Morphology and Ontogeny of a Cambrian Trilobite From China

Morphology and ontogeny of Hunanocephalus ovalis (trilobite) from the Cambrian of South China

Authors:

Dai et al

Abstract:

The juvenile morphology and ontogeny of the Cheiruroidid trilobite Hunanocephalus ovalis Lee, 1963 from the lower Cambrian Shuijingtuo Formation in Hubei Province, South China is presented. The new material comprises a relatively complete meraspid ontogenetic series (degree 0 to 10), which reveals more details on their morphological changes such as the contraction and disappearance of the pronounced posteromedial notch in the pygidium and the addition of the trunk segments, which are all documented for the first time and can also be used as developmental markers defining their ontogenetic phases. The trunk segmentation schedule of H. ovalis is also discussed, which is similar to the other early Cambrian oryctocephalid trilobites, i.e. as the boundary between the thorax and pygidium migrated posteriorly there is no change in the trunk segment number; the processes of liberation of the thoracic segment and segment insertion into the pygidium are separated from one another, implying that the control of trunk exoskeletal segment appearance and articulation might be decoupled in these trilobites.

Teleost Fish Reevolve Fins Multiple Times

Though present in more than 6,000 living species of fish, the adipose fin, a small appendage that lies between the dorsal fin and tail, has no clear function and is thought to be vestigial. However, a new study analyzing their origins finds that these fins arose repeatedly and independently in multiple species. In addition, adipose fins appear to have repeatedly and independently evolved a skeleton, offering a glimpse into how new tissue types and structural complexity evolve in vertebrate appendages.

Adipose fins therefore represent a unique example of convergent evolution and new model for exploring the evolution of vertebrate limbs and appendages, report scientists from the University of Chicago in the Proceedings of the Royal Society B on March 5.

"Vertebrates in general have conserved body plans, and new appendages, whether fins or limbs, evolve rarely," said senior author Michael Coates, PhD, chair of the Committee on Evolutionary Biology at the University of Chicago. "Here, we have a natural experiment re-run repeatedly, providing a superb new system in which to explore novelty and change."

Usually small and structurally simple, adipose fins tend to get attention only when they are clipped from farm-raised trout and salmon as a tag. Despite their presence in thousands of fish species, they have been dismissed as a remnant of a once-functional fin. This assumption puzzled Coates and co-authors, as they saw no evidence of deterioration in adipose fin structure or function in the fossil record.

To study the evolutionary origins of this fin, Coates and lead author Thomas Stewart, graduate student in organismal biology and anatomy at the University of Chicago, turned to a technique known as ancestral-state reconstruction. With co-author W. Leo Smith, PhD, from the Biodiversity Institute at the University of Kansas, they created an evolutionary tree describing the relationships between fish with and without adipose fins, using genetic information from more than 200 ray-finned fish and fossil data from known time points. They then used statistical models to predict when and in what species the adipose fin might have first evolved.

They found that adipose fins originated multiple times, independently, in catfish and other groups of ray-finned fishes—a striking example of convergent evolution over a vast range of species.

"It's pretty incredible that a structure which is incredibly common could be so misunderstood," Stewart said. "Our finding, that adipose fins have evolved repeatedly, shows that this structure, long assumed to be more-or-less useless, might be very important to some fishes. It's exciting because it opens up new questions."

link.

Mammal Morphology Has Roots in the Massively Creative Destruction of Permian Triassic Mass Extinction

The radiation of cynodonts and the ground plan of mammalian morphological diversity

Authors:

1. Marcello Ruta (a)
2. Jennifer Botha-Brink (b,c)
3. Stephen A. Mitchell (d)
4. Michael J. Benton (d)

Affiliations:

a. School of Life Sciences, University of Lincoln, Lincoln LN2 2LG, UK

b. Karoo Palaeontology, National Museum, PO Box 266, Bloemfontein 9300, South Africa

c. Department of Zoology and Entomology, University of the Free State, Bloemfontein 9300, South Africa

d. School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK

Abstract:

Cynodont therapsids diversified extensively after the Permo-Triassic mass extinction event, and gave rise to mammals in the Jurassic. We use an enlarged and revised dataset of discrete skeletal characters to build a new phylogeny for all main cynodont clades from the Late Permian to the Early Jurassic, and we analyse models of morphological diversification in the group. Basal taxa and epicynodonts are paraphyletic relative to eucynodonts, and the latter are divided into cynognathians and probainognathians, with tritylodonts and mammals forming sister groups. Disparity analyses reveal a heterogeneous distribution of cynodonts in a morphospace derived from cladistic characters. Pairwise morphological distances are weakly correlated with phylogenetic distances. Comparisons of disparity by groups and through time are non-significant, especially after the data are rarefied. A disparity peak occurs in the Early/Middle Triassic, after which period the mean disparity fluctuates little. Cynognathians were characterized by high evolutionary rates and high diversity early in their history, whereas probainognathian rates were low. Community structure may have been instrumental in imposing different rates on the two clades.

New Placental Phylogeny Based on 4500 Characters, Genetic and Morphological Traits

A groundbreaking six-year research collaboration has produced the most complete picture yet of the evolution of placental mammals, the group that includes humans. Placental mammals are the largest branch of the mammalian family tree, with more than 5,100 living species. Researchers from Carnegie Museum of Natural History are among the team of 23 that took part in this extensive interdisciplinary effort that utilizes molecular (DNA) and morphological (anatomy) data on an extraordinary scale. By combining these two types of data scientists reconstructed, to an unprecedented level of detail, the family tree of placental mammals. This study explored thousands of characteristics of the anatomy of both living and extinct placental mammals.

This new project produced a more complete picture of mammalian history and provides a huge dataset that will become the starting point of research for a number of scientific questions, including those of vital importance today: how mammals may have survived climate change in the past and what may that mean for our future. The paper appears today in the journal Science.

The collaboration is part of the Assembling the Tree of Life (ATOL) project funded by the National Science Foundation.

Joining forces, joining research

Today's article reveals the final results of the six-year ATOL project. The study began with two teams organizing data from two distinct approaches to evolutionary research: molecular data (DNA), and morphological data (anatomical features).

"In the field of mammal research, there had been a big divide between people working with DNA and others working on morphology," explains John Wible, PhD, Curator of Mammals at Carnegie Museum of Natural History and co-author on the paper. "They just weren't working with each other until now."

The molecular team collected DNA sequences of living animals and the morphology team examined the anatomy of both living and extinct mammals. The molecular team only sampled living mammals, because genetic material can't be extracted from fossils older than 30,000 years,. Thus, to include fossils, morphological information was essential. Researchers in morphology deal with individual physical features, from bone length to types of teeth to the presence of stripes in the fur; each one of these features is termed a 'character.' By collecting as many characters as possible and comparing their variation among dozens of specimens, relationships between species can be tested and broader patterns emerge.

The ATOL project became a morphological powerhouse. Generally, a group of 500 characters is considered to be a large dataset. The morphology researchers on the ATOL project generated an unprecedented 4,500 characters. Once both DNA and morphological datasets were produced, the resulting combined matrix provided an unprecedented amount of information for each of the 83 mammals included in the study.

"It's not that we hadn't combined morphology with DNA before." clarifies co-author Michelle Spaulding, PhD, the Rea Post-doctoral Fellow at Carnegie Museum of Natural History. "This time, we ratcheted up the amount of morphological detail phenomenally, providing a larger anatomical base for the study as compared with DNA than is typical.."

With the new Tree of Life matrix, researchers now have greater context for the fragmentary fossils they have in hand—often scant evidence such as a few teeth or a skull fragment—potentially shedding light on little-known species that have yet to find a solid home in the evolutionary tree.

Biomechanical Assessment of Evolutionary Changes in the Lepidosaurian Skull

1. Mehran Moazena,1,
2. Neil Curtisa,
3. Paul O'Higginsb,
4. Susan E. Evansc and
5. Michael J. Fagana

-Author Affiliations

1.
aDepartment of Engineering, University of Hull, Hull HU6 7RX, United Kingdom;
2.
bThe Hull York Medical School, University of York, York YO10 5DD, United Kingdom; and
3.
cResearch Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom

1.

Edited by R. McNeill Alexander, University of Leeds, Leeds, United Kingdom, and accepted by the Editorial Board March 24, 2009 (received for review December 23, 2008)

Abstract

The lepidosaurian skull has long been of interest to functional morphologists and evolutionary biologists. Patterns of bone loss and gain, particularly in relation to bars and fenestrae, have led to a variety of hypotheses concerning skull use and kinesis. Of these, one of the most enduring relates to the absence of the lower temporal bar in squamates and the acquisition of streptostyly. We performed a series of computer modeling studies on the skull of Uromastyx hardwickii, an akinetic herbivorous lizard. Multibody dynamic analysis (MDA) was conducted to predict the forces acting on the skull, and the results were transferred to a finite element analysis (FEA) to estimate the pattern of stress distribution. In the FEA, we applied the MDA result to a series of models based on the Uromastyx skull to represent different skull configurations within past and present members of the Lepidosauria. In this comparative study, we found that streptostyly can reduce the joint forces acting on the skull, but loss of the bony attachment between the quadrate and pterygoid decreases skull robusticity. Development of a lower temporal bar apparently provided additional support for an immobile quadrate that could become highly stressed during forceful biting.

* biomechanics
* Lepidosauria
* lower temporal bar
* streptostyly

Footnotes

* 1To whom correspondence should be addressed. E-mail: m.moazen@hull.ac.uk

Busy assessing what GPFS can do under our new configuration, so no time to comment.