Monday, July 26, 2010

Another time-based cladogram

Here is another time-based cladogram. This one is of maniraptors.
The predominance of the dromaeosaurids, troodontids and enantiornithes is quite striking. I have been making this point in a variety of ways throughout these posts. Each is a significant link between pterosaurs and modern birds.
"Fossils of more advanced birds are also first recorded at around 130 million years ago. Among these are the enantiornithines (Chiappe 2007; Chiappe and Witmer 2002), a group that constitutes the most important evolutionary radiation of premodern birds. Like most early birds, the majority of enantiornithines had toothed jaws and partially clawed wings (Figs. 1 and 5). Yet their skeletons show a series of key transformations that approach those of today's birds. Some of these include the shortening of the hand and fingers as well as changes in the proportions of the wing bones and the anatomy of the shoulder. Furthermore, these birds evolved important innovations in their plumage, namely, a safety device called the alula (a small tuft of feathers also known as the “bastard wing”), which assists modern birds during their take-off and landing (Sanz et al. 1996). The significant transformations of the skeleton and plumage of these birds suggest that, even at the onset of their evolutionary history, enantiornithines were able to take-off from a standstill position and maneuver in ways similar to those seen among living birds. It is most likely that the evolution of these enhanced flying capabilities played a key role in the evolutionary success of the enantiornithines, which by about 120 million years ago seem to have risen to dominance." (L. Chiappe)

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