Phylogenetic Interpretation Research Articles

Remarkably preserved benthic organisms and their traces from a Middle Triassic (Muschelkalk) mud flat

Knaust, D. 2010: Remarkably preserved benthic organisms and their traces from a Middle Triassic (Muschelkalk) mud flat. Lethaia, Vol. 43, pp. 344–356. A new Fossil-Lagerstatte is reported from the Middle Triassic of Germany, preserving Foraminifera, Nematoda, Platyhelminthes, Nemertea, Annelida and a range of Arthropoda together with their traces. This is the oldest fossil record of free-living nematodes and turbellarians, and the first occurrence of nemerteans in the Mesozoic. The rare preservation of the benthic associations together with their traces is unique; especially the abundant occurrence of different phyla as meiofauna (organisms with shortest dimension between 0.06 and 1 mm) provides an insight into the palaeoecological conditions of a 240-Ma-old muddy tidal flat. The preservation of benthic animals at the termination of their traces offers the exclusive opportunity to assign producers to the trace fossils. The results show that the discussed phyla were already established in the early Mesozoic in a similar diversity and composition as in modern analogues. The new Fossil-Lagerstatte has the potential to prove a number of soft-bodied taxa immediately after the end-Permian mass extinction, which has wide-ranging implications for phylogenetic interpretations. □Benthos, soft-bodied organisms, Fossil-Lagerstatte, Muschelkalk, trace fossils, Triassic.

Cladogenesis and anagenesis: a confusion of synapomorphies

Much cladistic theory is flawed because it confuses two temporal sequences: 1. cladogenetic (branching) chronology; 2. anagenetic (primitive-advanced) polarity. The first is largely inherent and exposed by a straigram; the second requires an independent polarisation of the changes subsequent to cladogenetic branchings. Failure to consistently distinguish between these always causes confusion, but destroys cladistic theory, because plesiomorphy and apomorphy refer to anagenesis, and autapomorphy and synapomorphy refer to cladogenetis. They cannot, however, be identified wholly independently, because cladogenetic chronology establishes anagenetic polarity by out-grouping, under limited conditions; and anagenetic polarity establishes cladogenetic chronology in multiple cladistic events. The principle ‘common characters are primitive’ is more accurately expressed as ‘characters of greater s read are cladogenetically earlier', and establishes cladogenetic relationships, never anagenetic polarity as usually thought. The full temporal analysis of biological patterns, therefore, involves eight stages: 1. Homologue identification; 2. Homolostrata delimitation and definition; 3. Stratigram formation; 4. Cladogenetic sequencing; 5. Anagenetic polarity determination (chronogramy); 6. Cladogenetic and anagenetic co-analysis; 7. Cladogram construction; 8. Phylogenetic interpretation.

Biochemical systematics of the Savi's bat (Hypsugo savii) (Chiroptera: Vespertilionidae)

In order to assess the controversial systematic position of the Savi's bat (Hypsugo savii), 43 ves-pertilionid bats belonging to 10 species were analyzed by mean of isozyme electrophoresis. The results were interpreted in two ways: first, we found that the amount of genetic differentiation between Hypsugo and the true Pipistrellus (D # 0.719) is of the same magnitude as the mean distance which separates the other pipistrelloid genera (D = 0.738). Secondly, the cladogram based on these biochemical results confirms the splitting of these “pipistrelles”, as Hypsugo is more closely related to Vespertilio than to any other palearctic genus. The other species analyzed in this study group themselves in a different clade, including Pipistrellus, Eptesicus and Nyctalus. This phylogenetic interpretation presents a testable hypothesis, which could be confirmed by an analysis of other loci or other allied species.

The phylogenetic role of ontogenies (recapitulation and morphogenesis)

Different approaches to evolutionary interpretation of ontogenies are compared, with special emphasis on the evolutionary role of morphogenetic mechanisms (construction technologies) substantially affecting the structure of definitive forms: they largely determine the structural characteristics of organs, types of anatomical and histological systems, and specificity of symmetry of organisms and their parts. The role of cellular morphogenesis inherited from protozoic ancestors in the morphogenesis of multicellular organisms is demonstrated. Two main ways of improving morphogeneses are considered, based on epithelial morphogenesis and early determined few-celled primordial. On the one hand, the phylogenetic role of archallaxes and deviations is emphasized, these events often switching evolution to a fundamentally new direction. On the other hand, many characteristics of developmental stages are explainable by rationalization of morphogeneses and do not recapitulate ancestral forms, which should be taken into consideration in phylogenetic interpretation of embryogeneses; in particular, this applies to interpretation of axial relationships.

Shoot Morphological Structure and Development in 5-Needle Pines of Northern and Eastern Asia: Phylogenetic and Climatic Interpretation

Shoot Morphological Structure and Development in 5-Needle Pines of Northern and Eastern Asia: Phylogenetic and Climatic Interpretation

Brief communication: Histology and micro CT as methods for assessment of facial suture patency

The extent of fusion in facial sutures has implications for topics ranging from biomechanics to phylogeny reconstruction. An unfortunate limitation of studying sutural fusion in skeletal specimens is that it is difficult to assess whether apparently patent sutures are in fact fused internally. Both histology and microcomputed tomography (CT) are potential tools for solving this, but relatively few studies have attempted to discern the limits of micro CT for visualization of microanatomical structures. We examined microanatomical aspects of facial sutures in adult cadaveric samples from captive bushbabies. Premaxillary and nasopremaxillary sutures were examined in serially sectioned snouts of four greater bushbabies (Otolemur garnettii) and four lesser bushbabies (Galago moholi). Sections containing sutures with osseous bridging were rated as "fused," and the presence or absence of grooves on the external side was recorded. One bushbaby was studied using micro CT prior to physical sectioning. O. garnettii and two of the G. moholi show multiple foci of fusion. Histological examination confirmed that sutural fusion is limited to the internal surface in numerous sections, resulting in an external notch. Such points of internal fusion could be clearly visualized in raw CT slices. The presence of such notches suggests that external examination can underestimate the degree of suture fusion. Thus, microanatomical evidence may be needed to fully assess biomechanical correlates and phylogenetic interpretations based on fusion of facial sutures. Our results also indicate micro CT may be a useful tool to obtain this evidence.

The most ancient bark beetle known: a new tribe, genus and species from Lebanese amber (Coleoptera, Curculionidae, Scolytinae)

Abstract Cylindrobrotus pectinatusgen. et sp.n., a new scolytine species from Cretaceous Lebanese amber, is described. A new tribe, Cylindrobrotini trib.n., is proposed for this unique species, which demonstrates an unusual combination of some archaic and many advanced characters. This finding suggests that the Scolytinae became a distinct lineage of Curculionoidea from the Lower Cretaceous. Fossil records are reviewed, and some remarks on the origin and taxonomic position of bark and ambrosia beetles are made. Some comments on the various phylogenetic interpretations of the last 30 years are given, particularly in respect of their correspondence with the fossil record. The early appearance of Scolytinae in the fossil record before other Curculionidae (which appeared in the Upper Cretaceous) can be used as evidence against the hypothesis of bark beetles as offspring of weevils. The question of the taxonomic rank of bark beetles (separate subfamily or family) and their placement among other groups of the superfamily remains unsolved.

Diversification trajectories and evolutionary life-history traits in early sharks and batoids

Different interpretations on the timing of early diversification and radiation of modern sharks and batoids (Neoselachii) in the Earth's history exist and are related to discrepancies in taxonomic and phylogenetic interpretations favouring a Late Triassic or earliest Jurassic diversification and subsequent radiation event, respectively. Sampling standardization based on pooled taxonomic occurrences made it possible to overcome the problem of a much richer neoselachian record in the Late Jurassic than earlier on. The standardized pattern of genus richness is one of low and fairly constant diversity in the Late Triassic and earliest Jurassic with a steep rise in the Toarcian (ca 180Myr ago), representing the maximum diversification rate in the Jurassic towards a Middle and Late Jurassic plateau. The major Toarcian diversification agrees with the conclusions based on phylogenetic analyses, but is in conflict with older interpretations based on raw data. Early Jurassic expansion of neoselachians was opportunistic in the aftermath of the end-Triassic mass extinction and the reasons for their rapid diversification and radiation probably include small body size, short lifespans and oviparity, enabling faster ecological reorganizations and innovations in body plans for adapting to changing environmental conditions.

Description and phylogenetic interpretation of chromatophore migration from larval air sacs to adult structures in some Chaoboridae (Diptera)

AbstractDuring development, many chromatophores on the air sacs of larvae of Chaoborus Lichtenstein disperse to the tracheal trunks and throughout the body of the pupae. In male pupae, chromatophores on the posterior air sacs move to the developing testes and vasa deferentia and some become the adventitious spotting previously reported for adults of Chaoborus. In larvae of Mochlonyx Loew, chromatophores have a similar development pattern, but in female pupae some also surround the spermathecae. Larvae of Eucorethra Underwood have chromatophores scattered throughout much of the body but it is uncertain whether these are homologous to those of Chaoborus and Mochlonyx. Outgroup comparisons show that the migration of chromatophores from the larval air sacs to the adult male testes and vasa deferentia is a synapomorphy of Chaoborinae. The presence of pigmented fat body on the larval testes in many Culicidae, Eucorethra, and Mochlonyx is plesiomorphic, and the transparent larval testes in Chaoborus are a synapomorphy of the genus. The dark adult testes in Mochlonyx are derived from pigmented larval fat body and chromatophores from the larval air sacs, and this is proposed as an intermediate evolutionary state. It is likely that the chromatophores surrounding the testes of pupae of Chaoborinae provide protection against ultraviolet radiation, but further study is needed.

Anatomy of the trunk mesoderm in tunicates: homology considerations and phylogenetic interpretation

The tadpole stage of tunicates has played a pivotal role in understanding chordate evolution. While the organization of the mesoderm has been given high importance in comparative anatomical studies of Bilateria, this morphological character remains largely unexplored in tunicate tadpoles. For larvae of the phlebobranch ascidian Ciona intestinalis, the presence of two mesodermal pockets had been claimed, raising the possibility that paired coelomes are present in the larval ascidian. Using computer assisted 3D-reconstructions based on complete series of 1 μm-sections analyzed by light microscopy complemented by TEM-investigation of selected regions a comparative anatomical study of tadpole stages from four major tunicate clades, Aplousobranchiata, Phlebobranchiata, Stolidobranchiata, and Appendicularia is presented. In the aplousobranch Clavelina lepadiformis numerous mesodermal cells are found throughout the entire trunk plus the unpaired ventral rudiment of the pericardium. In the phlebobranch Ascidia interrupta, massive mesodermal components occur in the posterior trunk, whereas more anteriorly situated mesoderm consists of loose streaks of cells or isolated cells. This is also the case in the stolidobranch ascidians Herdmania momus and Styela plicata. In the stolidobranch Molgula occidentalis and the appendicularian Oikopleura dioica the anterior trunk is entirely devoid of mesodermal cells. TEM-investigation revealed that all mesodermal structures in the trunk of tunicate tadpoles were mesenchymal with the exception of a ventral portion of the mesoderm in C. lepadiformis, which probably corresponds to the developing pericardium, and the differentiated pericardium of the juvenile O. dioica. Thus no evidence for paired coelomic cavities in Tunicata was found. Outgroup comparison suggests that the reduction of paired coelomic cavities is an apomorphic trait of Tunicata. Within Tunicata a stepwise evolutionary reduction of the anterior larval mesenchyme is documented.

Mitochondrial DNA of Vitis vinifera and the Issue of Rampant Horizontal Gene Transfer

The mitochondrial genome of grape (Vitis vinifera), the largest organelle genome sequenced so far, is presented. The genome is 773,279 nt long and has the highest coding capacity among known angiosperm mitochondrial DNAs (mtDNAs). The proportion of promiscuous DNA of plastid origin in the genome is also the largest ever reported for an angiosperm mtDNA, both in absolute and relative terms. In all, 42.4% of chloroplast genome of Vitis has been incorporated into its mitochondrial genome. In order to test if horizontal gene transfer (HGT) has also contributed to the gene content of the grape mtDNA, we built phylogenetic trees with the coding sequences of mitochondrial genes of grape and their homologs from plant mitochondrial genomes. Many incongruent gene tree topologies were obtained. However, the extent of incongruence between these gene trees is not significantly greater than that observed among optimal trees for chloroplast genes, the common ancestry of which has never been in doubt. In both cases, we attribute this incongruence to artifacts of tree reconstruction, insufficient numbers of characters, and gene paralogy. This finding leads us to question the recent phylogenetic interpretation of Bergthorsson et al. (2003, 2004) and Richardson and Palmer (2007) that rampant HGT into the mtDNA of Amborella best explains phylogenetic incongruence between mitochondrial gene trees for angiosperms. The only evidence for HGT into the Vitis mtDNA found involves fragments of two coding sequences stemming from two closteroviruses that cause the leaf roll disease of this plant. We also report that analysis of sequences shared by both chloroplast and mitochondrial genomes provides evidence for a previously unknown gene transfer route from the mitochondrion to the chloroplast.

The Relationship Between the Infraorbital Foramen, Infraorbital Nerve, and Maxillary Mechanoreception: Implications for Interpreting the Paleoecology of Fossil Mammals Based on Infraorbital Foramen Size

Osteological cranial features, such as foramina, assist in phylogenetic and ecological interpretations of fossil mammals. However, the validity of using foramina in these interpretations when their contents are not well documented is questionable. For decades, the infraorbital foramen (IOF) has been used to interpret aspects of the fossil record, yet there are conflicting accounts about what passes through the foramen and little known about how neural and vascular structures contribute to its contents. This study tracks and documents the neural and/or vascular anatomy of the IOF and examines the correlation of infraorbital nerve (ION) and IOF cross-sectional area. To address this question, 161 mammalian cadavers, including 80 primates, were injected with latex dye to track the vascular anatomy associated with the IOF. All ION fibers were then removed from the infraorbital canal, and ION cross-sectional area was calculated from histological slides. Latex injections and histological slides revealed that only the ION and a small infraorbital artery pass through the IOF. Variation in ION size explains 85% of variation in IOF area, and the artery represents a negligible portion of the foramen. The strong positive correlation between the ION and IOF size suggests that, in the absence of nerve tissue, the IOF can serve as a proxy for ION area. IOF area maybe used to evaluate differences in maxillary mechanoreception in both extinct and extant taxa.

A New Genus of Predaceous Midge (Diptera: Ceratopogonidae) from Costa Rica

A new monotypic genus and species of predaceous midge from Costa Rica, Spinellihelea brevicosta Borkent, Grogan, and Picado is described and illustrated. Phylogenetic interpretation of the group of Ceratopogonini in which females have their clypei fused laterally to the eyes, indicates that Spinellihelea is the sister group of Fittkauhelea Wirth and Blanton and that it likely arose in the Neotropical Region. The genus Leptohelea Wirth and Blanton is newly placed in a monophyletic group with Fittkauhelea, Spinellihelea, Diaphanobezzia Ingram and Macfie and Parabezzia Malloch.

Die Schattenlibelle auf Kreta (Boyeria cretensis spec. nov.) und die Monophylie der „Gattung”︁ Boyeria McLachlan, 1896. (Odonata Anisoptera, Aeshnidae)

Phenetic analysis and biostatistic comparision of Boyeria irene specimens (adults and exuviae) from the westmediterranean area of distribution with material coming from Crete led to the conclusion that the Brook Darner on the eastmediterranean island represents a distinct biological species (Boyeria cretensis spec. nov.). A phylogenetic interpretation of the differences between the two species (apomorphic tendencies in the character states of B. irene) falsifies the apparent concept, that the Crete populations of Boyeria might have been founded by migrants from the westmediterranean territories. The six extant species of Boyeria (three pairs of sister species) constitute a monophyletic taxon. Its relations to other groups of aeshnids are still unknown.

Quantitative genetics of modern human cranial variation

The anatomy and biology of the basicranial complex and its relationships to the other cranial complexes has long played a central role in functional and phylogenetic interpretations of the hominin fossil record. Cranial traits frequently populate character lists in phylogenetic analyses and are commonly described as comprising an anatomical or functional complex. Most often these traits are treated as individual independent characters of equal phyletic value. Implicit in such considerations, however, is the assumption that the genetic contribution to morphological variation is high and equivalent across traits, and that phenotypic and genetic correlations between traits, irrespective of their magnitude, introduce negligible confounding effects in phylogenetic reconstruction (Hlusko, 2004). While the ability to quantify and assess phenotypic variation in craniofacial variables has seen significant advances in recent years, the extent to which genetic and nongenetic factors influence this variation is typically not addressed. A key component to understanding the influences environmental and genetic factors have on the evolution of the craniofacial complex is a solid foundation of detailed knowledge of the genetic components underlying the development of normal craniofacial variation in modern populations. The aim of the present study is to elucidate fundamental aspects of the genetic architecture of normal variation in the human craniofacial complex. In the current context, genetic architecture refers to the characterization of: (1) the extent to which variation in a trait is under genetic control, and (2) the degree to which two traits are controlled by the same genes or set of genes. The first of these is the heritability (h2) of a trait, and the second is the genetic correlation (ρG) between traits. Heritability estimates provide important information regarding the potential evolutionary response of traits to selective forces—the rate of evolutionary change being determined by the product of the heritability and the selection coefficient (Lynch and Walsh, 1998). Genetic correlations provide a means for quantifying the shared effects of genes on two or more traits. Genetic correlations have become critical in understanding the phenotypic heterogeneity observed in many craniofacial syndromes (Cohen, 2002), and have significant implications for the evolution of the hominin craniofacial complex. Human cranial variation: evidence from family-based studies Craniofacial morphometrics of archaeological or museum osteological collections have provided the field of human evolution with a broad perspective of craniofacial variation. These studies, however, cannot address issues of the genetic influence on trait variation, or covariation between traits. In order to adequately approach such issues, a large number of individuals of known biological relatedness is necessary. One such population is the Fels Longitudinal Study, which includes over 3,000 individuals belonging to ~250 families. Participants of the Fels Longitudinal Study have been the focus of numerous research articles including many that have had significant anthropological and human evolutionary significance, such as several papers detailing the growth and development of cranial structures (Young, 1956, 1957; Garn et al., 1963; Lewis and Roche, 1972, 1974; Roche and Lewis, 1974, 1976; Roche et al., 1977; Lewis et al., 1982, 1985; Ohtsuki et al., 1982a,b) and a classic paper investigating ontogenetic changes in basicranial flexion (i.e., the saddle angle; Lewis and Roche, 1977). In this report we seek to continue and extend the analysis of the Fels Longitudinal Study cranial data by presenting the first quantitative genetic analysis of the cranial data available in the archives.

Structural insights into the function of the core-circadian factor TIMING OF CAB2 EXPRESSION 1 (TOC1).

BackgroundThe plant circadian clock has at its core a feedback loop that includes TIMING OF CAB2 EXPRESSION 1 (TOC1). This protein has an as of yet unknown biochemical activity. It has been noted that the extreme amino-terminus of this protein is distantly related in sequence to response regulators (RR), and thus TOC1 is a member of the so-called pseudo response regulator (PRR) family. As well, the extreme carboxy-terminus has a small sequence stretch related to the other PRRs and CONSTANS (CO)-like proteins, and this peptide stretch has been termed the CCT (for CONSTANS, CONSTANS-LIKE, TOC1) domain.MethodsTo extend further our understanding of the TOC1 protein, we performed a ROSETTA structural prediction on TOC1 orthologues from four plant species. Phylogenetic interpretations assisted in model construction.ResultsFrom our models, we suggest that TOC1 is a three-domain protein: TOC1 has an amino-terminal signaling-domain related to response receivers, a carboxy-terminal domain that could participate both in metal binding and in transcriptional regulation, and a linker domain that connects the two.ConclusionThe models we present should prove useful in future hypothesis-driven biochemical analyses to test the predictions that TOC1 is a multi-domain signaling component of the plant circadian clock.

Three-dimensional primate molar enamel thickness

Molar enamel thickness has played an important role in the taxonomic, phylogenetic, and dietary assessments of fossil primate teeth for nearly 90 years. Despite the frequency with which enamel thickness is discussed in paleoanthropological discourse, methods used to attain information about enamel thickness are destructive and record information from only a single plane of section. Such semidestructive planar methods limit sample sizes and ignore dimensional data that may be culled from the entire length of a tooth. In light of recently developed techniques to investigate enamel thickness in 3D and the frequent use of enamel thickness in dietary and phylogenetic interpretations of living and fossil primates, the study presented here aims to produce and make available to other researchers a database of 3D enamel thickness measurements of primate molars ( n = 182 molars). The 3D enamel thickness measurements reported here generally agree with 2D studies. Hominoids show a broad range of relative enamel thicknesses, and cercopithecoids have relatively thicker enamel than ceboids, which in turn have relatively thicker enamel than strepsirrhine primates, on average. Past studies performed using 2D sections appear to have accurately diagnosed the 3D relative enamel thickness condition in great apes and humans: Gorilla has the relatively thinnest enamel, Pan has relatively thinner enamel than Pongo, and Homo has the relatively thickest enamel. Although the data set presented here has some taxonomic gaps, it may serve as a useful reference for researchers investigating enamel thickness in fossil taxa and studies of primate gnathic biology.

Phylogeny of extant nephilid orb‐weaving spiders (Araneae, Nephilidae): testing morphological and ethological homologies

The Pantropical spider clade Nephilidae is famous for its extreme sexual size dimorphism, for constructing the largest orb‐webs known, and for unusual sexual behaviors, which include emasculation and extreme polygamy. We synthesize the available data for the generaNephila,Nephilengys,HerenniaandClitaetrato produce the first species level phylogeny of the family. We score 231 characters (197 morphological, 34 behavioral) for 61 taxa: 32 of the 37 known nephilid species plus twoPhonognathaand oneDeliochusspecies, 10 tetragnathid outgroups, nine araneids, and one genus each of Nesticidae, Theridiidae, Theridiosomatidae, Linyphiidae, Pimoidae, Uloboridae and Deinopidae. Four most parsimonious trees resulted, among which successive weighting preferred one ingroup topology. Neither an analysis of an alternative data set based on different morphological interpretations, nor separate analyses of morphology and behavior are superior to the total evidence analysis, which we therefore propose as the working hypothesis of nephilid relationships, and the basis for classification. Ingroup generic relationships are (Clitaetra(Herennia(Nephila,Nephilengys))). DeliochusandPhonognathagroup with Araneidae rather than Nephilidae. Nephilidae is sister to all other araneoids (contramost recent literature). Ethological data, although difficult to obtain and thus frequently missing for rare taxa, are phylogenetically informative. We explore the evolution of selected morphological and behavioral characters, discuss and redefine the homology of palpal sclerites, disprovesemientelegynyin spiders, trace the newly interpreted evolution of the orb web, and show that nephilid genital morphologies coevolve with sexual behaviors and extreme sexual size dimorphism. Phylogenetic interpretations of behavior suggest new insights into spider biology and avenues for future research.© The Willi Hennig Society 2007.

Pronounced karyological divergence of the North American congeners Sphaerium rhomboideum and S. occidentale (Bivalvia: Veneroida: Sphaeriidae)

Chromosome sets of two North American sphaeriid species, Sphaerium rhomboideum Say, 1822 and S. occidentale Lewis, 1856, were studied using conventional Giemsa staining and karyometric analysis. Pronounced karyological divergence of congeners was revealed. The diploid number of 2n ¼ 44 was reported for S. rhomboideum and this is the first record of a diploid species in the highly polychromosomic Nearctic sphaeriid fauna. The karyotype was characterized by medium-sized and small chromosomes, which decreased in size gradually from 5.77 to 1.9 mm. Biarmed chromosomes with medially and submedially located centromeres predominated, but six pairs of subtelo-telocentric elements were also observed in the karyotype. The estimated mitotic chromosome number for S. occidentale ranges from 189 to 213, but most of the cells examined contained about 204– 209 chromosomes. A first attempt to karyotype a polyploid sphaeriid was made. It was revealed that the comparatively large and middle-sized chromosomes could be grouped in four, so the karyotype presumably evolved through tetraploidization. The small chromosomes formed the large fraction, about 137. Due to their similar and indistinct morphologies, it was impossible to arrange them into subgroups with confidence. Revealed karyological characteristics are discussed with reference to the existing phylogenetic interpretations of the evolutionary history of the Sphaeriinae.

Restudy of the worm-like carbonaceous compression fossils Protoarenicola, Pararenicola, and Sinosabellidites from early Neoproterozoic successions in North China

The carbonaceous compression fossils Protoarenicola baiguashanensis Wang, 1982, Pararenicola huaiyuanensis Wang, 1982, and Sinosabellidites huainanensis Zheng, 1980, from the early Neoproterozoic Liulaobei and Jiuliqiao formations in northern Anhui, North China, were previously interpreted as worm-like metazoans, largely on the basis of transverse annulations and purported proboscis structures. If correct, these would be some of the earliest known bilaterian animals and would provide a key paleontological calibration to molecular clock analyses. In this study, we examine a large population of these carbonaceous fossils, clarify their taxonomy, and provide new insights into their morphological, paleoecological, and phylogenetic interpretations. Although all three species are characterized by annulated tubes, P. baiguashanensis bears a bulbous terminal structure at one end of its tube. P. huaiyuanensis is characterized by a constricted opening at one end and a closed termination at the other. The two ends of S. huainanensis tubes are both closed and round. The bulbous terminal structure in P. baiguashanensis was previously interpreted as an animal proboscis, but new observations suggest that it was more likely a holdfast structure analogous to discoidal holdfast structures of the Mesoproterozoic Tawuia-like fossil Radhakrishnania Kumar, 2001, and the frondose Ediacara fossil Charniodiscus Ford, 1958. Furthermore, it is possible that at least P. baiguashanensis and P. huaiyuanensis may represent reproductive or taphonomic fragments of the same organism. This reinterpretation weakens the previous interpretation that P. baiguashanensis and P. huaiyuanensis were worm-like bilaterian animals. Instead, they can be alternatively interpreted as erect epibenthic organisms, possibly coenocytic algae reaching a tiering height of 30 mm. The predominance of discoidal holdfasts, as opposed to rhizoidal holdfasts, in pre-Ediacaran epibenthic organisms was probably related to more stable substrates in the presence of microbial mats and in the absence of bioturbating animals.