Friday, September 30, 2011

A Baby Cadborosaur No More. Part 6b: Reptilian Reproduction

Here's that quote again, from LeBlond and Bousfield (1995), page 82:
The thinness and elongation of the body, the poikilothermy (or cold-bloodedness) which it seems to imply, and the great difference in size between the young and the adult are strong points in favour of a reptilian nature. 
The previous article argued that a "cold-blooded" 'Cadborosaurus' is actually strongly at odds with known 'reptilian' physiology; similarly, the birth of extremely small live young would in fact be highly unusual for a marine reptile.

Backing up, this is the evidence LeBlond and Bousfield (1995) present for comparatively tiny precocial young (page 80):
A very small individual, probably a baby, was caught (by W. Hagelund) and another one, perhaps, was seen at the shore (by P. Harsh); both in relatively warm water. If these very small individuals are correctly associated with the larger ones, their size and where they were found might provide more clues about Caddy's nature.
Woodley et al. (2011) is of course all about why the Hagelund specimen should not be used as evidence, but makes no mention of the Harsh case. Is this... a major flaw in our paper? Absolutely not. The Harsh sightings are vague to the degree that they can be graciously described as unanalyzable. Phyllis Harsh reportedly found a "baby dinosaur" 2 feet (0.61 meters) long on a beach (which was ultimately returned to the water) and (!) a "small dinosaur skeleton" beneath a Bald Eagle nest, both on Johns Island. The sheer lack of detail is remarkable and the description "dinosaur" can refer to just about anything. I find it interesting that LeBlond and Bousfield drew conclusions from this valueless anecdote, despite apparently having some reservations about it.

† For comparison, Hagelund's account had 24 traits, of which only a few were worthless. 
‡ Dinosauria proper has a diverse assortment of body plans, many other creatures are often incorrectly labeled as dinosaurs (ichthyosaurs, plesiosaurs, mosasaurs, Dimetrodon...), and some extant animals (snapping turtles, alligator gars, bichirs, sturgeon...) are often compared to "dinosaurs". 


LeBlond and Bousfield (1995) hypothesized that 'Cadborosaurus' "probably" gives live birth, reasoning that it doesn't have suitable limb morphology for digging nests and inhabits areas which are too cold for incubating eggs. Strangely, they also speculate that it has some reproductive tie to land, although whether it is to lay eggs or give live birth they don't specify. It is worth mentioning that there are only two reports of 'Cadborosaurus' on land and they are very very weird; in 1936 the Stephenson family reported a "90 foot-long, three-foot-thick animal wriggling over the reef into a lagoon" which was "yellow and bluish in colour" and in 1991 Terry Osland reported something "bigger than a killer whale" which was "hard to describe" and yet described as having the "smooth skin of a dogfish" which was of a "grey, silvery color" and had "no hair", a "tail rounded like a lizard tail" with "like little feet on the back of the tail" [sic] and no long neck.


There is another major problem in connecting the Hagelund specimen to 'Cadborosaurus', aside from the utter lack of resemblance - marine reptiles give birth to proportionally large young.

Determining exactly how large the Hagelund specimen is compared to a 'Cadborosaurus' is challenging due to the latter probably not being a valid concept. LeBlond and Bousfield claim a size range of 5-15 meters (which is not supported by the actual sightings), so let's go with a nice round 10 meters. This makes the 40 cm long Hagelund specimen only 4% of the adult length and somewhere in the neighborhood of 5 orders of magnitude less massive, say, around 0.0064%.

Out of the five or so extant clades of marine reptiles, only the "true" sea snakes (Hydrophiini) give live birth; however as this is by far the most speciose marine clade with ~60 representatives (Sanders et al. 2010) it could be argued that most extant marine reptiles are live-bearers. Anyways, sea snakes tend to have small clutches and large offspring; averaging data from 10 species in Lemen and Voris (1981) gives a mean reproductive effort per embryo of 6.8 (stdev = 2.5, min = 2.1, max = 10.9), reproductive effort being what percentage of the mother's mass the embryo is. While relative lengths were not recorded, assuming similar proportions, this could 'translate' into newborns averaging 41% of the maternal length (min = 27%, max = 48%). It's amazing that more than one of these can fit into the parent snake. The reproductive effort per clutch averaged 32 across the sampled species (stdev = 5, min = 23.6, max = 38.9) and appeared to be fairly stable compared to embryo size.

† The others being seaturtles (Chelonioidea), the marine iguana (Amblyrhynchus cristatus), sea kraits (Laticauda spp.), and saltwater crocodiles (Crocodylus porosus)... the lattermost makes me wonder if other reptiles deserve this status, certainly the softshell turtle Trionyx should be considered. As for how sea snakes, sea kraits, and other elapids are related (Wikipedia's article is highly untrustworthy), Catalogue of Organisms has an excellent summary.


Live birth appears to have been very common in extinct marine reptiles, although as can be imagined, data on this subject is quite scarce. It was recently confirmed that plesiosaurs gave live birth, with Polycotylus latippinis estimated to have a fetus 35% of the maternal length at full term (O'Keefe and Chiappe 2011). The mosasauroid Carsosaurus marchesetti was discovered with four embryos which (according to Figure 2) were around 30 cm long relative to a 2 meter adult (Caldwell and Lee 2001), making the young around 15% of the maternal length. Caldwell and Lee (2001) were uncertain how close to term the embryos were as they were placed posteriorly in the mother, but showed some signs of displacement. Then there is the famous fossil of the ichthyosaur Stenopterygius quadriscissus showing a juvenile half-emerged from its mother, which seems to be around a quarter of the parental length.


Thus, LeBlond and Bousfield's argument that tiny precocial young indicate a 'reptilian' identity is completely at odds with live birth in marine reptiles. There was a discussion of this in Woodley et al. (2011) but it was eventually deemed tangential as the Hagelund specimen was already reclassified and the dead horse was already beaten into a liquid.



References:

Caldwell, M. W., and Lee, M. S. Y. (2001). Live birth in Cretaceous marine lizards (mosasauroids). Proc. R. Soc. Lond. B. 268, 2397-2401. Available.

LeBlond, P. H. & Bousfield, E. L. (1995). Cadborosaurus, Survivor from the Deep. Victoria, British Columbia: Horsdal & Schubart.

Lemen, C. A. and Voris, H. K. A. (1981) Comparison of Reproductive Strategies among Marine Snakes. Animal Ecology 50, 89-101. Available.

O’Keefe, F. R. & Chiappe, L.M. (2011). Viviparity and K-selected life history in a Mesozoic marine reptile. Science 333, 870-873. DOI: 10.1126/science.1205689

Sanders, K. L., Mumpuni, Lee, M. S. Y. (2010). Uncoupling ecological innovation and speciation in sea snakes (Elapidae, Hydrophiinae, Hydrophiini). Journal of Evolutionary Biology 23(12) DOI: 10.1111/j.1420-9101.2010.02131.x

Woodley, M. A., Naish, D. & McCormick, C. A. (2011). A Baby Sea-Serpent No More: Reinterpreting Hagelund's Juvenile "Cadborosaur" Report. Journal of Scientific Exploration 25(3), 495-512.



Previous entries:
A Baby Cadborosaur No More. Part 4: What is 'Cadborosaurus'?
A Baby Cadborosaur No More. Part 5: Hagelund's Specimen And The Cadborosaurus
A Baby Cadborosaur No More. Part 6a: Cold Water on the 'Reptilian Hypothesis'

Tet Zoo Coverage: 
A baby sea-serpent no more: reinterpreting Hagelund’s juvenile Cadborosaurus

1 comment:

Andreas Johansson said...

I've heard mammoths described as "dinosaurs". I therefore irrefutably conclude that "Cadborosaurus" is a relict population of Columbian mammoths that have taken up a marine lifestyle.