Novel record of placodont remains including a Henodus cranium from the Upper Triassic Silves Group of the Algarve, southern Portugal

Recent fieldwork in the Upper Triassic deposits of the Silves Group in the Algarve, southern Portugal revealed novel cyamodontid placodont material. The collection includes a partial skull and numerous isolated armor plates from four localities in Silves and Loulé municipalities. The skull shows a strong affinity to henodontid placodonts, especially to Henodus chelyops from Tübingen-Lustnau in Germany. It shares features such as a rectangular outline of the cranium, occurrence of a broad spatulate rostrum, and toothless maxillae with curved longitudinally extending grooves. The only unambiguous difference observed pertains to the more robust and convex snout shape of the new specimen. Based on these multiple similarities, the specimen is identified as Henodus sp., but poor preservation prevents species-level identification. The new specimen from Portugal represents the second record of Henodus and illustrates a wider geographic distribution of that genus, extending beyond the Germanic Basin and reaching coastal areas near the westernmost branch of the Neotethys. The age of the deposits where the cranium was found is not well-established but refers to a time interval within the upper Carnian–Rhaetian, suggesting the specimen may be younger than other henodontid records. The novel Henodus material found in the continental, but likely the near-coastal depositional setting, concurs with the known records of brackish to the freshwater habitat of the other henodontid placodonts. The occurrence of abundant armor plates assigned to Cyamodontidae at multiple sites and stratigraphic horizons indicates that placodonts were common in the south Iberian margin.对葡萄牙南部阿尔加维地区西尔韦斯群（Silves Group）上三叠统地层开展的最新野外工作，发现了全新的圆齿龙科板齿龙类（cyamodontid placodont）标本。本次采集的化石来自西尔韦斯与卢莱市镇的4处化石点，包含一件部分头骨与大量孤立的骨板。该头骨与海诺龙科板齿龙类亲缘关系极强，尤其与产自德国图宾根-卢斯特瑙的海诺龙（Henodus chelyops）最为接近，二者共享多项鉴定特征：颅部呈矩形轮廓、具宽阔匙状吻部、上颌骨无齿且带有纵向延伸的弧形沟槽。本次新标本唯一明确的差异在于其吻部更为粗壮且凸起。基于上述多项相似特征，本次标本被鉴定为海诺龙未定种（Henodus sp.），但由于保存状态欠佳，无法完成物种级鉴定。这件产自葡萄牙的新标本是海诺龙属的第二笔正式记录，表明该属的地理分布范围远超日耳曼盆地，延伸至新特提斯洋（Neotethys）最西分支附近的沿海区域。发现该头骨的地层年代尚未精确厘定，但大致处于卡尼阶晚期—瑞替阶（upper Carnian–Rhaetian）的时间区间内，暗示该标本的时代可能晚于其他已报道的海诺龙科化石记录。本次发现的海诺龙类标本产自大陆沉积环境，但结合沉积背景推测其大概率接近海岸，这与已知的海诺龙科板齿龙类咸淡水至淡水的栖息环境相符。在多个化石点与地层位中均发现了归属圆齿龙科的大量骨板，这表明板齿龙类在伊比利亚南部陆缘曾较为繁盛。