Triassic

Global and temporal distribution of silesaurids shown on a Middle and Late Triassic (Ladinian-Norian) map of the northern and southern regions of Pangea.

A reconstruction of Erythrovenator jacuiensis based on a skeletal by Maurissauro. This basal theropod comes from the Late Triassic Candelária Formation of Brazil.

Ahvaytum is a saturnaliid sauropodomorph from the Late Triassic of what is now Wyoming. It is the oldest known dinosaur from the northern continent of Laurasia, challenging previous hypotheses of dinosaur origins and dispersal. Typical of basal dinosaurs from the Triassic, Ahvaytum was a small slender biped, reaching about 1 m in body length.

Life restoration of the large, Middle Triassic Nevadan ichthyosaur Cymbopsondylus petrinus. This illustration is primarily based on specimen UCMP 9950, with much of the tail restored following UCMP 9947. The size of the eye was reconstructed based on UCMP 9954 and UCMP 9913. The unknown distal portions of the flippers, as well as some of the tail, was reconstructed after the related genus Xinminosaurus. References Merriam, J. C. (1908) Triassic Ichthyosauria: With special reference to the American forms, Berkley, California: Berkley: The University Press Klein, N.; Schmitz, L.; Wintrich, T.; Sander, P. M. (2020). "A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA". Journal of Systematic Palaeontology 18 (14): 1167-1191. DOI:10.1080/14772019.2020.1748132. Jiang, D.; Motani, R.; Hao, W.; Schmitz, L.; Rieppel, O.; Sun, Y.; Sun, Z. (2008). "New primitive ichthyosaurian (Reptilia, Diapsida) from the Middle Triassic of Panxian, Guizhou, southwestern China and its position in the Triassic biotic recovery". Progress in Natural Science 18 (10): 1315. DOI:10.1016/j.pnsc.2008.01.039.

Life restoration of the Triassic ichthyosaur Callawayia neoscapularis. Three specimens of this ichthyosaur are known, the holotype, ROM 41993, and two referred specimens, TMP 94.380.11 and 94.382.2. The skull is primarily based on ROM 41993, cross-checked against TMP 94.380.11 and TMP 94.382.2. The vertebral column is based primarily on TMP 94.382.2 as it is the most complete of these specimens, while the ribs were based on ROM 41993. The forelimbs were mainly based on those of ROM 41993, with TMP 94.380.11 used to determine their breadth. The hindlimbs were based on TMP 94.380.11, especially the more complete right hindlimb. ROM 41993 was cross-scaled with TMP 94.380.11 by the dimensions of the forelimb epipodials, which produced similar vertebral dimensions. The two TMP specimens were cross-scaled based on femoral length, also producing similar vertebral dimensions. Nicholls & Manabe (2001) stated that no wedge-shaped caudal centra supporting a tailbend were found and that there was no evidence of a bend being present, though considered that they might have existed in the gap in the preserved caudals. Since various other Triassic ichthyosaurs have since been found to have tail bends, one was illustrated here. A modest downturn of roughly 15° was illustrated, comparable to that in Guanlingsaurus, and the location of the bend within the gap in the preserved vertebrae matches well with the location of the bend in Guizhouichthyosaurus. References McGowan, C. (1994). "A new species of Shastasaurus (Reptilia: Ichthyosauria) from the Triassic of British Columbia: The most complete exemplar of the genus". Journal of Vertebrate Paleontology 14 (2): 168–179. DOI:10.1080/02724634.1994.10011550. Nicholls, E. L.; Manabe, M. (2001). "A new genus of ichthyosaur from the Late Triassic Pardonet Formation of British Columbia: Bridging the Triassic-Jurassic gap". Canadian Journal of Earth Sciences 38 (6): 983–1002. Ji, C.; Jiang, D.Y.; Hao, W.; Sun, Y. (2011). "True tailbend occurred in the Late Triassic: Evidence from ichthyosaur skeletons of South China". Acta Scientiarum Naturalium Universitatis Pekinensis 47 (2): 309–314. Shang, Q. H.; Li, C. (2009). "On the occurrence of the ichthyosaur Shastasaurus in the Guanling biota (Late Triassic), Guizhou, China". Vertebrata PalAsiatica 47 (3): 178–193.

Californosaurus perrini, an ichthyosaur from the Late Triassic of North America, pencil drawing

Life restoration of the German Jurassic ichthyosaur Suevoleviathan disinteger. The dorsal and caudal fins are loosely based on those of Stenopterygius. References Maisch, M.W. (2020). "The best-preserved skeleton of Suevoleviathan integer (Bronn, 1844)(Reptilia: Ichthyosauria) from the lower Jurassic of south-western Germany, with a discussion of the genus". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 297 (2): 153–172. Maisch, M.W. (1998). "A new ichthyosaur genus from the Posidonia Shale (Lower Toarcian, Jurassic) of Holzmaden, SW-Germany with comments on the phylogeny of post-Triassic ichthyosaurs". Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen 209 (1): 47–78.

Fossil samples – e.g. ‘primitive’ bony fish (1, 2), a skull of a temnospondyl ‘amphibian’ (probably a metoposauroid) in dorsal view (3), a skull of an archosaur of the crocodile lineage (probably a phytosaur) in palatal view (4), holotype of the “gliding reptile” Icarosaurus siefkeri [1] (5) and Atreipus-Grallator-type dinosaur tracks (bottom right) – from the Newark Supergroup, i.e. a series of mainly Late Triassic to Early Jurassic sedimentary rocks of eastern North America ↑ Edwin H. Colbert: A gliding reptile from the Triassic of New Jersey. American Museum Novitates, 2230. American Museum of Natural History, New York 1966, digitallibrary.amnh.org, cf. fig. 3 therein.

Figure 1. Evolution of macroecological traits in Dinosauria. Large scale event in dinosaur evolution (a); the origin of dinosaurs (star), hyperthermals (volcano), the earliest fossil Avialae (bird), the earliest fossil angiosperm (flower), the Cretaceous/Palaeogene mass extinction (asteroid). Phylogeny of dinosaurs (b) redrawn from Sereno and adapted to the current consensus and upon which an ancestral state reconstruction of temperature niche (mean annual temperature) after Chiarenza et al. is plotted; Mesozoic palaeogeographies (c) for Triassic (T), Jurassic (J) and Cretaceous (K). Silhouette colours symbolize body mass for each of the taxa represented; information on dietary habits are plotted after Barrett and Zanno & Makovicky; numbers represent clades discussed through this study: 1, Ornithischia; 2, Thyreophora; 3, Ornithopoda; 4, Hadrosauroidea; 5, Marginocephalia; 6, Ceratopsia; 7, Saurischia; 8, Sauropodomorpha; 9, Sauropoda; 10, Theropoda; 11, Ceratosauria; 12, Tetanurae; 13, Coelurosauria; 14, Maniraptoriformes; 15, Maniraptora; 16, Deinonychosauria; 17, Avialae; 18, Ornithothoraces. Palaeogeographies modified from original plots via R package ‘mapast’ using plate models by Scotese.

Tawa is an early theropod from the Late Triassic. The genus is named after the Hopi word for the Puebloan sun god. It was a bipedal carnivore, estimated around 2.5 m in length, and weighing about 15 kg. A basal theropod, Tawa shares physical characteristics with coelophysoids and herrerasaurids, and its discovery supports the theory that dinosaurs originated in the southern supercontinent of Gondwanna, before diversifying as Pangea split apart.

Various fossils pertaining to the holotype of the Triassic ichthyosaur Toretocnemus (originally Leptocheirus, also Merriamia) zitteli. This image is derived from plate 23 in Merriam (1903), done by an uncredited artist. The arrangement of the individual figures has been modified from the original (most notably, figures 3 and 4 were swapped to minimize confusion). Original description: Leptocheirus zitteli n. gen. and sp. Figures reproduced natural size from the type specimen. Fig. 1.— Right side of skull. Fig. 2. — Cross-section of posterior portion of the lower jaw, taken above the point marked A on the lateral view of the skull. Fig. 3. — Cross-section of the upper and lower jaws, taken at the break immediately behind the point marked Sp on the lateral view of the skull. Fig. 4. — Lateral view of an anterior caudal centrum. Legend (modified from original): Ar - articular A - angular D - dentary J - jugal L - lacrimal Mx - maxilla Po - postorbital Sa - surangular Se - sclerotic ring Sp - spenial T - cross-section of tooth X - doubtful element

The shoulder girdle of the holotype of the Triassic ichthyosaur Toretocnemus (originally Leptocheirus, also Merriamia) zitteli. This image is derived from plate 21 in Merriam (1903), done by an uncredited artist. The arrangement of the individual figures has been slightly modified from the original. Original description: Leptocheirus zitteli n. gen. and sp. Figures reproduced natural size from the type specimen. Fig. 1.—Clavicles (cl) and probable interelavicle (Ic and Ic')- The interclavicle has been separated into two fragments by a crack in the matrix. Fig. 2.—Inner side of the coracoids and the left scapula.

Forelimb and partial hindlimb of the holotype of the Triassic ichthyosaur Toretocnemus (originally Leptocheirus, also Merriamia) zitteli. This image is derived from plate 22 in Merriam (1903), done by an uncredited artist. Original description: Leptocheirus zitteli n. gen. and sp. Figures reproduced natural size from the type specimen. Fig. 1. — Superior side of left anterior limb. r, radius. Fig. 2. — Posterior limb. t, tibia.

Various fossils pertaining to the holotype of the Triassic ichthyosaur Toretocnemus californicus. This image is derived from plate 24 in Merriam (1903), done by an uncredited artist. The arrangement of the individual figures has been modified from the original. Original description: Toretocnemus californicus n. gen. and sp. Figures reproduced natural size from the type specimen. Fig. 1. — Inferior side of right posterior limb. t, tibia. Fig. 2. — Right anterior limb. r, radius. Fig. 3.— Pelvic arch. Fig. 4. — Middle dorsal vertebrae and a rib from the same region.

Illustration of some anterior caudal vertebrae of the Californian ichthyosaur Torteocnemus californicus (specimen UCMP 8100), from Merriam's 1908 monograph on American Triassic ichthyosaurs. This illustration appeared as figure 4 of plate 14; it has been modified to remove the stamp placed on top of it. While Merriam credits two illustrators as having produced artwork for this publication, it is not clear which of them created this image.

Life restoration of the Triassic ichthyosaur Qianichthyosaurus xingyiensis. References Motani, Ryosuke; Jiang, Da-yong; Tintori, Andrea; Ji, Cheng; Huang, Jian-dong (2017). "Pre- versus post-mass extinction divergence of Mesozoic marine reptiles dictated by time-scale dependence of evolutionary rates". Proceedings of the Royal Society B 284 (1854): 20170241. DOI:10.1098/rspb.2017.0241.