营养孔是长骨中轴区域的骨膜表面的小开口,穿过皮质层并到达髓腔。它们对于将营养物质和氧气输送到骨组织很重要,并且随着时间的推移对于骨骼的修复和重塑至关重要。股骨骨干中的营养孔与股骨的能量需求有关,并且已被证明与分类群的最大代谢率(MMR)有关。这里,我们研究了营养孔大小和体重之间的关系,作为生活和灭绝的异种动物中类群的有氧能力的代理,包括活树懒,食蚁兽,和Armadillos,以及已灭绝的异种动物,如字形,Pampatheres,和地面树懒。对70只股骨进行了采样,包括现存分类群的20个和灭绝分类群的50个。我们基于孔面积获得了血液流速(Q),并进行了PGLS和系统发育ANCOVA,以探索哺乳动物群体之间的差异。我们的研究结果表明,在哺乳动物中,类群通常与较低的代谢相关,如活的异种动物表现出相对较小的孔眼,而巨大的已灭绝的异种动物的孔穴,如地面树懒和字形,与非异种动物的胎盘重叠。因此,Q估计表明有氧能力可与其他胎盘巨大类群如大象或一些有蹄类动物相媲美。此外,化石巨型分类群的MMR估计显示出类似的结果,几乎所有分类单元都显示出较高的价值,除了那些已经提出了强烈的半树栖或杂居习惯的分类单元。此外,结果与预测的灭绝类群的饮食一致,这表明大量食用类似于有蹄类动物的草,并且与现存的异种动物的食叶或食虫饮食相反。MMR值的祖先重建表明所有异种动物缺乏共同的模式,由于其特定的饮食偏好和树栖或植物性习惯,强烈支持现有形式的低代谢率的发生。我们的结果强调了考虑灭绝类群的系统发育位置之外的不同证据的重要性,特别是当灭绝的形式与它们现存的亲属异常不同时。未来的研究评估巨型已灭绝的异种动物的能量需求,不应仅根据其系统发育位置和对其现有亲属的观察结果来假设这些已灭绝动物的代谢率较低。
Nutrient foramina are small openings in the periosteal surface of the mid-shaft region of long bones that traverse the cortical layer and reach the medullary cavity. They are important for the delivery of nutrients and oxygen to bone tissue and are crucial for the repair and remodeling of bones over time. The nutrient foramina in the femur\'s diaphysis are related to the energetic needs of the femur and have been shown to be related to the maximum metabolic rate (MMR) of taxa. Here, we investigate the relationship between nutrient foramen size and body mass as a proxy to the aerobic capacity of taxa in living and extinct xenarthrans, including living sloths, anteaters, and armadillos, as well as extinct xenarthrans such as glyptodonts, pampatheres, and ground sloths. Seventy femora were sampled, including 20 from extant taxa and 50 from extinct taxa. We obtained the blood flow rate (Q̇) based on foramina area and performed PGLS and phylogenetic ANCOVA in order to explore differences among mammalian groups. Our results show that, among mammals, taxa commonly associated with lower metabolism like living xenarthrans showed relatively smaller foramina, while the foramina of giant extinct xenarthrans like ground sloths and glyptodonts overlapped with non-xenarthran placentals. Consequently, Q̇ estimations indicated aerobic capacities comparable to other placental giant taxa like elephants or some ungulates. Furthermore, the estimation of the MMR for fossil giant taxa showed similar results, with almost all taxa showing high values except for those for which strong semi-arboreal or fossorial habits have been proposed. Moreover, the results are compatible with the diets predicted for extinct taxa, which indicate a strong consumption of grass similar to ungulates and in contrast to the folivorous or insectivorous diets of extant xenarthrans. The ancestral reconstruction of the MMR values indicated a lack of a common pattern for all xenarthrans, strongly supporting the occurrence of low metabolic rates in extant forms due to their particular dietary preferences and arboreal or fossorial habits. Our results highlight the importance of considering different evidence beyond the phylogenetic position of extinct taxa, especially when extinct forms are exceptionally different from their extant relatives. Future studies evaluating the energetic needs of giant extinct xenarthrans should not assume lower metabolic rates for these extinct animals based solely on their phylogenetic position and the observations on their extant relatives.