Fairly new snake evolution and phylogeny

the toe cutter

Arachnobaron
Joined
Mar 20, 2010
Messages
424
Excerpt from college Biology concepts and investigations, McGraw Hill 2009. I thought it was pretty interesting...

"Fossils have answered the question of how tetrapods got their limbs, but until recently the same was not true for another important issuein vertebrate evolution: how did snakes lose their limbs? Molecular and anatomical information, including vestigal legs in some snakes, clearly indicated that snakes evolved lizards. Yet the precise four-legged ancestor has remained elusive.
Scientists proposed two competing hypotheses to explain the origin of snakes. Noting that snakes resemble two existing groups of burrowing lizards, some scientists suggested that snakes evolved on land. Opposing scientists contend that snakes decend from Mosasaurus, marine reptiles that thrived during the Cretaceous period, based on skull and jaw similarities.
Argentinian paleontologist Sebastian Apesteguia, along with Brazilian colleague Hussam Zaher, added a critical clue to the debate over snake origins in April 2006, when they reported finding three fossilized snakes in the Patagonia region of Argentina. The snakes, which theynamed Najash rionegrina, lived during the Upper Cretaceous period, about 90 MYA.
Najash is different from other ancient snakes for atleast two reasons. First, it is the first snake ever found to have not only functional legs and a pelvis but also a sacrum-a bone connecting the pelvis to the spine. (In other fossil snakes with limbs, the pelvis is "free floating" and not connected to the backbone.) The sacrum is important because lizards and other tetrapods, the ancestors of snakes, have the same bone. Najash is therefore more primitive than any snake ever found. Second, both the fossil's features and the rock where it was found suggest that itwas terrestrial, not marine. Taken together, these two pieces of evidence seem to settle the question: snakes originated on land, not in water."

Here's a BASIC phylogenic treebased on skeletal similarities

......._______________________________ Monitor lizard
......l... _____________________________ Najash
......l__l....__________________________ Scolecophidia
..........l__l....________________________ Dinilysia
..............l__l...._____________________ Anilioidea
..................l...l....____________________ Xenopeltis
..................l__l...l____________________ Loxocemus....__
......................l...l.............____________ Haasiophis.......l
......................l...l________l...._________ Pachyrhachis.....l_marine fossil
......................l...l.............l__l.....................................l snakes
......................l__l.................l_________ Eupodophis...__l
..........................l...___________________ Erycinae
..........................l...l___________________ Pythoninae
..........................l...l___________________ Ungaliophiidae
..........................l__l....________________ Wonambi
..............................l__l
..............................l...l________________ Boinae
..............................l...________________ Bolyeriidae
..............................l__l...._____________ Tropidophiidae
..................................l__l....__________ Acrochordidae
......................................l__l
..........................................l__________ Colubroidea

I hope this was a bit insightful to the evolution of snakes for anyone interested in that. I know that Phylogeny of reptiles is constantly in disarray, so please try to keep comments about the tree above to a minimum because NO ONE is correct. And I do realize it is most definitely not an all encompassing tree as well. Thanks again and any added comments that may be more up to date would be fantastic! Cheers
 
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the toe cutter

Arachnobaron
Joined
Mar 20, 2010
Messages
424
Wow that tree got pretty screwed up from how it was originally done before posting! Oh well some of you may be able to follow it. Well that is the best I can fix it, just ignore the periods!
 
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dtknow

Arachnoking
Old Timer
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Aug 18, 2004
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2,242
Interesting the monitors are placed as the snakes closest living relatives...(unfortunately no legless varanids around anymore eh?).

I wonder where Lathanotus and Heloderma would fit in?
 

the toe cutter

Arachnobaron
Joined
Mar 20, 2010
Messages
424
Heloderma Evolution
CNAH ANNOUNCEMENT
The Center for North American Herpetology
Lawrence, Kansas
http://www.cnah.org
23 February 2009

CONSERVATION PHYLOGENETICS OF HELODERMATID LIZARDS USING MULTIPLE MOLECULAR MARKERS AND A SUPERTREE APPROACH

Michael E. Douglas, Marlis R. Douglas, Gordon W. Schuett, Daniel D. Beck & Brian K. Sullivan

2010. Molecular Phylogenetics and Evolution 55: 153-167

Abstract: We analyzed both mitochondrial (MT-) and nuclear (N) DNAs in a conservation phylogenetic framework to examine deep and shallow histories of the Beaded Lizard (Heloderma horridum) and Gila Monster (H. suspectum) throughout their geographic ranges in North and Central America. Both MTDNA and intron markers clearly partitioned each species. One intron and MTDNA further subdivided H. horridum into its four recognized subspecies (H. n. alvarezi, charlesbogerti, exasperatum, and horridum). However, the two subspecies of H. suspectum (H. s. suspectum and H. s. cinctum) were undefined. A supertree approach sustained these relationships. Overall, the Helodermatidae is reaffirmed as an ancient and conserved group. Its most recent common ancestor (MRCA) was Lower Eocene [35.4 million years ago (mya)], with a ca. 25 my period of stasis before the MRCA of H. horridum diversified in Lower Miocene. Another ca. 5 my passed before H. h. exasperatum and H. h. horridum diverged, followed by ca. 1.5 my before H. h. alvarezi and H. h. charlesbogerti separated. Heloderma suspectum reflects an even longer period of stasis (ca. 30 my) before diversifying from its MRCA. Both H. suspectum (México) and H. h. alvarezi also revealed evidence of historic range expansion following a recent bottleneck.

Also Heloderma are considered living fossils, belonging to the Helodermatidae group, sole survivors of predatory lizards named Monstersaurus. Helodermatidae evolutionary history extends across Asia, Europe and North America. And the Monstersauria group dates back 100MYA well within the age of dinosaurs and have undergone little morphological change.
 
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