Major groups of jawed vertebrates exhibit contrasting conditions of dermal plates and scales. But the transition between these conditions remains unclear due to rare information on taxa occupying key phylogenetic positions. The 425-million-year-old fish Entelognathus combines an unusual mosaic of characters typically associated with jawed stem gnathostomes or crown gnathostomes. However, only the anterior part of the exoskeleton was previously known for this very crownward member of the gnathostome stem. Here, we report a near-complete post-thoracic exoskeleton of Entelognathus. Strikingly, its scales are large and some are rhomboid, bearing distinctive peg-and-socket articulations; this combination was previously only known in osteichthyans and considered a synapomorphy of that group. The presence in Entelognathus of an anal fin spine, previously only found in some stem chondrichthyans, further illustrates that many characters previously thought to be restricted to specific lineages within the gnathostome crown likely arose before the common ancestor of living jawed vertebrates.

主要的有颌脊椎动物类群表现出截然不同的真皮板和鳞片状况。但由于占据关键系统发育位置的类群信息很少，这些条件之间的转变仍不清楚。拥有 4.25 亿年历史的鱼类Entelognathus结合了一种不寻常的镶嵌特征，这些特征通常与有颌茎颌动物或冠颌动物有关。然而，以前只知道颚口茎的这个非常靠冠的成员的外骨骼的前部。在这里，我们报告了一个近乎完整的Entelognathus后胸外骨骼。引人注目的是，它的鳞片很大，有的呈菱形，带有独特的钉插座式关节。这种组合以前只在骨鱼类中已知，并被认为是该类群的共源型。Entelognathus中存在臀鳍棘，以前只在一些干软骨鱼类中发现过，这进一步说明了许多以前被认为仅限于颚口类冠内特定谱系的特征可能出现在现存有颌脊椎动物的共同祖先之前。