The Placerias/Downs’ Quarry complex in eastern Arizona, USA, is the most diverse Upper Triassic vertebrate locality known. We report a new short-faced archosauriform, Syntomiprosopus sucherorum gen. et sp. nov., represented by four incomplete mandibles, that expands that diversity with a morphology unique among Late Triassic archosauriforms. The most distinctive feature of Syntomiprosopus gen. nov. is its anteroposteriorly short, robust mandible with 3–4 anterior, a larger caniniform, and 1–3 “postcanine” alveoli. The size and shape of the alveoli and the preserved tips of replacement teeth preclude assignment to any taxon known only from teeth. Additional autapomorphies of S. sucherorum gen. et sp. nov. include a large fossa associated with the mandibular fenestra, an interdigitating suture of the surangular with the dentary, fine texture ornamenting the medial surface of the splenial, and a surangular ridge that completes a 90° arc. The external surfaces of the mandibles bear shallow, densely packed, irregular, fine pits and narrow, arcuate grooves. This combination of character states allows an archosauriform assignment; however, an associated and similarly sized braincase indicates that Syntomiprosopus n. gen. may represent previously unsampled disparity in early-diverging crocodylomorphs. The Placerias Quarry is Adamanian (Norian, maximum depositional age ~219 Ma), and this specimen appears to be an early example of shortening of the skull, which occurs later in diverse archosaur lineages, including the Late Cretaceous crocodyliform Simosuchus. This is another case where Triassic archosauriforms occupied morphospace converged upon by other archosaurs later in the Mesozoic and further demonstrates that even well-sampled localities can yield new taxa.

美国亚利桑那州东部的Placerias /Downs 采石场是已知的上三叠纪脊椎动物最多样化的地区。我们报告了一种新的短面弓龙类，Syntomiprosopus sucherorum gen。等人。nov.，以四个不完整的下颌骨为代表，扩大了这种多样性，其形态在晚三叠世的主龙类中是独一无二的。Syntomiprosopus gen最显着的特征。十一月 是其前后短而结实的下颌骨，具有 3-4 个前牙、一个较大的犬齿和 1-3 个“后犬齿”肺泡。肺泡的大小和形状以及替换牙齿的保留尖端排除了对仅从牙齿已知的任何分类单元的分配。S.sucherorum的其他自拟态将军 等人。十一月 包括与下颌窗相关的大颅窝，与齿牙的交错缝合线，装饰脾内侧表面的精细纹理，以及完成 90° 弧的边缘脊。下颌骨外表面有浅而密、不规则的细小凹坑和狭窄的弓形凹槽。这种字符状态的组合允许进行主龙形分配；然而，一个相关且大小相似的脑壳表明Syntomiprosopus n。将军 可能代表早期发散的鳄鱼形动物中先前未采样的差异。Placerias _采石场是 Adamanian（诺里安，最大沉积年龄 ~ 219 Ma），这个标本似乎是头骨缩短的早期例子，这种情况后来发生在不同的主龙谱系中，包括晚白垩世鳄鱼形Simosuchus。这是另一个例子，三叠纪的主龙类占据了中生代后期其他主龙类聚集的形态空间，并进一步证明即使是采样良好的地方也可以产生新的分类群。