Phil's phylogeny article

[Steve O'Shea]

Great stuff Phil!!! One question that I have has to do with those two little 'blips' at ~ 80 and 110 million years back on the ammonite section. It looks like there's a sudden explosion in diversity that just-as-suddenly decreases (the 'blips'). Has this got anything to do with excellent/more sedimentary deposits of certain ages that are more condusive to preserving ammonites, or do you think these rapid expansions (then decreases) in diversity are real?

It would be interesting to know, or have some indication of the number and distribution of sites with sediments of particular ages, and an indication of the amount of research that has been undertaken on sediments of particular ages (to aid determining whether increases in diversity are real, or just an artefact of the number and distribution of sites of certain ages, and the amount of effort that has gone into revising the ammonites of certain ages/sediments). Maybe in 2010 we could get to the bottom of this.

Isn't it strange how terrestrial groups seem to have survived many of these extinctions, whereas the marine groups haven't (even though the comparison is between something like reptiles and a subset of cephalopods, like ammonites and belemnites). Maybe I'm dreaming when it comes to looking for a living ammonite, because maybe it never really went extinct - the whole group could just as easily have dropped its shell and changed into a modern-day (Recent) form.

I know many phylogenetic systematists/geneticists might disagree, but the possibility simply cannot be discounted (personally I think 'parsimony' is nonsensical). I like chaos!

Looking forward to the next article!
Cheers
O

 

[Fujisawas Sake]

Kick Arse, Phil!!

Okay, that was cool. I think Steve's question on diversity kind of nods to our little debate on ceph body-plan diversity in the past few geologic ages.

Steve,

Actually, most terrestrial groups suffered MASSIVE losses during the major mass extinction level events (ELE's). As a group, I guess we came out okay, but the losses were severe. Oh, and as for geneticists? HA! I would love to see someone TRY to get DNA out of an Ammonite fossil.

Great post Phil! Sake for all!

John

 

[Architeuthoceras]

Great Chart Phil

Steve, the "blips" correspond with rising and falling sea level events, which would increase and decrease both the available sedimentary deposits for collection and the available habitat for diversification, so it is probably a combination of both factors. I think enough fossils from all preserved facies (basically habitats), the same age as those blips, have been collected worldwide to lean more towards the real diversity of the cephalopods.

 

[Phil]

Re: Phil's phylogeny article

Great stuff Phil!!! One question that I have has to do with those two little 'blips' at ~ 80 and 110 million years back on the ammonite section. It looks like there's a sudden explosion in diversity that just-as-suddenly decreases (the 'blips'). Has this got anything to do with excellent/more sedimentary deposits of certain ages that are more condusive to preserving ammonites, or do you think these rapid expansions (then decreases) in diversity are real?

Thanks John and Kevin!

Steve,

Speaking as a ‘rank amateur’ as Clem might say, I cannot be absolutely certain. However, I think that the increase in diversity of the ammonites is a genuine reflection of the group as a whole, and not necessarily a reflection of a ‘patchy’ fossil record. Having said that, I’m sure that the incompleteness of the fossil record does have a part to play.

Ammonites obviously do not require exceptional environmental conditions to fossilise, unlike most of the coleoids. Due to their robustness ammonites are extremely well documented and have an invaluable use in stratigraphy the world over. For example, here in Britain we have something approaching 60 ammonite zones for the Jurassic period alone, each being marked by a specific species of ammonite with a lifespan of just less than a million years or so. (In the Cretaceous chalk in Britain, belemnites are used as stratigraphical markers). This is not to say that there were no species of ammonite that lived for more than a million years, indeed there were several, but these are useless for biostratigraphy, which relies on species that evolved and changed rapidly. Each ammonite zone can used to correlate with other zones in different locations in order to date them by direct comparison.

As ammonites can be used for this purpose it follows that the fossil record is very good, and that fluctuations in the number of families that appear to be present is a genuine artefact. It does seem apparent from the diagram that there was a boom in ammonite diversity in the mid-late Cretaceous, which seems to coincide with the deposition of the Gault clays and chalk. (This is only my interpretation; I may be completely wrong). The tail off from the late Cretaceous is a widely recognised pattern; there are very few ammonite species known from just below the KT boundary.

I would not interpret the blips and bulges too closely! I based the chart on a combination of the Coleoid Tree on Theo Engesers’ site and a cephalopod tree in ENK Clarksons ‘Invertebrate Palaeontology and Evolution’ (1998) and represents my translation of the diagram in that book. I am happy with the overall shape of the groups and a rough idea of diversity, but I certainly would not try counting the pixels and assuming it is 100% accurate. I think a fair approximation would be an appropriate description.

Thanks!

 

[Clem]

Phil,

The chart is terrific. That's tricky data to render visually and you've done it awfully well.

Clem

ps: You will have to pry the "rank amateur" line from my cold, dead hands.

 

[Steve O'Shea]

Hmmmmm. Interesting stuff. A million years for the life of a species seems rather short.

It would be interesting to look at comparative species longevity for other groups - say soft-sediment dwelling epifauna, compared to infauna, and fish fauna (if we have good records). Myopsida, have you any data/information on fish species longevity for New Zealand, for say the Castlecliff series? BAM (secret code), have you species-longevity data for say pectinids, Struthiolaria/Pelicaria, Amalda/Baryspira, Alcithoe[/i], to compare with something like tellinid and venerid bivalves (for example).

Does habitat complexity/variability play any obvious role in speciation rate. Does the evidence (at least for New Zealand) support punctuated or gradual evolutionary concepts? If epifaunal habitat variability plays a role in speciation rate, and ammonites were particularly fast-evolving, then is it not possible that their environment was particularly variable (you wouldn't really expect this of the water column), and that maybe they were closely associated with the sea floor?

Just thinking aloud ... I know not what I'm talking about.
O

 

[Phil]

Hmmmmm. Interesting stuff. A million years for the life of a species seems rather short.

Steve,

Sorry, I was not very clear. Many ammonite species existed for much more than a million years, but only those with the shortest lifespans have any real use in biostratigraphy, and some ammonites did indeed evolve into new species very rapidly. It is almost certainly not a coincidence that during the Jurassic the climate was warmer than it is now with more of the land mass of the earth enjoying warm temperate or tropical conditions. Warmer seas to my mind would possibly indicate that there was greater potential for speciation, that is to say species may have been very diverse and widespread. (see Paleomap for climate details).

Here are a couple of useful references for the use of ammonites in biostratigraphy that reference species longevity:

WIEDMANN, J. & KULLMANN, J. (1980) Ammonoid Sutures in Ontogeny and Phylogeny. In The Ammonoidea (Ed House, M.R. & Senior, J.R.) Systematics Association Special Volume No. 18, Academic Press, London and New York, pp 215-255

MITCHENER, B. C., LAWRENCE, D. A., PARTINGTON, M. A., BOWMAN, M. B. J., & GLUYAS, J. (1992) Brent Group: Sequence Stratigraphy and regional implications, In Geology of the Brent Group (Ed. Morton, A. C., Haszeldine, R. S., Giles, M. R. & Brown, S.)Geological Society Special Publication, No.61 London, p. 45-80.

Sorry that reply is a bit naff, no time right now to look up a more detailed answer. Will try again tomorrow!

 

[myopsida]

Steve
The fossil record is fairly poor for fishes. Some work has been done on the otoliths - references Schwazans (sp?), and Greenwood of some work done in the 1980s. H.however, IMHO, otoliths are not much use below the generic level - even though the paleoguys love describing plenty of new species on the basis of fossil otoliths. Might be worth dropping a line to EF at Otago - he has had a student working on fossil fishes.

 

[Steve O'Shea]

Ta Myopsida and Phil. I'd be quite interested in some synopsis of speciation rates in marine animals - people have asked on many occasions 'what is the average life span of a species?'. Just thought someone online might have had an idea - it is bound to differ between terrestrial and marine environments, and on the group in question. Just thought there might have been soem interesting data there on ammonites.

I'll put an interloan in for those two references Phil; thanks.
Cheers
O