长集群大象经历了一个重要的进化阶段,其特征是下颌骨异常拉长。长下颌骨的初始伸长和随后的消退,随着它与树干的共同进化,提出了一个有趣的问题,仍然没有完全理解。通过比较功能和生态形态研究,以及喂养偏好分析,我们重建了主要类群longrostrine大象的摄食行为。在Platybelodon进化枝,在叙事区域观察到的快速进化变化,与下颌骨和象牙特征密切相关,提出了一个关键的进化过渡,其中进食功能从下颌骨转移到躯干,允许长生人将他们的利基市场扩展到更开放的地区。这种功能转变进一步导致大象完全依靠它们的树干来喂养。我们的研究提供了独特的环境压力如何塑造器官极端进化的见解,特别是在新生代晚期全球降温趋势中发展出各种特殊适应的大型哺乳动物中。
大象的树干是动物界最有效的食物采集器官之一。从大树枝到薄薄的草叶,它可以盘旋并为动物带来许多类型的植被,下颌骨短。这种多功能性使大象能够在各种环境中茁壮成长,包括草原。树干并不是Proboscideans中出现的唯一壮观特征,大象是唯一幸存的家族。在早期和中期(23至1160万年前),这些物种中的许多都有明显拉长的下颚;这种特征是如何以及为什么出现然后消失的,人们知之甚少。在进食过程中,下颌骨和树干加长的作用也尚不清楚。为了解决这些问题,李等人。专注于Platybelodon,Choerolophodon和Gomphotherium,属于三个在17到1500万年前漫游中国北方的长老家族。每个人都有细长的下颚,但长度和形态却截然不同.对搪瓷样品的化学分析有助于确定这些家庭占据的栖息地,而数学建模揭示了他们的下颌骨是如何对付不同类型的植物的。通过分析鼻部区域来评估躯干形状。结果表明,Choerolophodon的下颌骨更适合加工分支,“原始”树干。Gomphotherium拥有多功能的下巴,可以处理草和树,以及相当“象”的树干。Platybelodon的下巴似乎很适合割草,显着的骨骼结构指向长,强壮和灵活的树干。现代大象完全依靠树干吃饭,形态学限制表明,在这些物种中,附属物仅用于辅助喂养(例如,通过按下树枝)。所有家庭都有一个包括草原和森林的环境,但是分析表明,有一段时间,Choerolophodon偏爱相对封闭的栖息地,而Platybelodon蔓延到草原,Gomphotherium在这两种景观中航行。这表明,长期的进化,强壮而灵活的树干与放牧紧密相关。大约一千四百万年前,全球降温事件导致草原在全球范围内扩张。化石记录显示,在这段时间之后,长牙人的下颌骨开始缩短,包括Gomphotherium的后代,这将产生现代大象。Li等人的作品。揭示了这些进化过程,以及帮助塑造树干的环境压力。
The long-trunked elephantids underwent a significant evolutionary stage characterized by an exceptionally elongated mandible. The initial elongation and subsequent regression of the long mandible, along with its co-evolution with the trunk, present an intriguing issue that remains incompletely understood. Through comparative functional and eco-morphological investigations, as well as feeding preference analysis, we reconstructed the feeding behavior of major groups of longirostrine elephantiforms. In the Platybelodon clade, the rapid evolutionary changes observed in the narial region, strongly correlated with mandible and tusk characteristics, suggest a crucial evolutionary transition where feeding function shifted from the mandible to the trunk, allowing proboscideans to expand their niches to more open regions. This functional shift further resulted in elephantids relying solely on their trunks for feeding. Our research provides insights into how unique environmental pressures shape the extreme evolution of organs, particularly in large mammals that developed various peculiar adaptations during the late Cenozoic global cooling trends.
The elephant’s trunk is one of the most efficient food-gathering organs in the animal kingdom. From large branches to thin blades of grass, it can coil around and bring many types of vegetation to the animals’ strong, short mandibles. This versatility allows elephants to thrive in a range of environments, including grasslands. Trunks are not the only spectacular feature to emerge in Proboscideans, the family of which elephants are the only surviving group. During the early and middle Miocene (between 23 to 11.6 million years ago), many of these species had dramatically elongated lower jaws; how and why this trait emerged then disappeared is poorly understood. The role that lengthened mandibles and trunks played during feeding also remains unclear. To address these questions, Li et al. focused on Platybelodon, Choerolophodon and Gomphotherium, which belong to three Proboscidean families that roamed Northern China between 17 and 15 million years ago. Each had elongated lower jaws, but with strikingly distinct lengths and morphologies. Chemical analyses on enamel samples helped determine which habitat the families occupied, while mathematical modelling revealed how their mandibles tackled different types of plants. Trunk shape was assessed via analyses of the nasal region. The results suggest that Choerolophodon had mandibles better suited for processing branches and a short, ‘primitive’ trunk. Gomphotherium sported a versatile jaw that could handle both grass and trees, as well as a rather ‘elephant-like’ trunk. The jaw of Platybelodon seemed well-adapted to cut grass, and remarkable bone structures point towards a long, strong and flexible trunk. While modern elephants fully depend on their trunks to eat, morphological constraints suggest that, in these species, the appendage only served to assist feeding (e.g., by pressing down on branches). All families shared an environment that included grasslands and forests, but analyses suggest that, for a period, Choerolophodon favored relatively closed habitats while Platybelodon spread into grasslands and Gomphotherium navigated both landscapes. This suggests that the evolution of long, strong and flexible trunks is tightly associated with grazing. About 14 million years ago, a global cooling event led to grasslands expanding worldwide. The fossil record shows the mandibles of Proboscideans starting to shorten after this period, including in the descendants of Gomphotherium that would give rise to modern elephants. The work by Li et al. sheds light onto these evolutionary processes, and the environmental pressures which helped shape the trunk.