Search results
Results From The WOW.Com Content Network
A primary difference between ammonites and nautiloids is the siphuncle of ammonites (excepting Clymeniina) runs along the ventral periphery of the septa and camerae (i.e., the inner surface of the outer axis of the shell), while the siphuncle of nautiloids runs more or less through the center of the septa and camerae.
The ammonoids appeared early in the Devonian period (some 400 million years ago) and became abundant in the Mesozoic era, before their extinction at the end of the Cretaceous. Some workers apply the name Nautiloidea to a more exclusive group, called Nautiloidea sensu stricto. This taxon consists only of those orders that are clearly related to ...
Goniatite shells are small to medium in size, almost always less than 15 centimeters (5.9 inches) in diameter and often smaller than 5 centimeters (2.0 inches) in diameter. The shell is always planispirally coiled, unlike those of Mesozoic ammonites in which some are trochoidal and even aberrant (called heteromorphs).
Arietitidae is a family of true ammonites that make up part of the superfamily Psiloceratoidea, named after the type genus Arietites.They comprise medium-size to large or gigantic genera which in general are strongly ribbed, tuberculate in some, with keeled or grooved and keeled venters, and well differentiated ammonitic sutures.
In vascular plants, the diploid sporophyte has evolved as the dominant and visible phase of the life cycle. In seed plants and some other groups of vascular plants the gametophyte phases are strongly reduced in size and contained within the pollen and ovules. The female gametophyte is entirely contained within the sporophyte's tissues, while ...
The ancestors of true amniotes, such as Casineria kiddi, which lived about 340 million years ago, evolved from amphibian reptiliomorphs and resembled small lizards. At the late Devonian mass extinction (360 million years ago), all known tetrapods were essentially aquatic and fish-like.
The scale bars measure 150 microns (0.015 cm). Each specimen is similar in size to a grain of sand. Climate change during the last 65 million years as expressed by the oxygen isotope composition of benthic foraminifera. The Paleocene-Eocene thermal maximum is characterized by a brief but prominent excursion, attributed to rapid warming.
On top of the gradual growth of the plant, the image reveals the true meaning of phototropism and cell elongation, meaning the light energy from the sun is causing the growing plant to bend towards the light aka elongate. Plant growth and development are mediated by specific plant hormones and plant growth regulators (PGRs) (Ross et al. 1983). [10]