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Birds are the only living amniotes with coloured eggs1-4, which have long been considered to be an avian innovation1,3. A recent study has demonstrated the presence of both red-brown protoporphyrin IX and blue-green biliverdin5-the pigments responsible for all the variation in avian egg colour-in fossilized eggshell of a nonavian dinosaur6. This raises the fundamental question of whether modern birds inherited egg colour from their nonavian dinosaur ancestors, or whether egg colour evolved independently multiple times. Here we present a phylogenetic assessment of egg colour in nonavian dinosaurs. We applied high-resolution Raman microspectroscopy to eggshells that represent all of the major clades of dinosaurs, and found that egg colour pigments were preserved in all eumaniraptorans: egg colour had a single evolutionary origin in nonavian theropod dinosaurs. The absence of colour in ornithischian and sauropod eggs represents a true signal rather than a taphonomic artefact. Pigment surface maps revealed that nonavian eumaniraptoran eggs were spotted and speckled, and colour pattern diversity in these eggs approaches that in extant birds, which indicates that reproductive behaviours in nonavian dinosaurs were far more complex than previously known3. Depth profiles demonstrated identical mechanisms of pigment deposition in nonavian and avian dinosaur eggs. Birds were not the first amniotes to produce coloured eggs: as with many other characteristics7,8 this is an attribute that evolved deep within the dinosaur tree and long before the spectacular radiation of modern birds.
| Egg colour reconstruction. a, Top, eggshell-pigment surface maps. n = 8; selection criteria were pigment presence (Fig. 1) and sufficient surface exposure. Protoporphyrin was mapped (1,350 cm −1 ± 2 cm −1 , 2 accumulations, 5 s of exposure) with three independent repetitions, which yielded similar results. Increased signal intensity (yellow) is relative to the lowest signal intensity (black, which equals background noise in the absence of protoporphyrin IX). Bottom, egg reconstructions that combine information from panels above, b and Fig. 1 into a range of potential colours for the fossil eggshells. From left to right: H. huangi, Mongolian microtroodontid (MAE 14-40), Mongolian troodontid (AMNH FARB 6631), Mongolian troodontid (IGM 100/1003), D. antirrhopus, Mongolian enantiornithine, D. novaehollandiae and G. domesticus. b, Pigment depth profiles across vertical sections of eggs from A. mississipiensis, plus the taxa shown in a (n = 9 specimens). Depth profiles were repeated three times independently, which yielded similar results. Photographs and depth profiles are not at the same scale. The distribution of protoporphyrin IX (red), biliverdin (blue) and proteinaceous matter (grey) is based on Raman point measurements and line maps (1,166 cm −1 ± 2 cm −1 ). Droplet icons indicate pigment elution. oc, organic cuticle; mc, mineralized cuticle; pz, prismatic zone; mt, membrana testacea. c, Visualization of gradual colour change of eggshell pigments and proteinaceous matter through time, based on observations of eggshells (D. novaehollandiae and Casuarius casuarius) and on a previous study 26 .
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Dinosaur egg colour had a single evolutionary origin
Jasmina Wiemann1*, Tzu-Ruei Yang2 & Mark A. Norell3
Birds are the only living amniotes with coloured eggs
, which have
long been considered to be an avian innovation
. A recent study
has demonstrated the presence of both red-brown protoporphyrin
IX and blue-green biliverdin5—the pigments responsible for
all the variation in avian egg colour—in fossilized eggshell of
a nonavian dinosaur6. This raises the fundamental question of
whether modern birds inherited egg colour from their nonavian
dinosaur ancestors, or whether egg colour evolved independently
multiple times. Here we present a phylogenetic assessment of egg
colour in nonavian dinosaurs. We applied high-resolution Raman
microspectroscopy to eggshells that represent all of the major clades
of dinosaurs, and found that egg colour pigments were preserved
in all eumaniraptorans: egg colour had a single evolutionary
origin in nonavian theropod dinosaurs. The absence of colour in
ornithischian and sauropod eggs represents a true signal rather
than a taphonomic artefact. Pigment surface maps revealed that
nonavian eumaniraptoran eggs were spotted and speckled, and
colour pattern diversity in these eggs approaches that in extant birds,
which indicates that reproductive behaviours in nonavian dinosaurs
were far more complex than previously known3. Depth profiles
demonstrated identical mechanisms of pigment deposition in
nonavian and avian dinosaur eggs. Birds were not the first amniotes
to produce coloured eggs: as with many other characteristics7,8 this
is an attribute that evolved deep within the dinosaur tree and long
before the spectacular radiation of modern birds.
The huge diversity of avian egg colour
has previously been attributed
to the exploration of empty ecological niches after the extinction of
nonavian dinosaurs at the terminal Cretaceous event1. Different nesting
environments, as well as nesting behaviours, are thought to influence
egg colour1012. Egg colour may reflect selective pressure as a result of
an ecological interaction between the egg producer and an egg pred-
ator (camouflage) or parasite (egg recognition). Avian egg colour has
previously been shown to react in a plastic fashion to changes in the
incubation strategy or climate, or even in mating behaviour
However, all previously proposed selective factors rely on the fact that
the eggs are exposed to the environment
and, with scant exception,
not buried or covered. More-recent research suggests that egg colour
may have co-evolved with (partially) open nesting habits in nonavian
dinosaurs6 but offers only a single data point of egg colour outside
crown birds, in open-nesting oviraptorid dinosaurs. Information on
eggshell pigments in a larger sample of nonavian dinosaurs is required
to understand the evolution of egg colour.
Both eggshell pigments—biliverdin and protoporphyrin IX—are
tetrapyrroles with minor structural differences that affect their chemi-
cal properties and their distribution across the eggshell
. In contrast
to the more hydrophilic biliverdin, which extends deep into the pris-
matic zone of the eggshell, the more hydrophobic protoporphyrin—
which causes spots and speckles—is restricted to the waxy cuticle21,23.
The different solubility properties of biliverdin and protoporphyrin
appear to be key to their preservation potential
. Protoporphyrin
is more resilient to elution than biliverdin but both pigments are
preserved in detectable trace amounts
. Eggshell pigments appear to
be restricted, if not bound, to the proteinaceous scaffold of the eggshell
Proteins transform during diagenesis into pyrrole-, pyridine- and
imidazole-rich polymers through oxidative crosslinking
; the resulting
protein fossilization products (PFPs) appear similar to biliverdin and
protoporphyrin IX in their chemical composition. Raman spectros-
copy distinguishes between true egg-colour pigments and pigment-like
(Extended Data Fig.1), and identifies and maps out pigments
over eggshell surfaces and across vertical egg sections to characterize
colour patterns and pigment deposition in fossil eggs. Placing this
information in a phylogenetic context offers insights into whether
egg colour evolved once within nonavian dinosaurs or multiple times
independently, and might help to identify selective factors.
In our sample of nineteen archosaur eggshells, egg colour pigments
are absent in eggshells of Alligator mississipiensis, the North American
hadrosaurid Maiasaura peeblesorum, the South American saltasaurid,
the French titanosaurid and the North American troodontid (Fig.1,
Extended Data Figs.2, 3). Egg colour pigments are preserved in
eggshells from the oviraptorid Heyuannia huangi, Mongolian micro
troodontids, the Chinese and Mongolian troodontids, the dromaeo-
saurid Deinonychus antirrhopus, the Mongolian enantiornithine,
Psammornis rothschildi, Rhea americana, the North American ratite,
Dromaius novaehollandiae and Gallus domesticus (Fig.1, Extended
Data Figs.2, 3).
Only biliverdin was detected in D. novaehollandiae, whereas only
protoporphyrin IX was present in the eggshells of the Mongolian
microtroodontid (MAE 14-40(specimen codes in parentheses)), the
Chinese and Mongolian troodontids, the Mongolian enantiornithine,
P. rothschildi and G. domesticus. Both egg colour pigments were
detected in eggshells from H. huangi, the Mongolian microtroodon-
tid (IGM 100/1323) and macrotroodontid (AMNH FARB 6631),
D. antirrhopus, R. americana and the North American ratite. The
presence of eggshell pigments corresponds to (partially) open nesting
habits (Fig.1).
All eggshell and associated sediment samples were plotted on a whole
spectra-based principal component analysis (PCA) (Extended Data
Fig.4 and its Source Data). Principal component 1 (PC1, 57.118%)
represents variability in pigment type, concentration and mode of egg
shell alteration, whereas principal component 2 (PC2, 23.841%) sep-
arates samples into unpigmented and pigmented eggshells (Extended
Data Fig.5). The PCA (Extended Data Fig.4a) revealed that eggshell
biomolecules are distinct from organic material in the sediment, with
both clusters separating across PC1 (73.116%). Within the eggshell
cluster, extant and fossil materials are separated across PC2 (10.977%)
(Extended Data Fig.4a). A separate PCA (Extended Data Fig.4b) based
on the spectral fingerprint region of biliverdin and protoporphyrin IX
± 2cm
) included all fossil eggshell sam-
ples: the resulting chemo-space identified a characteristic cluster of
pigmented eggshells, distinct from a separate cluster of unpigmented
eggshells. Mapping protoporphyrin IX on the eggshell surface (Fig.2a)
demonstrated that the eggs of H. huangi were spotted, as were those
of the Mongolian microtroodontids and troodontids, D. antirrhopus,
and the Mongolian enantiornithine. Reconstructions of the egg colours
are shown in Fig.2a.
Depth profiles (Fig.2b) across vertical eggshell sections show that
pigments are absent in all layers of the A. mississipiensis eggshell as
1Department of Geology & Geophysics, Yale University, New Haven, CT, USA. 2Steinmann Institute for Geology, Mineralogy, and Paleontology, University of Bonn, Bonn, Germany. 3Division of
Vertebrate Paleontology, American Museum of Natural History, New York, NY, USA. *e-mail:
22 NOVEMBER 2018 | VOL 563 | NATURE | 555
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... Further studies on fossils use chemical imaging techniques such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy to search for chemical signals, e.g., of functional groups (e.g., amide or carbonyl group) in the samples [9,21,32]. FTIR excites the vibrations of chemical bonds using infrared irradiation. Each type of chemical bond will absorb infrared (IR) waves in a distinct wave number range in the near-IR (12,500-4000 cm −1 ), mid-IR (4000-400 cm −1 ), or far-IR (400-10 cm −1 ) regions. ...
... The produced signals are weak, often requiring prolonged periods of intense irradiation [48], which can lead to a degradation of thermolabile compounds due to the heat produced by the laser [32,49]. Raman spectroscopy has been used for the detection of heme in dinosaur bones [18] and for the detection of the heme degradation product biliverdin and of its precursor protoporphyrin IX in dinosaur eggshells [21]. ...
... (I) Djadokhta Formation, Mongolia [23]. (J) Hell Creek Formation, eastern Montana, USA [18][19][20] (K) Chinese provinces (Henan, Jiangxi, and Guangdong) [21,22]. Concept adapted from reference [76]. ...
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This review provides an overview of organic compounds detected in non-avian dinosaur fossils to date. This was enabled by the development of sensitive analytical techniques. Non-destructive methods and procedures restricted to the sample surface, e.g., light and electron microscopy, infrared (IR) and Raman spectroscopy, as well as more invasive approaches including liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), time-of-flight secondary ion mass spectrometry, and immunological methods were employed. Organic compounds detected in samples of dinosaur fossils include pigments (heme, biliverdin, protoporphyrin IX, melanin), and proteins, such as collagens and keratins. The origin and nature of the observed protein signals is, however, in some cases, controversially discussed. Molecular taphonomy approaches can support the development of suitable analytical methods to confirm reported findings and to identify further organic compounds in dinosaur and other fossils in the future. The chemical properties of the various organic compounds detected in dinosaurs, and the techniques utilized for the identification and analysis of each of the compounds will be discussed.
... [1,2] Applications of non-destructive, in situ Raman microspectroscopy have resulted in rapid progress in understanding biomolecule fossilization and the detection of biosignatures based on comparative statistical analyses of fossil organic matter. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The in situ approach facilitates rapid non-destructive analysis of surface-cleaned samples without requiring time-consuming extractions of the organic matter that may alter fossil molecular compounds. Raman spectroscopy not only characterizes molecular functional groups (small molecular units with distinct chemical properties), but also provides insights into higher-level structural organization by detecting intermolecular and organo-mineral interactions. ...
... [19,[24][25][26][27] A number of advantages, including time-efficient non-destructive analysis, availability and low operating cost of equipment, and the utility of results, make Raman and complementary types of light spectroscopy ideal for molecular tests of hypotheses based on the composition of paleontological and geological materials. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][20][21][22][23] A diversity of studies conducted by different laboratories have recovered similar patterns in the molecular makeup of fossil organic matter in independently acquired in situ Raman spectra. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][20][21][22][23] However, a recent Perspective by Alleon et al. [28] concluded that the biological results of a selected subset of these studies [3,4,6,11,12,15] are compromised, based on their detection of sinusoidal edge filter ripples, i.e., instrumental artefacts, in the Raman data. ...
... [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][20][21][22][23] A diversity of studies conducted by different laboratories have recovered similar patterns in the molecular makeup of fossil organic matter in independently acquired in situ Raman spectra. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][20][21][22][23] However, a recent Perspective by Alleon et al. [28] concluded that the biological results of a selected subset of these studies [3,4,6,11,12,15] are compromised, based on their detection of sinusoidal edge filter ripples, i.e., instrumental artefacts, in the Raman data. [28] The results in the disputed studies are based on the statistical evaluation of in situ Raman spectra obtained in the organic fingerprint region (500-1800 cm −1 ) for a diversity of modern, experimentally matured, and fossil tissues covering all major branches of extinct and modern invertebrates and vertebrates, as well as sedimentary host rocks, and represent the first large-scale explorative studies of their kind in the geosciences. ...
A recent article argued that signals from conventional Raman spectroscopy of organic materials are overwhelmed by edge filter and fluorescence artefacts. The article targeted a subset of Raman spectroscopic investigations of fossil and modern organisms and has implications for the utility of conventional Raman spectroscopy in comparative tissue analytics. The inferences were based on circular reasoning centered around the unconventional analysis of spectra from just two samples, one modern, and one fossil. We validated the disputed signals with in situ Fourier-Transform Infrared (FT-IR) Spectroscopy and through replication with different lasers, filters, and operators in independent laboratories. Our Raman system employs a holographic notch filter which is not affected by edge filter or other artefacts. Multiple lines of evidence confirm that conventional Raman spectra of fossils contain biologically and geologically meaningful information. Statistical analyses of large Raman and FT-IR spectral data sets reveal patterns in fossil composition and yield valuable insights into the history of life.
... Raman spectroscopy is a well-established method in taphonomy (Bernard et al., 2007;Jehlička, Jorge Villar & Edwards, 2004;Marshall et al., 2012;Thomas et al., 2007;Thomas et al., 2011;Wiemann, Yang & Norell, 2018;Witke et al., 2004). It is useful for assessing the degree of diagenetic alteration to bone (Thomas et al., 2007;Thomas et al., 2011) and Table 1 Materials used in this study. ...
... We also sampled fragments of associated gastralia (not pictured here) (B) Vessel containing spheres as well as non-spherical amorphous vessel fill (grey bracket) in thin section LJ98B-1 (sample area 1; originally prepared for (Yao, Zhang & Tang, 2002)). evaluating the origin of compounds and structures in fossil material (Marshall et al., 2012;Thomas et al., 2014;Wiemann, Yang & Norell, 2018). We employed Raman spectroscopy to test the alternative interpretation of the putative red blood cells as framboids of iron minerals (Martill & Unwin, 1997), and to assess the quality of bone preservation from a diagenetic perspective. ...
... The specimens used herein are accessioned at the IVPP in Beijing with the holotype under the museum number IVPP-V11559. The slide numbers are 2018-X1, 2018-X2, 2018-L1, 2018-L2, 2018-L3, 2018-L4, 2018-L5, HO-9601, HO-9602, LJ98B-1, and LJ98B-4, 2018-1, and 2018. The modern alligator bone sample is from un-accessioned material stored in the Virginia Tech osteology collection. ...
Full-text available
Red to red-orange spheres in the vascular canals of fossil bone thin sections have been repeatedly reported using light microscopy. Some of these have been interpreted as the fossilized remains of blood cells or, alternatively, pyrite framboids. Here, we assess claims of blood cell preservation within bones of the therizinosauroid theropod Beipiaosaurus inexpectus from the Jehol Lagerstätte. Using Raman spectroscopy, Energy Dispersive X-ray Spectrometry, and Time of Flight Secondary Ion Mass Spectroscopy, we found evidence of high taphonomic alteration of the bone. We also found that the vascular canals in the bone, once purported to contain fossil red blood cell, are filled with a mix of clay minerals and carbonaceous compounds. The spheres could not be analyzed in isolation, but we did not find any evidence of pyrite or heme compounds in the vessels, surrounding bone, or matrix. However, we did observe similar spheres under light microscopy in petrified wood found in proximity to the dinosaur. Consequently, we conclude that the red spheres are most likely diagenetic structures replicated by the clay minerals present throughout the vascular canals.
... Meanwhile, Raman spectroscopy, as a non-destructive test, has drawn much attention in fossil egg researchers. For example, Raman spectroscopy can be used to identify the chemical composition of fossil eggshell [25], such as the hydroxyapatite (HAP) preserved in the cuticle layer [26], phosphate in the membrane [27], and color-producing pigments [28][29][30], S-to N-heterocycles [31], and amorphous carbon [32]. Moreover, Raman spectroscopy with the deconvolution technique can be used to detect the maximum paleotemperature recorded in eggshells [33]. ...
Full-text available
Pterosaur eggs can offer information about pterosaur reproductive strategies and are extremely precious because only a small number of specimens have been discovered. Previous studies have mainly focused on morphological descriptions of pterosaur eggs and their embryos while the chemical composition of pterosaur eggs has received little attention. The conventional view believed that the eggshell was composed of calcite. However, previous SEM–EDS results for Hamipterus tianshanensis showed that the eggshell contains phosphorus. Therefore, the object of this research is to determine the mineral composition of the eggshell of H. tianshanensis. Two eggs were analyzed by scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM–EDS) and Raman spectroscopy. The SEM–EDS results show that both surface and cross section are porous and characterized by small irregularly shaped particulates. Moreover, the distribution of Ca and P has a strict coincidence in the cross-section of eggshells. Furthermore, neither the intense peaks of calcite nor organic peaks can be observed by Raman spectroscopy in eggshells. Meanwhile, the Raman spectroscopy mapping analysis result shows a sharp and intense peak at approximately 966 cm−1 among the white eggshell, which can be hard evidence that H. tianshanensis eggs are mainly composed of calcium phosphate. Combined with the present of F in the eggshell, it can be inferred that fluorapatite Ca5(PO4)3F is the main mineral. The fluorapatite eggshell can be interpreted in two ways. One explanation is that H. tianshanensis laid apatite-shelled eggs, similar to living Salvator merianae, and the bioapatite transformed to fluorapatite over geological time. Another possible explanation is that the fluorapatite comes from the result of phosphatization of soft egg membrane tissues through taphonomic processes, indicating that H. tianshanensis might have laid soft eggs. Regardless, the results show that fluorapatite, rather than calcite is the main preserved mineral composition of H. tianshanensis eggshell, correcting the previous view. This study contributes to the present understanding of the mineral composition of pterosaur eggshells and may offer some insight into the pterosaur reproduction pattern.
... Furthermore, Norell and colleagues (2020) used Raman Spectroscopy to characterize protein fossilization products (PFPs) in the eggshell of Mussaurus patagonicus. This new approach was developed by Wiemann and colleagues (Wiemann et al. 2018a) and was also used to determine the lack of external coloration in the eggs from Auca Mahuevo (Wiemann et al. 2018b), although some critics have been raised concerning these applications (see Sect. 3.4 for discussion). ...
The South American sauropodomorph egg record is unrivaled in its richness, with Jurassic and Early and Late Cretaceous eggshell occurrences of up to six different oospecies, included in the oofamilies Megaloolithidae, Fusioolithidae and, probably, Faveoloolithidae, and the oldest putative soft-shelled eggs of the fossil record. In addition, numerous clutches, some nests, exquisitely preserved embryos with skin impressions, and delicate embryological structures such as the egg tooth, and perinatal individuals of stem sauropodomorphs have been reported from South America. Thus, it represents one of the most complete oological and developmental records of an extinct clade and provides a unique opportunity to explore its palaeobiology and palaeoecology. In this chapter, the reader will find a detailed revision of the egg-bearing localities of South America, combined with a critical review of all specimens previously referred to as sauropodomorph taxa and parataxa. Detailed account of the impressive sauropodomorph embryo record is provided. Finally, the different Argentinean nesting grounds are discussed in their paleoenvironmental context, to provide an updated picture of the nesting strategies and reproductive traits of South American sauropodomorphs.
... Non-avian theropods possess a mixture of reproductive features, including some that are avian-like and seen in today's birds, but others that are inherited from early reptilian ancestors or are unique features restricted to particular extinct dinosaur lineages (Horner, 2000;Zelenitsky, 2006;Yang et al., 2019b). Much of our knowledge on dinosaur reproduction has been developed from the study of eggs and embryos (if preserved), providing us with information on egg morphology and color, nest structure, nesting behavior, and early ontogeny/growth (e.g., Mikhailov, 2014;Tanaka et al., 2015;Wiemann et al., 2018;Yang et al., 2019b;Bi et al., 2021;Reisz et al., 2005;Norell et al., 2001). ...
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Despite the discovery of many dinosaur eggs and nests over the past 100 years, articulated in-ovo embryos are remarkably rare. Here we report an exceptionally preserved, articulated oviraptorid embryo inside an elongatoolithid egg, from the Late Cretaceous Hekou Formation of southern China. The head lies ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg, in a posture previously unrecognized in a non-avian dinosaur, but reminiscent of a late-stage modern bird embryo. Comparison to other late-stage oviraptorid embryos suggests that prehatch oviraptorids developed avian-like postures late in incubation, which in modern birds are related to coordinated embryonic movements associated with tucking — a behavior controlled by the central nervous system, critical for hatching success. We propose that such pre-hatching behavior, previously considered unique to birds, may have originated among non-avian theropods, which can be further investigated with additional discoveries of embryo fossils.
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Birds and mammals independently evolved the highest metabolic rates among living animals¹. Their metabolism generates heat that enables active thermoregulation¹, shaping the ecological niches they can occupy and their adaptability to environmental change². The metabolic performance of birds, which exceeds that of mammals, is thought to have evolved along their stem lineage3–10. However, there is no proxy that enables the direct reconstruction of metabolic rates from fossils. Here we use in situ Raman and Fourier-transform infrared spectroscopy to quantify the in vivo accumulation of metabolic lipoxidation signals in modern and fossil amniote bones. We observe no correlation between atmospheric oxygen concentrations¹¹ and metabolic rates. Inferred ancestral states reveal that the metabolic rates consistent with endothermy evolved independently in mammals and plesiosaurs, and are ancestral to ornithodirans, with increasing rates along the avian lineage. High metabolic rates were acquired in pterosaurs, ornithischians, sauropods and theropods well before the advent of energetically costly adaptations, such as flight in birds. Although they had higher metabolic rates ancestrally, ornithischians reduced their metabolic abilities towards ectothermy. The physiological activities of such ectotherms were dependent on environmental and behavioural thermoregulation¹², in contrast to the active lifestyles of endotherms¹. Giant sauropods and theropods were not gigantothermic9,10, but true endotherms. Endothermy in many Late Cretaceous taxa, in addition to crown mammals and birds, suggests that attributes other than metabolism determined their fate during the terminal Cretaceous mass extinction.
Besides the key role of heme in biology across the whole range of living things in nature, its degradation products (bilirubin and biliverdin) as well as other related linear tetrapyrroles and their derivatives play an enormous role in the regulation of various biological processes, from the simplest organisms to human beings. The primary function of HMOX enzymes is to break the cyclic tetrapyrrolic structure of heme into linear tetrapyrrole biliverdin, releasing ferrous iron and CO as additional products. The role of bilirubin in protection against increased oxidative stress has now been generally accepted, but both bilirubin and biliverdin exert a number of other biological activities with important clinical consequences. These include cell signaling functions, resulting in substantial athero‐protective effects, intermediary metabolism‐modulating, antiproliferative, antimutagenic, antigenotoxic, immunomodulatory, antineurodegenerative, and antiaging activities. Not only bilirubin per se, but also other tetrapyrroles used by humans and present in our environment might have therapeutic potentials.
Our understanding of the early evolution of birds has advanced over the past 2 decades, thanks to an ever-improving fossil record. Extraordinary fossils have revealed new details about the evolution of the avian brain, respiratory system, digestive tract, and reproductive system. Many of the traits most strongly associated with birds first arose in nonavian theropod dinosaurs. Theropods evolved pennaceous feathers, incipient wings, and gliding flight long before modern birds appeared. Birds likewise inherited features such as an expanded forebrain, gizzard, dorsally immobile lung, pigmented eggs, and paternal brooding system from their theropod ancestors. Yet, the earliest birds also retained primitive traits such as teeth, clawed hands, long bony tails, partially buried nests, and slower growth. The evolution of birds was profoundly influence by the Cretaceous–Paleogene mass extinction, which wiped out the previously dominant Enantiornithines (“opposite birds”). This sets the stage for modern birds to radiate into the most diverse major clade of tetrapods.
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Vertebrate hard tissues consist of mineral crystallites within a proteinaceous scaffold that normally degrades post-mortem. Here we show, however, that decalcification of Mesozoic hard tissues preserved in oxidative settings releases brownish stained extracellular matrix, cells, blood vessels, and nerve projections. Raman Microspectroscopy shows that these fossil soft tissues are a product of diagenetic transformation to Advanced Glycoxidation and Lipoxidation End Products, a class of N-heterocyclic polymers generated via oxidative crosslinking of proteinaceous scaffolds. Hard tissues in reducing environments, in contrast, lack soft tissue preservation. Comparison of fossil soft tissues with modern and experimentally matured samples reveals how proteinaceous tissues undergo diagenesis and explains biases in their preservation in the rock record. This provides a target, focused on oxidative depositional environments, for finding cellular-to-subcellular soft tissue morphology in fossils and validates its use in phylogenetic and other evolutionary studies.
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Protoporphyrin (PP) and biliverdin (BV) give rise to the enormous diversity in avian egg coloration. Egg color serves several ecological purposes, including post-mating signaling and camouflage. Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration. Cryptic coloration evolved to match the predominant shades of color found in the nesting environment. Such a selection pressure for the evolution of colored or cryptic eggs should be present in all open nesting birds and relatives. Many birds are open-nesting, but protect their eggs by continuous brooding, and thus exhibit no or minimal eggshell pigmentation. Their closest extant relatives, crocodiles, protect their eggs by burial and have unpigmented eggs. This phylogenetic pattern led to the assumption that colored eggs evolved within crown birds. The mosaic evolution of supposedly avian traits in non-avian theropod dinosaurs, however, such as the supposed evolution of partially open nesting behavior in oviraptorids, argues against this long-established theory. Using a double-checking liquid chromatography ESI-Q-TOF mass spectrometry routine, we traced the origin of colored eggs to their non-avian dinosaur ancestors by providing the first record of the avian eggshell pigments protoporphyrin and biliverdin in the eggshells of Late Cretaceous oviraptorid dinosaurs. The eggshell parataxon Macroolithus yaotunensis can be assigned to the oviraptor Heyuannia huangi based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource.
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Animals achieve camouflage through a variety of mechanisms, of which background matching and disruptive coloration are likely the most common. Although many studies have investigated camouflage mechanisms using artificial stimuli and in lab experiments, less work has addressed camouflage in the wild. Here we examine egg camouflage in clutches laid by ground-nesting Snowy Plovers Charadrius nivosus and Least Terns Sternula antillarum breeding in mixed aggregations at Bahía de Ceuta, Sinaloa, Mexico. We obtained digital images of clutches laid by both species. We then calibrated the images and used custom computer software and edge detection algorithms to quantify measures related to three potential camouflage mechanisms: pattern complexity matching, disruptive effects and background color matching. Based on our image analyses, Snowy Plover clutches, in general, appeared to be more camouflaged than Least Tern clutches. Snowy Plover clutches also survived better than Least Tern clutches. Unexpectedly, variation in clutch survival was not explained by any measure of egg camouflage in either species. We conclude that measures of egg camouflage are poor predictors of clutch survival in this population. The behavior of the incubating parents may also affect clutch predation. Determining the significance of egg camouflage requires further testing using visual models and behavioral experiments.
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The reproductive biology of living birds differs dramatically from that of other extant vertebrates. Although some attributes of modern avian reproduction had their origin within theropod dinosaurs like oviraptors and troodontids, even the most derived non-avian theropods lack key features of modern birds. We review the current knowledge of reproduction in Mesozoic birds and 3 lines of evidence that contribute to our understanding of the evolution of the modern avian reproductive mode: (1) efforts to define the ancestral reproductive condition on the basis of extant birds, (2) the fossil record of non-avian theropod dinosaurs, and (3) the fossil record of reproduction in primitive Mesozoic birds (e.g., Enantiornithes). The fossil evidence from Mesozoic birds and non-avian theropods suggests that reproduction passed through 5 stages from basal theropods to neornithines: (1) pre-maniraptoran theropods, (2) oviraptor-grade maniraptorans, (3) troodontid-grade paravians, (4) Enantiornithes, and (5) basal Neornithes. Major changes occurred incrementally in egg size, shape, and microstructure; in nest form; in incubation method; and in parental care. Reproduction in troodontid theropods concurs with this clade representing the sister taxon to birds. Reproduction in enantiornithine birds included sequential ovulation from a single ovary and oviduct, eggs planted upright within sediments, and incubation by a combination of sediment and attendant adult or eggs fully buried with superprecocial young. Incubation modes of derived non-avian theropods and enantiornithines may have favored paternal care. Significant changes between enantiornithines and neornithines include an additional increase in relative egg size and sediment-free incubation. The latter permitted greater adult-egg contact and likely more efficient incubation. Associated changes also included improved egg shape, egg rotation, and chalazae-the albumin chords that suspend the yolk and facilitate proper embryonic development during rotation. Neornithes are the only Mesozoic clade of Dinosauria to nest completely free of sediment, and this may have played a crucial role in their surviving the K-Pg mass extinction event.
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Coelurosauria is the most diverse clade of theropod dinosaurs. Much of this diversity is present in Paraves—the clade of dinosaurs containing dromaeosaurids, troodontids, and avialans. Paraves has over 160 million years of evolutionary history that continues to the present day. The clade represents the most diverse living tetrapod group (there are over 9000 extant species of Aves—a word used here as synonomous with “bird”), and it is at the root of the paravian radiation, when dromaeosaurids, troodontids, and avialans were diverging from one another, that we find the morphology and soft tissue changes associated with the origin of modern avian flight. Within the first 15 million years of known paravian evolutionary history members of this clade exhibited a difference of nearly four orders of magnitude in body size, a value that is similar to the extreme body size disparity present today in mammalian carnivorans, avians, and varanoid squamates. In this respect, Paraves is an important case study in characterizing the patterns, processes, and dynamics of evolutionary size change. This last point is of particular interest because of the historical significance placed on the role of body size reduction in the origin of powered avian flight.Our study reviews and revises the membership of Dromaeosauridae and provides an apomorphy-based diagnosis for all valid taxa. Of the currently 31 named dromaeosaurid species, we found 26 to be valid. We provide the most detailed and comprehensive phylogenetic analysis of paravians to date in order to explore the phylogenetic history of dromaeosaurid taxa. The general pattern of paravian relationships is explored within the broader context of Coelurosauria with an emphasis on sampling basal avialans, because of their importance for character optimizations at the base of Paraves.A large dataset was constructed by merging two datasets, one examining coelurosaur relationships broadly (based on previous TWiG datasets) and the other examining avialan relationships specifically (Clarke et al., 2006). This merged dataset was then significantly revised and supplemented with novel character analysis focusing on paravian taxa. During character analysis, particular attention was given to basal members of Dromaeosauridae, enigmatic basal paravians such as Jinfengopteryx elegans and Anchiornis huxleyi, and the incorporation of new morphological information from two undescribed troodontid species from the Late Cretaceous of Mongolia. A final dataset of 474 characters scored for 111 taxa was used to address paravian evolution. This dataset is important in that it bridges a phylogenetic gap that had persisted between studies on birds and studies on all other coelurosaurs. Most scorings in this matrix were based on the direct observation of specimens.All most parsimonious trees recovered in the cladistic analysis support the monophyly of Paraves, Troodontidae, Dromaeosauridae, and Deinonychosauria. A new clade of basal troodontids is discovered including two undescribed Mongolian troodontids and Jinfengopteryx elegans. Xiaotingia and Anchiornis form a clade at the base of Troodontidae. Recently proposed relationships within Dromaeosauridae are further supported and a succession of clades from Gondwana and Asia form sister taxa to a clade of Laurasian dromaeosaurids. Avialan monophyly is strongly supported with Archaeopteryx, Sapeornis, Jeholornis, and Jixiangornis forming the successive sister taxa to the Confuciusornis node. This topology supports a more basal position for Sapeornis than previous phylogenetic analyses and indicates a progressive acquisition of a fully “avian” shoulder morphology.
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The tremendous increase in fossil egg and eggshell discoveries throughout the last decade necessitates the establishment of uniform methods for description and for a parataxonomical system for classification of fossil eggs. Principles and applications of fossil egg parataxonomy, which have been developing slowly over the last decades, are summarized in this paper. Adoption of these principles is advocated.A list of all described egg parataxa, ordered into respective oofamilies and oogenera, is presented. A simplified chart shows basic types of eggshell organizations, structural morphotypes, parataxonomical families, and corresponding higher order taxonomic relations. Familial and lower level correlation between fossil vertebrate taxa and egg parataxa are limited to the rare finds of identifiable embryos within their eggs.
Alfred Russel Wallace (1823-1913) is regarded as the co-discoverer with Darwin of the theory of evolution. It was an essay which Wallace sent in 1858 to Darwin (whom he greatly admired and to whom he dedicated his most famous book, The Malay Archipelago) which impelled Darwin to publish an article on his own long-pondered theory simultaneously with that of Wallace. As a travelling naturalist and collector in the Far East and South America, Wallace already inclined towards the Lamarckian theory of transmutation of species, and his own researches convinced him of the reality of evolution. On the publication of On the Origin of Species, Wallace became one of its most prominent advocates, and Darwinism, published in 1889, supports the theory and counters many of the arguments put forward by scientists and others who opposed it.
Avian eggshells are variable in appearance, including colouration. Here we demonstrate that Raman spectroscopy can provide accurate diagnostic information about major eggshell constituents, including the pigments biliverdin and protoprophyrin IX. Eggshells pigmented with biliverdin showed a series of pigment-diagnostic Raman peaks under 785 nm excitation. Eggshells pigmented with protoporphyrin IX showed strong emission under 1064 nm and 785 nm excitation, whereas resonance Raman spectra (351 nm excitation) showed a set of protoporphyrin IX informative peaks characterisitic of protoporphyrin IX. As representative examples, we identified biliverdin in the olive green eggshells of elegant crested tinamous (Eudromia elegans) and in the blue eggshells of extinct upland moa (Megalapteryx didinus). This study encourages the wider use of Raman spectroscopy in pigment and colouration research and highlights the value of this technique for non-destructive analyses of museum eggshell specimens. © 2015. Published by The Company of Biologists Ltd.
The fitness costs of egg loss for Seychelles warblers (Acrocephalus sechellensis) on Cousin Island are considerable because warblers have a single-egg clutch and no time to lay a successful replacement clutch. On the islands of Cousin and Cousine, with equal densities of Seychelles fodies (Foudia sechellarum), nearly 75% of artificial eggs placed in artificial nests were predated by fodies after 3 days. On Aride Island with no fodies present, loss of artificial eggs was not observed. Female warblers incubate the clutch, and male warblers guard the clutch when females are absent. Deterrence of fodies by male warblers is efficient: loss rate of eggs from unattended warbler nests was seven times as high as from attended nests, and the more nest guarding, the lower the egg loss and the higher the hatching success. Egg loss is independent of the amount of incubation by females. There is no trade-off between incubating and foraging by females. Nest guarding competes with foraging by males, and this trade-off has a more pronounced effect on egg loss when food availability is low. The transfer of breeding pairs from Cousin to either Cousine with egg-predating fodies or to Aride without fodies allowed us to experimentally investigate the presumed trade-off between nest guarding and foraging. On Cousine, individual males spent the same amount of time nest guarding and foraging as on Cousin, and egg loss was similar and inversely related to time spent nest guarding as on Cousin. Males that guarded their clutch on Cousin did not guard the clutch on Aride but allocated significantly more time to foraging and gained better body condition. Loss of warbler eggs on Aride was not observed. Time allocation to incubating and foraging by individual females before and after both translocations remained the same.
The avian plumage color gamut is the complete range of plumage colors, as seen by birds themselves. We used a tetrahedral avian color stimulus space to estimate the avian plumage color gamut from a taxonomically diverse sample of 965 plumage patches from 111 avian species. Our sample represented all known types of plumage coloration mechanisms. The diversity of avian plumage colors occupies only a portion (26--30%, using violet-sensitive and ultraviolet-sensitive models, respectively) of the total available avian color space, which represents all colors birds can theoretically see and discriminate. For comparison, we also analyzed 2350 plant colors, including an expansive set of flowers. Bird plumages have evolved away from brown bark and green leaf backgrounds and have achieved some striking colors unattainable by flowers. Feather colors form discrete hue "continents," leaving vast regions of avian color space unoccupied. We explore several possibilities for these unoccupied hue regions. Some plumage colors may be difficult or impossible to make (constrained by physiological and physical mechanisms), whereas others may be disadvantageous or unattractive (constrained by natural and sexual selection). The plumage gamut of early lineages of living birds was probably small and dominated by melanin-based colors. Over evolutionary time, novel coloration mechanisms allowed plumages to colonize unexplored regions of color space. Pigmentary innovations evolved to broaden the gamut of possible communication signals. Furthermore, the independent origins of structural coloration in many lineages enabled evolutionary expansions into places unreachable by pigmentary mechanisms alone. Copyright 2011, Oxford University Press.