Today I'm reporting on two papers, one good, one bad. Both involve cladistics, but besides that are basically unrelated.
Tom Holtz notified the DML of a new paper by Brazeau (2011). I highly recommend anyone making or examining a cladistic analysis read this work. He basically outlines many of the problems I describe in the Evaluating Phylogenetic Analyses page of my website.
- Don't make "pseudo-ordered" characters of the form "bone x absent (0); bone x lacks feature A (1); bone x has feature A (2)", because if it's unordered PAUP has no reason to know to group all taxa with bone x together. If it's ordered, it solves that problem, but has the probably undesired effect of assuming feature A is related to the loss of the bone.
- Don't have multiple characters implicitly coding for the same thing, with absence of that thing a state in addition to states coding for the presence/absence of a feature on the thing. So "bone x absent (0); bone x present (1)" and "bone x absent (0); bone x present and without feature A (1); bone x present and with feature A (2)" should not both exist. Have one character for the bones's absence/presence, and another character for each feature of the bone. Just code taxa without the bone as inapplicable for characters about that bone's feature. But be sure to set PAUP to collapse 0 length branches if you use inapplicable characters (TNT and NONA collapse them automatically).
- Don't make compound characters. Each character should code for only one variable.
- Remember that "0" does not mean "primitive". 0 has to be a distinct state just like 1, 2 or any other number. So don't make a character like "deltopectoral crest shape not described by any of the other states (0); crest round (1); crest triangular (2)", because there are lots of other shapes besides round and triangular, but PAUP could easily make state 0 synapomorphic for some clade. That could end up grouping taxa with rectangular, pentagonal, etc. crests together as having the same condition, which is clearly not justified.
- As a consequence of this, making ordered multistate characters is better than making a series of less inclusive bistate characters.
The second paper was announced today- the description of a new taxon of pterosaur. Frey et al. (2011) described Aurorazhdarcho, which is a damned cool name. Unfortunately, the paper goes downhill from there.
First, they assign Aurorazhdarcho to the new family Protazhdarchidae. Are there really people who still think you can make up a family-group name that's not eponymous with an existing genus? Without a Protazhdarcho (which doesn't exist), there can be no Protazhdarchidae. And Frey et al. can't use the excuse that Protazhdarchidae is "just a clade" since they explicitly say "nov. fam." and "we propose to erect a new family, the Protazhdarchidae..." Tim Williams brought up the possibility on the DML that maybe the genus was originally named Protazdarcho and later changed, but the family name wasn't caught in time (though barring a VERY last minute change or editorial messiness I would hope the peer reviewers would still catch it), and if that's the case I apologize to the authors for this insulting paragraph. Regardless, my insults in the next two paragraphs still apply. ;)
Second, Protazhdarchidae is monotypic, so is useless anyway. Maybe I was too hasty in dismissing Jaime's suggestion for purely monotypic theropod families in the year 2100, since apparently it's not just Ji and other Chinese workers who are stuck in the archaic typological mindset. The taxonomic world has moved beyond subjective difference being a reason to name a new clade/grade, please join the rest of us in the 21st century.
Third, Frey et al. include the highly flawed section "Problems with cladistic analysis". Note they don't actually include Aurorazhdarcho in an analysis. Why not? "The main reason is that the low wing attachment is reason enough to align the specimen with the azhdachoid construction, which separates the group from all other Pterosauria." I suppose Halloween IS a good time for Huene's ghost to rear its head, insisting on the importance of key characters. We then get this lovely gem-
"If the low position of the glenoid fossa is regarded as original tetrapod, the azhdarchoid pterosaur construction has retained the low articulation of the front limbs and thus must have separated in the early history of the Pterosauria, possibly during the Triassic. Then, the high wing articulation could have evolved several times independently within the Pterosauria. If the low wing articulation is regarded as derived, the re-development of the primitive position of the glenoid fossa has to be explained. To resolve this question, a reinvestigation of the shoulder girdle of early Pterosauria would be necessary. For now, this problem remains unresolved pending an engineering approach concerning the consequences of low wing attachment, too. Hence, the character should be dismissed because of its evident functional impetus and unclear origin (Frey et al. 2003a)."
Did anyone else hear a distinguished gentleman in a sepia photograph read the above statements? A single primitive character does not mean an entire clade is basal- we must examine the entire set of characters to determine which are more likely to be reversals or convergences. We don't have to explain why any character evolved, nor should our ability to hypothesize why one state could evolve from another affect our choice in character polarity. I'm very interested in what exactly all the characters we use were actually good for, but the analysis comes first THEN the evolutionary scenario. Frey et al. are guilty of the same thing BADists are- wanting to know the scenario first and basing the phylogeny off that. As for their last sentence, since every(?) character that's not the result of genetic drift has some functional importance (and how would we ever test that in extinct taxa?), that's not a reason to exclude them from analyses. And since origins are only made clear once you run an analysis, excluding a character due to its 'unclear origin' is just nonsensical.
The rest of their "problems" are basically of the form "character x influences character y since both are parts of some functional whole, and until we know how these influences work, we shouldn't include either character in cladistic analyses." So glenoid position influences deltopectoral crest shape and so on. Frey et al. are fundamentally wrong in their demand to know function before phylogeny, and that anatomy alone isn't enough to know when characters are strictly correlated. All you need to do is check the matrix to see if every taxon with character x also has character y, and if every taxon without x also lacks y. Now if you do find exact correlation and it's logically impossible to have a condition with x and without y and vice versa, THEN you can delete the character. Otherwise you might have a character complex like the paravian sickle claw where claw hyperextendability, size and curvature are certainly all functionally related, but should still be coded as separate characters since they're independent (e.g. Archaeopteryx lacks large size, Borogovia lacks strong curvature). Now I suppose some characters might be correlated due to combinations of osteology that are only logically impossible once soft tissues are taken into account, and not just simple muscular biomechanics as Frey et al. suggest, but even such details as involving expression of the same gene at the same time. Yet we'll never know most soft tissue anatomy for most fossil taxa (and even living taxa are poorly studied in this regard), so to rule out such correlation in our matrices is basically impossible. We can either try to determine phylogeny now while excluding the logically correlated characters, or wait forever until we have fully examined a complete living growing example of each taxon to eliminate the possibility of correlation for each character. I vote for the former.
Incidentally, given Frey et al.'s lack of a modern phylogenetic perspective, I don't trust their placement of Aurorazhdarcho in Azhdarchoidea. Maybe it is, I'm not qualified to say, but I await the results of someone using a modern approach.
References- Brazeau, 2011. Problematic character coding methods in morphology and their effects. Biological Journal of the Linnean Society. 104, 489-498.
Frey, Meyer and Tischlinger, 2011. The oldest azhdarchoid pterosaur from the Late Jurassic Solnhofen Limestone (Early Tithonian) of Southern Germany. Swiss Journal of Geosciences. DOI: 10.1007/s00015-011-0073-1
Tuesday, October 25, 2011
Friday, October 21, 2011
Xiaotingia commentary, is Archaeopteryx a deinonychosaur?
I just wrote this for the DML and figured it could be useful to post here.
The majority view, as in the conclusion found by almost every cladistic analysis which has tackled the problem, is that Archaeopteryx is a basal avialan. The recent controversy has been over the analysis in Xu et al.'s (2011) description of Xiaotingia. This is a version of the Theropod Working Group analysis which goes back to Norell et al. (2001). Specifically Xu et al. (2011) added a few taxa and several characters to...
- Zhang et al.'s (2008) analysis which added Epidexipteryx and a few characters to...
- Senter's (2007) analysis which completely recoded and added many characters and taxa to...
- Kirkland et al.'s (2005) analysis which added several characters and a few therizinosaurs to...
- Hwang et al.'s (2004), which is based on Xu et al.'s (2002), which is based on more analyses still all the way back to Norell et al. (2001).
So it's a re-re-re-re-re-analysis of a huge dataset. Running this dataset with Xiaotingia results in Archaeopteryx being a basal deinonychosaur instead of a basal avialan. Note this isn't a big move, since Deinonychosauria and Avialae are sister groups. It just moves from the base of one group to the base of the other. Note also that despite what the hype would indicate, this result isn't very well supported. Forcing Archaeopteryx back to its normal position as a basal avialan only takes TWO more evolutionary steps. That's not significant at all, and furthermore the analysis itself is flawed as detailed below.
When you run an analysis like this, certain characters need to be "ordered". So that for instance, taxa with six sacral vertebrae are seen as intermediate between taxa with five and taxa with seven sacrals. If you don't order the character, "six sacrals" is counted as a character that has no definite relationship to other numbers of sacral vertebrae, so you'd get weird results like grouping Rahonavis and Shenzhouraptor together to the exclusion of more derived birds because of their shared primitive sacral number. Also, ordering changes the amount of steps a character takes to evolve, since if it's unordered, you can go from five to nine sacrals as easily as you can go from five to six sacrals. When we try to find out if Xu et al. ordered their characters, we have to follow the lineage of analyses all the way back to Kirkland et al.'s (2005) version, which only says one character was ordered but doesn't say which. Xu et al. seem to ignore that anyway, since I get their results by running their analysis unordered. Running Xu et al.'s analysis with all characters ordered adds over 100 steps, which of course completely overpowers our two step difference we noted above. While not every character should be ordered, many should be. Importantly, when characters are ordered, Archaeopteryx comes out as a bird.
So how much of Xu et al.'s result is due to not having the right characters ordered? We don't know unless someone goes through the tedious steps of looking through all the characters and choosing which should be ordered. You can see how this could be important for Archaeopteryx, since any intermediate state it has between birds and deinonychosaurs will be counted as equally different from both instead of being a bit closer to birds (assuming the deinonychosaurian condition is primitive).
Another problem is that Xu et al.'s analysis doesn't include all of the relevent taxa and characters that other versions of the analysis do. Senter's newest (2010) analysis (which is a modification of his 2007 one) includes most of the same taxa but has many new codings and takes seven more steps to place Archaeopteryx in Deinonychosauria. Zanno et al.'s (2009) analysis (which has a rather different lineage going back to Hwang et al. 2004 and so doesn't include any of Senter's numerous modifications) contains a different mix of characters, adds Mahakala and Shanag, but lacks scansoriopterygids, Sapeornis, Protopteryx, NGMC 91 and Bambiraptor. Forcing deinonychosaurian Archaeopteryx is six steps longer in it. Makovicky et al.'s (2010) analysis (which is more similar to Zanno et al.'s) includes yet a different mix of characters and taxa needs eight more steps. Most recently, Turner et al. (2011) have a TWG-based analysis centered on deinonychosaurs and birds, including taxa not found in the Xiaotingia analysis like Hesperonychus, Graciliraptor, Tianyuraptor, Austroraptor, Mahakala, Jinfengopteryx, two undescribed basal troodontids, Jixiangornis and a lot of birds. Based on their taxon sample I bet they also included the numerous bird-related characters of Clarke's analyses. And this analysis found Archaeopteryx to be a bird, though I can't say how well supported that is since they haven't released their data matrix yet (grrr).
So we can see that most analyses find Archaeopteryx to be 6-8 steps more likely to be a bird, while Xu et al. found it to be 2 steps more likely to be a deinonychosaur. Each analysis includes some data others don't, and all have miscodings. Until someone combines the information (which I'm finishing up), we won't know if say adding Xiaotingia to Turner et al.'s analysis would make Archaeopteryx a deinonychosaur, or if adding Jinfengopteryx to Xu et al.'s analysis would make Archaeopteryx a bird.
Until that time, I'd say it could be either, but that both the number of analyses and the strength of support in those analyses slightly favor it being a bird.
The majority view, as in the conclusion found by almost every cladistic analysis which has tackled the problem, is that Archaeopteryx is a basal avialan. The recent controversy has been over the analysis in Xu et al.'s (2011) description of Xiaotingia. This is a version of the Theropod Working Group analysis which goes back to Norell et al. (2001). Specifically Xu et al. (2011) added a few taxa and several characters to...
- Zhang et al.'s (2008) analysis which added Epidexipteryx and a few characters to...
- Senter's (2007) analysis which completely recoded and added many characters and taxa to...
- Kirkland et al.'s (2005) analysis which added several characters and a few therizinosaurs to...
- Hwang et al.'s (2004), which is based on Xu et al.'s (2002), which is based on more analyses still all the way back to Norell et al. (2001).
So it's a re-re-re-re-re-analysis of a huge dataset. Running this dataset with Xiaotingia results in Archaeopteryx being a basal deinonychosaur instead of a basal avialan. Note this isn't a big move, since Deinonychosauria and Avialae are sister groups. It just moves from the base of one group to the base of the other. Note also that despite what the hype would indicate, this result isn't very well supported. Forcing Archaeopteryx back to its normal position as a basal avialan only takes TWO more evolutionary steps. That's not significant at all, and furthermore the analysis itself is flawed as detailed below.
When you run an analysis like this, certain characters need to be "ordered". So that for instance, taxa with six sacral vertebrae are seen as intermediate between taxa with five and taxa with seven sacrals. If you don't order the character, "six sacrals" is counted as a character that has no definite relationship to other numbers of sacral vertebrae, so you'd get weird results like grouping Rahonavis and Shenzhouraptor together to the exclusion of more derived birds because of their shared primitive sacral number. Also, ordering changes the amount of steps a character takes to evolve, since if it's unordered, you can go from five to nine sacrals as easily as you can go from five to six sacrals. When we try to find out if Xu et al. ordered their characters, we have to follow the lineage of analyses all the way back to Kirkland et al.'s (2005) version, which only says one character was ordered but doesn't say which. Xu et al. seem to ignore that anyway, since I get their results by running their analysis unordered. Running Xu et al.'s analysis with all characters ordered adds over 100 steps, which of course completely overpowers our two step difference we noted above. While not every character should be ordered, many should be. Importantly, when characters are ordered, Archaeopteryx comes out as a bird.
So how much of Xu et al.'s result is due to not having the right characters ordered? We don't know unless someone goes through the tedious steps of looking through all the characters and choosing which should be ordered. You can see how this could be important for Archaeopteryx, since any intermediate state it has between birds and deinonychosaurs will be counted as equally different from both instead of being a bit closer to birds (assuming the deinonychosaurian condition is primitive).
Another problem is that Xu et al.'s analysis doesn't include all of the relevent taxa and characters that other versions of the analysis do. Senter's newest (2010) analysis (which is a modification of his 2007 one) includes most of the same taxa but has many new codings and takes seven more steps to place Archaeopteryx in Deinonychosauria. Zanno et al.'s (2009) analysis (which has a rather different lineage going back to Hwang et al. 2004 and so doesn't include any of Senter's numerous modifications) contains a different mix of characters, adds Mahakala and Shanag, but lacks scansoriopterygids, Sapeornis, Protopteryx, NGMC 91 and Bambiraptor. Forcing deinonychosaurian Archaeopteryx is six steps longer in it. Makovicky et al.'s (2010) analysis (which is more similar to Zanno et al.'s) includes yet a different mix of characters and taxa needs eight more steps. Most recently, Turner et al. (2011) have a TWG-based analysis centered on deinonychosaurs and birds, including taxa not found in the Xiaotingia analysis like Hesperonychus, Graciliraptor, Tianyuraptor, Austroraptor, Mahakala, Jinfengopteryx, two undescribed basal troodontids, Jixiangornis and a lot of birds. Based on their taxon sample I bet they also included the numerous bird-related characters of Clarke's analyses. And this analysis found Archaeopteryx to be a bird, though I can't say how well supported that is since they haven't released their data matrix yet (grrr).
So we can see that most analyses find Archaeopteryx to be 6-8 steps more likely to be a bird, while Xu et al. found it to be 2 steps more likely to be a deinonychosaur. Each analysis includes some data others don't, and all have miscodings. Until someone combines the information (which I'm finishing up), we won't know if say adding Xiaotingia to Turner et al.'s analysis would make Archaeopteryx a deinonychosaur, or if adding Jinfengopteryx to Xu et al.'s analysis would make Archaeopteryx a bird.
Until that time, I'd say it could be either, but that both the number of analyses and the strength of support in those analyses slightly favor it being a bird.
Saturday, October 15, 2011
Theropoda in the Amazing Year 2100
One of my pet peeves is the cavalier attitude many dinosaur paleontologists have recently in regard to the priority and validity of old taxa. Whether it's lazy dismissal of genera as nomina dubia without an analysis showing this is true, dumping family-level names based on supposed nomina dubia despite the ICZN having no rules about this, making up new definitions for established clades, or just plain old replacement of clade names because the eponymous genus isn't as complete or deeply nested as another. If this trend continues, we may face the following horrifying vision of the future...
Theropoda
- Coelophysoidea (based on a complete neotype for Coelophysis bauri, the only known material for the first 66 years having been ignored as archosaur scrap; IT'S ALREADY TRUE!)
- Sinodilophosauridae (people still refuse to use Dilophosauridae, but the describers of what was originally Dilophosaurus sinensis came up with their own name for this clade)
- Averostra (because enough people misused Bakker's Neotheropoda so that they forgot he created it for this node and started using a term published 16 years later instead)
-- Ceratosauria
--- Majungasauroidea (Abelisaurus was deemed too fragmentary, and Carnotaurus is still only known from one specimen. Majungasaurus itself is now based on a complete neotype found in 2068)
---- Masiakasauridae
---- Majungasauridae
-- Tetanuriformes (someone finally got enough followers after redefining Tetanurae to be less inclusive, thus Tetanurae has different meanings depending on what year a paper was published)
--- Suchomimia
---- Tayntonsauridae (after a incomplete articulated megalosaur was found in Megalosaurus' type beds, it was named to 'solve' the confusion surrounding Megalosaurus' association. All Megalosaurus remains were then referred to Tayntonsaurus)
---- Suchomimidae (Yes, ignoring Spinosauridae, Baryonychidae, Irritatoridae and Cristatusaurus)
--- Tetanurae
----Sinraptoroidea (after Allosaurus fragilis was shown to be a nomen dubium, people incorrectly said a family level name couldn't be based on it)
----- Sinraptoridae (no comment needed)
----- Neoallosauridae (people declared Allosaurus, Labrosaurus, Creosaurus and Epanterias to be undiagnostic in a footnote of the paper describing Big Al as Neoallosaurus in 2035)
----- Carcharodontosauria
------ Neovenatoridae
------ Acrocanthosauridae
------ Shaochilongidae
------ Tyrannotitanidae
------ Carcharodontosauridae (ignoring the stable stem-based definition of Carcharodontosauridae, people kept redefining it to be less and less inclusive)
---- Tyrannosauroidea (despite including the following two families, both named prior to Tyrannosauridae...)
----- Coeluridae
----- Compsognathidae
----- Tyrannosauridae
---- Avesternes (someone named it in 2019 and people started to ignore Maniraptoriformes)
----- Ornithomimosauria (based on a neotype for Ornithomimus edmontonicus, even though O. velox was the type species and brevitertius has priority over edmontonicus)
----- Eunothronychia (Therizinosauria was defeated the same way it gained usage, once graffami was given its own genus)
----- Citipatia (Oviraptor was too fragmentary, so the clade was renamed once Citipati's holotype was fully described in 2023. IGM 100/42 remains undescribed and called the Zamyn Kondt oviraptorid as of 2100)
----- Bimedicamentodontidae (Troodon is a long forgotten name, and no the family hasn't been subdivided yet despite there being 73 described diagnostic genera)
----- Dromaeosauridae (miraculously unaffected, but Barsbold's estate owns Adasaurus, which no one is allowed to circulate holograms of)
----- Shuvuuiformes (because of... well, you get the drift by now)
----- Birdia (we finally got sick of the semantic arguments)
Only you can prevent this terrifying prediction from becoming reality. Support priority, follow the ICZN until another code is viable (the Phylocode remains unofficial as of 2100, but rumors are Phylonyms is almost complete and that it will start as of 1-1-21xx), and remember a named taxon is valid until shown otherwise by a detailed redescription and comparison.
Theropoda
- Coelophysoidea (based on a complete neotype for Coelophysis bauri, the only known material for the first 66 years having been ignored as archosaur scrap; IT'S ALREADY TRUE!)
- Sinodilophosauridae (people still refuse to use Dilophosauridae, but the describers of what was originally Dilophosaurus sinensis came up with their own name for this clade)
- Averostra (because enough people misused Bakker's Neotheropoda so that they forgot he created it for this node and started using a term published 16 years later instead)
-- Ceratosauria
--- Majungasauroidea (Abelisaurus was deemed too fragmentary, and Carnotaurus is still only known from one specimen. Majungasaurus itself is now based on a complete neotype found in 2068)
---- Masiakasauridae
---- Majungasauridae
-- Tetanuriformes (someone finally got enough followers after redefining Tetanurae to be less inclusive, thus Tetanurae has different meanings depending on what year a paper was published)
--- Suchomimia
---- Tayntonsauridae (after a incomplete articulated megalosaur was found in Megalosaurus' type beds, it was named to 'solve' the confusion surrounding Megalosaurus' association. All Megalosaurus remains were then referred to Tayntonsaurus)
---- Suchomimidae (Yes, ignoring Spinosauridae, Baryonychidae, Irritatoridae and Cristatusaurus)
--- Tetanurae
----Sinraptoroidea (after Allosaurus fragilis was shown to be a nomen dubium, people incorrectly said a family level name couldn't be based on it)
----- Sinraptoridae (no comment needed)
----- Neoallosauridae (people declared Allosaurus, Labrosaurus, Creosaurus and Epanterias to be undiagnostic in a footnote of the paper describing Big Al as Neoallosaurus in 2035)
----- Carcharodontosauria
------ Neovenatoridae
------ Acrocanthosauridae
------ Shaochilongidae
------ Tyrannotitanidae
------ Carcharodontosauridae (ignoring the stable stem-based definition of Carcharodontosauridae, people kept redefining it to be less and less inclusive)
---- Tyrannosauroidea (despite including the following two families, both named prior to Tyrannosauridae...)
----- Coeluridae
----- Compsognathidae
----- Tyrannosauridae
---- Avesternes (someone named it in 2019 and people started to ignore Maniraptoriformes)
----- Ornithomimosauria (based on a neotype for Ornithomimus edmontonicus, even though O. velox was the type species and brevitertius has priority over edmontonicus)
----- Eunothronychia (Therizinosauria was defeated the same way it gained usage, once graffami was given its own genus)
----- Citipatia (Oviraptor was too fragmentary, so the clade was renamed once Citipati's holotype was fully described in 2023. IGM 100/42 remains undescribed and called the Zamyn Kondt oviraptorid as of 2100)
----- Bimedicamentodontidae (Troodon is a long forgotten name, and no the family hasn't been subdivided yet despite there being 73 described diagnostic genera)
----- Dromaeosauridae (miraculously unaffected, but Barsbold's estate owns Adasaurus, which no one is allowed to circulate holograms of)
----- Shuvuuiformes (because of... well, you get the drift by now)
----- Birdia (we finally got sick of the semantic arguments)
Only you can prevent this terrifying prediction from becoming reality. Support priority, follow the ICZN until another code is viable (the Phylocode remains unofficial as of 2100, but rumors are Phylonyms is almost complete and that it will start as of 1-1-21xx), and remember a named taxon is valid until shown otherwise by a detailed redescription and comparison.
Saturday, September 17, 2011
Planet Dinosaur Review
Since I reviewed Dinosaur Revolution, I might as well tackle the other big dino documentary that came out this month. As with Dinosaur Revolution, this review only covers the first episode, which in this case was about Cenomanian North Africa.
Planet Dinosaur's special effects range from decent to sad. While I could go on about the little details like Ouranosaurus chewing like a mammal, having depressions where its laterotemporal fenestrae are, Microraptor lacking primaries attached to its second finger and having wings which are too short, etc., the simple truth is that the dinosaurs are less accurate and less believable as real objects. The maniraptorans (Troodon, Microraptor, Epidexipteryx) are especially poor. That's not to say it's all bad. The Rugops (possibly an Aucasaurus from the Auca Mahuevo episode) and Sarcosuchus look pretty good, the Spinosaurus is decent except for its short tail, and the Ouranosaurus dying had nice motions and rapid breathing. Seeing this show really made me realize how good the models and animation were in Dinosaur Revolution though. It's such a shame the talent/money spent on the latter couldn't have been used for a program like Planet Dinosaur.
As far as behavior goes, it was refreshing to see dinosaurs acting like dinosaurs. There are a few stupid things, like Spinosaurus eating part of a fish, then leaving to catch more ("with prey plentiful, Spinosaurus can afford to be wasteful"). Or Rugops' subsequent portrayal as an obligate scavenger. Or Spinosaurus slashing the fish with its hands, only to eat tiny bits at a time. But at least nothing they do is human-like. The behavior is largely defended by reference to actual studies (see below), and the show does a good job of making a story based on these. The larger narrative of Spinosaurus being the largest and last spinosaurid and dying from climate change was flawed because Late Cretaceous African dinosaurs are poorly known, and Hone et al. (2010) and Candeiro et al. (2004) described Santonian spinosaurids. But Candeiro et al.'s conclusion was doubted in their 2006 paper and Hone et al.'s study is quite new. Bearing in mind I don't know how accurate the paleoclimatology was, the larger story felt more plausible than Dinosaur Revolution's apparently tacked-on story of how dinosaur parenting helped their success.
My favorite part of Planet Dinosaur is that it manages to explicitly incorporate numerous journal articles. These are shown in informational panels with the year of publication, age, country, and figures from the original articles or photos of specimens referenced by them. They even managed to rotate one of Stromer's Spinosaurus vertebra drawings in 3D, haha. We have Stromer (1915), Dal Sasso et al. (2005), Amiot et al. (2010), Dal Sasso et al. (2009), Sereno et al. (1996), Tanke and Currie (2000), Sereno et al. (2008), Kellner (2004), Charig and Milner (1986), and a biomechanical strength analysis of Carcharodontosaurus' jaws. I don't know how much I agree with some of the conclusions (like amphibious spinosaurids), but at least they're actually from the scientific literature and not just random made-up possibilities.
There are ocassional errors, like overlaying a tyrannosaurid dentary on Sinraptor's skull, or using Stromer's reconstruction as the basis of the Spinosaurus skeletal, resulting in one of the worst reconstructions I've seen. It's good they knew to tilt it horizontal and give it the right skull, but the anatomy! Sacral neural spines lateral to the ilium, the femur articulating with the postacetabular process, two sets of pubes... I could insult it all day.
And yet other details of their informational panels are accurate, such as Irritator and Siamosaurus being inconspicuously listed as additional spinosaurids on the map. Overall, it's quite good. I actually learned what Onchopristis was, and that there's a partial Spinosaurus maxilla with an Onchopristis tooth embedded in it (not just MSNM V4047 with its embedded vertebra). There's also apparently a Spinosaurus neural spine found in 2008 in Morocco that had been broken in life, which I had never heard of. Any time a dinosaur show manages to teach ME something, I'm impressed.
So I quite liked Planet Dinosaur. It's almost the exact opposite of Dinosaur Revolution- generally inaccurate restorations behaving fairly realistically, packed full of references to specific discoveries in the literature, telling us what we know and why. I'll be watching the following episodes, and contra my earlier statement I'll probably tune in to the other Dinosaur Revolutions too. I'll just have to treat the latter like the Transformers 2 of dinosaur programs- pretty to watch, but turn off your brain. On the other hand, I'll be interested to see if Planet Dinosaur presents any more discoveries I hadn't heard of.
Planet Dinosaur's special effects range from decent to sad. While I could go on about the little details like Ouranosaurus chewing like a mammal, having depressions where its laterotemporal fenestrae are, Microraptor lacking primaries attached to its second finger and having wings which are too short, etc., the simple truth is that the dinosaurs are less accurate and less believable as real objects. The maniraptorans (Troodon, Microraptor, Epidexipteryx) are especially poor. That's not to say it's all bad. The Rugops (possibly an Aucasaurus from the Auca Mahuevo episode) and Sarcosuchus look pretty good, the Spinosaurus is decent except for its short tail, and the Ouranosaurus dying had nice motions and rapid breathing. Seeing this show really made me realize how good the models and animation were in Dinosaur Revolution though. It's such a shame the talent/money spent on the latter couldn't have been used for a program like Planet Dinosaur.
As far as behavior goes, it was refreshing to see dinosaurs acting like dinosaurs. There are a few stupid things, like Spinosaurus eating part of a fish, then leaving to catch more ("with prey plentiful, Spinosaurus can afford to be wasteful"). Or Rugops' subsequent portrayal as an obligate scavenger. Or Spinosaurus slashing the fish with its hands, only to eat tiny bits at a time. But at least nothing they do is human-like. The behavior is largely defended by reference to actual studies (see below), and the show does a good job of making a story based on these. The larger narrative of Spinosaurus being the largest and last spinosaurid and dying from climate change was flawed because Late Cretaceous African dinosaurs are poorly known, and Hone et al. (2010) and Candeiro et al. (2004) described Santonian spinosaurids. But Candeiro et al.'s conclusion was doubted in their 2006 paper and Hone et al.'s study is quite new. Bearing in mind I don't know how accurate the paleoclimatology was, the larger story felt more plausible than Dinosaur Revolution's apparently tacked-on story of how dinosaur parenting helped their success.
My favorite part of Planet Dinosaur is that it manages to explicitly incorporate numerous journal articles. These are shown in informational panels with the year of publication, age, country, and figures from the original articles or photos of specimens referenced by them. They even managed to rotate one of Stromer's Spinosaurus vertebra drawings in 3D, haha. We have Stromer (1915), Dal Sasso et al. (2005), Amiot et al. (2010), Dal Sasso et al. (2009), Sereno et al. (1996), Tanke and Currie (2000), Sereno et al. (2008), Kellner (2004), Charig and Milner (1986), and a biomechanical strength analysis of Carcharodontosaurus' jaws. I don't know how much I agree with some of the conclusions (like amphibious spinosaurids), but at least they're actually from the scientific literature and not just random made-up possibilities.
There are ocassional errors, like overlaying a tyrannosaurid dentary on Sinraptor's skull, or using Stromer's reconstruction as the basis of the Spinosaurus skeletal, resulting in one of the worst reconstructions I've seen. It's good they knew to tilt it horizontal and give it the right skull, but the anatomy! Sacral neural spines lateral to the ilium, the femur articulating with the postacetabular process, two sets of pubes... I could insult it all day.
 |
| Please put this travesty out of its misery |
So I quite liked Planet Dinosaur. It's almost the exact opposite of Dinosaur Revolution- generally inaccurate restorations behaving fairly realistically, packed full of references to specific discoveries in the literature, telling us what we know and why. I'll be watching the following episodes, and contra my earlier statement I'll probably tune in to the other Dinosaur Revolutions too. I'll just have to treat the latter like the Transformers 2 of dinosaur programs- pretty to watch, but turn off your brain. On the other hand, I'll be interested to see if Planet Dinosaur presents any more discoveries I hadn't heard of.
Tuesday, September 13, 2011
Dinosaur Revolution review
Well, that was painful. I decided to join the trend and review the show that's been so hyped- Dinosaur Revolution. Little did I know my yearly allowance of eyerolls would be used up. I only watched the frirst episode "Evolution's Winners" and frankly have no desire to sample more.
First the good. The models were usually excellent, with non-pronated hands and all that good stuff. I especially enjoyed the dilophosaurian snouts on the Cryolophosaurus, and the Mongolian mammals which weren't just shrews or mice. I also liked the homage to Dryptosaurus and Ceratosaurus artwork in the Cryolophosaurus section (though I don't think they could really stand on their tails, given how most theropod chevrons look). The Gigantoraptor's feathering was more problematic, as it seemed more like a naked theropod covered in feathers than an actual feathered creature like a bird, where body outlines are hidden and feathers interact and fold. Its wings were always held out in front, which for a display is fine, but even the female who wanders up is posed this way. The animation itself was a mixed bag. Most moved smoothly, but the Saurosuchus looked unnatural for instance. Similarly, the rendering was good for most, but the therapsids in the opening seen looked plasticy. What's that you say? My "good" paragraph's actually mostly full of criticisms? Guess that prepares the way for the rest of the review...
What made Dinosaur Revolution most difficult to watch is the rampant anthropomorphism. Basically none of the subjects actually behaves like a reptile, or a bird, or even a non-ape mammal for that matter. They're chock full of human mannerisms. You can always tell what they're supposed to be feeling, as if brains that size could even house such emotion. But it's not just behavior. My jaw dropped at the blatant 'sexy eyelash' marks on the female Eoraptors. Why not just go the whole hog and give them real eyelashes they can flutter alluringly? Then the male's heart (shaped like a heart of course) could project from its chest like a piston. Would have been almost as realistic as the expectant smile he shows as she approaches in the actual program. Even ignoring the behavior, the plotlines have so many "entertaining" improbable portions, like the Eoraptor unwittingly throwing a therapsid into Saurosuchus' mouth, that any illusion you're watching reality is destroyed. And what was up with that swarm of hostile flies chasing the Antarctic fauna and killing the lizard... for blood! Is this a 1950s horror movie or something?
Which would have all been excusable if the show at least taught us something. Then it'd be a Dinosaur Train for adults, which wouldn't be my idea of a good program to watch, but would at least educate the part of the public that finds documentaries boring. But no, I don't think there was any actual paleontological data contained in that hour, besides most of the portrayed anatomy and a few basic facts like "birds are dinosaurs" and "Cryolophosaurus is from Antarctica". I say "most" because while the models were largely accurate, they sometimes contained some fictional aspect. The rhamphorhynchoid tail fin on the female Eoraptors, for instance. Or the highly elaborate wattles and soft horns on the male Gigantoraptor. And when it comes to behavior, we have bower-building Eoraptors, color flushing Cryolophosaurus which killed the young of rival males, a stomping and twirling Gigantoraptor mating dance, Glacialisaurus which lived in harems (which we so know from the partial hindlimb...), etc. It's not that these soft parts or behaviors are impossible, but Joe Public's only going to remember Gigantoraptor as "that goofy rainbow-colored thing that dances" or Eoraptor as "those raptors that cutely chirp and build mounds to select mates, and then care for their baby who adorably falls down, awwww". So you're emphasizing the fictional aspects of these animals, while not going into any of the actual known interesting facts about them.
But maybe the show could have retained some use if all of this human-like/fictional appearance and behavior was there to illustrate some greater true scientific fact, that even network execs think viewers could remember. Alas, no. The implication of the Eoraptor portion was that dinosaur success was due to more complex parental care, but my impression has been that evidence for such care is limited to maniraptorans, supposed evidence for care in hadrosaurs (and thus Ornithischia) has been refuted, and that baby sauropods were too small to associate with adults and aren't apparent in herd trackways. And even the mosasaur cares for its babies enough to get revenge on sharks for eating them (vengeance is such a widespread trait in squamates...). As does the Cretaceous mammal, more realistically. If you want to make the point dinosaurs were probably often brightly colored with display structures as the Gigantoraptor portion tries to, a far superior method would be to show say ten different possibilities for a few species in quick succession. Changing colors and adding wattles wouldn't be that resource intensitive and would get the idea across to laymen without making it seem like we know they had definite soft features and patterns (I'm guessing the Yixian pigments were unknown when this was made). The Cryolophosaurus portion taught us about the factual behavior... of lions. The mosasaur segment taught us... er... "a mother's protective instinct is a force of nature than can change the world." And the Glacialisaurus one taught us "a little bad luck goes a long way." That's certainly scientific. Maybe the next episode will teach us "the disadvantaged underdog can succeed with perseverance and faith in himself." Sigh
To sum up, watch if you like largely accurate-looking dinosaurs acting like humans in zany situations and learning valuable life lessons. If you want a show that clearly indicates which parts are based on paleontology, shows dinosaurs as they may have been, and teaches you something about them, keep dreaming.
First the good. The models were usually excellent, with non-pronated hands and all that good stuff. I especially enjoyed the dilophosaurian snouts on the Cryolophosaurus, and the Mongolian mammals which weren't just shrews or mice. I also liked the homage to Dryptosaurus and Ceratosaurus artwork in the Cryolophosaurus section (though I don't think they could really stand on their tails, given how most theropod chevrons look). The Gigantoraptor's feathering was more problematic, as it seemed more like a naked theropod covered in feathers than an actual feathered creature like a bird, where body outlines are hidden and feathers interact and fold. Its wings were always held out in front, which for a display is fine, but even the female who wanders up is posed this way. The animation itself was a mixed bag. Most moved smoothly, but the Saurosuchus looked unnatural for instance. Similarly, the rendering was good for most, but the therapsids in the opening seen looked plasticy. What's that you say? My "good" paragraph's actually mostly full of criticisms? Guess that prepares the way for the rest of the review...
What made Dinosaur Revolution most difficult to watch is the rampant anthropomorphism. Basically none of the subjects actually behaves like a reptile, or a bird, or even a non-ape mammal for that matter. They're chock full of human mannerisms. You can always tell what they're supposed to be feeling, as if brains that size could even house such emotion. But it's not just behavior. My jaw dropped at the blatant 'sexy eyelash' marks on the female Eoraptors. Why not just go the whole hog and give them real eyelashes they can flutter alluringly? Then the male's heart (shaped like a heart of course) could project from its chest like a piston. Would have been almost as realistic as the expectant smile he shows as she approaches in the actual program. Even ignoring the behavior, the plotlines have so many "entertaining" improbable portions, like the Eoraptor unwittingly throwing a therapsid into Saurosuchus' mouth, that any illusion you're watching reality is destroyed. And what was up with that swarm of hostile flies chasing the Antarctic fauna and killing the lizard... for blood! Is this a 1950s horror movie or something?
Which would have all been excusable if the show at least taught us something. Then it'd be a Dinosaur Train for adults, which wouldn't be my idea of a good program to watch, but would at least educate the part of the public that finds documentaries boring. But no, I don't think there was any actual paleontological data contained in that hour, besides most of the portrayed anatomy and a few basic facts like "birds are dinosaurs" and "Cryolophosaurus is from Antarctica". I say "most" because while the models were largely accurate, they sometimes contained some fictional aspect. The rhamphorhynchoid tail fin on the female Eoraptors, for instance. Or the highly elaborate wattles and soft horns on the male Gigantoraptor. And when it comes to behavior, we have bower-building Eoraptors, color flushing Cryolophosaurus which killed the young of rival males, a stomping and twirling Gigantoraptor mating dance, Glacialisaurus which lived in harems (which we so know from the partial hindlimb...), etc. It's not that these soft parts or behaviors are impossible, but Joe Public's only going to remember Gigantoraptor as "that goofy rainbow-colored thing that dances" or Eoraptor as "those raptors that cutely chirp and build mounds to select mates, and then care for their baby who adorably falls down, awwww". So you're emphasizing the fictional aspects of these animals, while not going into any of the actual known interesting facts about them.
But maybe the show could have retained some use if all of this human-like/fictional appearance and behavior was there to illustrate some greater true scientific fact, that even network execs think viewers could remember. Alas, no. The implication of the Eoraptor portion was that dinosaur success was due to more complex parental care, but my impression has been that evidence for such care is limited to maniraptorans, supposed evidence for care in hadrosaurs (and thus Ornithischia) has been refuted, and that baby sauropods were too small to associate with adults and aren't apparent in herd trackways. And even the mosasaur cares for its babies enough to get revenge on sharks for eating them (vengeance is such a widespread trait in squamates...). As does the Cretaceous mammal, more realistically. If you want to make the point dinosaurs were probably often brightly colored with display structures as the Gigantoraptor portion tries to, a far superior method would be to show say ten different possibilities for a few species in quick succession. Changing colors and adding wattles wouldn't be that resource intensitive and would get the idea across to laymen without making it seem like we know they had definite soft features and patterns (I'm guessing the Yixian pigments were unknown when this was made). The Cryolophosaurus portion taught us about the factual behavior... of lions. The mosasaur segment taught us... er... "a mother's protective instinct is a force of nature than can change the world." And the Glacialisaurus one taught us "a little bad luck goes a long way." That's certainly scientific. Maybe the next episode will teach us "the disadvantaged underdog can succeed with perseverance and faith in himself." Sigh
To sum up, watch if you like largely accurate-looking dinosaurs acting like humans in zany situations and learning valuable life lessons. If you want a show that clearly indicates which parts are based on paleontology, shows dinosaurs as they may have been, and teaches you something about them, keep dreaming.
Friday, September 9, 2011
Tehuelchesaurus and how to describe the affinities of a taxon
I've often complained about the tendency for authors to view their most parsimonious cladogram as "the right" tree, such as here and here. I note that it's usually more helpful to describe how parsimonious different hypotheses are, since while new analyses usually change the topology somewhat, they rarely support relationships that were strongly rejected before. Carballido et al. (2011) recently redescribed the sauropod Tehuelchesaurus, and in addition to a detailed osteology and several other important discussions, their paper contains a phylogenetic analysis that did things just the way they should. The analysis (249 characters, 45 taxa) is based on Wilson's (2002) analysis with added data, including numerous newly added macronarians. Some characters were ordered, taxa which cause polytomies were deleted a posteriori, and Tehuelchesaurus emerged as a basal camarasauromorph sister to Galveosaurus, not a relative of Omeisaurus as originally thought by Rich et al. (1999). But instead of simply letting the matter rest there, Carballido et al. included the section "Testing Alternative Positions for Tehuelchesaurus." Music to my ears. They tested not only the Omeisaurus alternative (9 steps longer), but also positions slightly more (1 step longer) and less (2 steps longer) than Galveosaurus, and noted the character support for all of these. In addition, the authors wrote the following which basically covers any plausible position-
"Other positions within basal camarasauromorphs (in any position within the Janenschia/Tastavinsaurus clade, as sister taxon to Europasaurus, more basal than Europasaurus, and as sister taxon to Camarasaurus) and as a macronarian outside Camarasauromorpha, but more derived than Haplocanthosaurus, require three additional steps. Placing Tehuelchesaurus as sister taxon of Haplocanthosaurus results in a suboptimal tree four steps longer than the MPTs, and as the most basal macronarian needs even five additional steps. Even more steps are required to place this taxon in the Titanosauriformes (seven additional steps as a basal somphospondyl and eight additional steps as a basal brachiosaurid).
Any position outside Macronaria also results in considerably suboptimal tree lengths. Five additional steps are needed to make Tehuelchesaurus the most basal diplodocoid, but any position within higher diplodocoids results in trees that are at least ten steps longer than the MPTs. Likewise, placing Tehuelchesaurus outside Neosauropoda requires six additional steps, and any placement among basal, nonneosauropodan taxa results in trees at least nine steps longer than the MPTs. Thus, the possibility of a Jurassic Patagonian clade of sauropods, including Patagosaurus and Tehuelchesaurus, can also be rejected, as it requires 12 additional steps."
The paper succeeds in giving you a much clearer idea of Tehuelchesaurus' relationships than any one cladogram could. Anybody describing a new taxon should follow their example.
Carballido, Rauhut, Pol and Salgado, 2011. Osteology and phylogenetic relationships of Tehuelchesaurus benitezii (Dinosauria, Sauropoda) from the Upper Jurassic of Patagonia. Zoological Journal of the Linnean Society. DOI: 10.1111/j.1096-3642.2011.00723.x
"Other positions within basal camarasauromorphs (in any position within the Janenschia/Tastavinsaurus clade, as sister taxon to Europasaurus, more basal than Europasaurus, and as sister taxon to Camarasaurus) and as a macronarian outside Camarasauromorpha, but more derived than Haplocanthosaurus, require three additional steps. Placing Tehuelchesaurus as sister taxon of Haplocanthosaurus results in a suboptimal tree four steps longer than the MPTs, and as the most basal macronarian needs even five additional steps. Even more steps are required to place this taxon in the Titanosauriformes (seven additional steps as a basal somphospondyl and eight additional steps as a basal brachiosaurid).
Any position outside Macronaria also results in considerably suboptimal tree lengths. Five additional steps are needed to make Tehuelchesaurus the most basal diplodocoid, but any position within higher diplodocoids results in trees that are at least ten steps longer than the MPTs. Likewise, placing Tehuelchesaurus outside Neosauropoda requires six additional steps, and any placement among basal, nonneosauropodan taxa results in trees at least nine steps longer than the MPTs. Thus, the possibility of a Jurassic Patagonian clade of sauropods, including Patagosaurus and Tehuelchesaurus, can also be rejected, as it requires 12 additional steps."
The paper succeeds in giving you a much clearer idea of Tehuelchesaurus' relationships than any one cladogram could. Anybody describing a new taxon should follow their example.
Carballido, Rauhut, Pol and Salgado, 2011. Osteology and phylogenetic relationships of Tehuelchesaurus benitezii (Dinosauria, Sauropoda) from the Upper Jurassic of Patagonia. Zoological Journal of the Linnean Society. DOI: 10.1111/j.1096-3642.2011.00723.x
Wednesday, August 17, 2011
Do we have dromaeosaurid evolution backwards?
The basic evolution of Maniraptora has seemed pretty well established in the past decade, thanks to TWG papers describing Sinovenator, Mei, Mahakala, Xiaotingia and such. The basal paravian was a little bird-like taxon, like Microraptor on the dromaeosaurid end or Jinfengopteryx on the troodontid end, with genera like Rahonavis and Anchiornis breaking the boundaries even more. Going further towards the base of Maniraptora, the cranial similarities between scansoriopterygids and basal oviraptorosaurs have suggested a short-snouted herbivorous ancestor, while Shuvuuia and Pelecanimimus have similar skulls that suggest the first maniraptoriform was not a macropredator. Large, more obviously carnivorous taxa like eudromaeosaurs are seen as reversals to a more traditional theropod lifestyle. It's a nice story and may be right, but what if it's wrong?
Dromaeosaurid morphology forms a continuum from the extreme of Achillobator with its deep snout, mesially serrated teeth, low DSDI, rather short coracoid, posteriorly facing glenoid, relatively short arms, deep brevis fossa, large anterior pubic boot and proximally placed obturator process, though Deinonychus, Velociraptor, Bambiraptor, Sinornithosaurus, Microraptor, Buitreraptor/Unenlagia and ending at Rahonavis. Even if the unenlagiines are avialans though, dromaeosaurids need a lot of reversals no matter which direction evolution went. Note that stratigraphy doesn't strongly support either option. We have Utahraptor from the Barremian which is very similar to Achillobator, and dromaeosaurid-like teeth with mesial serrations resembling both dromaeosaurines and velociraptorines in the Late Jurassic. Then again, there's the microraptorian-like Graciliraptor and Shanag which also lived early, and the possible microraptorian "Paleopteryx" from the Morrison.
There's also a possible transitional form between basal coelurosaurs and dromaeosaurids- Ornitholestes. Like dromaeosaurids, Ornitholestes has a third premaxillary tooth much smaller than the first two, short cervical vertebrae with tall neural spines, prominent anterior cervical epipophyses, a crest-like ventral tuberosity on the humerus, an enlarged second pedal ungual and a transversely expanded metatarsal IV. It's also similar to paravians in the elongate distal caudals and bifurcated chevrons. Deriving dromaeosaurids from something of Ornitholestes-grade would explain why they are almost unique among derived maniraptorans in having prefrontals, which unlike the dental characters of eudromaeosaurs, are not plausibly due to macropredatory habits. In this scenario, microraptorians would be convergent with birds in their aerial characters.
Is there any other evidence for this idea? Don't troodontids show the same pattern as dromaeosaurids, going from Jinfengopteryx/Anchiornis to Mei/Sinovenator to Sinornithoides/Byronosaurus to Troodon? Maybe not. Jinfengopteryx and Anchiornis can switch to Avialae easily, and the same may be true for Mei and Sinovenator. They're often avialans in the in progress Lori matrix, even with Xu et al.'s troodontid characters. Lori itself emerged sister to Sinornithoides in Hartman et al.'s SVP poster and is Jurassic in age, with serrated teeth. Maybe that's the basal grade for troodontids, and birds are related but evolved serrationless teeth, long arms, dorsal ischial processes and such on their own branch.
The Jurassic Haplocheirus also supports this idea, since it shows serrated teeth and a general morphology so primitive that Cau's Sumrukia matrix found it to clade with compsognathids. Note therizinosaurs also have mesial and distal serrations, and that Falcarius has made the clade more basal in most matrices, unlike earlier ideas they were related to oviraptorosaurs. Maybe coelurosaurs were of the compsognathid-coelurid grade all through their evolution, with ornithomimosaurs, alvarezsaurids, therizinosaurs, dromaeosaurids and troodontids+birds each developing their birdlike and/or herbivorous characters separately. This idea is kind of anti-Paulian or anti-BCF in nature and has plenty of precedent in the literature. Ostrom long suggested Ornitholestes as a dromaeosaurid ancestor, and Makovicky (1995) found the two to be sister taxa to the exclusion of birds based on vertebral characters.
Of course the real test is with cladistic analyses, so how does the idea fare? The in progress Lori matrix finds a fairly traditional tree with Ornitholestes sister to Maniraptoriformes, microraptorians and Unenlagia basal among dromaeosaurids, and is somewhat unusual in finding troodontids sister to birds. Constraining Ornitholestes to be a dromaeosaurid and the dromaeosaurid topology 'backwards' from the consensus (Achillobator,Dromaeosaurus(Deinonychus,Velociraptor(Microraptor,Sinornithosaurus))) results in trees 11 steps longer. Not too bad when you consider enforcing Longrich and Currie's (2009) plausible-seeming traditional dromaeosaurid topology is 7 steps longer than the minimum.
Dromaeosaurid morphology forms a continuum from the extreme of Achillobator with its deep snout, mesially serrated teeth, low DSDI, rather short coracoid, posteriorly facing glenoid, relatively short arms, deep brevis fossa, large anterior pubic boot and proximally placed obturator process, though Deinonychus, Velociraptor, Bambiraptor, Sinornithosaurus, Microraptor, Buitreraptor/Unenlagia and ending at Rahonavis. Even if the unenlagiines are avialans though, dromaeosaurids need a lot of reversals no matter which direction evolution went. Note that stratigraphy doesn't strongly support either option. We have Utahraptor from the Barremian which is very similar to Achillobator, and dromaeosaurid-like teeth with mesial serrations resembling both dromaeosaurines and velociraptorines in the Late Jurassic. Then again, there's the microraptorian-like Graciliraptor and Shanag which also lived early, and the possible microraptorian "Paleopteryx" from the Morrison.
There's also a possible transitional form between basal coelurosaurs and dromaeosaurids- Ornitholestes. Like dromaeosaurids, Ornitholestes has a third premaxillary tooth much smaller than the first two, short cervical vertebrae with tall neural spines, prominent anterior cervical epipophyses, a crest-like ventral tuberosity on the humerus, an enlarged second pedal ungual and a transversely expanded metatarsal IV. It's also similar to paravians in the elongate distal caudals and bifurcated chevrons. Deriving dromaeosaurids from something of Ornitholestes-grade would explain why they are almost unique among derived maniraptorans in having prefrontals, which unlike the dental characters of eudromaeosaurs, are not plausibly due to macropredatory habits. In this scenario, microraptorians would be convergent with birds in their aerial characters.
Is there any other evidence for this idea? Don't troodontids show the same pattern as dromaeosaurids, going from Jinfengopteryx/Anchiornis to Mei/Sinovenator to Sinornithoides/Byronosaurus to Troodon? Maybe not. Jinfengopteryx and Anchiornis can switch to Avialae easily, and the same may be true for Mei and Sinovenator. They're often avialans in the in progress Lori matrix, even with Xu et al.'s troodontid characters. Lori itself emerged sister to Sinornithoides in Hartman et al.'s SVP poster and is Jurassic in age, with serrated teeth. Maybe that's the basal grade for troodontids, and birds are related but evolved serrationless teeth, long arms, dorsal ischial processes and such on their own branch.
The Jurassic Haplocheirus also supports this idea, since it shows serrated teeth and a general morphology so primitive that Cau's Sumrukia matrix found it to clade with compsognathids. Note therizinosaurs also have mesial and distal serrations, and that Falcarius has made the clade more basal in most matrices, unlike earlier ideas they were related to oviraptorosaurs. Maybe coelurosaurs were of the compsognathid-coelurid grade all through their evolution, with ornithomimosaurs, alvarezsaurids, therizinosaurs, dromaeosaurids and troodontids+birds each developing their birdlike and/or herbivorous characters separately. This idea is kind of anti-Paulian or anti-BCF in nature and has plenty of precedent in the literature. Ostrom long suggested Ornitholestes as a dromaeosaurid ancestor, and Makovicky (1995) found the two to be sister taxa to the exclusion of birds based on vertebral characters.
Of course the real test is with cladistic analyses, so how does the idea fare? The in progress Lori matrix finds a fairly traditional tree with Ornitholestes sister to Maniraptoriformes, microraptorians and Unenlagia basal among dromaeosaurids, and is somewhat unusual in finding troodontids sister to birds. Constraining Ornitholestes to be a dromaeosaurid and the dromaeosaurid topology 'backwards' from the consensus (Achillobator,Dromaeosaurus(Deinonychus,Velociraptor(Microraptor,Sinornithosaurus))) results in trees 11 steps longer. Not too bad when you consider enforcing Longrich and Currie's (2009) plausible-seeming traditional dromaeosaurid topology is 7 steps longer than the minimum.
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