New turtle clades: destined for revision due to taxon exclusion

Joyce et al. 2021 report,
“Over the last 25 years, researchers, mostly paleontologists, have developed a system of rank-free, phylogenetically defined names for the primary clades of turtles. As these names are not considered established by the PhyloCode, the newly created nomenclatural system that governs the naming of clades, we take the opportunity to convert the vast majority of previously defined clade names for extinct and extant turtles into this new nomenclatural framework.”

As long as Joyce et al. are working within a valid phylogenetic context, this sounds like a great idea!

“We are confident that we are establishing names that will remain accepted (valid in the terminology of the ICZN 1999) for years to come.”

Well, let’s see if Joyce et al. followed a valid phylogenetic context.

Archelosauria Crawford et al., 2015,
“The smallest crown clade containing the archosaur Crocodylus (orig. Lacerta) niloticus (Laurenti, 1768) and the turtle Testudo graeca Linnaeus, 1758, but not the lepidosaur Lacerta agilis Linnaeus, 1758 (Fig. 1b).”

Not a good start. In the large reptile tree (LRT, 1796+ taxa; subset Fig. 1) the smallest clade that includes Crocodylus and Testudo is a junior synonym for Reptilia (= Amniota). Joyce et al. are not familiar with the basal dichotomy that split reptiles into Lepidosauromorpha (lepidosaurs + turtles) and archosauromorpha (mammals and archosaurs) in the Viséan with Silvanerpeton as the last common ancestor. What can be done when turtle experts don’t agree (see below) on the origin of turtles?

Figure 1. Carbonodraco enters the LRT alongside another recent addition, Kudnu, at the base of the pareiasaurs + turtles.Figure 1. Carbonodraco enters the LRT alongside another recent addition, Kudnu, at the base of the pareiasaurs + turtles.

Joyce et al. continue:
“Comments—The name Archelosauria was recently introduced by Crawford et al. (2015) for the clade that unites Testudines and Archosauria Cope, 1869b [Gauthier and Padian, 2020] exclusively.” 

That was a mistake due to taxon exclusion. Don’t accept mistakes that put you into an invalid phylogenetic context.

Ankylopoda Lyson et al., 2012,
“Definition—The smallest crown clade containing the lepidosaur Lacerta agilis Linnaeus, 1758 and the turtle Chrysemys (orig. Testudo) picta (Schneider, 1783), but not the archosaur Crocodylus (orig. Lacerta) niloticus (Laurenti, 1768)

In the LRT that clade is the Millerettidae (Watson 1957) with Milleretta as the last common ancestor.

Figure 2. Milleretta, a Late Permian descendant of the Late Pennsylvanian ancestor of turtles and Eunotosaurus.

Joyce et al. continue:
“Comments—A clade consisting of Testudines and Lepidosauria Haeckel, 1866 [de Queiroz and Gauthier, 2020] to the exclusion of Archosauria has been retrieved in a number of phylogenetic hypotheses (e.g., Rieppel and Reisz 1999; Rieppel 2000; Li et al. 2008), but was only named Ankylopoda relatively recently (Lyson et al. 2012).”

What can be done when turtle experts don’t agree (see above) on the origin of turtles?

Testudinata Klein, 1760
“Definition—“The clade for which a complete turtle shell, as inherited by Testudo graeca Linnaeus, 1758, is an apomorphy. A ‘complete turtle shell’ is herein defined as a composite structure consisting of a carapace with interlocking costals, neurals, peripherals, and a nuchal, together with the plastron comprising interlocking epi-, hyo-, meso- (lost in Testudo graeca), hypo-, xiphiplastra and an entoplastron that are articulated with one another along a bridge” (Joyce et al. 2020b: 1044).

In the LRT (subset Fig. 1) soft-shell turtles (Fig. 3) had a separate parallel origin alongside hard-shell turtles (Fig. 4). Their last common ancestor had no shell: the pareiasaur, Bunostegos (Fig. 4). Workers like Joyce et al. 2021 are working under an assumption that is not true. Turtles are not monophyletic. You can read that manuscript on ResearchGate.net here. Turtle workers did not let this get published.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

Figure 4. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

The remainder of Joyce et al. 2021
lists and defines various clades of turtles. Without a clear understanding of parallel turtle origins, even some of these are subject to change when pertinent taxa are included. Most will likely remain the same as they distance themselves from turtle origins.

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References
Joyce et al. (15 co-authors) 2021. A nomenclature for fossil and living turtles using phylogenetically defined clade names. Swiss Journal of Palaeontology 140:5 https://doi.org/10.1186/s13358-020-00211-x

 

 

 

https://en.wikipedia.org/wiki/Millerettidae.

Huaxiapterus (Sinopterus) benxiensis enters the LPT basal to Tapejaridae

Lü et al. 2007
introduced us to the nearly complete crushed skeleton of Huaxiapterus benxiensis (Figs. 1, 2, BXGM V 0011) in a short paper with a short, three-sentence abstract.

Figure 1. Huaxiapterus benxiensis (BXGM V 0011) in situ, largely complete, crushed and articulated.

From the Lü et al. abstract
“A new species of Huaxiapterus: H. benxiensis sp. nov. is erected based on the new specimen. The diagnostic characters of Huaxiapterus benxiensis are well-developed premaxillary crest and parietal spine, the crest and spine parallel and extending posterodorsally, and a shallow groove present on the dorsal surface of the anterior portion of the mandibular symphysis. The different skull morphologies of Chinese tapejarid pterosaurs indicate that they are much more diverse than the previous thought.”

As in all known specimens of pterosaurs, no two adults are alike. That fact gives us an excellent view of microevolution at work in this and other pterosaur clades.

Unfortunately, other workers refuse to add pertinent largely complete taxa shown in the large pterosaur tree (LPT, 256 taxa), nor have they added valid outgroups with correct scores. So the taxonomy and nomenclature in those smaller studies tends to get confused.

Figure 2. DGS reconstruction from the low resolution in situ image in figure 1. Note the brevity of the distal wing phalanges, the robust hind limbs and the gracile humerus.

Huaxiapterus benxiensis (Lü et al. 2007, Early Cretaceous, BXGM V 0011, aka Sinopterus benxiensis) nests as the last common ancestor of the Tapejara clade + the Tupuxuara clade. Recently here, here and here we looked at other specimens assigned to Huaxiapterus that were later switched over to Sinopterus. This one (the BXGM specimen, Figs. 1, 2) is among those. They do nest closer to Sinopterus dongi (the holotype) than to Huaxiapterus jii, (the holotype), but H jii was also switched over to Sinopterus.

Almost flightless?
Different from other related pterosaurs Huaxiapterus benxiensis had shorter distal wing phalanges (m4.2, 4.3 and 4.4), a slender humerus and robust hind limbs. Together these traits suggest a trend to a reduced flight ability. Other, more clearly flightless pterosaurs are documented here, here, here and here.

Figure 4. Tapejaridae in the LPT. The BXGM specimen shows in the enlargement. It was about the size of Sinopterus dongi at the genesis of the Tupuxuara clade. 

A poor flyer at the base of the flying Tapejaridae
is possible, given that H. benxiensis is probably not the real last common ancestor, but more likely close to the real last common ancestor. It likely evolved its own way. The small size of H. benxiensis is in keeping with phylogenetic miniaturization at the start of other pterosaur clades and major clades in general.

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References
Lü JC, GAo YB, Xing LD, Li ZX and Ji Q 2007. A New Species of Huaxiapterus (Pterosauria: Tapejaridae) from the Early Cretaceous of Western Liaoning, China. Acta Geol Sinica – English 81: 683-687.

Asiatherium enters the LRT: mammal nomenclature issues follow

Everyone agrees
that Asiatherium (Figs, 1,2) nests close to Monodelphis, Caluromys and placentals. Trofimov and Szalay 1994 agreed. So did Denyer, Regnault and Hutchinson 2020. So did the large reptile tree (LRT, 1729+ taxa, subset Fig. 3).

Figure 1. Asiatherium in situ from Szalay and Trofimov 1996.

Asiatherium reshetovi (Trofimov and Szalay 1994, Szalay and Trofimov 1996; PIN 3907; Late Cretaceous; 80mya; Figs. 1, 2) is a key Mongolian metathere ancestral to monodelphids and Caluromys, which is ancestral to placentals. It is derived from Triassic sisters to extant late survivors, Didelphis, Gilronia and Marmosops.

Figure 2. Asiatherium skull slightly modified (longer lateral view premaxilla to match dorsal and ventral views) from Szalay and Trofimov 1996. Colors added here.

The problem is,
according to results recovered by the LRT, mammal clade nomenclature needs to go back to basics. Several modern mammalian clade names are found to be junior synonyms of traditional clades in the LRT.

Prototheria (Gill 1872) is a junior synonym
for Monotremata (Bonaparte 1837) in the LRT.

According to Wikipedia, “Prototheria is a paraphyletic subclass to which the orders Monotremata, Morganucodonta, Docodonta, Triconodonta and Multituberculata have been assigned, although the validity of the subclass has been questioned.”

In the LRT Morganucodon is a a marsupial (see below). Docodon is a taxon within Monotremata. Triconodon is a taxon within Monotremata. Multituberculata is a clade within the placental clade Glires (Fig. 4). So, the clade Monotremata is monophyletic and has precedence.

Theria (Parker and Haswell 1897) is a junior synonym
of Marsupialia (Illiger 1811). Metatatheria (Thomas Henry Huxley 1880) is also a junior synonym of Marsupialia.

The late-surviving basalmost marsupial in the LRT (Fig. 4), Ukhaatherium (Fig. 3), has epipubic (marsupial) bones. That long rostrum indicates this taxon is close to monotremes.

Figure 3. Ukhaatherium in situ.

Unlike the monophyletic clade Monotremata,
a series of nested marsupial clades are present. The last of these gives rise to Placentalia, only one of several that lose the pouch (Fig. 4). New names are proposed here where appropriate:

1. Marsupialia = Ukhaatherium and kin + all descendants (including placentals)
2. Paleometatheria = Morganucodon and kin + all descendants.
3. Didelphimetatheria = Eomaia and kin + all descendants
4. Phytometatheria = Marmosops and kin + all descendants
5. Carnimetatheria = Asiatherium and kin + all descendants
6. Transmetatheria = Caluromys and kin + all descendants
7. Placentalia = Vulpavus and kin + all descendants

Figure 4. Subset of the LRT cladogram of basal Mammalia. Note the new names proposed here.

Basal marsupial taxa are omnivores. 
Derived phytometatheres are herbivores. Derived carnimetatheres are carnivores to hyper-carnivores. Transmetatheres (Carluromys) and basal Placentalia remain omnivores.

In the LRT Eutheria (Gill 1872) is a junior synonym
of Placentalia (Owen 1837). Omnivorous civets like Nandinia are basal placentals. Carnivora is a basal placental clade following basal placental civets.

Competing cladograms
Denyer, Regnault and Hutchinson 2020 recently looked at the marsupial patella, or more specifically the widespread absence or reduction of the kneecap. The authors concluded, “metatherians independently ossified their patellae at least three times in their evolution.”

Unfortunately, Denyer et al. tested Caenolestes, the ‘shrew opossum’. Not surprisingly it nested close to placentals in their cladogram. Caenolestes was earlier nested in the LRT within the placental clade, Glires, closer to shrews than to opossums. It has no pouch, but converges with marsupials in several aspects. Inappropriate taxon inclusion, like Caenolestes, occurs due to taxon exclusion. Excluded taxa would have attracted and removed the inappropriate taxon. Taxon exclusion plagues Denyer et al.

Historically, you may remember,
Bi et al. 2018, while presenting Early Cretaceous Ambolestes, suffered from massive taxon exclusion and traditional bias in attempting to produce a cladogram of mammals. Bi et al. recovered Sinodelphys (Early Cretaceous) and Juramaia (Late Jurassic) as ‘eutherians’. In the LRT both are monotremes.

Other basal mammal cladograms
depend too much on tooth traits. Convergence in tooth traits creates problems, as documented earlier. We’ll look at this problem in more detail soon.

The above subset of the LRT appears to be a novel hypothesis
of interrelationships. If not, please provide a citation so I can promote it.

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References
Bi S, Zheng X, Wang X, Cignetti NE, Yang S, Wible JR. 2018. An Early Cretaceous eutherian and the placental marsupial dichotomy. Nature 558(7710):390395 DOI 10.1038/s41586-018-0210-3.
Denyer AL, Regnault S and Hutchinson JR 2020. Evolution of the patella and patelloid in marsupial mammals. PeerJ 8:e9760 http://doi.org/10.7717/peerj.9760
Szalay FS and Trofimov BA 1996. The Mongolian Late Cretaceous Asiatherium, and the early phylogeny and paleogeography of Metatheria. Journal of Vertebrate Paleontology 16(3):474–509.
Trofimov BA and Szalay FS 1994. New Cretaceous marsupial from Mongolia and the early radiation of Metatheria. Proceedings of the National Academy of Sciences 91:12569-12573

Recalibrating clade origins, part 1

Marjanovic 2019 reports on
the origin of several clades based on the fossil literature and molecules.

From the abstract:
“Molecular divergence dating has the potential to overcome the incompleteness of the fossil record in inferring when cladogenetic events (splits, divergences) happened, but needs to be calibrated by the fossil record.”

Testing has shown molecular testing leads to false positives over deep time. Phylogenetic testing using the large reptile tree (LRT, 1630+ taxa) has also shown the fossil record to be, at this date, more complete than Marjanovic (and, no doubt, others) imagine with no new clades appearing for quite some time and all known clades demonstrating a gradual accumulation of traits in the LRT.

“Ideally but unrealistically, this would require practitioners to be specialists in molecular evolution, in the phylogeny and the fossil record of all sampled taxa, and in the chronostratigraphy of the sites the fossils were found in.”

Ideally, but unrealistically, paleontologists would be better off omitting genomics and focusing on taxon exclusion within phenomics (trait-studies).

“Paleontologists have therefore tried to help by publishing compendia of recommended calibrations, and molecular biologists unfamiliar with the fossil record have made heavy use of such works.”

To their detriment and the deliver of false positives.

“Using a recent example of a large timetree inferred from molecular data, I demonstrate that calibration dates cannot be taken from published compendia without risking strong distortions to the results, because compendia become outdated faster than they are published.”

It is strongly recommended that no one infer anything from molecular data, including Dr. Marjanovic.

“The present work cannot serve as such a compendium either; in the slightly longer term, it can only highlight known and overlooked problems.”

The number one overlooked problem is genomics.

“Future authors will need to solve each of these problems anew through a thorough search of the primary paleobiological and chronostratigraphic literature on each calibration date every time they infer a new timetree; over 40% of the sources I cite were published after mid-2016. Treating all calibrations as soft bounds results in younger nodes than treating all calibrations as hard bounds.”

All calibrations involving genomics are going to have to be validated with last common ancestors recovered from phenomics. So, why not skip a step and just use phenomics?

“The unexpected exception are nodes calibrated with both minimum and maximum ages, further demonstrating the widely underestimated importance of maximum ages in divergence dating.”

Now let’s see what Marjanovic discovered, because his abstract does not give a clue. It’s an introduction, not a boiled-down synthesis. Comparisons with the LRT will be noted. Marjanovic’s cladogram is the first to include as wide a gamut as the LRT while employing only generic taxa. Unfortunately no fossil taxa are included. Only ten mammals and six birds are included.

Distinct from the LRT, the Marjanovic cladogram
nests turtles with archosaurs (creating the invalid clade, Archelosauria).

More tomorrow…

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References
Marjanovic D 2019. Recalibrating the transcriptomic timetree of jawed vertebrates.
bioRxiv 2019.12.19.882829 (preprint)
doi: https://doi.org/10.1101/2019.12.19.882829
https://www.biorxiv.org/content/10.1101/2019.12.19.882829v1

https://www.biorxiv.org/content/10.1101/2019.12.19.882829v1.full.pdf

New name and a name resurrection for two Solnhofen pterosaurs

Vidovic and Martill 2017
propose new and resurrect old generic names for two Solnhofen pterosaur specimens. Both are good and needed based on an earlier abstract (Peters 2007) and tree topology published here six years ago at ReptileEvolution.com in the large pterosaur tree (LPT, 232 taxa).

Unfortunately
Vidovic and Martill remain completely in the dark regarding pterosaur ontogeny. As we learned earlier here, here and here from several adult and juvenile specimens, pterosaurs juveniles and embryos had adult proportions and that’s why they were mechanically able to fly shortly after hatching. Vidovic and Martill report, “It is difficult to distinguish ‘G. rhamphastinus’ (Fig. 3 from the holotype of D. kochi (Fig. 2) other than by using size-related criteria.” And, “juvenile pterosaurs with small crests have been identified.”

Also unfortunately,
Vidovic and Martill still consider pterosaurs to be derived archosaurs or archosauriforms. They report, “A cladistic analysis of the Pterosauria, including all the taxa discussed here, was performed. The analysis included 104 operational taxonomic units (OTUs) comprising 99 pterosaurs and five archosauriforms as an outgroup.” We have to ask ourselves, how long will pterosaur workers remain in the dark on these basic questions that were answered years ago? Look here, here (Peters 2000, 2007) and here.

Pterodactylus wastebasket
Vidovic and Martill write: “Until relatively recently, the genus Pterodactylus Cuvier, 1809 had been a wastebasket taxon that has included many diverse pterosaurs, including some that are now recognized as basal nonpterodactyloids.” We looked at the Pterodactylus wastebasket here in 2011 (Fig. `1).

Figure 1. Click to enlarge. The Pterodactylus lineage and mislabeled specimens formerly attributed to this “wastebasket” genus

Wellnhofer 1970
provided catalog numbers for dozens of Solnhofen specimens. Since those numbers are simpler than their museum numbers that’s how they are named (Figs. 2, 3) at ReptileEvolution.com.

Figure 2. Basal Germanodactylia, Three taxa preceding Germanodactylus rhamphastinus: No. 6, No. 12 and No. 23, the last renamed Diopecephalus kochi. These are all adults.

No. 23 — BSP AS XIX 3 — Diopecephalus kochi (formerly Pterodactylus kochi).
(Fig. 1, left). Seeley had it right originally. Vidovic and Martill correct a century of error when they report, “The holotype of ‘P. kochi’ was considered to belong to a distinct genus by Seeley (1871), which he  unambiguously named Diopecephalus Seeley, 1871.”

No. 64 — B St AS I 745  —
Altmuehlopterus (formerly Germanodactylus) rhamphastinus
Vidovic and Martill reported, “Many phylogenetic studies demonstrate that the two species of Germanodactylus nest together (Kellner 2003; Unwin 2003; Andres & Ji 2008; Lu et al. 2009; Wang et al. 2009; Andres et al. 2014) in a monophyletic clade, but a more focussed analysis by Maisch et al. (2004) demonstrates the genus to be paraphyletic. Maisch et al. (2004) created the nomen nudum Daitingopterus, intended for the reception of ‘G. rhamphastinus’ by placing the name in a table with no specific reference to a specimen.”

Figure 3. Germanodactylus rhamphastinus, No. 64 in the Wellnhofer 1970 catalog. Vidovic and Martill renamed this specimen Altmuehlopterus, which is fine and appropriate.

The LPT separates A. (G.) rhamphastinus from G. cristatus by two taxa.

Problems with the Vidovic and Martill 2017 tree:

1. Lagerpeton nests with Marasuchus, both as proximal outgroups to the Pterosauria. Totally bogus. Tested, validated, real outgroups are listed here. The Fenestrasauria (Peters 2000) is overlooked in the text and references.
2. Preondactylus and Austriadactylus nest as basalmost pterosaurs. Bergamodactylus, the basalmost pterosaur in the LPT, is excluded.
3. Only one specimen each of Dorygnathus and Scaphognathus are employed. The LPT shows two clades of pterodactyloid-grade pterosaurs arise from various specimens of Dorygnathus while two others arise from tiny Scaphognathus specimens experiencing phylogenetic miniaturization.
4. As a result (perhaps) toothy ornithocheirids nest with toothless pteranodontids. In the LPT ornithocheirids arise from equally tooth cycnorhyamphids while shartp-face pteranodontids arise from similar germanodactylids.
5. The Darwinopterus clade nests as the proximal outgroup to the traditional Pterodactyloidea, when the LPT shows it to be a sterile clade with some pterodactyloid-grade traits.
6. Altmuehlopterus (formerly Germanodactylus) rhamphastinus nests with G. cristatus
7. Diopecephalus kochi nests with Pterodactylus antiquus.
8. Those are the big problems. There are more, but I want to keep it pertinent.

Vidovic and Martill provide clues to their observational problems
when they note, “The genera Pterodactylus and Diopecephalus are remarkably similar.” No they aren’t! Species within the Pterodactylus clade are not even that similar!

Re: Germanodactylus and Pterodactylus,
Vidovic and Martill write: “We agree that some of the differences could be ontogenetically variable and perhaps vary between sexes, so in 1996 it seemed possible that the two species could be at least congeneric.” They disagree with the “common opinion” that the two are distinct genera. Let’s go with the evidence of a large gamut phylogenetic analysis — not opinion — or any analysis lacking so many pertinent taxa.

Vidovic and Martill 2017 rename G. rhamphastinus
Altmuehlopterus rhamphastinus. That’s good. It is generically distinct from its proximal relatives in the LPT. They report, “This name is presented as an alternative to the geographically significant name Daitingopterus (Maisch et al., 2004) which is a nomen nudum.” Not sure how all that falls. I’ll leave such issues to the PhDs.

If you like long nomenclature puzzles
you’ll like Vidovic and Martill 2017. They do a good job of running down all the names that prior workers gave to these century-old specimens. Beware that they are clueless as to the origin of pterosaurs, the ontogeny of pterosaurs and previous work on the phylogeny of pterosaurs based on a much larger taxon list of ingroup and outgroup taxa.

References
Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336
Peters D 2007  The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27. Abstract online here.
Vidovic SU and Martill DM 2017. The taxonomy and phylogeny of Diopecephalus kochi (Wagner, 1837) and ‘Germanodactylus rhamphastinus’ (Wagner, 1851). From: Hone DWE., Witton MP and Martill DM (eds) New Perspectives on Pterosaur Palaeobiology. Geological Society, London, Special Publications, 455, https://doi.org/10.1144/SP455.12
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

wiki/Pterodactylus
wiki/Germanodactylus

Mammalian nomenclature problems

Several putative stem mammal clades
have not been recovered in the LRT, like the ‘Notoungulata’ and the ‘Allotheria.‘ Similarly several putative reptile clades were also not recovered.

Now
the base and stem of the mammal clade are showing some nomenclature problems relative to traditional results.

First, I added a few mammals
(Mus, Taeiniolabis, Paulchaffatia) just be sure I was comparing listed taxa (see below) with listed taxa. If you know of any pertinent taxa that will change the current tree topology back to traditional topologies, please let me know. So far, I’m coming up short. These are the changes recovered so far:

Carrano et al. (editors) 2006
reports the following pertinent definitions. Comments follow (not in boldface).

Mammalia Linneaus 1758
The least inclusive clade containing Ornithorhynchus and Mus. In the LRT, Sinoconodon is the last common ancestor and Pachygenelus nests at the base of the outgroup clade, the Trithelodontidae (including the Tritylodontidae). So, no problems with this definition.

Trithelodontidae Broom 1912
The most inclusive clade containing Pachygenelus, but not Tritylodon and Mus. In the LRT Pachygenelus is basal to both Tritylodon and Mus, so the most inclusive clade containing Pachygenelus includes Mammalia and Tritylodontidae, contra prior studies.

Tritylodontidae Kühne 1956|
The most inclusive clade containing Tritylodon, but not Pachygenelus or Mus. In the LRT, this clade is monophyletic, and now includes Repenomamus.

Mammaliamorpha Rowe 1988
The least inclusive clade containing Tritylodon, Pachygenelus and Mus. In the LRT this clade is a junior synonym of the Trithelodontidae (see above).

Mammaliformes Rowe 1988
The most inclusive clade containing Mus, but not Tritylodon or Pachygenelus. In the LRT, this clade is a junior synonym for the clade Mammalia because Pachygenelus is the proximal outgroup taxon to Mammalia.

Theria  Parker and Howell 1897
The least inclusive clade containing Mus and Didelphis. In the LRT this clade is monophyletic and unchanged.

Theriimorpha Rowe 1988
The most inclusive clade containing Mus but not Ornithorhynchus. In the LRT this clade is a junior synonym for Theria.

Metatheria Huxley 1880
The most inclusive clade containing Didelphis, but not Mus. This definition was meant to include all marsupials, but in the LRT the clade that includes most marsupials does not include Didelphis, which nests basal to and outside both monophyletic Marsupialia and Placentalia. So, strictly speaking, Metatheria in the LRT currently includes only Didelphis and perhaps its sister, Ukhaatherium.

Allotheria Marsh 1880
The most inclusive clade containing Taeniolabis, but not Mus or Ornithorhynchus. This was meant to indicate that Taeniolabis nested outside the Mammalia, but in the LRT Taeniolabis nests with Plesiadapis and Carpolestes and this clade is a sister to the clade containing Mus and the Multituberculata — within the Glires and Placentalia.

Multituberculata Cope 1884
The least inclusive clade containing Taeniolabis and Paulchofattia. This was meant to  include all the multituberculates and have them nest outside of the Mammalia, but in the LRT Taeniolabis nests with Plesiadapis and Paulchofattia nests with Carpolestes. So that is a clade of four taxa at present and it does not include Ptilodus and other multituberculates, the clade with a large and grooved lower last premolar. These traditional multis now need a new clade name. They are derived from a sister to the rodent clade in the LRT and they leave no descendants. Carpolestes is a sister to the ancestor of rodents and multis and Carpolestes (Fig. 1) has a large and barely-grooved lower last premolar, a precursor to that identifying trait in that second clade of multis.

Figure 1. Carpolestes simpsoni skull shows that large lower premolar with just a few grooves. Here in the LRT Carpolestes nests close to the base of the traditional multituberculates that emphasize this trait. But see text for strict definitions of this clade.

References
Editors: Carrano MT et al. 2006. Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds and Reptiles. University of Chicago Press.  online here.
Kermack KA, Mussett F, Rigney HW 1973. The lower jaw of Morganucodon. Zoological Journal of the Linnean Society.53 (2): 87–175.
Martin T et al. 2015. A Cretaceous eutriconodont and integument evolution of early mammals. Nature 526:380-384. online.

Same or Different? When Should You Invent a new Genus? or Just Add a Species? Or Revise the Whole Clade?

Now that new pterosaurs are being added to the large pterosaur tree on a fairly constant basis, it’s time to figure out what to name them.

In the old days everything was named “Pterodactylus,” no matter what it was. Sharp-eyed observers soon figured out that there were differences that set certain specimens apart and these were then renamed. Others have not yet been widely recognized as distinct, but they need to be (Fig. 1).

Figure 1. Click to enlarge. The Pterodactylus lineage and mislabeled specimens formerly attributed to this “wastebasket” genus

Nowadays, new pterosaurs distinct from all others are being given new generic names, and that’s a good thing. However some of the new specimens nest within long lists of other genera. Others are given new species names within certain genera without nesting near those genera. The problem is a result of the incompleteness of all previously published pterosaur trees. They simply do not include enough taxa. They have a priori deleted all tiny specimens and all congeneric variations that, in the large pterosaur tree, provide clues to the evolution of more derived variations, some of which are distinct genera, as in the Campylognathoides/Rhamphorhynchus transition.

Some examples
MPUM6009 was considered a Eudimorphodon and a Carniadactylus despite nesting far from both genera. MCSNB 8950 was considered a Eudimorphodon, but nested with anurognathids.

Nesodactylus nested within the genus Campylognathoides. Bellubrunnus and Qinglongopterus nested within the genus Rhamphorhynchus.

Fenghuangopterus, Sericipterus and Cacibupteryx nested within the genus Dorygnathus.

Eosipterus and Cuspicephalus nest within the genus Germanodactylus.

Kellner (2010) renamed one Pteranodon, Dawndraco, but it remains surrounded by other Pteranodon specimens.

The question is, do we revise all the old genera and give them new names now that we know how distant some were from each other? Or do we retain those genera and take away the new generic names of the new specimens between them to reflect their traditional generic nesting?

Now all this doesn’t take into account marginal generic names, like Ningchengopterus at the base of the Pterodactylus clade or Muzquizopteryx at the base of the Nyctosaurus clade. These names are likely to be valid because they are distinct genera, but so are many of the species within Pterodactylus and Nyctosaurus. If they were modern birds, not prehistoric pterosaurs, their differences would be recognized.

Part of the historical problem, of course, goes back to Chris Bennett and others who considered smaller species to be immature forms of larger species without adequately describing them or placing them in analysis. It turns out that the vast majority of those where simply smaller forms that were evolving to become the larger forms – or vice versa.

It’s a problem. It needs to be recognized and dealt with. But it will only be recognized if pterosaur specimens are not a priori deleted from analysis for whatever reason.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Kellner AWA 2010. Comments on the Pteranodontidae (Pterosauria, Pterodactyloidea) with the description of two new species. Anais da Academia Brasileira de Ciências 82(4): 1063-1084.

Double Blind Stradivarius Test and the Ornithodira

Holding its own tradition of greatness for centuries, the Stradivarius violin knows few equals. Aficionados swear that its tones cannot be duplicated. Experts have worked for years to duplicate its shape and discover its mystical varnish formulas, all to reveal the “secret” of its unique sound qualities — perhaps in vain, as it turns out.

Brand Loyalty
Unfortunately, all this work and all that status may come down to nothing more than a bad case of brand loyalty. In a recent double blind test, a Stradivarius violin was chosen as the least favorite of several, losing out to a modern instrument. Judges were seasoned violin players.

When the players were asked which violins they’d like to take home, almost two-thirds chose a violin that turned out to be new, rather than the Strad. The research was aimed at determining how people choose what they like, and what criteria they use.

Dale Purves, a professor of neuroscience at Duke University, says the research “makes the point that things that people think are ‘special’ are not so special after all when knowledge of the origin is taken away.” The research appears in the Proceedings of the National Academy of Sciences.

So what does all this have to do with paleontology?
Brand loyalty is keeping pterosaurs nested with Scleromochlus and dinosaurs despite scientific testing (Peters 2000a, b 2009) that recovered fenestrasaurs, lizards, even turtles as closer sister taxa. This is the “blind eye” I referred to earlier. The biggest names in paleontology have wrapped their arms and careers around their support for the “Ornithodira” — perhaps irrationally, as it turns out. The “Ornithodira” cannot be supported except by deleting lizards (Bennett 1996, Bursatte 2010, Nesbitt 2011) or by deleting and depleting fenestrasaurs (Hone and Benton 2007, 2008). Even the proponents of the “Ornithodira” throw up their hands in surrender when asked to identify which generic taxon is closer to pterosaurs than any other and what traits they share to the exclusion of all other known fossils reptiles. It’s sad really. Twelve years after the first challenge to the “Ornithodira”(Peters 2000), workers continue to cling to the status and comfort of that old notion rather than finding genuine support for it.

It’s hard to change textbooks and class notes.
If you’re a professor faced with a challenge to your pet hypotheses, do you suppress manuscripts that expose their weaknesses? Or do you engage opposing candidates to test their mettle? If you’re a student, do you support your mentor no matter what? Those who do choose to suppress, typically go “all the way.” They label the opposition a heretic. Ridicule him as a nut case. Make him a pariah. Ignore the taxa. Attack the challenger. Delete all references to opposing theories. If you do choose to suppress, thereafter you have two choices: 1) put your support behind a notion that is widely recognized as weak and unsupportable, even by its proponents (Hone and Benton 2007, 2008); or 2) shrug your shoulders and say, “Sorry, that’s one of the mysteries we’re still working on.”

Sorry for rant. The NPR story on the Stradivarius double blind test just “struck a familiar chord.” And it, too, solves an ancient mystery. We’ll be back to more reptiles tomorrow.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References

Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoological Journal of the Linnean Society 118:261-308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Brusatte SL, Benton MJ, Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330

Nomenclature revisions (part 4)

Today’s blog will tag on the heels of “Nomenclature revisions (parts 1, 2 and 3) to highlight a number of putative clades that are in need of revision, are no longer valid or are redundant in light of the new reptile tree (which is larger than any prior attempt and encompasses all the major clades). Today we’ll restrict our scope to the Ornithosuchia.

Ornithosuchia – retained with a revision
Gauthier (1986) defined Ornithosuchia as the taxon that included extant birds and all extinct archosaurs that are closer to birds than they are to crocodiles. This definition is retained, with a revision. Gauthier’s Ornithosuchia included Ornithosuchidae + Ornithodira. Since pterosaurs were included within Ornithodira, Gauthier’s Ornithosuchia is redundant with Reptilia. Given a new node-based definition that deletes Ornithosuchidae and Pterosauria, the new Ornithosuchia is proposed to include Turfanosuchus, Triceratops, their last common ancestor and all of its descendants. The outgroup is Crocodylomorpha.

Ornithodira – redundant
Gauthier (1986) defined “Ornithodira” as all forms closer to birds than to crocodiles. Here this definition is redundant with Ornithosuchia.

Sereno (1991) defined “Ornithodira” as the last common ancestor of the dinosaurs and the pterosaurs, and all its descendants. Here this definition is redundant with Reptilia.

Avesuchia – paraphyletic and redundant
Benton (1999) defined “Avesuchia/crown-group Archosauria” as the taxon comprising “Avemetatarsalia” and “Crurotarsi” (and sister taxa of “Crurotarsi” that are closer to Crocodylia than to Aves), and all their descendants. Because the definition included parasuchians, pterosaurs and Lagerpeton, here this created a paraphyletic clade redundant with Reptilia.

Avemetatarsalia – paraphyletic and redundant
Benton (1999) defined Avemetatarsalia as all “avesuchians/crown-group archosaurs” closer to Dinosauria than to Crocodylia. That definition is redundant with Ornithosuchia. Avemetatarsalia was meant to include Scleromochlus + pterosaurs + dinosauromorphs, but here that clade is paraphyletic (or redundant with Reptilia).

Dinosauriformes – no utility, paraphyletic
Novas defined Dinosauriformes as the most recent common ancestor of Marasuchus (Lagosuchus), Dinosauria and all descendants. Since Marasuchus is derived within the Theropoda here, that definition is now redundant with Dinosauria.

Benton (2004) redefined Dinosauriformes as Neornithes and all ornithodirans closer to Neornithes than to Lagerpeton. Since “Ornithodira” is now redundant with Reptilia (see above) and Lagerpeton now nests outside Euarchosauriformes, Benton’s definition has no utility.

Dinosauromorpha – no utility, paraphyletic
Sereno (1991) defined the Dinosauromorpha as all “Ornithodira” closer to Neornithes than to Pterosauria. Since the Pterosauria is far removed from the Dinosauria, this definition has no utility.

Sereno (1991) did not fix the problem when he stated the clade consisted of Passer and all species closer to Passer than to Pterodactylus, Ornithosuchus and Crocodylus. Sereno (1991) also provided a node clade definition: the last common ancestor of Lagerpeton, Lagosuchus, Pseudolagosuchus and the Dinosauria (including Aves) and all its descendants. Here Sereno’s definition is redundant with Archosauriformes. Removing the proterochampsid, Lagerpeton, from the definition creates a monophyletic clade, but one that would be redundant with Dinosauriformes (= Dinosauria). At present there are no non-dinosaur members to populate the Dinosauriformes or the Dinosauromorpha, since Crocodylomorpha is now the sister taxon of the Dinosauria.

Dinosauria – retained and expanded
Holtz and Padian (1995) defined the Dinosauria as all descendants of the most recent common ancestor of Triceratops and Passer, the sparrow. Standing firm, this definition still includes all taxa traditionally considered dinosaurs. It also adds members of the Poposauridae, Pisanosaurus, Silesaurus and Lotosaurus, a clade here labeled the Paraornithischia. Traditional clade names and inclusion lists for Theropoda, Sauropodomorpha and Ornithischia are retained.

Saurischia – no utility, paraphyletic
Seeley (1888) classified dinosaurs into two orders based on pelvis morphology. Here, with the Phytodinosauria, this division is polyphyletic and has lost its usefulness.

Phytodinosauria – resurrected
Bakker (1986) coined the term “Phytodinosauria” for a clade including Sauropodomorpha + Ornithischia. Here testing supports this clade.

Paraornithischia – new clade
The new clade Paraornithischia is proposed to include Effigia, Lotosaurus, their last common ancestor and all of its descendants. This clade of apparent herbivores (none have sharp, serrated teeth and some are toothless) demonstrates a variety that hints at a wider radiation of undiscovered forms, all currently restricted to the Middle and Late Triassic. The clade also includes Pisanosaurus, Shuvosaurus/Chatterjeea and Silesaurus. This clade consists only of herbivores, many of which had a predentary, paired predentaries or something like it that may have been fused to the often toothless dentaries.  While it may be tempting to consider this the clade basal to Ornithischia, at present moving this branch to the base of the Ornithischia adds four steps. More taxa will bring greater resolution.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
 Bakker RT 1986. The Dinosaur Heresies. New York: William Morrow. p. 203. ISBN 0-14-010055-5.
Benton MJ 1990. Origin and Interrelationships of dinosaurs, In Weishampel DB, Dodson P, and Osmólska H editors. The Dinosauria. 11–30. Berkeley: U Calif Press.
Benton MJ 1999. Scleromochlus taylori and the origin of dinosaurs and pterosaurs. London: Phil Trans Roy Soc B, 354: 1423–1446.
Benton MJ, Clark JC 1988. Archosaur phylogeny and the relationships of the Crocodylia. In Benton MJ editor. The phylogeny and classification of the tetrapods, 295–338. Syst Assoc, Sp Vol 35A, Clarendon:Oxford.
Bonaparte JF 1982. Classification of the Thecodontia. Geóbios, Mém Sp 6: 99–112.
Clark JM and Hernandez RR 1994. A new burrowing diapsid from the Jurassic La Boca formation of Tamaulipas, Mexico, J Vert Paleo 14: 180–195.
Dilkes D 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Phil Trans R Soc B 353: 501–541.
Gauthier JA 1986. Saurischian monophyly and the origin of birds, In Padian K editor. The Origin of Birds and the Evolution of Flight, 1–55. Memoirs Calif Acad Sc 8.
Gauthier J, Kluge AG and Rowe T 1988. Amniote phylogeny and the importance of fossils. Cladistics 4: 105–209.
Gauthier J, Estes R and de Queiroz K 1988. A phylogenetic analysis of Lepidosauromorpha, In Estes R, Pregill G, editors. Phylogenetic relationships of the lizard families, 15–98. Stanford: Stanford U Press.
Gauthier JA 1994. The diversification of the amniotes. In: Prothero DR, Schoch RM editors. Major Features of Vertebrate Evolution: 129-159. Knoxville: Paleo Society.
Gauthier JA, Padian K 1989. The origin of birds and the evolution of flight, In Padian K, Chure DJ editors. The Age of Dinosaurs: Short Courses in Paleontology, No. 2. 121–133. Paleo Soc Depart Geo Sci, Knoxville: U Tenn.
Holtz TR and Padian K 1995. Definition and diagnosis of Theropoda and related taxa. J Vert Paleo 15: 35A
Krebs B 1974. Die Archosaurier. Naturwissenschaften 61: 17–24.
Laurin M 1991.The osteology of a Lower Permian eosuchian from Texas and a review of diapsid phylogeny. Zoological Journal of the Linnean Society 101: 59–95.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Novas FE 1992. Phylogenetic relationships of the basal dinosaurs, the Herrerasauridae. Palaeontology 35: 51–62.
Parrish JM 1993. Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. J Vert Paleo 13:287–308.
Senter P 2004.Phylogeny of Drepanosauridae (Reptilia: Diapsida). J Syst Palaeo 2: 257–268.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. J Vert Paleo 11 (Supp) Mem 2: 1–53.
Sereno PC 2005. The logical basis of phylogenetic taxonomy. Syst Biol 54: 595-619.
Walker AD 1964. Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs. Phil Trans R Soc London. Ser B Bio Sci 248 (744): 53–134.

Nomenclature revisions (part 3)

Today’s blog will tag on the heels of “Nomenclature revisions (part 1 and part 2) to highlight a number of putative clades that are in need of revision, are no longer valid or are redundant in light of the new reptile tree (which is larger than any prior attempt and encompasses all the major clades). Today we’ll restrict our scope to the Archosauriformes.

Figure 1. The Euarchosauriformes. Click to see more.

Erythrosuchiformes – new clade
A new definition for a monophyletic clade Erythrosuchiformes is proposed to include Erythrosuchus, Triceratops, their last common ancestor and all of its descendants. Vjushkovia had been traditionally considered an erythrosuchid but here it nests outside the Erythrosuchidae.

The Rauisuchia – retained
Rauisuchia was erected by Bonaparte to represent the clade including Rauisuchidae, Prestosuchidae, Poposauridae and Chatterjeeidae. Because Chatterjeea and Poposaurus now nest as dinosaurs, this definition of the Rauisuchia now includes all dinosaurs. Redefined as a more inclusive monophyletic node-based clade, the new Rauisuchia is proposed to include Vjushkovia, Triceratops, their last common ancestor and all of its descendants. Members also include crown-clade Archosauria and Ticinosuchidae (including Stagonolepidae). The more restricted Rauisuchidae now includes Vjushkovia, Smok, the last common ancestor and all its descendants.

Ticinosuchidae – new clade
Yarasuchus and Ticinosuchus are basal to a clade that includes Qianosuchus and the Stagonolepidae. Within the new Rauisuchia, a definition for a monophyletic Ticinosuchia is proposed to include Ticinosuchus, Triceratops their last common ancestor and all of its descendants. The more restricted Ticinosuchidae is proposed to include Ticinosuchus, Qianosuchus, their last common ancestor and all its descendants.

Archosauria – retained
Still crocs, birds, their last common ancestor and all its descendants. No change here (except no pterosaurs, of course).

Suchia – paraphyletic
Krebs (1974) defined “Suchia,” as “Crocodylotarsi,” but not Parasuchia. Even so, such a clade remains paraphyletic here. “Suchia” had been described by Benton and Clark (1988) as Crocodylomorpha + “rauisuchians” + Stagonolepididae, but not Gracilisuchus =. Here, that assemblage also constitutes a paraphyletic group.

Pseudosuchia – redundant
In the pre-cladistic era, “Pseudosuchia” generally included Stagonolepidae, the old Rauisuchia, Ornithosuchidae and some basal crocodylomorphs. Here these form a a paraphyletic clade.

Gauthier and Padian (1989) defined “Pseudosuchia” as “crocodiles and all archosaurs closer to crocodiles than to birds. Gauthier 1986 and Senter (2004) created equivalent definitions. Unfortunately, here the “Pseudosuchia,” as defined by these authors, is redundant with the Crocodylomorpha.

Crocodylomorpha – retained, redefined
Parrish (1993) cited six synapomorphies from Walker (1964) when he embedded the old Crocodylomorpha within Rauisuchia.

Benton (1990) defined Crocodylomorpha as all archosaurs closer to Eusuchia than to Ornithosuchus or Postosuchus. While it is clear that Benton meant to include a clade similar to the present one, his definition with the present tree topology would include Ticinosuchidae (including Stagonolepidae), which was not his intention.

Sereno (2005) defined Crocodylomorpha as the most inclusive clade containing Crocodylus but not Poposaurus, Gracilisuchus, Prestosuchus and Aetosaurus. The omission of Gracilisuchus excludes a basal taxon in the present Crocodylomorpha.

A new node-based definition for the new Crocodylomorpha is proposed to include Crocodylus, Pseudhesperosuchus, their last common ancestor and all of its descendants. Ticinosuchidae is the outgroup. Scleromochlus, a taxon often nested with dinosaurs and pterosaurs [17–20,23] nests here (Figures 2) within the crocodylomorpha close to Gracilisuchus.

Crocodylotarsi – redundant
Benton and Clark (1988) defined “Crocodylotarsi” as the last common ancestor of crocodiles and Parasuchia. This represented the “crocodilian line” (Parasuchia, Rauisuchidae, Stagonolopedidae, Poposauridae and Crocodylomorpha) as opposed to the “bird line” (Ornithosuchia) as defined by Parrish (1993). In the present study that definition of Crocodylotarsi is redundant with Archosauriformes and furthermore the taxon list is paraphyletic.

Crurotarsi  – redundant
Sereno (1991) defined “Crurotarsi,” as all forms closer to Crocodylus than to Passer [146]. It was meant to include rauisuchians, phytosaurs (parasuchians), stagonolepids, poposaurs, sphenosuchians, and a few other groups including Ornithosuchidae. Here the definition is redundant with Crocodylomorpha. The taxon membership list is paraphyletic and redundant with Archosauriformes.

More coming in part 4. 

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Benton MJ 1990. Origin and Interrelationships of dinosaurs, In Weishampel DB, Dodson P, and Osmólska H editors. The Dinosauria. 11–30. Berkeley: U Calif Press.
Benton MJ, Clark JC 1988. Archosaur phylogeny and the relationships of the Crocodylia. In Benton MJ editor. The phylogeny and classification of the tetrapods, 295–338. Syst Assoc, Sp Vol 35A, Clarendon:Oxford.
Bonaparte JF 1982. Classification of the Thecodontia. Geóbios, Mém Sp 6: 99–112.
Clark JM and Hernandez RR 1994. A new burrowing diapsid from the Jurassic La Boca formation of Tamaulipas, Mexico, J Vert Paleo 14: 180–195.
Dilkes D 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Phil Trans R Soc B 353: 501–541.
Gauthier JA 1986. Saurischian monophyly and the origin of birds, In Padian K editor. The Origin of Birds and the Evolution of Flight, 1–55. Memoirs Calif Acad Sc 8.
Gauthier J, Kluge AG and Rowe T 1988. Amniote phylogeny and the importance of fossils. Cladistics 4: 105–209.
Gauthier J, Estes R and de Queiroz K 1988. A phylogenetic analysis of Lepidosauromorpha, In Estes R, Pregill G, editors. Phylogenetic relationships of the lizard families, 15–98. Stanford: Stanford U Press.
Gauthier JA 1994. The diversification of the amniotes. In: Prothero DR, Schoch RM editors. Major Features of Vertebrate Evolution: 129-159. Knoxville: Paleo Society.
Gauthier JA, Padian K 1989. The origin of birds and the evolution of flight, In Padian K, Chure DJ editors. The Age of Dinosaurs: Short Courses in Paleontology, No. 2. 121–133. Paleo Soc Depart Geo Sci, Knoxville: U Tenn.
Krebs B 1974. Die Archosaurier. Naturwissenschaften 61: 17–24.
Laurin M 1991.The osteology of a Lower Permian eosuchian from Texas and a review of diapsid phylogeny. Zoological Journal of the Linnean Society 101: 59–95.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Parrish JM 1993. Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. J Vert Paleo 13:287–308.
Senter P 2004.Phylogeny of Drepanosauridae (Reptilia: Diapsida). J Syst Palaeo 2: 257–268.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. J Vert Paleo 11 (Supp) Mem 2: 1–53.
Sereno PC 2005. The logical basis of phylogenetic taxonomy. Syst Biol 54: 595-619.
Walker AD 1964. Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs. Phil Trans R Soc London. Ser B Bio Sci 248 (744): 53–134.