Hungarian Academy of Sciences-Eötvös Loránd University Lendület Dinosaur Research Group, Eötvös Loránd University, Budapest, Hungary.
PLoS One. 2012;7(2):e31392. doi: 10.1371/journal.pone.0031392. Epub 2012 Feb 15.
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.
来自索伦霍芬石灰岩的 Rhamporhynchus 是最常见的长尾翼龙，其生活史存在争议。虽然形态学研究表明其生长策略缓慢，类似于鳄鱼，且幼体具有超早熟的飞行能力，但迄今为止对 Rhamporhynchus 进行的唯一组织学研究得出的结论是，该属的生长速度相对较高。这些有争议的结论可以通过对 Rhamporhynchus 发育系列的骨骼组织学调查来检验。
方法/主要发现：我们的结果表明，Bennett 的第二类体型并不能反映真实的发育阶段。组织学和形态学上成熟的标本存在显著的体型差异，表明存在发育可塑性。与“超早熟幼体”假说相反，早期幼体中纤维状骨的优势表明幼体具有较高的生长速度，但仅能达到成年翼展和体重的 30-50%和 7-20%。早期的快速生长阶段之后是一个长时间的缓慢生长阶段，表现为皮质中平行纤维骨的沉积和生长停止线，这种过渡也在 Pterodaustro 中观察到。所有研究标本均缺乏外部基本系统，但由于样本量有限，无法确定 Rhamporhynchus 是确定性生长还是非确定性生长。
结论/意义：Rhamporhynchus 发育早期的快速生长阶段支持其幼体的非飞行性质，并驳斥了广泛接受的“超早熟幼体”假说。我们认为，从快速生长阶段过渡到长时间缓慢生长阶段的原因是从非飞行到飞行的转变，而不是繁殖。快速生长的早期幼体可能得到了父母的照顾，或者可能是独立的、早熟的、但非飞行的树栖生物，直到达到一定的身体成熟度才能在空中飞行。这项研究增加了对翼龙生长策略多样性的理解。
