Introducing Dineobellator notohesperus

Life reconstruction of Dineobellator notohesperus. Artwork by Sergey Krasovskiy

 

The iconic Velociraptor mongoliensis, described by Osborn in 1924, belongs to the Dromaeosauridae, a family of highly derived small to mid-sized theropod dinosaurs closely related to birds. Their fossils have been found in North America, Europe, Africa, Asia, South America and Antarctica. They first appeared in the mid-Jurassic Period, but their fossil record in North America is very poor near the time of their extinction prior to the Cretaceous-Paleogene boundary. The group is characterized by the presence of long, three-fingered forelimbs that ended in sharp, trenchant claws and a tail stiffened by the elongated prezygapophyses.

The description of Dineobellator notohesperus, a new specimen discovered in 2008 in New Mexico, offers a glimpse into the biodiversity of Dromaeosaurids at the end of the Cretaceous. The generic name is derived from the Navajo word Diné, in reference to the people of the Navajo Nation, and the Latin suffix bellator, meaning warrior. The specific name is derived from the Greek word noto, meaning southern, or south; and the Greek word hesper, meaning western.

 

Skeletal reconstruction of Dineobellator notohesperus. From Jasinski et al., 2020

 

The holotype (SMP VP-2430), similar in size to Velociraptor and Saurornitholestes, includes elements of the skull, axial, and appendicular skeleton. The nearly complete right humerus measures 185.78 mm, with an estimated total length of 215 mm. The presence of quill knobs in Dineobellator provides further evidence for feathers throughout Dromaeosauridae. This new specimen co-existed with numerous other theropods, including caenagnathids, ornithomimids, troodontids, and tyrannosaurids.

Dineobellator exhibits some features in the forelimbs that suggest greater strength capabilities in flexion, in conjunction with a relatively tighter grip strength in the manual claws, while the possession of opisthocoelous proximal caudal vertebrae may have increased the agility of Dineobellator and thus may have implications for its predatory behavior, particularly with respect to the pursuit of prey.

 

References:

Jasinski, S.E., Sullivan, R.M. & Dodson, P. New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous. Sci Rep 10, 5105 (2020). https://doi.org/10.1038/s41598-020-61480-7

Senter, P., Kirkland, J. I., DeBlieux, D. D., Madsen, S. & Toth, N. New dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the evolution of the dromaeosaurid tail. PLoS One 7, e36790 (2012). https://doi.org/10.1371/journal.pone.0036790

Osborn, Henry F. (1924a). “Three new Theropoda, Protoceratops zone, central Mongolia”. American Museum Novitates. 144: 1–12. http://hdl.handle.net/2246/3223

 

Introducing Thanatotheristes degrootorum, the Reaper of Death

Thanatotheristes degrootorum. Illustration by Julius Csotonyi

Tyrannosauroidea, the superfamily of carnivorous dinosaurs that includes the iconic Tyrannosaurus rex, originated in the Middle Jurassic, approximately 165 million years ago, and was a dominant component of the dinosaur faunas of the Northern Hemisphere. All tyrannosaurs were bipedal predators characterized by premaxillary teeth with a D-shaped cross section, fused nasals, extreme pneumaticity in the skull roof and lower jaws, a pronounced muscle attachment ridge on the ilium, and an elevated femoral head. But for most of their evolutionary history, tyrannosauroids were mostly small-bodied animals and only reached gigantic size during the final 20 million years of the Cretaceous. To explain their geographic dispersal through Laurasia, one phylogenetic hypothesis suggested a scenario where basal tyrannosaurids (i.e., albertosaurines and Daspletosaurus) occurred in northern locations (Alberta and Montana) and derived tyrannosaurids (i.e. Bistahieversor, Lythronax, and Teratophoneus) occurred farther south (New Mexico and Utah), with the Tyrannosaurus evolving from the southern group during the Maastrichtian.

The recently described Thanatotheristes degrootorum, from the middle Campanian of the Foremost Formation of Alberta, Canada, is the oldest tyrannosauroid known from Canada and is approximately 2.5 million years older than Gorgosaurus libratus and Daspletosaurus torosus from the Oldman and Dinosaur Park formations. This new specimen provides a new tool to understand the evolution and paleogeographic distribution of Tyrannosauridae.

Jaw bones of Thanatotheristes degrootorum. Image credit: Jared Voris

The holotype (TMP 2010.5.7) includes the right maxilla, right jugal, right postorbital, right surangular, right quadrate, right laterosphenoid, left frontal, and both dentaries. The presence of a well-developed ornamentation on the maxilla suggests the individual was probably sexually mature. A referred specimen (TMP 2018.016.0001) is based on a partial right maxilla from a subadult individual, and it was found approximately 10 km northeast of Hays, Alberta. The name derived from Thanatos the Greek god of death, and theristes (Greek), harvester or reaper. The specific name honors John and Sandra De Groot, who discovered the holotype specimen.

The new taxon is one of the earliest tyrannosaurid from North America, and is roughly equivalent in age to Dynamoterror dynastes from the Menefee Formation of northern New Mexico, but is slightly younger than Lythronax argestes from the Wahweap Formation of southern Utah.

Thanatotheristes skull. Image credit: Jared Voris

Phylogenetic analysis suggests that Thanatotheristes is most closely related to Daspletosaurus. Together, they form the clade Daspletosaurini, a group of long and deep-snouted tyrannosaurines. Thanatotheristes differs from Daspletosaurus in several characters. For instante, in Thanatotheristes the contact surface for the jugal on the postorbital is braced by a robust ridge that extends to the posterior margin of the postorbital. Furthermore, Thanatotheristes lacks two synapomorphies diagnostic for Daspletosaurus. First, the posterior bifurcation of the antotic crest of the laterosphenoid is an indistinct ridge rather than a prominent shelf-forming crest. Second, the symphyseal surface of the dentary only displays low anteroposterior ridges and lacks large interlocking bony projections.

The addition of more basal tyrannosaurid clades reveals that at least five major lineages evolved within Tyrannosauridae, with different skeletal morphotypes linked to differences in paleoecology, such as prey composition or hunting/feeding strategies.

 

References:

Voris, J.T., Therrien, F., Zelenitsky, D.K., Brown, CM., A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids, Cretaceous Research, https://doi.org/10.1016/j.cretres.2020.104388.

 

Introducing Wulong bohaiensis, the dancing dragon

Wulong bohaiensis. From Poust et al., 2020

Birds are the most species-rich class of tetrapod vertebrates. They originated from a theropod lineage more than 160 million years ago. The evolutionary history of Birds is at the root of the paravian radiation, when dromaeosaurids, troodontids, and avialans were diverging from one another. Within the clade Paraves we found the morphology and soft tissue changes associated with the origin of modern avian flight. One of this key changes was the difference of nearly four orders of magnitude in body size, a pivotal element in the origin of powered avian flight. 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.
The Jehol Biota included two formations: the Yixian Formation, and the Jiufotang Formation, and contain the most diversified avifauna known to date. Among them are the long bony-tailed Jeholornis, only slightly more derived than Archaeopteryx, and many fossils of troodontids like Mei long, Sinovenator changii, Sinusonasus magnodens and Jinfengopteryx elegans. Now, the recently described Wulong bohaiensis, from the Jiufotang Formation, shed new light on the evolution of Birds. This small, feathered dromaeosaurid theropod lived in the Early Cretaceous (Aptian) and was discovered by a farmer more than a decade ago. The holotype (D2933) is a complete articulated skeleton (only some ribs are missing)and exhibits special preservation of keratinous structures.

An X-ray of Wulong showing wrist and vertebra detail on the right. (Poust et al., 2020)

Wulong (meaning “dancing dragon”) is distinguished by the following autapomorphic features: long jugal process of quadratojugal, cranially inclined pneumatic foramina on the cranial half of dorsal centra, transverse processes of proximal caudals significantly longer than width of centrum, presence of 30 caudal vertebrae producing a proportionally long tail, distally located and large posterior process of the ischium, and large size of supracoracoid fenestra (>15% of total area). The holotype has several gross osteological markers of immaturity like the unfused dorsal and sacral vertebrae, but mature feathers are present across the entire body of Wulong.

The feathered dinosaurs from the Jehol Biota are key to understand the origin of birds and dinosaur behavior. In modern birds development of ornamental feathers is generally timed to co-occur with sexual maturity. The presence of such elaborate feathers in the immature Wulong demonstrates that nonavian dinosaurs had a very different strategy of plumage development then their living relatives.

References:

Poust, AW; Gao, C; Varricchio, DJ; Wu, J; Zhang, F (2020). “A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids”. The Anatomical Record. American Association for Anatomy. doi:10.1002/ar.24343

Introducing Asfaltovenator vialidadi

Skeletal reconstruction and postcranial anatomy of Asfaltovenator vialidadi, MPEF PV 3440. From Rauhut and Pol, 2019.

During the Jurassic (201-145 mya) the breakup of the supercontinent Pangaea continued and accelerated with the opening of the North Atlantic by the rifting of Africa and North America, giving rise to the supercontinents of Laurasia and Gondwana. The sea level rise flooded continental areas around Pangaea, forming huge epicontinental seas, especially in northern Africa and eastern Laurasia (modern China). The world was predominantly warm with at least four times the present level of atmospheric CO2. The period is also characterized by the explosive adaptive radiation of dinosaurs.

By the Mid-Jurassic, Gondwana, the southern margen of supercontinent Pangea started to break up in different blocks: Antarctica, Madagascar, India, and Australia in the east, and Africa and South America in the west. During this period, the Tetanurae reached a global distribution. Tetanuran theropods comprise the majority of Mesozoic predatory dinosaurs, including Allosaurus and Tyrannosaurus, and the lineage leading to extant birds. Unfortunatelly, the fragmentary nature of the earliest known members of this group difficults our understanding of their early radiation. Asfaltovenator vialidadi gen. et sp. nov., a new basal tetanuran from the Middle Jurassic of Argentina, shed new ligth on the early radiation of this group. The generic name refers from Cañadón Asfalto Formation, the site where the fossil was found, and venator, a Greek word for hunter. The specific name honors the Administración de Vialidad Provincial of Chubut and the Dirección Nacional de Vialidad, for their aid to the Museo Paleontológico Egidio Feruglio.

Cranial anatomy of Asfaltovenator vialidadi. From Rauhut and Pol, 2019.

Discovered in 2002 by Leandro Canesa, the holotype (MPEF PV 3440) includes an almost complete skull and a partial skeleton. The skull is high and slightly arched, similar to that of other allosauroids and reached 75–80 cm long. The estimated body length of the holotype is 7–8 m, which makes Asfaltovenator comparable in size to the well-known Allosaurus.

Asfaltovenator shows an unusual mosaic of tetanuran characters. Megalosauroid characters include a pronounced kink in the anterodorsal margin of the maxillary ascending process, a medially closed maxillary fenestra, a deep posterior groove on ventral process of postorbital, and a broad fossa below the occipital condyle. Allosauroid characters include the presence of a pronounced supranarial fossa, the nasal participation in the antorbital fossa, presence of pneumatic foramina in the nasal, and lateral nasal crests.

llustration of the Asfaltovenator (Credit: Gabriel Lio/Conicet)

Tetanurae has been tradionally divided in three major clades: Megalosauroidea, Coelurosauria, and Allosauroidea. The phylogenetic analysis of A. vialidadi suggest that Allosauroidea  and Megalosauroidea have a common ancestor that they do not share with coelurosaurs. The new study also suggest that the Pliensbachian-Toarcian extinction event was a potential driver of tetanuran radiation.

References:

Rauhut, Oliver W. M.; Pol, Diego (2019), Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs https://www.nature.com/articles/s41598-019-53672-7

Carrano, M. T., Benson, R. B. J., & Sampson, S. D. (2012). The phylogeny of Tetanurae (Dinosauria: Theropoda). Journal of Systematic Palaeontology, 10(2), 211–300. doi:10.1080/14772019.2011.630927

Gnathovorax cabreirai and the origin of predatory dinosaurs

Skull of Gnathovorax cabreirai. From Pacheco et al., 2019

Herrerasauridae is a basal clade of predatory, obligatorily bipedal dinosaurs recorded from the Upper Triassic of Argentina and Brazil (although are putative records of herrerasaurids from the mid-late Norian strata of Europe and North America). The clade unequivocally comprises three species: Herrerasaurus ischigualastensis, Sanjuansaurus gordilloi, both from the Ischigualasto Formation of Argentina, and Staurikosaurus pricei, from the lower portion of the Santa Maria Formation of southern Brazil. Now, a new specimen from the Santa Maria Formation shed light into poorly understood aspects of the Herrerasauridae anatomy.

Named Gnathovorax cabreirai, the new dinosaur was found in 2014 at the Marchezan site, municipality of São João do Polêsine, Rio Grande do Sul, Brazil. The generic name means “jaws inclined to devour”. The specific name honors Dr. Sérgio Furtado Cabreira, the palaeontologist that found the specimen. The Santa Maria Formation in southern Brazil, comprises a succession of Middle to Late Triassic sedimentary rocks that have been long renowned for their rich tetrapod fossils including one of the oldest (and the best preserved) associations of dinosaur and dinosaur precursor.

Photographs and reconstruction of the braincase and endocast of Gnathovorax cabreirai. From Pacheco et al., 2019.

Gnathovorax lived around 230 million years ago and measured about three meters in length. The holotype (CAPPA/UFSM 0009) is an almost complete and partially articulated skeleton. The skull is almost entirely preserved. Among other characters, Gnathovorax presents three premaxillary teeth; an additonal fenestra between the maxilla and premaxilla contact; two well defined laminae in the antorbital fossa of the maxilla, with a depression between them. The proximal portion of the femur lacks a caudomedial tuber. The tibia equals 90% of the femoral length and there are three phalanges in pedal digit V.

The study of the internal anatomy of the skull through CT-scanning reveals several aspects of the neuroanatomy of this group. The presence of a well-developed floccular fossa lobes of the cerebellum is related to motor control of the eye and head, which in turn may be related to the predatory habit of the group.

References:
Pacheco C, Müller RT, Langer M, Pretto FA, Kerber L, Dias da Silva S. 2019. Gnathovorax cabreirai: a new early dinosaur and the origin and initial radiation of predatory dinosaurs. PeerJ 7:e7963 https://doi.org/10.7717/peerj.7963

Meet Ferrisaurus sustutensis, the iron lizard from the Sustut River.

 

Preserved elements of the holotype of Ferrisaurus sustutensis. From Arbour and Evans, 2019.

In 1971, during uranium and thorium exploration in the Sustut Basin of northern British Columbia, Canada, Kenny F. Larsen registered above-background levels of radiation from a talus slope near the confluence of Birdflat Creek and the Sustut River. The source of this radiation were the fossil remains of an unknow dinosaur. Larsen, an economic geologist, donated the bones to the Dalhousie University (Halifax, NS) in 2004. Later, the specimen was accessioned into the collection of the Royal British Columbia Museum in Victoria, BC.

Initially described as a pachycephalosaur or a basal ornithopod similar to Thescelosaurus, a new study determined that the remains belongs to a new genus and species: Ferrisaurus sustutensis. The holotype (RBCM P900) includes portions of the pectoral girdles, left forelimb, left hindlimb, and right pes. The name derived from Latin ferrum (=iron) and Greek sauros (=lizard), referencing to the specimen’s discovery along a railway line. The specific name honors its provenance near the Sustut River and within the Sustut Basin.

Pedal elements of Ferrisaurus sustutensis compared to other Laramidian small-bodied ornithischians. From Arbour and Evans, 2019.

Despite the lack of cranial material Ferrisaurus can be placed within leptoceratopsids based on several aspects of the preserved phalanges. Leptoceratopsids were short-frilled, hornless ceratopsians that lived in Campanian–Maastrictian aged dinosaur assemblages from Asia and North America. Ferrisaurus measured about 1.75 metres in length and 150 kilograms in weight and is similar in size to large specimens of Leptoceratops and Cerasinops.

 

References:

Arbour VM, Evans DC. 2019. A new leptoceratopsid dinosaur from Maastrichtian-aged deposits of the Sustut Basin, northern British Columbia, Canada. PeerJ 7:e7926 https://doi.org/10.7717/peerj.7926

Arbour, V. M., & Graves, M. C. (2008). An ornithischian dinosaur from the Sustut Basin, north-central British Columbia, Canada. Canadian Journal of Earth Sciences, 45(4), 457–463. doi:10.1139/e08-009 

A new dinosauriform specimen from the Chañares Formation of north-western Argentina.

 

(A) preserved bones of CRILAR-Pv 552 in approximate anatomical arrangement. (B) skeletal reconstruction of Lewisuchus admixtus. From Ezcurra et. al, 2019.

Formed during the breakup of Gondwana, the Chañares Formation is part of the Ischigualasto-Villa Unión Basin, and represents one of the most continuous continental Triassic succesions in South America. Volcanism have played an important role in the generation and preservation of the Chañares Formation’s exceptional tetrapod fossil record. The diverse and well-preserved tetrapod assemblage includes proterochampsids, pseudosuchians, ornithodirans, large dicynodonts and smaller cynodonts. Almost all dinosauromorphs are preserved in diagenetic concretions that erode out of a thick siltstone interval 15–20 m above the base of the formation, and include Lagosuchus talampayensis, Marasuchus lilloensis, Lewisuchus admixtus, and Pseudolagosuchus major. 

Unfortunatelly, our knowledge about Lewisuchus admixtus, and Pseudolagosuchus major are based on partial skeletons that has generated a contentious debate during the last 20 years about the synonymy between two of these species. The discovery of a new dinosauriform partial skeleton (CRILAR‐Pv 552) allows comparisons for the first time with both Lewisuchus admixtus and Pseudolagosuchus major.

Geological map of the Chañares–Gualo area in Talampaya National Park (From Marsicano et al., 2015)

The new specimen was found in 2013, and includes fragments of both premaxillae and maxillae, partial right jugal, right quadrate, fragment of right pterygoid, supraoccipital, both prootics, parabasisphenoid, right dentary lacking posterior end, anterior end of left dentary, partial right retroarticular complex, an isolated tooth, three or four anteriormiddle cervical vertebrae, distal half of a posterior cervical or dorsal neural spine, two middleposterior dorsal vertebrae, two sacral vertebrae, two consecutive anterior caudal vertebrae, eight to ten middle-distal caudal vertebrae, two haemal arches, base of the left scapular blade, partial left coracoid, distal half of right humerus, proximal region and distal end of left ulna, distal end of left radius, proximal region of a metacarpal, partial ilia, proximal end of left pubis, distal end of both pubes, partial left ischium, both partial femora, almost complete left tibia, distal end of right tibia, partial left half of fibula, partial fibular shaft, and some possible metatarsal shaft fragments. Based on the unique combination of cranial and postcranial characters, CRILAR-Pv 552 can be referred to Lewisuchus admixtus, and supports the hypothesis that Pseudolagosuchus major is a subjective junior synonym of Lewisuchus admixtus.

 

References:

Ezcurra, M. D., Nesbitt, S. J., Fiorelli, L. E., & Desojo, J. B. (2019). New specimen sheds light on the anatomy and taxonomy of the early Late Triassic dinosauriforms from the Chañares Formation, NW Argentina. The Anatomical Record. doi:10.1002/ar.24243

Marsicano, C. A.Irmis, R. B.Mancuso, A. C.Mundil, R. & Chemale, F., The precise temporal calibration of dinosaur origins, Proc. Natl Acad. Sci. USAhttp://dx.doi.org/10.1073/pnas.1512541112 (2015).

Introducing Notatesseraeraptor frickensis.

Notatesseraeraptor frickensis at the Sauriermuseum Frick. (From Wikimedia Commons)

Over the last two decades our knowledge of the fossil record of early theropod dinosaurs has greatly improved. However, there are different hypotheses about their relationships. Theropods are relatively abundant in post-Carnian Triassic faunas, including the European Liliensternus, the South American Zupaysaurus, and the North American Coelophysis. Those taxons represent the earliest major radiation of Neotheropoda. Two primitive branches of this clade are the Coelophysoidea and the Dilophosauridae. More recent studies suggest that at least some members of the ‘traditional Coelophsoidea’ are more closely related to the tetanurans and that the Dilophosauridae may represent a second clade of early non-averostran neotheropods. Notatesseraeraptor frickensis gen. et sp, from the Late Triassic of Switzerland, provides new clues about the relationships of the early theropods.

The new specimen belong to an immature individual of length 2.6–3.0 m, and it was collected in 2006 from Gruhalde clay pit in Frick (Aargau, Switzerland), a place well known for its abundant, articulated Plateosaurus material. The genus name derives from the Latin “nota” meaning feature and “tesserae”, a word used to describe glass, or other material used in the construction of a mosaic, in reference to the interesting mixture of characters found in the fossil.

Skeletal anatomy of N. frickensis gen. et sp. nov. From Zahner and Brinkmann, 2019.

The new specimen was described based on a cranium (SMF 09-2) and partial postcranial skeleton (SMF 06-1). The cranium is proportionally long and low as is commonly found in traditional coelophysoid-grade neotheropods. But in contrast to coelophysids, the premaxillary tooth crowns of N. frickensis are all strongly recurved, laterally compressed and bear fine serrations. The postcranial skeleton includes two articulated forelimbs, 13 dorsal, four sacral and four proximal caudal vertebrae; cervical, dorsal and sacral ribs; chevrons; gastralia; and even stomach contents ( a well-preserved maxilla of the rhynchocephalian Clevosaurus). The preserved postcranial elements share most of their morphological similarities with ‘Syntarsus’ kayentakatae. N. frickensis has plesiomorphically long forelimbs. The radius is about three-quarters of the length of the humerus. The manus is composed of four digits, whereas the fourth is reduced to a very slim metacarpal. The shape of the ilium are similar to those found in Coelophysis.  

The phylogenetic analyses, with emphasis on early neotheropods, suggests that Notatesseraeraptor is a basal member of Dilophosauridae, a clade that comprises Dilophosaurus, and Cryolophosaurus.

 

References:

Marion Zahner; Winand Brinkmann (2019). “A Triassic averostran-line theropod from Switzerland and the early evolution of dinosaurs”. Nature Ecology & Evolution. doi:10.1038/s41559-019-0941-z

Martín D. Ezcurra, and Federico L. Agnolín (2017). Gondwanan perspectives: Theropod dinosaurs from western Gondwana. A brief historical overview on the research of Mesozoic theropods in Gondwana. Ameghiniana 54: 483–487. https://doi.org/10.5710/102.054.0501

 

Hesperornithoides miessleriis and the evolution of flight.

Primary blocks of Hesperornithoides specimen WYDICE-DML-001. Images taken by Levi Shinkle. From Hartman et al., 2019.

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. In recent years, several discovered fossils as well as innovative studies of living bird behavior, have enriched our understanding of early paravian evolution and flight origins. The discovered fossils demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system have a sequential and stepwise transformational pattern, with many arising early in dinosaur evolution, like the unusually crouched hindlimb for bipedal locomotion,the furcula and the “semilunate” carpal that appeared early in the theropod lineage.

The new paravian theropod, Hesperornithoides miessleriis, from the Late Jurassic Morrison Formation of east–central Wyoming, provides new clues about paravian relationships, as well as the acquisition of flight-related characters in stem avians. Nicknamed “Lori”, and with an estimated length of 89 cm, the new specimen is significantly smaller than other relatively complete theropods from the Morrison Formation. Hesperornithoides lived in a wetland environments with herbaceous plants, but no trees. The habitat, combined with limb proportions indicate that the new specimen was clearly terrestrial.

Association of skeletal elements of Hesperornithoides miessleriis assembled from 3D scans of specimen blocks. Scale bar = 6 cm. From Hartman et al., 2019

Hesperornithoides exhibits the following combination of characters: pneumatic jugal; short posterior lacrimal process; quadrate forms part of lateral margin of paraquadrate foramen; small external mandibular fenestra, humeral entepicondyle >15% of distal humeral width; manual ungual III subequal in size to ungual II; mediodistal corner of tibia exposed anteriorly. The holotype (WYDICE-DML-001) is a partially articulated skeleton consisting of an almost articulated skull, five cervical vertebrae, isolated anterior dorsal rib, portions of 12 caudal vertebrae, five chevrons, partial left scapula and coracoid, portions of the proximal left humerus and distal right humerus, left ulna and radius, radiale, semilunate carpal, left metacarpals I–III, manual phalanges III-2 and 3, manual unguals I, II, and III, ilial fragment, most of an incomplete femur, right and left tibiae and fibulae, left astragalus and calcaneum, portions of right and left metatarsal packets, left pedal phalanges III-1, III-2, III-3, IV-1, IV-2, IV-3, IV-4, and pedal unguals II and III and the proximal portion of IV. The cranial elements are preserved in a separate “skull block”, whereas the axial skeleton is distributed across three blocks.

The acquisition of powered flight in birds was preceded in the course of paravian evolution by a complex sequence of anatomical and functional innovations, and many characters associated with avian flight evolved in a terrestrial context. For this reason, a refined and robust phylogeny of paravians is imperative in order to elucidate the sequence of evolutionary stages that resulted in the acquisition of major avian traits.

 

References:

Hartman S, Mortimer M, Wahl WR, Lomax DR, Lippincott J, Lovelace DM. 2019A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flightPeerJ 7:e7247 https://doi.org/10.7717/peerj.7247

Agnolin FL, Motta MJ, Egli FB, Lo Coco G, Novas FE. 2019. Paravian phylogeny and the dinosaur-bird transition: an overview. Frontiers in Earth Science 6:252 https://www.frontiersin.org/articles/10.3389/feart.2018.00252/full

Introducing Kaijutitan, the strange beast.

The entrance to the town of Rincón de los Sauces.

Since the discovery of dinosaur remains in the Neuquen basin in 1882, Argentina has gained the title of Land of the Giants. The tittle was reinforced by the discoveries of titanosaurs like Argentinosaurus, Dreadnoughtus, Notocolossus, Puertasaurus, and Patagotitan. The study of this diverse group of sauropod dinosaurs embrace an extensive list of important contributions, which started with Richard Lydekker’s pioneering work on Patagonian dinosaurs, and by the classic Friedrich von Huene monograph on Argentinean saurischians and ornithischians.

Titanosaurus were a diverse group of sauropod dinosaurs represented by more than 30 genera, which included all descendants of the more recent common ancestor of Andesaurus and Saltasaurus. The group includes the smallest (e.g. Rinconsaurus, Saltasaurus; with estimated body masses of approximately 6 tonnes) and the largest sauropods known to date. They had their major radiation during the middle Early Cretaceous. The evolution of body mass in this clade is key element to understand sauropod evolution.

 

Cranial elements of MAU-Pv-CM-522/1. From Filippi et al., 2019.

Kaijutitan maui, is the first basal sauropod titanosaur from the Sierra Barrosa Formation (Upper Coniacian, Upper Cretaceous). The holotype (MAU-Pv-CM-522) consists of cranial, axial, and appendicular elements presenting an unique combination of plesiomorphic and apomorphic characters. The generic name Kaijutitan is derived from Kaiju, Japanese word that means “strange beast” or “monster”, and titan, from the Greek “giant”.  The species name refers to the acronym of the Museo Municipal Argentino Urquiza, Rincon de los Sauces, Neuquén, Argentina.

The cranial elements of this specimen include the complete neurocranium (the supraoccipital, exoccipital, left paraoccipital process, left exoccipital-opisthotic-prootic complex, left laterosphenoid and orbitosphoid, and basioccipital-basisphenoid complex). The impossibility of recognizing clear sutures suggest an ontogenetic adult stage of the specimen. One of the most notable autapomorphies exhibited by Kaijutitan is the anterior cervical vertebra with bifid neural spine, a feature usually found in diplodocids and dicraeosaurids. Unfortunately, the femur and humerus of Kaijutitan maui are incomplete, therefore the body mass of this titanosaur can only be estimated by comparison with other titanosauriforms. Kaijutitan would have had a body mass similar or intermediate to that of Giraffatitan (38.000 kg) and Notocolossus (60.398 kg).

 

References:

Filippi, L.S., Salgado, L., Garrido, A.C., A new giant basal titanosaur sauropod in the Upper Cretaceous (Coniacian) of the Neuquén Basin, Argentina, Cretaceous Research, https://doi.org/10.1016/j.cretres.2019.03.008.