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Mammals feed using a jaw hinge formed by dentary and squamosal bones. Fossil evidence reveals that this type of joint evolved independently in an extinct species of mammalian relatives called cynodonts. Fossil evidence sheds light on how jaw joints can evolve.

Evolution of the earliest mammals shows successive episodes of diversification. Lineage-splitting in Mesozoic mammals is coupled with many independent evolutionary experiments and ecological specializations. Classic scenarios of mammalian morphological evolution tend to posit an orderly acquisition of key evolutionary innovations leading to adaptive diversification, but newly discovered fossils show that evolution of such key characters as the middle ear and the tribosphenic teeth is far more labile among Mesozoic mammals. Successive diversifications of Mesozoic mammal groups multiplied the opportunities for many dead-end lineages to iteratively evolve developmental homoplasies and convergent ecological specializations, parallel to those in modern mammal groups.

Background Over 5,488,000 cases of coronavirus disease-19 (COVID-19) have been reported since December 2019. We aim to explore risk factors associated with mortality in COVID-19 patients and assess the use of D-dimer as a biomarker for disease severity and clinical outcome. Methods We retrospectively analyzed the clinical, laboratory, and radiological characteristics of 248 consecutive cases of COVID-19 in Renmin Hospital of Wuhan University, Wuhan, China from January 28 to March 08, 2020. Univariable and multivariable logistic regression methods were used to explore risk factors associated with in-hospital mortality. Correlations of D-dimer upon admission with disease severity and in-hospital mortality were analyzed. Receiver operating characteristic curve was used to determine the optimal cutoff level for D-dimer that discriminated those survivors versus non-survivors during hospitalization. Results Multivariable regression that showed D-dimer > 2.0 mg/L at admission was the only variable associated with increased odds of mortality [OR 10.17 (95% CI 1.10–94.38), P = 0.041]. D-dimer elevation (≥ 0.50 mg/L) was seen in 74.6% (185/248) of the patients. Pulmonary embolism and deep vein thrombosis were ruled out in patients with high probability of thrombosis. D-dimer levels significantly increased with increasing severity of COVID-19 as determined by clinical staging (Kendall’s tau-b = 0.374, P = 0.000) and chest CT staging (Kendall’s tau-b = 0.378, P = 0.000). In-hospital mortality rate was 6.9%. Median D-dimer level in non-survivors ( n = 17) was significantly higher than in survivors ( n = 231) [6.21 (3.79–16.01) mg/L versus 1.02 (0.47–2.66) mg/L, P = 0.000]. D-dimer level of > 2.14 mg/L predicted in-hospital mortality with a sensitivity of 88.2% and specificity of 71.3% (AUC 0.85; 95% CI = 0.77–0.92). Conclusions D-dimer is commonly elevated in patients with COVID-19. D-dimer levels correlate with disease severity and are a reliable prognostic marker for in-hospital mortality in patients admitted for COVID-19.

Many hypotheses have been postulated regarding the early evolution of the mammalian brain. Here, x-ray tomography of the Early Jurassic mammaliaforms Morganucodon and Hadrocodium sheds light on this history. We found that relative brain size expanded to mammalian levels, with enlarged olfactory bulbs, neocortex, olfactory (pyriform) cortex, and cerebellum, in two evolutionary pulses. The initial pulse was probably driven by increased resolution in olfaction and improvements in tactile sensitivity (from body hair) and neuromuscular coordination. A second pulse of olfactory enhancement then enlarged the brain to mammalian levels. The origin of crown Mammalia saw a third pulse of olfactory enhancement, with ossified ethmoid turbinals supporting an expansive olfactory epithelium in the nasal cavity, allowing full expression of a huge odorant receptor genome.

We report a new Jurassic docodontan mammaliaform found in China that is preserved with the hyoid bones. Its basihyal, ceratohyal, epihyal, and thyrohyal bones have mobile joints and are arranged in a saddle-shaped configuration, as in the mobile linkage of the hyoid apparatus of extant mammals. These are fundamentally different from the simple hyoid rods of nonmammaliaform cynodonts, which were likely associated with a wide, nonmuscularized throat, as seen in extant reptiles. The hyoid apparatus provides a framework for the larynx and for the constricted, muscularized esophagus, crucial for transport and powered swallowing of the masticated food and liquid in extant mammals. These derived structural components of hyoids evolved among early diverging mammaliaforms, before the disconnection of the middle ear from the mandible in crown mammals.

An early date for mammal divergence Almost all living mammals are placentals. A key event in mammalian evolution was the divergence between the ancestors of today's placentals and those of the marsupials. The discovery of a fossil on the placental side of the split takes that divergence back 35 million years, to around 160 million years ago, deep into the Jurassic period. The fossil, from China, shows that the earliest members of the group that includes ourselves and most familiar mammals was a small creature adapted for climbing and scampering among the trees, presumably keeping well clear of the dinosaurs below. The age of the fossil suggests that there was a higher rate of mammal evolution in the Jurassic than previously believed. Placentals are the most abundant mammals that have diversified into every niche for vertebrates and dominated the world’s terrestrial biotas in the Cenozoic. A critical event in mammalian history is the divergence of eutherians, the clade inclusive of all living placentals, from the metatherian–marsupial clade 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . Here we report the discovery of a new eutherian of 160 Myr from the Jurassic of China, which extends the first appearance of the eutherian–placental clade by about 35 Myr from the previous record, reducing and resolving a discrepancy between the previous fossil record and the molecular estimate for the placental–marsupial divergence 9 , 10 , 11 , 12 , 13 . This mammal has scansorial forelimb features, and provides the ancestral condition for dental and other anatomical features of eutherians.

Ecology and biomechanics play central roles in the generation of phenotypic diversity. When unrelated taxa invade a similar ecological niche, biomechanical demands can drive convergent morphological transformations. Thus, examining convergence helps to elucidate the key catalysts of phenotypic change. Gliding mammals are often presented as a classic case of convergent evolution because they independently evolved in numerous clades, each possessing patagia (“wing” membranes) that generate lift during gliding. We use phylogenetic comparative methods to test whether the skeletal morphologies of the six clades of extant gliding mammals demonstrate convergence. Our results indicate that glider skeletons are convergent, with glider groups consistently evolving proportionally longer, more gracile limbs than arborealists, likely to increase patagial surface area. Nonetheless, we interpret gliders to represent incomplete convergence because (1) evolutionary model-fitting analyses do not indicate strong selective pressures for glider trait optima, (2) the three marsupial glider groups diverge rather than converge, and (3) the gliding groups remain separated in morphospace (rather than converging on a single morphotype), which is reflected by an unexpectedly high level of morphological disparity. That glider skeletons are morphologically diverse is further demonstrated by fossil gliders from the Mesozoic Era, which possess unique skeletal characteristics that are absent in extant gliders. Glider morphologies may be strongly influenced by factors such as body size and attachment location of patagia on the forelimb, which can vary among clades. Thus, convergence in gliders appears to be driven by a simple lengthening of the limbs, whereas additional skeletal traits reflect nuances of the gliding apparatus that are distinct among different evolutionary lineages. Our unexpected results add to growing evidence that incomplete convergence is prevalent in vertebrate clades, even among classic cases of convergence, and they highlight the importance of examining form-function relationships in light of phylogeny, biomechanics, and the fossil record.

The earliest evolution of mammals and origins of mammalian features can be traced to the mammaliaforms of the Triassic and Jurassic periods that are extinct relatives to living mammals. Here we describe a new fossil from the Middle Jurassic that has a mandibular middle ear, a gradational transition of thoracolumbar vertebrae and primitive ankle features, but highly derived molars with a high crown and multiple roots that are partially fused. The upper molars have longitudinal cusp rows that occlude alternately with those of the lower molars. This specialization for masticating plants indicates that herbivory evolved among mammaliaforms, before the rise of crown mammals. The new species shares the distinctive dental features of the eleutherodontid clade, previously represented only by isolated teeth despite its extensive geographic distribution during the Jurassic. This eleutherodontid was terrestrial and had ambulatory gaits, analogous to extant terrestrial mammals such as armadillos or rock hyrax. Its fur corroborates that mammalian integument had originated well before the common ancestor of living mammals. Haramiyids were Mesozoic era animals that until now have been identified only from their distinctive teeth, and are thought to be related to the better-known multituberculates: here the authors describe a haramiyid that is very primitive in terms of its jaw and ankle characteristics, suggesting a lack of relationship to the multituberculates. The tangled world of the early mammals Independent reports of two newly discovered fossils from the Jurassic of China (around 160–165 million years old) produce conflicting reconstructions of the origins of mammals. Haramiyids were Mesozoic mammals with strange, highly derived rodent-like teeth. Because of this they have been allied with multituberculates, a larger and highly successful group of rodent-like mammals that lived until the Eocene. The problem with haramiyids is that they were until recently known only from teeth. A report by Jin Meng and colleagues reveals a much more complete creature whose features ally it with multituberculates, confirming earlier views — but also implying that the roots of extant mammals lie well back in the Triassic. By contrast, the haramiyid described by Zhe-Xi Luo and colleagues is startlingly primitive in many features of the jaw and ankle, implying that the haramiyids go way back in the mammalian scheme of things and are not related to multituberculates at all. This dichotomy is a reminder of just how little we know about fossils whose interpretation is crucial to the early evolution of mammals.

The evolution of the mammalian jaw is one of the most important innovations in vertebrate history, and underpins the exceptional radiation and diversification of mammals over the last 220 million years 1 , 2 . In particular, the transformation of the mandible into a single tooth-bearing bone and the emergence of a novel jaw joint—while incorporating some of the ancestral jaw bones into the mammalian middle ear—is often cited as a classic example of the repurposing of morphological structures 3 , 4 . Although it is remarkably well-documented in the fossil record, the evolution of the mammalian jaw still poses the paradox of how the bones of the ancestral jaw joint could function both as a joint hinge for powerful load-bearing mastication and as a mandibular middle ear that was delicate enough for hearing. Here we use digital reconstructions, computational modelling and biomechanical analyses to demonstrate that the miniaturization of the early mammalian jaw was the primary driver for the transformation of the jaw joint. We show that there is no evidence for a concurrent reduction in jaw-joint stress and increase in bite force in key non-mammaliaform taxa in the cynodont–mammaliaform transition, as previously thought 5 – 8 . Although a shift in the recruitment of the jaw musculature occurred during the evolution of modern mammals, the optimization of mandibular function to increase bite force while reducing joint loads did not occur until after the emergence of the neomorphic mammalian jaw joint. This suggests that miniaturization provided a selective regime for the evolution of the mammalian jaw joint, followed by the integration of the postdentary bones into the mammalian middle ear. Biomechanical analyses of mammaliaform and cynodont fossils demonstrate that miniaturization drove the evolutionary transformation of the mammalian jaw, which preceded the optimization of bite force-to-joint load in the mandible

Black phosphorus has been revisited recently as a new two-dimensional material showing potential applications in electronics and optoelectronics. Here we report the anisotropic in-plane thermal conductivity of suspended few-layer black phosphorus measured by micro-Raman spectroscopy. The armchair and zigzag thermal conductivities are ∼20 and ∼40 W m −1  K −1 for black phosphorus films thicker than 15 nm, respectively, and decrease to ∼10 and ∼20 W m −1  K −1 as the film thickness is reduced, exhibiting significant anisotropy. The thermal conductivity anisotropic ratio is found to be ∼2 for thick black phosphorus films and drops to ∼1.5 for the thinnest 9.5-nm-thick film. Theoretical modelling reveals that the observed anisotropy is primarily related to the anisotropic phonon dispersion, whereas the intrinsic phonon scattering rates are found to be similar along the armchair and zigzag directions. Surface scattering in the black phosphorus films is shown to strongly suppress the contribution of long mean-free-path acoustic phonons. The two-dimensional material black phosphorus could find uses in energy applications. Here, the authors study the difference in in-plane thermal conductivity along the armchair and zigzag directions in suspended few-layer black phosphorus, and show the dependence of this anisotropy on sample thickness.