Data from: A new Upper Cretaceous titanosaur nesting site from La Rioja (NW Argentina), with implications for titanosaur nesting strategies

Cretaceous titanosaur nesting sites are currently known only from Europe, Asia and South America. In the latter, only the Auca Mahuevo and Sanagasta nesting sites have been confidently assigned to this clade of sauropod dinosaurs. Here we report the discovery of the first eggs and egg clutches found at Tama, a new Upper Cretaceous fossiliferous locality in the Los Llanos Formation, Sierra de Los Llanos (La Rioja, NW Argentina). At least five egg clutches, several partially preserved, isolated eggs and many eggshell fragments were discovered in a single outcrop of a sandstone horizon which represents a cumulative palaeosol profile. Although the mechanical and digital preparation of eggs did not reveal any embryonic remains in ovo, the morphology of the eggs and eggshells closely matches that of titanosaur eggs and eggshells found worldwide. The morphology and spatial grouping of the titanosaur eggs from Tama, along with geological observations support a burrow-nesting strategy for these dinosaurs. Although the Sanagasta and Tama eggs were found in the same stratigraphical unit and share several morphological characters, they clearly differ in shell thickness and egg size. This, coupled with the interpretation of different sedimentary contexts for these nesting sites, strongly suggests that at least two different titanosaur species nested in La Rioja during the Late Cretaceous, using different nesting strategies. The occurrence of this new titanosaur nesting site in a semiarid palaeoenvironment represents an interesting case study for the reproductive biology of the titanosaur dinosaurs, particularly their labile nesting behaviour.

目前已发现的白垩纪泰坦龙（titanosaur）巢穴仅分布于欧洲、亚洲与南美洲。其中仅在南美洲的奥卡马韦约（Auca Mahuevo）与萨纳加斯塔（Sanagasta）两处巢穴被确切归属于该蜥脚类恐龙演化支。本研究报道了阿根廷西北部拉里奥哈省塞拉德洛斯利亚诺斯地区洛斯利亚诺斯组内一处新的晚白垩世化石产地——塔马（Tama），首次在该产地发现了恐龙蛋与蛋窝。在一处代表叠加古土壤剖面的砂岩露头中，共发现至少5枚蛋窝、若干部分保存的孤立蛋体与大量蛋壳碎片。尽管通过机械与数字化制备处理的蛋件未在卵内发现胚胎残骸，但该蛋与蛋壳的形态特征与全球已发现的泰坦龙蛋及蛋壳高度吻合。塔马泰坦龙蛋的形态特征与空间分布格局，结合地质观测结果，表明这类恐龙采用穴居筑巢的繁殖策略。尽管萨纳加斯塔与塔马的蛋发现于同一地层单元，且具备若干共同形态特征，但二者在蛋壳厚度与蛋体尺寸上存在显著差异。结合这两处巢穴不同的沉积环境背景，这一差异有力表明：晚白垩世时期拉里奥哈地区至少有两种不同的泰坦龙物种采用不同的筑巢策略进行繁殖。该新型泰坦龙巢穴发现于半干旱古环境中，为研究泰坦龙类恐龙的繁殖生物学，尤其是其多变的筑巢行为，提供了极具学术价值的案例。