Australia: The Land Where Time Began

A biography of the Australian continent 

Earliest Known Terrestrial Forelimbs - Contrasting Developmental trajectories

The earliest tetrapods that are known from multiple skeletons that are near-complete are Ichthyostega and Acanthostega, of which the more primitive has been considered to be Acanthostega. More recent material that has been found indicates they had different ontogenetic trajectories for their forelimbs - the muscle attachment patterns of processes on upper-arm bones (small humori) in Ichthyostega resemble "fish" members of the stem group of tetrapods, such as Tiktaalik, but large humeri approach, though they don't attain, the condition seen in the tetrapod crown-group, though in Acanthostega all humeri display the pattern of the crown-group. The authors1 say they infer a greater degree of locamotory terrestrialisation was undergone by Ichthyostega during ontogeny. It is suggested by the newly-recognised primitive characteristic that Ichthyostega be the more basal than Acanthostega.  


Sources & Further reading

  1. Callier, Viviane, Jennifer A. Clack, and Per E. Ahlberg. "Contrasting Developmental Trajectories in the Earliest Known Tetrapod Forelimbs." Science 324, no. 5925 (April 17, 2009 2009): 364-67.


Author: M. H. Monroe
Last updated  26/05/2013 

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