OK...back to some real science....
This just came out in PNAS and discusses recent calibrations of the molecular clock that tentatively suggest a Late Triassic origin for angiosperm plants.
Smith, S. A., Beaulieub, J. M., and M. J. Donoghue. 2010. An uncorrelated relaxed-clock analysis suggests an earlier origin for flowering plants. PNAS 107:5897-5902. www.pnas.org/cgi/doi/10.1073/pnas.1001225107
Abstract - We present molecular dating analyses for land plants that incorporate 33 fossil calibrations, permit rates of molecular evolution to be uncorrelated across the tree, and take into account uncertainties in phylogenetic relationships and the fossil record.We attached a prior probability to each fossil-based minimum age, and explored the effects of relying on the first appearance of tricolpate pollen grains as a lower bound for the age of eudicots. Many of our divergence-time estimates for major clades coincide well with both the known fossil record and with previous estimates. However, our estimates for the origin of crown-clade angiosperms,which center on the Late Triassic, are considerably older than the unequivocal fossil record of flowering plants or than the molecular dates presented in recent studies. Nevertheless,we argue that our older estimates should be taken into account in studying the causes and consequences of the angiosperm radiation in relation to other major events, including the diversification of holometabolous insects. Although the methods used here do help to correct for lineage-specific heterogeneity in rates of molecular evolution (associated, for example, with evolutionary shifts in life history), we remain concerned that some such effects (e.g., the early radiation of herbaceous clades within angiosperms) may still be biasing our inferences.
Supplimental data for this article can be found at: www.pnas.org/cgi/content/full/1001225107/DCSupplemental.
Showing posts with label angiospermy. Show all posts
Showing posts with label angiospermy. Show all posts
A Well-preserved Thallatosaur and new Evidence on the First Appearance of Angiospermy in the Mesozoic
Things have been a bit slow in Triassic-land lately and I've been too busy to be creative; however, Jeff has posted some new pics over at Paleo Errata as things start to thaw out in some places.
There is one recent paper on on Triassic marine reptiles from China:
Zhao, L.-J., Sato, T., Liu, J., Li, C., and X.-C. Wu. 2010. A new skeleton of Miodentosaurus brevis (Diapsida:Thalattosauria) with a further study of the taxon. Vertebrata Palasiatica 48:1-10.
Abstract: A new thalattosaurian skeleton from the Upper Triassic Wayao Member of the Falang Formation, Guanling area, Guizhou Province, China can be referred to Miodentosaurus brevis. The postcranial skeleton of the specimen is well-preserved and so complete that it is worthy to be described. This new specimen provides a full knowledge of the osteology of the thalattosaurian, especially the anatomy of the pectoral girdle and both the fore and hindlimbs. The presence of a few teeth restricted to the anterior ends of both the upper and lower jaws and dorsoventrally flattened ungual phalanges indicate that M. brevis is not a pure carnivore. With new information, some individual variations are recognized and the digital formula(2-3-4-5-5) of the pes can be identified as one of the diagnostic features for the thalattosaurian.
This also may be of interest, although not containing a phylogenetic analysis, the seed plant described here is proposed to be the 'sister taxon' of angiosperms and thus angiospermy evolved more than once in separate groups, or it is derived from a common ancestor in the Triassic or early Jurassic.
Wang, X., and S. Wang. 2010. Xingxueanthus: An Enigmatic Jurassic Seed Plant and Its Implications for the Origin of Angiospermy. Acta Geologica Sinica [English Edition] 84:47-55.
Abstract: The origin of angiosperms has been tantalizing botanists for centuries. Despite the efforts of palaeobotanists, most of the pre-Cretaceous angiosperms are regarded either non convincing or misdated. The applications of SEM and LM (light microscope) enable us to recognize a coalified fossil plant, Xingxueanthus sinensis gen. et sp. nov., from the Haifanggou Formation (Middle Jurassic, >160 Ma) in western Liaoning, China. Xingxueanthus is an ''inflorescence'' with more than 20 female units spirally arranged. Each female unit is situated in the axil of a bract. The female unit is composed of an ovule-container and a style-like projection at the top. There is a vertical column bearing several ovules in the ovule-container. The general morphology and the internal structure of Xingxueanthus distinguish itself from any known fossil and extant gymnosperms, and its structures are more comparable to those of angiosperms. Xingxueanthus, if taken as a gymnosperm, would represent a new class, demonstrate an evolutionarily advanced status of ovule-protection in gymnosperms never seen before, and provide new insights into the origin of angiospermy. Alternatively, if taken as an angiosperm, together with Schmeissneria, it would increase the diversity of Jurassic angiosperms, which has been underestimated for a long time, and suggest a much earlier origin of angiospermy than currently accepted.
There is one recent paper on on Triassic marine reptiles from China:
Zhao, L.-J., Sato, T., Liu, J., Li, C., and X.-C. Wu. 2010. A new skeleton of Miodentosaurus brevis (Diapsida:Thalattosauria) with a further study of the taxon. Vertebrata Palasiatica 48:1-10.
Abstract: A new thalattosaurian skeleton from the Upper Triassic Wayao Member of the Falang Formation, Guanling area, Guizhou Province, China can be referred to Miodentosaurus brevis. The postcranial skeleton of the specimen is well-preserved and so complete that it is worthy to be described. This new specimen provides a full knowledge of the osteology of the thalattosaurian, especially the anatomy of the pectoral girdle and both the fore and hindlimbs. The presence of a few teeth restricted to the anterior ends of both the upper and lower jaws and dorsoventrally flattened ungual phalanges indicate that M. brevis is not a pure carnivore. With new information, some individual variations are recognized and the digital formula(2-3-4-5-5) of the pes can be identified as one of the diagnostic features for the thalattosaurian.
This also may be of interest, although not containing a phylogenetic analysis, the seed plant described here is proposed to be the 'sister taxon' of angiosperms and thus angiospermy evolved more than once in separate groups, or it is derived from a common ancestor in the Triassic or early Jurassic.
Wang, X., and S. Wang. 2010. Xingxueanthus: An Enigmatic Jurassic Seed Plant and Its Implications for the Origin of Angiospermy. Acta Geologica Sinica [English Edition] 84:47-55.
Abstract: The origin of angiosperms has been tantalizing botanists for centuries. Despite the efforts of palaeobotanists, most of the pre-Cretaceous angiosperms are regarded either non convincing or misdated. The applications of SEM and LM (light microscope) enable us to recognize a coalified fossil plant, Xingxueanthus sinensis gen. et sp. nov., from the Haifanggou Formation (Middle Jurassic, >160 Ma) in western Liaoning, China. Xingxueanthus is an ''inflorescence'' with more than 20 female units spirally arranged. Each female unit is situated in the axil of a bract. The female unit is composed of an ovule-container and a style-like projection at the top. There is a vertical column bearing several ovules in the ovule-container. The general morphology and the internal structure of Xingxueanthus distinguish itself from any known fossil and extant gymnosperms, and its structures are more comparable to those of angiosperms. Xingxueanthus, if taken as a gymnosperm, would represent a new class, demonstrate an evolutionarily advanced status of ovule-protection in gymnosperms never seen before, and provide new insights into the origin of angiospermy. Alternatively, if taken as an angiosperm, together with Schmeissneria, it would increase the diversity of Jurassic angiosperms, which has been underestimated for a long time, and suggest a much earlier origin of angiospermy than currently accepted.
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