly vegetated hill side. With only two legs and no grasping appendage this bipedal land bird left the pursuing human in the dust- who had not the slightest clue as to how to navigate the difficult terrain. It was startling how easily the cassowary put up distance. Ok, now let's take this observation of a modern theropod in difficult, thickly vegetated terrain and do a little Mesozoic thought experiment.

Pushed out by it's larger brethren from the lowlands the teenage albertosaur had settled in this mountain valley in the Laramidian highlands. At about 2000 meters the winters were cool but not frigid, a little bit like the Malaysain highlands, vegetation was dense and the larger herbivores were rare- but they were too large for the 15 foot, 1000 lb predator to tackle anyways. More importantly larger tyrannosaurs, including those of his own species who would just as soon predate on him as steal his kills, were basically absent. Through much of the year pickings were slim for the predator- a pachy here or there, an unwary smaller theropod or even a smaller albertosaur snagged occasionally. But the albertosaur had remained because at least during a few months of the year, what you might call the Fall season, hunting was exceptionally good. And this is when the ginkgo trees were in mast.

Growing only at these higher elevations the gingko trees when fruiting attracted a multitude of dinos to consume the stinking fruits seasonally. But by far the biggest emigrant to the mountain valleys were numerous bands of Struthiomimus altus. Now the young albertosaur had learned through trial and error that these ornithomimids were a particularly hard catch. Excellent vision and group foraging strategy meant they were almost impossible to stalk. And even if you did sneak up close to one they were more maneuverable and just as fast as the theropod. And now that the young albertosaur was getting bigger it was slowing down so any speed advantage was becoming a wash.

But the young albertosaur had learned of a particular spot where it had a distinct advantage. The most productive mountain valley narrowed down into a 50 meter draw and in order to enter the valley one had to negotiate this draw. In addition to being narrow this draw was highly disturbed by landslides and seasonal flooding. So much so that trees could not get a good toehold but instead vast thickets of gleichenaceous ferns dominated growing 4 meters high with a thick miry substrate of decaying vegetation. 

So here in this particular microhabitat our young albertosaur would set up ambush after ambush. In the thick vegetation the speed and maneuverability of the ornithomimids were neutralized and the larger albertosaur, being absolutely taller in leg and stature than the ornithomimids, actually had a distinct advantage. It was actually able to walk over and through the thick vegetation more easily than the smaller ornithomimids- who sometimes got mired in the tangle of growth. In this manner, during the gingko mast, the young albertosaur hunted efficiently and easily during several months of the year dining on intrepid ornithomimids and eventually growing large enough to move down to lower elevations and dine on larger dinos.

So, long story short, pay attention to them ferns- especially Gleicheniales- as they may offer unique insight and context to dino mediated Mesozoic ecosystems. And for any paleoartists out there put more of these ferns in your art- they offer a lot of unique patterns, angles, and textures in their growth. Go here to look at some examples. And if you want to go further on Mesozoic ferns I have some links below to pertinent papers.

Gleichenia polypodiodes. Africa. wiki. Paul Venter

Cheers!!

Pertinencia

Biodiversity and the Reconstruction of Early Jurassic Flora from the Mecsek Mtns (S. Hungary)

Early Cretaceous Gleicheniaceae and Matoniaceae (Gleicheniales) from Alexander Island, Antarctica

Ecology of the Early Cretaceous Ferns of China

Ecology of Some Late Triassic to Early Cretaceous Ferns of Eurasia

Fern Ecological Implication from the Lower Jurassic in Western Hubei, China

Ferns in an Angiosperm World: Cretaceous Radiation into the Epiphytic Niche and Diversification on the Forest Floor

Floral and Environmental Gradients on a Late Cretaceous Landscape

Fern Spore Diversity and Abundance in Australia During the Cretaceous

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Strange Ornithopods of South America

Talenkauen. Gabriel Lio (c)

It's patently obvious that dinosaur paleontology, like all sciences, does not arrive devoid of cultural trappings and the limitations imposed on it by the socio-political boundaries of the time. One need merely look back a few decades ago when the iconic dinosaur faunas of late Cretaceous Western North America were heralded as the "typical" dinosaur fauna of the time. Fortunately ventures to far flung places around the globe by both western and non-western scientists has increased our knowledge of dinosaur faunas. Because of this more globally conscious awareness of dinosaur faunas it can now be argued that the famed North American fauna of the late Cretaceous, you know the iconic tyrannosaurid-ceratopsid-hadrosaurid triumvirate,  is actually a bit of an outlier for the time. In some areas primitive tyrannosaurids held sway while in many areas of Gondwana a rotating cast of abelisaurs, carcharodonotsaurs, unenglianes, spinosaurids, and neovenatorid allosaurids duked it out. Titanosaurid sauropods were ubiquitous in almost all areas as well as dicreasosaurid and rebbachiasaurid sauropods. Nodosaurid ankylosaurs persisted in many areas, even Antarctica. And ornithopods were around too, yeah those boring guys that only drink, nibble and act scared in dinosaur pictures. Ornithopods are at best portrayed as "meals on wheels" for the theropods hordes- movable cannon fodder for the infinitely more interesting predatory dinosaurs. Even among herbivores they take second stage to prickly horned/armored dinos, feathered dinos and massive sauropods. But I want to challenge this idea of boring ornithopods. A steady trickle of discoveries of gondwanan ornithopods has been coming to light for several decades suggesting a previously unheralded diversity of Gondwanan ornithopods. Some types may have been semi-aquatic, some highly cursorial, and others may have been specialized browsers converging with the northern therizinosaurid dinos. And some may have been massive, based on the ichnological (footprint) evidence.

For this post I want to concentrate on Cretaceous ornithopods of South America. Much of the information for this post is taken from the awesome tome The Age of Dinosaurs in South America by Fernando E. Novas. An excellent book by the way full of loads of illustrations, comprehensive but pretty technical- check it out. This is by no means meant to be a comprehensive review of what is known for these guys- I just want to highlight some of the more interesting aspects of these critters that caught my attention.

While South America has gained notoriety in dino circles in recent years for the massive saurischians found there such as Giganotosaurus and Argentinosaurus, it has also become apparent that diverse and sometimes fairly large ornithopods also inhabited the South American land mass during the Cretaceous.  So far this data consists of abundant ichnological evidence from multiple localities throughout the epoch and osteological remains from the upper Cretaceous of Patagonia. Although the skeletal remains are limited in scope and abundance, what we do see suggests a unique radiation of southern ornithopods- possibly representing one or more families unique to Gondwana. Recognized by Cambiaso (2007) these derived iguanodontid ornithopods of South America form a clade of the genera Talenkauen, Macrogrhyphosaurus, and Anabisetia - nestled between Muttabaurrasaurs and Camptosaurus.  The fourth South American ornithopod known from good remains, Gasparinisaurua, is more basal- nestled between Yandusaurus and Hypsilophodon. 

Gasparinisaura cingosaltensis for all intents and purposes looks like a throw-back to the types of ornithopods seen scampering under the feed of massive sauropods in many dinosaur illustrations. And there is some truth to this- as most research points out this species is fairly basal among ornithopods even though it comes from the early late Cretaceous of about 83 mya. Despite its generally conservative design it featured some derived characters, such as a first metatarsal reduced to splint and subtriangular distal caudal chevrons. The second feature is unique among ornithopods, with the exception of Macrogryphosaurus, and is accompanied with a reduction of transverse processes and elongation of the prezygophyses. All together these features are interpreted as adaptations towards extreme cursoriality and converge with tyrannosaurids and ornithomimids (Novas, 2009). Other notable feature of this taxon is large orbits and evidence for gastroliths (see below).

Gasparinisaura gastrolith. Coria and Salgado. 1996 (c)

Anabisetia saldiviai from the Nequeun basin, Patagonia-Agentinia is slightly older than Gasparinisaura but more derived and slightly larger at about 2 meters. Known from four partial skeletons Anabisetia, like Gasparinia, shows several obvious adaptations towards a cursorial lifestyle as seen in the skeletal reconstruction towards the left, most notably

the long lower leg bones. The most unique feature of this ornithopods is the well developed acromial process which is taken further than in any other ornithopod. In humans the acromial process is an important site for muscle attachment and, in concert with the trapezius muscle, allow us to raise our arm above our head and pull back. Given that Anabisetia also had grasping fingers, it stands to reason that such shoulder development in this animal possibly assisted it in grasping and bringing down low branches and vegetation. Coupled with the long, gracile neck such an adaptation may have proved useful for a small browser.

Talenkauen santacrucensis was much larger than Gasparinisaura and Anabisetia at about 4 meters. Being substantially larger, this ornithipod starts to show a skeleton more reflective of a graviportal animal- with stouter lower leg bones and thicker femurs than the other smaller ornithopods we discussed. However the neck, forelimbs, and general build suggest an interesting compromise between a robust and gracile animal. One of the more unusual features of this critter are the ovoid bony growths visible between the ribs.

Talenkauen. Novas 2001 (c)

Too thin to offer much protection, they have been proposed to assist in ventilation- although a lack of muscle attachments calls this idea into question. It is quite possible that they are homologous to uncinate processes present in many diapsids and are more widespread than thought in many dinosauria. Perhaps they served as a repository for calcium to be drawn upon during egg laying? All in all Talenkauen is not too dissimilar to Dryosaurus in appearance but with longer neck and forelimbs- both consistent with a habit of low browsing.

Macrogryphosaurus gondwanicus is the largest non-hadrosaurid ornithopod known from skeletal remains in South America. The name means "big enigmatic lizard" and it fits. Unfortunately lacking skull and leg bones the remains indicate a subadult animal at 6 meters longs, so the adult may have been well over 20 feet long. I drew a very liberally interpretive drawing below, however on retrospect I should have given it a smaller head- but like the other ornithopods discussed it was likely an obligate biped with grasping arms/hands and a fairly long neck. More discoveries await. Together with Talenkauen this dinosaur has been proposed to form the clade Elasmaria (Calvo, Novas 2007). It also was found with those interesting quasi uncinate plates on its thoracic areas. Thescelosaurus from North America Maastrichtian is also known for these growths. One is forced to wonder if Thescelosaurus is not actually fairly close/or a member of the Elasmaria and is actually a southern transplant like Alamosaurus? I don't know but it is an interesting idea to explore because at least superficially they look Thescelosaurus looks a little like the southern ornithopods....

Macrogryphosaurus gondwanicus. Duane Nash (c)

Was Thescelosaurus related to South American Ornithopods?

In addition to the above species Novas also details the scanty remains of several "hen-sized" ornithopods, the enigmatic Notohypsilophodon/Loncosaurus, and a putative Ouraanosaurus like caudal vertebrate from South America.

Ichnological evidence offers a very compelling body of evidence suggesting abundant/diverse ornithopods from the South American Cretaceous. Large quadrupedal ornithopod footprints of at least 50 cm are known from the early Cretaceous, the only known quadrupedal ornithopod from South America. These footprints also give evidence of unknown large ornithopods in the early Cretaceous South America. Later in the Cenomanian we have evidence of very large- 60-65 cm- bipedal ornithopod footprints suggestive of an animal at least 9 meters long.

Although not as well publicized as other recently discovered dinosaurs in South America, what we do have from South America is suggestive of a previously unrecognized diversity of ornithopods there. Hopefully future discoveries will shed more light on the interesting ornithopods of South America.

Cheers!!

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