Category Archives: News

Neonates and Embryos of Lufengosaurus

Are making waves in newsmedia… ☺

Reisz, R. R., Huang, T. D., Roberts, E. M., Peng, S., Sullivan, C., Stein, K., LeBlanc, A. R. H., Shieh, D., Chang, R., Chiang, C., Yang, C. & Zhong, S., 2013: Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains.
–Nature: Vol. 496, #7444, pp. 210-214 [doi: 10.1038/nature11978]

Abstract:

Fossil dinosaur embryos are surprisingly rare, being almost entirely restricted to Upper Cretaceous strata that record the late stages of non-avian dinosaur evolution. Notable exceptions are the oldest known embryos from the Early Jurassic South African sauropodomorph Massospondylus and Late Jurassic embryos of a theropod from Portugal. The fact that dinosaur embryos are rare and typically enclosed in eggshells limits their availability for tissue and cellular level investigations of development. Consequently, little is known about growth patterns in dinosaur embryos, even though post-hatching ontogeny has been studied in several taxa. Here we report the discovery of an embryonic dinosaur bone bed from the Lower Jurassic of China, the oldest such occurrence in the fossil record. The embryos are similar in geological age to those of Massospondylus and are also assignable to a sauropodomorph dinosaur, probably Lufengosaurus. The preservation of numerous disarticulated skeletal elements and eggshells in this monotaxic bone bed, representing different stages of incubation and therefore derived from different nests, provides opportunities for new investigations of dinosaur embryology in a clade noted for gigantism. For example, comparisons among embryonic femora of different sizes and developmental stages reveal a consistently rapid rate of growth throughout development, possibly indicating that short incubation times were characteristic of sauropodomorphs. In addition, asymmetric radial growth of the femoral shaft and rapid expansion of the fourth trochanter suggest that embryonic muscle activation played an important role in the pre-hatching ontogeny of these dinosaurs. This discovery also provides the oldest evidence of in situ preservation of complex organic remains in a terrestrial vertebrate.

Molluscan spikes explained by physical properties of the growing mantle!

Hi,

That paper might interest some of you

Mechanical basis of morphogenesis and convergent
evolution of spiny seashells
Régis Chirat, Derek E. Moultonb, and Alain Goriely

Abstract

Convergent evolution is a phenomenon whereby similar traits
evolved independently in not closely related species, and is often
interpreted in functional terms. Spines in mollusk seashells are
classically interpreted as having repeatedly evolved as a defense in
response to shell-crushing predators. Here we consider the morphogenetic
process that shapes these structures and underlies their
repeated emergence. We develop a mathematical model for spine
morphogenesis based on the mechanical interaction between the
secreting mantle edge and the calcified shell edge to which the
mantle adheres during shell growth. It is demonstrated that a large
diversity of spine structures can be accounted for through small
variations in control parameters of this natural mechanical process.
This physical mechanism suggests that convergent evolution of
spines can be understood through a generic morphogenetic process,
and provides unique perspectives in understanding the phenotypic
evolution of this second largest phylum in the animal kingdom.

Best,
Elodie

Evolutionary novelty in a rat with no molars

This might be an interesting species for the EvoDevo people.

I saw this article several months ago when I was looking for the diets of vermivore species.
Today I was reading an article of the development of cetacean dentition, and it occurred to me that this rodent might be an interesting species to study. Or perhaps you already knew this one.

“… a new species and genus of shrew-rat from Sulawesi Island, Indonesia that is distinguished from all other rodents by the absence of cheek teeth. Moreover, rather than gnawing incisors, this animal has bicuspid upper incisors, also unique among the more than 2200 species of rodents. Stomach contents from a single specimen suggest that the species consumes only earthworms.”

http://rsbl.royalsocietypublishing.org/content/early/2012/08/21/rsbl.2012.0574

-Kari

Highlatitude camel and the evolution of Plestocene cold adapted fauna

Another element of Pleistocene faunal community ancestors has been found.
Reported in the Nature Communications.

Rybczynski, N., Gosse, J. C., Richard Harington, C., Wogelius, R. A., Hidy, A. J. & Buckley, M., 2013: Mid-Pliocene warm-period deposits in the High Arctic yield insight into camel evolution.
–Nature Communications: Vol. 4, pp. 1550 [doi: 10.1038/ncomms2516]

Abstract:
“The mid-Pliocene was a global warm period, preceding the onset of Quaternary glaciations. Here we use cosmogenic nuclide dating to show that a fossiliferous terrestrial deposit that includes subfossil trees and the northern-most evidence of Pliocene ice wedge casts in Canada’s High Arctic (Ellesmere Island, Nunavut) was deposited during the mid-Pliocene warm period. The age estimates correspond to a general maximum in high latitude mean winter season insolation, consistent with the presence of a rich, boreal-type forest. Moreover, we report that these deposits have yielded the first evidence of a High Arctic camel, identified using collagen fingerprinting of a fragmentary fossil limb bone. Camels originated in North America and dispersed to Eurasia via the Bering Isthmus, an ephemeral land bridge linking Alaska and Russia. The results suggest that the evolutionary history of modern camels can be traced back to a lineage of giant camels that was well established in a forested Arctic.”

–Mikko

Representational bias in phytoliths from modern soils of central North America: Implications for paleovegetation reconstructions

Representational bias in phytoliths from modern soils of central North
America: Implications for paleovegetation reconstructions
Ethan Hyland, , Selena Y. Smith, Nathan D. Sheldon

http://www.sciencedirect.com/science/article/pii/S0031018213000837#

Abstract
Understanding localized patterns and community compositions of
vegetation in an environment is critical to the reconstruction of
climatic and ecological conditions across all spatiotemporal scales.
One of the most accurate and useful ways to characterize vegetation,
and therefore to describe the climatic and ecological conditions of a
location, is through the plant fossil record. Phytoliths (plant silica
microfossils) are often preserved in the absence of other
paleobotanical data and are becoming more widely used for deep-time
vegetation reconstructions. Significant work has been done to
standardize the analytical methodology of phytolith extraction,
statistical analysis, and interpretation, but more detailed
investigations are needed to understand how well a given soil
assemblage represents the actual aboveground plant biomass for a given
ecosystem.

We present results from paired soil phytolith assemblages and local
vegetation assemblages across the central United States, including
temperate forest, grassland, and rangeland/scrubland ecosystems.
Phytolith assemblages obtained via extractions from soil A-horizons
were compared to percent cover of species and plant biomass estimates
obtained via in situ field observations and aerial estimates of tree
cover to analyze differences in the relative abundance of forest/woody
vegetation vs. grasses. Soil phytolith assemblages from all sites
average a 29% bias toward the grass morphotypes as compared to actual
aboveground biomass observations, and comparisons to percent cover
yielded broadly comparable bias figures. Percent bias estimates do not
show significant correlations to most environmental factors
(temperature, precipitation, local elevation), however, an extremely
strong correlation (p < 0.001) was observed with soil order type. This
is likely due to the fact that soil order reflects both vegetation
type and chemical factors known to affect overall phytolith
assemblages; therefore, soil order is a proxy that aggregates several
sources of bias. As a result, we suggest further research into the
development of correction factors between phytolith sample assemblages
and their interpreted past counterpart ecosystems based on estimates
derived from modern analyses of each major soil order type. Such
background corrections are essential to the continued use of
phytoliths as a proxy for past vegetation and ecological
reconstructions of temperate ecosystems throughout the Phanerozoic
record.

Cetacean teeth and a new journal

Armfield et al. (2013) Development and evolution of the unique cetacean dentition. PeerJ 1:e24 http://dx.doi.org/10.7717/peerj.24

The evolutionary success of mammals is rooted in their high metabolic rate. A high metabolic rate is sustainable thanks to efficient food processing and that in turn is facilitated by precise occlusion of the teeth and the acquisition of rhythmic mastication. These major evolutionary innovations characterize most members of the Class Mammalia. Cetaceans are one of the few groups of mammals in which precise occlusion has been secondarily lost. Most toothed whales have an increased number of simple crowned teeth that are similar along the tooth row. Evolution toward these specializations began immediately after the time cetaceans transitioned from terrestrial-to-marine environments. The fossil record documents the critical aspects of occlusal evolution of cetaceans, and allows us to pinpoint the evolutionary timing of the macroevolutionary events leading to their unusual dental morphology among mammals. The developmental controls of tooth differentiation and tooth number have been studied in a few mammalian clades, but nothing is known about how these controls differ between cetaceans and mammals that retain functional occlusion. Here we show that pigs, a cetacean relative with regionalized tooth morphology and complex tooth crowns, retain the typical mammalian gene expression patterns that control early tooth differentiation, expressing Bmp4 in the rostral (mesial, anterior) domain of the jaw, and Fgf8 caudally (distal, posterior). By contrast, dolphins have lost these regional differences in dental morphology and the Bmp4 domain is extended into the caudal region of the developing jaw. We hypothesize that the functional constraints underlying mammalian occlusion have been released in cetaceans, facilitating changes in the genetic control of early dental development. Such major developmental changes drive morphological evolution and are correlated with major shifts in diet and food processing during cetacean evolution.

-Ian

Decoupling the spread of grasslands from the evolution of grazer-type herbivores

Decoupling the spread of grasslands from the evolution of grazer-type herbivores in South America

Caroline A.E. Strömberg, Regan E. Dunn, Richard H. Madden, Matthew J. Kohn & Alfredo A. Carlini
Nature Communications 4, Article number: 1478

http://www.nature.com/ncomms/journal/v4/n2/full/ncomms2508.html?WT.ec_id=NCOMMS-20130212

The evolution of high-crowned cheek teeth (hypsodonty) in herbivorous mammals during the late Cenozoic is classically regarded as an adaptive response to the near-global spread of grass-dominated habitats. Precocious hypsodonty in middle Eocene (~38 million years (Myr) ago) faunas from Patagonia, South America, is therefore thought to signal Earth’s first grasslands, 20 million years earlier than elsewhere. Here, using a high-resolution, 43–18 million-year record of plant silica (phytoliths) from Patagonia, we show that although open-habitat grasses existed in southern South America since the middle Eocene (~40 Myr ago), they were minor floral components in overall forested habitats between 40 and 18 Myr ago. Thus, distinctly different, continent-specific environmental conditions (arid grasslands versus ash-laden forests) triggered convergent cheek–tooth evolution in Cenozoic herbivores. Hypsodonty evolution is an important example where the present is an insufficient key to the past, and contextual information from fossils is vital for understanding processes of adaptation.

— Jacqueline

Mammal Wars/Cladistics Strikes Back/Return Of The Morphology

I can’t believe this hasn’t been posted yet:

The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals

Science 8 February 2013:
Vol. 339 no. 6120 pp. 662-667
DOI: 10.1126/science.1229237

Maureen A. O’Leary and about 20 others

To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.

-Ian

Stop the Press!! – Extinction Galore!

Latest Science contains an interesting K/Pg (K/T)-extinction related article.

Renne, P. R., Deino, A. L., Hilgen, F. J., Kuiper, K. F., Mark, D. F., Mitchell, W. S., Morgan, L. E., Mundil, R. & Smit, J., 2013: Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary.
–Science: Vol. 339, #6120, pp. 684-687 [doi: 10.1126/science.1230492]

http://www.sciencemag.org/content/339/6120/684.full

Abstract:

“Mass extinctions manifest in Earth’s geologic record were turning points in biotic evolution. We present 40Ar/39Ar data that establish synchrony between the Cretaceous-Paleogene boundary and associated mass extinctions with the Chicxulub bolide impact to within 32,000 years. Perturbation of the atmospheric carbon cycle at the boundary likely lasted less than 5000 years, exhibiting a recovery time scale two to three orders of magnitude shorter than that of the major ocean basins. Low-diversity mammalian fauna in the western Williston Basin persisted for as little as 20,000 years after the impact. The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress.”

And what happened after:

O’Leary, M. A., Bloch, J. I., Flynn, J. J., Gaudin, T. J., Giallombardo, A., Giannini, N. P., Goldberg, S. L., Kraatz, B. P., Luo, Z.-X., Meng, J., Ni, X., Novacek, M. J., Perini, F. A., Randall, Z. S., Rougier, G. W., Sargis, E. J., Silcox, M. T., Simmons, N. B., Spaulding, M., Velazco, P. M., Weksler, M., Wible, J. R. & Cirranello, A. L., 2013: The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals.
–Science: Vol. 339, #6120, pp. 662-667 [doi: 10.1126/science.1229237]

http://www.sciencemag.org/content/339/6120/662.full

Abstract:

“To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.!