Simiosaurs such as Megalancosaurus are one of the most controversial groups of diapsids. While generally placed among basal archosauromorphs, they've also been considered non-saurians (Senter, 2004), euryapsids (Muller, 2004), lepidosauromorphs (Peters, 2007) and theropods (Olshevsky, 1991). They've also been attached to both pterosaur (Peters, 2000; Renesto and Binelli, 2006) and bird (Feduccia and Wild, 1993) ancestry.
Enforcing Cosesaurus and Longisquama to be pterosauromorphs is five steps longer, and they along with simiosaurs and Langobardisaurus end up as basal avemetatarsalians. Enforcing Cosesaurus and Longisquama to be pterosauromorphs and placing the clade outside Archosauriformes is thirteen steps longer. In this topology, they are prolacertiforms, simiosaurs and closest to pterosaurs, with Longisquama one node out. This is ten steps longer than Renesto and Binelli's (2006) topology where simiosaurs+pterosaurs are sister to archosauriforms and prolacertiforms with Langobardisaurus and more basal. Enforcing Megalancosaurus to be a theropod is 34 steps longer (Longisquama and Vallesaurus follow it). I neglected to mention last time that Olshevsky also placed Cosesaurus in Theropoda, which takes 41 more steps, with simiosaurs, Longisquama and Langobardisaurus following. So Olshevsky was near certainly wrong about either Megalancosaurus or Cosesaurus being theropods, though Longisquama is more equivocal.
Notice the trend for how much less parsimonious it is to contrain pterosaurs as non-archosauriforms.
- Longisquama added. 23 more steps.
- Longisquama and Cosesaurus added. 22 more steps.
- Longisquama, Cosesaurus and Langobardisaurus added. 15 more steps.
- Longisquama, Cosesaurus, Langobardisaurus and simiosaurs added. 13 more steps.
Next up before I add Preondactylus and Pteranodon (and check the other pterosaurs' coding) is Peters' (2000) last "key taxon" Sharovipteryx. Will it make non-archosauriform pterosaurs even more parsimonious?
Sunday, May 8, 2011
Saturday, May 7, 2011
Langobardisaurus in Nesbitt's matrix
Continuing the series, I added the tanystropheid Langobardisaurus to Nesbitt's new archosauriform analysis. Langobardisaurus is another taxon which Peters (2000) considered key to connecting prolacertiforms with pterosaurs. It's very odd in its own right, especially its somewhat artiodactyl-like skull. Luckily, several specimens have been well described and it's better preserved than Longisquama or Cosesaurus. Once coded, it groups with Longisquama and Cosesaurus, but this clade can vary in position. It can be anywhere outside Pseudosuchia or Ornithodira. Constraining prolacertiform pterosaurs is now only 15 steps longer, compared to 22 steps before Langobardisaurus was added. What will happen when Vallesaurus and Megalancosaurus are added?
Cosesaurus in Nesbitt's matrix
I haven't written the Cosesaurus entry for my site yet, but to me it always seemed the BANDits best bet, though instead they went with the weird Megalancosaurus and parafeathered Longisquama. Cosesaurus looks outwardly like a little theropod, though of course it differs in the details. Like Longisquama, its anatomy has not been redescribed since the 70s and the existing reconstructions involve lots of imagination. The thing's preserved as a sandstone impression, and Ellenberger (1977) saw lots of feathers and drew numerous lines in and around the skull that have no guarantee of reflecting morphology. Peters (2000) handled it better, but like in Longisquama identified antorbital fenestrae and suture details that Ellenberger didn't see, which makes me suspicious. So again I coded it conservatively, using only the sutures agreed upon by both authors and Peters' interpretation of the pelvis. I'm curious about including Cosesaurus not only because it's one of Peters' proposed non-archosaurian pterosaur relatives but also to address the argument that pterosaurs only clade with avemetatarsalians because there's nothing better in the matrix. Would Cosesaurus also clade with avemetatarsalians despite its primitive anatomy? Would it draw pterosaurs out of Archosauria?
The answer is that Cosesaurus emerges basal to Erythrosuchus, in a polytomy with Mesosuchus, Prolacerta, proterosuchids and higher archosauriforms. If Longisquama is included as well, both clade with Prolacerta. So it seems Nesbitt's matrix handles basal taxa just fine. Only four steps move it sister to pterosaurs in Avemetatarsalia though, which is somewhat worrying. It takes 22 more steps to move pterosaurs out with them in Prolacertiformes.
We'll see how this develops with the addition of unambiguous tanystropheid Langobardisaurus, a couple simiosaurs, Preondactylus and Pteranodon. I'll also be checking the general pterosaur codings when coding them, to make sure Nesbitt didn't assume homology a priori by e.g. coding manual digit IV as unknown in amount of reduction.
The answer is that Cosesaurus emerges basal to Erythrosuchus, in a polytomy with Mesosuchus, Prolacerta, proterosuchids and higher archosauriforms. If Longisquama is included as well, both clade with Prolacerta. So it seems Nesbitt's matrix handles basal taxa just fine. Only four steps move it sister to pterosaurs in Avemetatarsalia though, which is somewhat worrying. It takes 22 more steps to move pterosaurs out with them in Prolacertiformes.
We'll see how this develops with the addition of unambiguous tanystropheid Langobardisaurus, a couple simiosaurs, Preondactylus and Pteranodon. I'll also be checking the general pterosaur codings when coding them, to make sure Nesbitt didn't assume homology a priori by e.g. coding manual digit IV as unknown in amount of reduction.
Longisquama in Nesbitt's matrix
Here's an interesting one. Longisquama has an extremely controversial phylogenetic position. It's been placed outside Sauria, as a lepidosauromorph, a tanystropheid, a non-dinosaurian archosauromorph and even a theropod. See my discussion here for details. Nesbitt's matrix cannot test most of these, since it only covers archosauriforms. But I was curious what would happen if it was added to the matrix, since it's been allied with pterosaurs by some, and the BAND crowd insists it's an archosauriform. Not that the latter would believe a cladistic analysis, but meh...
Unfortunately, Longisquama's morphology is also controversial, and has yet to be studied in depth. Such basic features as the antorbital fenestra and tooth implantation are not agreed on by all authors. So I coded Longisquama twice. One uses Peters' (2000) interpretation of skull elements and the sternum-interclavicle structure. The other uses the minimum codable without dividing the skull into discreet elements and treating the aforementioned pectoral structure as "bony wisps that defy interpretation" as interpreted by Senter (2003).
Perhaps unsurprisingly, its position depends on how it's coded. Coding it conservatively results in Longisquama being outside Archosauriformes alongside Mesosuchus and Prolacerta. Constraining it and pterosaurs to be sister taxa is only two steps longer, and puts both in Avemetatarsalia. Constraining it as a theropod is seven steps longer, and it emerges as the basalmost one. Coding Longisquama as Peters illustrates it (this was before he thought he saw the hindlimbs and such) results in it being a pterosauromorph, with pterosaurs in their usual position. Constraining it to be outside Archosauriformes is only three steps longer.
In conclusion, Longisquama desperately needs redescribed. Ignore the parafeathers, we need its basic anatomy established. While moderately rejected as a theropod, I'd say it could equally well be a non-archosauriform or a pterosauromorph regardless whose reconstruction is used.
Unfortunately, Longisquama's morphology is also controversial, and has yet to be studied in depth. Such basic features as the antorbital fenestra and tooth implantation are not agreed on by all authors. So I coded Longisquama twice. One uses Peters' (2000) interpretation of skull elements and the sternum-interclavicle structure. The other uses the minimum codable without dividing the skull into discreet elements and treating the aforementioned pectoral structure as "bony wisps that defy interpretation" as interpreted by Senter (2003).
Perhaps unsurprisingly, its position depends on how it's coded. Coding it conservatively results in Longisquama being outside Archosauriformes alongside Mesosuchus and Prolacerta. Constraining it and pterosaurs to be sister taxa is only two steps longer, and puts both in Avemetatarsalia. Constraining it as a theropod is seven steps longer, and it emerges as the basalmost one. Coding Longisquama as Peters illustrates it (this was before he thought he saw the hindlimbs and such) results in it being a pterosauromorph, with pterosaurs in their usual position. Constraining it to be outside Archosauriformes is only three steps longer.
In conclusion, Longisquama desperately needs redescribed. Ignore the parafeathers, we need its basic anatomy established. While moderately rejected as a theropod, I'd say it could equally well be a non-archosauriform or a pterosauromorph regardless whose reconstruction is used.
Lukousaurus in Nesbitt's matrix
Back in ye olde days when I was new to the DML, I wrote a post on Lukousaurus to determine its phylogenetic affinities- http://dml.cmnh.org/2000Sep/msg00086.html . I didn't have anywhere near the amount of knowledge and resources I do now, and I considered it an abelisaurid or sphenosuchian. Times have changed and now we have Nesbitt's huge new analysis which is perfect for coding Lukousaurus in. It doesn't have abelisaurids, but does have Dilophosaurus and Allosaurus along with several sphenosuchians. Note the caveat that Lukousaurus is coded from Young's 1948 figures and description. So after entering Lukousaurus, there are 4683 MPTs with Lukousaurus as an archosaur in all of them. It is not a member of Ornithosuchidae, Revueltosaurus+Aetosauria, Poposauroidea, Loricata or Dinosauromorpha. So it's probably some sort of basal pseudosuchian...
By the way, I noticed when coding that as in Smith et al.'s matrix, Marasuchus is not coded for its maxilla, even though Nesbitt lists the specimen as one of those he used for scoring, and lists the maxilla's presence in the material. Also Coelophysis is oddly coded for osteoderm character 408, despite lacking osteoderms.
More added taxa to follow...
By the way, I noticed when coding that as in Smith et al.'s matrix, Marasuchus is not coded for its maxilla, even though Nesbitt lists the specimen as one of those he used for scoring, and lists the maxilla's presence in the material. Also Coelophysis is oddly coded for osteoderm character 408, despite lacking osteoderms.
More added taxa to follow...
Wednesday, May 4, 2011
Nesbitt's excellent new analysis
I just wanted to state my praise for Sterling Nesbitt and his amazing new archosaurian phylogeny paper. The taxon sampling is extensive, with discussions of which material is used for each taxon. The characters are described in great detail and illustrated wonderfully, with the specimens they're found in often listed. Alternative phylogenies are examined and character support is discussed. The matrix seems completely coded. I chuckled at the dismissals of Lucas' "superficial" taxonomic discussions. :) This is surely one of the best archosaurian analyses published, and that includes ALL archosaurian analyses, on theropods, birds, crocs, you name it. But it just wouldn't be like me to not include some criticisms, so I offer the following...
On page 236, Nesbitt discusses the position of pterosaurs, which is as basal avemetatarsalians. Note this doesn't mean much in regard to the controversy of their wider relationships among reptiles, since simiosaurs, Longisquama and tanystropheids were not included. Nesbitt tries to counter Bennett's (1996) statement that pterosaurs don't have many synapomorphies of archosauriform clades more inclusive than Ornithodira with a list of the synapomorphies of Crurotarsi sensu lato, Archosauria, Archosauriformes, etc., detailing which are found in pterosaurs. This is all fine except that 13 of the characters are simply stated to be "not known in basal pterosaurs". I can't help but wondering if these (generally difficult to observe features in the braincase, tarsals and such) are known to be absent in derived pterosaurs. If so, they should still count against pterosaurs being in the listed clades. In fact, I wonder why no derived pterosaur like Pteranodon was included, when derived members of other clades (e.g. Alligator, Allosaurus, Velociraptor) were used to increase the informativeness of characters.
Note Nesbitt's Rauisuchidae should be called Teratosauridae, assuming Teratosaurus is in its standard position by Polonosuchus and Postosuchus.
I would have liked to see Doswellia, Trialestes, "Zanclodon" arenaceus, Erpetosuchus (oddly included in the character descriptions, but not the matrix), Hallopus and/or Macelognathus, Scleromochlus and Preondactylus included.
On page 187, Nesbitt is right to note that many analyses have "Characters just listed with no, little, or
vague explanations". How reduced is "reduced"? How tapered is "tapered"? Unfortunately, Nesbitt's characters sometimes have the same problem. For instance, character 282 is "Pubis, length: (0) shorter or subequal to the ischium; (1) longer than ischium." The word "subequal" should be expunged from character descriptions, since it's not quantified. If I have a taxon with a puboischial ratio of 101%, that's presumably subequal. But what if it's 103%? 106%? Everyone's conception will be different, and this will lead to miscodings. Or character 259- "Metacarpal IV: (0) present; (1) reduced to a nubbin or absent." When is a metacarpal a "nubbin"? Or character 266- "Ilium, crest dorsal to the supraacetabular crest/rim: (0) vertical; (1) anterodorsally inclined." Vertical compared to what basis of horizontal (sacrum axis, axis between anterior and posterior tips, axis formed by ventral extent of peduncles, etc.), and would 92 degrees count as vertical or inclined? These kinds of issues are found in almost every analysis, so this isn't a critique of Nesbitt as much as it's an urging to all of us to explicitly define our character states.
But these issues aside, the paper is extremely well done. Besides the above taxa, someone should use this matrix to place Arganasuchus, "Cryptoraptor", Lagosuchus, Lukousaurus, Razanandrongobe, Saltopus, Spondylosoma, Stagonosuchus, Yarasuchus and Zanclodon.
Nesbitt, 2011. The early evolution of archosaurs: Relationships and the origin of major clades. Bulletin of the American Museum of Natural History. 352, 292 pp.
On page 236, Nesbitt discusses the position of pterosaurs, which is as basal avemetatarsalians. Note this doesn't mean much in regard to the controversy of their wider relationships among reptiles, since simiosaurs, Longisquama and tanystropheids were not included. Nesbitt tries to counter Bennett's (1996) statement that pterosaurs don't have many synapomorphies of archosauriform clades more inclusive than Ornithodira with a list of the synapomorphies of Crurotarsi sensu lato, Archosauria, Archosauriformes, etc., detailing which are found in pterosaurs. This is all fine except that 13 of the characters are simply stated to be "not known in basal pterosaurs". I can't help but wondering if these (generally difficult to observe features in the braincase, tarsals and such) are known to be absent in derived pterosaurs. If so, they should still count against pterosaurs being in the listed clades. In fact, I wonder why no derived pterosaur like Pteranodon was included, when derived members of other clades (e.g. Alligator, Allosaurus, Velociraptor) were used to increase the informativeness of characters.
Note Nesbitt's Rauisuchidae should be called Teratosauridae, assuming Teratosaurus is in its standard position by Polonosuchus and Postosuchus.
I would have liked to see Doswellia, Trialestes, "Zanclodon" arenaceus, Erpetosuchus (oddly included in the character descriptions, but not the matrix), Hallopus and/or Macelognathus, Scleromochlus and Preondactylus included.
On page 187, Nesbitt is right to note that many analyses have "Characters just listed with no, little, or
vague explanations". How reduced is "reduced"? How tapered is "tapered"? Unfortunately, Nesbitt's characters sometimes have the same problem. For instance, character 282 is "Pubis, length: (0) shorter or subequal to the ischium; (1) longer than ischium." The word "subequal" should be expunged from character descriptions, since it's not quantified. If I have a taxon with a puboischial ratio of 101%, that's presumably subequal. But what if it's 103%? 106%? Everyone's conception will be different, and this will lead to miscodings. Or character 259- "Metacarpal IV: (0) present; (1) reduced to a nubbin or absent." When is a metacarpal a "nubbin"? Or character 266- "Ilium, crest dorsal to the supraacetabular crest/rim: (0) vertical; (1) anterodorsally inclined." Vertical compared to what basis of horizontal (sacrum axis, axis between anterior and posterior tips, axis formed by ventral extent of peduncles, etc.), and would 92 degrees count as vertical or inclined? These kinds of issues are found in almost every analysis, so this isn't a critique of Nesbitt as much as it's an urging to all of us to explicitly define our character states.
But these issues aside, the paper is extremely well done. Besides the above taxa, someone should use this matrix to place Arganasuchus, "Cryptoraptor", Lagosuchus, Lukousaurus, Razanandrongobe, Saltopus, Spondylosoma, Stagonosuchus, Yarasuchus and Zanclodon.
Nesbitt, 2011. The early evolution of archosaurs: Relationships and the origin of major clades. Bulletin of the American Museum of Natural History. 352, 292 pp.
Sunday, May 1, 2011
Pneumatocrania and Holtz's thesis
Everyone knows Holtz's famous 1994 paper revolutionizing theropod phylogeny. What fewer people have seen is the 1992 thesis that preceded it, which included its own phylogenetic analysis. The analysis had largely similar characters (128 vs. 126) and included Procompsognathus, Piatnitzkysaurus, Eustreptospondylus and Chilantaisaurus in addition to the taxa from 1994. It also split Ornithomimosauria into Harpymimus, Garudimimus and Ornithomimidae, and did not include Abelisauridae.
The results are similar to the 1994 paper, with the following differences.
- Procompsognathus is outside Eutheropoda.
- Elaphrosaurus is a non-avetheropod tetanurine more derived than Torvosaurus, though on page 264 he notes the characteristics of abelisaurids indicates they and Elaphrosaurus are neoceratosaurs.
- Megalosaurus is a basal carnosaur (along with Piatnitzkysaurus).
- Chilantaisaurus is carnosaur in a trichotomy with Allosaurus and Acrocanthosaurus, and Eustreptospondylus is sister to this group.
Some new names are proposed.
- Eutheropoda is the group containing Ceratosauria sensu lato and Tetanurae, but not Procompsognathus. It's been used informally this way online since the 90s, including on Holtz's site, but I think Novas et al. (2003) have been the only authors to publish it. They used it in the same way (excluding Herrerasaurus and Eoraptor this time), but it's just an abstract.
- Eumaniraptora is first used here, though in a different sense than what was later adopted once it was published in 1997. In Holtz's thesis, Eumaniraptora is what we would now call Maniraptoriformes- the group containing paravians, oviraptorids and arctometatarsalian taxa.
- Holtz used Dinoaves for the Paraves group of dromaeosaurids and Archaeopteryx, though this originally referred to something like Tetanurae when Bakker coined it.
- Arctometatarsalia is proposed here, with the same content as the 1994 paper.
- Pneumatocrania is a name that hasn't made it to the internet before now. It was Holtz's name for his clade of oviraptorids and 'arctometatarsalians', since they were diagnosed in part by pneumatic skulls. Of course, we now know dromaeosaurines reduced their pneumaticity and most of the characters used are problematic (see characters 17, 64, 68, 69, 103, 115, 116 and 121 in my link above), so the topology hasn't been found since.
My favorite part of the thesis is the detailed discussion of twenty-nine poorly known theropod taxa. This includes prescient aspects such as a maniraptoriform Microvenator and a suggestion of elaphrosaur affinity for Chuandongocoelurus almost a decade before I thought the same thing on the DML. It also features some common but incorrect ideas of the early 90's though, such as neoceratosaurian spinosaurids and Carcharodontosaurus.
Thanks to Tom Holtz for permission to write about this interesting piece of theropod history.
References- Holtz, 1992. An unusual structure of the metatarsus of Theropoda (Archosauria: Dinosauria: Saurischia) of the Cretaceous. Unpublished PhD thesis. Yale University. 347 pp.
Holtz, 1994. The phylogenetic position of the Tyrannosauridae: Implications for theropod systematics. Journal of Paleontology. 68(5), 1100-1117.
Novas, Haro and Canale, 2003. Un nuevo terópodo basal de la Formación Ischigualasto (Carniano) de la provincia de San Juan, Argentina. Ameghiniana. 40(4), 63R.
The results are similar to the 1994 paper, with the following differences.
- Procompsognathus is outside Eutheropoda.
- Elaphrosaurus is a non-avetheropod tetanurine more derived than Torvosaurus, though on page 264 he notes the characteristics of abelisaurids indicates they and Elaphrosaurus are neoceratosaurs.
- Megalosaurus is a basal carnosaur (along with Piatnitzkysaurus).
- Chilantaisaurus is carnosaur in a trichotomy with Allosaurus and Acrocanthosaurus, and Eustreptospondylus is sister to this group.
Some new names are proposed.
- Eutheropoda is the group containing Ceratosauria sensu lato and Tetanurae, but not Procompsognathus. It's been used informally this way online since the 90s, including on Holtz's site, but I think Novas et al. (2003) have been the only authors to publish it. They used it in the same way (excluding Herrerasaurus and Eoraptor this time), but it's just an abstract.
- Eumaniraptora is first used here, though in a different sense than what was later adopted once it was published in 1997. In Holtz's thesis, Eumaniraptora is what we would now call Maniraptoriformes- the group containing paravians, oviraptorids and arctometatarsalian taxa.
- Holtz used Dinoaves for the Paraves group of dromaeosaurids and Archaeopteryx, though this originally referred to something like Tetanurae when Bakker coined it.
- Arctometatarsalia is proposed here, with the same content as the 1994 paper.
- Pneumatocrania is a name that hasn't made it to the internet before now. It was Holtz's name for his clade of oviraptorids and 'arctometatarsalians', since they were diagnosed in part by pneumatic skulls. Of course, we now know dromaeosaurines reduced their pneumaticity and most of the characters used are problematic (see characters 17, 64, 68, 69, 103, 115, 116 and 121 in my link above), so the topology hasn't been found since.
My favorite part of the thesis is the detailed discussion of twenty-nine poorly known theropod taxa. This includes prescient aspects such as a maniraptoriform Microvenator and a suggestion of elaphrosaur affinity for Chuandongocoelurus almost a decade before I thought the same thing on the DML. It also features some common but incorrect ideas of the early 90's though, such as neoceratosaurian spinosaurids and Carcharodontosaurus.
Thanks to Tom Holtz for permission to write about this interesting piece of theropod history.
References- Holtz, 1992. An unusual structure of the metatarsus of Theropoda (Archosauria: Dinosauria: Saurischia) of the Cretaceous. Unpublished PhD thesis. Yale University. 347 pp.
Holtz, 1994. The phylogenetic position of the Tyrannosauridae: Implications for theropod systematics. Journal of Paleontology. 68(5), 1100-1117.
Novas, Haro and Canale, 2003. Un nuevo terópodo basal de la Formación Ischigualasto (Carniano) de la provincia de San Juan, Argentina. Ameghiniana. 40(4), 63R.
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