Link between sea and land animals found

I don't see any post about this anywhere on Sciforums and I think it's an important discovery. The more the fossil record grows, the more it supports the fact of evolution.

http://news.bbc.co.uk/1/hi/sci/tech/4879672.stm

 

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That's awesome. It's kinda funny to think that thing might be my great^1000 grandfather

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. Now why would god create an animal that swims in water, but has an early development of wrists?

 

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Allows fish to move easier through shallow waters probably.

 

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I was going to start a thread on it as well.
Transition Fossil Found

Before I latch on to this I will want to do more research. There have been in the past remarkable fake fossil records.

Just because they say it is does not mean it is.
I'm a skeptic about any thing until I feel that the original source is trustworthy in my mind especially now a days in our media driven technological society that can create identity theft and make plain women stunning.

 

Skepticism is a good thing. However, I have seen this reported on several highly rated news outlets. I am quite sure this is the real deal.

I have been to several evolution forums, and they are all abuzz.

Here is another article on it, complete with picture of the fossil and a model.

http://articles.news.aol.com/news/article.adp?id=20060406093109990001&ncid=NWS00010000000001

 

For those of us who study paleontology and vertebrate evolution, this is no surprise. Just read any books on the subject over the last fifty years and you'll see what I mean: we've known this all along. The morphological facts have always been there, but the creationists (now called "intelligent design" advocates) have been constantly denying and fighting the logical derivatives of what lies before their eyes that we have been excavating. We've already given them Coelacanths and Lungfishes as evidence of ocean-dwelling animals that evolved features that adapted them to be land-dwelling. Don't be surprised to read denials about this new finding as well.

 

Am I to infer from this that you study paleontology and vertebrate evolution?

 

Tiktaalik roseae now has its own homepage at: http://tiktaalik.uchicago.edu/

 

The important trait in Tiktaalik roseae (375 mya) is not that it had fins with structured bones that enabled it to walk on land, but that it has a fully-developed jawed crocodile-like mobile head, and that means that it had a well-developed brain. This is what links it to be an ancestor to modern tetrapods. It is thought to have evolved from Panderichthys – a lobed-finned Sarcopterygii fish (see below). For current discussions about Tiktaalik rosea go to: http://www.earthhistory.co.uk/technical-issues/tiktaalik-roseae/
http://scienceblogs.com/pharyngula/2006/04/tiktaalik_makes_another_gap.php

http://graphics8.nytimes.com/images/2006/04/05/science/05cnd-fossil.190.jpg[IMG/]

The earliest known fish fossils are being found in the Chengjiang fauna area near Kunming China in Yunnan Province are the best example we have of fast evolution radiating out from the “Cambrian Explosion.” Thousands of fossils have been found there dating back to 535 mya. Most of these are jawless soft-bodied fish in the subphylum Cephalochordates, but two species are among the oldest fossil “vertebrate” fish ever found, however none have bony skeletons or teeth. One species is a form of Cathaymyrus, a subphylum of Cephalochordates that include the present-day lancelets (Amphioxus). Lancelets are an important marine species to study because they have neural crest-like cells: a sign of a developing brain. DNA comparisons using lancelets suggests that vertebrate lineages may go back as far as 750 mya. Some paleontologists even believe that Cathaymyrus are the lineage that eventually evolved into humans. But the most well-known fossil at Chengjiang is the Myllokunmingia (530 mya) – a primitive Agnatha vertebrate fish that is thought to be related to present-day hagfish. Hagfish (and lampreys) are thought to have branched out from lancelets.

Other earliest known vertebrate fossils were found in the Deadwood Formation of Wyoming and the Burgess Shale Site in British Columbia Canada. These Late Cambrian (~500 mya) bone fossils are in the class called Agnatha that include lampreys and hagfish. Agnatha is a class in the phylum Chordata that is thought to be a sister class to Cephalochordata (see chart below). They are vertebrates, but they do not have a fully-developed compartmentalized brain like modern-day tetrapods have. They have a very simple brain. In the embryonic stage the nerve cord does not develop a neural crest that leads to separate compartments, such as a hypothalamus, or to a organized sensory limbic system that would enable it to have complex sense organs.

Placoderms (360-420 mya) are extinct but are said to have evolved from an advanced Agnatha. They were heavily-armored “jawed” fish with a cartilaginous skeleton. Some, however, evolved with a partial bony skeleton and a mobile head (sharks are thought to have evolved from an ancestral Placoderm). The mobile head of Placoderms is also articulated with a bony joint but is certainly not as advanced as Tiktaalik roseae. Placoderms lacked teeth.

Most fish today (95%) are bony fish called Teleostomi fish in the class Osteichthyes – a sister group ancestral related to the jawless Agnatha vertebrates. Sarcopterygii are “lobe-finned” Teleostomi fish that include rhipidistian fish, lungfish, and coelacanths. Rhipidistian fish evolved into lungfish. Most all paleontologists today think that either lungfish or coelacanths evolved into tetrapods that eventually evolved into humans. Lungfish - as the name implies - have lungs that it can use to breathe in or out of the water and have been around for 400 million years. Coelacanths, however, give birth to live young (live birth), and this sets them apart from all other fish.

Chordata:
A. Tunicata: sea squirts and tunicates
B. Cephalochordata:
1. Cathaymyrus or Branchiostoma: lancelet Amphioxus*
2. Pikaia: extinct invertebrate, a very primitive chordata, (Burgess Shale, 505 mya)
C. Vertebrata (7 classes):
1. Agnatha: jawless vertebrates
a. Myllokunmingia (530 mya)
b. Myxini or Hyperotreti: present-day hagfish,
c. Cephalaspidomorphi or Osteostracans
1. Hyperoartia: present-day lampreys
d. Gnathostomata: vertebrates with jaws
1. Placoderms: extinct, evolved from Agnatha
2. Chondrichthyes or “cartilaginous” fish: present-day sharks
3. Osteichthyes or “bony fish”:
1. Actinopterygii/Teleostoi or “ray-finned” fish: ~24,000 species, comprises 95%
of present-day fish and half of all vertebrates
2. Sarcopterygii or “lobe-finned” fish: present-day lungfish and coelacanths
4. amphibia
5. reptilia
6. aves
7. mammalian

* The lancelet does not have a vertebrate column: it has a notochord that gives it skeletal support. Above the notochord is a nerve cord but it has no brain, no eyes, and no heart; although it does have a single ventral blood vessel. It is thought that vertebrates evolved from ancestors similar to lancelets. However some paleontoligists believe that chordates evolved from tunicates via way of neotomy – the retention of juvenile features into the adult stage (tunicates have notochord, dorsal nerve cord, and a heart).
See: “The Biology of Chordates” [url]http://ebiomedia.com/prod/BOchordates.html[/url]
also “The Early Vertebrates”
[url]http://www-geology.ucdavis.edu/~cowen/HistoryofLife/CH07.html[/url]

Evolution of Tetrapod Legs from Sacropterygian Fish:

[IMG]http://people.eku.edu/ritchisong/forelimbs3.gif

Source: http://people.eku.edu/ritchisong/342notes1.htm

For a list of subphylum and classes of fish in the phylum Chordata, and a hypothetical list of the subclasses that led to tetrapod amphibians and mammals, see: http://en.wikipedia.org/wiki/Chordata
http://www.fmnh.helsinki.fi/users/h...ostoma/Chordata/Vertebrata.htm#Actinopterygii

For a list of websites related to the Myllokunmingia or Haikouella found in China see:
http://www.factbites.com/topics/Myllokunmingia

 

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Valich:

Thanks for the links. I personally find vertebrate evolution exceptionally fascinating, even though I specialized in botany.

Got any good links for the evolutionary loss of the sperm flagella in the flowering plants (which flagella are still present in the conifers)?

 

I'm very interested in the evolution of eukaryotes and prokaryotes but I don't know much about botany. Do any flowering plants have flagella? Flagella need a lquid - usually water - in order to fertilize. In terms of evolution the origin of flagella and the loss of flagella seem to coincide. Flagella are found in some mosses, ferns, and in some protists (some green algae - not all, heterokonts, dinoflagellates, cryptomonads, haptophytes, and euglenids). This seems to be the transition area. In his study guide, Dr. David Dilkes asks his students, "Give two reasons for the loss of flagella in plants." He doesn't give the answer, but I'm sure that contacting him would be an excellent resource for you. One answer would have to be lack of accessible surrounding moisture (ddilkes@credit.erin.utoronto.ca).

"Several hypotheses on the origin of cilia and flagella in eukaryotes have been proposed. The endosymbiont model postulates that these organelles may have derived from the symbiotic inclusion of spirochete bacteria, while the autogenous hypothesis favors the idea that cilia developed from further specialization of the cytoskeleton. In either case, the ancestral origin of the axoneme has been key for establishing main phylogenetic divergences. For instance, at the root of the eukaryote tree, the distinction between opisthokonts (animals, fungi, Chonozoa) and anterokonts (all other eukaryotes comprising plants and biciliates/bikonts) is based on whether the cilium is posterior or anterior. Cilia and flagella structure and function are very well conserved across evolution. The high degree of sequence conservation between flagellar proteins of unicellular organisms such as the biflagellate alga Chlamydomonas reinhardtii and mammalian ciliary proteins suggests that the functional role of the genes encoding cilia has been preserved throughout evolution. Chlamydomonas has been an advantageous system for studies of assembly and motility of cilia due to the ability to generate and detect mutants that cannot swim, and then to biochemically characterize their flagella. From these studies we can know that eukaryotic flagella are composed of more than 200 proteins. This large number of components is also present in mammalian cilia. Despite their overall structural similarities, the specialization of cilia for particular functions has resulted in significant variations of structure and regulation. To address these functional adaptations, a variety of model systems have been used. For instance, the gill cilia in mollusks have been studied for their capability to coordinate a precise filter feeding mechanism, the sperm flagellum in sea urchin employed for waveform motion analysis, the oviduct cilia in quail for analysis of ciliogenesis, and the cilia of the fish lateral line organ probed to understand sensory mechanistics. In the last few years, the generation of gene-targeted mice with deficient axonemal components has been critical for the investigation of numerous ciliary functions necessary for mammalian physiology, and their relation to human pathology." http://hmg.oxfordjournals.org/cgi/content/full/12/suppl_1/R27

"the ancestor of all extant eukaryotes must have been a single-celled organism with a 9+2 flagellum. Therefore, the central pair microtubule complex evolved very early as an essential element in flagellar motility, and this machinery has survived with little modification during evolution into today's phylogenetically diverse organisms. Flagella become paralyzed when either the central pair or radial spokes are missing."
http://www.jcb.org/cgi/content/full/166/5/709

In spermophyta seed plants the flagella is very reduced. See excellent evolutionary chart: http://www.erin.utoronto.ca/~w3bio151y/Dilkes10.html

Flagella in methanogens, cyanobacteria, spirochetes, spirilla, pseudomonads, vibrios:
http://www.bact.wisc.edu/Bact303/MajorGroupsOfProkaryotes

"Extreme segregation distortion [of alleles] occurs most commonly in spermatogenesis; meiotic drive alleles increase their transmission to the next generation by sabotaging gametes carrying alternative alleles. Causes defective, “curlicue” flagella, poor motility and impairs capacitation in wild-type sperm [in mice]."
http://www.universitychica.com/

Flagella need a liquid for fertilization: "The synapomorphies of the group [Charophyta] are said to include the the dissolution of the nuclear membrane during mitosis and the presence of paired flagella (when flagella are present at all) directed perpendicularly to each other.In addition, the charophytes are strongly inclined toward growth as long filaments." Evidently in some Charophyta green algae flagella are present and in some they are not, so this might be the place to look for the evolutionary transition.
http://www.palaeos.com/Plants/default.2.htm

There's a number of websites related to loss of flagella in protists:

"Flagella become paralyzed when either the central pair or radial spokes are missing," see "Bend propagation drives central pair rotation in Chlamydomonas reinhardtii flagella": http://72.14.207.104/search?q=cache...f the sperm flagella&hl=en&gl=us&ct=clnk&cd=3

Loss of phototrophic nanoflagellates (PNAN): http://www.pubmedcentral.gov/articlerender.fcgi?artid=239220

Loss of flagella in Pennales:
http://www.elsevier.de/elsevier/journals/files/protist/issue4_99/0025.pdf.

No flagella found in pelobiont protist Pelomyxa corona:
http://72.14.207.104/search?q=cache... flagella in protist&hl=en&gl=us&ct=clnk&cd=4

Loss of flagella in Volvox with pics:
http://protist.i.hosei.ac.jp/PDB/Images/Chlorophyta/Volvox/

Flagella in ferns: http://www.yorku.ca/plants/163.PDF

Links to evolution of flagella: http://www.simonyi.ox.ac.uk/dawkins/WorldOfDawkins-archive/Catalano/box/published.shtml

 

"Because of multiciliate sperm, cycads show a nice connecting link with the more primitive spore-producing ferns, which must depend on free environmental water for the transport of their sperm, and the advanced seed plants in which the sperm are non-flagellated and non-motile." http://waynesword.palomar.edu/ww0803.htm

"The cilium in its early form would have been too short to function as a rowing device. What could it have done? The first flagellates are long gone, but we can still learn from the ones at the base of the family tree as it now exists. The soil dwelling flagellate Phalansterium is about as basal as any. It is hard to watch in action, but it probably uses its cilium to sense the environment and to collect bacteria to eat. The eukaryote family tree has two main branches, leading to plants and animals. At the base of these branches we find water dwelling flagellates that push water in opposite directions. Mastigamoeba creep along surfaces and move their cilium to create a slight current toward themselves, drawing in food particles. Choanoflagellates, on the line leading to animals, use their cilium to push water away. This draws in more water, and food along with it." http://www.talkdesign.org/faqs/icdmyst/ICDmyst.html

"Endogonales linker group from chytrids (loss of flagella) to ascomycetes and stem of other zygomycetes" http://taipan.nmsu.edu/EPWS472/zygo.html

"A monophyletic Kingdom Fungi is well defined and supported, and contemporary studies support the group as being most closely related to animals, possibly through a choanoflagellate-like ancestor....The Chytridiomycota is the only taxon within Kingdom Fungi that includes representatives which produce a flagellated stage at some point in their life cycle. Current phylogenetic analyses agree that some lineage of the Chytridiomycota occupies the most basal branch of Kingdom Fungi --a finding consistent with a choanoflagellate ancestor; however, there is conflict in the literature as to which group of the Chytridiomycota is most basal.... Is a choanoflagellate ancestor for fungi well supported? Where is the origin of DAP lysine biosynthesis in the fungal ancestry? Can character evolution (flagella, hyphae, etc.) be traced?.... Limited molecular data do not support the monophyly of either the chytrids or the zygomyctes, suggesting multiple losses of the flagellum. In addition the association of many zygomycete groups with arthropods suggests the possibility of multiple origins of a terrestrial fungus. We should be able to address the paraphyly of the Chytridiomycota/Zygomycota clades, the origin of nonplant associated terrestrial fungi (i.e., multiple orgins of terrestrial fungi), character evolution (loss of flagella, modes of sexual reproduction, etc.), and realignment of major taxa of early diverging fungi....aquatic fungi known as chytrids. Controversy exists still about whether the group is monophyletic and about the number of times flagella were lost among the group." http://lsb380.plbio.lsu.edu/network folder/network proposal

"soil-dwelling -proteobacterium Sinorhizobium meliloti engages in a symbiosis with legumes....Expression of chemotaxis and flagellar biosynthetic genes decreased sharply in minimal medium; these made up one-quarter of the 250 genes whose expression decreased. Loss of motility and partial loss of flagella were previously found in starved S. meliloti cultures (36). However, because our exponentially growing cultures were obviously not starving, this suggests that motility in S. meliloti is additionally linked to metabolic state. Alternatively, down-regulation of motility and chemotaxis may be linked to increased exo expression in minimal medium. Faster-swarming S. meliloti mutants show an increased proportion of motile and flagellated cells, more and longer flagella per cell, and decreased EPS synthesis (37). Consistent with this idea, we saw similar decreases in flagellar and chemotaxis gene expression when nodD3 is overexpressed during growth in TY, another condition that increases EPS synthesis (see below). Moreover, strains overproducing succinoglycan, either by deletion of exoR or by constitutive expression of exoS, show greatly reduced expression of flagellar and chemotaxis genes (data not shown); motility assays and microscopy show that these two mucoid strains are nonmotile and lack flagella (D. H. Wells, E. J. Chen, and S.R.L., unpublished data). This pattern of coordinate synthesis suggests that genes involved in EPS production and motility may be part of a complex multitrait adaptation, perhaps related to biofilm formation, that responds to diverse environmental stimuli." http://www.pnas.org/cgi/content/full/101/47/16636

 

Valich:

The sea plants have a very intersting morphology. They are also very diverse, from the extensively abundant unicellular diatoms, to the red algae, green algae, brown algae, etc., all of which seem to have arisen separately from non-plant eukaryotic ancestors by ingestion of prokaryotic photosynsthesizing cells which survived to become a 'chloroplast' with its own separate circular DNA [similar to mitochondria in the eukaruyotes] in each respective lineage.

Some sea plants have both haploid and diploid as the same full-sized adult morphology, whereas others have a diminutive haploid, and still others have the standard haploid as a single cell (egg and sperm), diploid as the adult plant.

It is far more complex than in animals (which have diploid as the adult, haploid as the sex cells, always).

In the land plants, which are believed derived from a green-algae ancestor, the mosses-liverworts have the haploid as the larger morphology, and the diploid is just a small little growth that arises where the egg cell is fertilized inside of an 'archegonium' which contains the egg, by a flagellated sperm that swims through rain water. The small diploid growth then 'fruits' and produces haploid spores (with four cell-nuclei inside each spore body), starting the process anew.

In the fern alliance, the haploid is about the same size as in the mosses/liverworts - about the size of your little pinky's fingernail, and likewise photosynthetic, but the diploid that arises by essentially the same method (flagellated sperm swimming through rainwater, fertilizing an egg inside of an 'archegonium') grows large and becomes vascular, with roots and shoots. It too produces 'fruiting bodies' (sori in ferns, on the underside of the leaves) that release spores, starting the process anew.

In the conifers and cycads, the spores are pollen and are produced in male cone structures, and when they land on a cone with a haploid archegonium (female cone), they grow a pollen-tube down into the archegonium, and release their flagellated sperm, which swim not through rain-water, but through the watery-medium of the pollen-tube, and fertilize the egg, which then grows into the baby diploid plant, but with subsequent arrested growth to allow the baby diploid to be coated and become a seed.

In flowering plants (both monocots and dicots), the same release of pollen occurs, but from a flower, not a cone, and when the pollen lands on a female flower, it grows a pollen tube down towards a very-highly-reduced archegonial structure. However, the sperm that are released are not flagellated as in the cone-plants and in the spore-bearing plants.

It would be interesting to see if they still have the DNA mechanisms for the formation of flagella, and perhaps just a few changes to prevent them from forming (much like chickens have the DNA mechanism for the formation of teeth - they just need the right hormone, but it is not longer produced because of a minor DNA change). I suspect they do.

So, what is the evolutionary advantage of not having the flagella on the sperm?

As you know from your readings, flagella and cilia are hypothesized to have originated from ingestion of prokaryotic cells, which became incorporated in the eukaryote which ingested them, conferring some advantage when they were not 'eaten alive' but instead became part of the eukaryotic cell.

Anyway, I find all of this fascinating, and every time a question is answered, it raises another one anew.

You appear to be well-read in biology - so perhaps you might pose this as an area of research to budding biologists.

Thanks for your efforts here. You might want to check out some of my other posts in nuclear physics, which is my field of expertise.

Regards,



Walter L. Wagner (Dr.)


PS On the post re biofuels, it's been suggested that various algae produce copious amounts of oils that could become bio-diesel. Do you have any ideas on how best to go about growing such algae, and can this be done in tanks on land? To me, it seems difficult to grow large quantities of algae on an economic basis competitive with growing of land plants for their oils, sugars, etc., though I know we routinely harvest some kelps, etc. for some purposes for our agars, ice-creams, and spam-musubis, etc.

Your insight might be a boon to a future bio-fuel economy!

 

No need for skepticism here, Tiktaalik is a great find! And it was reported in Nature, so: rock!
We've been talking about it in one latvian forum for weeks.

p.s. I'm extasic about the name they've given it, it sounds very cute when pronounced in latvian.

 

I’m not referring specifically to this case, but in general publication in Nature is by no means and assurance of accuracy. Nature and Science, the two premier generalist journals, have more retractions and corrections than any other high-impact journal. This is because they give high priority to publishing novel and exciting new discoveries which, by their nature, have only a relatively small amount of data and limited research performed on them.

 

Slightly out of topic: which journal would you suggest then?
I'm not a science student, but have a very keen interest in nature sciences and cosmology,
and don't like being fed bullshit or dumbed down text.

 

Actually the usual way is that novel findings are verfied independently in various journals. Nature and Science actually do not provide dumbed down text but rather more compressed versions as you would see in other journals. Fossil finds are a special case because they are not based on experiments that could be reproduced in similar systems. What could happen is that it turns out to be a fake, like the fake fossil bird that was presented in National Geographics (not science journal btw.). Interestingly, Nature and Science both rejected manuscripts regardings the finds of that fossil bird (before it turned out to be a fake, of course). Anyway, with time this finding might get consolidated, however it is already exciting as it is.

 

I didn't say I think Nature is dumbed down, of course not, I suggested criteria upon which Hercules might suggest me some other good journals on subjects that interest me.
I like Nature, but I'm not competent to judge which other less known journals are good.

 

Unless of course a 3m fish with arms was just another reject from God's R&D labs.

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