Anchiornis or not? And what about Pedopenna?

Xu et al. 2009
described a new genus, Anchiornis huxleyi IVPP V14378 (the holotype), along with LPM-B00169A, BMNHC PH828 as referred specimens), from the Late Jurassic of China. Two of these (Fig. 1) were added to the large reptile tree (LRT, 1315 taxa, subset Fig. 2). They nest in the LRT in the clade traditionally considered Troodontidae, between Velociraptor and Archaeopteryx. (Note other traditional troodontids, like Sinornithoides and Sauronithoides, do not nest in this pre-bird clade, but within the Haplocheirus clade.

Last year
a paper by Pei et al. 2017 described “new specimens of Anchiornis huxleyi“. Two of these (Fig. 1) were also added to the LRT (subset in Fig. 2).

Figure 1. Four specimens attributed to Anchiornis along with two others related to Anchiornis, but given different names. Two of these Anchiornis specimen nest apart from two others (see figure 2).

In the LRT
only two of the four tested Anchiornis specimens nested together (one was the holotype). That means the two other specimens were originally mislabeled. Moreover, a specimen attributed to a separate genus, Jinfengopteryx, nests with the holotype of Anchiornis and a referred specimen.

So do a few of the referred specimens need to be renamed? Perhaps so. Beyond the distinctly different skulls (Fig. 1), various aspects of the post-crania are also divergent.

Figure 2. Cladogram of taxa surrounding four specimens attributed to Anchiornis, which do not nest together in the LRT. The holotype is the IVPP specimen in a darker tone and white arrowhead.

Pedopenna daohugouensis
(Xu and Zhang 2005; IVPP V 12721, Fig. 3) is a fossil theropod foot with long stiff feathers from the Middle or Late Jurassic, 164mya.

According to Wikipedeia
“Pedopenna was originally classified as a paravian, the group of maniraptoran dinosaurs that includes both deinonychosaurs and avialans (the lineage including modern birds), but some scientists have classified it as a true avialan more closely related to modern birds than to deinonychosaurs.”

Figure 3. Pedopenna in situ. The large alphanumerics are original. The color is added here. Very little is known of this specimen, but clearly long feathers arise from the metatarsus.

The first step
in figuring out what Pedopenna is, is to create a clear reconstruction (Fig. 4). Only then will we be able to score the pedal elements in the LRT.

Figure 4. Pedopenna in situ and reconstructed using DGS techniques.

Surprisingly,
and despite the relatively few pedal traits, the LRT is able to nest Pedopenna between and among the several Anchiornis specimens (Fig. 5). Specifically it nests between the holotype IVPP specimen and the LPM specimen. So is Pedopenna really Anchiornis? Or do all these taxa, other than the holotype, need their own generic names?

Figure 5. Where feathers on the foot are preserved on the LRT.

Earlier we looked at the development of foot feathers to aid in stability in pre-birds and other bird-like taxa just learning to flap and fly, convergent with uropatagia in pre-volant pterosaur ancestors.

A note to Anchiornis workers:
Try to test all your specimens in a phylogenetic analysis for confirmation, refutation or modification of the above recovery. Pei et al. considered all the specimens conspecific. They are not conspecific, as one look at their skulls alone (Fig. 1) will tell the casual observer.

References
Pei R, Li Q-G, Meng Q-J, Norell MA and Gao K-Q 2017. New specimens of Anchiornis huxleyi (Theropoda: Paraves) from the Late Jurassic of Northeastern China. Bulletin of the American Museum of Natural History 411:66pp.
Xu X, Zhao Q, Norell M, Sullivan C, Hone D, Erickson G, Wang X, Han F and Guo Y 2009. A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin. Chinese Science Bulletin 54 (3): 430–435. doi:10.1007/s11434-009-0009-6
Xu X and Zhang F 2005. A new maniraptoran dinosaur from China with long feathers on the metatarsus. Naturwissenschaften. 92 (4): 173–177. doi:10.1007/s00114-004-0604-y.

wiki/Pedopenna

 

SVP 2018: new Whatcheeria data from nearly 100 specimens

Last one for this year.
This post finishes up an inundation of about 40 2018 SVP abstract reviews. We’ll get back to a regular one-a-day look at paleo news later today.

Otoo, Bolt and Lombard 2018
bring us new information on Whatcheeria (Fig. 1), a basal tetrapod (Fig. 2) now known from nearly 100 specimens. In the large reptile tree (subset Fig. 2, LRT) the Whatcheeria clade nests between the primitive Ossinodus clade and the Ichthyostega clade plus all higher tetrapods. The authors report, “Whatcheeria is key for establishing character polarities on the tetrapod stem, particularly in the context of recent controversies about age of the tetrapod crown group and the timing and pattern of the lissamphibian/amniote split.” In the LRT Tulerpeton and Eucritta have taken over that role.

Figure 1. Pederpes is a basal taxon in the Whatcheeria + Crassigyrinus clade.

After a short description
of key Whatcheeria traits, and without describing a phylogenetic analysis, Otoo, Lombard and Bolt conclude: “This combination of features in the femur emphasizes the moasic of characters present in Whatcheeria, and, in conjunction with recent Tournaisian discoveries, emphasizes the complexity of post-Devonian tetrapod evolution.”

A subset of the LRT
(Fig. 2) portrays post-Devonian tetrapod evolution rather differently and rather simply

Figure 2. Subset of the LRT focusing on basal tetrapods, colorized according to chronology. Note the wide dispersal of Early Carboniferous taxa, suggesting a Late Devonian radiation as yet largely undiscovered.

References
Otoo BK, Bolt JR, Lombard E 2018. A leg up: Whatcheeria and its new contributions to tetrapod anatomy. SVP abstracts.

SVP 2018: Paleocene mammal phylogeny

Williamson et al. 2018
note that Mesozoic and Eocene mammals have been the subjects of phylogenetic and macroevolutionary studies, but Paleocene mammals have been “mostly ignored”.

The authors are “building a comprehensive higher-level phylogeny consisting of anatomical and genetic data for a large number of mammalian taxa (including extinct and extant forms).” Suggestion: drop the genetic data, it produces false positives.

An “unprecedented number of Paleocene taxa” will be employed. Will we see reconstructions side-by-side for comparisons? That’s what ReptileEvolution.com has done for seven years.

Their “comprehensive phylogeny builds upon previous large datasets”, which can be an excuse not to check the prior data, but simply use it, as is. Better to create reconstructions, run the data yourself, correct errors, etc.

The authors are going to score using 2000 characters.
Presumably (based on the stated early mammal status of the taxa), many of those will be dental only traits, which, like DNA tend to revert (e.g. odontocetes have peg-like molars) and converge, leading to more false positives.

Their preliminary results indicate
“many Paleocene taxa are stem members of major extant clades (e.g., Primates, Afrotheria, Laurasiatheria, Carnivoramorpha, Euungulata).”

Stop right there.
Afrotheria and Laurasiatheria are invalid genetic clades according to the large reptile tree (LRT, 1315 taxa ordered by skeletal traits). Drop the DNA data and just look at the traits. And, more importantly, what is the proximal outgroup? Is Caluromys? It is not O.K. to list suprageneric taxa. The LRT does everything with species.

The authors conclude:
“Our analyses show that many major mammalian clades probably
originated very early in the Paleogene.” The LRT finds that prior to the invention of large browsing herbivores (like Onychodectes), all mammal clades were Triassic and Jurassic in origin.

Or did they mean, ‘all placental clades’?
Even then, derived placentals (multituberculates) appear in the Middle Jurassic (Fig. 1). So do basal pangolins, like Zhangheotherium. The LRT currently includes at least eight Mesozoic metatherians and ten Eutherians.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

One more 2018 SVP abstract to go.
Then we’ll be back to current daily issues in vert paleo.

References
Williamson TE et al. (5 co-authors) 2018. The beginning of the age of mammals: new insights on the rise of Placentalia based on a preliminary comprehensive phylogeny. SVP Abstracts.

SVP 2018: Ancestral dinosaur integument

Holtz 2018 tackles the question:
What sort of dermal covering did basal dinosaurs, like Herrerasaurus have? Naked skin (Fig. 1)? Scales? Dorsal osteoderms? Pre-feather filaments? Or combinations thereof?

We looked at this question
earlier. In the poultry section of grocery stores chickens are nude and have no scales.

Holtz concludes,
“In some of these analyses, the more likely ancestral status for Dinosauria or Ornithoscelida was recovered as filamentous. However, the fact that the basal relationships are indeed poorly resolved at present requires an acceptance of ambiguity for the integumentary condition of the original dinosaur.”

Figure 1. Primordial feathers on the back of a 10-day-old chick embryo. Ontogeny sometimes recapitulates phylogeny. Perhaps this embryo provides just such a clue.

In the non-ambiguous
large reptile tree (LRT,  1315 taxa) the ancestral state (based on phylogenetic bracketing) is nudity with filaments and dorsal osteoderms transformed into subcutaneous spine tables that disappear shortly thereafter. Given that Holtz did not recover a clade Phytodinosauria, he is not likely to have included basal bipedal crocs as proximal outgroups, as recovered in the LRT.

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

References
Holtz TR 2018. Integumentary status: It’s complicated: phylogenetic sedimentary, and biological impediments to resolving the ancestral integument of Mesozoic Dinosauria. SVP abstracts.

SVP 2018: Junggarsuchus µCT scans

Ruebenstahl and Clark 2018
pull new data from the basalmost crocodylomorph, Junggarsuchus (Fig. 1) using µCT scans. They consider it a sphenosuchian nesting uneasily deep within Crocodylomorpha. I hope they test it with basal bipedal crocs listed in the large reptile tree (LRT, 1315 taxa, subset Fig. 3). PVL 4597 is a LRT sister that will provide clues to the hind quarters of Junggarsuchus, currently missing.

Figure 1 The CAPPA specimen of Buriolestes (a dinosaur) compared to the more primitive Junggarsuchus, basal to the other branch of archosaurs, the crocs.

The authors report, “In addition to braincase characters, we also identify a unique morphology in the palate and pterygoid of Junggarsuchus, which, although similar to the condition in other sphenosuchians, has several aspects that are unlike anything reported in any ‘sphenosuchians’, including a far reaching anterior process of the pterygoid.” A similar pterygoid is found in the basal dinosaur, Herrerasaurus (Fig. 2) and the poposaur, Silesaurus.

Figure 2. The basalmost dinosaur, Herrerasaurus. Note the palate and the long pterygoid.

Ruebenstahl and Clark 2018
provide no indication that they understand the close relationship of Junggarsuchus to basal dinosaurs, basal poposaurs and Decuriasuchus. If the authors only see croc interrelationships it’s time to add taxa.

Figure 3. Subset of the LRT focusing on Crocodylomorpha (basal Archosauria) including Armadillosuchus.

References
Ruebenstahl AA and Clark JM 2018. Junggarsuchus sloani: a transitional ‘sphenosuchian’ and the evolution of the crocodilian skull.” SVP abstracts.

SVP 2018: More complete material of Mixodectes

I know nothing about Mixodectes as I write this.
But based on the abstract description, I will put it into a phylogenetic perspective.

Sargis et al. 2018 report: 
“Mixodectids are eutherian mammals from the Paleocene of North America that have been considered close relatives of the extinct plagiomenids, microsyopid plesiadapiforms,and/or dermopterans, making them relevant to better understanding euarchontan relationships. We analyzed a new dentally associated skeleton of Mixodectes pungent (NMMNH P-54501). It is the most complete skeleton of a mixodectid known, preserving a partial skull with all teeth erupted and previously unknown elements of the axial skeleton, forelimbs, and hind limbs, all with epiphyses fused.”

The authors believe plesiadapiforms are basal to primates,
which is invalid based on the results in the large reptile tree (LRT, 1315 taxa). Plesiadapiforms are more closely related to carpolestids (including Daubentonia, the extant aye-aye) and multituberculates.

The NMMNH P-54501 mixodectid has

1. Humeral traits indicating a mobile shoulder and elbow.
2. The humerus has a large medial epicondyle and the proximal phalanges have
   pronounced flexor sheath ridges, both indicating powerful flexion of the digits.
3. Pelvis traits as in arboreal euarchontans.
4. The femur suggests a habitually flexed knee.
5. The astragalus and calcaneum indicates mobility in the ankle joints and is often present in arboreal taxa capable of pedal inversion.
6. The authors do not discuss the teeth…which are important: are they rodent-like (with large incisors as in Glires)?… or carnivore like (with canine fangs as in other primates)?

Sargis et al. conclude: “In summary, the postcranial morphology of Mixodectes is very similar to that of arboreal euarchontans, including plesiadapiforms, supporting inferences based on less complete material that mixodectids were both arboreal and members of Euarchonta.”

Euarchonta (Waddell et al. 1999) = Scandentia (tree shrews), Dermoptera (colugos), Plesiadapiformes (Plesiadapis) and Primates (lemurs to humans). Together these taxa are not monophyletic in the LRT (subset Fig. 1).

Figure 1. Subset of the LRT focusing on Glires, rodents and multituberculates. Primates are the sister clade to the clade shown above.

References
Sargis EJ et al. (4 co-authors) 2018. Functional morphology of a remarkably complete skeleton of Mixodectes pnugens: evidence for arboreality in an enigmatic eutherian from the Early Paleocene. SVP abstracts.

SVP 2018: Hindlimb feathers useful as brood covers in oviraptorids?

Hopp and Orsen 2018
bring a novel and well documented hypothesis to light: “Here we present evidence gleaned from our studies of a number of fossils that possess hind-limb feathers, as well as two examples of nesting Citipati. Two well preserved individuals sitting on nests with large egg clutches (IGM-100/979, IGM-100/1004) clearly demonstrate a lack of complete coverage of the eggs by the animals’ bodies and limbs. We previously showed that pennaceous feathers would have aided the coverage of eggs near the ulna and manus. We also noted a deficiency of egg coverage at the rear quarters laterally adjacent to the pelvis and tail. Here we demonstrate how pennaceous feathers, recently described on the tibiae and tarsi of several non-flying theropods and some primitive birds as well, could have served very effectively to cover eggs in these rear quarter positions.”

FIgure 1. From Zheng et al. 2013 showing the maximum extent of hind leg feathers in Anchiornis. Pedopenna nests with Anchiornis.

Excellent hypothesis. But…
Zheng et al. 2013 also studied this problem. They wrote, “parallel pennaceous feathers are preserved along the distal half of the tibiotarsus and nearly the whole length of the metatarsus in each hindlimb [of Sapeornis]. The feathers are nearly perpendicular to the tibiotarsus and metatarsus in orientation and form a planar surface as in some basal deinonychosaurs with large leg feathers.”

Zheng et al. 2013 also report similar leg and/or foot feathers are found in
“Basal deinonychosaurians (= Microraptor), the basal avialan Epidexipteryx, Sapeornis, confuciusornithids, and enantiornithines. In these taxa, the femoral and crural feathers are large, and in most cases they are pennaceous feathers that have curved rachises and extend nearly perpendicular to the limbs to form a planar surface.”

The distribution of foot feathers
in theropods in the large reptile tree (LRT, subset Fig. 2) is shown in blue (cyan). Few included taxa preserve feathers. The question is: do foot feathers appear, then disappear, then reappear? Or do all intervening taxa have foot feathers?

Figure 2. Where feathers on the foot are preserved on the LRT.

Back to the brooding question:
Citipati is an oviraptorid and oviraptorids are outside of the occurrences of foot feathers in theropods in the LRT. Note: all specimens with foot feathers are a magnitude smaller than oviraptorids. Hopp and Orsen do not differentiate (in their abstract, I did not see their presentation) between tibial feathers and foot feathers. Citipati nests outside of the current phylogenetic bracket for foot feathers. Tibial feathers have a much wider distribution in fossils. Tibial feathers are more likely to be present in Citipati, but note: tibial and foot feathers are not present in Caudipteryx (Fig. 3) an oviraptorid sister in the LRT .

Figure 3. Caudipteryx preserves forelimb and tail feathers, but no leg or foot feathers. It nests with oviraptorids in the LRT.

Back to the question of pennaceous hind limb feathers in pre-birds:
Here’s one answer, perhaps convergent with the presence of large uropatagia in flapping, but non-volant fenestrasaurs (like Cosesaurus Fig. 4). And look at the long legs and large uropatagia of the basalmost pterosaur, Bergamodactylus (Fig. 4)! It was just learning how to flap and fly and could use a little aerodynamic help in keeping steady.

When pre-birds, like Anchiornis,
and other convergent theropods, like Microraptor, first experimented with flapping and leaving the ground, they were necessarily new at it, not perfect at coordinated symmetrical flapping. Perhaps pre-birds used a bit of aerodynamic stabilization in the form of hind limb feathers as they phylogenetically became better and better at flapping, then flying. Tibial and foot feathers may have provided that aerodynamic stability, acting like vertical stabilizers in most airplanes. Exceptionally, present-day flying wing-type airplanes no longer require a vertical stabilizer because computers assist the pilot in controlling the aircraft, just as modern birds control flight without vertical stabilizers. That’s because modern birds with unfeathered feet have established neural networks not present or only tentatively present in pre-birds.

Figure 4. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown. Look at those large uropatagia. Those are for stability in this student pilot, not yet as coordinated as in later, more derived pterosaurs.

References
Hopp TP and Orsen MJ 2018. Evidence that ‘four-winged’ paravian dinosaurs may have used hindlimb feathers for brooding.” SVP abstracts.
Hu D, Hou L, Zhang L and Xu X 2009. A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus. Nature 461(7264):640-3. doi: 10.1038/nature08322.
Longrich N 2006. Structure and function of hindlimb feathers in Archaeopteryx lithographica. Paleobiology 32 (3), 417-431
Xu X and Zhang F 2005. A new maniraptoran dinosaur from China with long feathers on the metatarsus. Naturwissenschaften. 92(4): 173–177.
Zhang F-C and Zhou Z-H 2004. Palaeontology: Leg feathers in an Early Cretaceous bird. Nature 431, 925(2004). doi:10.1038/431925a
Zheng X-T et al. 2013. Hind wings in basal birds and the evolution of leg feathers. Science 339:1309-1312. DOI: 10.1126/science.1228753

SVP 2018: Doswellia skull chimaera reconfigured

Wynd, Newbitt and Heckert 2018
“redescribe Doswellia sixmilensis on the basis of extensive repreparation of the skull material to identify cranial elements, morphological details previously not described, and cranial suture patterns. As such, we reinterpret what was previously regarded as the antorbital fenestra to be the orbit and, as a consequence, the identification of bones and the diagnosis of the taxon must be substantially modified.”

Today I learned
the larger rostrum was attributed to a second Doswellia species, D. sixmilenesis. (Heckert et al. 2012). The reconstructions below created a chimaera of the two skulls, and two reconstructions based on the old and new interpretations of the larger rostrum.

Figure 1. Doswellia restored two ways using two species. In this restoration, the pmx ascending process is gracile and missing, along with the anterior naris. The insert shows the vestige of the lateral temporal fenestra. If the large specimen includes an orbit and jugal here is a new reconstruction reflecting that change.

Either way
the sum of the parts largely match sister taxa (Fig. 2) in the large reptile tree (LRT, 1315 taxa).

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciate the similarities and slight differences that are gradual accumulations of derived traits.

The taxon list for the abstract
was not published, but I hope it includes the taxa used in the LRT where Doswellia nests closer to certain proterochampsids than to proterochampsids.

The authors report,
“What is clear, is that D. sixmilensis shares character states with typical proterochampsians (e.g., rimmed orbit) that are not found in D. kaltenbachi.” In the first (earlier) reconstruction (Fig. 1), the orbits were not preserved, except ventrally by the large jugal.

Figure 3. Cladogram of basal archosauriforms. Note the putative basalmost archosauriform, Teyujagua (Pinheiro et al 2016) nests deep within the proterosuchids. The 6047 specimen that Ewer referred to Euparkeria nests as the basalmost euarchosauriform now.

The genus Doswellia
is distinct from all other genera, but trait scores nest it closest to a derived proterosuchid, the SAMPK K10603 specimen (Figs. 1, 2).

References
Dilkes D and Sues H-D 2009. Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29(1):58-79
Heckert AB, Lucas SG and Spielmann JA 2012. A new species of the enigmatic archosauromorph Doswellia from the Upper Triassic Bluewater Creek Formation, New Mexico, USA. Palaeontology 55(6):1333–1348.
Weems RE 1980. An unusual newly discovered archosaur from the Upper Triassic of Virginia, U.S.A. Transactions of the American Philosophical Society, New Series 70(7):1-53.
Wynd BM, Nesbitt SJ, Heckert AB 2018. Skull elongation in stem archosaur cranial displarity: Reevaluationg Doswellia sixmilensis (Archosauriformes: Proterochampsia) to examime phylogenetic distribution of morphological disparity. SVP Abstracts.

wiki/Doswellia

SVP 2018: A new 3D thalattosaur from Oregon

Metz, Druckenmiller, Boone and Kelley 2018
describe a new well-preserved thalattosaur from Oregon. They report, “The nodule
preserves the semi-articulated and three dimensionally preserved remains of multiple
individuals of different ontogenetic stages, including several complete and well-preserved
braincases.”

The authors err when they report, 
“Thalattosauria is a poorly known clade of exclusively Triassic, secondarily aquatic
tetrapods. Currently, thalattosaurian phylogeny is poorly understood, both in terms of their placement within Diapsida, as well as their ingroup relationships.”

The large reptile tree (LRT, 1315) confidently nests thalattosaurs and each genus within the clade alongside mesosaurs and ichthyosaurs. I hope the authors add Vancleavea (Fig. 1) to their studies. It is also preserved three-dimensionally.

Figure 1. Vancleavea is a thalattosaur with 3D preservation.

References
Metz ET, Druckenmiller PS, Boone NR and Kelley NP 2018. Thalattosauria braincase anatomy revealed through complete and three-dimensional material of a new genus from the Carnian Vester Formation of Oregon. SVP abstracts.

SVP 2018: Thaisaurus, basal ichthyosaur

Liu, Samathi and Chanthasit 2018
study for the first time Thaisaurus (Fig. 1), a basal ichthyosaur in the large reptile tree (LRT, 1315 taxa). We first looked at Thaisaurus in April, 2015 here.

The authors report, “Since its first brief description, however, T. chonglakmanii has never been restudied in detail, and its exact stratigraphic and phylogenetic position remained elusive. Here we revisit the well prepared holotype specimen of T. chonglakmanii.  This is the earliest record of Mesozoic marine reptiles, two million years earlier
than the earliest previous record.” The authors do not record an outgroup for the Ichthyosauria. The LRT provides dozens in a lineage going back to Devonian tetrapods. Late surviving Wumengosaurus nests as the basalmost ichthyosaur in the LRT (Fig. 2) and mesosaurs are the sister clade appearing as early as the Early Permian. So that gives plenty of time for ichthyosaurs to diverge from primitive mesosaur/sauropterygians. And we should be finding basal ichthyosaurs throughout the Permian.

Figure 1. Thaisaurus in situ, traced using DGS, elements of tracing shifted using DGS and restored.

From 2015
Thaisaurus chonglakmanii (Mazin et al. 1991; Early Triassic; Fig. 1.) was considered the most basal ichthyosaur by Maisch (2010). That is largely confirmed in the large reptile tree where Thaisaurus nests between Wumengosaurus and the remainder of the Ichthyosauria (sensu Maisch 2010, Fig. 2).

Figure 2. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Nice to see that everyone is in agreement
on the taxonomic nesting of Thaisaurus.

Figure 2. Click to enlarge. The origin of ichthyosaurs and thalattosaurs from basal diapsids and basal mesosaurs. Relationships are rather apparent when seen in this context.

Thaisaurus was a late-survivor in the Early Triassic,
a time in which ichthyosaurs were diversifying rapidly. Or did ichthyosaurs just appear in the fossil record then, having diversified throughout the Permian?

References
Liu J, Samathi A and Chanthasit P 2018. The earliest ichthyosaur from the middle Lower Triassic of Thailand.
Maisch MW 2010. Phylogeny, systematics, and the origin of the Ichthyosauria – the state of the art. Palaeodiversity 3:151-214.
Mazin J-M et al. 1991. Preliminary description of Thaisaurus chonglakmanii n. g. n. sp. a new ichthyopterygian (Reptilia) from the Early Triassic of Thailand. – Comptes- Rendus des Séances de l’Académie de Sciences Paris, Série II, 313: 1207-1212.