Zuul, the Gatekeeper

Skull of Zuul (Photograph: Brian Boyle/Royal Ontario Museum)

The Ankylosauria is a group of herbivorous, quadrupedal, armoured dinosaurs subdivided in two major clades, the Ankylosauridae and the Nodosauridae. Zuul crurivastator, from the Coal Ridge Member of the Judith River Formation of northern Montana, is the most complete ankylosaurid ever found in North America. The generic name refers to Zuul the Gatekeeper of Gozer (from the 1984 film Ghostbusters), and the species epithet combines crus (Latin) for shin or shank, and vastator (Latin) for destroyer, in reference to the sledgehammer-like tail club. The extraordinary preservation of abundant soft tissue in the skeleton, including in situ osteoderms and skin impressions make this specimen an important reference for understanding the evolution of dermal and epidermal structures in this clade. Until the discovery of Zuul, Laramidian ankylosaurin specimens were primarily assigned to three taxa: Euoplocephalus tutus and Ankylosaurus magniventris from northern Laramidia, and Nodocephalosaurus kirtlandensis from southern Laramidia.

The holotype (ROM 75860)  is a partial skeleton consisting of a nearly complete cranium, and a partially articulated postcranium. It is estimated to be over 6 metres long, and it would have weighed approximately 2500 kg. It has been dated to approximately 75 million years ago, and it was discovered accidentally on 16 May 2014 during overburden removal for a scattered tyrannosaurid skeleton, when a skid-steer loader encountered the tail club knob.

Overview of the tail of Zuul crurivastator in dorsal view, with insets of detailed anatomy (From Arbour and Evans, 2017)

The skull is almost complete, missing only the tip of the right quadratojugal horn and the ventral edge of the vomers, and is the largest ankylosaurine skull recovered from Laramidia. The skull is relatively flat dorsally, and had an elaborate ornamentation across the snout. The squamosal horns are robust and pyramid-shaped, and the quadratojugal horns had a sharp, posteriorly offset apex.

The tail club (including the 13 caudal vertebrae in the handle and the knob) is at least 210 cm long. Osteoderms are preserved not only in the anterior, flexible portion of the tail but also along the tail club handle. The first three pairs of caudal osteoderms are covered with a black film, that probably represent preserved keratin, and is similar to the texture observed at the base of bovid horn sheaths.

The discovery of Zuul fills a gap in the ankylosaurine record and further highlights that Laramidian ankylosaurines were undergoing rapid evolutionary rates and stratigraphic turnover as observed for Laramidian ceratopsids, hadrosaurids, pachycephalosaurids and tyrannosaurids.

References:

Arbour V. M., Evans D. C., (2017), A new ankylosaurine dinosaur from the Judith River Formation of Montana, USA, based on an exceptional skeleton with soft tissue preservation , Royal Society Open Science, rsos.royalsocietypublishing.org/lookup/doi/10.1098/rsos.161086

Arbour, V. M.; Currie, P. J. (2015). “Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs”. Journal of Systematic Palaeontology: 1–60. doi: 10.1080/14772019.2015.1059985

Jianianhualong and the evolution of feathers.

Jianianhualong tengi holotype (From Xu, X. et al., 2017)

In recent years, several discovered fossils of theropods and early birds have filled the morphological, functional, and temporal gaps along the line to modern birds. Most of these fossils are from the Jehol Biota of northeastern China, dated between approximately 130.7 and 120 million years ago. Among them are many fossils of troodontids, which are considered as the closest relatives of birds. Previous reported troodontid species include Mei long, Sinovenator changii, Sinusonasus magnodens and Jinfengopteryx elegans. Now a new troodontid, Jianianhualong tengi gen. et sp. nov., has anatomical features that shed light on troodontid character evolution.

The holotype (DLXH 1218) is a nearly complete skeleton with associated feathers, and is inferred to be an adult. It is estimated to be 112 cm in total skeletal body length with a fully reconstructed tail, and its body mass is estimated to be 2.4 kg, similar to most other Jehol troodontids, such as Sinovenator. The skull and mandible are in general well preserved, and  has a relatively short snout and highly expanded skull roof. There are probably 21 maxillary teeth and 25 dentary teeth on each side of the jaw. The vertebral column is nearly completely represented and  the tail is 54 cm long. The furcula is poorly preserved, and the humerus is 70% of femoral length. The manus is typical of maniraptoran theropods, and measures 112 mm in length. The pelvis is in general similar to those of basal troodontids, with a proportionally small ilium, a posteroventrally oriented pubis, and a short ischium. A phylogenetic analysis places Jianianhualong in an intermediate position together with several species between the basalmost and derived troodontids.

Plumage of Jianianhualong tengi (Adapted from Xu, X.  et al, 2017)

The tail frond of Jianianhualong preserves an asymmetrical feather, the first example of feather asymmetry in troodontids. Feathers were once considered to be unique avialan structures. Since the discovery of the feathered Sinosauropteryx in 1996, numerous specimens of most theropod groups and even three ornithischian groups preserving feathers have been recovered from the Jurassic and Cretaceous beds of China, Russia, Germany, and Canada. These feathers fall into several major morphotypes, ranging from monofilamentous feathers to highly complex flight feathers.

Evidence indicates that the earliest feathers evolved in non-flying dinosaurs for display or thermoregulation, and later were co-opted into flight structures with the evolution of asymmetrical pennaceous feathers in Paraves, therefore, the discovery of tail feathers with asymmetrical vanes in a troodontid theropod indicates that feather asymmetry was ancestral to Paraves.

 

 

References:

Xu, X. et al. Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features. Nat. Commun. 8, 14972 doi: 10.1038/ncomms14972 (2017).

Xu, X. et al. An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215 (2014). DOI: 10.1126/science.1253293

Introducing Zhongjianosaurus.

 

Photograph of Zhongjianosaurus yangi holotype (From Xu & Qin, 2017).

Dromaeosaurids are a group of carnivorous theropods, popularly known as “raptors”. Most of them were small animals, ranging from about 0.7 metres in length to over 7 metres. They had a relatively large skull with a narrow snout and the forward-facing eyes typical of a predator. They also had serrated teeth, and their arms were long with large hands, a semi-lunate carpal, with three long fingers that ended in big claws. The earliest known representatives are from the Lower Cretaceous Jehol Group of western Liaoning, China. The most recent described dromaeosaurid is Zhongjianosaurus yangi. The new taxon was named in honor of  Yang Zhongjian, who is the founder of vertebrate paleontology in China.

The Early Cretaceous Jehol dromaeosaurids not only display a great size disparity, but also show a continuous size spectrum. Zhongjianosaurus represents the ninth dromaeosaurid species reported from the Jehol Biota. It was first reported in 2009, and is notable for its small size (about 25 cm tall), compact body, and extremely long legs.

Zhongjianosaurus yangi holotype. A. right scapulocoracoid in lateral view and furcula in posterior view; B. right humerus in anterior view; C. left ulna and radius in lateral view; D. ‘semilunate’ carpal, metacarpals II and III in ventral view and phalanges II-1 and -2 in lateral view; scale bars equal 5 mm (From Xu & Qin, 2017)

The holotype is an adult individual distinguishable from other microraptorines in possessing many unique features, most of them are present in the forelimbs. For example, the humerus has a strongly offset humeral head, a large fenestra near the proximal end, and a large ball-like ulnar condyle. Zhongjianosaurus also displays several other features which are absent in other Jehol dromaeosaurids. For instance, the uncinate processes are proportionally long and fused to the dorsal ribs, the caudal vertebral transitional point is located anteriorly, and the pes exhibits a full arctometatarsalian condition.

The coexistence of several closely related Jehol dromaeosaurids can be interpreted as niche differentiation. Tianyuraptor have limb proportions and dental morphologies typical of non-avialan carnivorous theropods, suggesting that they were ground-living cursorial predators, meanwhile Microraptor are more likely to have been arboreal or even gliding animals.

References:

Xu X , Qin Z C, 2017, in press. A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of western Liaoning and niche differentiation among the Jehol dromaeosaurids. Vertebrata PalAsiatica

Xu X, 2002. Deinonychosaurian fossils from the Jehol Group of western Liaoning and the coelurosaurian evolution. Ph.D thesis, Beijing: Chinese Academy of Sciences. 1–322

Re-examining the dinosaur evolutionary tree.

Close up of “Sue” at the Field Museum of Natural History in Chicago, IL (From Wikimedia Commons)

In the nineteen century, the famous Victorian anatomist Richard Owen diagnosed Dinosauria using three taxa: Megalosaurus, Iguanodon and Hylaeosaurus, on the basis of three main features: large size and terrestrial habits, upright posture and sacrum with five vertebrae (because the specimens were from all Late Jurassic and Cretaceous, he didn’t know that the first dinosaurs had three or fewer sacrals). Later, in 1887, Harry Govier Seeley summarised the works of Edward Drinker Cope, Thomas Huxley and Othniel Charles Marsh, and subdivide dinosaurs into Saurischians and the Ornithischians. He wrote: The characters on which these animals should be classified are, I submit, those which pervade the several parts of the skeleton, and exhibit some diversity among the associated animal types. The pelvis is perhaps more typical of these animals than any other part of the skeleton and should be a prime element in classification. The presence or absence of the pneumatic condition of the vertebrae is an important structural difference…” Based on these features, Seeley denied the monophyly of dinosaurs.

Seeley’s (1901) diagram of the relationships of Archosauria. From Padian 2013

At the mid 20th century, the consensual views about Dinosauria were: first, the group was not monophyletic; second almost no Triassic ornithischians were recognised, so they were considered derived morphologically, which leads to the third point, the problem of the ‘‘origin of dinosaurs’’ usually was reduced to the problem of the ‘‘origin of Saurischia,’’ because theropods were regarded as the most primitive saurischians. But the discovery of Lagosuchus and Lagerpeton from the Middle Triassic of Argentina induced a change in the views of dinosaurs origins. Also from South America came Herrerasaurus from the Ischigualasto Formation, the basal sauropodomorphs Saturnalia, Panphagia, Chromogisaurus, and the theropods Guibasaurus and Zupaysaurus, but no ornithischians except a possible heterodontosaurid jaw fragment from Patagonia. The 70s marked the beginning of a profound shift in thinking on nearly all aspects of dinosaur evolution, biology and ecology. Robert Bakker and Peter Galton, based on John Ostrom’s vision about Dinosauria, proposed, for perhaps the first time since 1842, that Dinosauria was indeed a monophyletic group and that it should be separated (along with birds) from other reptiles as a distinct ‘‘Class”. In 1986, the palaeontologist Jacques Gauthier showed that dinosaurs form a single group, which collectively has specific diagnostic traits that set them apart from all other animals.

The dinosaur evolutionary tree (From Padian, 2017.

Phylogenetic analyses of early dinosaurs have  supported the traditional scheme. But a new study authored by Matthew Baron, David Norman and Paul Barrett, reach different conclusions from those of previous studies by incorporating some different traits and reframing others. Baron and colleagues, analysed a wide range of dinosaurs and dinosauromorphs, including representatives of all known dinosauromorph clades. 74 taxa were scored for 457 characters. The team  arrived at a dinosaur evolutionary tree containing one main branch that subdivides into the groupings of Ornithischia and Theropoda, and a second main branch that contains the Sauropoda and Herrerasauridae (usually positioned as either basal theropods or basal Saurischia, or outside Dinosauria but close to it). The union between ornithischians and theropods is called Ornithoscelida. The term was coined in 1870 by Thomas Huxley for a group containing the historically recognized groupings of Compsognatha, Iguanodontidae, Megalosauridae and Scelidosauridae.

From Baron et al., 2017.

The synapomorphies that support the formation of the clade Ornithoscelida includes: an anterior premaxillary foramen located on the inside of the narial fossa; a sharp longitudinal ridge on the lateral surface of the maxilla; short and deep paroccipital processes; a post-temporal foramen enclosed within the paroccipital process; a straight femur, without a sigmoidal profile; absence of a medioventral acetabular flange; a straight femur, without a sigmoidal profile; and fusion of the distal tarsals to the proximal ends of the metatarsals.

Of course, those results have great implications for the very origin of dinosaurs. Ornithischia don’t begin to diversify substantially until the Early Jurassic. By contrast, the other dinosaurian groups already existed by at least the early Late Triassic. If the impoverished Triassic record of ornithischians reflects a true absence, ornithischians might have evolved from theropods in the Late Triassic (Padian, 2017). The study also suggest that dinosaurs might have originated in the Northern Hemisphere, because most of their basal members, as well as their close relatives, are found there. Furthermore, their analyses places the origin of dinosaurs at the boundary of the Olenekian and Anisian stages (around 247 Ma), slightly earlier than has been suggested previously.

 

References:

Baron, M. G., Norman, D. B. & Barrett, P. M. A new hypothesis of dinosaur relationships and early dinosaur evolution.  Nature 543, 501–506  (2017).  doi:10.1038/nature21700

Padian K. Dividing the dinosaurs. Nature 543, 494–495 (2017) doi:10.1038/543494a

Padian K. The problem of dinosaur origins: integrating three approaches to the rise of Dinosauria. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, Available on CJO 2013 doi:10.1017/S1755691013000431 (2013).

Seeley, H. G. On the classification of the fossil animals commonly named Dinosauria. Proc. R. Soc. Lond. 43, 165171 (1887).

Huxley, T. H. On the classification of the Dinosauria, with observations on the Dinosauria of the Trias. Quarterly Journal of the Geological Society, London 26, 32-51. (1870).

 

Mary Anning and the Hunt of Primeval Monsters.

mary_anning_plesiosaurus

Autograph letter concerning the discovery of plesiosaurus, from Mary Anning (From Wikimedia Commons)

Since the End of the 17th century to the beginning of the 19th, several discoveries of dinosaur remains and other large extinct ‘saurians’, were reported for first time. It was an exciting time full of discoveries and the concept of an ancient Earth became part of the public understanding. The most popular aspect of geology was  the collecting of fossils and minerals and the nineteenth-century geology, often perceived as the sport of gentlemen, was in fact, “reliant on all classes”.

The study of the Earth became central to the economic and cultural life of the Victorian Society and Literature influenced the pervasiveness of geological thinking. The Geological Society of London was founded on 13 October 1807 at the Freemasons’ Tavern, in the Covent Garden district of London, with the stated purpose of “…making geologists acquainted with each other, of stimulating their zeal, of inducing them to adopt one nomenclature, of facilitating the communications of new facts and of ascertaining what is known in their science and what remains to be discovered”. During this time, women were free to take part in collecting fossils and mineral specimens, and they were allowed to attend lectures but they were barred from membership in scientific societies. However, it was common for male scientists to have women assistants, often their own wives and daughters.

Plesiosaurus battling Temnodontosaurus (Oligostinus), front piece the Book of the Great Sea-Dragons by Thomas Hawkins.

Plesiosaurus battling Temnodontosaurus (Oligostinus), front piece the Book of the Great Sea-Dragons by Thomas Hawkins.

Mary Anning (1799-1847), was an special case. Despite her lower social condition, Mary became the most famous ‘fossilist’ of her time. She was born on Lyme Regis on May 21, 1799. Her father was a carpenter and an amateur fossil collector who died when Mary was eleven. He trained Mary and her brother Joseph in how to look and clean fossils. After the death of her father, Mary and Joseph used those skills to search fossils on the local cliffs,  that sold as “curiosities”. The source of the fossils was the coastal cliffs around Lyme Regis, one of the richest fossil locations in England and part of a geological formation known as the Blue Lias. The age of the formation corresponds to the Jurassic period. In 1811, she caught the public’s attention when she and her brother Joseph unearthed the skeleton of a ‘primeval monster’. They sold it for £23. Later, in 1819, the skeleton was purchased by Charles Koenig of the British Museum of London who suggested the name “Ichthyosaur” for the fossil.

On December 10, 1823, she discovered the first complete Plesiosaur skeleton at Lyme Regis in Dorset. The fossil was acquired by the Duke of Buckingham. Noticed about the discovery, George Cuvier wrote to William Conybeare suggesting that the find was a fake produced by combining fossil bones from different animals. William Buckland and Conybeare sent a letter to Cuvier including anatomical details, an engraving of the specimen and a sketch made by Mary Morland (Buckland’s wife) based on Mary Anning’s own drawings and they convinced Cuvier that this specimen was a genuine find. From that moment, Cuvier treated Mary Anning as a legitimate and respectable fossil collector and cited her name in his publications.

The holotype specimen of Dimorphodon macronyx found by Mary Anning in 1828 (From Wikimedia Commons)

On December of 1828, Mary found the first pterosaur skeleton outside Germany. William Buckland made the announcement of Mary’s discovery in the Geological Society of London and named Pterodactylus macronyx in allusion to its large claws. The skull of Anning’s specimen had not been discovered, but Buckland thought that the fragment of jaw in the collection of the Philpot sisters of Lyme belonged to a pterosaur.

In her later years, Mary Anning suffered some serious financial problems. She died of breast cancer on 9 March, 1847, at the age of 47. She was buried in the cemetery of St. Michaels. In the last decade of her life, Mary received  three accolades. The first was an annuity of £25, in return for her many contributions to the science of geology. The second was in 1846, when the geologists of the Geological Society of London organized a further subscription for her. The third accolade was her election, in July 1846, as the first Honorary Member of the new Dorset County Museum in Dorchester (Torrens, 1995). After her death, Henry de la Beche, Director of the Geological Survey and President of the Geological Society of London, wrote a very affectionate obituary published in the Quarterly Journal of the Geological Society on February 14, 1848, the only case of a non Fellow who received that honour.

References:

Davis, Larry E. (2012) “Mary Anning: Princess of Palaeontology and Geological Lioness,”The Compass: Earth Science Journal of Sigma Gamma Epsilon: Vol. 84: Iss. 1, Article 8.

Hugh Torrens, Mary Anning (1799-1847) of Lyme; ‘The Greatest Fossilist the World Ever Knew’, The British Journal for the History of Science Vol. 28, No. 3 (Sep., 1995), pp. 257-284. Published by: Cambridge University Press.

De la Beche, H., 1848a. Obituary notices. Quarterly Journal of the Geological Society of London, v. 4: xxiv–xxv.

Dickens, C., 1865. Mary Anning, the fossil finder. All the Year Round, 13 (Feb 11): 60–63.

 

A Brief Introduction to Conservation Paleobiology

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

Over the past 50 years, the pace and magnitude of human-induced global changes has accelerated dramatically. The term defaunation was created to designate the declining of top predators and herbivores triggered by human activity, that results in a lack of agents that control the components of the ecosystems vegetation. Although anthropogenic climate change is playing a growing role, the primary drivers of modern extinctions seem to be habitat loss, human predation, and introduced species. The same drivers that contributed to ancient megafaunal and island extinctions.

The emerging discipline of conservation paleobiology is supplying necessary information to understand how ecosystems vary naturally through time and space and how they respond to major perturbations. The fossils that have provided such data include phytoplankton, zooplankton, fossil pollen, seeds, leaves, wood, invertebrate animals with hard parts, and vertebrate animals. They are particularly useful because they often show high fidelity to the living communities. Quaternary fossils have proven especially informative for addressing conservation questions, but useful information has also come from much older fossil deposits, reaching back millions of years.

1024px-bison_near_a_hot_spring_in_yellowstone

Bison near a hot spring in Yellowstone National Park (From Wikimedia Commons).

The analytical methods that allow comparing present with past fall into two main categories: taxon-based and taxon-free. Taxon-based methods rely on the presence, absence, or abundances of certain taxa and their underlying diversity. Taxon-free methods use metrics that reflect ecosystem function rather than structure. Depending on the availability of fossils and the type of conservation question being asked, one or the other approach may be more appropriate.

Taxon-based paleontological data are critical in deciding if a “natural” landscape represents a historical or a novel ecosystem. Historical ecosystems are those that still have at least 70% of the habitats that were present 500 years ago and that contain fewer than 5 people/km2. In the world’s first national park, Yellowstone National Park, USA, paleontological data influenced critical management decisions by demonstrating that Yellowstone preserves a historical ecosystem. Fossil deposits verified that almost all of the mammal species that had occupied the region for millennia are still present. Also, palynological records show that the current vegetation has persisted with only minor fluctuations in abundance of dominant taxa for at least 8000 years.

Lyuba, the best preserved mammoth mummy in the world, at the Field Museum of Natural History (From Wikimedia Commons).

Lyuba, the best preserved mammoth mummy in the world, at the Field Museum of Natural History (From Wikimedia Commons).

Taxon-free paleontological can often be related to environmental parameters with statistical significance data, and are critical for understanding whether certain ecosystems are approaching “tipping points,” as demonstrated by analysis of diatoms, pollen, and sediments from lake cores.

Fossils have also figured prominently  with efforts to reconstruct copies of species that humans have driven to extinction either recently (passenger pigeons) or in the deeper past (mammoths). Unfortunately, the ecosystems that supported many extinct species no longer exist, so survival outside of captivity would be difficult. In addition, preventing the extinction of extant species and habitats numbering in the thousands already is challenging, so the prospects of sustaining “de-extincted” species are poor at best. Media reports are presenting de-extinction in an optimistic framework, and conveying the impression that we face a real possibility of bringing mammoth back from extinction in  the near future. Of course, this is far from truth. We will never be able to recreate most extinct species in their purest form. Ultimately,  genetic engineering to simulate extinct life also raises ethical and legal concerns.

 

References:

Anthony D. Barnosky et al. Merging paleobiology with conservation biology to guide the future of terrestrial ecosystems. Science, 2017 DOI: 10.1126/science.aah4787

Rodolfo Dirzo et al., Defaunation in the Anthropocene, Science 345, 401 (2014); DOI: 10.1126/science.1251817

Braje, T.J., Erlandson, J.M., Human acceleration of animal and plant extinctions: A Late Pleistocene, Holocene, and Anthropocene continuum. Anthropocene (2013), http://dx.doi.org/10.1016/j.ancene.2013.08.003

Richmond, D.J., Sinding, M-H.S., Gilbert, M.T.P. (2016). The potential and pitfalls of de-extinction. — Zoologica Scripta, 45, 2236DOI: 10.1111/zsc.12212

Introducing Isaberrysaura

Isaberrysaura skull in lateral view and maxillary teeth (Adapted from Salgado et al., 2017)

Isaberrysaura mollensis gen. et sp. nov. is the first dinosaur recovered in the marine-deltaic deposits of the Los Molles Formation (Neuquén Province, Argentina), and the first neornithischian dinosaur known from the Jurassic of South America. So far, the South American record of Jurassic ornithischian dinosaurs was limited to a few specimens belonging to Heterodontosauriformes, a clade of small-sized forms that survived in Europe up to the Early Cretaceous. The name Isaberrysaura is derived from “Isa Berry” (Isabel Valdivia Berry, who reported the initial finding) and the Greek word “saura” (lizard).

The holotype of Isaberrysaura is an incomplete articulated skeleton with an almost complete skull, and a partial postcranium consisting of 6 cervical vertebrae, 15 dorsal vertebrae, a sacrum with a partial ilium and an apparently complete pubis, 9 caudal vertebrae, part of a scapula, ribs, and unidentifiable fragments. One of the most notable features of the discovery is the presence of permineralized seeds in the middle-posterior part of the thoracic cavity. The seeds were assigned to the Cycadales (Zamiineae) on the basis of a well-defined coronula in the micropylar region. The findings suggest the hypothesis of interactions (endozoochory) between cycads and dinosaurs, especially in the dispersion of seeds.

Gut content of Isaberrysaura mollensis gen. et sp. nov. (a–c), seeds of cycads (c), and other seeds (s); rib (r). From Salgado et al., 2017

The cranium of Isaberrysaura is reminiscent of that of the thyreophorans. The skull is estimated to be 52 cm long and 20 cm wide across the orbits. The jugal is triradiate and the nasals are ~20 cm long. There are two supraorbital bones; one is elongated (~10 cm), as in stegosaurs, and the other element interpreted as a posterior supraorbital is located on the posterior margin of the orbit. It has at least six premaxillary teeth, and there is no diastema between the premaxillary and the maxillary tooth row. Despite the many similarities between Isaberrysaura and the thyreophorans, the phylogenetic analysis indicates that Isaberrysaura is a basal ornithopod, suggesting that both Thyreophora and neornithischians could have achieved significant convergent features.

References:

Salgado, L. et al. A new primitive Neornithischian dinosaur from the Jurassic of Patagonia with gut contents. Sci. Rep. 7, 42778; doi: 10.1038/srep42778 (2017)

Liaodactylus primus and the ecological evolution of Pterodactyloidea.

Skull of the newfound species Liaodactylus primus (Credit: Chang-Fu Zhou)

Skull of the newfound species Liaodactylus primus (Credit: Chang-Fu Zhou)

Pterosaurs are an extinct monophyletic clade of ornithodiran archosauromorph reptiles from the Late Triassic to Late Cretaceous. The group achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 150 species recognized so far. During their 149 million year history, the evolution of pterosaurs resulted in a variety of eco-morphological adaptations, as evidenced by differences in skull shape, dentition, neck length, tail length and wing span. Pterosaurs have traditionally been divided into two major groups, “rhamphorhynchoids” and “pterodactyloids”. Rhamphorhynchoids are characterized by a long tail, and short neck and metacarpus. Pterodactyloids have a much larger body size range, an elongated neck and metacarpus, and a relatively short tail. Darwinopterus from the early Late Jurassic of China appear to be a transitionary stage that partially fills the morphological gap between rhamphorhynchoids and pterodactyloids.

Pterodactyloidea, the most species-diverse group of pterosaurs, ruled the sky from Late Jurassic to the end of Cretaceous. Liaodactylus primus, a new specimen, discovered in northeast China’s Liaoning province, documents the only pre-Tithonian (145–152 Ma) pterodactyloid known with a complete skull, shedding new light on the origin of the Ctenochasmatidae, a group of exclusive filter feeders, and the timing of the critical transition from fish-catching to filter-feeding, a major ecological shift in the early history of the pterodactyloid clade. The holotype specimen is a nearly complete skull (133 mm long) and mandibles, with the first two cervical vertebrae preserved in articulation with the skull. The elongation of the rostrum, almost half the length of the skull, is accompanied by a significant increase in the number of marginal teeth, giving a total of 152 teeth in both sides of the upper and lower jaws. The teeth are closely spaced to form a ‘comb dentition’, a filter-feeding specialization.

Pterodaustro guinazui cast (Museo Argentino de Ciencias Naturales)

Pterodaustro guinazui cast (Museo Argentino de Ciencias Naturales)

Liaodactylus is the oldest known ctenochasmatid, predating the previously Tithonian (152 Ma) record (Gnathosaurus and Ctenochasma from Germany) by at least 8–10 Myr . The Ctenochasmatidae, represents a long-ranged clade (160–100 Ma), and the only pterodactyloid clade that crossed the Jurassic-Cretaceous transition. The group includes the Early Cretaceous Pterodaustro from Argentina. Popularly called the ‘flamingo pterosaur’, Pterodaustro represents the most remarkable filter-feeding pterosaur known from the fossil record, with a huge number (more than 1000) of densely spaced ‘teeth’ (elastic bristles) in its lower jaws, for filtering small crustaceans, microscopic plankton or algae from open water along lake shores.

Pterosaurs display an extraordinary eco-morphological disparity in feeding adaptations, expressed in skull, jaws and dentition. The Late Triassic Eopterosauria, the basalmost pterosaur clade, were mainly insectivorous. Jurassic insectivores include the Dimorphodontia, Campylognathoididae and Darwinoptera, whereas the Anurognathidae were the only Jurassic insectivores that survived the Jurassic–Cretaceous transition, but became extinct in the Early Cretaceous. The rise of the ctenochasmatid clade was the first major ecological shift in pterosaur evolution from insectivorous-piscivorous to filter-feeding. During Cretaceous time,  the Eupterodactyloidea, a group of advanced pterodactyloids, engaged in a variety of feeding adaptations, including filter-feeding, fish-eating, carnivory and scavenging, herbivory including frugivory, durophagy and omnivory. The Early Cretaceous tapejarids may have been herbivorous, while the pteranodontids, with large skull but tapering and toothless jaws were suitable for seizing fish in open-water environments. Finally, the Late Cretaceous azhdarchids have been hypothesized as foragers feeding on small animals and carrion in diverse terrestrial environments.

Time-calibrated cladogram showing stratigraphic range, eco-morphological diversity of pterosaur clades. (Adapted from Zhou et al., 2017)

Time-calibrated cladogram showing stratigraphic range, eco-morphological diversity of pterosaur clades. (Adapted from Zhou et al., 2017)

References:

Chang-Fu Zhou, Ke-Qin Gao, Hongyu Yi, Jinzhuang Xue, Quanguo Li, Richard C. Fox, Earliest filter-feeding pterosaur from the Jurassic of China and ecological evolution of Pterodactyloidea, 

Andres, B., Clark, J., & Xu, X. (2014). The earliest pterodactyloid and the origin of the group. Current Biology, 24(9), 1011-1016.

WITTON, M. P., 2010 Pteranodon and beyond: the history of giant pterosaurs from 1870 onwards. In: Moody, R.T.J., Buffetaut, E., Naish, D., Martill, D.M. (Eds.), Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications 343, 287–311.

 

Christmas edition: Geologizing with Dickens, part II.

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Charles Dickens at his desk, by George Herbert Watkins (National Portrait Gallery. From Wikimedia Commons)

Charles Dickens (1812- 1870) revitalized the traditions of Christmas, and to Victorian England, Dickens was Christmas. He had only 31, when began to write A Christmas Carol. The novella tells the story of  Ebenezer Scrooge, a bitter old man who finds salvation through the visits of the three Ghosts of Christmas (Ghost of Christmas Past, Ghost of Christmas Present, and Ghost of Christmas Yet to Come). But Dickens also contributed to the popularity of geology in the nineteenth century. Among his friends were Richard Owen and Sir Roderick Murchison. For Dickens, the ideal science is Geology. In his review of Hunt’s Poetry of Science, he wrote: “Science has gone down into the mines and coal-pits, and before the safety-lamp the Gnomes and Genii of those dark regions have disappeared … Sirens, mermaids, shining cities glittering at the bottom of quiet seas and in deep lakes, exist no longer; but in their place, Science, their destroyer, shows us whole coasts of coral reef constructed by the labours of minute creatures; points to our own chalk cliffs and limestone rocks as made of the dust of myriads of generations of infinitesimal beings that have passed away; reduces the very element of water into its constituent airs, and re-creates it at her pleasure…” (London Examiner, 1848).

In 1846, Dickens visited Naples and climbed the Mount Vesuvius. He described that experience in Pictures from Italy. He wrote: “Stand at the bottom of the great market-place of Pompeii, and look up the silent streets, through the ruined temples of Jupiter and Isis, over the broken houses with their inmost sanctuaries open to the day, away to Mount Vesuvius, bright and snowy in the peaceful distance; and lose all count of time, and heed of other things, in the strange and melancholy sensation of seeing the Destroyed and the Destroyer making this quiet picture in the sun.”

An eruption of Vesuvius circa 1845. Credit: Enrico La Pira.

An eruption of Vesuvius circa 1845. Credit: Enrico La Pira.

Mount Vesuvius is a stratovolcano, consisting of an external truncated cone, the extinct Mt. Somma,  a smaller cone represented by Vesuvius. For this reason, the volcano is also called Somma-Vesuvio. It was formed by the collision of two tectonic plates, the African and the Eurasian. When Mount Vesuvius erupted in 79 AD released deadly cloud of ash and molten rocks, and lasted eight days, burying and destroying the cities of Pompeya, Herculaneum and Stabiae. Vesuvius has the world’s oldest volcano observatory, established in 1845, and Dickens’s own magazine Household Words, frequently ran travel pieces describing the ascent and descent of Vesuvius, alongside trips to Pompei.

The same year, Dickens began to to write Dombey and Son, using his experiences in Italy to describe a violent eruption: “Hot springs and fiery eruptions, the usual attendants upon earthquakes, lent their contributions of confusion to the scene. Boiling water hissed and heaved within dilapidated walls; whence, also, the glare and roar of flames came issuing forth; and mounds of ashes blocked up rights of way, and wholly changed the law and custom of the neighbourhood”. 

Benjamin Waterhouse Hawkins unveiled the first ever sculptures of Iguanodons.

Benjamin Waterhouse Hawkins unveiled the first ever sculptures of Iguanodons.

It was an exciting time full of discoveries and the concept of an ancient Earth became part of the public understanding. The study of the Earth was central to the economic and cultural life of the Victorian Society and Literature influenced the pervasiveness of geological thinking. So when the Crystal Palace was reconstructed at Sydenham in 1854, Dickens and his Household Words were very enthusiastic. Megalosaurus became so popular that is mentioned in his novel Bleak House. In this novel the dinosaurs uncovered by the railway in Dombey and Son move centre stage: “Implacable November weather. As much mud in the streets as if the waters had but newly retired from the face of the earth, and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill.”  

In Bleak House and Dombey and Son, Dickens encourage reader to perceive the scene of the city as a geological fragment of a much broader spatial and temporal vision. In his last novel Our Mutual Friend (1864–65), Mr Venus, the taxidermist was slightly based on Richard Owen. By the time when Dickens wrote this novel, Owen was the curator of the Hunterian Museum of the Royal College of Surgeons. Our Mutual Friend, also exhibits  traces of the work of Lyell, Jean-Baptiste Lamarck, and Darwin.

References:

A. BUCKLAND, ‘“The Poetry of Science”: Charles Dickens, Geology and Visual and Material Culture in Victorian London’, Victorian Literature and Culture, 35 (2007), 679–94 (p. 680).

A. BUCKLAND. Novel Science: Fiction and the Invention of Nineteenth-Century Geology. Chicago, IL and London: University of Chicago Press, 2013. 400 pp. 9 plts. $45.00. ISBN 978-0-226-07968-4

High variation in postnatal development of Early Dinosaurs.

Cleveland Museum of Natural History Coelophysis block, originally AMNH Block XII collected in 1948 by Colbert and crew

Cleveland Museum of Natural History Coelophysis block, originally AMNH Block XII collected in 1948 (From Wikimedia Commons)

Birds originated from a theropod lineage more than 150 million years ago. Their evolutionary history is one of the most enduring and fascinating debates in paleontology. They are members of the theropod dinosaur subgroup Coelurosauria, a diverse clade that includes tyrannosauroids and dromaeosaurids, among others. Features like “hollow” bones and postcranial skeletal pneumaticity, feathers, a unique forelimb digit formula, endothermy, and rapid growth rate arose in non-avian dinosaurs in a gradual process occurring over tens of millions of years.

In contrast with all other living reptiles, birds grow extremely fast and possess unusually low levels of intraspecific variation during postnatal development, suggesting that this avian style of development must have evolved after its most recent common ancestor with crocodylians but before the origin of Aves. Most studies indicates that the low levels of variation that characterize avian ontogeny were present in close non-avian relatives as well.

Two C. bauri casts mounted at the Denver Museum of Nature and Science (From Wikimedia Commons)

Two C. bauri casts mounted at the Denver Museum of Nature and Science (From Wikimedia Commons)

Compared with birds, the theropod Coelophysis bauri possess a large amount of intraspecific variation. Coelophysis bauri is the type species of the genus Coelophysis, a group of small, slenderly-built, ground-dwelling, bipedal carnivores, that lived approximately 203 million years ago during the latter part of the Triassic Period in what is now the southwestern United States. Using this taxon to interpret development among early dinosaurs, geoscientists Christopher Griffin and Sterling Nesbitt discovered that the earliest dinosaurs had a far higher level of variation in growth patterns between individuals than crocodiles and birds. The presence of scars on the bones left from muscle attachment and marks where bones had fused together helped the researchers assess how mature the animals were compared with their size.

Body size and extinction risk have been found to be related in various vertebrate groups, therefore a high level of variation within a species may be advantageous in an ecologically unstable environment and may have contributed to the early success of dinosaurs relative to many pseudosuchian clades in the latest Triassic and through the End-Triassic Mass Extinction into the Early Jurassic.

References:

Christopher T. Griffin and Sterling J. Nesbitt, Anomalously high variation in postnatal development is ancestral for dinosaurs but lost in birds. PNAS 2016 : 1613813113v1-201613813.

Brusatte SL, Lloyd GT, Wang SC, Norell MA (2014) Gradual assembly of avian body plan culminated in rapid rates of evolution across the dinosaur-bird transition. Curr Biol 24(20):2386–2392

Puttick, M. N., Thomas, G. H. and Benton, M. J. (2014), HIGH RATES OF EVOLUTION PRECEDED THE ORIGIN OF BIRDS. Evolution, 68: 1497–1510. doi: 10.1111/evo.12363 A.