Guillermo Rougier

• Professor
• Professor (Full) at University of Louisville

Dryolestoid mammals are classical members of the Jurassic faunas of Laurasia but mostly absent during the Cretaceous. The reverse is true in Gondwana in general and South America in particular, where meridiolestid dryolestoids are dominant in the Late Cretaceous. We describe here 21 new mammalian specimens from the Upper Cretaceous locality Cerro T...

La Formación La Colonia aflora en el borde sureste de la meseta de Somún Curá, en el norte de la provincia de Chubut. Los ambientes de depositación corresponden a fluviales, marino-marginales y marino-someros y se estima una edad entre el Campaniano y el Paleoceno para toda la unidad. Numerosas campañas paleontológicas llevadas a cabo desde princip...

The ichnogenus Ameghinichnus patagonicus described by Casamiquela in 1960, from the Middle Jurassic of Patagonia was the first evidence of a Mesozoic mammal in the continent. The trackways showed a sophisticated, ricochetal locomotion pattern, largely unsuspected at the time and with a surprisingly numerical abundant in the fossil site. Later on, o...

Non-mammaliaform cynodonts, formerly called “mammal-like reptiles,” illustrate earlier states of the morphological architecture in the mammalian lineage. These mammalian forerunners show unique character combinations without direct counterparts among living vertebrates reflecting adaptations long lost along the millions of years of cynodont history...

The enigmatic Gondwanatheria includes mammals with a mosaic of plesiomorphic and apomorphic cranial and dental features challenging our attempts to reconstruct their phylogenetic affiliation. They are generally perceived as sharing a closer ancestor with multituberculates than with therians in a variably conceived Allotheria. Two major groups are c...

Dryolestoids are iconic members of the Mesozoic mammalian associations in South America. They achieved a large taxonomic diversity in this region with disparate dental and cranial morphotypes ranging from the classical role of sharp-toothed insectivores to bunodont, complex dentitions reflecting omnivore/herbivore adaptations. The South American ra...

The cranium of Adalatherium hui, as represented in the holotype and only specimen (UA 9030), is only the second known for any gondwanatherian mammal, the other being that of the sudamericid Vintana sertichi. Both Adalatherium and Vintana were recovered from the Upper Cretaceous (Maastrichtian) Maevarano Formation of northwestern Madagascar. UA 9030...

The lower jaw of the holotype of Adalatherium hui, from the Late Cretaceous of Madagascar, is the most complete yet known for a gondwanatherian mammal. It reveals for the first time the morphology of the character-rich ascending ramus of the dentary in a gondwanatherian. Each half of the lower jaw is composed of only one bone, the dentary, which is...

The phylogenetic position of Gondwanatheria within Mammaliaformes has historically been controversial. The well-preserved skeleton of Adalatherium hui from the Late Cretaceous of Madagascar offers a unique opportunity to address this issue, based on morphological data from the whole skeleton. Gondwanatheria were, until recently, known only from fra...

The dentition in the only known specimen of Adalatherium hui, a gondwanatherian mammal from the Late Cretaceous of Madagascar, is markedly different from that of any previously known mammaliaform, extinct or extant. The two preserved upper incisors and single lower incisor of Adalatherium are each very large, open-rooted, and bear a restricted band...

We describe here a new small bunodont metatherian from Priabonian deposits of the Geste Formation exposed in the Puna of Catamarca Province (Argentina). The material, an isolated right M2?, was recovered by screen-washing techniques and allows us to erect the new species Apeirodon sorianoi. The combination of diagnostic characters includes triangul...

A fossil gastric pellet from the Danian 'Banco Negro Inferior' of the Salamanca Formation at Punta Peli-gro Locality (Chubut, Argentina) and its 3D preserved fossil content is studied herein. The structure of the pellet and the condition of the enclosed bones suggest that it was produced by a bird of prey, although birds of any kind are as yet unkn...

The fossil record of mammaliaforms (mammals and their closest relatives) of the Mesozoic era from the southern supercontinent Gondwana is far less extensive than that from its northern counterpart, Laurasia1,2. Among Mesozoic mammaliaforms, Gondwanatheria is one of the most poorly known clades, previously represented by only a single cranium and is...

The development of caenolestid marsupials (order Paucituberculata) is virtually unknown. We provide here the first description of Caenolestes fuliginosus embryos collected in the Colombian Central Andes. Our sample of four embryos comes from a single female caught during a fieldtrip at Río Blanco (Manizales, Caldas), in 2014. The sample was process...

New dental and dentary fossils collected in the Upper Cretaceous La Colonia Formation in central Patagonia provide new evidence on the morphology, feeding ecology, and relationships of the enigmatic mammal Reigitherium. The newly discovered specimens described here include elements of the upper dentition and several partial dentaries, elucidating f...

Madtsoiids constitute a successful group of extinct snakes widely distributed across Gondwana and the European archipelago during Late Cretaceous times, surviving in reduced numbers to the Pleistocene. They are renowned for including some of the largest snakes that have ever crawled on earth, yet diverse small madtsoiids are also known. Uncovering...

Here we describe the bony anatomy of the inner ear and surrounding structures seen in three plesiomorphic crown mammalian petrosal specimens. Our study sample includes the triconodont Priacodon fruitaensis from the Upper Jurassic of North America, and two isolated stem therian petrosal specimens colloquially known as the Höövör petrosals, recovered...

The Paleogene record of notoungulates in Northwestern Argentina is relatively abundant and most taxa are endemic. Additionally, until now different fossil-bearing units have no species in common, preventing biostratigraphic correlations, general comparisons for some fossil-bearing units, and the discovery of biogeographic patterns. Here we present...

In non-mammalian amniotes, the parasphenoid is a midline dermal element with a narrow rostral portion, the cultriform process, linked to the interorbital septum and an expanded distal portion, the alae or wings, forming part of the ventral skull base. In mammals, the parasphenoid has not been found in extant monotremes and only a handful of reports...

Here we describe the bony anatomy of the inner ear and surrounding structures seen in three of the most plesiomorphic crown mammalian petrosal specimens in the fossil record. Our study sample includes the stem therian taxa Priacodon fruitaensis from the Upper Jurassic of North America, and two isolated petrosal specimens colloquially known as the H...

To interpret the fundamental differences in the structure and origin of the braincase sidewalls of monotremes, multituberculates, and therians, we examined MicroCT scans of a mammaliaform, Morganucodon; two non-mammalian cynodonts, Massetognathus and Probainognathus; a stem therian, Vincelestes; a juvenile and adult monotreme, Ornithorhynchus; and...

The first Mesozoic mammals in North America were discovered in the Morrison Formation during the closing decades of the 19th century, as by-products of dinosaurs quarried by teams led by O.C. Marsh. These tiny fossils served as foundational specimens for our understanding of Mesozoic mammal evolution. There are now nearly 25 mammal-bearing localiti...

The first Mesozoic mammals in North America were discovered in the Morrison Formation during the closing decades of the 19th century, as by-products of dinosaurs quarried by teams led by O.C. Marsh. These tiny fossils served as foundational specimens for our understanding of Mesozoic mammal evolution. There are now nearly 25 mammal-bearing localiti...

Among the collections made during the 1896–1899 Princeton Expeditions to Patagonia are three specimens with partial crania and postcrania of Necrolestes patagonensis Ameghino, 1891, from Santa Cruz Province, Argentina. Necrolestes has anatomical specializations found in extant subterranean mammals, and other features identifying Necrolestes as a la...

Saltasaurine titanosaurs are characterized by their relatively small size compared to other sauropods, extreme postcranial pneumaticity, and dermal armour covering the body. This group has been reported in the Upper Cretaceous of the Lecho, Allen, and Anacleto formations of Argentina. We describe here a new saltasaurine specimen (MACN-Pv RN 233) fr...

Eoastrapostylops riolorense Soria and Powell, 1981, is a primitive meridiungulate mammal known by two specimens from the early Paleogene Río Loro Formation, in NW Argentina. The holotype and most complete specimen is an almost complete skull, mandible, and a few associated postcranial elements. Eoastrapostylops is one of the oldest South American u...

The multituberculate Mangasbaatar udanii gen. et sp. n., represented by two specimens from Udan Sayr locality in the Gobi desert (Mongolia), is a derived member of a speciose group of Late Cretaceous Mongolian multituberculates (LCMM), clustering together with large-size forms such as Catopsbaatar, Tombaatar, and Djadochtatherium, forming a monophy...

Background. Condorchelys antiqua is a stem turtle previously described from the Queso Rallado Locality, Cañadón Asfalto Formation (Early-Middle Jurassic), Chubut, Argentina. In 2014 a skull (MPEF-PV 10900) and an articulated shell with associated postcranial remains (MPEF-PV 10884) of C . antiqua were discovered in the mentioned locality. Methods....

Background. Condorchelys antiqua is a stem turtle previously described from the Queso Rallado Locality, Cañadón Asfalto Formation (Early-Middle Jurassic), Chubut, Argentina. In 2014 a skull (MPEF-PV 10900) and an articulated shell with associated postcranial remains (MPEF-PV 10884) of C . antiqua were discovered in the mentioned locality. Methods....

Rhynchocephalian lepidosaurs, though once widespread worldwide, are represented today only by the tuatara (Sphenodon) of New Zealand. After their apparent early Cretaceous extinction in Laurasia, they survived in southern continents. In South America, they are represented by different lineages of Late Cretaceous eupropalinal forms until their disap...

We describe a new species of the basal mammaliaform Docodon, D. apoxys, sp. nov., represented by three nearly complete dentaries from the Upper Jurassic Morrison Formation of central Colorado. This species differs from other known species of Docodon in the relative heights of the principal molar cusps and in the size of the distal molars. In additi...

Tree-building with diverse data maximizes explanatory power. Application of molecular clock models to ancient speciation events risks a bias against detection of fast radiations subsequent to the Cretaceous-Paleogene (K-Pg) event. Contrary to Springer et al., post–K-Pg placental diversification does not require “virus-like” substitution rates. Even...

To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated wit...

We report here the first amphilestid triconodont from the Jurassic of South America. The specimen, a single isolated molariform, was found at the Queso Rallado locality from where a growing mammalian fauna is known (including a triconodontid, two australosphenidans, and an as yet undescribed allotherian). The specimen, interpreted as a left lower t...

The early Miocene mammal Necrolestes patagonensis from Patagonia, Argentina, was described in 1891 as the only known extinct placental "insectivore" from South America (SA). Since then, and despite the discovery of additional well-preserved material, the systematic status of Necrolestes has remained in flux, with earlier studies leaning toward plac...

The Punta Peligro fauna includes some of the oldest Cenozoic South American mammals, and the oldest ones for Patagonia. In addition to frogs, turtles, and crocodiles, an unusual mammalian assemblage is formed by a mixture of Mesozoic lineages of Gondwanan origin and therians (eutherians and metatherians) derived from Laurasian immigrants. This pape...

Herein we describe a new rhynchocephalian taxon from the Middle Jurassic of Patagonia, Argentina, representing the first Jurassic record of the group in South America. The new taxon, consisting of a complete dentary, is ascribed to Sphenodontia based on the presence of a deep and wide Meckelian groove, long posterior process, well-developed coronoi...

Abstract: Enantiornithes is a diverse clade of Mesozoic birds first recognized from the Upper Cretaceous sediments of a south American locality in northern Argentina. Extensive discoveries of mesozoic birds have since been made globally, and three other South American localities have subsequently produced enantiornithine material. here, we report a...

Dryolestoids are an extinct mammalian group belonging to the lineage leading to modern marsupials and placentals. Dryolestoids are known by teeth and jaws from the Jurassic period of North America and Europe, but they thrived in South America up to the end of the Mesozoic era and survived to the beginnings of the Cenozoic. Isolated teeth and jaws f...

Argentoconodon fariasorum is the only triconodont from the Jurassic of South America. Originally described on the basis of an upper molariform, A. fariasorum is now known by several specimens, including one that preserves most of its dentition, upper and lower jaws, and several postcranial elements. Close anatomical similarity exists between Argent...

Almost 25 years ago, an isolated mammalian molar from the Late Cretaceous Los Alamitos Formation, Patagonia, Argentina was reported by Bonaparte and Soria (1985). The specimen served as the type of Mesungulatum houssayi and was originally interpreted as a condylarth-eutherian. However, it was promptly re-interpreted as a non-tribosphenic mammal pos...

Abstract  Western Liaoning of northeastern China is world-renowned for the Mesozoic Jehol biota, especially for yielding many feathered dinosaurs, primitive birds, mammals and fossil angiosperm. This paper describes a complete specimen of a symmetrodont mammal with well-preserved hairs and soft tissue from the basal part of the Yixian Formation in...

Maelestes gobiensis Wible et al., 2007, is the second new eutherian mammal to be named from the rich Mongolian Late Cretaceous locality of Ukhaa Tolgod, Ukhaatherium nessovi Novacek et al., 1997, being the first. Maelestes is only the seventh Late Cretaceous eutherian known from the skull and the upper and lower dentitions, and the fifth known from...

Knowledge of the latest Late Cretaceous mammalian fauna in the South America was, until now, mostly based on den− tally known taxa recovered at Los Alamitos (Río Negro, Argentina). Here we describe new mammalian remains collected in outcrops of the La Colonia Formation (Campanian–Maastrichtian) exposed in Chubut Province, Argentina, warranting the...

Metatherian remains from Punta Peligro (Chubut Province, Argentina; Salamanca Formation, early Paleocene) are scarce, but at present, there are at least four different taxa known by dental remains. We describe here an incomplete petrosal showing metatherian affinities. Among the dentally known taxa from the same stratigraphic levels, the overall si...

A mammalian fauna from the Late Cretaceous locality of “Cerro Tortuga,” Allen Formation, Río Negro Province, Argentina, is described here based on a sample, represented by 7 isolated teeth which shows similarities with those reported from the Late Cretaceous Los Alamitos Formation. These two mammalian faunas largely agree on their overall compositi...

We report the first record of anilioids from southern South America, a region where they do not live today. The fossils come from the Allen Formation (Late Campanian–Early Maastrichtian) at Bajo Trapalcó and Bajo de Santa Rosa localities, Río Negro province, Argentina. The remains consist of several vertebrae, most of which belong to the mid–poster...

A complete cranial and postcranial anatomy and a phylogenetic analysis of Palaeochersis talampayensis, the oldest turtle from South America, is presented here. Palaeochersis talampayensis was found in Los Colorados Formation (Norian-Rhaetian) of La Rioja Province, Argentina. The Late Triassic turtle record is scarce worldwide, being represented by...

T. S. Kemp, the author of the much revered and useful Mammal-like Reptiles and the Origin of Mammals (1982), has produced a new book with the explicit aims of (1) updating the 1982 book with regard to new fossils and (2) elaborating “at a similar level the story of what happens next—the radiation of mammals after the end of the Cretaceous” (preface...

At the end of the Early Cretaceous the once abundant sphenodontians vanished from the Laurasian record and were thought to have become virtually extinct, with the sole exception of Sphenodon, the living tuatara. Recent findings of large and abundant eilenodontine sphenodontids in the Early Late Cretaceous (Cenomanian-Turonian) and fragmentary mater...

A new mammal from the Middle Jurassic Cañ adon Asfalto Formation, Patagonia, Argentina, is reported. The specimen, an isolated lower? molariform, is erected as the type of a new genus and species of triconodont, Argentoconodon fariasorum. The molariform presents a peculiar combination of primitive and derived features that makes recognition of its...

Estimates of the time of origin for placental mammals from DNA studies span nearly the duration of the Cretaceous period (145 to 65 million years ago), with a maximum of 129 million years ago and a minimum of 78 million years ago. Palaeontologists too are divided on the timing. Some support a deep Cretaceous origin by allying certain middle Cretace...

We generated a digital cranial endocast (infilling of the braincase) of Vincelestes neuquenianus, a Cretaceous theriiform mammal from Argentina, to achieve two goals. First, we described this endocast of Vincelestes to reconstruct the brain, associated soft-tissue structures, and internal osteological features. This report represents the first desc...

A new specimen of Chaliminia musteloides Bonaparte is described from the upper section of the Los Colorados Formation (Late Carnian–Early Norian) of Argentina. A cladistic analysis of ictidosaurians supports its monophyly. Chaliminia and Elliotherium, grouped in the new subfamily Chalimininae, were placed as sister taxa to the new subfamily Pachyge...

The Punta Peligro fauna includes some of the oldest Cenozoic South American mammals, and the oldest ones for Patagonia. In addition to frogs, turtles, and crocodiles, an unusual mammalian assemblage is formed by a mixture of Mesozoic lineages of Gondwanan origin and therians (eutherians and metatherians) derived from Laurasian immigrants. This pape...

We describe here one of the oldest known Japanese mammals, a triconodont lower jaw from the Early Cretaceous Kuwajima Formation, Tetori Group, Japan. This mammal is recognized as the type of Hakusanodon archaeus, new genus, new species, and as closely related to Eurasian and North American Jurassic “amphilestid” triconodonts (Simpson 1925b–c; Jenki...

The Punta Peligro fauna includes some of the oldest Cenozoic South American mammals, and the oldest ones for Patagonia. In addition to frogs, turtles, and crocodiles, an unusual mammalian assemblage is formed by a mixture of Mesozoic lineages of Gondwanan origin and therians (eutherians and metatherians) derived from Laurasian immigrants. This pape...

A new mammal, Henosferus molus, n.gen, and n.sp., from the Callovian-Oxfordian (latest Middle to earliest Late Jurassic) Cañadón Asfalto Formation from Chubut Province (Argentina) is described. This taxon corresponds to a new species clearly different from Asfaltomylos patagonicus from the same locality and stratigraphic level. This new species is...

A new specimen of Chaliminia musteloides Bonaparte is described from the upper section of the Los Colorados Formation (Late Carnian–Early Norian) of Argentina. A cladistic analysis of ictidosaurians supports its monophyly. Chaliminia and Elliotherium, grouped in the new subfamily Chalimininae, were placed as sister taxa to the new subfamily Pachyge...

Fossil specimens from a new Cretaceous locality near Gongzhuling City in Jilin Province, China, include two incomplete mammalian dentaries which represent a new genus and species referable to the eutherian family Zalambdalestidae. The locality is in basin-margin outcrops of the Quantou Formation, which is widely spread in the subsurface of Songliao...

The previously unknown enamel microstructure of a variety of Mesozoic and Paleogene mammals ranging from monotremes and docodonts to therians is described and characterized here. The novel information is used to explore the structural diversity of enamel in early mammals and to explore the impact of the new information for systematics. It is presen...

Teinolophos specimens continues anteriorly inside the dentary at least up to the level of the antepenultimate molar and would transmit the hypertrophied trigeminal system, as in the platypus (6). Teinolophos jaws NMV P216575, P212933, and P216680 indicate that the lingual edge of the mandibular foramen (the mandibular canal entrance) was posterior...

We describe several fossils referable to Gomphos elkema from deposits close to the Paleocene-Eocene boundary at Tsagan Khushu, Mongolia. Gomphos shares a suite of cranioskeletal characters with extant rabbits, hares, and pikas but retains a primitive dentition and jaw compared to its modern relatives. Phylogenetic analysis supports the position of...

The holotype and only known maxillary dentition of Deltatheroides cretacicus, collected in 1925 from the Upper Cretaceous Djadokhta Formation of Bayn Dzak, Mongolia, has teeth that are badly damaged and worn, obscuring many details of their structure. Reported is a new specimen of D. cretacicus collected in 2000 from the Red Rum (Kholbot) locality...

We describe a new spalacotheriid (acute-angled) "symmetrodont" (Mammalia, Trechnotheria), Symmetrolestes parvus gen. et sp. nov., from the Lower Cretaceous, likely Barremian, Kitadani Formation of the Tetori Group, central Japan. The specimen consists of a fragmentary right lower jaw with first incisor and five preserved postcanine teeth (interpret...

dryolestoid mammals had an important south american chapter and here is depicted an early analysis of their diversity

Exquisitely preserved specimens of the Late Cretaceous eutherian Zalambdalestes recently collected from the Djadokhta Formation (Early Campanian) of the Gobi Desert by the Mongolian Academy of Sciences–American Museum of Natural History Expeditions are the centerpiece of a thorough redescription of this taxon's craniodental morphology. Resolved and...

Exquisitely preserved specimens of the Late Cretaceous eutherian Zalambdalestes recently collected from the Djadokhta Formation (Early Campanian) of the Gobi Desert by the Mongolian Academy of Sciences-American Museum of Natural History Expeditions are the centerpiece of a thorough redescription of this taxon's craniodental morphology. Resolved and...

A new specimen of the tinodontid ''symmetrodont'' Eurylambda (Simpson, 1925a, 1929) from the Late Jurassic Como Bluff Quarry, Morrison Formation, is described. The specimen, a complete upper left molariform, is probably an M1. The major crown cusps of Eurylambda show similarities to those of triconodontids on the one hand and to spalacotherioids on...

We describe here the first discovered mammalian remains from the Mongolian Early Cretaceous locality Oshih (Ashile). Four fragmentary, tooth-bearing specimens, probably corresponding to three individuals, have been recovered. All the fossils can be assigned to the family Gobiconodontidae (Chow and Rich, 1984). The specimens include three lower jaw...

Mesozoic mammals are those mammals that lived during the Mesozoic era, from 245 to 65 million years before the present. The lineage leading to mammals, Synapsida, is truly ancient; it branched off the trunk leading to reptiles at least 350 million years ago.

A right petrosal from the ?Aptian or Albian Khoobur locality is referred on the basis of size and morphology to Prokennalestes trofimovi, the earliest eutherian previously known only from dentigerous elements. The petrosal shows a mosaic of primitive and derived features, bearing on the purported therian and eutherian morphotypes. Among the primiti...