On kannemeyeriiform dicynodonts from the Shaanbeikannemeyeria Assemblage Zone of the Ordos Basin, China

doi:10.19615/j.cnki.2096-9899.220601

Abstract

Abstract:

Shaanbeikannemeyeria is a common tetrapod from the lower part of the Ermaying Formation of the Ordos Basin, China. There are taxonomical questions surrounding this genus, such as the validity of the genus, and how many species are included within it. Several specimens have been collected since 1978. Shaanbeikannemeyeria first appeared from the top of the Heshanggou Formation. These specimens are described to clarify the diagnostic characters, the individual variations and the phylogenetic position of Shaanbeikannemeyeria. Only one species, S. xilougouensis, is recognized. It is characterized by the following autapomorphies: occiput strongly inclined relative to the palate such that the skull is much shorter basally than dorsally, sword tip-like premaxillary posterodorsal processes, tall and dorsally-convex cutting blade on the medial edge of the dorsal surface of the dentary, reflected lamina with a separated posteroventral process, and 15 dorsal vertebrae. This species shows variations on the cranial morphology, such as the occiput height relative to the width, the snout tip (sharp or obtuse), the shape of the orbital portion of the zygomatic arch, and the shape of caniniform process. Some variations could be ontogenetically related, such as the development of the caniniform process and tusk, the posterior extension of the maxilla on the zygomatic arch, the distance between the frontal and the premaxilla, the intertemporal bar width, and the exposing degree of the parietals. Based on postcranial bones, the second dicynodont genus (possibly Parakannemeyeria) is present in the lower Ermaying Formation.

Key words: Ordos Basin, Middle Triassic, Anisian, Heshanggou Formation, Ermaying Formation, Kannemeyeriiformes

摘要：

陕北肯氏兽(Shaanbeikannemeyeria)是二马营组下部常见的四足动物。这个属在分类学上还有一些问题没有解决,例如本属是否有效,包括几个种等。自1978年以来又陆续采集到一些材料。陕北肯氏兽首现于和尚沟组顶部。描述了发现的所有陕北肯氏兽化石,厘清其鉴定特征,了解个体差异,确认其系统位置。陕北肯氏兽只包含一个有效种：戏楼沟种(S. xilougouensis), 其独有衍征包括：枕部相对腭部强烈倾斜因而头骨腹面短,前颌骨有剑尖状的后背突,齿骨背侧内缘呈背凸的刀片状,隅骨的反折翼有一独立的后腹突,15枚背椎。这一属种在头骨形态上存在个体间差异,例如枕高相对枕宽比、吻尖形态(尖或钝)、颧弓眼眶部分形状以及齿突形态。有些差异可能与个体发育有关,例如齿突和长牙的发育程度、前颌骨在颧弓上向后延伸程度、前颌骨与额骨的距离、间颞部宽度及顶骨出露程度。基于头后骨骼可以判定二马营组下部还存在第二种肯氏兽类,可能是副肯氏兽(Parakannemeyeria)。

关键词: 鄂尔多斯盆地, 中三叠世, 安尼期, 和尚沟组, 二马营组, 肯氏兽型类

CLC Number:

Q915.864

LIU Jun. On kannemeyeriiform dicynodonts from the Shaanbeikannemeyeria Assemblage Zone of the Ordos Basin, China. Vertebrata Palasiatica, 2022, 60(3): 212-248.

刘俊. 2022, 60(3): 212-248, 鄂尔多斯盆地陕北肯氏兽组合带的肯氏兽型二齿兽类. 古脊椎动物学报.

Figures/Tables 21

Fig. 1 Stratigraphic column of tetrapod fossil horizons in the studied area

Table 1 List of studied specimens in this paper (cm)

	skull	skull basal length	lower jaw	postcranial bones
Shaanbeikannemeyeria
adult
IGCAGS V315¹⁾	nearly complete	27	absent	absent
IVPP V 6033²⁾	incomplete	31	present	present
IVPP V 11674	nearly complete	24	present	absent
IVPP V 11675	incomplete	~27	present	absent
IVPP V 11677	incomplete	29	present	absent
IVPP V 30728	absent		absent	left humerus
subadult
IVPP V 11676	nearly complete	16	present	scapula, humerus, clavicle
IVPP V 17904	incomplete	~21	absent	absent
IVPP V 30725	incomplete	~14	present	absent
IVPP V 30726	incomplete	~18	present	nearly complete
juvenile
IVPP V 30729^*	incomplete	<10	absent	absent
?Parakannemeyeria
IVPP V 30727	absent		absent	partial skeleton
IVPP V 30730^*	absent		absent	partial skeleton

Fig. 2 Holotype of Shaanbeikannemeyeria xilougouensis (IGCAGS V315) from the Ermaying Formation Drawings of the skull in dorsal (A), ventral (B), lateral (C), and occipital (D) views Revised from Cheng, 1980. Scale bars equal 4 cm

Fig. 3 Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 11674) Skull: photos and interpretive drawings in dorsal (A) and ventral (B) views. Scale bars equal 4 cm

Fig. 4 Photos and interpretive drawings of the skull of Shaanbeikannemeyeria xilougouensis (IVPP V 11674) in right lateral (A) and occipital (B) views Scale bars equal 4 cm

Fig. 5 Shaanbeikannemeyeria xilougouensis (IVPP V 11674), lower jaw, photo and interpretive drawing in dorsal (A), right lateral (B), and right medial (C) views; posterior portion of left ramus in lateral view (D) Scale bars equal 2 cm

Fig. 6 Holotype of Shaanbeikannemeyeria buerdongia (IVPP V 6033) from the Ermaying Formation Skull with lower jaw: photo (A) and interpretive drawing (B) in ventral view, drawing (C) in left lateral view (drawing revised from Li, 1980). Scale bars equal 4 cm

Fig. 7 Photos and drawings of the skull with lower jaw of Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 11677) A. ventral view; B. right lateral view; C. dorsal view; D. occipital view. Scale bars equal 4 cm

Fig. 8 Shaanbeikannemeyeria xilougouensis from the Heshanggou Formation (IVPP V 11675) A, B. skull in lateral (A) and ventral (B) views; C. quadrate and quadratojugal in anterolateral view; D. the region around the parietal foramen in dorsal view; E, F. lower jaw, part of the left ramus (E) and the right ramus (F) in lateral view

Fig. 9 Ventral-posterior portion of skull of Shaanbeikannemeyeria xilougouensis from the Heshanggou Formation (IVPP V 11675) in right lateral (A), dorsal (B) and ventral (C) views

Fig. 10 Skull of Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 17904) in dorsal (A), ventral (B), and right lateral (C) views Scale bars equal 4 cm

Fig. 11 Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 11676) Photos and interpretive drawings of the skull in dorsal (A), right lateral (B), ventral (C) and occipital (D) views; left quadrate and quadratojugal complex in anterior (E) and posterior (F) views

Fig. 12 Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 11676) Lower jaw in dorsal (A), ventral (B) and right lateral (C) views. Scale bars equal 4 cm

Fig. 13 Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 30725) Incomplete skull with lower jaw in dorsal (A), ventral (B), and right lateral (C) views; part of the pterygoid showing the interpterygoid vacuity (D). Scale bars equal 4 cm

Fig. 14 Photos and interpretive drawings of the skull of Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 30729) A. left portion in dorsal view; B. right portion in lateral and slightly dorsal view. Scale bars equal 1 cm

Fig. 15 Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 30726) A. skeleton in dorsal view; B. right anterior presacral ribs; C. left forelimb, humerus in lateral and slightly dorsal view, ulna and radius in lateral view; D. left pelvic girdle in lateral view, right ilia in lateral view, right pubis and ischium in medial view; E. right hind limb, tibia and fibula in anterior view, pes in dorsal view; F. photo and drawing of right pes mainly in ventral view The numbers in (A) mark the dorsal ribs

Fig. 16 Shaanbeikannemeyeria xilougouensis from the Ermaying Formation, postcranial bones IVPP V 6033: incomplete sternum in ventral (A) and dorsal (B) views; right clavicle in anterior (C) and posterior (D) views; right scapula in medial (E) and lateral (F) views IVPP V 11676: right scapula in medial (G) and lateral (H) views; right clavicle and interclavicle in ventral (I) and dorsal (J) views; left humerus in ventral (K), dorsal (L), anterior (M) and posterior (N) views IVPP V 30726: left scapula in lateral view (O). Scale bars equal 2 cm

Fig. 17 Shaanbeikannemeyeria xilougouensis from the Ermaying Formation (IVPP V 6033), limbs Right humerus in ventral (A) and dorsal (B) views; left radius in proximal (C), anterior (D) and posterior (E) views; right ulna in medial (F) and lateral (G) views; left ulna in lateral (H) and medial (I) views; left femur in ventral (J) and dorsal (K) views; fibula in medial (L) and lateral (M) views; left tibia in anterior (N), medial (O), posterior (P) and lateral (Q) views. Scale bars equal 2 cm

Fig. 18 ?Parakannemeyeria from the lower portion of the Ermaying Formation IVPP V 30730: A. partial posterior skeleton in dorsal view; B. five dorsal vertebrae and associated ribs in left dorsolateral view; C, D. last dorsal vertebra and four sacral vertebrae and associated ribs in left dorsolateral (C) and ventral (D) views IVPP V 30727: E, F. right scapula, procoracoid and metacoracoid in lateral (E) and medial (F) views; G, H. right humerus in dorsal (G) and ventral (H) views; I-K. right radius in anterior (I), medial (J), and posterior (K) views; L, M. right ulna in posterior (L) and anterior (M) views. Scale bars equal 2 cm

Fig. 19 Results of the phylogenetic analysis, showing the interrelationships within Dicynodontoidea Numbers below nodes represent symmetric resampling values

Table 2 Variations of some cranial features among different specimens

	ratio of occipital width/height	snout tip	orbital portion of the zygomatic arch	caniniform process
IGCAGS V315	1.22	obtuse	rod-like	flat
IVPP V 11674	1.20	sharp	nearly flat dorsoventrally	flat
IVPP V 6033	1.61		nearly flat dorsoventrally	rounded
IVPP V 11675			rod-like	rounded
IVPP V 11676	1.27	obtuse	rod-like	undeveloped
IVPP V 11677	1.54	sharp	rod-like	rounded

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