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Re: Caudipteryx suffered from osteoarthritis

>From Ben Creisler
Here are a few passages from the Discussion section of the article:
 Our study shows that Early Cretaceous birds from the Liaoning fauna in China 
(with the exception of Caudipteryx) seldom manifest osteoarthritis (Table 1). 
The rarity of osteoarthritis in Early Cretaceous birds mirrors that in 
Cretaceous dinosaurs. The frequency in the oviraptosaur Caudipteryx is 
significantly greater. In modern birds, osteoarthritis shows a species specific 
variability in prevalence (Rothschild and Panza, 2005, 2006). There is also an 
inverse relationship to body mass in recent birds (Rothschild and Panza, 2008). 
In contrast, the Mesozoic sample shows a positive correlation with body size 
(Table 1) with the highest incident in the comparatively large Caudipteryx. 
Caudipteryx is classified as an oviraptorsaur (Lü et al., 2002), but were 
oviraptorsaurs feathered dinosaurs or birds (Dyke and Norell, 2005; Hwang et 
al., 2002)?
The next largest form, Microraptor, with its feathered feet, is unlikely to 
have been a ground bird (Alexander et al., 2010). It is not surprising that it 
avoided osteoarthritis (less than 1%). Landing on tree trunks apparently did 
not overstress its ankle joint, and an inherent sprawling posture distributed 
the stresses, in spite of the geocentric nature of the ankle. A geocentric 
joint rotates as well as flexes and extends and is subject to greater stresses 
than a hinge joint.
Why then isn’t Caudipteryx as well protected from osteoarthritis as are the 
modern ratites that it resembles? Its reduced wing parallels that seen in 
flightless birds and suggests that Caudipteryx also had a flighted ancestor, at 
least as capable as the gliding dromaeosaur Microraptor (Alexander et al., 
2010). This means that the adaptation for terrestrial locomotion seen in 
Caudipteryx developed de novo in that genus and may not have been perfected to 
a point that prevented development of osteoarthritis. We have not yet had an 
rs including forms that are more cursorially adapted, but such a study might 
help illuminate the reasons for osteoarthritis in these animals.