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    20 January 2024, Volume 62 Issue 1
    Decline in phylogenetic diversity of Arthrodira (stem-group Gnathostomata) correlates with major Devonian bioevents
    XUE Qin-Yuan, YU Yi-Lun, PAN Zhao-Hui, ZHU You-An, ZHU Min
    2024, 62(1):  1-12.  DOI: 10.19615/j.cnki.2096-9899.231124
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    Arthrodira, the most diverse subgroup of placoderms, or jawed stem gnathostomes, is noted for their occupation of high trophic levels, especially in the later stage of their evolutionary history. Despite the relatively complete fossil record of arthrodires, the results of previous studies on the arthrodire diversity, based on counting the numbers of taxa in each time interval (raw or taxic diversity), correlate poorly with major Devonian bioevents. Here, we assemble a new, exhaustive dataset of arthrodires, comprising 450 species of 219 genera. Most taxa are integrated into a supertree integrating the results from various phylogenetic investigations. Our analysis of the phylogenetic diversity, accounting for the presence of ghost lineages, reveals a very different pattern compared to the raw diversity. The phylogenetic diversity of arthrodires exhibited a typical early burst pattern, peaking in the Early Devonian (Lochkovian-Pragian Boundary), and followed by declines that aligned well with several major bioevents. Near each of the first four events, the arthrodire diversity experienced only minor drops and generally persisted at high levels. The later three events, particularly the Frasnian-Famennian Boundary and Devonian-Carboniferous Boundary Events, led to steep declines in arthrodire diversity, from which they never recovered before their complete extinction in the end-Devonian. All these declines were not evident in the raw or taxic diversity pattern, except that related to the Frasnian-Famennian Boundary Event.

    A small-sized dinocephalosaurid archosauromorph from the Middle Triassic of Yunnan, southwestern China
    WANG Wei, LEI Hong, LI Chun
    2024, 62(1):  13-32.  DOI: 10.19615/j.cnki.2096-9899.231013
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    Among numerous marine reptiles discovered in the Triassic eastern Tethys, today’s Southern China, Dinocephalosaurus is a bizarre animal comparable to European Tanystropheus in developing a prominently long neck. These two taxa are respectively assigned to Dinocephalosauridae and Tanystropheidae, and the two families and other basal members collectively form an early-diverging clade of Archosauromorpha. Here we report a new archosauromorph specimen, IVPP V18579, excavated from the lower Middle Triassic (Anisian), from Luoping, Yunnan in southwestern China. Compared with all the hitherto known dinocephalosaurids and tanystropheids, this skeletally mature individual is exclusively similar to Dinocephalosaurus in a number of characteristics, particularly with the long posterodorsal process of the premaxilla extending posteriorly beyond the level of the external nares, the concave posterior margin of the anteroposteriorly broad quadrate, and the strongly expanded distal end of the chevron in most of the caudal vertebrae. However, this reptile is much smaller than Dinocephalosaurus and different from Dinocephalosaurus and the other dinocephalosaurid, Pectodens, in many aspects, such as an anteriorly tapering long rostrum, the dentition composed of short conical teeth with less heterodonty, relatively but obviously tall neural spines of the axis and the anterior cervical vertebrae. Our phylogenetic analysis suggests that the new archosauromorph is a dinocephalosaurid, and then we erect Austronaga minuta gen. et sp. nov. based on this specimen. Detailed comparisons in osteological anatomy and the discussion about its potential aquatic adaptation of this new taxon are also provided.

    Reassessment of Trilophodon connexus Hopwood, 1935 and attributing it to the Choerolophodontidae
    LI Chun-Xiao, CHEN Jin, WANG Shi-Qi
    2024, 62(1):  33-46.  DOI: 10.19615/j.cnki.2096-9899.230917
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    Trilophodon connexus Hopwood, 1935 has long been considered a typical species of Gomphotherium in China. However, due to the unknown state of the mandibular symphysis and tusks, there is no definite evidence to assign “T. connexus” to Gomphotherium. Here we describe and reevaluate a hemimandible from the Halamagai Formation, Ulungur region, northern Junggar Basin, which was previously identified as Gomphotherium cf. G. shensiensis. The mandibular symphysis is deeply troughed and lacks mandibular tusks; therefore, it undoubtedly belongs to the Choerolophodontidae. Further comparison revealed that the cheek tooth morphology is identical to that of the type specimen of Trilophodon connexus. The characteristic features include high bunodonty, elongation of the m3 with four lophids, an only weakly chevroned lophid 2, enlargement of the posterior pretrite central conule 2, unfused state of the pretrite mesoconelet 2 (if present) and anterior pretrite central conule 2, as well as the absence of ptychodonty, choerodonty, and cementodonty. Therefore, T. connexus Hopwood, 1935 is a choerolophodontid rather than a species of Gomphotherium. Based on the above features, we provisionally refer to it as “Choerolophodonconnexus. “Choerolophodonconnexus is characterized by the following features: weak or absent ptychodonty, choerodonty, and loph chevron (which were all strong in the typical species of Choerolophodon), as well as multiplication of the lophids in the m3, which were similar to that of the North American Gnathabelodon. Therefore, Gnathabelodon might represent a distinct lineage within the Choerolophodontidae, and may be derived from the East Asian “Choerolophodonconnexus.

    A skull of Early Pleistocene Paracamelus gigas (Artiodactyla, Mammalia) from Luotuo Hill in Dalian, Northeast China
    DONG Wei, LIU Wen-Hui, BAI Wei-Peng, LIU Si-Zhao, WANG Yuan, LIU Jin-Yuan, JIN Chang-Zhu
    2024, 62(1):  47-68.  DOI: 10.19615/j.cnki.2096-9899.230616
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    Originated in North America in the Middle Eocene, camelids were a successful group with very large diversity. But the camels emigrated to the Old World from North America, probably during the middle stage of the Middle Miocene, and did not radiate much as those in North America, represented by only two genera Paracamelus and Camelus. The former was considered as giving rise to the latter, but the detailed relationship of the Old World camelines was controversial. The new camel material unearthed from Layer 4 in the Jinyuan Cave at Luotuo Hill in Dalian, Liaodong peninsula in Northeast China, was described and referred to as Paracamelus gigas. Its dentition length is slightly longer than that of Camelus knoblochi but evidently larger than that of C. ferus and C. dromedarius. Based on the fossil records and morphometric evidences, P. gigas originated from a form similar to P. alexejevi in the Late Pliocene in the Old World, instead of from Megatylopus gigas of North America and then migrated into Asia as previously thought. The morphometric similarities between the Early Pleistocene Dalian specimens and those of the Middle and Late Pleistocene C. knoblochi indicate that P. gigas probably gave rise to C. knoblochi as formerly postulated and likely in the late Early Pleistocene by reduction or simplifying of P3 and P4, disappearance of p3 and shortening of dentition length. P. gigas inhabited in the forest steppe environment of Liaodong peninsula from 1.1 to 1.52 Ma based on paleomagnetic dating and pollen evidence.

    New suoid remains (Mammalia, Artiodactyla) from the Late Miocene of Haritalyangar, India
    2024, 62(1):  69-84.  DOI: 10.19615/j.cnki.2096-9899.231120
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    We report here a number of mandibular, maxillary and dental fossil remains of Indian Suoidea from the Middle Siwalik of Haritalyangar area in Bilaspur District of Himachal Pradesh, North India. Haritalyangar is well known for the diversity of the Late Miocene fauna and the hominoids and other primates. The suoid remains were collected by one of the authors (ARS) during different field seasons and their localities were plotted on the map, along with those of the proboscidean reported recently, including the hominoid localities. The fossil localities are spread over the ‘Lower Alternations’ and the ‘Upper Alternations’ from Makkan Khad to Sir Khad. We have assigned the fossils into three genera, Propotamochoerus (P. hysudricus), Hippopotamodon (H. sivalense) and Yunnanochoerus (Y. dangari). Propotamochoerus hysudricus represents the most common suid in the Middle Siwaliks. The new remains of the suoid Yunnanochoerus dangari further documents this rare palaeochoerid only known in the Haritalyangar area by a few fossils. The new suoid remains show clear affinities with the Nagri fauna of the Pakistan Siwaliks. Biochronological correlations with the Potwar Plateau based on suoids indicate an age bracket of ~10-9 Ma for the ‘Lower Alternations’ of Haritalyangar, close to the bracket mostly recently proposed on the basis of magnetic polarity stratigraphy.