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- Chen, Donglei, 1985-, et al.
(författare)
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A Partial Tetrapod Lower Jaw from “Romer’s Gap”
- 2009
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Ingår i: SVP 69th Annual Meeting and the 57th Symposium of Vertebrate Palaeontology and Comparative Anatomy (SVPCA).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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- Chen, Donglei, 1985-, et al.
(författare)
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Scale morphology and squamation of the Late Silurian osteichthyan Andreolepis from Gotland, Sweden
- 2012
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Ingår i: Historical Biology. - 0891-2963 .- 1029-2381. ; 24:4, s. 411-423
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Tidskriftsartikel (refereegranskat)abstract
- The origin of osteichthyans (bony fishes and tetrapods) dates back to the Late Silurian, but the early evolution of the group is poorly understood. Andreolepis is one of the oldest known osteichthyans, but exclusively documented by detached and fragmentary dermal microremains. A large data-set of Andreolepis scales from the Silurian of Gotland has been used to explore the scale morphology on different parts of the body. Landmark-based geometric morphometrics together with comparative anatomy and functional morphology has allowed 10 morphotypes to be identified and incorporated into a squamation model, in which scales are allocated to anterior-mid lateral flank scales, posterior lateral flank scales, caudal peduncle scales, pectoral peduncle scales, dorsal flank scales, dorsal fulcral scales, caudal fulcral scales, ventral flank scales, medioventral scales and cranial scales. The scale morphology and squamation pattern ofAndreolepis may be primitive for the Osteichthyes and thus informative about the acquisition of the osteichthyan body plan.
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| 8. |
- Chen, Donglei, 1985-, et al.
(författare)
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The developmental relationship between teeth and dermal odontodes in the most primitive bony fish Lophosteus
- 2020
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Ingår i: eLIFE. - 2050-084X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The ontogenetic trajectory of a marginal jawbone of Lophosteus superbus (Late Silurian, 422 Million years old), the phylogenetically most basal stem osteichthyan, visualized by synchrotron microtomography, reveals a developmental relationship between teeth and dermal odontodes that is not evident from the adult morphology. The earliest odontodes are two longitudinal founder ridges formed at the ossification center. Subsequent odontodes that are added lingually to the ridges turn into conical teeth and undergo cyclic replacement, while those added labially achieve a stellate appearance. Stellate odontodes deposited directly on the bony plate are aligned with the alternate files of teeth, whereas new tooth positions are inserted into the files of sequential addition when a gap appears. Successive teeth and overgrowing odontodes show hybrid morphologies around the oral-dermal boundary, suggesting signal cross-communication. We propose that teeth and dermal odontodes are modifications of a single system, regulated and differentiated by the oral and dermal epithelia.
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- Chen, Donglei, 1985-
(författare)
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The Origin of Tooth Replacement : Three-dimensional Synchrotron Histology Visualizes the Dental Development of Silurian Stem Osteichthyans
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mechanisms of tooth replacement distribute incongruently among extant gnathostomes (jawed vertebrates): a permanent tooth-generating dental lamina exists in chondrichthyans (cartilaginous fish) and tetrapods but not teleosts, whereas tooth shedding by basal hard tissue resorption occurs in tetrapods and teleosts but not chondrichthyans. Theories about the evolution of tooth development have been biased towards the chondrichthyan conveyor-belt replacement, since there has been no fossil evidence for the origin of osteichthyan (bony fish and tetrapods) tooth replacement until now. 3D virtual dissections with submicron-scale resolution, based on propagation phase contrast synchrotron microtomography (PPC-SRµCT), reveal the growth history of the dentitions of Andreolepis and Lophosteus, 423-Myr-old Silurian stem osteichthyans close to the common ancestor of tetrapods and teleosts. Their marginal jawbones and “tooth cushions” (possible homologues of coronoids) shed teeth by in situ cyclic basal resorption, the earliest examples of osteichthyan-style tooth replacement. The replacement cycles were site-autonomic, and occurred in broad irregular multi-row tooth fields, including at sites separated from the margin of the bone by intervening teeth, showing that the production of replacement teeth did not occur in a single deep dental lamina, but in pockets associated with each tooth, as in many teleosts. It suggests that the functionally and anatomically similar laminae of chondrichthyans and tetrapods are convergent. The marginal jaw bones of both genera carry an initial non-shedding dentition arranged in alternate transverse files, labial to the shedding tooth field, overgrown by later dermal ornament and probably not belonging to the oral domain, but bearing in vivo biting damage showing that they functioned as teeth. The most lingual of these odontodes have been resorbed apically and are overlain by shedding teeth. The first-generation teeth on the tooth cushions display basal resorption in Andreolepis, but semi-basal resorption in Lophosteus. The latter leaves a basal dentine ring from each tooth, implying only odontoclasts are involved in the semi-basal resorption, which is probably the first step towards evolving a site-specific resorption. The polarized displacement of each generation of resorption surfaces reflects the fact that the cyclic replacement, as well as the sequential addition of tooth sites, is closely related to bone growth. Resorption surfaces and growth arrest surfaces also record the life history and the replacement rate. These data provide unique insights into the origin of osteichthyan tooth replacement.
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