Postdoctoral Fellowship: EAR-PF: Geochemical taphonomy of a rare dicynodont bonebed and its paleobiological implications of social behavior in the stem-mammalian lineage

Zoe T. Kulik被授予NSF EAR博士后奖学金，研究一个罕见的富含化石的骨床的沉积历史，该骨床保存了超过100个与哺乳动物谱系称为Dolichuranus的双齿兽物种的化石。从这个骨床中获得的见解可以为我们提供一个潜在的快照，让我们了解这些已经灭绝的哺乳动物亲戚在大约2.4亿年前的生活是什么样的。例如，利用周围寄主岩石的地质情况，可以作出解释，以证实或反驳这个化石组合是否代表一个单一的种群。此外，从化石骨组织组成的微观细节中获得的见解可以用来重建该物种（也许是种群）在生长和发育到大体型期间所经历的骨骼和组织学变化。的确，硬组织组织学——研究牙齿和骨组织的微观结构和组成——为了解化石记录中的生长速度提供了唯一的见解。为此，该项目的目标是表征骨床的沉积历史，以便从那里发现的化石遗骸中理解古生物学解释的背景，这可以为哺乳动物深层进化史中的社会行为，大体型进化和种群年龄结构提供新的信息。这项工作的更广泛的影响包括：(1)与菲尔德自然历史博物馆合作，通过在Grainger科学中心的临时展览向广大观众传播研究结果；(2)指导芝加哥洛约拉大学的本科生和研究生；(3)为马卡莱斯特学院的大学生开发一门以地球化学地学和骨组织学为重点的课程。本项目旨在利用传统方法和地球化学地层学方法研究双齿龙占主导地位的骨层的沉积历史。该骨床是坦桑尼亚Lifua成员化石地点地层演替中的最低层，将用于评估河流和洪泛平原沉积物中脊椎动物遗骸的时间和空间改造程度。此外，本项目旨在测试大型双齿兽物种的形态、大小和年龄是否相关，这是由于缺乏混合年龄双齿兽组合而尚未完成的新颖工作。初步的地球化学和传统的埋藏学结果表明，双齿齿骨床保存了一个反映单一、快速埋葬的同质埋藏学历史，但需要更大的样本来验证这个骨床是单一种群的快照。通过独立的证据线，包括沉积学、岩石学、生物碎屑保存、微量元素分析和硬组织组织学的尺寸-年龄评估，本项目将从微观结构到整体尺度重建该骨床的双齿螈的生活史和保存历史。这种新颖的方法组合将为长期研究的哺乳动物社会行为问题建立一条新的探究路线，并将填补我们对最丰富的二叠纪-三叠纪干哺乳动物群体生长和发育的理解的关键空白，为更广泛地确定双齿动物的个体发育阶段提供有价值的比较数据。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Zoe T. Kulik has been awarded an NSF EAR Postdoctoral Fellowship to investigate the depositional history of a rare fossil-rich bonebed that preserves over 100 fossils of a dicynodont species allied with the mammalian lineage called Dolichuranus. Insights from this bonebed can provide a potential snapshot of what life was like for these extinct mammal-relatives from ~240 million years ago. For example, using the geology of the surrounding host rock, interpretations can be made to confirm or refute if this fossil assemblage represents a single population. Furthermore, insights from the microscopic details of fossilized bone tissue composition can be used to reconstruct the skeletal and histological changes that this species (and perhaps population) experienced during growth and development to large body size. Indeed, hard tissue histology- the study of dental and bone tissue microstructure and composition- provide the only insights to understand growth rates in the fossil record. To this end, the project goals are to characterize the depositional history of the bonebed in order to contextualize palaeobiological interpretations that can be understood from the fossilized remains that were recovered there, which can provide new information on social behavior, evolution of large body size, and population age structures in the deep evolutionary history of mammals. Broader impacts of this work include (1) working with the Field Museum of Natural History to disseminate results to a broad audience through a temporary exhibit in the Grainger Science Hub, (2) mentoring undergraduate and graduate students at Loyola University Chicago, and (3) developing a curriculum for college students focused on geochemical taphonomy and bone histology at Macalester College.This project aims to investigate the depositional history of a dicynodont-dominated bonebed using traditional and geochemical taphonomic approaches. This bonebed is the lowermost occurrence in a stratigraphic succession of fossil localities in the Lifua Member of Tanzania that will be used to assess the degree of temporal and spatial reworking of vertebrate remains in fluvial and floodplain deposits. In addition, this project aims to test whether morphology, size, and age are correlated in the large dicynodont species, novel work that has not yet been done due to the scarcity of mix-aged dicynodont assemblages. Preliminary geochemical and traditional taphonomic results suggest that the dicynodont bonebed preserves a homogenous taphonomic history reflective of a single, rapid burial, but a larger sample is needed to validate that this bonebed is a snapshot of a single population. Through independent lines of evidence including sedimentology, petrography, bioclast preservation, trace-element analysis, and size-age assessment through hard tissue histology, this project will reconstruct the life history and preservational history of dicynodonts from this bonebed from microstructural to assemblage-wide scales. This novel combination of methods will establish a new line of inquiry in the long- studied question of mammalian social behavior and will also fill critical gaps in our understanding of growth and development in the most abundant group of Permo-Triassic stem-mammals to provide valuable comparative data to identify ontogenetic stages in dicynodonts more broadly.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.