Fibrolamellar bone in basal Archosauromorpha: Tracing the evolution of high growth rates.

吸热起源是脊椎动物进化生物学中的一个重要问题。传统上，它被解释为提高敏捷性或改善父母照顾的选择压力。然而，内温也可能与高增长率的进化有关，而高增长率反过来需要高基础代谢率，从而导致内温。高增长率似乎是多色调陆地动物(如蜥脚类和大象)进化的先决条件，因为低增长率会导致存活到成熟的可能性大大降低。探测灭绝的四足动物高生长率的唯一方法是通过骨组织学。具体地说，纤维板层骨组织是高生长率的代用品。虽然我们在上一个资助时期的研究表明，在最早的蜥脚类恐龙中已经存在高增长率，这也表明它们是巨人症的先决条件，但目前尚不清楚这些高增长率是由于增加身体尺寸的选择压力还是在另一种选择性制度的框架下演变的。因此，我们需要对始龙形态系统发育的前侏罗纪和非恐龙部分进行全面采样，以检测纤维板层骨的出现模式。目前，在几个始祖龙型群体中，重复丢失的单一起源与收敛起源的可能性是一样的。了解基础始祖龙的纤维板骨进化模式将解决高基础代谢率是对较大体型的适应的假说。

The origin of endothermy is a major issue in the evolutionary biology of vertebrates. Traditionally, it has been explained by selection pressure for increased agility or improved parental care. However, endothermy may also be linked to the evolution of high growth rates, which in turn require high basal metabolic rates, which lead to endothermy. High growth rates appear to be a precondition for the evolution of multi-tone land animals (such as sauropods and elephants) because low growth rates lead to a dramatically decreased likelihood of survival to maturity. The only way to detect high growth rates in an extinct tetrapod is through bone histology. Specifically, fibrolamellar bone tissue serves as a proxy for high growth rates. While our research in the previous funding period has shown that high growth rates were already present in the earliest sauropod dinosaurs, also suggesting they were a prerequisite for gigantism, it is not clear whether these high growth rates evolved due to the selection pressure for increased body size or in the framework of another selective regime. Thus, we need to comprehensively sample the pre-Jurassic and nondinosaurian part of the archosauromorph phylogeny to detect the patterns of occurrence of fibrolamellar bone. At present, a single origin with repeated loss appears equally as likely as a convergent origin in several archosauromorph groups. Understanding the pattern of fibrolamellar bone evolution in basal archosauromorphs will address the hypothesis of high basal metabolic rates being an adaptation to large body size.