Pycnonemosaurus nevesi

Pycnonemosaurus nevesi inhabited the Cachoeira do Bom Jardim Formation in what is now Mato Grosso, Brazil, during the Campanian to Maastrichtian of the Late Cretaceous (~75-70 Ma). The environment was semi-arid, representing intermediate alluvial fan deposits in a semi-arid climate. The red conglomeratic sandstones where the fossil was found indicate energetic fluvial transport in seasonally flooded arid plains. Contemporary fauna included titanosaur sauropods and crocodilians, as well as chelonians and other reptiles. The ecosystem was part of Western Gondwana, with faunal connections to Argentina, Africa, and India via continental drift.

As the largest predator in the Late Cretaceous Mato Grosso ecosystem, Pycnonemosaurus nevesi likely hunted titanosaur sauropods found at the same locality, which explains its large body size. Similar to its close relatives Carnotaurus and Aucasaurus, it had small but sharp teeth adapted to grip struggling prey. Biomechanical studies of related abelisaurids suggest high-speed frontal bites with moderate force. The robust, muscular tail, inferred from the known caudal transverse processes, provided explosive locomotor power for short-distance ambushes.

Based on phylogenetic analogy with other abelisaurids, Pycnonemosaurus was likely a solitary, territorial predator. Studies of close relatives such as Skorpiovenator documented an exceptional neurovascular system in cranial bones, possibly used for thermoregulation or intraspecific communication. Derived abelisaurids such as Carnotaurus exhibit robust cranial morphology that may have been used in display behaviors or intraspecific combat. The unique pubic features of Pycnonemosaurus, with a small rounded foot and bowed anterior end, may reflect specific postural adaptations of this species.

As a large theropod (8.9 meters, 3.6 metric tons), Pycnonemosaurus exhibited the general physiological pattern of derived abelisaurids: robust hindlimbs for explosive propulsion, muscular tail with a large M. caudofemoralis (inferred by analogy with Carnotaurus), completely vestigial forelimbs, and scaly skin without feathers (based on Carnotaurus evidence). Bone histology of related abelisaurids indicates relatively rapid growth, partial endothermy, and determinate growth at maturity. The fragmentary fossil record of Pycnonemosaurus, possibly from a subadult, suggests adults could have been even larger.

Founding paper establishing Pycnonemosaurus nevesi as the first formally described abelisaurid from the Bauru Group in Upper Cretaceous Brazil. Kellner and Campos describe holotype DGM 859-R, collected at Fazenda Roncador locality in Mato Grosso, comprising teeth, caudal vertebrae, pubis, tibia, and fibula. The authors identify diagnostic features distinguishing this specimen from other known abelisaurids: the pubis with a small rounded foot and ventrally bowed anterior distal end, and hook-shaped caudal transverse processes. The species name honors Brazilian paleontologist Iedo Batista Neves. The paper first placed Brazil as abelisaurid territory, expanding the known distribution of this Gondwanan group.

Skeletal reconstruction of Pycnonemosaurus nevesi by Gunnar Bivens (2018), using Carnotaurus as a guide for unpreserved parts. Known bones include caudal vertebrae, pubis, tibia, and fibula.

Size comparison of carnotaurins (left to right): Carnotaurus, Abelisaurus, Pycnonemosaurus, Aucasaurus, and Quilmesaurus. Pycnonemosaurus is the largest known abelisaurid at 8.9 meters.

Complete morphological revision of Pycnonemosaurus nevesi by Rafael Delcourt, presenting new material including three additional caudal transverse processes. The phylogenetic analysis demonstrates a strong relationship between Pycnonemosaurus and the most derived abelisaurids, such as Carnotaurus and Aucasaurus, within the clade Furileusauria. The work also discusses the taxonomic validity of the genus, which had been questioned by Carrano and Sampson (2008). Delcourt concludes Pycnonemosaurus is a valid genus with clear autapomorphies, repositioning its phylogeny within South American Brachyrostra.

Sixth caudal vertebra of the Carnotaurus sastrei holotype in lateral, anterior, and dorsal views. Comparable caudal structure to Pycnonemosaurus transverse processes, key to its phylogenetic position within Furileusauria.

Phylogenetic tree of Ceratosauria based on Rauhut and Carrano (2016), showing evolutionary relationships within the group that includes Pycnonemosaurus. The Brazilian specimen positions among the most derived brachyrostran abelisaurids.

Fundamental allometric study reevaluating body size of abelisauroids using bivariate equations applied to 40 measurements of skulls, vertebrae, and appendicular elements. The authors conclude Pycnonemosaurus nevesi measured 8.9 ± 0.3 meters, surpassing Carnotaurus (7.8 ± 0.3 m) and making it the largest formally described abelisaurid. The study also demonstrates prior estimates underestimated the animal by up to 30%. The analysis uses reference specimens including Carnotaurus, Majungasaurus, Aucasaurus, and Rugops, establishing a new methodological standard for size estimates in theropods with partial preservation.

Size comparison among Carnotaurinae members including Pycnonemosaurus (third from left). The allometric estimates of Grillo and Delcourt (2017) established Pycnonemosaurus as the largest of all abelisaurids.

Comparison of distal femora of Quilmesaurus curriei and Carnotaurus sastrei, two abelisaurids whose data were used by Grillo and Delcourt (2017) to calibrate allometric equations for body size estimation.

Comprehensive review of ceratosaur paleobiology by Delcourt, examining evolution and ecology of the Southern Hemisphere rulers. The study establishes the new clade Etrigansauria, containing Abelisauridae and Ceratosauridae, and documents evidence of cranial soft tissues in abelisaurids suggesting low-displacement butting behavior. The work demonstrates that derived ceratosaurs inhabited semi-arid environments and functioned as ecological analogs to northern tyrannosaurs. Pycnonemosaurus is discussed as a representative of a clade of Late Cretaceous South American abelisaurids that achieved exceptional body sizes.

Phylogenetic tree of Ceratosauria based on Rauhut and Carrano (2016), edited for clarity. Pycnonemosaurus positions within the most derived South American abelisaurid clades, within Furileusauria.

Geographic distribution, era, and phylogenetic relationships of Ceratosauria. Pycnonemosaurus is one of the Southern Hemisphere representatives during the Late Cretaceous, the period of maximum abelisaurid diversity.

High-impact study describing Eoabelisaurus mefi from Middle Jurassic Patagonia, extending the known abelisaurid record by over 40 million years. The nearly complete skeleton reveals the earliest evolutionary stages of abelisaurid distinctive features, such as forelimb modification. The phylogenetic analysis includes Pycnonemosaurus as a derived member of South American Brachyrostra. The study suggests a central Gondwanan desert may have restricted certain vertebrate groups to southern continents, explaining abelisaurid endemism in Gondwana.

Reconstruction of the skull of Eoabelisaurus mefi, the most basal and ancient known abelisaurid, described by Pol and Rauhut (2012). The reconstruction reveals the earliest evolutionary stages of cranial adaptations that would culminate in derived forms such as Pycnonemosaurus.

Comparison of forelimbs of Carnotaurus, Dilophosaurus, and Eoabelisaurus, showing the progressive forelimb reduction throughout abelisaurid evolution. Pycnonemosaurus would have had even more reduced forelimbs than Eoabelisaurus.

Analysis of the caudal musculature of Carnotaurus sastrei, the closest known relative of Pycnonemosaurus within Furileusauria, revealing an exceptionally large caudofemoralis muscle that provided explosive running capability. Digital muscle models indicate that, relative to body size, Carnotaurus had the largest M. caudofemoralis of any studied theropod. These findings have implications for the locomotor evolution of South American abelisaurids such as Pycnonemosaurus, which likely shared similar adaptations for hunting large titanosaur prey.

Lateral and dorsal views of the robustly modeled tail of Carnotaurus sastrei, with caudal and pelvic skeleton and reconstructed digital musculature. The highlighted M. caudofemoralis in red is exceptionally developed, conferring explosive running capability to the animal.

Cross-section through the tail of Carnotaurus showing caudal vertebra 6 and accompanying musculature. The large muscle volume in this region is analogous to what would be expected for Pycnonemosaurus, given its close phylogenetic position.

Pioneering study applying a 'biomechanical profiling' method to 41 theropod taxa, calculating mechanical advantage at each biting position along the tooth row. The analysis reveals that abelisaurids such as Carnotaurus, the closest known relative of Pycnonemosaurus, occupy unique functional space associated with high-speed frontal bites. The work demonstrates strong phylogenetic signal in theropod bite performance evolution, concluding that major functional shifts occurred at major clade origins. These data are relevant for inferring Pycnonemosaurus's predation strategy, which shared with other furileusaurs a reduced skull and small teeth.

Comparison of skulls of six abelisaurid genera: Rajasaurus, Rugops, Abelisaurus, Majungasaurus, Aucasaurus, and Carnotaurus. The different biomechanics of each skull reflect varied predation strategies within the group, the central theme of Sakamoto's study.

Skull diagram of Ekrixinatosaurus novasi, a South American abelisaurid, whose cranial proportions were studied in comparative theropod jaw biomechanics analysis. The reduced snout morphology is characteristic of derived abelisaurids.

Comprehensive review of Bauru Group dinosaurs, a set of Cretaceous rocks in Brazil covering approximately 370,000 km². The study demonstrates a diverse dinosaur fauna, including titanosaur herbivores and abelisaurid carnivores such as Pycnonemosaurus, that survived until the end of the Cretaceous (Maastrichtian). The authors argue these Southern Hemisphere dinosaurs were still diversifying when the asteroid impact caused mass extinction, analogously to Northern Hemisphere faunas. The paper presents Pycnonemosaurus estimated at 8.9 meters as one of the largest predators of Late Cretaceous Brazil.

Scale comparison between five abelisaurids: Carnotaurus, Aucasaurus, Ekrixinatosaurus, Skorpiovenator, and Majungasaurus. Pycnonemosaurus, not included in this image, would be the largest of all these animals, underscoring its role as apex predator of Cretaceous Brazil.

Osteological replica of Pycnonemosaurus nevesi displayed at the Natural History Museum of Mato Grosso in Cuiabá. This is the largest confirmed predator of Upper Cretaceous Brazil, up to 8.9 meters in length.

Study documenting specimen MUVP 477, a partial cervical vertebra of a medium-sized abelisaurid from Cenomanian rocks in Egypt. Represents the earliest confirmed abelisaurid record in northeastern Africa. The phylogenetic analysis, which includes Pycnonemosaurus nevesi among reference taxa, positions the Egyptian specimen in polytomy with all included abelisaurids or as a basal member of the South American clade. The work confirms that abelisaurids dominated Africa, India, and South America during the Cretaceous.

Skull of Abelisaurus comahuensis, an Argentine Campanian abelisaurid. The Gondwanan distribution of abelisaurids, with representatives in Brazil (Pycnonemosaurus), Argentina (Abelisaurus, Carnotaurus), Africa, India, and Madagascar, is a central theme of the group's biogeographic studies.

Artistic reconstruction of Carnotaurus sastrei by Nobu Tamura, a close relative of Pycnonemosaurus within Furileusauria. The typical abelisaurid morphology with short skull, orbital horns, and vestigial forelimbs is shared across the group.

CT-scan-based study documenting an exceptional neurovascular system in the skull of abelisaurid Skorpiovenator bustingorryi, a derived relative close to Pycnonemosaurus. A row of large foramina on the dorsal surface of nasal bones connects internally through canals that likely housed blood vessels and nerves. The authors propose three functional hypotheses: thermoregulation through vascular heat exchange, vascularization of display structures for intraspecific communication, or sensory organ support. The work reveals unexpected cranial complexity in abelisaurids.

Reconstruction of Carnotaurus sastrei (2017) by Fred Wierum, showing the typical derived abelisaurid cranial morphology: short, bony skull with ornamentations and supra-orbital horns. This type of robust skull houses the neurovascular system described by Cerroni et al. in Skorpiovenator.

Caudal skin impression of Carnotaurus (MACN-CH 894), published as part of abelisaurid soft tissue morphology studies. The scaly skin, with large conical scales and small basal scales, is likely representative for the entire family, including Pycnonemosaurus.

Description of Kurupi itaata, a new abelisaurid from the Marília Formation (Bauru Group, Upper Cretaceous) of the municipality of Monte Alto, São Paulo. Holotype MPMA 27-0001/02 consists of three caudal vertebrae and partial pelvic girdle, representing the first named tetrapod from the Marília Formation and the second named abelisaurid from the Bauru Group after Pycnonemosaurus nevesi. The work includes phylogenetic analysis positioning both Brazilian species as derived brachyrostran abelisaurids and discusses the growing diversity of Cretaceous predators in Brazil.

Osteological replica of Pycnonemosaurus nevesi at the Natural History Museum of Mato Grosso. The expansion of Brazilian abelisaurid diversity with the description of Kurupi itaata (2021) confirms that the Bauru Group hosted multiple large predators in the Upper Cretaceous.

Six representatives of Ceratosauria (top to bottom): Rugops, Elaphrosaurus, Majungasaurus, Carnotaurus, Ceratosaurus, and Berthasaura. Pycnonemosaurus and Kurupi itaata (described in 2021) position within the Abelisauridae of this group, as large Late Cretaceous predators of Brazil.

Comprehensive phylogenetic analysis of Ceratosauria by Carrano and Sampson, published in the Journal of Systematic Palaeontology. The work presents dense taxon and character sampling across all Ceratosauria, including noasaurids and abelisaurids. This publication classified Pycnonemosaurus as a nomen dubium (dubious name) due to the scarcity and fragmentation of fossil material. This classification was subsequently rejected by Delcourt (2017), who demonstrated valid autapomorphies in the holotype. Carrano and Sampson's analysis remains an essential reference for ceratosaur systematics.

Reconstructed skeleton of Majungasaurus crenatissimus, a Maastrichtian abelisaurid from Madagascar, a relative of Pycnonemosaurus. The Brazilian Bauru Group, which housed Pycnonemosaurus, hosted one of the most diverse Southern Hemisphere dinosaur faunas on the eve of end-Cretaceous extinction.

Fossil skull of Majungasaurus crenatissimus at the Royal Ontario Museum, Canada. Majungasaurus was one of the abelisaurids included in Carrano and Sampson's (2008) taxon sampling, whose phylogenetic study established the foundations for classifying abelisaurids such as Pycnonemosaurus.

Documentation of the first titanosaur nesting site of the Late Cretaceous of Brazil, at the Serra da Galga Formation, Minas Gerais. The site includes multiple egg clutches with preserved shell fragments, indicating burial nesting strategy in an arid paleosoil environment. The study documents the semi-arid, warm paleoenvironment that characterized the Bauru Group at the end of the Cretaceous, the environment in which Pycnonemosaurus lived as apex predator. The titanosaurs documented at this site are representative of the prey that Pycnonemosaurus potentially hunted.

9-meter replica of Pycnonemosaurus nevesi at the Natural History Museum of Mato Grosso, built by paleoartist Carlos Scarpini. The animal lived in the same semi-arid Bauru Group environment where the titanosaur nesting sites documented by Fiorelli et al. (2022) were found.

Replica of Pycnonemosaurus nevesi at the Natural History Museum of Mato Grosso. The Bauru Group environment, habitat of this dinosaur, was semi-arid with broad alluvial fans, an environment similar to that documented at Late Cretaceous titanosaur nesting sites in Brazil.

Description of Koleken inakayali, a new furileusaurian abelisaurid from the La Colonia Formation (Maastrichtian, Upper Cretaceous) of Patagonia. The most complete phylogenetic analysis of Furileusauria to date includes Pycnonemosaurus nevesi among Campanian-Maastrichtian brachyrostrans from South America, alongside Aucasaurus, Niebla, and Carnotaurus. The study also examines evolutionary rates among ceratosaurs, revealing that abelisaurids exhibited high cranial evolutionary rates during the Cretaceous. Pycnonemosaurus and Koleken are identified as part of the same diverse furileusaurian fauna of the latest Cretaceous.

CT scans of caudal vertebrae of Aucasaurus garridoi, a relative of Pycnonemosaurus. Carrano and Sampson's (2008) cladistic analysis examined caudal vertebra features such as hook-shaped transverse processes to distinguish taxa within abelisaurids.

Skull of Aucasaurus garridoi, an Argentine Campanian abelisaurid and one of the Furileusauria members closest to Pycnonemosaurus. Pol et al.'s (2024) analysis is the most recent and comprehensive for this clade, refining the phylogenetic position of the Brazilian dinosaur.

Taxonomic reevaluation of Quilmesaurus curriei, an Argentine Maastrichtian abelisaurid found in the Allen Formation. The study compares Quilmesaurus material with other South American abelisaurids, including Pycnonemosaurus nevesi, and analyzes the phylogenetic relationships of carnotaurins. The comparison of distal femora of Quilmesaurus and Carnotaurus, a key image of the paper, demonstrates how morphological variations of hindlimb extremities are used to distinguish taxa within abelisaurids. The work contributes to understanding kinship relationships among large Late Cretaceous South American predators.

Comparison of tibiae of Quilmesaurus curriei with other abelisaurids. Tibiae are important diagnostic elements in fragmentary abelisaurids such as Pycnonemosaurus. The titanosaurian environment documented by Fiorelli et al. (2022) was inhabited by animals with similar hindlimbs.

Pathologic fossil elements of Patagonian abelisaurids: Quilmesaurus curriei tibia, Aucasaurus garridoi caudal vertebrae, and Elemgasem nubilus vertebrae. Quilmesaurus, the main subject of Juárez Valieri et al.'s paper, is a carnotaurin like Pycnonemosaurus, sharing several anatomical characteristics of hindlimbs.

Full-size T-rex animatronic from the Jurassic Park franchise, with the iconic red Jeep — Amaury Laporte · CC BY 2.0