Fig 1.- Shastasaurus sikanniensis is the largest known ichthyosaur with an estimated length of some 20 meters.
A new paper published in PLoS by P. Martin Sander and co-workers, just made the ichthyosaurs an even more interesting and intriguing prehistoric critters. Ichthyosaurs are a group of extinct marine reptiles with streamline fish-like bodies that roamed the oceans from the Early Triassic to the Early Cretaceous periods.
A well-preserved specimen of the species previously described as Guanlingsaurus liangae from the Late Triassic of China shed light to a peculiar group of medium to large size ichthyosaurs called Shastasauridae.
Compared to the standard body shape of ichthyosaurs (think Ophthalmosaurus of WWD fame), the new specimen is characterized by a diminutive head, with an entirely toothless and greatly reduced snout. The description of this new specimen led to a general revision of the genus Shastasaurus, based on S. pacificus from the Late Triassic of California, to include not only G. liangae (re-baptized S. liangae) but also the largest known ichthyosaur, S. sikanniensis (formerly Shonisaurus sikanniensis) from the Late Triassic of British Columbia.
Fig 2.- The medium size Shastasaurus liangae may have hunted bioluminescent squids in the deep sea using the technique of suction feeding, similarly to some modern Odontocete cetaceans.
The peculiar skull anatomy of S. liangae lead the authors of the study to hypothesize that the three species of Shastasaurus were specialized suction feeder that preyed on squids and fish. The relative rarity of Shastasaurus fossils as well as their association with fully pelagic invertebrates, indicates a pelagic lifestyle. An interesting idea suggested by the authors is that their relatively large eyes would have been perfect to hunt bioluminescent cephalopods in the deep sea.
References:
Nicholls EM, Manabe M (2004) Giant ichthyosaurs of the Triassic-A new species of Shonisaurus from the Pardonet Formation (Norian, Late Triassic) of British Columbia. Journal of Vertebrate Paleontology 24: 838–849.
Sander PM, Chen X, Cheng L, Wang X (2011) Short-Snouted Toothless Ichthyosaur from China Suggests Late Triassic Diversification of Suction Feeding Ichthyosaurs. PLoS ONE 6(5): e19480.
Yin G, Zhou X, Cao Z, Yu Y, Luo Y (2000) A preliminary study on the early Late Triassic reptiles from Guanling, Guizhou, China (in Chinese). Geology- Geochemistry 28: 1–23.
Fig 1.- Iberian worm lizards (Blanus cinereus) by Richard Avery, from Wikipedia.
The worm lizards form a peculiar group of burrowing and legless reptiles that have a superficial resemblance to earthworms. These odd critters were traditionally placed in their own suborder, the Amphisbaenians, alongside the other two groups of Squamates, the snakes (Serpentes) and the lizards (Lacertilia). Molecular data (Townsend et al., 2004; Vidal et al., 2005) however have shown that they are in fact closely related to a particular family of old-world lizards, the Lacertidae (with representatives such as the European Green Lizard, Lacerta viridis and the common Wall Lizard, Podarcis muralis).
The fossil record of amphisbaenians is slim and their evolutionary history clouded with mystery. Previously, a paper published in Nature (Wu et al., 1993) described the taxon Sineoamphisbaena hexatabularis from the Upper Cretaceous of Inner Mongolia, as a stem amphisbaenian, but this conclusion turned out to be quite erroneous (Kearny, 2003).
Fig 2.- My reconstruction of Cryptolacerta hassiaca.
Now, a new Nature paper, written by Johannes Müller and co-workers present Cryptolacerta hassiaca from the Eocene Messel pit in Germany as a new ancestral amphisbaenian (Müller et al., 2011). Cryptolacerta is known from a single specimen consisting of a nearly complete articulated skeleton (missing only the end of the tail). It was small, very lizard-like in appearance but with relatively tiny limbs and a thickened skull. The structure of the skull of Cryptolacerta moreover supports the Lacertidae-Amphisbaenian molecular connection and indicates that skull reinforcement evolved before snake-like body in this particular group of headfirst burrowing reptiles.
References:
Kearny, M. 2003. The phylogenetic position of Sineoamphisbaena hexatabularis reexamined. J. Vert. Paleont. 23, 394-403.
Müller J., Hipsley C.A., Head J.J., Kardjilov N., Hilger A., Wuttke M. & reisz R.R. 2011. Eocene lizard from Germany reveals amphisbaenian origins. Nature 473, 364-367.
Townsend, T.M., Larson, A., Louis, E. & Macey, J.R. 2004. Molecular phylogenetics of Squamata: the position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree. Syst. Biol. 53, 735-757.
Vidal, N. & Hedges, S.B. 2005. The phylogeny of squamate reptiles (lizards, and amphisbaenians) inferred from nine protein-coding genes. C. R. Biol. 328, 1000-1008.
Wu, X.-C. et al. 1993. Oldest known amphisbaenian from the Upper cretaceous of Chinese Inner Mongolia. Nature, 57-59.
A friend of mine has asked me for a reconstruction of Rhomaleosaurus cramptoni to illustrate a book he is writing on prehistoric animals from England. R. cramptoni is one of these marine reptiles belonging to a group called plesiosaurs. It lived during the Early Jurassic in the shallow sea that was covering most of Western Europe at that time.
Plesiosaurs were traditionally divided into two morphology-based clades: the long-necked small-headed Plesiosauroidea (the plesiosaurs sensu stricto) with forms such as Plesiosaurus and Elasmosaurus, and the short-necked large-headed Pliosauroidea (the pliosaurs), represented by such animals as Kronosaurus and Liopleurodon of WWD fame.
Rhomaleosaurus and related taxa (the rhomaleosaurid family) were kind of oddballs among the plesiosaurs, as they combine features of the two morphotypes, i.e. they have relatively long necks and relatively large heads. A comprehensive phylogenetic analysis by Adam S.Smith and Gareth J. Dyke (2008) placed them firmly within the pliosaurs as sister group to the Leptocleidoidea and the Pliosauridae (pliosaur sensu stricto).
Rhomaelosaurus cramptoni, originally described in 1863 as a species of Plesiosaurus, was medium-size, measuring something like 7 meters in length. It is known from a complete skeleton of an adult specimen, which was unearthed in 1848 near Whitby, Yorkshire. Besides R. cramptoni, two other species are still tentatively recognized within the genus, R. zetlandicus and R. thorntoni, both from the Early Jurassic of England. The species R. propinquus is considered a junior synonym of R. cramptoni. “R. victor” (Early Jurassic of Germany) was transferred in 2010 to the new genus Meyerasaurus and “R. megacephalus” (Lower Jurassic, England) was found to be more closely related to Eurycleidus and Macroplata than to the other species of Rhomaleosaurus and will most likely be redescribed as a new genus in the near future. Rhomaelosaurids were a remarkably shorted lived family, being present only in the Early and perhaps in the Middle Jurassic.
Proportions for my reconstruction is based on the skeletal published by A. S. Smith (2008).
References:
Carte A, Bailey WH. 1863. “Description of a new species of Plesiosaurus, from the Lias, near Whitby, Yorkshire”. J R Dublin Soc 4:160–170.
O’Keefe FR. 2001. “A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia)”. Acta Zool Fenn 213: 1–63.
Smith AS, Dyke GJ. 2008. “The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics” Naturwissenschaften. 95, pp 975-980.
Smith AS, Vincent P. 2010. "A new genus of pliosaur (Reptilia: Sauropterygia) from the Lower Jurassic of Holzmaden, Germany". Palaeontology 53 (5): 1049–1063.
Taylor MA. 1992. Functional anatomy of the head of the large aquatic predator Rhomaleosaurus zetlandicus (Plesiosauria: Reptilia) from the Toarcian (Lower Jurassic) of Yorkshire, England. Philos Trans R Soc Lond Ser B 335:247–280.
I was recently asked for a few drawings representing the late cretaceous fauna found in the Coahuila province of Northeastern Mexico. The last decade indeed saw some interesting discoveries there including the hadrosaur Velafrons, a large but not fully described species of Kritosaurus (unofficially baptized “Sabinosaurio”) and the ceratopsian Coahuilaceratops which have the largest horns on record among the dinosaurs (this might be a subject of an upcoming post, so stay tune).
Fig 1.- A pair of Muzquizopteryx at sunset
This was a good opportunity for me to get into that peculiar group of pterosaurs called Nyctosaurids. The medium size Muzquizopteryx coahuilensis from the Late Cretaceous of Coahuila is known from a relatively complete articulated skeleton missing the front of the skull and the ends of the wings and feet (a picture of the fossil can be found here). The name somehow reminds me of mosquitoes and I first imagined tiny pterosaurs buzzing among gigantic hadrosaurs, but the wingspan was actually close to 2 meters (the name refers to the county, Múzquiz, where the fossil was found).
Fig 2.- Close up view of Muzquizopteryx.
Nyctosaurids show adaptation to an aerial lifestyle pushed to the extreme. They have lost the three-clawed fingers characterizing other pterosaurs, with only the wing finger remaining and their feet were relatively small, indicating that they would fare very badly on the ground so probably spent most of their time in the air. The remaining body characteristics and proportions are comparable to those of the related pteranodontids (Pteranodon and friends). After Muzquizopteryx, how could you resist representing the amazing Nyctosaurus from the Niobrara chalk of Kansas with its large antler-like crest that is apparently present only on adults and the function of which is still unclear.
Fig 3.- Nyctosaurus over the Western Interior Seaway.
References:
Bennett, S.C. 2003. "New crested specimens of the Late Cretaceous pterosaur Nyctosaurus." Paläontologische Zeitschrift, 77: 61-75.
Frey, E., Buchy, M.-C., Stinnesbeck, W., González, A.G., and di Stefano, A. 2006. “Muzquizopteryx coahuilensis n.g., n. sp., a nyctosaurid pterosaur with soft tissue preservation from the Coniacian (Late Cretaceous) of northeast Mexico (Coahuila)”. Oryctos 6:19-39.
The peculiar skull anatomy of S. liangae lead the authors of the study to hypothesize that the three species of Shastasaurus were specialized suction feeder that preyed on squids and fish. The relative rarity of Shastasaurus fossils as well as their association with fully pelagic invertebrates, indicates a pelagic lifestyle. An interesting idea suggested by the authors is that their relatively large eyes would have been perfect to hunt bioluminescent cephalopods in the deep sea.
