Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
5 online now:
Newest Member: popoi
Post Volume: Total: 915,808 Year: 3,065/9,624 Month: 910/1,588 Week: 93/223 Day: 4/17 Hour: 1/1


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Evolution of the Mammalian Jaw
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


(1)
Message 3 of 13 (647331)
01-09-2012 9:57 AM
Reply to: Message 1 by herebedragons
01-08-2012 4:36 PM


I don't know anything as to the merits of your lecturer's comments that this was due to selection for increased strength, but looking for some relevant references I came upon an interesting paper on the overall trend for the reduction in bone number in Synapsid skulls (Sidor, 2001 PDF).
The author suggests that rather than being driven by selection this trend, which includes the bones of the lower jaw, may be driven by an underlying bias in morphological changes which favours a reduction in the number of centers of ossification during development as opposed to their gain.
This argument doesn't really address the very acute size reduction of many of the remaining elements, but there at least their co-option to the auditory system provides a clear selective pressure at work.
TTFN,
WK

This message is a reply to:
 Message 1 by herebedragons, posted 01-08-2012 4:36 PM herebedragons has replied

Replies to this message:
 Message 5 by Dr Adequate, posted 01-09-2012 3:22 PM Wounded King has replied
 Message 8 by herebedragons, posted 01-09-2012 8:05 PM Wounded King has seen this message but not replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 7 of 13 (647476)
01-09-2012 7:16 PM
Reply to: Message 5 by Dr Adequate
01-09-2012 3:22 PM


Oh, we're going to be orthogenesists now?
I believe the preferred current term is 'Process Structuralist'
But if you read the paper you will see that it isn't really an argument along orthogenetic lines but rather a probabilistic one based on the comparative frequencies of bone loss to bone gain in the fossil record.
Sidor writes:
Evolutionary trends in morphological characters pose a problem similar to that of transition and/or transversion substitution probabilities in molecular systematics; not all character state changes are equally likely to occur [...]. The difference resides in the fact that whereas there are biophysical explanations for transition and/or transversion bias [...], the mechanisms underlying morphological biases are far less clear. In addition, not only can active evolutionary trends make some types of characters more probable to change than others (i.e., presence/absence characters), but they set up a systematic bias in the direction of character state change (i.e., changes from presence to absence). Perhaps because of the intractibility of assigning an objective differential weighting scheme to these types of characters, paleontologists have, on the whole, been content to consider all transitions to be equally likely [...]. Recognizing instances of biased morphological change is imperative for appropriately modeling character evolution in phylogeny reconstruction.
The fact that not all genotype changes are equiprobable should surely render wholly uncontroversial the suggestion that all phenotype changes are similarly not equiprobable. It follows naturally that the distribution of likelihood of possible phenotypic changes (and their associated genotypes) is going to affect the evolutionary trajectory of the population.
Dr. A writes:
Should we also paint ourselves with ochre and worship trees?
You totally should.
TTFN,
WK

This message is a reply to:
 Message 5 by Dr Adequate, posted 01-09-2012 3:22 PM Dr Adequate has replied

Replies to this message:
 Message 12 by Dr Adequate, posted 01-10-2012 4:25 PM Wounded King has seen this message but not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024