CYNOCEPHALUS

["Matthew Troutman" <m_troutman@hotmail.com>]

To those who read my recent CLIMBING post I want to elaborate on some 
thoughts on _Cynocephalus_, the cobego.  

Other than the phylogenetic position of _Cynocephalus_ (close relative 
to Chiroptera or Megachiroptera, depending on what bat phylogeny you 
believe), there has been alot of attention paid to the climbing ability 
of the animal.  _Cynocephalus_ (Dermatoptera) is a well-known flying 
lemur that happens to be a scansorial climber.  Yalden (1985) considered 
_Cynocephalus_ to be the closest living analog to _Archaeopteryx for 
several reasons.  

First, the claws of _Cynocephalus_ and _Archaeopteryx_ both conform to 
the trunk-climbing condition described by Yalden (eg. strongly curved, 
laterally compressed with needle-like points).  

Second, the forelimb proportions of _Cynocephalus_ and _Archaeopteryx_ 
are very similiar.   Using a log graph based on limb length and trunk 
length first published by Thornington and Heany (1981), Yalden showed 
that both _Archaeopteryx_ and _Cynocephalus_ have more elongate limb 
bones (humerus+radius, femur+tibia) than typical flying squirrels.  If 
the longest finger is added to the measurement, both animals have 
forelimbs that are 1.7 times their trunk length.  

Third, using another log graph based on wing loading, Yalden showed that 
both _Cynocephalus_ and _Archaeopteryx_ can be placed in between gliders 
and fliers (this is subject to change because of the small wing estimate 
used by Yalden. However, if the tail is added to ratio, _Archaeopteryx) 
has a larger wing loading ratio, but still plots with _Cynocephalus_). 

Finally, Yalden put the whole thing best:

"The analogies and homologies discussed here suggest to me that 
_Archaeopteryx_ was a trunk-climbing vertebrate, and further suggest a 
moderately close analogy with the cobego _Cynocephalus_.  The curved 
claws, their orientation, the elongated limbs, and the general anatomy 
of the hand all conform to that ananlogy at least as well to Ostrom's 
predatory analogy, and sharpness of the claws fits a tree climbing 
analogy better.  Ostrom (1974) argued that a "fly-swatting" predator 
would need powerful pectoralis muscles, and thus explained the 
development of the downstroke muscles in birds.  Equally, an animal 
hugging a trunk in the manner of a squirrel or cobego would need 
powerful pectoralis muscles.  Ostrom further questioned the arboreality 
of _Archaeopteryx_ on tthe grounds that the claw of the hallux is 
relatively short; perching birds, as he noted, tend to have long 
hallucial claws.  However, this is not true of trunk climbers- 
Piciformes, _Sitta_, _Certhia_ and similiar birds tend t have claws of 
more nearly equal length on their toes. 

I don not wish to pursue the analogy with _Cynocephalus_ too far; I am 
certainly not suggesting that _Archaeopteryx was at the gliding stage of 
flight evolution, as is that mammal.  The highly assymetrical primary 
feathers (Feduccia&Tordoff, 1979_, the fact that the primaries and 
secondaries are differenciated, their curved shafts (R.A. Norberg, this 
volume), the stout furcula (Olson &Feduccia, 1979), the prominent 
deltopectoral crests on the humerus (Yalden 1971), and the depth of the 
furcula, projecting 6mm (ventrally to) the coracoid plate (Yalden, 1984) 
all indicate that flapping flight was possible, and that the pectoralis 
muscles were well developed."  (Yalden 1985; 96-97).   

Given the similiarites between _Archaeopteryx_ and _Cynocephalus_, it 
seems most likely that the two were similiar in most parts of their 
behavior.

Matt Troutman

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