Interpreting fossilized nervous tissues.

Paleoneuranatomy is an emerging subfield of paleontological research with great potential for the study of evolution. However, the interpretation of fossilized nervous tissues is a difficult task and presently lacks a rigorous methodology. We critically review here cases of neural tissue preservation reported in Cambrian arthropods, following a set of fundamental paleontological criteria for their recognition. These criteria are based on a variety of taphonomic parameters and account for morphoanatomical complexity. Application of these criteria shows that firm evidence for fossilized nervous tissues is less abundant and detailed than previously reported, and we synthesize here evidence that has stronger support. We argue that the vascular system, and in particular its lacunae, may be central to the understanding of many of the fossilized peri-intestinal features known across Cambrian arthropods. In conclusion, our results suggest the need for caution in the interpretation of evidence for fossilized neural tissue, which will increase the accuracy of evolutionary scenarios. Also see the video abstract here: https://youtu.be/2_JlQepRTb0.

Late Ordovician eurypterid preserves oldest euchelicerate musculature in pyrite.

Pyritization of soft tissues of invertebrates is rare in the fossil record. In New York State, it occurs in black shales of the Lorraine Group (Late Ordovician), the best-known example of which is Beecher's Trilobite Bed. Exceptional preservation at the quarry where this bed is exposed allowed detailed examination of trilobite and ostracod soft-tissue anatomy. Here, we present the first example of a eurypterid (sea scorpion) currently ascribed to Carcinosomatidae from this deposit that also preserves the first evidence for mesosomal musculature in eurypterids. This specimen demonstrates that eurypterid musculature can be preserved in pyrite and evidences the oldest example of euchelicerate muscles within the fossil record. Sulfur isotope data illustrate that pyrite rapidly replicated muscle tissue in the early burial environment, prior to the pyritization of biomineralized exoskeleton and cuticular trilobite limbs. This discovery therefore expands the limited fossil record of euchelicerate musculature, while extending the taphonomic scope for preservation of detailed internal structures, more broadly, within arthropods.

Formation of the 'Great Unconformity' as a trigger for the Cambrian explosion.

The transition between the Proterozoic and Phanerozoic eons, beginning 542 million years (Myr) ago, is distinguished by the diversification of multicellular animals and by their acquisition of mineralized skeletons during the Cambrian period. Considerable progress has been made in documenting and more precisely correlating biotic patterns in the Neoproterozoic-Cambrian fossil record with geochemical and physical environmental perturbations, but the mechanisms responsible for those perturbations remain uncertain. Here we use new stratigraphic and geochemical data to show that early Palaeozoic marine sediments deposited approximately 540-480 Myr ago record both an expansion in the area of shallow epicontinental seas and anomalous patterns of chemical sedimentation that are indicative of increased oceanic alkalinity and enhanced chemical weathering of continental crust. These geochemical conditions were caused by a protracted period of widespread continental denudation during the Neoproterozoic followed by extensive physical reworking of soil, regolith and basement rock during the first continental-scale marine transgression of the Phanerozoic. The resultant globally occurring stratigraphic surface, which in most regions separates continental crystalline basement rock from much younger Cambrian shallow marine sedimentary deposits, is known as the Great Unconformity. Although Darwin and others have interpreted this widespread hiatus in sedimentation on the continents as a failure of the geologic record, this palaeogeomorphic surface represents a unique physical environmental boundary condition that affected seawater chemistry during a time of profound expansion of shallow marine habitats. Thus, the formation of the Great Unconformity may have been an environmental trigger for the evolution of biomineralization and the 'Cambrian explosion' of ecologic and taxonomic diversity following the Neoproterozoic emergence of animals.

Mechanism for Burgess Shale-type preservation.

Exceptionally preserved fossil biotas of the Burgess Shale and a handful of other similar Cambrian deposits provide rare but critical insights into the early diversification of animals. The extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft-bodied fossil assemblages has remained enigmatic since Walcott's initial discovery in 1909. Here, we demonstrate the mechanism of Burgess Shale-type preservation using sedimentologic and geochemical data from the Chengjiang, Burgess Shale, and five other principal Burgess Shale-type deposits. Sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation. Low sulfate concentrations in the global ocean and low-oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability. Subsequently, rapid entombment of fossils in fine-grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments. A permeability barrier, provided by bed-capping cements that were emplaced at the seafloor, is a feature that is shared among Burgess Shale-type deposits, and resulted from the unusually high alkalinity of Cambrian oceans. Thus, Burgess Shale-type preservation of soft-bodied fossil assemblages worldwide was promoted by unique aspects of early Paleozoic seawater chemistry that strongly impacted sediment diagenesis, providing a fundamentally unique record of the immediate aftermath of the "Cambrian explosion."

The "slide technique": an improvement on the "funnel technique" for safe pedicle screw placement in the thoracic spine.

STUDY DESIGN: Technical note. OBJECTIVES: To report and describe a new free-hand technique for pedicle screw placement in the thoracic spine especially in severe deformities. Because of distortion of anatomic landmarks scoliosis, this free-hand placement technique based on pedicle access through the decancelled transverse process is a safe procedure. METHODS: Transverse process is widely exposed and its posterior cortex is decorticated. The cancellous bone content of the transverse process is completely removed using a small curette. Bone wax is applied to avoid local bleeding and then the decancelled transverse process is inspected. The entry of the pedicle is then easily identified by the presence of remaining cancellous bone. A pedicular probe is then inserted and gently advanced. During pedicle probe insertion, the cortex of the anterior aspect of transverse process and the lateral margin of the pedicle act as a "slide" to permit safe insertion of the instrument. RESULTS: In our experience, no patient required additional procedures for screw revision, and no neurologic deficit occurred stemming from malpositioning of pedicle screws. The key point of the "slide technique" is to use the cortex of the anterior aspect of transverse process and the lateral margin of the pedicle as a "slide" to permit correct probe positioning during pedicle probe insertion. CONCLUSIONS: This technique is very close to the "funnel technique". The "funnel" and then the "slide" technique are mostly useful in complex spinal deformities as in neuromuscular patients. The "slide technique" is a safe, effective and cost-effective technique for pedicle screw placement in the thoracic spine especially in severe deformities. LEVEL OF EVIDENCE: IV.

The Emu Bay Shale: A unique early Cambrian Lagerstätte from a tectonically active basin.

The Emu Bay Shale (EBS) of South Australia is anomalous among Cambrian Lagerstätten because it captures anatomical information that is rare in Burgess Shale-type fossils, and because of its inferred nearshore setting, the nature of which has remained controversial. Intensive study, combining outcrop and borehole data with a compilation of >25,000 fossil specimens, reveals that the EBS biota inhabited a fan delta complex within a tectonically active basin. Preservation of soft-bodied organisms in this setting is unexpected and further underscores differences between the EBS and other Cambrian Lagerstätten. Environmental conditions, including oxygen fluctuations, slope instability, high suspended sediment concentrations, and episodic high-energy events, inhibited colonization of the lower prodelta by all but a few specialist species but favored downslope transportation and preservation of other largely endemic, shallow-water benthos. The EBS provides extraordinary insight into early Cambrian animal diversity from Gondwana. These results demonstrate how environmental factors determined community composition and provide a framework for understanding this unique Konservat-Lagerstätte.

A new sponge from the Marjum Formation of Utah documents the Cambrian origin of the hexactinellid body plan.

Modern poriferans are classified into four classes-Calcarea, Demospongiae, Hexactinellida and Homoscleromorpha-the recognition of which in fossil specimens almost exclusively relies on spicule morphology and arrangement. Early fossil representatives of the phylum Porifera are morphologically diverse, and many of them problematically display characteristics that are incompatible with the classification scheme developed for modern taxa. Critically, hexactine spicules-a diagnostic feature of hexactinellids among modern taxa-are found in various Cambrian and Ordovician taxa that cannot be accommodated within the hexactinellid body plan. Here we describe a new poriferan from the Drumian Marjum Formation of Utah, Polygoniella turrelli gen. et sp. nov., which exhibits a unique combination of complex anatomical features for a Cambrian form, including a syconoid-like organization, a thick body wall, and a multi-layered hexactin-based skeleton. The hexactinellid-like body wall architecture of this new species supports a Cambrian origin of the hexactinellid body plan and provides valuable insights into character evolution in early glass sponges.

Tectonic trigger to the first major extinction of the Phanerozoic: The early Cambrian Sinsk event.

The Cambrian explosion, one of the most consequential biological revolutions in Earth history, occurred in two phases separated by the Sinsk event, the first major extinction of the Phanerozoic. Trilobite fossil data show that Series 2 strata in the Ross Orogen, Antarctica, and Delamerian Orogen, Australia, record nearly identical and synchronous tectono-sedimentary shifts marking the Sinsk event. These resulted from an abrupt pulse of contractional supracrustal deformation on both continents during the Pararaia janeae trilobite Zone. The Sinsk event extinction was triggered by initial Ross/Delamerian supracrustal contraction along the edge of Gondwana, which caused a cascading series of geodynamic, paleoenvironmental, and biotic changes, including (i) loss of shallow marine carbonate habitats along the Gondwanan margin; (ii) tectonic transformation to extensional tectonics within the Gondwanan interior; (iii) extrusion of the Kalkarindji large igneous province; (iv) release of large volumes of volcanic gasses; and (v) rapid climatic change, including incursions of marine anoxic waters and collapse of shallow marine ecosystems.

Rapid volcanic ash entombment reveals the 3D anatomy of Cambrian trilobites.

Knowledge of Cambrian animal anatomy is limited by preservational processes that result in compaction, size bias, and incompleteness. We documented pristine three-dimensional (3D) anatomy of trilobites fossilized through rapid ash burial from a pyroclastic flow entering a shallow marine environment. Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system. Previously unknown anatomy includes a soft-tissue labrum attached to the hypostome, a slit-like mouth, and distinctive cephalic feeding appendages. Our findings resolve controversy over whether the trilobite hypostome is the labrum or incorporates it and establish crown-group euarthropod homologies in trilobites. This occurrence of moldic fossils with 3D soft parts highlights volcanic ash deposits in marine settings as an underexplored source for exceptionally preserved organisms.

The Cambrian microfossil Qingjiangonema reveals the co-evolution of sulfate-reducing bacteria and the oxygenation of Earth's surface.

Sulfate reduction is an essential metabolism that maintains biogeochemical cycles in marine and terrestrial ecosystems. Sulfate reducers are exclusively prokaryotic, phylogenetically diverse, and may have evolved early in Earth's history. However, their origin is elusive and unequivocal fossils are lacking. Here we report a new microfossil, Qingjiangonema cambria, from ∼518-million-year-old black shales that yield the Qingjiang biota. Qingjiangonema is a long filamentous form comprising hundreds of cells filled by equimorphic and equidimensional pyrite microcrystals with a light sulfur isotope composition. Multiple lines of evidence indicate Qingjiangonema was a sulfate-reducing bacterium that exhibits similar patterns of cell organization to filamentous forms within the phylum Desulfobacterota, including the sulfate-reducing Desulfonema and sulfide-oxidizing cable bacteria. Phylogenomic analyses confirm separate, independent origins of multicellularity in Desulfonema and in cable bacteria. Molecular clock analyses infer that the Desulfobacterota, which encompass a majority of sulfate-reducing taxa, diverged ∼2.41 billion years ago during the Paleoproterozoic Great Oxygenation Event, while cable bacteria diverged ∼0.56 billion years ago during or immediately after the Neoproterozoic Oxygenation Event. Taken together, we interpret Qingjiangonema as a multicellular sulfate-reducing microfossil and propose that cable bacteria evolved from a multicellular filamentous sulfate-reducing ancestor. We infer that the diversification of the Desulfobacterota and the origin of cable bacteria may have been responses to oxygenation events in Earth's history.

Lithium isotopic constraints on the evolution of continental clay mineral factory and marine oxygenation in the earliest Paleozoic Era.

The evolution of oxygen cycles on Earth's surface has been regulated by the balance between molecular oxygen production and consumption. The Neoproterozoic-Paleozoic transition likely marks the second rise in atmospheric and oceanic oxygen levels, widely attributed to enhanced burial of organic carbon. However, it remains disputed how marine organic carbon production and burial respond to global environmental changes and whether these feedbacks trigger global oxygenation during this interval. Here, we report a large lithium isotopic and elemental dataset from marine mudstones spanning the upper Neoproterozoic to middle Cambrian [~660 million years ago (Ma) to 500 Ma]. These data indicate a dramatic increase in continental clay formation after ~525 Ma, likely linked to secular changes in global climate and compositions of the continental crust. Using a global biogeochemical model, we suggest that intensified continental weathering and clay delivery to the oceans could have notably increased the burial efficiency of organic carbon and facilitated greater oxygen accumulation in the earliest Paleozoic oceans.

Pubic symphysis diastasis with urinary incontinence: collaborative surgical management.

Pubic symphysis diastasis during obstetric delivery occurs rarely. Symptoms usually respond to conservative management. A nulliparous 39-year-old delivered spontaneously with an audible pop noted. Pubic symphysis diastasis of 4.6 cm was diagnosed on pelvic X-ray. She developed severe pain with ambulation and stress urinary incontinence. After neither of these symptoms improved significantly in response to conservative management, the patient underwent open reduction internal fixation with plating of her pubic symphysis, and bladder neck sling placement using autologous rectus fascia. Postoperatively she experienced urinary retention, which resolved with continuous bladder drainage for 1 week. Both her urinary incontinence and pain resolved, and she had resumed normal activities 3 months following her surgery. Pubic symphysis diastasis is a rare obstetric complication with a paucity of literature to guide its management. A coordinated multidisciplinary approach to management is necessary when multiple organ systems are involved.

First record of growth patterns in a Cambrian annelid.

Early annelid evolution is mostly known from 13 described species from Cambrian Burgess Shale-type Lagerstätten. We introduce a new exceptionally well-preserved polychaete, Ursactis comosa gen. et sp. nov., from the Burgess Shale (Wuliuan Stage). This small species (3-15 mm) is the most abundant Cambrian polychaete known to date. Most specimens come from Tokumm Creek, a new Burgess Shale locality in northern Kootenay National Park, British Columbia, Canada. Ursactis has a pair of large palps, thin peristomial neurochaetae and biramous parapodia bearing similarly sized capillary neurochaetae and notochaetae, except for segments six to nine, which also have longer notochaetae. The number of segments in this polychaete range between 8 and 10 with larger individuals having 10 segments. This number of segments in Ursactis is remarkably small compared with other polychaetes, including modern forms. Specimens with 10 segments show significant size variations, and the length of each segment increases with the body length, indicating that body growth was primarily achieved by increasing the size of existing segments rather than adding new ones. This contrasts with most modern polychaetes, which typically have a larger number of segments through additions of segments throughout life. The inferred growth pattern in Ursactis suggests that annelids had evolved control over segment addition by the mid-Cambrian.

Evolution of orthopaedic reconstructive care.

The patterns and severity of injury sustained by service members have continuously evolved over the past 10 years of combat in Iraq and Afghanistan. The 2010 surge of combat troops into Afghanistan, combined with a transition to counterinsurgency tactics with an emphasis on dismounted operations, resulted in increased exposure of US service members to improvised explosive devices and a new pattern of injury termed dismounted complex blast injury. This constellation of injuries typically includes multiple extremity injuries, high bilateral transfemoral amputations, amputated or mangled upper extremities, open pelvis fractures, and injury to the perineal and/or genital regions. These polytraumatized patients frequently present with head, abdominal, and genitourinary injuries, as well. Traditional methods of reconstruction must be optimized because tissue availability may be limited.

Reprioritization of research for combat casualty care.

Since the beginning of the conflicts in Iraq and Afghanistan more than a decade ago, much has been learned with regard to combat casualty care. Although progress has been significant, knowledge gaps still exist. The seventh Extremity War Injuries symposium, held in January 2012, reviewed the current state of knowledge and defined knowledge gaps in acute care, reconstructive care, and rehabilitative care in order to provide policymakers information on the areas in which research funding would be the most beneficial.

Injury to the tarsometatarsal joint complex during fixation of Lisfranc fracture dislocations: an anatomic study.

BACKGROUND: The cause of posttraumatic arthritis in Lisfranc injuries is argued in the literature. The purpose of this study was to determine whether the involved joint surface area increased with repositioning of the guidewire before screw placement. MATERIALS: Nine matched pairs of cadaveric feet were disarticulated at the tibiotalar joint. Under fluoroscopic guidance, cannulated screws were placed over guidewires after a single pass across the joint for right feet and two passes across the joint for left feet. Specimens were disarticulated through the midfoot, and the digital images of the joint surface were evaluated for joint surface area and the surface area of cartilaginous damage resulting from screw placement. RESULTS: Mean injury area for the first metatarsal (MT1) was 0.106 cm2 for one pass and 0.168 cm2 for two passes of the guidewire before screw advancement (p = 0.003) The mean injury area for the second metatarsal (MT2) was 0.123 and 0.178 cm2 for one and two passes, respectively (p = 0.018). Four of nine (44%) of the left foot specimens (2 passes of the guidewire) sustained fractures across the MT2 base and three of those specimens also revealed fractures on the middle cuneiform side of the joint (33%). CONCLUSION: Changing the placement of the guidewire across the midfoot significantly increased the joint surface affected by screw placement. Screws placed plantar to the midline of the joint increased the risk of fracture on both sides of the tarsometatarsal complex.

A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic.

Atmospheric oxygen levels control the oxidative side of key biogeochemical cycles and place limits on the development of high-energy metabolisms. Understanding Earth's oxygenation is thus critical to developing a clearer picture of Earth's long-term evolution. However, there is currently vigorous debate about even basic aspects of the timing and pattern of the rise of oxygen. Chemical weathering in the terrestrial environment occurs in contact with the atmosphere, making paleosols potentially ideal archives to track the history of atmospheric O2 levels. Here we present stable chromium isotope data from multiple paleosols that offer snapshots of Earth surface conditions over the last three billion years. The results indicate a secular shift in the oxidative capacity of Earth's surface in the Neoproterozoic and suggest low atmospheric oxygen levels (<1% PAL pO2 ) through the majority of Earth's history. The paleosol record also shows that localized Cr oxidation may have begun as early as the Archean, but efficient, modern-like transport of hexavalent Cr under an O2 -rich atmosphere did not become common until the Neoproterozoic.

The Qingjiang biota-A Burgess Shale-type fossil Lagerstätte from the early Cambrian of South China.

Burgess Shale-type fossil Lagerstätten provide the best evidence for deciphering the biotic patterns and magnitude of the Cambrian explosion. Here, we report a Lagerstätte from South China, the Qingjiang biota (~518 million years old), which is dominated by soft-bodied taxa from a distal shelf setting. The Qingjiang biota is distinguished by pristine carbonaceous preservation of labile organic features, a very high proportion of new taxa (~53%), and preliminary taxonomic diversity that suggests it could rival the Chengjiang and Burgess Shale biotas. Defining aspects of the Qingjiang biota include a high abundance of cnidarians, including both medusoid and polypoid forms; new taxa resembling extant kinorhynchs; and abundant larval or juvenile forms. This distinctive composition holds promise for providing insights into the evolution of Cambrian ecosystems across environmental gradients.

The use of surgical drains in orthopedics.

The use of postsurgical drains have a long history in thoracic and abdominal surgery. In orthopedics these devices have been used to decrease local edema, lessen the potential for hematoma or seroma formation, and to aid in the efflux of infection. However, the role of postoperative surgical drains in clean, elective cases has not been firmly established. In fact, most studies fail to show a statistical difference in outcome between drained and undrained patients. Despite the paucity of clinical evidence demonstrating any benefit supporting their use, drains continue to be placed after elective orthopedic procedures.

Arthroscopic superior labrum anterior-posterior repair in military patients.

The purpose of this retrospective study was to determine the efficacy of arthroscopic superior labrum anterior-posterior (SLAP) repair in a military population. In this study, 27 patients (of 30 consecutive patients) who had suture anchor repair of a type II SLAP lesion were evaluated at a mean of 30.5 months postoperatively. Fifteen patients had isolated tears, whereas twelve also had a concomitant diagnosis. At follow-up, the overall mean American Shoulder and Elbow Surgeons score was 86.9 points and the mean University of California, Los Angeles score was 30.4 points. The results were excellent in 4 patients, good in 20, and fair in 3. Of the patients, 96% returned to full duty (mean, 4.4 months). Patients treated for concomitant diagnoses and a SLAP tear had significantly higher American Shoulder and Elbow Surgeons scores and tended to have higher University of California, Los Angeles scores than those treated for an isolated SLAP tear. The findings indicate that arthroscopic SLAP repair in military patients results in a high rate of return to duty. The results suggest that concomitant shoulder pathology should be treated at the time of SLAP repair.