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

佐伊·T·库利克被授予NSF EAR博士后奖学金，以研究一种罕见的富含化石的骨床的沉积史，该骨床保存了100多个与哺乳动物血统Dolichuranus结盟的双齿动物物种的化石。从这张骨床上的洞察可以为这些已灭绝的哺乳动物提供一个潜在的快照，这些哺乳动物是大约2.4亿年前的近亲。例如，利用周围主岩的地质学，可以做出解释来证实或驳斥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(也许还有种群)在生长和发育到体型庞大的过程中经历的骨骼和组织学变化。事实上，硬组织组织学--研究牙齿和骨组织的微结构和成分--为了解化石记录中的增长率提供了唯一的见解。为此，该项目的目标是描述骨床的沉积历史，以便从在那里发现的化石遗骸中理解的古生物学解释，可以提供关于哺乳动物深层进化史中的社会行为、大型身体的进化和种群年龄结构的新信息。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，通过在格兰杰科学中心的临时展览向广大观众传播成果，(2)指导芝加哥洛约拉大学的本科生和研究生，以及(3)在Macalester学院为专注于地球化学挖掘和骨组织学的大学生开发课程。该项目旨在使用传统和地球化学挖掘方法调查以二齿齿类动物为主的骨床的沉积史。这一骨层是坦桑尼亚利福阿地区化石地点地层序列中最低的出现率，将用于评估河流和泛滥平原沉积中脊椎动物遗骸的时间和空间改造程度。此外，该项目旨在测试大型双齿动物的形态、大小和年龄是否相关，这是由于混合年龄的双齿动物组合的稀缺而尚未完成的新工作。初步的地球化学和传统的埋藏学结果表明，Diynodon骨层保存了反映一次快速埋葬的均质埋藏史，但需要更大的样本来验证该骨层是单个种群的快照。通过沉积学、岩石学、生物碎屑保存、微量元素分析以及通过硬组织组织学进行大小年龄评估等独立的证据，该项目将从微结构到组合范围重建双齿齿动物的生活史和保存史。这种新颖的方法组合将在哺乳动物社会行为这一长期研究的问题上建立一条新的调查路线，并将填补我们对二叠纪-三叠纪最丰富的干哺乳类动物生长和发育理解的关键空白，以提供有价值的比较数据，以更广泛地识别双齿动物的个体发育阶段。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.