This profile is no longer maintained. Please visit https://www.researchgate.net/profile/Martin_Smith9. Phone: 0191 334 2320 Address: Department of Earth Sciences Lower Mount Joy Durham University DH1 3LE
The present-day distribution of velvet worms corresponds neatly to the ancient supercontinent Gon... more The present-day distribution of velvet worms corresponds neatly to the ancient supercontinent Gondwana — except for a puzzling outpost in southeast Asia. Jaw-dropping new fossil material now establishes when and how peripatid onychophorans reached this isolated spot.
The fossil record paints a thin picture of early terrestrial life. Useful diagnostic features are... more The fossil record paints a thin picture of early terrestrial life. Useful diagnostic features are rare in the organic-walled fossils of the first land colonizers, and at first glance the Silurian–Devonian Tortotubus protuberans seems no exception. Now, new material from New York, Gotland and Scotland reveals the ontogenesis and affinity of this problematic organism. Its filamentous early stages (previously referred to Ornatifilum lornensis) demonstrate simple septal perforations and a bilayered cell wall; threads of entwined filaments, bounded by an elaborately sculptured surface, arose via the retrograde growth and subsequent proliferation of secondary branches. This morphology and pattern of growth together indicate an affinity with the ‘higher’ fungi (Dikarya) and document the formation of differentiated mycelium. The presence of complex mycelial fossils in the earliest Silurian corroborates the likely contribution of fungi to the colonization of land and the establishment of modern sedimentological systems; their rise seemingly accompanied the diversification of early embryophytes and the vegetation of the terrestrial biosphere.
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an earl... more The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land‐plant, despite the absence of a convincing modern analogue. Exceptionally well‐preserved nematophyte cuticle from the Late Silurian Burgsvik Sandstone Formation, Gotland provides additional insight into the organism’s anatomy, phylogenetic affiliations and ecology. Because this material exhibits additional characters not present in the type material we assign it to Nematothallopsis gotlandii gen. et sp. nov. The organism was constituted of a close‐packed layer of palisade‐like filaments covered by a cuticle that bears a characteristic pseudocellular pattern on its inner surface. Apertures in this cuticle are often encircled by a ring of multicellular filaments, which are sometimes associated with spheroidal, spore‐like entities. In the light of the conspicuous similarity of the palisade layers to the pseudoparenchymatous tissue of coralline red algae, and of the filamen...
Wiwaxiids are a problematic group of scale-covered lophotrochozoans known from Cambrian Stages 3–... more Wiwaxiids are a problematic group of scale-covered lophotrochozoans known from Cambrian Stages 3–5. Their imbricating dorsal scleritome of leaf-like scales has prompted comparison with various annelids and molluscs, and has been used as a template to reconstruct the articulation pattern of isolated Small Shelly Fossils. The first articulated specimens of Wiwaxia from the Cambrian Stage 3 Chengjiang Konservat-Lagerstätte show that the Wiwaxia scleritome comprised nine equivalent transverse rows associated with outgrowths of soft tissue, but did not possess a separate zone of anterior sclerites. This serial construction is fundamentally incompatible with the circumferential disposition of sclerites in early molluscs, but does closely resemble the armature of certain annelids. A deep homology with the annelid scleritome must be reconciled with Wiwaxia’s mollusc-like mouthparts and foot; together these point to a deep phylogenetic position, close to the common ancestor of annelids and molluscs.
The Palaeozoic form-taxon Lobopodia encompasses a diverse range of soft-bodied ‘legged worms’ kno... more The Palaeozoic form-taxon Lobopodia encompasses a diverse range of soft-bodied ‘legged worms’ known from exceptional fossil deposits1, 2, 3, 4, 5, 6, 7, 8, 9. Although lobopodians occupy a deep phylogenetic position within Panarthropoda, a shortage of derived characters obscures their evolutionary relationships with extant phyla (Onychophora, Tardigrada and Euarthropoda)2, 3, 5, 10, 11, 12, 13, 14, 15. Here we describe a complex feature in the terminal claws of the mid-Cambrian lobopodian Hallucigenia sparsa—their construction from a stack of constituent elements—and demonstrate that equivalent elements make up the jaws and claws of extant Onychophora. A cladistic analysis, informed by developmental data on panarthropod head segmentation, indicates that the stacked sclerite components in these two taxa are homologous—resolving hallucigeniid lobopodians as stem-group onychophorans. The results indicate a sister-group relationship between Tardigrada and Euarthropoda, adding palaeontological support to the neurological16, 17 and musculoskeletal18, 19 evidence uniting these disparate clades. These findings elucidate the evolutionary transformations that gave rise to the panarthropod phyla, and expound the lobopodian-like morphology of the ancestral panarthropod.
"The soft-bodied Cambrian organism Wiwaxia poses a taxonomic conundrum. Its imbricated dorsal scl... more "The soft-bodied Cambrian organism Wiwaxia poses a taxonomic conundrum. Its imbricated dorsal scleritome suggests a relationship with the polychaete annelid worms, whereas its mouthparts and naked ventral surface invite comparison with the molluscan radula and foot.
476 new and existing specimens from the 505 million year old Burgess Shale cast fresh light on Wiwaxia’s sclerites and scleritome. My observations illuminate the diversity within the genus, and demonstrate that Wiwaxia did not undergo discrete moult stages: rather, its scleritome developed gradually, with piecewise addition and replacement of individually-secreted sclerites.
I recognize a digestive tract and creeping foot in Wiwaxia, solidifying its relationship with the contemporary Odontogriphus. Similarities between the scleritomes of Wiwaxia, halkieriids, Polyplacophora and Aplacophora hint that the taxa are related. A molluscan affinity is robustly established, and Wiwaxia provides a good fossil proxy for the ancestral aculiferan – and perhaps molluscan – body plan."
We recently redescribed the Middle Cambrian organism Nectocaris pteryx, known from 92 specimens f... more We recently redescribed the Middle Cambrian organism Nectocaris pteryx, known from 92 specimens from the Burgess Shale (Smith & Caron 2010). In contrast to the single, ill-preserved specimen that formed the basis to earlier studies, this new material allowed us to identify new features consistent with a cephalopod affinity. But Nectocaris clearly lies outside the cephalopod crown-group, not least because it lacks a mineralized shell – a plesiomorphy of the crowngroup Cephalopoda. Mazurek & Zaton´ (2011) object to our classification of Nectocaris in the cephalopod stem lineage because of perceived differences between Nectocaris and crown-group cephalopods. As the authors themselves state, such differences are tangential to Nectocaris’s affinity. Rather, synapomorphies hold the key to classifying Cambrian oddballs: but Nectocaris shares no homologous characters with the anomalocaridids (stem-group Arthropoda), where the authors propose it belongs. Mazurek and Zaton´ present no meaningful challenge or alternative to Nectocaris’s interpretation as a ‘primitive’ – that is, stem-group – cephalopod.
Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type de... more Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type deposits in Canada, China, and Australia. Originally described as unrelated species, they have recently been interpreted as a clade; their flexible tentacles, camera-type eyes, lateral fins, internal gills, axial cavity, and funnel point to a relationship with the cephalopods. However, aspects of this reinterpretation, including the relevance of the group to cephalopod evolution, have been called into question.
Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime.
Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.
The exquisite preservation of soft-bodied animals in Burgess Shale-type deposits provides importa... more The exquisite preservation of soft-bodied animals in Burgess Shale-type deposits provides important clues into the early evolution of body plans that emerged during the Cambrian explosion. Until now, such deposits have remained silent regarding the early evolution of extant molluscan lineages—in particular the cephalopods. Nautiloids, traditionally considered basal within the cephalopods, are generally depicted as evolving from a creeping Cambrian ancestor whose dorsal shell afforded protection and buoyancy. Although nautiloid-like shells occur from the Late Cambrian onwards, the fossil record provides little constraint on this model, or indeed on the early evolution of cephalopods. Here, we reinterpret the problematic Middle Cambrian animal Nectocaris pteryx as a primitive (that is, stem-group), non-mineralized cephalopod, based on new material from the Burgess Shale. Together with Nectocaris, the problematic Lower Cambrian taxa Petalilium and (probably) Vetustovermis, form a distinctive clade, Nectocarididae, characterized by an open axial cavity with paired gills, wide lateral fins, a single pair of long, prehensile tentacles, a pair of non-faceted eyes on short stalks, and a large, flexible anterior funnel. This clade extends the cephalopods’ fossil record by over 30 million years, and indicates that primitive cephalopods lacked a mineralized shell, were hyperbenthic, and were presumably carnivorous. The presence of a funnel suggests that jet propulsion evolved in cephalopods before the acquisition of a shell. The explosive diversification of mineralized cephalopods in the Ordovician may have an understated Cambrian ‘fuse’.
"Rindal and Brower (2011) present the surprising
conclusion that likelihood and parsimony criter... more "Rindal and Brower (2011) present the surprising
conclusion that likelihood and parsimony criteria produce the same “optimal” tree topologies, based on a
meta-analysis of studies from Molecular Phylogenetics
and Evolution. I enlarged this dataset, which is heavily
biased towards low taxonomic levels, by adding studies
that addressed relationships between higher taxa
(Table S1). Whereas parsimony and likelihood tree
topologies are often identical at species level, major
differences occurred in one-third of studies above the
familial level (Fig. 1)...."
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an earl... more The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land-plant, despite the absence of a convincing modern analogue. Exceptionally well-preserved nematophyte cuticle from the Late Silurian Burgsvik Sandstone Formation, Gotland provides additional insight into the organism’s anatomy, phylogenetic affiliations and ecology. Because this material exhibits additional characters not present in the type material we assign it to Nematothallopsis gotlandii gen. et sp. nov. The organism was constituted of a close-packed layer of palisade-like filaments covered by a cuticle that bears a characteristic pseudocellular pattern on its inner surface. Apertures in this cuticle are often encircled by a ring of multicellular filaments, which are sometimes associated with spheroidal, spore-like entities. In the light of the conspicuous similarity of the palisade layers to the pseudoparenchymatous tissue of coralline red algae, and of the filament-fringed apertures to their reproductive conceptacles, we reconstruct the Nematothallopsis organism as an extinct rhodophyte and re-evaluate the putative terrestrial habit of cuticular nematophytes in general.
Proceedings of the Royal Society B: Biological Sciences, Jul 31, 2013
"Burgess Shale-type deposits are renowned for their exquisite preservation of
soft-bodied organi... more "Burgess Shale-type deposits are renowned for their exquisite preservation of
soft-bodied organisms, representing a range of animal body plans that evolved
during the Cambrian ‘explosion’. However, the rarity of these fossil deposits
makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive
chronicle of early animal evolution—but are difficult to interpret in the absence
of corresponding whole-body fossils. Here, we provide new observations on the
dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia
sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a
distinctive scaly microstructure and layered (cone-in-cone) construction that
together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus,
RushtonitesandRhombocorniculum—as spines ofHallucigenia-type lobopodians.
Hallucigeniids are thus revealed as an important and widespread component of
disparate Cambrian communities from late in the Terreneuvian (Cambrian
Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in
the latest Cambrian may be partly taphonomic. The cone-in-cone construction
of hallucigeniid sclerites is shared with the sclerotized cuticular structures ( jaws
and claws) in modern onychophorans. More generally, our results emphasize
the reciprocal importance and complementary roles of Burgess Shale-type
fossils and isolated microfossils in documenting early animal evolution."
Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaet... more Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaete annelid worm. Extensive material from the Burgess Shale provides a detailed picture of its morphology and ontogeny, but the fossil record outside this lagerstätte is scarce, and complete wiwaxiids are particularly rare. Here we report small articulated specimens of Wiwaxia foliosa sp. nov. from the Xiaoshiba fauna (Cambrian Stage 3, Hongjingshao Formation, Kunming, south China). Although spines are absent, the fossils' sclerites – like those of W. corrugata – are symmetrically arranged in five distinct zones. They form rows across the body, and were individually added and shed throughout growth to retain an approximately symmetrical body shape. Their development pattern suggests a molluscan affinity. The basic body plan of wiwaxiids is fundamentally conserved across two continents through Cambrian Stages 3–5 – revealing morphological stasis in the wake of the Cambrian explosion.
The present-day distribution of velvet worms corresponds neatly to the ancient supercontinent Gon... more The present-day distribution of velvet worms corresponds neatly to the ancient supercontinent Gondwana — except for a puzzling outpost in southeast Asia. Jaw-dropping new fossil material now establishes when and how peripatid onychophorans reached this isolated spot.
The fossil record paints a thin picture of early terrestrial life. Useful diagnostic features are... more The fossil record paints a thin picture of early terrestrial life. Useful diagnostic features are rare in the organic-walled fossils of the first land colonizers, and at first glance the Silurian–Devonian Tortotubus protuberans seems no exception. Now, new material from New York, Gotland and Scotland reveals the ontogenesis and affinity of this problematic organism. Its filamentous early stages (previously referred to Ornatifilum lornensis) demonstrate simple septal perforations and a bilayered cell wall; threads of entwined filaments, bounded by an elaborately sculptured surface, arose via the retrograde growth and subsequent proliferation of secondary branches. This morphology and pattern of growth together indicate an affinity with the ‘higher’ fungi (Dikarya) and document the formation of differentiated mycelium. The presence of complex mycelial fossils in the earliest Silurian corroborates the likely contribution of fungi to the colonization of land and the establishment of modern sedimentological systems; their rise seemingly accompanied the diversification of early embryophytes and the vegetation of the terrestrial biosphere.
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an earl... more The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land‐plant, despite the absence of a convincing modern analogue. Exceptionally well‐preserved nematophyte cuticle from the Late Silurian Burgsvik Sandstone Formation, Gotland provides additional insight into the organism’s anatomy, phylogenetic affiliations and ecology. Because this material exhibits additional characters not present in the type material we assign it to Nematothallopsis gotlandii gen. et sp. nov. The organism was constituted of a close‐packed layer of palisade‐like filaments covered by a cuticle that bears a characteristic pseudocellular pattern on its inner surface. Apertures in this cuticle are often encircled by a ring of multicellular filaments, which are sometimes associated with spheroidal, spore‐like entities. In the light of the conspicuous similarity of the palisade layers to the pseudoparenchymatous tissue of coralline red algae, and of the filamen...
Wiwaxiids are a problematic group of scale-covered lophotrochozoans known from Cambrian Stages 3–... more Wiwaxiids are a problematic group of scale-covered lophotrochozoans known from Cambrian Stages 3–5. Their imbricating dorsal scleritome of leaf-like scales has prompted comparison with various annelids and molluscs, and has been used as a template to reconstruct the articulation pattern of isolated Small Shelly Fossils. The first articulated specimens of Wiwaxia from the Cambrian Stage 3 Chengjiang Konservat-Lagerstätte show that the Wiwaxia scleritome comprised nine equivalent transverse rows associated with outgrowths of soft tissue, but did not possess a separate zone of anterior sclerites. This serial construction is fundamentally incompatible with the circumferential disposition of sclerites in early molluscs, but does closely resemble the armature of certain annelids. A deep homology with the annelid scleritome must be reconciled with Wiwaxia’s mollusc-like mouthparts and foot; together these point to a deep phylogenetic position, close to the common ancestor of annelids and molluscs.
The Palaeozoic form-taxon Lobopodia encompasses a diverse range of soft-bodied ‘legged worms’ kno... more The Palaeozoic form-taxon Lobopodia encompasses a diverse range of soft-bodied ‘legged worms’ known from exceptional fossil deposits1, 2, 3, 4, 5, 6, 7, 8, 9. Although lobopodians occupy a deep phylogenetic position within Panarthropoda, a shortage of derived characters obscures their evolutionary relationships with extant phyla (Onychophora, Tardigrada and Euarthropoda)2, 3, 5, 10, 11, 12, 13, 14, 15. Here we describe a complex feature in the terminal claws of the mid-Cambrian lobopodian Hallucigenia sparsa—their construction from a stack of constituent elements—and demonstrate that equivalent elements make up the jaws and claws of extant Onychophora. A cladistic analysis, informed by developmental data on panarthropod head segmentation, indicates that the stacked sclerite components in these two taxa are homologous—resolving hallucigeniid lobopodians as stem-group onychophorans. The results indicate a sister-group relationship between Tardigrada and Euarthropoda, adding palaeontological support to the neurological16, 17 and musculoskeletal18, 19 evidence uniting these disparate clades. These findings elucidate the evolutionary transformations that gave rise to the panarthropod phyla, and expound the lobopodian-like morphology of the ancestral panarthropod.
"The soft-bodied Cambrian organism Wiwaxia poses a taxonomic conundrum. Its imbricated dorsal scl... more "The soft-bodied Cambrian organism Wiwaxia poses a taxonomic conundrum. Its imbricated dorsal scleritome suggests a relationship with the polychaete annelid worms, whereas its mouthparts and naked ventral surface invite comparison with the molluscan radula and foot.
476 new and existing specimens from the 505 million year old Burgess Shale cast fresh light on Wiwaxia’s sclerites and scleritome. My observations illuminate the diversity within the genus, and demonstrate that Wiwaxia did not undergo discrete moult stages: rather, its scleritome developed gradually, with piecewise addition and replacement of individually-secreted sclerites.
I recognize a digestive tract and creeping foot in Wiwaxia, solidifying its relationship with the contemporary Odontogriphus. Similarities between the scleritomes of Wiwaxia, halkieriids, Polyplacophora and Aplacophora hint that the taxa are related. A molluscan affinity is robustly established, and Wiwaxia provides a good fossil proxy for the ancestral aculiferan – and perhaps molluscan – body plan."
We recently redescribed the Middle Cambrian organism Nectocaris pteryx, known from 92 specimens f... more We recently redescribed the Middle Cambrian organism Nectocaris pteryx, known from 92 specimens from the Burgess Shale (Smith & Caron 2010). In contrast to the single, ill-preserved specimen that formed the basis to earlier studies, this new material allowed us to identify new features consistent with a cephalopod affinity. But Nectocaris clearly lies outside the cephalopod crown-group, not least because it lacks a mineralized shell – a plesiomorphy of the crowngroup Cephalopoda. Mazurek & Zaton´ (2011) object to our classification of Nectocaris in the cephalopod stem lineage because of perceived differences between Nectocaris and crown-group cephalopods. As the authors themselves state, such differences are tangential to Nectocaris’s affinity. Rather, synapomorphies hold the key to classifying Cambrian oddballs: but Nectocaris shares no homologous characters with the anomalocaridids (stem-group Arthropoda), where the authors propose it belongs. Mazurek and Zaton´ present no meaningful challenge or alternative to Nectocaris’s interpretation as a ‘primitive’ – that is, stem-group – cephalopod.
Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type de... more Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type deposits in Canada, China, and Australia. Originally described as unrelated species, they have recently been interpreted as a clade; their flexible tentacles, camera-type eyes, lateral fins, internal gills, axial cavity, and funnel point to a relationship with the cephalopods. However, aspects of this reinterpretation, including the relevance of the group to cephalopod evolution, have been called into question.
Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime.
Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.
The exquisite preservation of soft-bodied animals in Burgess Shale-type deposits provides importa... more The exquisite preservation of soft-bodied animals in Burgess Shale-type deposits provides important clues into the early evolution of body plans that emerged during the Cambrian explosion. Until now, such deposits have remained silent regarding the early evolution of extant molluscan lineages—in particular the cephalopods. Nautiloids, traditionally considered basal within the cephalopods, are generally depicted as evolving from a creeping Cambrian ancestor whose dorsal shell afforded protection and buoyancy. Although nautiloid-like shells occur from the Late Cambrian onwards, the fossil record provides little constraint on this model, or indeed on the early evolution of cephalopods. Here, we reinterpret the problematic Middle Cambrian animal Nectocaris pteryx as a primitive (that is, stem-group), non-mineralized cephalopod, based on new material from the Burgess Shale. Together with Nectocaris, the problematic Lower Cambrian taxa Petalilium and (probably) Vetustovermis, form a distinctive clade, Nectocarididae, characterized by an open axial cavity with paired gills, wide lateral fins, a single pair of long, prehensile tentacles, a pair of non-faceted eyes on short stalks, and a large, flexible anterior funnel. This clade extends the cephalopods’ fossil record by over 30 million years, and indicates that primitive cephalopods lacked a mineralized shell, were hyperbenthic, and were presumably carnivorous. The presence of a funnel suggests that jet propulsion evolved in cephalopods before the acquisition of a shell. The explosive diversification of mineralized cephalopods in the Ordovician may have an understated Cambrian ‘fuse’.
"Rindal and Brower (2011) present the surprising
conclusion that likelihood and parsimony criter... more "Rindal and Brower (2011) present the surprising
conclusion that likelihood and parsimony criteria produce the same “optimal” tree topologies, based on a
meta-analysis of studies from Molecular Phylogenetics
and Evolution. I enlarged this dataset, which is heavily
biased towards low taxonomic levels, by adding studies
that addressed relationships between higher taxa
(Table S1). Whereas parsimony and likelihood tree
topologies are often identical at species level, major
differences occurred in one-third of studies above the
familial level (Fig. 1)...."
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an earl... more The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land-plant, despite the absence of a convincing modern analogue. Exceptionally well-preserved nematophyte cuticle from the Late Silurian Burgsvik Sandstone Formation, Gotland provides additional insight into the organism’s anatomy, phylogenetic affiliations and ecology. Because this material exhibits additional characters not present in the type material we assign it to Nematothallopsis gotlandii gen. et sp. nov. The organism was constituted of a close-packed layer of palisade-like filaments covered by a cuticle that bears a characteristic pseudocellular pattern on its inner surface. Apertures in this cuticle are often encircled by a ring of multicellular filaments, which are sometimes associated with spheroidal, spore-like entities. In the light of the conspicuous similarity of the palisade layers to the pseudoparenchymatous tissue of coralline red algae, and of the filament-fringed apertures to their reproductive conceptacles, we reconstruct the Nematothallopsis organism as an extinct rhodophyte and re-evaluate the putative terrestrial habit of cuticular nematophytes in general.
Proceedings of the Royal Society B: Biological Sciences, Jul 31, 2013
"Burgess Shale-type deposits are renowned for their exquisite preservation of
soft-bodied organi... more "Burgess Shale-type deposits are renowned for their exquisite preservation of
soft-bodied organisms, representing a range of animal body plans that evolved
during the Cambrian ‘explosion’. However, the rarity of these fossil deposits
makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive
chronicle of early animal evolution—but are difficult to interpret in the absence
of corresponding whole-body fossils. Here, we provide new observations on the
dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia
sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a
distinctive scaly microstructure and layered (cone-in-cone) construction that
together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus,
RushtonitesandRhombocorniculum—as spines ofHallucigenia-type lobopodians.
Hallucigeniids are thus revealed as an important and widespread component of
disparate Cambrian communities from late in the Terreneuvian (Cambrian
Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in
the latest Cambrian may be partly taphonomic. The cone-in-cone construction
of hallucigeniid sclerites is shared with the sclerotized cuticular structures ( jaws
and claws) in modern onychophorans. More generally, our results emphasize
the reciprocal importance and complementary roles of Burgess Shale-type
fossils and isolated microfossils in documenting early animal evolution."
Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaet... more Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaete annelid worm. Extensive material from the Burgess Shale provides a detailed picture of its morphology and ontogeny, but the fossil record outside this lagerstätte is scarce, and complete wiwaxiids are particularly rare. Here we report small articulated specimens of Wiwaxia foliosa sp. nov. from the Xiaoshiba fauna (Cambrian Stage 3, Hongjingshao Formation, Kunming, south China). Although spines are absent, the fossils' sclerites – like those of W. corrugata – are symmetrically arranged in five distinct zones. They form rows across the body, and were individually added and shed throughout growth to retain an approximately symmetrical body shape. Their development pattern suggests a molluscan affinity. The basic body plan of wiwaxiids is fundamentally conserved across two continents through Cambrian Stages 3–5 – revealing morphological stasis in the wake of the Cambrian explosion.
The soft-bodied fossils preserved in Burgess Shale-type deposits provide a unique window on the
o... more The soft-bodied fossils preserved in Burgess Shale-type deposits provide a unique window on the origin and early evolution of complex animals some 500 million years ago, but their relationships to modern phyla can be difficult to determine. Using new fossils collected by the Royal Ontario Museum, I reconstruct the morphology, ecology and affinity of three contentious fossil organisms: Wiwaxia corrugata, Odontogriphus omalus, and Nectocaris pteryx. Nectocaris pteryx is reconstructed as a dorso-ventrally flattened organism with flexible tentacles, lateral fins, internal gills, camera-type eyes, and an axial cavity and funnel that were adapted for efficient jet propulsion. Detailed analysis of the slug-like animals Wiwaxia and Odontogriphus revises some anatomical interpretations, in particular showing that their mouthparts represent serial unipartite rows that comprise multiple teeth. Despite the proposed similarities between Wiwaxia sclerites and annelid chaetae, my new observations are not consistent with an annelidan interpretation. The relationships of these taxa are evaluated using Maximum Parsimony and Bayesian approaches, based on 59 taxa coded for 804 ‘characters’. Both methods strongly support the molluscan affinity of Odontogriphus and Wiwaxia, and indicate that Nectocaris is related to the cephalopods. Nectocaris would place the origin of the cephalopods much earlier than the fossil record suggests, whereas the basal position of Odontogriphus and Wiwaxia implies that the molluscs had a non-mineralized early history, evolving from ancestor that had a Wiwaxia-like scleritome.
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Papers by Martin R Smith
476 new and existing specimens from the 505 million year old Burgess Shale cast fresh light on Wiwaxia’s sclerites and scleritome. My observations illuminate the diversity within the genus, and demonstrate that Wiwaxia did not undergo discrete moult stages: rather, its scleritome developed gradually, with piecewise addition and replacement of individually-secreted sclerites.
I recognize a digestive tract and creeping foot in Wiwaxia, solidifying its relationship with the contemporary Odontogriphus. Similarities between the scleritomes of Wiwaxia, halkieriids, Polyplacophora and Aplacophora hint that the taxa are related. A molluscan affinity is robustly established, and Wiwaxia provides a good fossil proxy for the ancestral aculiferan – and perhaps molluscan – body plan."
Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime.
Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.
conclusion that likelihood and parsimony criteria produce the same “optimal” tree topologies, based on a
meta-analysis of studies from Molecular Phylogenetics
and Evolution. I enlarged this dataset, which is heavily
biased towards low taxonomic levels, by adding studies
that addressed relationships between higher taxa
(Table S1). Whereas parsimony and likelihood tree
topologies are often identical at species level, major
differences occurred in one-third of studies above the
familial level (Fig. 1)...."
soft-bodied organisms, representing a range of animal body plans that evolved
during the Cambrian ‘explosion’. However, the rarity of these fossil deposits
makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive
chronicle of early animal evolution—but are difficult to interpret in the absence
of corresponding whole-body fossils. Here, we provide new observations on the
dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia
sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a
distinctive scaly microstructure and layered (cone-in-cone) construction that
together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus,
RushtonitesandRhombocorniculum—as spines ofHallucigenia-type lobopodians.
Hallucigeniids are thus revealed as an important and widespread component of
disparate Cambrian communities from late in the Terreneuvian (Cambrian
Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in
the latest Cambrian may be partly taphonomic. The cone-in-cone construction
of hallucigeniid sclerites is shared with the sclerotized cuticular structures ( jaws
and claws) in modern onychophorans. More generally, our results emphasize
the reciprocal importance and complementary roles of Burgess Shale-type
fossils and isolated microfossils in documenting early animal evolution."
476 new and existing specimens from the 505 million year old Burgess Shale cast fresh light on Wiwaxia’s sclerites and scleritome. My observations illuminate the diversity within the genus, and demonstrate that Wiwaxia did not undergo discrete moult stages: rather, its scleritome developed gradually, with piecewise addition and replacement of individually-secreted sclerites.
I recognize a digestive tract and creeping foot in Wiwaxia, solidifying its relationship with the contemporary Odontogriphus. Similarities between the scleritomes of Wiwaxia, halkieriids, Polyplacophora and Aplacophora hint that the taxa are related. A molluscan affinity is robustly established, and Wiwaxia provides a good fossil proxy for the ancestral aculiferan – and perhaps molluscan – body plan."
Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime.
Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.
conclusion that likelihood and parsimony criteria produce the same “optimal” tree topologies, based on a
meta-analysis of studies from Molecular Phylogenetics
and Evolution. I enlarged this dataset, which is heavily
biased towards low taxonomic levels, by adding studies
that addressed relationships between higher taxa
(Table S1). Whereas parsimony and likelihood tree
topologies are often identical at species level, major
differences occurred in one-third of studies above the
familial level (Fig. 1)...."
soft-bodied organisms, representing a range of animal body plans that evolved
during the Cambrian ‘explosion’. However, the rarity of these fossil deposits
makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive
chronicle of early animal evolution—but are difficult to interpret in the absence
of corresponding whole-body fossils. Here, we provide new observations on the
dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia
sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a
distinctive scaly microstructure and layered (cone-in-cone) construction that
together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus,
RushtonitesandRhombocorniculum—as spines ofHallucigenia-type lobopodians.
Hallucigeniids are thus revealed as an important and widespread component of
disparate Cambrian communities from late in the Terreneuvian (Cambrian
Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in
the latest Cambrian may be partly taphonomic. The cone-in-cone construction
of hallucigeniid sclerites is shared with the sclerotized cuticular structures ( jaws
and claws) in modern onychophorans. More generally, our results emphasize
the reciprocal importance and complementary roles of Burgess Shale-type
fossils and isolated microfossils in documenting early animal evolution."
origin and early evolution of complex animals some 500 million years ago, but their relationships
to modern phyla can be difficult to determine. Using new fossils collected by the Royal Ontario
Museum, I reconstruct the morphology, ecology and affinity of three contentious fossil
organisms: Wiwaxia corrugata, Odontogriphus omalus, and Nectocaris pteryx.
Nectocaris pteryx is reconstructed as a dorso-ventrally flattened organism with flexible tentacles,
lateral fins, internal gills, camera-type eyes, and an axial cavity and funnel that were adapted for
efficient jet propulsion. Detailed analysis of the slug-like animals Wiwaxia and Odontogriphus
revises some anatomical interpretations, in particular showing that their mouthparts represent
serial unipartite rows that comprise multiple teeth. Despite the proposed similarities between
Wiwaxia sclerites and annelid chaetae, my new observations are not consistent with an annelidan
interpretation.
The relationships of these taxa are evaluated using Maximum Parsimony and Bayesian
approaches, based on 59 taxa coded for 804 ‘characters’. Both methods strongly support the
molluscan affinity of Odontogriphus and Wiwaxia, and indicate that Nectocaris is related to the
cephalopods. Nectocaris would place the origin of the cephalopods much earlier than the fossil
record suggests, whereas the basal position of Odontogriphus and Wiwaxia implies that the
molluscs had a non-mineralized early history, evolving from ancestor that had a Wiwaxia-like
scleritome.