If it’s aberrant, watch out! It probably isn’t what you think it is.

Several “aberrant” taxa have been promoted recently.


Vancleavea campi

Figure 1. Vancleavea skeleton, sans osteoderms.

Vancleavea was postulated (Nesbitt et al. 2009) to be an aberrant archosauriform close to DoswelliaTurfanosuchusChanaresuchus and Erythrosuchus. Nested in the large reptile tree it turned out to be a sister to Helveticosaurus, a thalattosaur.

Pterosaurs have been traditionally and most recently postulated (Nesbitt 2011) to be aberrant archosaurs close to parasuchians and dinosaurs. The large reptile tree nested them with fenestrasaurs like Longisquama.


Figure 2. Casea, not a synapsid!

Caseasaurs were postulated (Romer and Price 1940) to be aberrant synapsids. The large reptile tree nested them with millerettids.

Turtles were postulated to be aberrant archosaurs, sauropterygians and pareiasaurs. The large reptile tree nested them distinct from but closer to pareiasaurs, close to the largely forgotten diadectid, Stephanospondylus.

Diadectes, Chroniosuchus and Limnoscelis (Berman, Reisz and Scott 2010 – who reported, “diadectomorphs comprise a nonamniote sister clade to all amniotes”) were traditionally postulated to be outgroup taxa to the Reptilia . The large reptile tree found they all nested within the Reptilia.

Tetraceratops was considered an aberrant synapsid close to the base of the therapsida (Amson and Laurin 2011), but here it nested with Tseajaia.

Mesosaurus was postulated (Laurin and Reisz 1995; Modesto 2006, 2010) to be an aberrant basal reptile between synapsids and milllerettids + captorhinids. The large reptile tree nested mesosaurs at the base of the Enaliosauria (plesiosaurs, thalattosaurs and ichthyosaurs), close to Wumengosaurus and Claudiosaurus.

Tanystropheus was considered an aberrant prolacertiform, but here it nests with a new clade of lizards, the Tritosauria, along with an ‘island of misfit toys’ including drepanosaursSharovipteryx, Longisquama and pterosaurs.

Eudibamus was considered an aberrant bolosaurid (Berman et al. 2000). The large reptile tree found it nested with the basal diapsids, Petrolacosaurus and Spinoaequalis.

Colobomycter was originally considered an aberrant caseid pelycosaur (Vaughn 1958). Later Modesto and Reisz (2008) considered it close to Acleistorhinus. The large reptile tree nested it with basal placodonts.

Choristoderes, like Doswellia and Champsosaurus, were considered aberrant proterochampsids (Dilkes and Sues 2009) and basal lepidosauromorphs respectively. Here they nest together derived from Youngina BPI 2871.

Lagerpeton was considered a dinosaur-ancestor (Irmis et al. 2007 and Nesbitt et al. 2009) despite the weird feet and a strange pelvis. Here it nested with the bipedal chanaresuchid, Tropidosuchus.

Lotosaurus compared to sister taxa and other finback archosaurs.

Figure 3. Lotosaurus compared to sister taxa and other finback archosaurs.

Lotosaurus was considered an aberrrant herbivorous rauisuchid close to the carnivorous Arizonasaurus (Nesbitt 2003). The large reptile tree nested it with Silesaurus and the poposaurids, within the Dinosauria.

Diandongosuchus was considered an aberrant basal poposaurid. Here it nests as a basal parasuchian, not far from Proterochampsa.

Scleromochlus was considered (Benton 1999, Senter 2003) an aberrant sister to pterosaurs (or pterosaurs were aberrant, take your pick because they are wildly different). Here it nests with other basal bipedal crocs.

Revueltosaurus was considered (Nesbitt 2011) to be an aberrant sister to aetosaurs. Here it nests with the rauisuisuchid, Postosuchus.

Effigia and Shuvosaurus were considered (Nesbitt and Norell 2006; Brusatte et al. (2010) aberrant poposaurid rauisuchians that only looked like dinosaurs. The large reptile tree nested it with other poposaurids within the Dinosauria.

Daemonosaurus was considered (Sues et al. 2011) an aberrant theropod dinosaur. Here it nested with basal ornithischian dinosaurs.

Well, basically this is a summary of most of the PterosaurHeresies highlights, all arrived at by applying the misfit taxa to a larger matrix granting more opportunity to nest most parsimoniously. A priori assumptions are fine, if you’re sure of what you have. If not… if you have an aberrant fossil, then test it in the large reptile tree to see what it recovers before making your assumptions. It will save you from having to read a criticism here.

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.

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
Berman, DS, Reisz RR, Scott D, Henrici AC, Sumida SS and Martens T 2000. Early Permian bipedal reptile. Science 290: 969-972.
Berman DS Reisz RR and Scott D 2010. Redescription of the skull of Limmoscelis paludis Williston (Diadectomorpha: Limnoscelidae) from the Pennsylvanian of Canon del Cobre, northern New Mexico: In: Carboniferous-Permian Transition in Canon del Cobre, Northern New Mexico, edited by Lucas, S. G., Schneider, J. W., and Spielmann, New Mexico Museum of Natural History & Science, Bulletin 49, p. 185-210.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Laurin M and Reisz R 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society, 113: 165–223.
Modesto SP and Reisz RR 2008. New material of Colobomycter pholeter, a small parareptile from the Lower Permian of Oklahoma.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218.
Nesbitt SJ 2003. Arizonasaurus and its implications for archosaur divergence. Proceedings of the Royal Society, London B (Suppl.) 270, S234–S237. DOI 10.1098/rsbl.2003.0066
Nesbitt S 2007
The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History, 302: 84 pp. online pdf
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.
Nesbitt SJ and Norell MA 2006.
Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society B 273:1045–1048. online
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.
Parker WG., et al. 2005. T
he Pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. In Proceedings of the Royal Society London B 272(1566):963–969.
Romer AS and Price LI 1940. 
Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.
Senter P 2003. 
Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Vaughn PP 1958. 
On a new pelycosaur from the Lower Permian of Oklahoma, and on the origin of the family Caseidae. Journal of Paleontology 32:981–991.

AMNH Effigia webpage

8 thoughts on “If it’s aberrant, watch out! It probably isn’t what you think it is.

  1. I’d actually treat this as a problem with your tree instead of a benefit. Looking at phylogenies for living taxa that can be tested with DNA, we find that there are a lot of abberant taxa. Iguanians are nested within scleroglossans, not basal. Bats are related to carnivores, artiodactyls and perrisodactyls, not archontans. Afrotheria is a weird mix instead of being ‘ungulates’ and ‘insectivores’. Tinamous are oddly flighted ratites, not basal to them. The list goes on. Some of your reassignments may be right, but all the lack of abberant taxa says to me is that your tree is prone to group ecologically similar taxa together.

  2. Actually it groups morphologically similar taxa, all of which are also ecologically similar. DNA not so great as fossils for determining sisters among extinct taxa. DNA studies also contradict each other.

    • First, you can’t just use “DNA studies also contradict each other” as a talking point to imply molecular phylogenies are doubtful. They can contradict each other, but not when performed well and not for well supported clades. You’ve probably noticed that in the past decade, there have been no big debates among molecular workers about intraordinal relationships among mammals for instance, in areas where the phylogenies are well supported. There are certainly poorly supported areas, like whether xenarthrans are basal to other placentals, related to afrotheres, etc., but the examples I listed aren’t among them.

      Another problem is that DNA is not just a single dataset that can be compared to a single dataset called morphology. Various genes from both nuclear and mitochondrial DNA support bats as laurasiatheres, for instance. So your position would have to explain why all of these give the same wrong result. Indeed, Nishihara et al. (2006) found sixteen(!) retroposons that were shared between bats and other laurasiatheres. As they state-

      “To date, no mechanism has been described for the reversal of retroposon integration, and it is highly unlikely that the same type of retroposon would integrate into the same genomic locus independently in different lineages. Because of these characteristics, retroposons are quite useful as nearly homoplasy-free phylogenetic markers”

      So these basically prove bats are laurasiatheres and that any morphological analysis suggesting otherwise is wrong, as we know plenty of ways anatomy can converge and reverse.

      • My morphological work nests bats and lemurs with carnivores, and Wiki puts carnivores in Laurasiatheres. So it seems we agree. To your point, my tree uses specimens in the lineage of civets, not supra-suprageneric taxa that includes everything from shrews to whales. So, let’s get specific and roll up our sleeves.

      • Carnivores are laurasiatheres, but lemurs are not. Bats are closest not only to carnivores, but also to perissodactyls. Keep in mind that with retroposons, you can’t claim extinct basal taxa are needed, since retroposons don’t exhibit much homoplasy. Thus if a horse and a bat share a particular retroposon, a basal perissodacyl like Hyracotherium would as well, since it’s so unlikely Hyracotherium would lose it or that Equus would develop it in parallel to the bat. DNA studies like Nishihara et al. also use species instead of suprageneric taxa, of course. The retroposon study used Pipistrellus abramus, Cynopterus brachyotis and Pteropus dasymallus for their bat exemplars, for instance (supplementary table 7). Thus figure 2 of Nishihara et al. is a specific topology, using the species listed in their supplementary table 7.

    • The only decent species and fossil based analysis of Mammalia is Zack’s (2009) thesis. This found bats to be closest to flying lemurs, then to Tupaia. So it’s wrong.

      When constrained to be laurasiatheres in that analysis, bats are sister to eulipotyphlans, with that whole group sister to Viverravus. Which might be similar to your topology, but is still wrong since retroposons show the laurasiathere topology to be-




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