The pelvic morphology, and whether the pelvic fin is present or absent in the earliest jawed vertebrates are key in interpreting the origin of vertebrate paired fins. Parayunnanolepis xitunensis, an antiarch placoderm from the Early Devonian of Yunnan, South China, was previously described to possess the earliest evidence of both dermal and endoskeletal pelvic girdles, presumably for the attachment of the pelvic fins. Here, we redescribe the pelvic region of the holotype based on high-resolution computed tomographic data. Instead of having two large plates previously designated as dermal pelvic girdles, Parayunnanolepis possesses three pairs of lateral pelvic plates, and one large oval median pelvic plate. The paired pelvic plates are flat ventral plates, and differ from other dermal pelvic girdles in lacking a dorsal extension. There is no definitive evidence for the presence of an endoskeletal pelvic girdle in Parayunnanolepis, although the possibility cannot be ruled out. A comparison of the dermal pelvic plates in various jawed stem-gnathostomes suggests the presence of both paired and median pelvic plates is shared by different lineages and might be plesiomorphic. The jawed stem-gnathostomes may have recruited the ventral dermal skeleton of the post-thoracic body into different functional units.
The Enantiornithes is the most speciose clade of Mesozoic avialans with over 60 named taxa reported from most continents that span the whole Cretaceous. Most of the fossil remains of this clade, as well as those of other early diverging avialans are preserved in two-dimensions. This complicates efforts to extract detailed anatomical information from the skull, in which the composite elements are delicate and thus not easily observable through conventional methods. The scarcity of well-preserved early avialan skulls, as well as the limited number of specimens that have been analyzed using computed tomography scanning, consequently circumscribes a large morphological gap in the fossil record during the transition from the heavy and akinetic dinosaurian skull to the lightweight and kinetic bird skull. Here, we present a three-dimensional digital reconstruction of the skull and part of the cervical vertebrae of a new specimen of the enantiornithine Parabohaiornis martini from the Early Cretaceous of China. Our results demonstrate that Parabohaiornis retains the plesiomorphic non-avialan dinosaurian temporal and palatal configurations, reinforcing the recent hypothesis that the temporal and palatal regions are evolutionarily conservative and that the akinetic skull has been conserved well into diversification of early branching avialans.
Chondrocytes with remnants of nuclei and biomolecules were recently reported in two Cretaceous dinosaurs from North America and China. For multiple reasons, it was hypothesized that calcified cartilage (CC) had a better potential than bone to preserve ancient cells. Here we provide the first experimental test to this hypothesis by focusing on the most important variable responsible for cellular preservation: the postmortem blockage of autolysis. We compare the timing of autolysis between chondrocytes and osteocytes in an avian model (Anas platyrhynchos domesticus) buried for up to 60 days under natural conditions that did not inhibit autolytic enzymes. Within 15 days post-burial, almost all osteocytes were already cytolyzed but chondrocytes in CC were virtually unaffected. All osteocytes were cytolyzed after 30 days, but some chondrocytes were still present 60 days post-burial. Therefore, even in harsh conditions some CC chondrocytes still survive for months postmortem on a time scale compatible with permineralization. This is consistent with other data from the forensic literature showing the extreme resistance of hyaline cartilage (HC) chondrocytes after death and does support the hypothesis that CC has a better potential than bone for cellular preservation, especially in fossils that were not permineralized rapidly. However, because the samples used were previously frozen, it is possible that the pattern of autolysis observed here is also a product of cell death due to ice crystal formation and not strictly autolysis, meaning a follow-up experiment on fresh (non-frozen samples) is necessary to be extremely accurate in our conclusions. Nevertheless, this study does show that CC chondrocytes are very resistant to freezing, suggesting that chondrocytes are likely better preserved than osteocytes in permafrost fossils and mummies that underwent a freezing-thawing cycle. It also suggests that cartilage (both hyaline and calcified) may be a better substrate for ancient DNA than bone. Moreover, even though we warrant follow-up taphonomy experiments with non-frozen samples paired with DNA sequencing, we already urge ancient DNA experts to test CC as a new substrate for ancient DNA analyses in fossils preserved in hot and temperate environments as well.
The micromammal fossils collected from the upper part of the Jiaozigou Formation near Mansancun in 2015 are described. The sample consists of 10 species of six previously known genera (Amphechinus, Sinolagomys, Parasminthus, Litodonomys, Heterosminthus and Yindirtemys) belonging to three orders. Of them, four genera (Sinolagomys, Litodonomys, Heterosminthus and Yindirtemys) made their first appearance in the Late Oligocene and Sinolagomys kansuensis and Heterosminthus lanzhouensis are known only in the Late Oligocene. In comparison with the other Late Oligocene mammalian faunas known in China and Mongolia, the above assemblage appears to be contemporaneous with Xiagou, Taben-buluk, Yikebulage faunas and Tieersihabahe assemblages, but slightly younger than the Shargaltein-Tal Fauna in age. The Mansancun Fauna is also younger than the three Late Oligocene biozones recognized recently in Asia. Compared with the Yagou Fauna collected from the lower part of the Jiaozigou Formation, the Mansancun Local Fauna is clearly younger. Consequently, the Yagou Fauna would be early Late Oligocene, while the Mansancun Local Fauna may be considered late Late Oligocene. Thus, as a whole, the Jiaozigou Formation is Late Oligocene in age.
The zygodont proboscideans from the Miocene strata of China are widely distributed. However, the materials are scarce, and their classification has experienced a longtime controversy, from the chaotic state of multiple Zygolophodon species to the only one species, Zygolophodon gobiensis. The combined species Z. gobiensis comprises both the gracile type with a high degree of zygodonty and the robust type that is between the typical bunodont and zygodont morphology. Recently, as the robust type has been re-allocated to another genus Miomastodon and new fossil remains were discovered, it is necessary to further evaluate and classify the zygodont proboscideans from the Miocene of China. In the present paper, we restudied the previously published zygodont specimens of the gracile type, as well as several unpublished Mammutidae specimens. The former including Z. nemonguensis, Z. gromovae, Z. jiningensis, Z. chinjiensis and two specimens of Gomphotherium xiaolongtanensis, represents Zygolophodon in the original sense in China. In these specimens, the tip of the loph(ids) are sharp. The anterior and posterior pretrite central conules are absent or very weak, and the anterior and posterior crescentoids are sharp and slender. The posttrite mesoconelets are well subdivided and the zygodont crests are developed. In buccal view, the loph(id)s are “Ʌ-shaped” and the interloph(id)s are “V-shaped”. Their molar morphology resembles that of Z. turicensis, and hereby, they were identified as Zygolophodon cf. Z. turicensis. Several unpublished specimens from Hezheng, Gansu, Tunggur, Nei Mongol, Tongxin, Ningxia and Junggar, Xinjiang exhibit a lower degree of zygodonty, corresponding to the “robust type of Zygolophodon” in which the molar morphology is between the typical bunodonts and zygodonts. The pretrite crescentoids are thicker than Zygolophodon cf. Z. turicensis, and the pretrite central conules usually present on the first and second interloph(id)s. According to the stratigraphic age and characteristics, two species, Miomastodon gobiensis and Mio. tongxinensis were identified. The anterior and posterior pretrite crescentoids of Mio. tongxinensis are weaker and the pretrite central conules are larger than Mio. gobiensis. Geographical distribution indicates that Miomastodon is the predominant member of zygolophodonts in the Early and Middle Miocene in northern China. The discovery of new materials and the reclassification of zygolophodonts provide further evidence for dispersal of Mammutidae from Eurasia to North America and the evolutionary relationships among the species of the family Mammutidae in China.