The first galeaspid fish (stem-gnathostomata) from the Silurian Xiushan formation of Hunan Province, China

ABSTRACT

A new species of Dayongaspidae, Dayongaspis colubra sp. nov., is described from the Telychian (Llandovery, Silurian) Xiushan Formation at Maoyanhe Town, Zhangjiajie, Hunan Province, China. The new species is distinguished from the type species D. hunanensis by its larger-sized headshield, tiny and dense granular tubercles, and triangular-shaped inner cornual processes. Additionally, it reveals more galeaspid plesiomorphic characters than D. hunanensis, such as the inverted splayed posterior supraorbital canals (soc₂) and the paired endolymphatic openings on the headshields. This new finding represents the first fossil record of galeaspids in the Xiushan Formation, thereby enriching the diversity of galeaspids. Furthermore, it extends the Wentang Vertebrate Assemblage upwards into the lower part of Xiushan Formation, indicating a broader stratigraphic range than previously assumed.urn:lsid:zoobank.org:pub:387EB969-03DA-4534-9265-4DCC69E6CF77urn:lsid:zoobank.org:act:2871FCD2-8D6C-40C3-86E1-99618D47485D

KEYWORDS:

• Galeaspids
• Dayongaspidae
• Silurian
• Xiushan fauna

Character description

[1] Median dorsal opening: (0) absent; (1) present.

[2] Festooned pattern of sensory canals on dorsal surface of headshield:(0) absent; (1) present.

[3] Aspidine tubercles: (0) absent; (1) present.

[4] Shape of headshield: (0) trapezoid-like; (1) triangular-like; (2) oval-like; (3)armet-like; (4) fork-like

[5] Margin of headshield: (0) serrated; (1) smooth.

[6] Shape of median dorsal opening: (0) transverse slit-like; (1) oval-like;(2) slender longitudinal oval(3)transverse crescent

[7] Longitudinal oval dorsal opening: (0) not slit-like (length/width<6); (1) slit-like (length/width>6).

[8] Heart-shaped median dorsal opening: (0) absent; (1) present.

[9] Position of median dorsal opening: (0) not subterminal; (1) subterminal.

[10] Anterior end of median dorsal opening: (0) subterminal; (1) some distancebehind rostral margin of shield; (2) terminal.

[11] Posterior end of median dorsal opening: (0) in front of or level with anteriormargin of orbital opening; (1) between anterior margin of orbital openingand posterior margin of orbital opening; (2) posteriorly beyond posteriormargin of orbital opening.

[12] Size of orbital openings: (0) large; (1) small.

[13] Position of orbital openings: (0) dorsal position and close to mid-line ofheadshield; (1) dorsal position and not close to mid-line of headshield; (2) lateral position; (3) ventrolaterally placed orbital openings

[14] Cornual process: (0) absent; (1) present.

[15] Extending trajectory of cornual process: (0) projecting posterolaterally;(1) projecting laterally; (2) projecting backward.

[16] Portion of headshield behind cornual process: (0) short; (1) long.

[17] Position of cornual process base: (0) near posterior end of headshield; (1)away from posterior end of headshield.

[18] Spines on cornual process: (0) absent; (1) present.

[19] Inner cornual process: (0) present; (1) absent.

[20] Shape of inner cornual process: (0) broad leaf-shaped; (1) spine-shaped.

[21] Rostral margin of headshield: (0) without rostral angle; (1) with rostral angle.

[22] Rostral process: (0) absent; (1) present.

[23] Shape of rostral process: (0) broad; (1) slender.

[24] Spines or tubercles on margin of rostral process: (0) absent; (1) present.

[25] Fenestrae on dorsal surface of headshield: (0) absent; (1) present.

[26] Size of dorsal fenestra: (0) small; (1) large.

[27] Shape of dorsal fenestra: (0) slender oval-like; (1) broad bean-like.

[28] Position of dorsal fenestra: (0) lateral-dorsal position; (1) dorsal position.

[29] Position of dorsal fenestra relative to orbital opening: (0) orbital openinginside, fenestra outside; (1) orbital opening outside, fenestra inside.

[30] Median transverse canals (mtc): (0) two; (1) one; (2) more than two.

[31] Short branches running from posterior supraorbital canal (soc2): (0) absent;(1) present.

[32] Lateral transverse canal: (0) short; (1) long.

[33] Branching end of lateral transverse canal: (0) absent; (1) present.

[34] Lateral transverse canals leaving from infraorbital canal: (0) present;(1) absent.

[35] The lateral transverse canals leaving from infraorbital canal before ltc_d:(0) present; (1) absent.

[36] Fourth lateral transverse canal (ltc4): (0) present; (1) absent.

[37] Lateral transverse canals behind ltc4: (0) present; (1) absent.

[38] Anterior supraorbital canal (soc1): (0) absent; (1) present.

[39] Posterior supraorbital canal (soc2): (0) present; (1) absent.

[40] Posterior supraorbital canals (soc2) meet with infraorbital canal (ifc): (0)no; (1) yes.

[41] Posterior supraorbital canals (soc2): (0) funnel-shaped; (1) parallel; (2)V-shaped.

[42] Branching end of posterior supraorbital canals (soc2):(0) absent; (1) present.

[43] Medial dorsal canal (mdc): (0) develeped; (1) degenerated; (2) absent.

[44] Medial dorsal canal and posterior supraorbital canal: (0) unjointed;(1) contact. ?

[45] U-shaped medial dorsal canal: (0) absent; (1) present.

[46] Portion of headshield behind dorsal commissure proportionally: (0) long;(1) short.

[47] Postbranchial wall: (0) short; (1) long.

[48] Elongated branchial region: (0) absent; (1) present.

[49] Number of branchial fossae: (0) 5~7 pairs; (1) 9~17 pairs; (2) morethan 20 pairs.

[50] Maximum width of headshield placed: (0) posteriorly; (1) medially.

[51] Width/length in oval-like headshield: (0) < 1; (1) >1.

[52] Nearly parallel lateral margins of headshield: (0) absent; (1) present.

[53] Broad and large middle dorsal spine of headshield: (0) absent; (1) present.

[54] Broad ventral rim: (0) absent; (1) present.

[55] The unclosed rostral margin: (0) present; (1) absent.

[56] The ornamentation of the head-shield: (0) star-shaped tubercles; (1) tiny granular tubercles; (2) coarse granular tubercles;(3) polygon-shapedtubercles;(4) central big tubercles surronded by radiallyarranged tubercles.

[57] Pineal organ: (0) on front of or level with posterior margin of orbitalopening; (1) behind posterior margin of orbital opening.

[58] Ratio between pre-pineal length and post-pineal length in mid-line ofcephalic shield larger than 1.0: (0) no; (1) yes.

[59] The preorbital commissure:(0) absent; (1) presen

[60] Ventrally curved branchial fossae: (0) absent; (1) present

[61] Ventral rim of head-shield: (0) absent; (1) present.

[62] Sickle-like complex of cornual and inner cornual processes (the angle of thecornual and inner cornual processes is equal to or more than 90 degrees):(0) absent; (1) present

[63] The inner cornual process exceeds the posterior edge of the cornual processin the galeaspids with triangular headshields: (0) absent; (1) present

[64] Middle dorsal spine of headshield: (0) absent; (1) present.

Acknowledgments

We are grateful to Ridong Zhao and Xinyuan Meng for the great help in the field work, Fang Gui and Aijuan Shi for the illustrations and ecological restoration.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the the National Nature Science Foundation of China [41972006, 42072026, 92255301]; the Surface Programs of Science, Technology Commission of Yunnan Province [202101BA070001-076]; The Mee-mann Chang Academician Workstation in Yunnan Province [202205AF150002];the Innovation Training Programs for Undergraduates, CAS;