Prum, R.O., Berv, J.S., Dornburg, A., Field, D.J., Townsend,
J.P, Lemmon, E.M., Lemmon, A.R. A comprehensive
phylogeny of birds using targeted next-generation DNA
sequencing. Nature 526: 569-573. doi:10.1038/nature15697.
Summary: The origin of Earth’s incredible diversity of birdlife
has been the subject of intense research. However, the
apparently rapid pace of the extant avian radiation has greatly
obscured the evolutionary interrelationships of many groups
of modern birds. Here, we evaluate avian phylogeny using
an unprecedented sample of living birds (198 species), and
259 phylogenetically informative genetic markers obtained
through Anchored Phylogenomics. Our results shed new
light on avian interrelationships, and are consistent with the
idea that birds underwent a rapid radiation in the wake of
the Cretaceous-Paleogene mass extinction. This extinction event
apparently wiped out the entire dinosaurian clade, with the exception of the earliest
branches of the extant avian tree of life.
Bever, G.S., Lyson, T.R., Field, D.J., Bhullar, B.-A.S. 2015.
Evolutionary origin of the turtle skull. Nature 525: 239-242.
doi:10.1038/nature14900.
Summary: The evolutionary origin of turtles has emerged as
a topic of extreme contention in vertebrate systematics.
Phylogenetic analyses of molecular sequence data
consistently group turtles in an exclusive clade with birds and
crocodilians, suggesting that turtles evolved from ancestors
exhibiting an anatomically ‘diapsid’ skull. However, the skulls
of turtles exhibit no temporal openings, and instead resemble
the condition of early stem amniotes, supporting
a phylogenetic position that is inconsistent with the molecular
signal. Here, we demonstrate that the earliest-known stem
turtle, Eunotosaurus, does in fact exhibit an anatomically diapsid
skull. These results reconcile the phylogenetic position of turtles
as the descendents of anatomically diapsid animals, and reveal that the ‘closed’ skull of
modern turtles reflects the convergent loss of temporal openings, rather than the
plesiomorphic amniote condition.
Feo, T.J., Field, D.J., Prum, R.O. 2015. Barb geometry of
asymmetrical feathers reveals a transitional morphology
in the evolution of avian flight. Proceedings
of the Royal Society B 282: 20142864.
[Winner of the 2015 G.G. Simpson Prize]
Summary: The flight feathers of Mesozoic bird-like dinosaurs,
such as Archaeopteryx and Confuciusornis, have
always been assumed to be identical to those of modern
birds (such as those of the Anhinga, pictured), implying
150 million years of evolutionary stasis. Using an
unprecedentedly large sample of modern bird feathers and
statistical analysis, we discovered that the microstructure
of Mesozoic fossil feathers differs substantially from
that of modern birds. Our results illustrate fundamental insights
into the architecture of modern asymmetrical feathers, and show that modern feathers
arose much later in avian evolutionary history than has been traditionally assumed.
Field, D.J., Leblanc, A., Gau, A., Behlke, A.D. 2015. Pelagic
neonatal fossils support viviparity and precocial life history
of Cretaceous mosasaurs. Palaeontology 58(3): 401-407.
doi: 10.1111/pala.12165.
Summary: Mosasaurs were a successful group of gigantic
marine lizards that lived at the time of the dinosaurs. They
flourished in ancient seas, and their remains are particularly
diverse and abundant in modern day Kansas. Although many
aspects of mosasaur biology have been studied in detail,
little was known about the breeding biology of these iconic
animals due to a lack of baby mosasaur fossils. This study
describes the youngest mosasaur specimens yet found, which illustrate that baby
mosasaurs were likely born alive in the open ocean, fully capable of surviving in a marine
environment. These findings improve our understanding of the early life history of
mosasaurs–shedding new light on the biology of animals that went extinct 66 million
years ago.
Hsiang, A.Y., Field, D.J., Webster, T.H., Belker, A.D., Davis,
M., Racicot, R.A., Gauthier, J.A. 2015. The origin of snakes:
Revealing the ecology, behavior, and evolutionary history
of early snakes using genomics, phenomics, and the fossil
record. BMC Evolutionary Biology 15:87.
doi:10.1186/a12862-015-0358-5. [Winner of the 2016
G.G. Simpson Prize]
Summary: The iconic body plan and diversity of living snakes
has always stimulated interest in the evolutionary origins of
this fascinating clade. In this study, we perform a suite of
phylogenetic analyses incorporating genomic data, critical
fossils, and modern snake anatomy to reveal the evolutionary
interrelationships of snakes, as well as comprehensive
analytical reconstructions of ancestral states. Our analyses
suggest that the most recent common ancestor of snakes, as well as the earliest stem
group relatives of snakes, were nocturnal, widely foraging, non-constricting stealth
hunters. These data reveal new details about the origins of snakes–one of the most
diverse and charismatic groups of terrestrial vertebrates.
Snow, S.S, Field, D.J., Musser, J.M. 2015. Competitive
interactions in Grallaria antpittas: observations at a feeder.
Bulletin of the Peabody Museum of Natural History 56(1): 89-93.
Summary: The Jocotoco Antpitta (pictured) is an extremely
rare and little-known bird that was first discovered in 1999.
While visiting the antpitta’s native habitat in remote southern
Ecuador, we observed previously undocumented aggressive
behavior between this species and a close relative, revealing
new insights into the behavioral ecology of antpittas, an
elusive clade of tropical birds in need of more study.
Field, D.J., Gauthier, J.A.G., King, B.L., Pisani, D., Lyson,
T.R.L., Peterson, K.J. 2014. Toward consilience in reptile
phylogeny: miRNAs support an archosaur, not lepidosaur,
affinity for turtles. Evolution & Development 16(4): 189-196.
doi: 10.1111/ede.12081. [Cover]
Summary: Inferring the evolutionary relationships
of living reptiles has become one of the defining zoological
problems of the early 21st Century. Despite intensive
efforts on the part of paleontologists, morphologists, and
molecular systematists, no less than three mutually exclusive
hypotheses regarding the phylogenetic position of turtles
relative to other reptiles have recently been put forward.
Perhaps the most distressing aspect of this debate is the fact
that congruence has been elusive even within molecular
datasets: microRNAs (miRNAs) have recently been suggested
to uphold a turtle-lepidosaur (lizards, snakes, and tuatara)
clade, while most gene sequence analyses have suggested that turtles are the sister
group of archosaurs (birds and crocodilians). Here, we generated new miRNA data, and
reanalyzed the recently published data suggesting a turtle-lepidosaur sister-relationship.
Amazingly, we find that these data in fact strongly support a turtle-archosaur clade
(contrary to the original study), which provides some much-sought congruence
among molecular phylogenetic hypotheses. Although fossil and anatomical studies
continue to indicate that turtles are the sister taxon to all diapsid reptiles, our results
represent an important step towards establishing a congruent hypothesis for the
interrelationships of these fascinating animals.
Field, D.J., Lynner, C., Brown, C., Darroch, S.A.F. 2013.
Skeletal correlates for body mass estimation in modern and
fossil flying birds. PLoS ONE 8(11): e82000.
doi: 10.1371/journal.pone.0082000.
Summary: Accurate estimates of body mass are critical to
paleobiological inference, since many important biological
parameters covary with body size. Such parameters include
relative encephalization, metabolic rate, and locomotor function.
However, few prior studies have explicitly provided upper and
lower prediction intervals associated with avian body mass
regressions, preventing the incorporation of uncertainty in fossil
body mass estimates, and therefore rendering many inferences
regarding mass-dependent parameters overly confident. Here,
we provide thirteen different regressions for estimating body
mass in fossil flying birds that explicitly incorporate statistical
measurements of uncertainty, and suggest that shoulder
dimensions provide particularly accurate estimates of body mass
in flying birds, such as the Black-capped Petrel pictured here.
Mcnamara, M.E., Briggs, D.E.G., Orr, P.J., Field, D.J.,
Wang, Z. 2013. Experimental maturation of feathers:
implications for reconstructions of fossil feather colour.
Biology Letters 9: 20130184.
Summary: Recent advances have indicated that clues to the
original colour of ancient feathered organisms can be
discerned from the shape of microscopic pigment grains,
called melanosomes. However, the response of feather
colour to the high pressures and temperatures experienced
during fossilization had never been examined. Here, we
performed a series of experiments investigating the effects
of high pressure and temperature on fossil feather
preservation, and discovered that certain hints of original
feather colour (like the brilliant colours of the
Velvet-purple Coronet pictured) may be irrevocably altered during fossilization.
Field, D.J., D’Alba L., Vinther, J., Webb, S.M., Gearty, W.,
Shawkey, M.D. 2013. Melanin concentration gradients in
modern and fossil feathers. PLoS ONE 8(3): e59451.
doi: 10.1371/journal.pone.0059451.
[Winner of the 2013 G.G. Simpson Prize]
Summary: Although many complex pigmentation patterns
exhibited by bird feathers have been studied in detail, the
evolution of simple within-feather colour gradients had not.
In this study, we present new methods for quantifying the
original tone of melanin-pigmented feathers in the fossil
record, by assessing the concentration of pigment bearing
organelles within modern and fossil feathers. We also
discovered that feather darkness gradients are most
commonly exhibited by aquatic birds (such as the Atlantic
Puffin pictured here), indicating that a melanized feather tip coupled with an
unmelanized feather base may represent a specialization associated with heat retention
or buoyancy regulation.
Longrich, N.R., Field, D.J. 2012. Torosaurus is not Triceratops:
Ontogeny in chasmosaurine ceratopsids as a case study in
dinosaur taxonomy. PLoS ONE 7(2): e32623.
doi:10.1371/journal.pone.0032623.
Summary: Dinosaur taxonomy is complicated by the fact
that many species undergo radical skeletal transformations
throughout life. This fact has led to debate regarding the
taxonomic status of Torosaurus, with certain authors arguing
that Torosaurus represents the mature morphology of
Triceratops. Here, we provide evidence that supports the
view that Torosaurus and Triceratops are in fact distinct
dinosaur taxa, by outlining a repeatable, explicit protocol
for assessing putative cases of taxonomic synonymy in the
fossil record.
Longrich, N., Tokaryk, T., Field, D.J. 2011. Mass extinction
of birds at the Cretaceous-Paleogene (K-Pg) boundary.
Proceedings of the National Academy of Sciences
108(37):15253-15257.
Summary: Fossil beds from the latest Cretaceous (~65
million years ago) are found throughout western North
America. These beds boast a diverse array of fossil bird
bones; however, their fragmentary nature had previously
discouraged workers from studying them in detail. In this
study, we were able to refer many of these bones to lineages
of extinct, archaic birds. The appearance of these lineages in
the latest Cretaceous (and their complete absence from
more recent deposits) strongly argues for a major mass
extinction of archaic birds at the K-Pg (formerly K-T)
boundary, resolving a longstanding debate, and emphasizing
the devastating effects of the end-Cretaceous mass extinction on virtually every biotic
component of terrestrial ecosystems.
Field, D.J., Ben-Zvi, M., Lin, S.C., Goldbogen, J.A.,
Shadwick, R.E. 2011. Convergent evolution in rorqual
whales and pelicans driven by similar feeding mechanics.
The Anatomical Record 294:1273-1282. [Cover]
Summary: Rorqual whales and pelicans feed by engulfing
large volumes of food-laden water in their mouths, and
filtering out their prey. These animals exhibit a number of
anatomical similarities related to feeding, but the mechanics
of engulfment feeding in these groups had never previously
been compared. We developed a computer program called
BendCT that enabled us to non-invasively examine the
mechanical properties of rorqual and pelican jaws through
CT scanning. We discovered that the jaws of rorquals and
pelicans exhibit similar mechanical specializations related to
engulfment feeding, demonstrating a previously unappreciated
level of convergence in these groups.
Field, D.J., Campbell-Malone, R., Goldbogen, J.A., Shadwick, R. 2010. Quantitative
computed tomography of humpback whale (Megaptera novaeangliae) mandibles:
mechanical implications for rorqual lunge-feeding.
The Anatomical Record 293:1240-1247.
Summary: The feeding method of rorqual whales, termed
engulfment or ‘lunge’ feeding, has been described as the largest
biomechanical event in the animal kingdom. These whales
approach a school of small fish or krill at high speed, open their
mouths to extreme angles, and inflate a huge, extensible pouch
between their jaws in order to engulf a mass of water that can
approach their own body size. This process exerts extreme drag
on the pouch, which causes strong downward bending forces on
a whale’s lower jaws. By examining the pattern of bone density
and shape variation in rorqual jaws, we discovered that these
bones exhibit a specialized mechanical design that resists downward bending forces to
protect themselves from breakage.
