Heterochrony is considered to be an important and ubiquitous mechanism of evolutionary change. Three components are necessary to describe heterochrony: phylogenetic relationships, size and shape change, and timing of developmental events. Patterns and processes of heterochrony are all too often invoked before all three components have been investigated. Phylogenetic hypotheses affect the interpretation of heterochrony in three ways: rooting of a clade, topology of a clade, and character polarity. To study these effects we examined the distribution of shell microstructure, lophophore support structures, and body size in four different phylogenetic hypotheses of thecideide brachiopods (Triassic to Recent), a group of minute, cryptic, benthic marine invertebrates.Thecideides are consistently monophyletic in experiments using terebratulide, strophomenate, and spire-bearing outgroups together and separately, varying ingroup membership, and experimentally withholding certain character complexes. Thecideide monophyly is also supported by bootstrap analysis. Hypotheses of heterochrony in thecideide origins and evolution are therefore not merely artifacts of classification and can be pursued further. Using either strophomenate or spire-bearing outgroups, Triassic Thecospira is the most primitive thecideide. Trees constructed using terebratulide outgroups are rooted instead at Eudesella, a taxon derived in every other phylogenetic reconstruction, and the Triassic thecideides occupy derived rather than primitive positions.Our phylogenetic results support the traditional interpretation of the reduction or loss of the secondary fibrous shell layer as a paedomorphic pattern, whereas the evolution of lophophore support structures suggests a peramorphic pattern. Reduction in thecideide adult body size is gradual, phylogenetically, and results in an overall paedomorphic pattern. Heterochrony in these three character suites may play a role in the subsequent evolution of the clade, but apparently not in the origin of the clade, as is commonly thought. Heterotopy, rather than—or in addition to—heterochrony, may account for both the origin and evolution of the lophophore support structures and in the reduction and loss of the secondary shell layer. These phylogenetic hypotheses suggest that heterochrony can result from a complex mosaic of processes and provide specific, testable predictions about the processes responsible for producing the patterns, whether heterochronic or not. Categorizing an entire clade (such as thecideides), rather than individual characters, as globally paedomorphic may allow interesting peramorphic patterns in individual characters to be overlooked.
Kratka vsebinaMed karnijskimi karbonatnimi kamninami v okolici Me'ice in ^rne na Koro{kem le'ijo v treh nivojih laporno-skrilave kamnine, pod katerimi so razvite plasti oolitnega in onkoidnega apnenca. Vsi cefalopodi, med katerimi je najpogostej{a vrsta Carnites floridus (Wulfen) so bili najdeni v najni'jem t. im. prvem klasti~nem horizontu skupaj s {koljkami, pol'i in redkimi ostanki vreten~arjev. Za drugi klasti~ni horizont je zna~ilna plast s {tevilnimi {koljkami vrste Hoernesia sturi (Wöhrmann), ki je prisotna tudi v prvem horizontu. V tretjem najvi{jem klasti~nem horizontu fosilna makrofavna ni bila ugotovljena.V fosilnih zdru'bah oolitno-onkoidnih plasti v talnini vseh treh klasti~nih horizontov so poleg lupin mehku'cev prisotni {tevilni morski je'ki, krinoidi in redki najstarej{i brahiopodi skupine Thecideida.Litostratigrafski razvoj karnijskih plasti v okolici Me'ice ka'e na cikli~ne evstati~ne spremembe morske gladine, ki so opazne tudi v litologiji "Rabeljske skupine" {ir{ega prostora Vzhodnih Alp. AbstractThree clastic marly-shaly horizons occur within the Carnian carbonate rocks near Me'ica and ^rna na Koro{kem, Slovenia. The marly-shaly beds directly overlie oolitic and oncoidal limestones. In the lowermost of these clastic horizons, several cephalophod species, including the most common Carnites floridus (Wulfen), were collected. In addition, bivalves, gastropods and sparse vertebrate remains are present.Within the second clastic horizon, there is a distinctive layer characterized by numerous specimens of the bivalve Hoernesia sturi (Wöhrmann), which was also found, though less commonly, in the lowermost clastic horizon. No fossil macrofauna was found in the third, uppermost clastic horizon.The oolitic and oncoidal layers at the base of all three clastic horizons also contain abundant echinoids and crinoids, as well as rare earliest thecideide brachiopods.The lithostratigraphic associations of the Carnian beds in the Me'ica area express the same eustatically-driven cyclicity that is exhibited regionally in the "Raibl group" of the Eastern Alps. UvodPreko 300 m debelo zaporedje karnijskih karbonantnih kamnin v okolici Me'ice, ki vklju~uje tri laporno-skrilave horizonte (sl. 2) na terenu ni mogo~e opazovati v sklenjenem profilu. Zato je bilo dolgoletno vzorevanje odvisno predvsem od ob~asne dostopnosti plasti z makrofavno (sl. 1).Rudonosni "wettersteinski" apnenec in dolomit vklju~no z apnen~evim oolitom v talnini prvega skrilavca je bil `e pred leti raziskan v revirju Navr{nik na sedmem obzorju me`i{kega rudnika ( J u r k o v { e k , 1978), ob izgradnji gozdne poti v neposredni bli`ini jalovi{~a Kolerca so bile na povr{ini odkrite plasti z bogato favno igloko`cev. Makrofavna prvega laporno-skrilavega horizonta v rudniku zaradi geomehanskih lastnosti kamnine ni bilo mogo~e neposredno vzor~e-vati, zato je bila zbrana na jalovi{~u Kolerca, Ide in Na Klinih. Vzor~evanje makrofosilov od oolitno-onkoidne talnine drugega klasti~-nega horizonta, do krovnine tretjega horizonta je bilo opravljeno v ve~ fazah ...
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