Letteratura scientifica selezionata sul tema "Fossil Pterobranchia"

Rhabdopleura Allman, 1869 is one of the longest surviving animal genera. The five-known species are the only living Graptolithina, a group well known from their diverse Paleozoic fossil record. Here we add information on the soft-bodied zooids and molecular phylogenetics of Rhabdopleura annulata Norman, 1921, which was previously only known from its tubes. Tubes and zooids were collected from Heron Island, Queensland, Australia. Zooids have a single pair of tentaculated arms. Dark pigment granules are found throughout the body, and particularly dense in the pair of arms and the anterior lip of the cephalic shield. Colonies grow encrusted in and on coral debris. The tubes are either creeping or erect, but no stolon has been found. Inside of the coral matrix lacunae, the tube cortex formed a parchment-like wallpaper. Phylogenetic analysis based on combined 18S+16S rRNA sequences placed R. annulata as sister to the remaining rhabdopleurids, albeit with weak support. The biogeographic range of R. annulata extends from Indonesia to Tasmania, and New Zealand. Its occurrence on Heron Island does not extend this range, but highlights that rhabdopleurids may be more common, and in shallower waters, than previously appreciated, permitting further studies that may shed light on graptolite paleobiology.

The early origin and evolutionary radiation of graptolites (Hemichordata:Pterobranchia) is a story told almost entirely in the fossil record, but for four extant species of the genus Rhabdopleura Allman, 1869. Here we report the discovery of a fifth species, Rhabdopleura recondita, sp. nov., at a depth range of 2–70m from the Adriatic and Ionian Seas, always associated with bryozoans in coralligenous habitats. This is the first pterobranch record in Italian waters, and the second in the Mediterranean Sea. The new species is characterised by: (1) tubaria with smooth creeping tubes adherent to the inside of empty bryozoan zooecia; (2) erect outer tubes with a graptolite, fusellar-like organisation; and (3) zooids that extend from a black stolon, which is free from the creeping tube. Each of the paired feeding arms has two rows of tentacles that do not extend to the arm tip. The distal ends of the arms, the collar and the cephalic shield are replete with black granules. Phylogenetic analyses of individual and concatenated gene sequences of mitochondrial 16S rDNA and nuclear 18S rDNA support the validity of R. recondita as a new species. Finally, we discuss the global biogeographic and habitat distributions of the extant Rhabdopleura representatives. http://zoobank.org/urn:lsid:zoobank.org:pub:82C6A51E-F8F4-44AF-AD8F-16873BE80D03

Higher taxonomic ranks typically distinguish morphologically disparate groups whose within-group common ancestry is assumed to be more recent than that between groups. Because in practice this assumption is rarely tested, common wisdom now advocates that the relationship between traditional classifications and phylogenies be made more explicit. Classifications of organisms were established originally to serve a variety of purposes, which may or may not have had an evolutionary rationale. Thus, if named superspecific taxa are to play an interpretable role in macroevolutionary studies, their status as clades should at least be investigated, if not demonstrated unambiguously.The monophyly of the Brachiopoda is supported by a large number of synapomorphies, both morphological and embryological. Within the Brachiopoda, systematists have focused historically on single character (“key innovation”) definitions of higher taxa (e.g., attitude of the pedicle relative to the valves, nature of articulation between the valves, valve mineralogy); this procedure has resulted in intraphylum divisions whose evolutionary significance is uncertain. For example, monophyly of the Inarticulata continues to be debated vigorously; the position of the calcareous inarticulates (craniaceans) is particularly contentious. The traditional classification, based largely on the presence or absence of teeth and sockets, has been challenged recently by the following arguments: lack of articulation is primitive for brachiopods and, as a symplesiomorphy, cannot define a major clade; valve mineralogy is a more reliable indicator of phylogenetic affinity because phosphatic and calcareous-shelled brachiopods both appear very early in the fossil record.To test these arguments in the broader context of metazoan phylogeny, I chose to investigate not only relationships among brachiopod higher taxa, but also of brachiopods to other lophophorates and selected protostome and deuterostome taxa. I analyzed (using PAUP 3.0) the phylogenetic relationships among the seven Recent brachiopod superfamilies (assuming each to be monophyletic), using 119 characters of soft and hard anatomy and embryology. Four outgroup taxa were used: Phoronida, Bryozoa, Sipunculida, Pterobranchia. One most parsimonious cladogram of length 219, C.I. = .722, resulted. In this cladogram, Inarticulata and Articulata are each monophyletic, with 9 and 32 synapomorphies, respectively. Calcareous skeletal mineralogy is clearly primitive for metazoans; there is no justification for claiming it as a synapomorphy of a clade within the Brachiopoda. Outgroup analysis has no power, in this instance, to determine the polarity of articulation, since no outgroups possess two valves (molluscs and other animals have evolved the bivalved condition independently, based on numerous other characters); thus, the lack of valve articulation is not unambiguously primitive, by this polarity criterion.Although many textbooks continue to refer to Lophophorates as a group distinct from other metazoans, presumably by virtue of common ancestry, “lophophorates” do not appear to be monophyletic unless the possession of a lophophore is selectively weighted; among the outgroups in this cladogram, bryozoans cluster with sipunculids, and phoronids with pterobranchs. The notion that lophophorates, as a group, are in some sense “intermediate” between protostomes and deuterostomes must be investigated in greater detail, phylogenetically.

AbstractGraptolites are common fossils in Early Palaeozoic strata, but little is known of their soft-part anatomy. However, we report a long-overlooked specimen ofDicranograptusaff.ramosusfrom Late Ordovician strata of southern Scotland that preserves a strongly polymorphic, recalcitrant, organic-walled network hitherto unseen in graptoloid graptolites. This network displays three morphologies: proximally, a strap-like pattern, likely of flattened tubes; these transform distally into isolated, hourglass-shaped structures; then, yet more distally, revert to a (simpler) strap-like pattern. The network most likely represents a stolon-like system, hitherto unknown in graptoloids, that connected individual zooids. Its alternative interpretation, as colonial xenobionts that infested a graptoloid colony and mimicked its architecture, is considered less likely on taphonomic and palaeobiological grounds. Such polymorphism is not known in non-graptolite pterobranchs, which are less diverse and morphologically more conservative: a division of labour between graptoloid zooids for such functions as feeding, breeding and rhabdosome construction may have been the key to their remarkable evolutionary success.

AbstractPterobranchs are rare in Cambrian strata of North America despite discoveries of more than 30 exceptionally preserved fossil biotas. Miaolingian pterobranchs from this continent typically form low‐diversity and low‐abundance assemblages. Here we describe an abundant pterobranch material from the Drumian Marjum Formation recently collected at the Gray Marjum Quarry in the House Range of Utah, USA. The faunule is composed of two new species: Sphenoecium marjumensis, an encrusting representative forming compact bushy colonies of more than 80 tubes with poorly developed rhizomes, and Tarnagraptus cupidus, an erect growing taxon characterized by intertwining stems and a monopodial colonial growth. Known in extant rhabdopleurids, this mode of colonial growth had hitherto never been observed in fossil pterobranchs. Its documentation in a c. 500‐myr‐old taxon attests to its deep origin in the evolutionary history of the group. Although the new species almost exclusively occur in the Marjum strata, this pterobranch faunule is broadly similar to those recovered from other Miaolingian Burgess Shale‐type deposits of North America in terms of genus‐level composition, species richness, and ecological structure. This may indicate that pterobranchs were poorly diverse components of animal communities at that time, or that they mostly thrived in more proximal shelf environments where conditions conducive to their preservation rarely developed. The common co‐occurrence of taxa with fundamentally different ecomorphotypes in the Miaolingian Series of North America strongly suggests an earlier phase of morphological diversification of benthic pterobranchs during the early Cambrian, which remains insufficiently documented by fossils.

AbstractEvidence of interspecific interactions in the fossil record is rare but offers valuable insights into ancient ecologies. Exceptional fossiliferous sites can preserve complex ecological interactions involving non-biomineralized organisms, but most of these examples are restricted to Cambrian Lagerstätten. Here we report an exceptionally preserved cross-phylum interspecific interaction from the Tremadocian-aged Lower Fezouata Shale Formation of Morocco, which consists of the phragmocone of an orthocone cephalopod that has been extensively populated post-mortem by tubicolous epibionts. Well-preserved transverse bands in a zig-zag pattern and crenulations along the margin of the unbranched tubes indicate that they correspond to pterobranch hemichordates, with a close morphological similarity to rhabdopleurids based on the bush-like growth of the dense tubarium. The discovery of rhabdopleurid epibionts in the Fezouata Shale highlights the paucity of benthic graptolites, which also includes the rooted dendroids Didymograptus and Dictyonema, relative to the substantially more diverse and abundant planktic forms known from this biota. We propose that the rarity of Paleozoic rhabdopleurid epibionts is likely a consequence of their ecological requirement for hard substrates for initial settlement and growth. The Fezouata rhabdopleurid also reveals a 480-million-year-old association of pterobranchs as epibionts of molluscs that persist to the present day.

AbstractBenthic graptolites (Graptolithina) were surprisingly common and diverse in the Miaolingian (Cambrian), but have rarely been described in detail. Encrusting and erect growing colonies already evolved and can be differentiated in early Miaolingian faunas. The Rhabdopleuridae with their encrusting colonies provide few fossils, but members of the erect growing, bushy colonies of the Dithecodendridae are more common, at least as fragments indicating considerable fragmentation and transport. In the Wuliuan, the benthic graptolites reached a considerable diversity at the genus level with at least 6 genera appearing in this interval. The most common taxon is the encrusting genus Sphenoecium with its robust colonies, showing a worldwide distribution. Most taxa, however, are known from few records and their biostratigraphical and palaeogeographical distribution cannot be established yet. Erroneously, the widely distributed Tarnagraptus with its conical thecae has often been misidentified as the Ordovician Mastigograptus, but differs considerably in its tubarium construction and both might not be closely related.