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Acritarchs are organic microfossils, known from approximately 1.8 billion years ago to the present. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion.
In evolutionary biology, megatrajectories are the major evolutionary milestones and directions in the evolution of life.
Marginocephalia is a clade of ornithischian dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. There are two clades included in Marginocephalia: the thick-skulled Pachycephalosauria and the horned Ceratopsia. All members of Marginocephalia were primarily herbivores. They basally used gastroliths to aid in digestion of tough plant matter until they convergently evolved tooth batteries in Neoceratopsia and Pachycephalosauria. Marginocephalia first evolved in the Jurassic Period and became more common in the Cretaceous. They are basally small facultative quadrupeds while derived members of the group are large obligate quadrupeds. Primitive marginocephalians are found in Asia, but the group migrated upwards into North America.
Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that terminate in sporangia. The name literally means many sporangia plant. The clade includes all land plants (embryophytes) except for the bryophytes whose sporophytes are normally unbranched, even if a few exceptional cases occur. While the definition is independent of the presence of vascular tissue, all living polysporangiophytes also have vascular tissue, i.e., are vascular plants or tracheophytes. Fossil polysporangiophytes are known that have no vascular tissue, and so are not tracheophytes.
The Khatyspyt Formation is a Neoproterozoic formation exposed in the Olenëk Uplift of north central Siberia, which contains the only known instance of the Ediacara biota preserved in a limestone bed. The Khatyspyt Formation forms one of the major parts of the Khorbusuonka Group; underlying the Khatyspyt are dolomites of the Mastakh Formation and their overlying red beds; the Turkut Formation overlies the Khatyspyt. The Khatyspyt and part of the overlying Turkut comprise a major shallowing upward marine carbonate sequence. Khatyspytia is named after this formation.
Khatyspytia is a frondose member of the Ediacara biota. It is slender, with many short branches, and is named after the Khatyspyt Formation.
Guangnania was a genus of Early Devonian land plant with branching axes. It is thought to be related to the zosterophylls.
Grisellatheca was a genus of land plant with branching axes. It is known from charcoalified Early Devonian deposits, its type locality being the Brown Clee Hill lagerstatten. Its Terahedraletes spores form permanent tetrads.
Fusitheca was a genus of land plant with branching axes. It is known from charcoalified Early Devonian deposits, its type locality being the Brown Clee Hill lagerstätten. Its spores form smooth-walled, unfused, naked dyads. Its axis comprises length-parallel filaments, and their dichotomies are T-shaped, with the branches bending to continue upwards.
Culullitheca was a genus of land plant with branching axes. It is known from charcoalified Early Devonian deposits, its type locality being the Brown Clee Hill lagerstätten. Its spores formed permanent dyads.
Bathurstia was a genus of scrambling Silu-Devonian land plant with isotomously-branching axes that grew to heights of 30 cm. It is aligned with the Zosterophylls, and produced Calamospora-type spores.
Thrinkophyton was a genus of Silu-Devonian land plant with branching axes.
Gosslingia was a genus of Silu-Devonian land plant with branching axes.
Serrulacaulis was a genus of Silu-Devonian land plant with branching axes.
Tarella was a genus of Silu-Devonian land plant with branching axes.
Oricilla was a genus of Silu-Devonian land plant with branching axes.
Konioria was a genus of Silu-Devonian land plant with branching axes.
Deheubarthia was a genus of Silu-Devonian land plant with branching axes.
Anisophyton was a genus of Silu-Devonian land plant with branching axes.
Sporogonites was a genus of Lower Devonian land plant with branching axes. It is known from Europe, Australia and Newfoundland. It resembles a moss in that many straight axes, which grew to about five centimetres in height and possess terminal sporangia, grow from a planar basal surface. Its spores were trilete and around 30 µm across.
References
- ↑ Buick, R.; Knoll, A.H. (1999). "Acritarchs And Microfossils From The Mesoproterozoic Bangemall Group, Northwestern Australia". Journal of Paleontology. 73 (5): 744–764. ISSN 0022-3360. PMID 11543499.
- ↑ Butterfield, N.J. (2004). "A vaucheriacean alga from the middle Neoproterozoic of Spitsbergen: implications for the evolution of Proterozoic eukaryotes and the Cambrian explosion". Paleobiology. 30 (2): 231–252. doi:10.1666/0094-8373(2004)030<0231:AVAFTM>2.0.CO;2. ISSN 0094-8373.
- ↑ Li, J.; Servais, T.; Yan, K.; Zhu, H. (2004). "A nearshore — offshore trend in acritarch distribution from the Early-Middle Ordovician of the Yangtze Platform, South China". Review of Palaeobotany and Palynology. 130 (1–4): 141–161. doi:10.1016/j.revpalbo.2003.12.005.
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