美国芝加哥大学Michael I. Coates小组的最新研究提出了有颌脊椎动物姐妹群中头-躯干界面的新组合。相关论文发表在2025年8月6日出版的《自然》杂志上。

通过同步加速器x射线显微断层扫描，研究人员发现了这种无颌鱼在独特的骨化头干界面上的咬颌特征。北颌龙的内耳显示出在颌骨起源之前就已经发育的感觉器官（下耳部和上耳部增大）。与冠状颌口一样，成对的静脉引流管将血液输送到大容量的心脏道。该课题组还证实了一个特征，据他们所知，在任何其他脊椎动物中都没有发现：最前干神经将它的单干延伸到胸鳍。

在这方面，他们的重建挑战了假说，即颌石肩是从鳃器进化而来的。他们的观察结果强调，颚骨龙是关节颈部和喉部嵌入的前哨，这将为它们早期的下颌器官提供动力。因此，脊椎动物的下颚——通常被认为是“颌口”创新的功能驱动者——进化为感觉增强的追随者，增加心输出量和更好的运动控制，现在在无颚的姐妹组中推断出来。

据了解，有颌脊椎动物起源的标准设想是，由底栖食草动物向捕食动物过渡，这得益于一系列解剖学上的创新，包括复杂的感觉系统、高流量的心脏和颌部开口与颅胸铰链的整合。然而，为颚类脊椎动物的姐妹类群骨赘动物重建的类似七鳃鳗的内部解剖，似乎缺乏这些颌赘动物的特征，这意味着尽管系统发育接近，但形态上存在差距。

附：英文原文

Title: Novel assembly of a head–trunk interface in the sister group of jawed vertebrates

Author: Miyashita, Tetsuto, Janvier, Philippe, Tietjen, Kristen, Berenguer, Felisa, Schder, Sebastian, Marone, Federica, Gueriau, Pierre, Coates, Michael I.

Issue&Volume: 2025-08-06

Abstract: The standard scenario for the origin of jawed vertebrates depicts a transition from benthic grazers to nektonic predators1,2,3, facilitated by a suite of anatomical innovations, including elaborate sensory systems, a high-flow heart and the integration of jaw-opening muscles with the craniothoracic hinge4,5,6,7. However, the lamprey-like internal anatomy8,9,10,11,12,13 reconstructed for osteostracans, the sister group of jawed vertebrates, seem to lack these gnathostome traits, implying a morphological gap despite phylogenetic proximity. Here, using synchrotron-based X-ray microtomography on the model osteostracan Norselaspis glacialis, we reveal derived gnathostome traits straddling a uniquely ossified head–trunk interface in this jawless fish. The inner ear of Norselaspis shows sensory elaborations (enlarged pars inferior and sinus superior) acquired well before the origin of jaws. As in crown gnathostomes, paired venous drainage channels blood into a high-volume cardiac tract. We also confirm a feature not yet demonstrated in any other vertebrate, to our knowledge: the most anterior trunk nerve extends its single trunk to the pectoral fin. In this respect, our reconstruction challenges the hypotheses14,15,16 that the gnathostome shoulder evolved from the gill apparatus. Our observations highlight Norselaspis as a prelude to the intercalation of the muscular neck and throat that would power the early jaw apparatus. Therefore, the vertebrate jaw—often considered the functional driver for ‘gnathostome’ innovations1,2,3—evolved instead as a follower to the sensory enhancement, increased cardiac output and greater locomotory control now inferred in the jawless sister group.

DOI: 10.1038/s41586-025-09329-9

Source: https://www.nature.com/articles/s41586-025-09329-9