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The primary (baby) teeth generally start coming in by 6 months of age, and all 20 teeth may be in by two and a half years of age. The eruption timing varies greatly. There may be an incomplete formation of the enamel on the teeth (enamel hypoplasia) that makes the teeth more vulnerable to caries (cavities). There may be missing teeth eruptions.
In biology, homology is similarity in anatomical structures or genes between organisms of different taxa due to shared ancestry, regardless of current functional differences. Evolutionary biology explains homologous structures as retained heredity from a common ancestor after having been subjected to adaptive modifications for different ...
Whereas ordinary homology is seen in the pattern of structures such as limb bones of mammals that are evidently related, deep homology can apply to groups of animals that have quite dissimilar anatomy: vertebrates (with endoskeletons made of bone and cartilage) and arthropods (with exoskeletons made of chitin) nevertheless have limbs that are constructed using similar recipes or "algorithms".
A thin paper strip with its ends joined to form a Möbius strip can bend smoothly as a developable surface or be folded flat; the flattened Möbius strips include the trihexaflexagon. The Sudanese Möbius strip is a minimal surface in a hypersphere, and the Meeks Möbius strip is a self-intersecting minimal surface in ordinary Euclidean space ...
By targeting the USAG-1 gene, researchers believe that they can help people without a full set of teeth regrow teeth. The team says that humans have a third set of teeth available as buds, ready ...
Sawfish (a group of rays related to guitarfish), unrelated sawsharks (a group of sharks), and the extinct sawskates (another group of rays related to modern skates) all convergently evolved a saw-like rostrum with sharp transverse teeth for hunting. [130] This evolutionary process has been named "pristification". [131]
They may have also had thicker dermis like mammals today. The jaws of cynodonts resembled modern mammal jaws; the anterior portion, the dentary, held differentiated teeth. This group of animals likely contains a species which is the ancestor of all modern mammals. Their temporal fenestrae merged with their orbits.
The nodal plane of the orbitals, viewed as a ribbon, is a Möbius strip, rather than a cylinder, hence the name. The pattern of orbital energies is given by a rotated Frost circle (with the edge of the polygon on the bottom instead of a vertex), so systems with 4 n electrons are aromatic, while those with 4 n + 2 electrons are anti-aromatic/non ...