Daniel Field

Our understanding of the earliest stages of crown bird evolution is hindered by an
exceedingly sparse avian fossil record from the Mesozoic era. The most ancient
phylogenetic divergences among crown birds are known to have occurred in the
Cretaceous period1–3, but stem-lineage representatives of the deepest subclades of
crown birds—Palaeognathae (ostriches and kin), Galloanserae (landfowl and
waterfowl) and Neoaves (all other extant birds)—are unknown from the Mesozoic era.
As a result, key questions related to the ecology4,5, biogeography3,6,7 and divergence
times1,8–10 of ancestral crown birds remain unanswered. Here we report a new
Mesozoic fossil that occupies a position close to the last common ancestor of
Galloanserae and fills a key phylogenetic gap in the early evolutionary history of
crown birds10,11. Asteriornis maastrichtensis, gen. et sp. nov., from the Maastrichtian
age of Belgium (66.8–66.7 million years ago), is represented by a nearly complete,
three-dimensionally preserved skull and associated postcranial elements. The fossil
represents one of the only well-supported crown birds from the Mesozoic era12, and is
the first Mesozoic crown bird with well-represented cranial remains. Asteriornis
maastrichtensis exhibits a previously undocumented combination of galliform
(landfowl)-like and anseriform (waterfowl)-like features, and its presence alongside a
previously reported Ichthyornis-like taxon from the same locality13 provides direct
evidence of the co-occurrence of crown birds and avialan stem birds. Its occurrence in
the Northern Hemisphere challenges biogeographical hypotheses of a Gondwanan
origin of crown birds3, and its relatively small size and possible littoral ecology may
corroborate proposed ecological filters4,5,9 that influenced the persistence of crown
birds through the end-Cretaceous mass extinction.

Strisores is a clade of neoavian birds that include diurnal aerial specialists such as swifts and hummingbirds, as well as several predominantly nocturnal lineages such as nightjars and potoos. Despite the use of genome-scale molecular datasets, the phylogenetic interrelationships among major strisorean groups remain controversial. Given the availability of next-generation sequence data for Strisores and the clade's rich fossil record, we reassessed the phylogeny of Strisores by incorporating a large-scale sequence dataset with anatomical data from living and fossil strisoreans within a Bayesian total-evidence framework. Combined analyses of molecular and morphological data resulted in a phylogenetic topology for Strisores that is congruent with the findings of two recent molecular phylogenomic studies, supporting nightjars (Caprimulgidae) as the extant sister group of the remainder of Strisores. This total-evidence framework allowed us to identify morphological synapomorphies for strisorean clades previously recovered using molecular-only datasets. However, a combined analysis of molecular and morphological data highlighted strong signal conflict between sequence and anatomical data in Strisores. Furthermore, simultaneous analysis of molecular and morphological data recovered differing placements for some fossil taxa compared with analyses of morphological data under a molecular scaffold, highlighting the importance of analytical decisions when conducting morphological phylogenetic analyses of taxa with molecular phylogenetic data. We suggest that multiple strisorean lineages have experienced convergent evolution across the skeleton, obfuscating the phylogenetic position of certain fossils, and that many distinctive specializations of strisorean subclades were acquired early in their evolutionary history. Despite this apparent complexity in the evolutionary history of Strisores, our results provide fossil support for aerial foraging as the ancestral ecological strategy of Strisores, as implied by recent phylogenetic topologies derived from molecular data.

Fossil bird remains from the Pliocene hominin-bearing locality of Kanapoi comprise >100 elements representing at least 10 avian families, including previously undescribed elements referred to the 'giant' Pliocene marabou stork Leptoptilos cf. falconeri. The taxonomic composition of the Kanapoi fossil avifauna reveals an assemblage with a substantial aquatic component, corroborating geological evidence of this locality's close proximity to a large, slow-moving body of water. Both the taxonomic composition and relative abundance of avian higher-level clades at Kanapoi stand in stark contrast to the avifauna from the slightly older (~4.4 Ma vs. 4.2 Ma) hominin-bearing Lower Aramis Member of Ethiopia, which has been interpreted as representing a mesic woodland paleoenvironment far from water. In general, the taxonomic composition of the Kanapoi avifauna resembles that from the Miocene hominoid-bearing locality of Lothagam (though Kanapoi is more diverse), and the aquatic character of the Kanapoi avifauna supports the idea that the environmental conditions experienced by Australopithecus anamensis at Kanapoi were markedly different from those experienced by Ardipithecus ramidus at Aramis. Additionally , the relative abundance of marabou stork (Leptoptilos) remains at Kanapoi may suggest a long-standing commensal relationship between total-clade humans and facultatively scavenging marabous. Additional avian remains from nearby fossil localities (e.g., the Nachukui Formation), ranging in age from 3.26 to 0.8 Ma, reveal the long-term persistence of an aquatic avifauna in the region.

Transitional fossils informing the origin of turtles are among the most sought-after discoveries in palaeontology. Despite strong genomic evidence indicating that turtles evolved from within the diapsid radiation (which includes all other living reptiles), evid- ence of the inferred transformation between an ancestral turtle with an open, diapsid skull to the closed, anapsid condition of modern turtles remains elusive. Here we use high-resolution com- puted tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil rep- tile from the Karoo Basin of South Africa, whose distinctive post- cranial skeleton shares many unique features with the shelled body plan of turtles. Scepticism regarding the status of Eunotosaurus as the earliest stem turtle arises from the possibility that these shell-related features are the products of evolutionary convergence. Our phylogenetic analyses indicate strong cranial support for Eunotosaurus as a critical transitional form in turtle evolution, thus fortifying a 40-million-year extension to the turtle stem and moving the ecological context of its origin back onto land. Furthermore, we find unexpected evidence that Eunotosaurus is a diapsid reptile in the process of becoming secondarily anapsid. This is important because categorizing the skull based on the number of openings in the complex of dermal bone covering the adductor chamber has long held sway in amniote systematics10, and still represents a common organizational scheme for teaching the evolutionary history of the group. These discoveries allow us to articulate a detailed and testable hypothesis of fenestral closure along the turtle stem. Our results suggest that Eunotosaurus represents a crucially important link in a chain that will eventually lead to consilience in reptile systematics, paving the way for syn- thetic studies of amniote evolution and development.

Background: The highly derived morphology and astounding diversity of snakes has long inspired debate regarding the ecological and evolutionary origin of both the snake total-group (Pan-Serpentes) and crown snakes (Serpentes). Although speculation abounds on the ecology, behavior, and provenance of the earliest snakes, a rigorous, clade-wide analysis of snake origins has yet to be attempted, in part due to a dearth of adequate paleontological data on early stem snakes. Here, we present the first comprehensive analytical reconstruction of the ancestor of crown snakes and the ancestor of the snake total-group, as inferred using multiple methods of ancestral state reconstruction. We use a combined-data approach that includes new information from the fossil record on extinct crown snakes, new data
on the anatomy of the stem snakes Najash rionegrina, Dinilysia patagonica, and Coniophis precedens, and a deeper understanding of the distribution of phenotypic apomorphies among the major clades of fossil and Recent snakes. Additionally, we infer time-calibrated phylogenies using both new ‘tip-dating’ and traditional node-based approaches, providing new insights on temporal patterns in the early evolutionary history of snakes.
Results: Comprehensive ancestral state reconstructions reveal that both the ancestor of crown snakes and the ancestor of total-group snakes were nocturnal, widely foraging, non-constricting stealth hunters. They likely consumed soft-bodied vertebrate and invertebrate prey that was subequal to head size, and occupied terrestrial settings in warm, well-watered, and well-vegetated environments. The snake total-group – approximated by the Coniophis node – is inferred to have originated on land during the middle Early Cretaceous (~128.5 Ma), with the crown-group following about 20 million years later, during the Albian stage. Our inferred divergence dates provide strong evidence for a major radiation of henophidian snake diversity in the wake of the Cretaceous-Paleogene (K-Pg) mass extinction, clarifying the pattern and timing of the extant snake radiation. Although the snake crown-group most likely arose on the supercontinent of Gondwana, our results suggest the possibility that the snake total-group originated on Laurasia.
Conclusions: Our study provides new insights into when, where, and how snakes originated, and presents the most complete picture of the early evolution of snakes to date. More broadly, we demonstrate the striking influence of including fossils and phenotypic data in combined analyses aimed at both phylogenetic topology inference and ancestral state reconstruction.
Keywords: Serpentes, Phylogeny, Ancestral state reconstruction, Divergence time estimation, Combined analysis, Fossil tip-dating

The geometry of feather barbs (barb length and barb angle) determines feather vane asymmetry and vane rigidity, which are both critical to a feath- er’s aerodynamic performance. Here, we describe the relationship between barb geometry and aerodynamic function across the evolutionary history of asymmetrical flight feathers, from Mesozoic taxa outside of modern avian diversity (Microraptor, Archaeopteryx, Sapeornis, Confuciusornis and the enantiornithine Eopengornis) to an extensive sample of modern birds. Contrary to previous assumptions, we find that barb angle is not related to vane-width asymmetry; instead barb angle varies with vane function, whereas barb length variation determines vane asymmetry. We demonstrate that barb geometry significantly differs among functionally distinct portions of flight feather vanes, and that cutting-edge leading vanes occupy a distinct region of morphospace characterized by small barb angles. This cutting-edge vane morphology is ubiquitous across a phylogenetically and functionally diverse sample of modern birds and Mesozoic stem birds, revealing a funda- mental aerodynamic adaptation that has persisted from the Late Jurassic. However, in Mesozoic taxa stemward of Ornithurae and Enantiornithes, trailing vane barb geometry is distinctly different from that of modern birds. In both modern birds and enantiornithines, trailing vanes have larger barb angles than in comparatively stemward taxa like Archaeopteryx, which exhibit small trailing vane barb angles. This discovery reveals a previously unrecognized evolutionary transition in flight feather morphology, which has important implications for the flight capacity of early feathered theropods such as Archaeopteryx and Microraptor. Our findings suggest that the fully modern avian flight feather, and possibly a modern capacity for powered flight, evolved crownward of Confuciusornis, long after the origin of asymmetrical flight feathers, and much later than previously recognized.

"Understanding the phylogenetic position of
crown turtles (Testudines) among amniotes has been a source
of particular contention. Recent morphological analyses
suggest that turtles are sister to all other reptiles, whereas
the vast majority of gene sequence analyses support turtles as
being inside Diapsida, and usually as sister to crown
Archosauria (birds and crocodilians). Previously, a study
using microRNAs (miRNAs) placed turtles inside diapsids, but as
sister to lepidosaurs (lizards and Sphenodon) rather than
archosaurs. Here, we test this hypothesis with an expanded
miRNA presence/absence dataset, and employ more rigorous
criteria for miRNA annotation. Significantly, we find no support
for a turtleþlepidosaur sister‐relationship; instead, we recover
strong support for turtles sharing a more recent common
ancestor with archosaurs. We further test this result by
analyzing a super‐alignment of precursor miRNA sequences
for every miRNA inferred to have been present in the most
recent common ancestor of tetrapods. This analysis yields a
topology that is fully congruent with our presence/absence
analysis; our results are therefore in accordance with most
gene sequence studies, providing strong, consilient molecular
evidence from diverse independent datasets regarding the
phylogenetic position of turtles."