Dinosaurs Probably had Color Vision

Earlier this year, scientists used zebra finches to pinpoint the gene that enables birds to produce and display the colour red.

Now, a new study shows the same 'red gene' is also found in turtles, which share an ancient common ancestor with birds. Both share a common ancestor with dinosaurs.

The gene, called CYP2J19, allows birds and turtles to convert the yellow pigments in their diets into red, which they then use to heighten colour vision in the red spectrum through droplets of red oil in their retinas.

Birds and turtles are the only existing tetrapods, or land vertebrates, to have these red retinal oil droplets. In some birds and a few turtle species, red pigment produced by the gene is also used for external display: red beaks and feathers, or the red neck patches and rims of shells seen in species such as the painted turtle.

The scientists mined the genetic data of various bird and reptile species to reconstruct an evolutionary history of the CYP2J19 gene, and found that it dated back hundreds of millions of years in the ancient archelosaur genetic line - the ancestral lineage of turtles, birds and dinosaurs.

link.

Turtles are probably archosaurs, btw.

Turtles Developed Their Shell to Help Them Burrow

Fossorial Origin of the Turtle Shell

Authors:

Lyson et al

Abstract:

The turtle shell is a complex structure that currently serves a largely protective function in this iconically slow-moving group [ 1 ]. Developmental [ 2, 3 ] and fossil [ 4–7 ] data indicate that one of the first steps toward the shelled body plan was broadening of the ribs (approximately 50 my before the completed shell [ 5 ]). Broadened ribs alone provide little protection [ 8 ] and confer significant locomotory [ 9, 10 ] and respiratory [ 9, 11 ] costs. They increase thoracic rigidity [ 8 ], which decreases speed of locomotion due to shortened stride length [ 10 ], and they inhibit effective costal ventilation [ 9, 11 ]. New fossil material of the oldest hypothesized stem turtle, Eunotosaurus africanus [ 12 ] (260 mya) [ 13, 14 ] from the Karoo Basin of South Africa, indicates the initiation of rib broadening was an adaptive response to fossoriality. Similar to extant fossorial taxa [ 8 ], the broad ribs of Eunotosaurus provide an intrinsically stable base on which to operate a powerful forelimb digging mechanism. Numerous fossorial correlates [ 15–17 ] are expressed throughout Eunotosaurus’ skeleton. Most of these features are widely distributed along the turtle stem and into the crown clade, indicating the common ancestor of Eunotosaurus and modern turtles possessed a body plan significantly influenced by digging. The adaptations related to fossoriality likely facilitated movement of stem turtles into aquatic environments early in the groups’ evolutionary history, and this ecology may have played an important role in stem turtles surviving the Permian/Triassic extinction event.

Turtles are Diapsids Follow up

link.

That's Settled: New Triassic Fossils Show Turtles Were had Diapsid, not Parareptilian Ancestry

The diapsid origin of turtles

Authors:

Schoch et al

Abstract:

The origin of turtles has been a persistent unresolved problem involving unsettled questions in embryology, morphology, and paleontology. New fossil taxa from the early Late Triassic of China (Odontochelys) and the Late Middle Triassic of Germany (Pappochelys) now add to the understanding of (i) the evolutionary origin of the turtle shell, (ii) the ancestral structural pattern of the turtle skull, and (iii) the phylogenetic position of Testudines. As has long been postulated on the basis of molecular data, turtles evolved from diapsid reptiles and are more closely related to extant diapsids than to parareptiles, which had been suggested as stem group by some paleontologists. The turtle cranium with its secondarily closed temporal region represents a derived rather than a primitive condition and the plastron partially evolved through the fusion of gastralia.

Dakotaraptor is a Chimera: Part of Maastrichtian Cretaceous Dromaeosaurid is a Piece of a Turtle

The furculae of the dromaeosaurid dinosaur Dakotaraptor steini are trionychid turtle entoplastra

Authors:

Arbour et al

Abstract:

Dakotaraptor steini is a recently described dromaeosaurid dinosaur from the Upper Cretaceous (Maastrichtian) Hell Creek Formation of South Dakota. Included within the D. steini hypodigm are three elements originally identified as furculae, one of which was made part of the holotype specimen. We show that the elements described as D. steini ‘furculae’ are not theropod dinosaur furculae, but are rather trionychid turtle entoplastra referable to cf. Axestemys splendida. The hypodigm of D. steini should be adjusted accordingly.

What's Weirder Than Weird? Turtles Grooming a Warthog (not kidding)

link.

A Turtle Fossil Preserving Blood Vessels and Osteocytes From Paleogene Colombia

A Pelomedusoid Turtle from the Paleocene–Eocene of Colombia Exhibiting Preservation of Blood Vessels and Osteocytes

Authors:

Cadena et al

Abstract:

We describe a Paleocene–Eocene pelomedusoid turtle from tropical South America in a new fossiliferous locality, from Los Cuervos Formation, at the Calenturitas Coal Mine, Colombia. Although no further systematic precision beyond Pelomedusoides incertae sedis can be supported, the presence of an ischial scar positioned far anteriorly to the anal notch, and a strongly decorated ventral surface of the plastron, indicate that this specimen is potentially related to the bothremydid clade formed by Puentemys–Foxemys. We also demonstrate the potential organic preservation of osteocytes and blood vessels for this specimen, indicating that preservation of soft tissue such as vessels and bone cells in the fossil record is independent of bone type, fossil site, or locality; occurring in different lineages of vertebrates; and that it is even possible to occur in tropical depositional environments during a period of maximum global warming such as the Paleocene–Eocene.

When Turtles Learned to Breathe Their Way

Through the careful study of modern and early fossil tortoise, researchers now have a better understanding of how tortoises breathe and the evolutionary processes that helped shape their unique breathing apparatus and tortoise shell. The findings published in a paper, titled: Origin of the unique ventilatory apparatus of turtles, in the scientific journal, Nature Communications, on Friday, 7 November 2014, help determine when and how the unique breathing apparatus of tortoises evolved.

Lead author Dr Tyler Lyson of Wits University's Evolutionary Studies Institute, the Smithsonian Institution and the Denver Museum of Nature and Science said: "Tortoises have a bizarre body plan and one of the more puzzling aspects to this body plan is the fact that tortoises have locked their ribs up into the iconic tortoise shell. No other animal does this and the likely reason is that ribs play such an important role in breathing in most animals including mammals, birds, crocodilians, and lizards."

Instead tortoises have developed a unique abdominal muscular sling that wraps around their lungs and organs to help them breathe. When and how this mechanism evolved has been unknown.

"It seemed pretty clear that the tortoise shell and breathing mechanism evolved in tandem, but which happened first? It's a bit of the chicken or the egg causality dilemma," Lyson said. By studying the anatomy and thin sections (also known as histology), Lyson and his colleagues have shown that the modern tortoise breathing apparatus was already in place in the earliest fossil tortoise, an animal known as Eunotosaurus africanus.

link.

paper link.

Thalassodromeus sebesensis Wasn't a Pterosaur...It was a Turtle

Thalassodromeus sebesensis - a new name for an old turtle. Comment on “Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur”, Grellet-Tinner and Codrea

Authors:

Dyke et al

Abstract:

In a recent Gondwana Research article Grellet-Tinner and Codrea (2014) (hereafter “GTC”) describe a single bone (UBB ODA-28, collections of Babeş-Bolyai University, Cluj Napoca, Romania) from the Upper Cretaceous Şard Formation (= middle section of the Sebeş Formation) (Transylvanian Basin, Romania) as a pterosaur premaxillary cranial crest. They assign this fossil to a new species of small pterosaur, Thalassodromeus sebesensis (a name first coined in a conference abstract published in 2013; Grellet-Tinner et al., 2013). GTC build a taxonomic argument on the basis of this single incomplete specimen that posits the presence of a major group of pterosaurs hitherto entirely restricted to the Early Cretaceous of South America - thalassodromines (Kellner and Campos, 2007) or thalassodromids (Witton, 2009) - in the European Late Cretaceous. GTC note that “this important discovery doubles the thalassadromine fossil record and demonstrates a 42 million years temporal displacement between the Romanian species and its older Aptian Gondwanan congener Thalassodromeus sethi”. If GTC are correct, this new fossil represents a remarkably unexpected and potentially very important discovery that could rewrite aspects of pterosaur evolutionary history.

We have assembled a large international team who disagree with the arguments presented by GTC. As we demonstrate, the fossil fragment they describe is misidentified; it is, firstly, not from a pterosaur but is clearly a piece of the shell of the turtle Kallokibotion Nopcsa, 1923 and, secondly, is therefore not the groundbreaking discovery of an ‘anachronistic’ Gondwanan pterosaur in Europe as claimed. Because ODA-28 is not a pterosaur, yet alone a Thalassodromeus, GTC’s conclusions on migration routes and insular dwarfism are also unsupported.

 Original authors stick to their guns, but not nicely.

Turtles are Archosaurs?!

Turtles are more closely related to birds and crocodilians than to lizards and snakes, according to a study from Dartmouth, Yale and other institutions that examines one of the most contentious questions in evolutionary biology.

The findings appear in the journal Evolution & Development. A PDF of the study is available on request.

The research team looked at how the major groups of living reptiles, which number more than 20,000 species, are interrelated. The relationships of some reptile groups are well understood -- birds are most closely related to crocodilians among living reptiles, while snakes, lizards and New Zealand's tuatara form a natural group. But the question of how turtles fit into this evolutionary picture has remained unclear. Are turtles more closely related to archosaurs (birds and crocodilians) or to lepidosaurs (lizards, snakes and tuatara)? Or are these other reptiles more closely related to each other than to turtles?

A growing number of studies examining DNA sequences have suggested a close evolutionary kinship between turtles and archosaurs, but those results were contradicted by anatomical studies and a recent study of small biomolecules called microRNAs. Because microRNAs are viewed by some as excellent evolutionary markers, the conflict between the microRNA and DNA results meant the turtle-archosaur link was viewed skeptically by many.

But the Dartmouth-led team's research suggests the earlier microRNA conclusions were erroneous, and instead indicates that microRNAs and DNA sequences yield a common signal -- that turtles share a more recent common ancestor with birds and crocodilians than with lizards and snakes.

link.

The Trouble With Turtles...and Their Phylogenic Placement

Traditional paleontological research has been upended over the past few decades, as less traditional fields, such as genomics and developmental biology, have weighed in on vertebrate evolution. Researchers have examined the lingering color elements in dinosaur feathers, the genetics of woolly mammoths, purported proteins and blood from dinosaurs, and other ancient fossil signatures using modern tools. But the question of turtle evolution has remained resistant to both traditional and novel methods.

More than 300 species of turtles exist today, but where they came from isn’t entirely clear. Turtles are the last big living vertebrate group to be placed firmly on the tree of life, and the arguments are getting messy. Three fields in particular — paleontology, developmental biology and microbiology/genomics — disagree about how, and from what, turtles may have evolved.

Traditional paleontologists have placed turtles, which are indisputably reptiles, in relation to a group of mostly extinct reptilian animals called anapsids, which don’t have holes in their skulls; however, analyses in the 1990s put turtles in the diapsid camp, which originally had two holes in their skulls, and closer to modern reptiles like snakes. Morphology places them near the group made up of lizards and birds and crocodiles.

Within that group, genomicists have found molecular data that places turtles closer to birds and crocodiles, rather than lizards and snakes. But even within genomics, there is debate.

Meanwhile, developmental biologists have figured out that turtles have very special shells, giving them unusual characteristics that might be found in the fossil record, though what that might look like remains to be seen.

All this disagreement thus leads back to paleontology. Find more fossils and you find more answers. But until that happens, what else can be done to solve the mystery of turtle evolution?

link.

Sea Turtle Lost Years Become Semi Found

Small satellite-tracking devices attached to sea turtles swimming off Florida's coast have delivered first-of-its-kind data that could help unlock they mystery of what endangered turtles do during the "lost years."

The "lost years" refers to the time after turtles hatch and head to sea where they remain for many years before returning to near-shore waters as large juveniles. The time period is often referred to as the "lost years" because not much has been known about where the young turtles go and how they interact with their oceanic environment -- until now.

"What is exciting is that we provide the first look at the early behavior and movements of young sea turtles in the wild," said UCF biologist Kate Mansfield, who led the team. "Before this study, most of the scientific information about the early life history of sea turtles was inferred through genetics studies, opportunistic sightings offshore, or laboratory-based studies. With real observations of turtles in their natural environment, we are able to examine and reevaluate existing hypotheses about the turtles' early life history. This knowledge may help managers provide better protection for these threatened and endangered species."

Findings from the study appear today in the journal Proceedings of the Royal Society B. (link to article here).

A team of scientists from the UCF, Florida Atlantic University, University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, and University of Wisconsin, tracked 17 loggerhead turtles for 27 to 220 days in the open ocean using small, solar-powered satellite tags. The goal was to better understand the turtles' movements, habitat preferences, and what role temperature may play in early sea turtle life history.

Some of the findings challenge previously held beliefs.

While the turtles remain in oceanic waters (traveling between 124 miles to 2,672 miles) off the continental shelf and the loggerhead turtles sought the surface of the water as predicted, the study found that the turtles do not necessarily remain within the currents associated with the North Atlantic subtropical gyre. It was historically thought that loggerhead turtles hatching from Florida's east coast complete a long, developmental migration in a large circle around the Atlantic entrained in these currents. But the team's data suggest that turtles may drop out of these currents into the middle of the Atlantic or the Sargasso Sea.

The team also found that while the turtles mostly stayed at the sea surface, where they were exposed to the sun's energy, the turtles' shells registered more heat than anticipated (as recorded by sensors in the satellite tags), leading the team to consider a new hypothesis about why the turtles seek refuge in Sargassum. It is a type of seaweed found on the surface of the water in the deep ocean long associated with young sea turtles.

"We propose that young turtles remain at the sea surface to gain a thermal benefit," Mansfield said. "This makes sense because the turtles are cold blooded animals. By remaining at the sea surface, and by associating with Sargassum habitat, turtles gain a thermal refuge of sorts that may help enhance growth and feeding rates, among other physiological benefits."

link.

Soft Shelled Turtles From Cenomanian Cretaceous Uzbekistan

Soft-shelled turtles (Trionychidae) from the Cenomanian of Uzbekistan

Authors:

Vitek et al

Abstract:

Localities from the Cenomanian of Uzbekistan are the oldest in Middle Asia and Kazakhstan to preserve two broadly sympatric species of trionychid turtle. Material described here comes from multiple Cenomanian formations from the Itemir locality, and from multiple localities in the Cenomanian Khodzhakul Formation. The first taxon from the locality, “Trionyx” cf. kyrgyzensis, has multiple morphological similarities with the older, Early Cretaceous “Trionyx” kyrgyzensis. In contrast, the second taxon, “Trionyx” dissolutus, has multiple similarities with “Trionyx” kansaiensis, one of two species of trionychid found in younger Late Cretaceous localities. “Trionyx” dissolutus bears some superficial resemblance to other trionychid taxa within the clade Plastomenidae because of its highly ossified plastron with a hyoplastral lappet and an epiplastral notch. However, Plastomenidae is diagnosed primarily through characters that are absent or cannot be observed in the available material of “T.” dissolutus, and other shared features are plesiomorphic. In addition, “T.” dissolutus shares other synapomorphies with Trionychinae. A heavily ossified plastron may be more homoplastric within Trionychidae than has been previously recognized. Finally, we provide an improved understanding of the subtle similarities and differences between several closely related Cretaceous turtle assemblages of Middle Asia and Kazakhstan.

How Dark is Your Santonian Cretaceous Mosasaur? Your Sinemurian Jurassic Ichthyosaur?

Unique finds of original pigment in fossilised skin from three multi-million-year old marine reptiles attract considerable attention from the scientific community. The pigment reveals that these animals were, at least partially, dark-coloured in life, which is likely to have contributed to more efficient thermoregulation, as well as providing means for camouflage and UV protection. Researchers at Lund University are among the scientists that made the spectacular discovery.

During the Age of the dinosaurs, huge reptiles, such as mosasaurs and ichthyosaurs, ruled the seas. Previously, scientists could only guess what colours these spectacular animals had; however, pigment preserved in fossilised skin has now been analysed at SP Technical Research Institute of Sweden and MAX IV Laboratory, Lund University, Sweden. The unique soft tissue remains were obtained from a 55 million-year-old leatherback turtle, an 85 million-year-old mosasaur and a 196 million-year-old ichthyosaur. This is the first time that the colour scheme of any extinct marine animal has been revealed.

"This is fantastic! When I started studying at Lund University in 1993, the film Jurassic Park had just been released, and that was one of the main reasons why I got interested in biology and palaeontology. Then, 20 years ago, it was unthinkable that we would ever find biological remains from animals that have been extinct for many millions of years, but now we are there and I am proud to be a part of it", said Johan Lindgren about the discovery of the ancient pigment molecules.

link.

Turtles: The Phylogenic Hockey Puck of Modern Zoology/Paleontology

Using Genes as Characters and a Parsimony Analysis to Explore the Phylogenetic Position of Turtles

Authors:

Lu et al

Abstract:

The phylogenetic position of turtles within the vertebrate tree of life remains controversial. Conflicting conclusions from different studies are likely a consequence of systematic error in the tree construction process, rather than random error from small amounts of data. Using genomic data, we evaluate the phylogenetic position of turtles with both conventional concatenated data analysis and a “genes as characters” approach. Two datasets were constructed, one with seven species (human, opossum, zebra finch, chicken, green anole, Chinese pond turtle, and western clawed frog) and 4584 orthologous genes, and the second with four additional species (soft-shelled turtle, Nile crocodile, royal python, and tuatara) but only 1638 genes. Our concatenated data analysis strongly supported turtle as the sister-group to archosaurs (the archosaur hypothesis), similar to several recent genomic data based studies using similar methods. When using genes as characters and gene trees as character-state trees with equal weighting for each gene, however, our parsimony analysis suggested that turtles are possibly sister-group to diapsids, archosaurs, or lepidosaurs. None of these resolutions were strongly supported by bootstraps. Furthermore, our incongruence analysis clearly demonstrated that there is a large amount of inconsistency among genes and most of the conflict relates to the placement of turtles. We conclude that the uncertain placement of turtles is a reflection of the true state of nature. Concatenated data analysis of large and heterogeneous datasets likely suffers from systematic error and over-estimates of confidence as a consequence of a large number of characters. Using genes as characters offers an alternative for phylogenomic analysis. It has potential to reduce systematic error, such as data heterogeneity and long-branch attraction, and it can also avoid problems associated with computation time and model selection. Finally, treating genes as characters provides a convenient method for examining gene and genome evolution.

and...

Turtle origins: insights from phylogenetic retrofitting and molecular scaffolds

Author:

M. S. Y. Lee

Abstract:

Adding new taxa to morphological phylogenetic analyses without substantially revising the set of included characters is a common practice, with drawbacks (undersampling of relevant characters) and potential benefits (character selection is not biased by preconceptions over the affinities of the ‘retrofitted’ taxon). Retrofitting turtles (Testudines) and other taxa to recent reptile phylogenies consistently places turtles with anapsid-grade parareptiles (especially Eunotosaurus and/or pareiasauromorphs), under both Bayesian and parsimony analyses. This morphological evidence for turtle–parareptile affinities appears to contradict the robust genomic evidence that extant (living) turtles are nested within diapsids as sister to extant archosaurs (birds and crocodilians). However, the morphological data are almost equally consistent with a turtle–archosaur clade: enforcing this molecular scaffold onto the morphological data does not greatly increase tree length (parsimony) or reduce likelihood (Bayesian inference). Moreover, under certain analytic conditions, Eunotosaurus groups with turtles and thus also falls within the turtle–archosaur clade. This result raises the possibility that turtles could simultaneously be most closely related to a taxon traditionally considered a parareptile (Eunotosaurus) and still have archosaurs as their closest extant sister group.

Ocepechelon: A Monster Sized Turtle From Maastrichtian Cretaceous Morocco

A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique among Tetrapods

Authors:

1. Nathalie Bardet (a)
2. Nour-Eddine Jalil (b)
3. France de Lapparent de Broin (a)
4. Damien Germain (a)
5. Olivier Lambert (c)
6. Mbarek Amaghzaz (d)

Affiliations:

a. CNRS UMR 7207, Département Histoire de la Terre, Muséum National d’Histoire Naturelle, Paris, France

b. Cadi Ayyad University, Faculty of Sciences Semlalia, Department of Earth Sciences, Vertebrate Evolution and Palaeoenvironnements, Marrakech, Morocco

c. Institut Royal des Sciences Naturelles de Belgique, Département de Paléontologie, Bruxelles, Belgium

d. Office Chérifien des Phosphates, Centre Minier de Khouribga, Khouribga, Morocco

Abstract:

Secondary adaptation to aquatic life occurred independently in several amniote lineages, including reptiles during the Mesozoic and mammals during the Cenozoic. These evolutionary shifts to aquatic environments imply major morphological modifications, especially of the feeding apparatus. Mesozoic (250–65 Myr) marine reptiles, such as ichthyosaurs, plesiosaurs, mosasaurid squamates, crocodiles, and turtles, exhibit a wide range of adaptations to aquatic feeding and a broad overlap of their tooth morphospaces with those of Cenozoic marine mammals. However, despite these multiple feeding behavior convergences, suction feeding, though being a common feeding strategy in aquatic vertebrates and in marine mammals in particular, has been extremely rarely reported for Mesozoic marine reptiles.
Principal Findings

A relative of fossil protostegid and dermochelyoid sea turtles, Ocepechelon bouyai gen. et sp. nov. is a new giant chelonioid from the Late Maastrichtian (67 Myr) of Morocco exhibiting remarkable adaptations to marine life (among others, very dorsally and posteriorly located nostrils). The 70-cm-long skull of Ocepechelon not only makes it one of the largest marine turtles ever described, but also deviates significantly from typical turtle cranial morphology. It shares unique convergences with both syngnathid fishes (unique long tubular bony snout ending in a rounded and anteriorly directed mouth) and beaked whales (large size and elongated edentulous jaws). This striking anatomy suggests extreme adaptation for suction feeding unmatched among known turtles.
Conclusion/Significance

The feeding apparatus of Ocepechelon, a bony pipette-like snout, is unique among tetrapods. This new taxon exemplifies the successful systematic and ecological diversification of chelonioid turtles during the Late Cretaceous. This new evidence for a unique trophic specialization in turtles, along with the abundant marine vertebrate faunas associated to Ocepechelon in the Late Maastrichtian phosphatic beds of Morocco, further supports the hypothesis that marine life was, at least locally, very diversified just prior to the Cretaceous/Palaeogene (K/Pg) biotic crisis.

How the Turtle Got Its Shell: A Study of the Permian's Eunotosaurus

Through careful study of an ancient ancestor of modern turtles, researchers now have a clearer picture of how the turtles' most unusual shell came to be. The findings, reported on May 30 in Current Biology, a Cell Press publication, help to fill a 30- to 55-million-year gap in the turtle fossil record through study of an extinct South African reptile known as Eunotosaurus.

"The turtle shell is a complex structure whose initial transformations started over 260 million years ago in the Permian period," says Tyler Lyson of Yale University and the Smithsonian. "Like other complex structures, the shell evolved over millions of years and was gradually modified into its present-day shape."

The turtle shell isn't really just one thing—it is made up of approximately 50 bones. Turtles are the only animals that form a shell through the fusion of ribs and vertebrae. In all other animals, shells are formed from bony scales on the surface; they don't stick their bones on the outsides of their bodies.

"The reason, I think, that more animals don't form a shell via the broadening and eventually suturing together of the ribs is that the ribs of mammals and lizards are used to help ventilate the lungs," Lyson says. "If you incorporate your ribs into a protective shell, then you have to find a new way to breathe!" Turtles have done just that, with the help of a muscular sling.

Until recently, the oldest known fossil turtles, dating back about 215 million years, had fully developed shells, making it hard to see the sequence of evolutionary events that produced them. That changed in 2008 with the discovery of Chinese Odontochelys semitestacea, a reptile about 220 million years old, which had a fully developed plastron—the belly side of the shell—but only a partial carapace on its back.

Eunotosaurus takes the turtle and its shell back another 40 million years or so. It had nine broadened ribs found only in turtles. And like turtles, it lacked the intercostal muscles running between its ribs. But Eunotosaurus didn't have other features common to Odontochelys and turtles, including broad spines on their vertebrae.

Lyson says he and his colleagues now plan to investigate various other aspects of turtles' respiratory systems, which allow them to manage with their ribs locked up into a protective outer shell. "It is clear that this novel lung ventilation mechanism evolved in tandem with the origin of the turtle shell," he says.

Painted Turtle Genome Mapped, Yields Surprises, Supports Archosaur Affinities

UCLA conservation biologist and lead author Brad Shaffer collaborated with the Genome Institute at Washington University in St. Louis and 58 co-authors on the multi-year research project. Their paper, which appears in the journal Genome Biology, describes the genome of the western painted turtle, one of the most widespread and well-studied turtles in the world.

Researchers were somewhat surprised to find that the painted turtle's extraordinary adaptations were not the result of previously unknown genes but of gene networks that are common in vertebrates — including humans, said Shaffer, a professor at UCLA's Institute of the Environment and Sustainability (IoES) and UCLA's Department of Ecology and Evolutionary Biology.

"They're the same genes we have, and the turtles are just using them in different ways and really cranking up their activity in most cases," said Shaffer, who also directs the La Kretz Center for California Conservation Science at the IoES.

"Given how extreme their adaptations are, I imagined we would see weird new genes, so I was surprised," he added. "But the fact that they're common means they may have direct relevance to human health conditions, especially those related to oxygen deprivation, hypothermia and possibly longevity."

Inside the turtle genome, the researchers found 19 genes in the brain and 23 in the heart that became more active in low-oxygen conditions, including one that became 130 times more active. These genes, all of which are present in humans, may be important candidates for exploring oxygen-deprivation treatment in humans, the researchers noted.

Many of the extreme adaptations the researchers studied, such as the ability to survive months of anoxia — total oxygen depletion — are primarily seen in painted turtles, and the western painted turtle is the most anoxia-tolerant terrestrial vertebrate known. At low temperatures, such as in the ice-covered ponds where they hibernate, painted turtles can survive for four months underwater without coming up for air. Turtles are also famous for their extreme longevity, with some species even continuing to reproduce into their second century of life.

But when the research team examined genes that may be responsible for turtles' longevity, instead of finding super-active genes like the ones protecting them from oxygen deprivation, the scientists found indications that turtles' long life spans may come from silencing "life-shortening" genes.

"We looked at two genes that are either absent or severely down-regulated in other animals that live a long time," Shaffer said. "We found turtles have only non-functioning vestiges of these genes, if they have them at all. Both of these genes are present and active in humans, so they're an appealing candidate to learn about human longevity."

Analysis of the turtle genome confirmed that the shelled creatures are more closely related to birds and crocodilians than any other vertebrates. The researchers also discovered that turtles have an extraordinarily slow rate of genomic evolution and that the turtle genome evolves at about a third the rate of the human genome.

Awesome and bummer at the same time.  I was hoping the turtles were the last of the parareptiles.  Alas.

Why No Turtles Are Viviparous

Limited Oxygen Availability In Utero May Constrain the Evolution of Live Birth in Reptiles

Authors:

1. Anthony R. Rafferty (a)

2. Roger G. Evans (b)

3. T. Franciscus Scheelings (c)

4. Richard D. Reina (a)

Affiliations:

a. Australian Centre for Biodiversity, School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia

b. Department of Physiology, Monash University, Clayton, Victoria 3800, Australia

c. Australian Wildlife Health Centre, Healesville Sanctuary, Healesville, Victoria 3777, Australia

Abstract:

Although viviparity (live birth) has evolved from oviparity (egg laying) at least 140 times in vertebrates, nearly 120 of these independent events occurred within a single reptile taxon. Surprisingly, only squamate reptiles (lizards and snakes) are capable of facilitating embryonic development to increasingly advanced stages inside the mother during extended periods of oviducal egg retention. Viviparity has never evolved in turtle lineages, presumably because embryos enter and remain in an arrested state until after eggs are laid, regardless of the duration of egg retention. Until now, the limiting factor that initiates and maintains developmental arrest has remained elusive. Here, we show that oviducal hypoxia arrests embryonic development. We demonstrate that hypoxia can maintain developmental arrest after oviposition and that subsequent exposure of arrested embryos to normoxia triggers resumption of their development. We discovered remarkably low oxygen partial pressure in the oviducts of gravid turtles and found that secretions produced by the oviduct retard oxygen diffusion. Our results suggest that an extremely hypoxic environment in the oviduct arrests embryonic development and may constrain the evolution of viviparity in turtles, with the reduced diffusive capacity of oviducal secretions possibly creating or contributing to this hypoxia. We anticipate that these findings will allow us to better understand the mechanisms underlying the evolutionary transition between reproductive modes.

Turtles: Back to Parareptilia You Go!

The position of turtles based on molecular (1: e.g. Hugall et al. 2007) and morphological datasets (2: e.g. deBraga & Rieppel 1997; 3: Gauthier et al. 1988). The addition of key fossils eliminates the apparent disagreement among morphological datasets in support of turtles outside Diapsida (3). The Permian ‘parareptile’ Eunotosaurus shares uniquely derived features with turtles that help fill important gaps in the evolutionary origin of the turtle shell. Bootstrap (top) and Bremer (bottom) support values are provided for the Eunotosaurus-turtle clade. Star indicates complete shell.

Transitional fossils and the origin of turtles

1. Tyler R. Lyson (a,*)
2. Gabe S. Bever (a)
3. Bhart-Anjan S. Bhullar (b)
4. Walter G. Joyce (c)
5. Jacques A. Gauthier (a)

a. Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA

b. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA

c. Institut für Geowissenschaften, University of Tübingen, 72076 Tübingen, Germany

* Author for correspondence (tyler.lyson@yale.edu).

Abstract:

The origin of turtles is one of the most contentious issues in systematics with three currently viable hypotheses: turtles as the extant sister to (i) the crocodile–bird clade, (ii) the lizard–tuatara clade, or (iii) Diapsida (a clade composed of (i) and (ii)). We reanalysed a recent dataset that allied turtles with the lizard–tuatara clade and found that the inclusion of the stem turtle Proganochelys quenstedti and the ‘parareptile’ Eunotosaurus africanus results in a single overriding morphological signal, with turtles outside Diapsida. This result reflects the importance of transitional fossils when long branches separate crown clades, and highlights unexplored issues such as the role of topological congruence when using fossils to calibrate molecular clocks.

The tug of war continues over the turtles! Once anapsida then parareptilia, then diapsida and back once more into parareptilia! Oy!

That said, I am beginning to think that the molecular clock isn't nearly as regular as is often assumed. I get the distinct feeling that there are bursty times of rapid mutation and other quieter moments of stasis and little change. Perhaps the molecular clock just needs more fiber in its diet, eh?