Picture of the Indiscriminate Interval #000002 - Common Greenbrier

What's this strange, sessile, photosynthesizer doing on The Lord Geekington?

Common Greenbrier (Smilax rotundifolia) frequently forms immense thickets which make trekking through the woods nigh-impossible without a machete or flamethrower. I fondly recall one instance of getting hooked into a patch below a nest of angry hornets; somehow I remain among the few souls to go through these things voluntarily. Judging by the capacity of this species to form bleak monocultures, I assumed this was an introduced species that went invasive - how wrong I was.

Transition into a woody portion of the stem.

In the 19th century, nearly 80% of the Northeastern USA was cleared for agriculture (mostly pasture) but by the mid-20th forest covered exceeded 70%, where it remains to this day (Bellemare et al. 2002). Smilax rotundifolia is a native species that goes 'invasive' in post-agricultural sites, growing over and eventually shading out other shrubs and herbaceous plants (Hemond et al. 1983, Ohman 2006). The super-dominant species can turn grasslands into scrublands, making naturally occurring fires less frequent and more intense (Ohman 2006). Greenbrier also forms a dense understory in post-agricultural forests where it has a deleterious impact on forest regeneration, causing low tree density and diversity (Abrams and Hayes 2008). In some areas it appears Smilax will continue to run rampant without intervention (Abrams and Hayes 2008), but curiously it has been reduced in at least one locale due to peripheral shading from a maturing forest (Hemond et al. 1983).

I challenged myself to take the ugliest photo possible. This is supposed to be a trail, by the way.

It doesn't seem clear if Greenbrier will eventually return to its pre-disturbance state any time soon, if at all, as the degree of human disturbance in the Northeast is a singular situation. Smilax is very hard to get rid of as rhizomes (underground stems) allow for dispersal, can persist for years without above-ground stems, and the plants are resistant to herbicides (Richburg et al. 2000 - citing Gleason and Cronquist 2001, Carey 1994). In an ironic twist - the species is Threatened in Ontario! What a topsey-turvey world we humans have unwittingly created.

References:

Abrams, M., and Hayes, V. (2008). Impacts of contrasting land-use history on composition, soils, and development of mixed-oak, coastal plain forests on Shelter Island, New York. Journal of the Torrey Botanical Society 135(1), 37–52. Available.

Bellemare, J., et al. (2002). Legacies of the agricultural past in the forested present: an assessment of historical land-use effects on rich mesic forests. Journal of Biogeography 29, 1401–1420. Available.

Hemond, H., et al. (1983). Two Decades of Vegetation Change in the Connecticut Arboretum Natural Area. Bulletin of the Torrey Botanical Club 110(2), 184-194.

Ohman, M. (2006). Characteristics of fuel beds invaded by Smilax rotundifolia. Master's Thesis presented to UMass Amherst. Available.

Richburg, J. (2001). Woody invasive species and their role in altering fire regimes of the Northeast and Mid-Atlantic States. Proceedings of the Invasive Species Workshop: the Role of Fire in the Control and Spread of Invasive Species. Fire Conference 2000: the First National Congress on Fire Ecology, Prevention, and Management. Miscellaneous Publication No. 11, Tall Timbers Research Station, Tallahassee, FL. Available.

Picture of the Indiscriminate Interval #000001 - Barred Owl

Strix varia (Barred Owl) suffering from a cataract. From my Flickr.

The Lord Geekington has a proud history of haphazard posting frequency, so sharing my infrequent competent animal photographs seems like a logical extension of this. Unlike most bloggers, I am utterly incapable of just sharing a photo.


Barred owls are medium-sized (0.5-1.0 kg, ~1 m span) strigid owls easily recognized as the only 'true' owl in the eastern half of North America with dark brown eyes. They have recently and quite rapidly expanded into the western portion of North America; in California the owls were first sighted in 1981 and by 1996 were known from 61 specimens in 12 counties (Dark et al. 1998). Hybrids between male Barred Owls and native female Spotted Owls (S. occidentalis) have been recorded - as have backcrosses (hybrid x non-hybrid) - but this phenomenon may be uncommon and thus fairly inconsequential (Kelly and Forsman 2004). It is still worth noting that hybrid x Barred Owl progeny are rather numerous (implying high fitness?) and that those F2 specimens are hard to correctly identify in the field (Kelly and Forsman 2004, Funk et al. 2007). It appears that the most problematic aspect of the Barred Owl invasion is the aggressive nature of that species and its apparent overlap in niche with the Spotted Owl, despite occupying somewhat different habitats (Buchanan et al. 2004). Computer modelling predicted that most of the Spotted Owl's northern range (down to about 38° N) has the potential to be invaded by Barred Owls (Peterson and Robins 2003).

It is hypothesized that the range expansion of Barred Owls is due to anthropogenic changes, as it is difficult to explain the very recent range expansion otherwise (Dark et al. 1998). So what can be done against the invasion? Buchanan et al. (2007) note that most aspects of the invasion remain uncertain and controversial - most importantly if the Barred Owl is indeed directly causing the Spotted Owl population decline - and that further research of the Strix species interrelationship is needed. This is a highly complicated issue, especially considering the interests of some groups, but it certainly appears that the situation for the Spotted Owls is dire and that research and management plans are needed (Buchanan et al. 2007). It is unfortunate that most biological invasions are past the point of no return once they are recognized - but this does not always have to be the case!

References:

Buchanan, J. et al. (2007). A synopsis of suggested approaches to address potential competitive interactions between Barred Owls (Strix varia) and Spotted Owls (S. occidentalis). Biological Invasions 9, 679-691. DOI 10.1007/s10530-006-9068-7

Buchanan, J. et al. (2004). A Comparison of Barred and Spotted Owl Nest-Site Characteristics in the Eastern Cascade Mountains, Washington. Journal of Raptor Research 38(3), 231-237. Available.

Dark, S., et al. (1998). The Barred Owl (Strix varia) invasion in California. The Auk 115(1), 50-56. Available.

Funk, W., et al. (2007). Microsatellite loci for distinguishing spotted owls (Strix occidentalis), barred owls (Strix varia), and their hybrids. Molecular Evolution Notes 7, 284-286. doi: 10.1111/j.1471-8286.2006.01581.x

Kelly, E., and Forsman, E. (2004). Recent Records of Hybridization between Barred Owls (Strix varia) and Spotted Owls (S. occidentalis caurina). The Auk 121(3), 806-810. Available.

Peterson, A., and Robins, R. (2003). Using Ecological-Niche Modeling to Predict Barred Owl Invasions with Implications for Spotted Owl Conservation. Conservation Biology 17(4), 1161-1165. Available.

Stupendemys: Giant Amongst Mega-Turtles

In the first post of this accidental series, I raved about using Strait Carapace Length (SCL) to compare turtle sizes, made up the designation 'Mega-Turtle' for species regularly exceeding a 2 meter SCL, and to my horror discovered that proper descriptions of most Mega-Turtle specimens are either very hard to find or currently non-existent. At some point I'd love to cover the more obscure Mega-Turtle and near-Mega-Turtle species, but my taste of the topic thus far was of sheer frustration. This post will finally cover my intention of writing about Mega-Turtles in the first place: giving some attention to the largest species of them all, for once.

Oh, and here's the teaser graphic from last time with proper captions:

Left to Right: Archelon ischyros (black) with speculative 2.5 m SCL (4.5 m total length); A. ischyros (gray) with 1.93 m SCL - also representing speculative Protostega gigas of similar size (both 3.4 m total length);  Psephophorus sp. (black) with speculative 2.1 m SCL (model based on extant leatherback); average extant leatherback (Dermochelys coriacea) (gray) with 1.5 m SCL; Drazinderetes tethyensis with known 1.25 m bony shell (black) and speculative ~2 m soft shell (gray); Stupendemys geographicus specimens, discussed below.

The colorfully named Stupendemys geographicus is a pleurodire, or side-necked turtle, and hence a very distant relative of the other Mega-Turtles. Stupendemys was discovered in 1972 from "late Tertiary" deposits in Venezuela and first described in Wood (1976). The paratype specimen described by Wood (1976) had a fairly complete carapace (amongst other bits and pieces) with an SCL of 2.35 m and carapace width of 1.85 m - it is the gray shell in the above figure. Another author (Wood 1982) estimated the specimen had a total length of 3.65 m and weight of roughly 2 tonnes, presumably from scaling up extant relatives. The type specimen was more fragmentary and even larger, with an estimated SCL of 2.50 m and width of 1.90-1.95 m (Wood 1976). The Pierre Shale Archelon probably has an SCL comparable to the Stupendemys type specimen, although it is hard to say which is larger as Archelon has a very wide carapace and Wood (1982) suggests it was lightweight compared to Stupendemys geographicus due to reduced ossification. It is curious that popular sources claimed Archelon to be the 'largest turtle ever' in the first place - possible explanations include the discovery of Archelon in the English-speaking world and subsequent bias, the impressive completeness of the Yale and Vienna specimens, and only having the 4.5 m total length figure reproduced*. There is no longer any excuse to claim Archelon as the record-holder.

* Heuvelmans (1968) humorously stated the Yale specimen had a 12 foot carapace and 25 foot total length - despite a plate in the book clearly demonstrating otherwise! He then goes on to claim that "[t]here are some reasons for thinking that such giants might have survived" and listed some vague Father-of-all-the-Turtles type legends. Curiously, he tossed the type in the end due to vagueness.



In 1992, and the same locale as the type and first paratype, a Stupendemys geographicus was uncovered with a 3.3 m SCL and 2.18 m carapace width (Scheyer and Sanchez-Villagra 2007, Orenstein 2001) - this specimen is portrayed as the black shell on the increasingly distant figure. It is astounding that the largest known turtle shell is only from the late Miocene, or approximately 5-6 million years ago. Scaling up from the extrapolations in Wood (1982) gives a possible total length of 5.25 m and weight of around 6 tonnes - however the shell is proportionally narrow in this specimen, as the type and paratype predicted ~2.5 m and 2.6 m, respectively. It is unfortunate that I cannot find the original publication and any photographs within, but it is at least cited by several papers (i.e. it exists!). Scheyer and Sanchez-Villagra (2007) investigated fragmentary costals from the same individual and determined that the turtle had a normal mode of growth, unlike fast-growing Archelon and the extant leatherback, and took at the very least three decades to reach a 3.3 m carapace - possibly as long as 60 or 110 years! The authors also hinted at the possibility that Stupendemys geographicus had size variants due to sexual dimorphism, presumably with other specimens in mind (Scheyer and Sanchez-Villagra 2007).

The vast shell of Stupendemys geographicus. From Wikipedia Commons, author Ghedoghedo.

Scheyer and Sanchez-Villagra (2007) noted that Stupendemys geographicus has a shell with a lightweight diploe construction - and retained stability - as a consequence of scaling effects, however it does not resemble the spongy bone typical of Archelon and other tetrapods with an open marine habitat. The flattened shell of S. geographicus is a strong indicator of an aquatic habitat, while the vast size suggests the turtle probably only left the water to lay eggs (Wood 1976). Wood (1976) was uncertain if S. geographicus was a marine or freshwater species, but it has been determined the formation it was recovered from was near-shore/low coastal savanna/freshwater river (Bocquentin and Melo 2006). Fossil associations seem to imply that S. geographicus was littoral (Bocquentin and Melo 2006), and Wood (1976) speculated that it may have had flippers. Bocquentin and Melo (2006) described another Stupendemys species, S. souzai, which was smaller in size, had a strange vertical collar-like structure suggesting poor swimming ability, and was found in continental areas where it may have inhabited swamps and small streams. Subsequent workers criticized the placement of the assorted solitary elements into S. souzai and argue that material may not even represent Stupendemys (Meylan et al. 2009). That's right, there were other large - but perhaps not giant - pleurodires from the Amazonian Miocene...

One of those other species is Caninemys tridentata, which is known only from a skull with a bulldog-like shape and canine-like projections (Meylan et al. 2009). This skull was assumed to be from a Stupendemys at first, but is only half the expected size (estimated SCL of 1.2-1.5 m) and probably represents a different taxa (Meylan et al. 2009). It is possible that the suggestion of Stupendemys being a predaceous species from Bocquentin and Melo (2006) was based off this skull, as I can't think of any other morphology that would be telling in this regard. Wood (1976) claimed that S. geographicus was "largely if not entirely herbivorous" because "all of the largest living turtles... are totally (or nearly totally) herbivorous" - I have no idea why someone would think this. The largest extant podocnemidid pleurodire, Podocnemis expansa - with an SCL up to 0.82 m (Wood 1976) - is herbivorous, although diet in the genus is rather variable (Teran et al. 1995). Until cranial remains which can be unambiguously assigned to Stupendemys are found, this area of its biology should best be left a blank.

Stupendemys geographicus with somebody else's skull. From Wikipedia Commons, author Ryan Somma.

Could Stupendemys actually have been a prey item? It appeared to overlap in time and range with the Mega-Caiman Purussaurus which had a 1.5 m head and ~12 m total length - and possible weight of ~10+ tonnes. This website has a photo of a "tortoise" shell (from Stupendemys or another pleurodire?) with a Purussaurus bite... which the turtle survived. It seems unlikely that a 3 m+ SCL Stupendemys would have been easy prey, and may have been effectively predator-free. This could suggest that extreme size and a carapace only reduced for mechanical purposes could have evolved at least partially in response to such a gargantuan predator.


It appears that a lot of Stupendemys biology remains a mystery, undoubtedly thanks in part to the lack of anything analogous in this Megafauna-deprived era. There are some vague references to other South American pleurodires of a size comparable to Stupendemys, such as some very large cervicals (Orenstein 2001) - but it would probably be best to wait and see how things get sorted out. The diversity of this not-to-distant time was truly staggering - there were 12 probably sympatric crocodile from the same locale as the Stupendemys holotype - so I can't imagine what other surprises the continent has in store. 

References:

Bocquentin, J. and Melo, J. (2006) Stupendemys souzai sp. nov. (Pleurodira, Podocnemididae) from the Miocene-Pliocene of the Solimões Formation, Brazil. Revista Brasileira de Paleontologia 9(2), 187-192. Available.


Heuvelmans, B. (1968). In the Wake of the Sea-Serpents. Hill and Wang: New York.


Meylan, P., et al. (2009). Caninemys, a New Side-Necked Turtle (Pelomedusoides: Podocnemididae) from the Miocene of Brazil. American Museum Novitates 3639.

Orenstein, R. (2001). Turtles, Tortoises & Terrapins: Survivors in Armor. Firefly Books: Buffalo, New York USA.

Scheyer, T. and Sanchez-Villagra, M. (2007). Carapace bone histology in the giant pleurodiran turtle Stupendemys geographicus: Phylogeny and function. Acta Palaeontol. Pol. 52(1), 137–154


Teran, F. et al. (1995). Food Habits of an Assemblage of Five Species of Turtles in the Rio Guapore, Rondonia, Brazil Augusto. Journal of Herpetology 29(4), 536-547. URL

Wood, G. (1982). The Guinness Book of Animal Facts and Feats. Guinness Superlatives Limited: Middlesex, England.

Wood, R. (1976). Stupendemys geographicus, the world's largest turtle. Brevoria 436, 1-31. Available.

A Brief Mega-Turtle Background

I've had Mega-Turtles on the mind after working on the Great Snapper, a speculative species with a size ranging from being comparable to a very large Alligator Snapping Turtle up to very large Alligators. What a strange sentence. Anyways, while it may seem that Markus and I were being a little... overenthusiastic for creating a freshwater turtle capable of weighing over a tonne, it is actually rather conservative compared with some fossil species, a few of which lived remarkably recently.


But first, a brief discussion of turtle measurement. Size is mass, but as Mega-Turtles are known only from fossil remains, linear measurements will have to be primarily relied upon. Strait Carapace Length (SCL) should be used as the most basic unit of turtle measurement, as Curved Carapace Length, Carapace Width, and Total Length are of limited value outside of its context. I'll be defining 'Mega-Turtles' as species regularly exceeding 2 m SCL, as such sizes were not confirmed until quite recently and are extreme in comparison to extant species.

Archelon ischyros from Wikipedia Commons. This specimen has a 1.93 m SCL, 2.18 m carapace width (partially over the curve), 3.4 m total length, and 4.58 distance from the tips of the flippers (Wieland 1909).

The Cretaceous sister taxa Archelon and Protostega are both reported to exceed 2 meters in carapace length (Shimada and Hook 2004) - alas, I have been unable to find descriptions of these specimens in peer-reviewed literature. The website Oceans of Kansas mentions a 3.4 m total length Protostega in the Dallas Museum of Natural History which has the potential to fit the bill, if barely. The 4.6 m Archelon mentioned may be the same as the Pierre Shale specimen reported to have a 4.5 m total length and 5.25 m flipper span. The former figure yields an estimated SCL of about 2.5 m - I really would have preferred if it was mentioned in the description though! 

The sister clade of protostegids also appears prone to gigantism; extant leatherback turtles (Dermochelys coriacea) commonly exceed 1.5 m SCL and have a reported maximum of 1.85 m SCL with a 0.95 m width (Wood 1976, Head et al. 1999 - citing Pritchard 1971). The proportionally narrow carapace in leatherbacks, even accounting for measured curvature in Archelon, probably means that a similarly-sized protostegid would be far more massive. Apparently, the extinct stem-leatherback Psephophorus sp. was in fact capable of exceeding 2 meters SCL (see here) or even 12 feet total length (3.65 m) but - and you may detect a pattern here - I have not been able to find any proper write-ups! Psephophorus species were alive until quite recently, reportedly the Pliocene, with the 2+ m specimen being found in the Miocene. I may explore this highly obscure clade at a later date - if I feel like getting frustrated - but I had another taxa in mind for the origin of this post. 

Not all potential Mega-Turtles are close relatives of leatherbacks, a notable exception being the marine(?) Eocene trionychid Drazinderetes tethyensis which probably had a 2 m SCL carapace (1.5-2.282 m SCL, 1.279-1.447 m CW) (Head et al. 1999). The Pleistocene Mega(?)-Tortoise Colossochelys atlas is reported to have a  ~2 m SCL by some (Head et al. 1999 - citing Auffenberg 1974), however Wood (1976) argues that the length should be 1.8 m and the specimen in question was apparently abnormally large. Whatever the case, I will not get into it here, as these were also not the species for whom this introduction was intended. 

STUPENDEMYS AWAITS

References:

Head, J., et al. (1999). Drazinderetes tethyensis, a new large trionychid (Reptilia: Testudines) from the Marine Eocene Drazinda Formation of the Sulaiman Range, Punjab (Pakistan). Contribution from the Museum of Paleontology 30(7), 199-214.

Shimada, K. and Hooks, G. (2004). Shark-bitten protostegid turtles from the Upper Cretaceous Mooreville Chalk, Alabama. Journal of Paleontology 78(1), 205-210. DOI: 10.1666/0022-3360(2004)078<0205:SPTFTU>2.0.CO;2

Wieland, G. (1909). Revision of the Protostegidae. American Journal of Science. 4 (27). 101–130. Available

Wood, G. (1982). The Guinness Book of Animal Facts and Feats. Guinness Superlatives Limited: Middlesex, England.

Wood, R. (1976). Stupendemys geographicus, the world's largest turtle. Brevoria 436, 1-31. Available.