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Crocodile nervous system growth

From: Ben Creisler

Some recent items about crocodilians:

Ayanda Ngwenya, Nina Patzke, Muhammad A. Spocter,, Jean-Leigh Kruger,
Leigh-Anne Dell, Richard Chawana, Pedzisai Mazengenya, Brendon K.
Billings, Olatunbosun Olaleye, Suzana Herculano-Houzel & Paul R.
Manger (2013)
The Continuously Growing Central Nervous System of the Nile Crocodile
(Crocodylus niloticus).
The Anatomical Record (advance online publication)
DOI: 10.1002/ar.22752

It is a central assumption that larger bodies require larger brains,
across species but also possibly within species with continuous growth
throughout the lifetime, such as the crocodile. The current study
investigates the relationships between body growth (length and mass)
and the rates of growth of various subdivisions of the central nervous
system (CNS) (brain, spinal cord, eyes) in Nile crocodiles weighing
between 90 g and 90 kg. Although the brain appears to grow in two
phases in relation to body mass, initially very rapidly then very
slowly, it turns out that brain mass increases continuously as a power
function of body mass with a small exponent of 0.256, such that a
10-fold increase in body mass is accompanied by a 1.8-fold in brain
mass. Eye volume increases slowly with increasing body mass, as a
power function of the latter with an exponent of 0.37. The spinal
cord, however, grows more rapidly in mass, accompanying body mass
raised to an exponent of 0.54, and increasing in length as predicted,
with body mass raised to an exponent of 0.32 (close to the predicted
1/3). While supporting the expectation formulated by Jerison that
larger bodies require larger brains to operate them, our findings show
that: (1) the rate of increase in brain size is very small compared to
body growth; and (2) different parts of the CNS grow at different
rates accompanying continuous body growth, with a faster increase in
spinal cord mass and eye volume, than in brain mass.


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