Asioaspis, a new genus of Polybranchiaspiformes (Galeaspida, stem-gnathostomes) from the Lower Devonian of Yunnan, China

doi:10.19615/j.cnki.2096-9899.260113

Abstract

Abstract:

A new genus and species, Asioaspis brachyotus gen. et sp. nov. of Polybranchiaspiformes, is described from the Lower Devonian Lochkovian Xishancun Formation near Miandian Reservoir, Qujing City, Yunnan Province, China. The new genus is characterized by an elongated ovoid headshield with serrated lateral margins, a small subcircular median dorsal opening, short and laterally projecting cornual processes, an exceptionally broad ventral rim, 12 pairs of branchial fossae, and coarse granular tubercles (~3/mm²). It displays a mosaic of characters of the most primitive polybranchiaspiform (Platylomaspis), derived Polybranchiaspiformes, and even the basal members of the galeaspid family Dayongaspidae. Phylogenetic analysis resolves A. brachyotus as an intermediate taxon between the most primitive Gumuaspidae and other derived Polybranchiaspiformes. Although A. brachyotus also shares the broad ham-brim-like ventral rim with the Gumuaspidae, its other characters are more like other derived Polybranchiaspiformes. In particular, its median dorsal opening and paired orbital openings are not highly close-set on the top of the headshield as in the Gumuaspidae, but rather significantly separated from each other and close to the margin of the ventral rim as in the Pentathyraspidae, Duyunolepididae, and Polybranchiaspidae. These proportions indicate that it was unlikely to have lived a semi-infaunal lifestyle and are more consistent with the epibenthic habit typical of most galeaspids, representing an evolutionary transition from the semi-infaunal benthic to epibenthic lifestyle within Polybranchiaspiformes.

Key words: Qujing, Yunnan, Xishancun Formation, Lower Devonian, Polybranchiaspiformes, Galeaspida, Asioaspis, phylogenetic analysis

摘要：

描述了盔甲鱼亚纲多鳃鱼目一新属种，短耳鸮甲鱼(Asioaspis brachyotus gen. et sp. nov.)。材料采自云南省曲靖市面店水库附近的下泥盆统洛霍赫考夫阶西山村组。新属的特征包括：长卵形头甲，侧缘具锯齿；中背孔小且呈亚圆形；向侧向延伸的短耳状的角；腹环异常宽阔；鳃囊12对；头甲表面布满粗粒状瘤点(约3个/mm²)。其形态特征呈现出镶嵌组合模式，兼具最原始多鳃鱼目宽腹鱼属、进步型多鳃鱼类，甚至基干盔甲鱼类大庸鱼科的特征。系统发育分析表明，短耳鸮甲鱼是最原始的古木鱼科与其他进步型多鳃鱼类之间的中间类群。尽管新属与古木鱼科共同拥有宽阔的 “帽檐状” 腹环，但其他特征更接近进步型多鳃鱼类，尤其中背孔与成对眶孔并未像古木鱼科那样紧凑聚集于头甲顶部，而是彼此远离且靠近腹环边缘，这一特征与五窗鱼科、都匀鱼科及多鳃鱼科一致。这表明短耳鸮甲鱼无法像古木鱼科那样营半埋藏生活，而是与大多数盔甲鱼类一样营表层底栖的生活方式，代表了多鳃鱼目从半埋藏向表层底栖生活方式演化的过渡类型。

关键词: 云南曲靖, 西山村组, 下泥盆统, 多鳃鱼目, 盔甲鱼亚纲, 短耳鸮甲鱼, 系统发育分析

CLC Number:

Q915.861

ZHANG Rui-Rui, ZHANG Ning, LI Qiang, ZHU Min, GAI Zhi-Kun. Asioaspis, a new genus of Polybranchiaspiformes (Galeaspida, stem-gnathostomes) from the Lower Devonian of Yunnan, China. Vertebrata Palasiatica, 2026, 64(2): 137-150.

张睿睿, 张宁, 李强, 朱敏, 盖志琨. 2026, 64(2): 137-150, 云南早泥盆世多鳃鱼类一新属——鸮甲鱼. 古脊椎动物学报.

Figures/Tables 9

Fig. 1 Photograph of Asioaspis brachyotus gen. et sp. nov. from Lower Devonian Xishancun Formation, Qujing, Yunnan in ventral view A. an incomplete headshield, paratype, IVPP V26676. 2; B. a nearly complete dorsal headshield, holotype, V26676. 1

Table 1 Measurements of Asioaspis brachyotus gen. et sp. nov. (mm)

Item	IVPP V26676
Item	.1	.2	.3a	.3b	.4a	.4b	.5
Maximum length of the headshield	47.3	48.9	55.1	59.9	51.4	-	53.3
Maximum width of the headshield	52.3	46.6	47.0	47.6	44.5	48.1	46.4
Length of the headshield in midline	27.2	42.1	32.5	45.6	29.4	-	-
Diameter of the orbital opening	2.4	2.2	-	-	2.9	2.4	3.0
Distance between the orbital openings	14.5	12.2	-	-	13.5	-	15.3
Diameter of the median dorsal opening	4.7	4.1	4.9	4.9	4.1	-	5.0
Distance between the orbital opening and the lateral margin of the headshield	12.4	13.2	-	-	13.5	-	14.5
Distance between the orbital opening and the median dorsal opening	9.4	9.8	10.5	10.8	8.9	-	10.8

Fig. 2 Photographs of Asioaspis brachyotus gen. et sp. nov. from Lower Devonian Xishancun Formation, Qujing, Yunnan in ventral views A. an incomplete dorsal headshield, IVPP V26676.5; B. an incomplete dorsal headshield, V26676.4b

Fig. 3 Photograph of Asioaspis brachyotus gen. et sp. nov. from Lower Devonian Xishancun Formation, Qujing, Yunnan A. a complete ventral headshield, IVPP V26676.3a; B. a complete ventral headshield, V26676.3b; C. an incomplete ventral headshield V26676.6; D. a nearly complete dorsal headshield, V26676.4a A, C. in ventral views; B, D. in dorsal views

Fig. 4 Restoration of Asioaspis brachyotus gen. et sp. nov. in dorsal (A) and ventral (B) views No scaled

Fig. 5 Strict consensus tree of the 6 most parsimonious trees and cladistically based classification of the Galeaspida Tree length = 270, consistency index (CI) = 0.348, retention index (RI) = 0.773

Fig. 6 Morphological comparison of Polybranchiaspiformes, Dayongaspidida, and Huananaspidiformes A. Asioaspis; B. Dayongaspis (Zhang et al., 2024); C. Foxaspis (Gai et al., 2023); D. Platylomaspis (redrawn after Gai et al., 2018); E. Rhegmaspis (Gai et al., 2015); F. Rhegmaspis (Gai et al., 2015); G. Nanningaspis (redrawn after Gai et al., 2018) A-E, G. in dorsal views; F. in ventral view. No scaled

Fig. 7 Phylogenetic diagram of Dayongaspidida, Polybranchiaspiformes, and Huananaspidiformes Dayongaspis (Zhang et al., 2024); Platylomaspis (redrawn after Gai et al., 2018); Nanningaspis (redrawn after Gai et al., 2018); Polybranchiaspis (Liu, 1965); Foxaspis (Gai et al., 2023); Rhegmaspis (Gai et al., 2015).No scaled

Fig. 8 Life restoration of Asioaspis brachyotus gen. et sp. nov.

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