Marine Invertebrates Ebook
Other groups that survived into the Carboniferous seem to have been heavily depleted. Of the 70 families of fishes currently recognized as present in the Late Devonian (Benton, 1993a), 51 died out during the next 15 Myr, a total extinction rate of 73 , which is high by any standards. The extinctions seem to have been spread through the Late Devonian, but only 17 families (24 ) survived into the Carboniferous. A multiphase Late Devonian extinction event also has been recognized among marine invertebrates such as corals, brachiopods and ammonoids, as well as phytoplankton. The Devonian fish faunas were replaced in the Carboniferous by new groups (see Chapter 7).
This character is of developmental interest, especially given the ontologi-cal significance, relative to the adult condition. The example provided by Raff (1996) will suffice to establish to some degree the likely significance of these two deciduous dental characters. He reminds us that early in the 19th century, ascidians (marine invertebrates that as adults are saclike filter feeders) were classified as molluscs, but they were later shown to have larvae unlike any mollusc. Their larvae would resemble tiny tadpoles, complete with dorsal chord and notochord. These larvae are built along the same overall body plan as vertebrates and as such were reclassified. While perhaps an extreme example relative to the deciduous dentition, it does, however, highlight the need to examine processes that can be partly identified by examining stages of ontogeny.
It is impossible to plot an accurate diagram of species numbers through time, because so many species were never fossilized, and others are yet to be found and identified. Paleontologists have focused on those parts of the fossil record where the results might be believable. Valentine (1969) presented the first serious effort, when he plotted the numbers of families of skeletonized shallow-marine invertebrates through the Phanerozoic (Fig. 20.1a). The pattern showed a jerky increase, with several declines, and a particularly dramatic rate of increase from the Cretaceous to the present. Valentine argued that this pattern might be representative of the pattern of diversification of all of life.
The lack of new phyla and the paucity of new classes after the end of the Cambrian Explosion may again be an artifact of the fossil record perhaps many new higher taxa did evolve and subsequently went extinct. This seems unlikely. It is far more likely that the great surge of innovation that marked the Cambrian came to an end as most ecological niches became occupied by the legions of newly evolved marine invertebrates.
Nutrients and productivity may affect diversity on evolutionary timescales not only through their effects on the origin of species, but also through their effects on the extinction of species. A number of studies have noted a correlation between trophic pattern and susceptibility to extinction in benthic marine invertebrates, specifically the apparently higher extinction rate of suspension feeders compared with nonsuspension feeders, although interpretations for the cause of these correlations vary. Levinton (1974) noted that suspensionfeeding bivalves showed lower generic survivorship (and therefore higher extinction probability) over the entire Phanerozoic than deposit-feeding bivalves and attributed this difference to the greater instability of the suspension feeders' food source. (He reversed himself in 1996, arguing that differences in extinction rates among bivalve trophic patterns may relate to other, nontrophic factors.) Similarly, Paleozoic gastropod genera inferred to have...
Remoteness in time could influence the assignment of two taxa to different taxonomic groups of equal rank. Raup (1983) found that the mean geologic age of first occurrences of the 27 readily preservable class-level taxa of marine invertebrates is 533 million years. Twenty of the 27 taxa first occur in the Cambrian at the time of this study. Because high taxonomic rank is based on genealogical relationship, overall similarity, and species richness, it is not clear whether this early origin is a function of true early morphological diversification or just an inherent property of higher taxa, whose early origins are bound to make them subtend many subordinate taxa that arise by branching of the stem taxon. But it is not unusual to draw an equivalence between high taxonomic rank and fundamental body plans or occupancy of major adaptive zones (Gould 1989 Simpson 1944, Valentine 1969, Van Valen 1984).
If conditions promoting isolate formation, persistence, and differentiation at Anewetak were common to dozens or hundreds of other atoll localities prior to high amplitude sea level fluctuations, then one might also expect to see higher speciation rates in the Indo-Pacific region at this time. Circumstantial evidence, consisting of estimates of a slowdown in late Cenozoic speciation during high amplitude sea level fluctuations in several groups of Indo-Pacific marine invertebrates, suggests that this may indeed be the case. Both the evidence and its link to nutrients remain open to interpretation, but we can provide a preliminary model for testing.
Ton often show gradualistic patterns of evolution and speciation. Marine invertebrates from continental shelves tend to exhibit punctuational patterns. Terrestrial vertebrates, at least where the fossil record allows speciation patterns to be identified, present a variety of patterns, but no records of gradual speciation events exist.
Improved data, especially on marine invertebrates, led to a better appreciation of species origination, extinction, and diversity through the Phanerozoic. It became apparent that several mass extinctions had indeed befallen the world biota. Two issues arose what caused these extinction events and were they random or periodic As to there first question, there is a choice of catastrophes - bolide impacts, volcanism, sea-level change, and many more -that has formed the basis of heated arguments, especially since evidence of a huge impact at the close of the Cretaceous emerged in 1980. Suggestions that mass extinctions are periodic, following a galactic or geological timetable, have fuelled equally heated exchanges of views. researchers question the reality of coordinated stasis. Its causes are also the subject of deliberation. Even more controversial perhaps is the assertion that there have been cycles in diversity through the Phanerozoic. The latest analysis of an extensive dataset of...
Despite the obvious role fungi play in modern ecosystems as decomposers, parasites, and mutualists, the interactions between fungi and animals are not extensively documented in the fossil record. A common fungus-animal interaction known from the Paleozoic to the recent is evidence of borings made by endolithic fungi (also algae and bacteria) in calcium carbonate skeletons of marine invertebrates (Gatrall and Golubic, 1970 Grahn, 1981). This represents a trace fossil (or ichnofossil), in that no organic material of the fungus remains, only trace evidence in the form of damage to shells, and so on. Another early example of fungus-animal interactions involves middle Silurian fungal remains from Sweden (Sherwood-Pike and Gray, 1985). These rocks contain spindle-shaped aggregates of hyphae associated with amorphous material up to 260 m long. The fungal remains are interpreted as frass (fecal pellets) produced by a micro-arthropod. Another explanation is that the arthropod was using the...
Oceans can also represent dispersal barriers to certain animals which are adapted to live in relatively shallow marine environments. The widespread dispersal of marine invertebrates can only occur in their larval stages when they form part of the plankton (Hallam, 1973b). For most species the larval stage is too shortlived to exist for the duration of the crossing of a large ocean. Consequently, ancient faunal province boundaries frequently correlate with sutures, which represent the join lines between ancient continents brought into juxtaposition by the consumption of an intervening ocean. The distribution of Cambrian trilobites strongly
However, in many ways, the Ordovician radiation provides a simpler opportunity to examine paleoecological changes through the course of a radiation because there is a record of skeletal metazoans long before and after the Ordovician radiation, and there is a continuous marine record. In particular, it is not complicated by such phenomena as the advent of skeletalization or taph-onomic biases associated with soft-bodied faunas. Paleoecological changes associated with the Ordovician radiation of marine invertebrates include second, third, and fourth level changes. However, evidence from both spores (Gray 1985) and trace fossils (Retallack and Feakes 1987) suggests that the
1 Fossils are generally preserved in sedimentary rocks, and these record all kinds of features about the conditions of deposition. Fossil plants may be found at certain levels in a cyclical succession that tells a story of the repeated buildup of an ancient delta as it fingers into the sea, the development of soils and forests on top, and its eventual flooding by a particularly high sea level. Marine invertebrates may be found in rocks that indicate deposition in a shallow lagoon, offshore from a reef, on the deep abyssal plain or many other
A third type of osmoregulatory plasticity is seen in another estuarine animal, the crab-eating frog Rana cancrivora (Gordon et al., 1961 tip 80 in Fig. 1). This frog can live in freshwater or marine habitats as an adult and typically consumes marine invertebrates that are isosmotic with seawater. Plasma osmolarity varies in relation to environmental salinity for example, at 250 mOsm. in the environment, the plasma osmolarity is 340 mOsm, but at 800 mOsm, the plasma osmolarity is 830 mOsm (Gordon et al., 1961 we use a value of 290 mOsm for this species, which represents animals acclimated to freshwater). The frog does this by increasing or decreasing internal concentrations of one molecule, urea, while regulating the other ions and proteins at constant levels, independent of habitat. A similar mechanism is at work in freshwater elasmobranchs, such as Carcharhinus leucas (Thorson et al., 1973 tips 150-151 in Fig. 1) and some skates and rays (Holmes and Donaldson, 1969 Withers, 1992)....
Markevich and Bugdaeva (2001) reiterated the assertion that both the vegeta-tional change and dinosaur extinction in the Russian Far East took place at the locally defined middle Maastrichtian-upper Maastrichtian boundary. They asserted that the tripartite division of the Maastrichtian Stage is based on paleontological data from marine invertebrates (inoceramids) and terrestrial vertebrates (dinosaurs), as well as from paleobotany (Golovneva 1994a, b) and palynology (Markevich et al. 1994).
The key synapomorphy uniting the ecdysozoans is the possession of a cuticle that is periodically molted (a process named ecdysis). The ecdysozoan phyla are the arthropods (e.g., insects, crustaceans, myriapods, and chelicerates), onycho-phorans (velvet worms), tardigrades (water bears), nematodes (roundworms), nematomorphs (horsehair worms), priapulids, loriciferans, and kinorhynchs (mud dragons). Probably concomitant with the evolution of a cuticle that covers the entire body surface, the ecdysozoans lost the motile epidermal cilia that are widespread in other animal phyla. Moreover, in contrast to many other invertebrates, the life cycle of ecdysozoans does not include a free-living ciliated larval stage. They are therefore referred to as exhibiting direct development, instead of indirect development via a larval stage, which characterizes the life cycles of many marine invertebrates.
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