Publications by authors named "Ricardo N Martinez"

11 Publications

  • Page 1 of 1

Skull anatomy and phylogenetic assessment of a large specimen of Ecteniniidae (Eucynodontia: Probainognathia) from the Upper Triassic of southern Brazil.

Zootaxa 2018 Aug 9;4457(3):351-378. Epub 2018 Aug 9.

Programa de Pós-Graduação em Biodiversidade Animal, Universidade Federal de Santa Maria, 97105-120 Santa Maria, RS, Brazil..

Ecteniniidae comprises an endemic radiation of carnivore probainognathian cynodonts from the Late Triassic of South America. Three taxa have been included in this clade: Ecteninion lunensis Martínez et al., 1996 and Diegocanis elegans Martínez et al., 2013 from Argentina, and Trucidocynodon riograndensis Oliveira et al., 2010 from Brazil. Herein, a new specimen (skull and mandible) assigned to T. riograndensis from the Carnian of the Candelária Sequence (Southern Brazil) is described. A phylogenetic analysis recovered the new specimen as the sister taxon of the holotype of T. riograndensis, and both in a trichotomy with E. lunensis and D. elegans, all supporting the monophyly of Ecteniniidae. The new specimen of T. riograndensis is almost 20% larger than its holotype. Therefore, it represents one of the largest specimens of a carnivorous probainognathian from the Late Triassic known to date and contributes to knowledge of size variation in ecteniniids.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.11646/zootaxa.4457.3.1DOI Listing
August 2018

An early trend towards gigantism in Triassic sauropodomorph dinosaurs.

Nat Ecol Evol 2018 08 9;2(8):1227-1232. Epub 2018 Jul 9.

Instituto y Museo de Ciencias Naturales, Centro de Investigaciones de la Geósfera y la Biósfera (CIGEOBIO), Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de San Juan, San Juan, Argentina.

Dinosaurs dominated the terrestrial ecosystems for more than 140 Myr during the Mesozoic era, and among them were sauropodomorphs, the largest land animals recorded in the history of life. Early sauropodomorphs were small bipeds, and it was long believed that acquisition of giant body size in this clade (over 10 tonnes) occurred during the Jurassic and was linked to numerous skeletal modifications present in Eusauropoda. Although the origin of gigantism in sauropodomorphs was a pivotal stage in the history of dinosaurs, an incomplete fossil record obscures details of this crucial evolutionary change. Here, we describe a new sauropodomorph from the Late Triassic of Argentina nested within a clade of other non-eusauropods from southwest Pangaea. Members of this clade attained large body size while maintaining a plesiomorphic cyclical growth pattern, displaying many features of the body plan of basal sauropodomorphs and lacking most anatomical traits previously regarded as adaptations to gigantism. This novel strategy highlights a highly accelerated growth rate, an improved avian-style respiratory system, and modifications of the vertebral epaxial musculature and hindlimbs as critical to the evolution of gigantism. This reveals that the first pulse towards gigantism in dinosaurs occurred over 30 Myr before the appearance of the first eusauropods.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41559-018-0599-yDOI Listing
August 2018

Bone cells in birds show exceptional surface area, a characteristic tracing back to saurischian dinosaurs of the late Triassic.

PLoS One 2015 1;10(4):e0119083. Epub 2015 Apr 1.

Museo de Ciencias Naturales, Universidad Nacional de San Juan, San Juan, Argentina.

Background: Dinosaurs are unique among terrestrial tetrapods in their body sizes, which range from less than 3 gm in hummingbirds to 70,000 kg or more in sauropods. Studies of the microstructure of bone tissue have indicated that large dinosaurs, once believed to be slow growing, attained maturity at rates comparable to or greater than those of large mammals. A number of structural criteria in bone tissue have been used to assess differences in rates of osteogenesis in extinct taxa, including counts of lines of arrested growth and the density of vascular canals.

Methodology/principal Findings: Here, we examine the density of the cytoplasmic surface of bone-producing cells, a feature which may set an upper limit to the rate of osteogenesis. Osteocyte lacunae and canaliculi, the cavities in bone containing osteocytes and their extensions, were measured in thin-sections of primary (woven and parallel fibered) bone in a diversity of tetrapods. The results indicate that bone cell surfaces are more densely organized in the Saurischia (extant birds, extinct Mesozoic Theropoda and Sauropodomorpha) than in other tetrapods, a result of denser branching of the cell extensions. The highest postnatal growth rates among extant tetrapods occur in modern birds, the only surviving saurischians, and the finding of exceptional cytoplasmic surface area of the cells that produce bone in this group suggests a relationship with bone growth rate. In support of this relationship is finding the lowest cell surface density among the saurischians examined in Dinornis, a member of a group of ratites that evolved in New Zealand in isolation from mammalian predators and show other evidence of lowered maturation rates.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0119083PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4382344PMC
December 2015

Age constraints on the dispersal of dinosaurs in the Late Triassic from magnetochronology of the Los Colorados Formation (Argentina).

Proc Natl Acad Sci U S A 2014 Jun 19;111(22):7958-63. Epub 2014 May 19.

Instituto y Museo de Ciencias Naturales, Universidad Nacional de San Juan, San Juan 5400, Argentina.

A measured magnetozone sequence defined by 24 sampling sites with normal polarity and 28 sites with reverse polarity characteristic magnetizations was established for the heretofore poorly age-constrained Los Colorados Formation and its dinosaur-bearing vertebrate fauna in the Ischigualasto-Villa Union continental rift basin of Argentina. The polarity pattern in this ∼600-m-thick red-bed section can be correlated to Chrons E7r to E15n of the Newark astrochronological polarity time scale. This represents a time interval from 227 to 213 Ma, indicating that the Los Colorados Formation is predominantly Norian in age, ending more than 11 My before the onset of the Jurassic. The magnetochronology confirms that the underlying Ischigualasto Formation and its vertebrate assemblages including some of the earliest known dinosaurs are of Carnian age. The oldest dated occurrences of vertebrate assemblages with dinosaurs in North America (Chinle Formation) are younger (Norian), and thus the rise of dinosaurs was diachronous across the Americas. Paleogeography of the Ischigualasto and Los Colorados Formations indicates prolonged residence in the austral temperate humid belt where a provincial vertebrate fauna with early dinosaurs may have incubated. Faunal dispersal across the Pangean supercontinent in the development of more cosmopolitan vertebrate assemblages later in the Norian may have been in response to reduced contrasts between climate zones and lowered barriers resulting from decreasing atmospheric pCO2 levels.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1402369111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4050597PMC
June 2014

A new sphenodontian (Lepidosauria: Rhynchocephalia) from the Late Triassic of Argentina and the early origin of the herbivore opisthodontians.

Proc Biol Sci 2013 Dec 16;280(1772):20132057. Epub 2013 Oct 16.

Instituto y Museo de Ciencias Naturales, Universidad Nacional de San Juan, , Avenida España 400 Norte, 5400 San Juan, Argentina, Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, , Buenos Aires, Argentina.

Sphenodontians were a successful group of rhynchocephalian reptiles that dominated the fossil record of Lepidosauria during the Triassic and Jurassic. Although evidence of extinction is seen at the end of the Laurasian Early Cretaceous, they appeared to remain numerically abundant in South America until the end of the period. Most of the known Late Cretaceous record in South America is composed of opisthodontians, the herbivorous branch of Sphenodontia, whose oldest members were until recently reported to be from the Kimmeridgian-Tithonian (Late Jurassic). Here, we report a new sphenodontian, Sphenotitan leyesi gen. et sp. nov., collected from the Upper Triassic Quebrada del Barro Formation of northwestern Argentina. Phylogenetic analysis identifies Sphenotitan as a basal member of Opisthodontia, extending the known record of opisthodontians and the origin of herbivory in this group by 50 Myr.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rspb.2013.2057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3813332PMC
December 2013

A new basal sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), northwestern Argentina.

PLoS One 2011 9;6(11):e26964. Epub 2011 Nov 9.

Museo de Ciencias Naturales, Universidad Nacional de San Juan, San Juan, Argentina.

Background: Argentinean basal sauropodomorphs are known by several specimens from different basins; Ischigualasto, El Tranquilo, and Mogna. The Argentinean record is diverse and includes some of the most primitive known sauropodomorphs such as Panphagia and Chromogisaurus, as well as more derived forms, including several massospondylids. Until now, the Massospondylidae were the group of basal sauropodomorphs most widely spread around Pangea with a record in almost all continents, mostly from the southern hemisphere, including the only record from Antarctica.

Methodology/principal Finding: We describe here a new basal sauropodomorph, Leyesaurus marayensis gen. et sp. nov., from the Quebrada del Barro Formation, an Upper Triassic-Lower Jurassic unit that crops out in northwestern Argentina. The new taxon is represented by a partial articulated skeleton that includes the skull, vertebral column, scapular and pelvic girdles, and hindlimb. Leyesaurus is diagnosed by a set of unique features, such as a sharply acute angle (50 degrees) formed by the ascending process of the maxilla and the alveolar margin, a straight ascending process of the maxilla with a longitudinal ridge on its lateral surface, noticeably bulging labial side of the maxillary teeth, greatly elongated cervical vertebrae, and proximal articular surface of metatarsal III that is shelf-like and medially deflected. Phylogenetic analysis recovers Leyesaurus as a basal sauropodomorph, sister taxon of Adeopapposaurus within the Massospondylidae. Moreover, the results suggest that massospondylids achieved a higher diversity than previously thought.

Conclusions/significance: Our phylogenetic results differ with respect to previous analyses by rejecting the massospondylid affinities of some taxa from the northern hemisphere (e.g., Seitaad, Sarahsaurus). As a result, the new taxon Leyesaurus, coupled with other recent discoveries, suggests that the diversity of massospondylids in the southern hemisphere was higher than in other regions of Pangea. Finally, the close affinities of Leyesaurus with the Lower Jurassic Massospondylus suggest a younger age for the Quebrada del Barro Formation than previously postulated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0026964PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3212523PMC
April 2012

A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea.

Science 2011 Jan;331(6014):206-10

Instituto y Museo de Ciencias Naturales, Universidad Nacional de San Juan, San Juan 5400, Argentina.

Upper Triassic rocks in northwestern Argentina preserve the most complete record of dinosaurs before their rise to dominance in the Early Jurassic. Here, we describe a previously unidentified basal theropod, reassess its contemporary Eoraptor as a basal sauropodomorph, divide the faunal record of the Ischigualasto Formation with biozones, and bracket the formation with (40)Ar/(39)Ar ages. Some 230 million years ago in the Late Triassic (mid Carnian), the earliest dinosaurs were the dominant terrestrial carnivores and small herbivores in southwestern Pangaea. The extinction of nondinosaurian herbivores is sequential and is not linked to an increase in dinosaurian diversity, which weakens the predominant scenario for dinosaurian ascendancy as opportunistic replacement.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1198467DOI Listing
January 2011

A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina.

Zookeys 2010 Oct 19(63):55-81. Epub 2010 Oct 19.

Museo de Ciencias Naturales, San Juan 5400, Argentina.

Herrerasauridae comprises a basal clade of dinosaurs best known from the Upper Triassic of Argentina and Brazil, which have yielded remains of Herrerasaurus ischigualastensis and Staurikosaurus pricei, respectively. Systematic opinion regarding the position of Herrerasauridae at the base of Dinosauria has varied. Here we describe a new herrerasaurid, Sanjuansaurus gordilloi gen. n., sp. n., based on a partial skeleton from Carnian-age strata of the the Upper Triassic Ischigualasto Formation of northwestern Argentina. The new taxon is diagnosed by numerous features, including long, band-shaped and posterolaterally oriented transverse process on the posterior cervical vertebrae; neural spines of the sixth to eighth dorsal vertebrae, at least, bearing acute anterior and posterior processes; scapula and coracoid with everted lateral margins of the glenoid; and short pubis (63% of the femoral length). Phylogenetic analysis placed Sanjuansaurus within a monophyletic Herrerasauridae, at the base of Theropoda and including Herrerasaurus and Staurikosaurus. The presence of Sanjuansaurus at the base of the Ischigualasto Formation, along with other dinosaurs such as Herrerasaurus, Eoraptor, Panphagia, and Chromogisaurus suggests that saurischian dinosaurs in southwestern Pangea were already widely diversified by the late Carnian rather than increasing in diversity across the Carnian-Norian boundary.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3897/zookeys.63.550DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3088398PMC
October 2010

A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha.

PLoS One 2009 11;4(2):e4397. Epub 2009 Feb 11.

Museo de Ciencias Naturales, San Juan, Argentina.

Background: The earliest dinosaurs are from the early Late Triassic (Carnian) of South America. By the Carnian the main clades Saurischia and Ornithischia were already established, and the presence of the most primitive known sauropodomorph Saturnalia suggests also that Saurischia had already diverged into Theropoda and Sauropodomorpha. Knowledge of Carnian sauropodomorphs has been restricted to this single species.

Methodology/principal Findings: We describe a new small sauropodomorph dinosaur from the Ischigualsto Formation (Carnian) in northwest Argentina, Panphagia protos gen. et sp. nov., on the basis of a partial skeleton. The genus and species are characterized by an anteroposteriorly elongated fossa on the base of the anteroventral process of the nasal; wide lateral flange on the quadrate with a large foramen; deep groove on the lateral surface of the lower jaw surrounded by prominent dorsal and ventral ridges; bifurcated posteroventral process of the dentary; long retroarticular process transversally wider than the articular area for the quadrate; oval scars on the lateral surface of the posterior border of the centra of cervical vertebrae; distinct prominences on the neural arc of the anterior cervical vertebra; distal end of the scapular blade nearly three times wider than the neck; scapular blade with an expanded posterodistal corner; and medial lamina of brevis fossa twice as wide as the iliac spine.

Conclusions/significance: We regard Panphagia as the most basal sauropodomorph, which shares the following apomorphies with Saturnalia and more derived sauropodomorphs: basally constricted crowns; lanceolate crowns; teeth of the anterior quarter of the dentary higher than the others; and short posterolateral flange of distal tibia. The presence of Panphagia at the base of the early Carnian Ischigualasto Formation suggests an earlier origin of Sauropodomorpha during the Middle Triassic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004397PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2635939PMC
April 2009

Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina.

PLoS One 2008 Sep 30;3(9):e3303. Epub 2008 Sep 30.

Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, USA.

Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.

Methodology/principal Findings: We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia ("stomach ribs"), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax.

Conclusions/significance: We present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds: (1) Phase I-Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic. (2) Phase II-Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation. (3) Phase III-Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic. (4) Phase IV-Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic. In addition, we conclude: (5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation. (6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0003303PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2553519PMC
September 2008