Guest Post - Roland Sookias Discusses His New Study Examining How Dinosaurs Came to Fill Most Ecological Niches During the Mesozoic

Why were dinosaurs, and other archosauromorphs (the group of animals including crocodiles, dinosaurs, pterosaurs and several other extinct groups), so big? Was natural selection for increasing size responsible for archosauromorphs’ dramatic rise to larger sizes and did selection for decreasing size drive therapsids’ (‘mammal-like reptiles’, which were the dominant land vertebrates before archosauromorphs) reduction in size during the Triassic (see picture)? These are the questions which my, Richard Butler’s and Roger Benson’s recent publication in Proceedings of the Royal Society B – “Rise of dinosaurs reveals major body size transitions are driven by passive processes of trait evolution” – attempts to answer.
Most of the work in the paper was done as part of my MSc thesis project, which Richard, Roger and Andrew Smith supervised. To carry out the project I spent a good deal of last summer collecting femur and skull length measurements (which we used as proxies for body mass) in the Natural History Museum Library, London. Though barely seeing daylight for a month or two, I managed to collect measurements for ~200 species, which, in combination with data from Benson et al. 2011 got us to >400 species in total. To answer the questions above we focused on getting data for archosauromorphs and therapsids from the Late Permian to Middle Jurassic. This allowed comparison between the two groups, and the interval brackets the rise of archosauromorphs to become the dominant terrestrial vertebrates, replacing therapsids. Thus it allowed us to look at body size evolutionary dynamics during a major faunal transition.

Archosauromorphs (dinosaurs, crocodiles, pterosaurs and their relatives) increased greatly in maximum size (black line, black triangles) from the Permian to Jurassic, and therapsids (‘mammal-like reptiles’) decreased. However in both this was due to expansion in the size variance (i.e. both size increase and decrease), but with subsequent extinction of larger therapsid species. Figure from Sookias et al. 2012, Proc Roy Soc B.

Once we’d got the data together we analysed them using maximum likelihood model fitting approaches. We tried both phylogenetic – i.e. incorporating evolutionary relationships – and time series (ignoring within-group evolutionary relationships and simply averaging size within time ‘bins’) models. Time series models confirmed that on average archosauromorphs tended to increase across the time interval, and that therapsids got smaller. However when we included phylogeny (evolutionary relationships) we found that there was no directional trend in either group along individual lineages. Thus the apparent trends through time were in fact due to ‘passive expansion’ in size, but as the original size was nearer the bottom than the top of the eventual size range the average size tended to increase (see picture). We thus can say that the long-repeated idea of “Cope’s rule” – that taxa in a clade tend to get larger over time due to within-lineage natural selection for larger body sizes – is not found in either archosauromorphs or therapsids during this time interval.

Our work excludes larger size in archosauromorphs as an explanation for their success, as if larger size was especially beneficial one would expect a directional evolutionary trend towards larger sizes. Instead, archosauromorphs probably replaced therapsids opportunistically, as many have hypothesized before. However, the exceptionally high growth, and thus reproductive, rates of archosauromorphs may have allowed them to re-fill empty ecological niches especially easily and rapidly after they went empty due to extinction of therapsids. Thus, while size and growth rate probably did not allow archosauromorphs to outcompete therapsids, it did allow them to fill up free niches quickly.

We also found that archosauromorph predators exceeded the size of the largest herbivores – anomodont therapsids – during the Middle-early Late Triassic. This finding – that the largest carnivores are larger than herbivores - is extremely rare in ecosystems throughout time. It demonstrates that extinct archosauromorphs really were exceptionally large, and that they were able to grow to larger sizes than therapsids given the same resources.

Well, there’s not much more to say about that paper except hope you enjoy it! However, we should be publishing some more work based on my MSc thesis in the near future, so stay tuned, and I’ve just started a PhD with Richard Butler on the early archosauromorph radiation, so hopefully I’ll be involved in answering a few more interesting questions in the coming years. Finally, a very big thank you to Bill Parker for giving us a guest slot here on the esteemed Chinleana.

The paper’s full citation is:


Sookias, R. B., Butler, R. J., Benson, R. B. J. (2012). Rise of dinosaurs reveals major body size transitions are driven by passive processes of trait evolution. Proceedings of the Royal Society B.
doi: 10.1098/rspb.2011.2441 



Abstract- A major macroevolutionary question concerns how long-term patterns of body-size evolution are underpinned by smaller scale processes along lineages. One outstanding long-term transition is the replacement of basal therapsids (stem-group mammals) by archosauromorphs, including dinosaurs, as the dominant large-bodied terrestrial fauna during the Triassic (approx. 252–201 million years ago). This landmark event preceded more than 150 million years of archosauromorph dominance. We analyse a new body-size dataset of more than 400 therapsid and archosauromorph species spanning the Late Permian–Middle Jurassic. Maximum-likelihood analyses indicate that Cope’s rule (an active within-lineage trend of body-size increase) is extremely rare, despite conspicuous patterns of body-size turnover, and contrary to proposals that Cope’s rule is central to vertebrate evolution. Instead, passive processes predominate in taxonomically and ecomorphologically more inclusive clades, with stasis common in less inclusive clades. Body-size limits are clade-dependent, suggesting intrinsic, biological factors are more important than the external environment. This clade-dependence is exemplified by maximum size of Middle–early Late Triassic archosauromorph predators exceeding that of contemporary herbivores, breaking a widely accepted ‘rule’ that herbivore maximum size greatly exceeds carnivore maximum size. Archosauromorph and dinosaur dominance occurred via opportunistic replacement of therapsids following extinction, but were facilitated by higher archosauromorph growth rates.



Popular press coverage:

http://news.discovery.com/animals/how-dinosaurs-got-so-big-120131.html

http://news.sciencemag.org/sciencenow/2012/01/the-secret-of-dinos-success.html?ref=hp

Largocephalosaurus, a New Eosauropterygian from the Middle Triassic of China

Cheng, L., Chen, X., Zeng, X., and Y. Cai. 2012. A new eosauropterygian (Diapsida: Sauropterygia) from the Middle Triassic of Luoping, Yunnan Province. Journal of Earth Science 23:33-40. DOI: 10.1007/s12583-012-0231-z

Abstract - A new eosauropterygian, Largocephalosaurus polycarpon gen. et sp. nov., was described based on a skeleton from the Middle Triassic of Luoping, Yunnan Province, southwestern China. The new taxon is characterized by a big skull, paired frontal, laterally expanded upper temporal fossa, anterior process of squamosal entering orbit, robust teeth with basally expanded crown and blunt tip, short cervical region, distinctly elongated transverse process of the dorsal vertebrae, short and broad dorsal ribs, stout gastralia, scapula with distinctly posterodorsally extending blade, distinctly robust humerus, eleven carpal ossifications, and a manual fomula of 2-3-4-5-5. A phylogenetic analysis suggests that Largocephalosaurus is the basal-most member of a clade including Wumengosaurus, European pachypleurosaurs, and Nothosauroidea.

Tikiguania Is Not From the Triassic

Hutchinson, M. H., Skinner, A., and M. S. Y. Lee. 2012. Tikiguania and the antiquity of squamate reptiles (lizards and snakes). Biology Online published before print. doi: 10.1098/rsbl.2011.1216

Abstract - Tikiguania estesi is widely accepted to be the earliest member of Squamata, the reptile group that includes lizards and snakes. It is based on a lower jaw from the Late Triassic of India, described as a primitive lizard related to agamids and chamaeleons. However, Tikiguania is almost indistinguishable from living agamids; a combined phylogenetic analysis of morphological and molecular data places it with draconines, a prominent component of the modern Asian herpetofauna. It is unlikely that living agamids have retained the Tikiguania morphotype unchanged for over 216 Myr; it is much more conceivable that Tikiguania is a Quaternary or Late Tertiary agamid that was preserved in sediments derived from the Triassic beds that have a broad superficial exposure. This removes the only fossil evidence for lizards in the Triassic. Studies that have employed Tikiguana for evolutionary, biogeographical and molecular dating inferences need to be reassessed.                 

New Postcranial material of Proterochampsa barrionuevoi from the Upper Triassic of Argentina

Trotteyn, M. J. 2011. Material postcraneano de Proterochampsa barrionuevoi Reig, 1959 (Diapsida: Archosauriformes) del Triásico Superior del centro-oeste de Argentina. Ameghiniana 48:424-446. 

 

Resumen - Los proterochámpsidos son miembros del clado Archosauriformes y se distinguen del resto por presentar cráneo predominantemente deprimido, transversalmente expandido en el extremo posterior, hocico angosto y alargado longitudinalmente, y narinas ubicadas sobre la línea media, ausencia de postfrontal y presencia de pie asimétrico. La familia Proterochampsidae se compone de cinco géneros presentes en las formaciones triásicas de Argentina y Brasil. En esta familia se incluye la especie argentina Proterochampsa barrionuevoi Reig, proveniente de la Formación Ischigualasto (Triásico Superior). Este taxón era conocido por el cráneo y algunas vértebras cervicales, pero el resto del material poscraneano era totalmente desconocido hasta el presente. En esta contribución se describe detalladamente un ejemplar de Proterochampsa barrionuevoi (PVSJ 606), incluyendo el cráneo, toda la serie vertebral, escápulas, coracoides, cintura pélvica, húmero derecho, radio y ulna del mismo lado, ambos fémures y miembro posterior derecho casi completo. Asimismo se presenta una diagnosis enmendada para la especie, constando de los siguientes caracteres neurocraneales diagnósticos: depresión semilunar expuesta ventrolateralmente, fosa basiesfenoidea rodeada rostrolateralmente por un reborde con forma de “V” con sus ramas convexas. Entre los caracteres que diferencian a P. barrionuevoi de la especie brasilera P. nodosa se citan: angostamiento anterior del hocico menos gradual que el de P. nodosa, occiput más deprimido, narinas lanceoladas con ambos extremos aguzados y frontal menos irregular que el de P. nodosa.

POSTCRANIAL MATERIAL OF PROTEROCHAMPSA BARRIONUEVOI REIG, 1959 (DIAPSIDA: ARCHOSAURIFORMES) FROM THE UPPER TRIASSIC OF CENTRAL-WESTERN ARGENTINA.

Abstract - Proterochampsids are members of the clade Archosauriformes, a group distinguished from others because of its depressed skulls transversely expanded at the posterior end, narrow and longitudinally long snout, nares located close to the midline, absence of postfrontals, and presence of an assymmetric pes. The family Proterochampsidae includes five genera recorded in Triassic formations of Argentina and Brazil. In this family is included the Argentinean species Proterochampsa barrionuevoi Reig, from the Late Triassic Ischigualasto Formation. This taxon was known from skulls and cervical vertebrae, but the rest of the postcranium remained unknown until now. Herein, a new and almost complete specimen of Proterochampsa barrionuevoi is described in detail (PVSJ 606). The specimen includes skull, complete vertebral series, scapulae, coracoids, pelvic girdle, right humerus, right radius and ulna, both femora, and complete right hindlimb. An emended diagnosis considering neurocranial features –semilunar depression ventrolaterally exposed, basisphenoidal fossa surround by a rostrolateraly V-shaped ridge with convex branches– is provided. The features distinguishing P. barrionuevoi from the Brazilian species P. nodosa are: snout becoming narrow anteriorly in a less gradual manner than in P. nodosa, lower occiput, nares lanceolate with narrow anterior and posterior ends, and frontal less irregular that in P. nodosa.

Oldest Known Dinosaurian Nesting Site

Here is the abstract and link to the article discussed in the linked news report from yesterday.

Reisz, R. R., Evans, D. C., Roberts, E. M., Sues, H.-D., and A. M. Yates. 2012. Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus. PNAS online before print. DOI 10.1073/pnas.1109385109

Abstract - The extensive Early Jurassic continental strata of southern Africa have yielded an exceptional record of dinosaurs that includes scores of partial to complete skeletons of the sauropodomorph Massospondylus, ranging from embryos to large adults. In 1976 an incomplete egg clutch including in ovo embryos of this dinosaur, the oldest known example in the fossil record, was collected from a road-cut talus, but its exact provenance was uncertain. An excavation program at the site started in 2006 has yielded multiple in situ egg clutches, documenting the oldest known dinosaurian nesting site, predating other similar sites by more than 100 million years. The presence of numerous clutches of eggs, some of which contain embryonic remains, in at least four distinct horizons within a small area, provides the earliest known evidence of complex reproductive behavior including site fidelity and colonial nesting in a terrestrial vertebrate. Thus, fossil and sedimentological evidence from this nesting site provides empirical data on reproductive strategies in early dinosaurs. A temporally calibrated optimization of dinosaurian reproductive biology not only demonstrates the primary significance of the Massospondylus nesting site, but also provides additional insights into the initial stages of the evolutionary history of dinosaurs, including evidence that deposition of eggs in a tightly organized single layer in a nest evolved independently from brooding.

Massospondylus Nesting Site from the Early Jurassic of South Africa

http://www.cbc.ca/news/technology/story/2012/01/23/sci-dinosaur-nesting-site.html

Aetobarbakinoides brasiliensis, a New Aetosaur from the Late Triassic of Brazil

This is an interesting new specimen from the Santa Maria Formation of Brazil. I've had the chance to personally study this material and although poorly preserved and despite possesses a radial patterning of the dorsal osteoderms it clearly does not belong to the South American genera Aetosauroides or Neoaetosauroides mainly because of characteristics of the vertebrae. In fact, the vertebrae with their well developed accessory processes and lack of ventral keels strongly resemble those of desmatosuchines. This is supported by the phylogenetic analysis.

Notably this is the first aetosaur taxon to be diagnosed using postcranial characters rather than those of the osteoderms. Indeed only a few poorly preserved osteoderms are present in the specimen. I've argued in the past that despite the long use of armor ornamentation to diagnose aetosaur species, new specimens are demonstrating that these characters are highly convergent between hypothesized main aetosaur clades and caution must be used.

This paper also finds Aetosaurinae (sensu Parker, 2007) to be paraphyletic. Again this is not surprising given the poor support for the clade in the original analysis, the fact that Aetobarbakinoides possesses "Aetosaurinae"-like armor with desmatosuchine-like vertebrae, and the fact that lateral armor is lacking in this new taxon whereas lateral armor characters strongly affect the topology of Parker (2007). This is not surprising given that the analysis of Parker (2007) was explicitly testing the phylogenetic signal of lateral osteoderms in aetosaurs.

This analysis also recovers Aetosauroides outside of Stagonolepididiae (sensu Heckert and Lucas, 2000), which demonstrates the presence of non-stagonolepidid aetosaurs. Thus the names Stagonolepididae and Aetosauria cannot be used interchangeably (as they commonly are) as I cautioned in 2007.

There is much more work today with the phylogeny of the Aetosauria and many new undescribed specimens.  I am focusing on a lot of these in my ongoing PhD work.

Desojo, J. B., Ezcurra, M. D., and E. E. Kischlat. 2012. A new aetosaur genus (Archosauria: Pseudosuchia) from the early Late Triassic of southern Brazil. Zootaxa 3166:1-33.

Abstract - We describe the new aetosaur Aetobarbakinoides brasiliensis gen. et sp. nov. from the early Late Triassic (late Carnian early Norian) Brazilian Santa Maria Formation. The holotype is composed of a partial postcranium including several cervical and dorsal vertebrae and ribs, one anterior caudal vertebra, right scapula, right humerus, right tibia, partial right pes, and anterior and mid-dorsal paramedian osteoderms. Aetobarbakinoides is differentiated from other aetosaurs by the presence of cervical vertebrae with widely laterally extended prezygapophyses, mid-cervical vertebrae with anterior articular facet width more than 1.2 times wider than the posterior one, anterior caudal vertebrae with extremely anteroposteriorly short prezygapophyses, elongated humerus and tibia in relation to the axial skeleton, and paramedian osteoderms with a weakly raised anterior bar. A cladistic analysis recovered the new species as more derived than the South American genera Aetosauroides (late Carnian-early Norian) and Neoaetosauroides (late Norian-Rhaetian), and it is nested as the sister-taxon of an unnamed clade, composed of Typothoracisinae and Desmatosuchinae, due to the absence of a ventral keel in the cervical vertebrae. Aetobarbakinoides presents a skeletal anatomy previously unknown among South American aetosaurs, with the combination of presacral vertebrae with hyposphene, anteroposteriorly short and unkeeled cervical vertebrae, gracile limbs, and paramedian osteoderms with a weakly raised anterior bar. Aetobarbakinoides is among the oldest known aetosaurs together with Aetosauroides from Argentina and Brazil and Stagonolepis robertsoni from Scotland, indicating Aetobarbakinoides, which is one of the oldest known aetosaurs, is in agreement with an older origin for the group, as it is expected by the extensive ghost lineages at the base of the main pseudosuchian clades.

Evolution of Bipedality and Herbivory Among Triassic Dinosauromorphs

Note that this paper is in Japanese with an English version of the abstract.

Kubo, T. 2011. Evolution of bipedality and herbivory among Triassic dinosauromorphs. Memoir of the Fukui Prefectural Dinosaur Museum 10:55－62．

Abstract - Discoveries of Triassic non-dinosaur dinosauromorphs since 2000 revealed that they were more widely spread chronologically and geographically than previously thought. A member of silesaurids, the sister clade of dinosaurs, Silesaurus was a quadrupedal and herbivorous animal that differs considerably from the condition previously assumed for the ancestor of dinosaurs that are bipedal and carnivorous. Currently, stance and diet of the common ancestor of dinosaurs are not clear. To redeem this situation, Ancestral State Reconstruction methods were conducted to infer how quadrupedality and herbivory were evolved among dinosauromorphs. The results of analyses indicate that quadrupedal stance evolved only among silesaurids. Herbivorous diet was readily evolved from carnivorous diet among Dinosauromorpha and the ancestral state reconstruction using likelihood methods indicated that the possibility of the common ancestor of dinosaurs being herbivore is more than 60%.

Two New Triassic Temnospondyl Papers in the Journal Palaeontology

Witzmann, F., Schoch, R. R., Hilger, A., and N. Kardjilov. 2012. Braincase, palatoquadrate and ear region of the plagiosaurid Gerrothorax pulcherrimus from the Middle Triassic of Germany. Palaeontology 55:31-50. DOI: 10.1111/j.1475-4983.2011.01116.x

Abstract - The complete neurocranium plus palatoquadrate of the plagiosaurid temnospondyl Gerrothorax pulcherrimus from the Middle Triassic of Germany is described for the first time, based on outer morphological observations and micro-CT scanning. The exoccipitals are strong elements with paroccipital processes and well-separated occipital condyles. Anterolaterally, the exoccipitals contact the otics, which are mediolaterally elongated and have massive lateral walls. The otics contact the basisphenoid, which shows well-developed sellar processes. Anteriorly, the basisphenoid is continuous with the sphenethmoid region. In its posterior portion, the sphenethmoid gives rise to robust, laterally directed laterosphenoid walls, a unique morphology among basal tetrapods. The palatoquadrate is extensively ossified. The quadrate portion overlaps the descending lamina of squamosal and ascending lamina of pterygoid anteriorly, almost contacting the epipterygoid laterally. The epipterygoid is a complex element and may be co-ossified with otics and laterosphenoid walls. It has a broad, sheet-like footplate and a horizontally aligned ascending process that contacts the laterosphenoid walls. The degree of ossification of the epipterygoid, however, is subject to individual variation obviously independent from ontogenetic changes. The stapes of Gerrothorax is a large, blade-like element that differs conspicuously from the plesiomorphic temnospondyl condition. It has a prominent anterolateral projection which has not been observed in other basal tetrapods. Morphology of neurocranium and palatoquadratum of Gerrothorax most closely resembles that of the Russian plagiosaurid Plagiosternum danilovi, although the elements are less ossified in the latter. The extensive endocranial ossification of Gerrothorax is consistent with the general high degree of ossification in the exo- and endoskeleton of this temnospondyl and supports the view that a strong endocranial ossification cannot be evaluated as a plesiomorphic character in basal tetrapods.

Dias-da-Silva, S., Sengupta, D. P., Cabriera, S. F., and L. R. Da Silva. 2012. The presence of Compsocerops (Brachyopoidea: Chigutisauridae) (Late Triassic) in southern Brazil with comments on chigutisaurid palaeobiogeography. Palaeontology 55:163-172. DOI: 10.1111/j.1475-4983.2011.01120.x

Abstract - Chigutisauridae is the longest-lived trematosaurian clade (from early Triassic to early Cretaceous). They were reported in Argentina, Australia, India and South Africa. This contribution reports a putative chigutisaurid specimen in the Carnian of southern Brazil (Santa Maria Formation, Paraná Basin). The material comprises two skull fragments, a mandibular fragment, a clavicular blade and a humerus. Ontogenetic features point to an early development stage of the specimen. The presence of a long, straight and pointed tabular horn, which runs parallel to the skull midline towards its tip, and a distinctive projection in the posterior border of the postparietal indicates a close relationship of the Brazilian chigutisaurid with the Indian Compsocerops cosgriffi. Three distinctive and combined characters suggest that the Brazilian chigutisaurid is a distinctive specimen: the presence of an alar process of the jugal in the ventral margin of the orbit; jugal does not extend well beyond the anterior margin of the orbit; and tabular does not contact the parietal. These characters could justify the erection of a new taxon; however, they might reflect its immature ontogenetic stage as well. Accordingly, we attribute this new specimen to Compsocerops sp. Argentinean and Indian occurrences are dated as Norian, so the presence of a Carnian chigutisaurid in southern Brazil indicates that western Gondwana chigutisaurids have first occupied the Paraná Basin and later migrated towards west (to Argentina) and east (India). However, the presence of ghost chigutisaurid taxa cannot be dismissed, because their long temporal range contrasts with their still short (in comparison with other temnospondyl groups) geographic distribution. Hence, they might have been more geographically widespread than their fossil record suggests.

Revisiting the Cranial Anatomy of the Thalattosaur Anshunsaurus huangnihensis

Cheng, L., Chen, X., Zhang, B., and Y. Cai. 2011. New Study of Anshunsaurus huangnihensis Cheng, 2007 (Reptilia: Thalattosauria): Revealing its Transitional Position in Askeptosauridae. Acta Geologica Sinica (English Edition) 85: 1231–1237. doi: 10.1111/j.1755-6724.2011.00584.x

Abstract - The skull of Anshunsaurus huangnihensis Cheng, 2007, especially the skull roof, is described in detail in this paper. Compared to other genera and species of Askeptosauroidea, Anshunsaurus huangnihensis has some important transitional characters from Askeptosaurus italicus to Anshunsaurus huangguoshuensis: the rostral length related to the skull length between Askeptosaurus italicus and Anshunsaurus huangguoshuensis; the postfrontal existing but distinctly reduced; the posterolateral process relatedly short and overlapping the parietal. The phylogenetic analysis weakly supports the evolutional progress from Anshunsaurus huangnihensis to Anshunsaurus huangguoshuensis. The skeletal ratios indicated that the node among the Askeptosauridae ingroup. The evolutional direction of Askeptosauridae should be from Askeptosaurus italicus to Anshunsaurus huangguoshuensis. The skeletal ratios indicated that the evolutional progress is Askeptosaurus italicus -- Anshunsaurus huangnihensis -- Anshunsaurus huangguoshuensis. In biogeography provinces, the Askeptosauroidea taxa from south China have a close relationship with those from western Tethys; however, Xinpusaurus from the Late Triassic is more related to those from the eastern Pacific.

Happy Holidays!

HAPPY HOLIDAYS FROM CHINLEANA!

New Open Access Paper Publishing Field Notes from the 1932 Excavations at Trossingen, Germany

Schoch, R. R. 2011. Tracing Seemann’s dinosaur excavation in the Upper Triassic of Trossingen: his field notes and the present status of the material. Palaeodiversity 4: 245–282.

Abstract - The field notes of Reinhold Seemann, who conducted the 1932 dinosaur excavation at Trossingen, are published for the first time. An English translation of the whole text is also provided. Quarry maps and stratigraphic sections were redrawn and compared with new data gathered in ongoing excavations. Of the 65 finds listed by Seemann, only 21 have survived the Second World War (Plateosaurus: 18, Proganochelys: 3). This includes most of the well-preserved skeletons, which had been moved to safe places during the war. An overview of these finds and their present state is given for the first time. This reveals major differences in preservation of bones, and it adds to the knowledge of bone completeness classes at Trossingen. The missing finds were probably destroyed by fire in 1944, and there are no remains from these specimens left. In combination with the field notes and sketches, the new data on Seemann’s material may serve as a platform for future studies of and excavations at the Trossingen lagerstaette.

There Goes "Dicynodon" Biostratigraphy!

In the latest Journal of Vertebrate Paleontology Memoir Christian Kammerer, Kenneth Angielczyk, and Jörg Fröbisch (an allstar team of synapsid workers) readily handle the taxonomic mess more commonly known as Dicynodon. They find that the taxon is polyphyletic, is restricted to two species, and reassign all of the other material to a variety of old and new genera. Moreover, I think that their abstract sets a record for the number of included taxonomic names. 

Hey guys, want to tackle "Rutiodon" next?

Kammerer, C. F., Angielczyk, K. D., and J. Fröbisch. 2011. A comprehensive taxonomic revision of Dicynodon (Therapsida, Anomodontia) and its implications for dicynodont phylogeny, biogeography, and biostratigraphy. Journal of Vertebrate Paleontology 31, Supplement 1: 1-158 DOI:10.1080/02724634.2011.627074

Abstract - The dicynodont wastebasket genus Dicynodon is revised following a comprehensive review of nominal species. Most nominal species of Dicynodon pertain to other well-known dicynodont genera, especially Oudenodon and Diictodon. Of the Karoo Permian species that are referable to "Dicynodon" sensu lato, we recognize four common, valid morphospecies: Dicynodon lacerticeps, D. leoniceps, D. woodwardi, and Dinanomodon gilli, comb. nov. Eleven additional species of "Dicynodon" are recognized worldwide: D. alticeps, D. amalitzkii, D. bathyrhynchus, D. benjamini, D. bogdaensis, D. huenei, D. limbus, D. sinkianensis, D. traquairi, D. trautscholdi, and D. vanhoepeni. Morphometric analysis of D. lacerticeps and D. leoniceps specimens recovers statistically significant separation between these species in snout profile and squamosal shape, supporting their distinction. A new phylogenetic analysis of Anomodontia reveals that "Dicynodon" is polyphyletic, necessitating taxonomic revision at the generic level. D. benjamini and D. limbus are basal cryptodonts, whereas the other valid "Dicynodon" species are basal dicynodontoids. The genus Dicynodon is restricted to D. lacerticeps and D. huenei. We reinstate use of Daptocephalus, Sintocephalus, Turfanodon, Daqingshanodon, Jimusaria, and Gordonia for other species. We synonymize Vivaxosaurus permirus and Dicynodon trautscholdi (as V. trautscholdi, comb. nov.) We establish new generic names for several species formerly included in Dicynodon: Peramodon amalitzkii, comb. nov., Keyseria benjamini, comb. nov., Euptychognathus bathyrhynchus, comb. nov., Syops vanhoepeni, comb. nov., and Basilodon woodwardi, comb. nov. Of the main Karoo Permian taxa, Dicynodon, Basilodon, and Dinanomodon range throughout the Cistecephalus and Dicynodon assemblage zones, but Daptocephalus is restricted to the Dicynodon Assemblage Zone.

Hitchcock's Birds

Brian Switek has a wonderful post on the dinosaur trackways of New England over at the Dinosaur Tracking Blog.  I grew up in Connecticut and as a boy enjoyed going to Dinosaur State Park to see the trackways.  My first foray into the Triassic.