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Rhamphorhynchus life history



From: Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:


Prondvai, E., Stein, K., Ősi, A. & Sander, M.P. (2012)
Life History of Rhamphorhynchus Inferred from Bone Histology and the
Diversity of Pterosaurian Growth Strategies.
PLoS ONE 7(2): e31392.
doi:10.1371/journal.pone.0031392
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0031392



Background

Rhamphorhynchus from the Solnhofen Limestones is the most prevalent
long tailed pterosaur with a debated life history. Whereas
morphological studies suggested a slow crocodile-like growth strategy
and superprecocial volant hatchlings, the only histological study
hitherto conducted on Rhamphorhynchus concluded a relatively high
growth rate for the genus. These controversial conclusions can be
tested by a bone histological survey of an ontogenetic series of
Rhamphorhynchus.

Methodology/Principal Findings

Our results suggest that Bennett's second size category does not
reflect real ontogenetic stage. Significant body size differences of
histologically as well as morphologically adult specimens suggest
developmental plasticity. Contrasting the ‘superprecocial hatchling’
hypothesis, the dominance of fibrolamellar bone in early juveniles
implies that hatchlings sustained high growth rate, however only up to
the attainment of 30–50% and 7–20% of adult wingspan and body mass,
respectively. The early fast growth phase was followed by a prolonged,
slow-growth phase indicated by parallel-fibred bone deposition and
lines of arrested growth in the cortex, a transition which has also
been observed in Pterodaustro. An external fundamental system is
absent in all investigated specimens, but due to the restricted sample
size, neither determinate nor indeterminate growth could be confirmed
in Rhamphorhynchus.

Conclusions/Significance

The initial rapid growth phase early in Rhamphorhynchus ontogeny
supports the non-volant nature of its hatchlings, and refutes the
widely accepted ‘superprecocial hatchling’ hypothesis. We suggest the
onset of powered flight, and not of reproduction as the cause of the
transition from the fast growth phase to a prolonged slower growth
phase. Rapidly growing early juveniles may have been attended by their
parents, or could have been independent precocial, but non-volant
arboreal creatures until attaining a certain somatic maturity to get
airborne. This study adds to the understanding on the diversity of
pterosaurian growth strategies.