Stepwise formation of autostyly in lungfishes revealed by comparative analysis of palatoquadrate

doi:10.19615/j.cnki.2096-9899.260408

Abstract

Abstract:

Autostyly, defined by fusion of the palatoquadrate to the neurocranium and loss of the hyomandibula as a suspensory element, is a hallmark of lungfish cranial organization among sarcopterygians, yet its evolutionary origin remains incompletely understood. This study elucidates this transition through a detailed comparative analysis of the palatoquadrate and its articulations in three sequentially diverging stem dipnoans: Youngolepis, Diabolepis, and the earliest eudipnoan Paleolophus. Youngolepis exhibits a reoriented palatoquadrate, indicating functional reorganization of jaw mechanics prior to autostyly. In Diabolepis, reduction of the pars autopalatina and retention of a primitive suborbital articulation suggest further modification of jaw suspension. Paleolophus documents the earliest unambiguous autostyly, with direct palatoquadrate-neurocranial integration preceding complete fusion with the lateral commissure, along with an enlarged adductor fossa. Comparison with Middle and Late Devonian lungfishes indicates that full autostyly was achieved only after the development of a robust, integrated otic process. These results demonstrate that lungfish autostyly evolved stepwise, driven by increasing biomechanical demands associated with durophagous feeding.

Key words: Devonian, lungfish, autostyly, palatoquadrate, evolution

摘要：

自接型颌骨是肺鱼类头部骨骼的一个重要特征，但其起源演化尚未完全明晰。对肺鱼类干群三个重要代表——杨氏鱼(Youngolepis)、奇异鱼(Diabolepis)以及最早的真肺鱼古嵴鱼(Paleolophus)——的腭方骨及其关节结构进行了详细的比较解剖学研究，揭示了这一重要特征的递进式演化过程。杨氏鱼的腭方骨后部接近垂直，表明在自接型颌骨形成之前，其颌骨的力学功能已经发生重组。在奇异鱼中，颌骨连接结构进一步演化：腭方骨的自腭部分明显缩减，但保留了原始的眶下关节。古嵴鱼是最原始的真肺鱼类，也是具有肺鱼自接型颌骨的最早化石代表，其腭方骨与脑颅愈合，但尚未与侧联合骨完全融合。中、晚泥盆世的肺鱼进一步演化出强壮且与侧联合愈合的耳突，标志着自接型颌骨的最终形成。这些结果表明，肺鱼的自接型颌骨是在与食壳性取食相关的生物力学驱动下逐步演化形成的。

关键词: 泥盆纪, 肺鱼, 自接型, 腭方骨, 演化

CLC Number:

Q915.862

QIAO Tuo, LIU Cheng-Xi, CUI Xin-Dong, ZHU Min. Stepwise formation of autostyly in lungfishes revealed by comparative analysis of palatoquadrate. Vertebrata Palasiatica, 2026, 64(2): 167-182.

乔妥, 刘城希, 崔心东, 朱敏. 2026, 64(2): 167-182, 腭方骨比较解剖学分析揭示肺鱼自接型头骨的递进式起源. 古脊椎动物学报.

Figures/Tables 6

Fig. 1 Right palatoquadrate complex of Youngolepis praecursor (IVPP V28375) Virtual rendering (A, B) and interpretive drawing (C, D) in lateral (A, C) and medial (B, D) views Abbreviations: add.fo. adductor fossa; dpl. dermopalatine; dpl.t. dermopalatine teeth; ecpt. ectopterygoid; ecpt.t. ectopterygoid teeth; enpt. entopterygoid; enpt.t. entopterygoid teeth; n.ml. notch for ramus of maxillaris and mandibularis; ob.r. oblique ridge; p.ap. pars autopalatina; p.q. pars quadrata; pr.a. ascending process; pr.ap. autopalatine process; pr.pt?. paratemporal process; q.c. quadrate condyle; re.sh. spiraculo-hyomandibular recess. Scale bars = 2 mm

Fig. 2 Right palatoquadrate complex of Diabolepis speratus (IVPP V9054) A, B. virtual rendering in ventral (A) and dorsal (B) view; C. interpretive drawing in dorsal view Abbreviations: dlp. dorsal lateral process; mp. medial process; rp. ridge-like process. Scale bar = 5 mm

Fig. 3 Craniums of gnathostomes in ventral view, indicating palatoquadrate articulations A. Youngolepis from Chang, 1982; B. Powichthys from Jessen, 1980; C. Diabolepis from Chang, 1995; D. Guiyu from Qiao and Zhu, 2010; E. Psarolepis from Yu, 1998; F. Cladodoides from Maisey, 2005 Not to scale Abbreviations: art.e. ethmoid articulation; art.o. orbital articulation; pr.bp. basipterygoid process; pr.po. postorbital process

Fig. 4 CT slices through the skull of Paleolophus yunnanensis (IVPP V17917), indicating the boundary (red arrows) between palatoquadrate and neurocranium A. transverse slice; B, C. sagittal slices. Not to scale

Fig. 5 Skull and palate of Paleolophus yunnanensis (IVPP V17917) A. skull in lateral view; B. interpretive drawing of the palate in lateral view; C. 3D virtual models of the palate in lateral view; D. 3D virtual models of upper toothplates in ventral view; E. interpretive drawing of the palate in dorsal view; F. 3D virtual models of upper toothplates in dorsal view Abbreviations: art.pq. hypothetical position of the jaw joint on the palatoquadrate; dlp. dorsal lateral process; lcom. lateral commissure; mp. medial process; psp. parasphenoid; rp. ridge-like process. Scale bar = 2 mm

Fig. 6 Palatoquadrate evolution of early lungfishes Eusthenopteron from Jarvik, 1963; Glyptolepis from Jarvik, 1972; Youngolepis from Cui et al., 2022; Diabolepis from Chang, 1995; Paleolophus from Qiao et al., 2026; Neoceratodus from Fox, 1965 Abbreviations: am.art. anteromedial articulation lamina; Pq.aup. pars autopalatina of palatoquadrate; Pq.qu. pars pterygoquadrate of palatoquadrate; pr.a. ascending process; pr.bp. basipterygoid process; pr.o. otic process; pr.pt. paratemporal process

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