David Varricchio | Montana State University - Bozeman (original) (raw)

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Papers by David Varricchio

Research paper thumbnail of Ichnology, Paleodepositional Environments and Paleohydrology of the Non-Marine Upper Cretaceous (Coniacian) Frontier Formation Deposits of the Western Centennial Mountains, Montana

GSA 2020 Connects Online, 2020

Research paper thumbnail of Insect Trace Fossils and Their Paleontological Importance in the Two Medicine Formation (Campanian), Choteau, Montana

GSA Annual Meeting in Phoenix, Arizona, USA - 2019, 2019

Research paper thumbnail of New occurrence of Neurankylus sp. (Testudines: Paracryptodiria: Baenidae) in the Upper Cretaceous Frontier Formation of south western Montana (USA)

Cretaceous Research, Apr 1, 2020

Research paper thumbnail of Autopod and track morphology elucidate on the putative producer in hadrosauriform ornithopods: a case study of manus tracks from the Frontier Formation (Coniacian), Montana

Historical Biology, Apr 5, 2023

Research paper thumbnail of Preservation of aragonite in Late Cretaceous (Campanian) turtle eggshell

Palaeogeography, Palaeoclimatology, Palaeoecology, 2022

Research paper thumbnail of Developmental strategies underlying gigantism and miniaturization in non-avialan theropod dinosaurs

Science

In amniotes, the predominant developmental strategy underlying body size evolution is thought to ... more In amniotes, the predominant developmental strategy underlying body size evolution is thought to be adjustments to the rate of growth rather than its duration. However, most theoretical and experimental studies supporting this axiom focus on pairwise comparisons and/or lack an explicit phylogenetic framework. We present the first large-scale phylogenetic comparative analysis examining developmental strategies underlying the evolution of body size, focusing on non-avialan theropod dinosaurs. We reconstruct ancestral states of growth rate and body mass in a taxonomically rich dataset, finding that contrary to expectations, changes in the rate and duration of growth played nearly equal roles in the evolution of the vast body size disparity present in non-avialan theropods—and perhaps that of amniotes in general.

Research paper thumbnail of Pelvic Coevolution with Egg Size and Shape in Modern Birds: Implication for Reproductive Biology of Extinct Dinosaurs

Geological Society of America Abstracts with Programs, 2017

Research paper thumbnail of Ichnology and sedimentology of the Coniacian non-marine Frontier Formation, western Centennial Mountains, southwestern Montana, USA

Research paper thumbnail of Photogrammetry of the Oryctodromeus cubicularis type locality burrow and the utility of preexisting, standard field photographs for three dimensional digital reconstruction

Research paper thumbnail of Dinosaur tracks from the Frontier Formation, Montana: preservation, distribution and palaeoecological significance for the middle Cretaceous terrestrial ecosystems of North America

Research paper thumbnail of Montana Climatic Changes Associated with the Cretaceous Claggett and Bearpaw Transgressions

ABSTRACT Two transgressions of the Cretaceous interior sea, the Claggett and Bearpaw, greatly red... more ABSTRACT Two transgressions of the Cretaceous interior sea, the Claggett and Bearpaw, greatly reduced the quantity of terrestrial habitats. Dinosaur lineages of the terrestrial Two Medicine and Judith River Formations of central Montana show evolutionary changes associated with at least the more extensive Bearpaw transgression. A lacustrine varve-like sequence assodated with a pulmonate-dominated gastropod fauna is reported from the uppermost Two Medidne Formation and together with abundant caliche horizons suggests sporadic or possibly seasonal precipitation. This together with a review of paleodimatic data and models as well as comparisons with geographically similar modern localities indicate that the more extensive Bearpaw transgression had a climatic impact which also qualitatively affected terrestrial ecosystems. This elimination of a wetter coastal region would have been an evolutionary barrier mainly for lower coastal plain dinosaurs.

Research paper thumbnail of Paleoenvironmental Implications of Invertebrate Fecal Pellets (Edaphichnium ISP.) at an Ichnofossil-Rich Dinosaur Nesting Locality, Upper Cretaceous Two Medicine Formation, Montana, Usa

PALAIOS, Sep 28, 2021

ABSTRACTThe terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the ... more ABSTRACTThe terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the Pleistocene and is characterized by tubular burrows with ellipsoidal fecal pellets, indicating substrate feeding by earthworms or other invertebrates. We describe 11 specimens attributable to Edaphichnium isp. from Egg Mountain, a terrestrial locality with a diverse fossil assemblage from the Upper Cretaceous Two Medicine Formation in Montana, USA, and assess their paleoenvironmental and paleoecological implications. These ichnofossils were recovered from a 1.5 meter stratigraphic succession comprised of calcareous siltstones and limestones with abundant fossil insect pupal cases, representing well-drained paleosols. Although burrows are not always present, three recurring arrangements of Edaphichnium isp. fecal pellets are identified: linearly arranged pellets, horizon-confined pellets, and pellets in clusters dispersed vertically and horizontally throughout the matrix. Two color patterns (light and dark pellets) are also distinguished. Pellets are fine-grained and have a consistently ellipsoidal shape (length:diameter of 1.57), with maximum lengths ranging from 1.9–6.7 mm (mean 4.1 mm) and maximum diameters ranging from 1.0–4.1 mm (mean 2.6 mm). Geochemical analyses indicate pellets are comprised of varying proportions of calcite, plagioclase, and quartz, and are enriched in phosphorus relative to the sedimentary host matrix. Possible trace makers include chafer or other coleopteran larvae, millipedes, and earthworms, suggesting a range of capable trace makers of Edaphichnium-like fecal pellets. Edaphichnium isp. at specific stratigraphic horizons suggests increased organic content in the subsurface, potentially connected to depositional hiatuses. Edaphichnium isp. adds a secondary component to the Celliforma ichnofacies known from Egg Mountain and surrounding strata, and to the array of nesting, feeding, and dwelling traces of wasps, beetles, other invertebrates, mammals, and dinosaurs from the locality.

Research paper thumbnail of Insect trace fossils elucidate depositional environments and sedimentation at a dinosaur nesting site from the Cretaceous (Campanian) Two Medicine Formation of Montana

Palaeogeography, Palaeoclimatology, Palaeoecology, Nov 1, 2019

Research paper thumbnail of Gut Contents from a Cretaceous Tyrannosaurid: Implications for Theropod Dinosaur Digestive Tracts

Journal of Paleontology, Mar 1, 2001

Research paper thumbnail of Paleoecological implications of two closely associated egg types from the Upper Cretaceous St. Mary River Formation, Montana

Cretaceous Research, Nov 1, 2017

Research paper thumbnail of A New Enantiornithine Bird From the Upper Cretaceous Two Medicine Formation of Montana

Journal of Vertebrate Paleontology, Mar 14, 1995

Research paper thumbnail of Preservation of aragonite in Late Cretaceous (Campanian) turtle eggshell

Zenodo (CERN European Organization for Nuclear Research), Nov 1, 2021

Research paper thumbnail of Nevadadromeus schmitti (gen. et sp. nov.), a New Basal Neornithischian with Affinities to the Thescelosaurinae, from the Upper Cretaceous (Cenomanian) Willow Tank Formation of Southern Nevada

Journal of the Arizona-Nevada Academy of Science

Research paper thumbnail of Microstructural description of the maniraptoran egg Protoceratopsidovum

Papers in Palaeontology

Since their discovery in the 1920s, some asymmetric, elongated dinosaur eggs from the Upper Creta... more Since their discovery in the 1920s, some asymmetric, elongated dinosaur eggs from the Upper Cretaceous of Mongolia have been interpreted as ceratopsian eggs. However, recent views support a maniraptoran affinity mainly based on macroscopic features. Technical advancements in palaeontology provide a novel approach to diagnose maniraptoran eggs, and the discovery of soft ceratopsian eggs makes the debate a timely issue worth revisiting. Here, we analysed Protoceratopsidovum eggshell from southern Mongolia with electron backscatter diffraction and the results were compared with East Asian and North American maniraptoran and ornithischian eggs. The microstructure and crystallography of Protoceratopsidovum confirms the maniraptoran hypothesis, given that it shows diagnostic features of the clade absent from ornithischian (e.g. hadrosaur) eggs. Additional characters, such as egg shape, ornamentation, egg pairing and clutch structure also support a maniraptoran affinity. Protoceratopsidovu...

Research paper thumbnail of Tiny, ornamented eggs and eggshell from the Upper Cretaceous of Utah represent a new ootaxon with theropod affinities

Scientific Reports, 2021

A new Cretaceous ootaxon (eggshell type) from the Kaiparowits Formation of Grand Staircase-Escala... more A new Cretaceous ootaxon (eggshell type) from the Kaiparowits Formation of Grand Staircase-Escalante National Monument is among a growing number of very small eggs described from the Mesozoic. Analyses of two partial eggs (~ 17.7 mm in diameter) and 29 eggshell fragments reveal that this new ootaxon exhibits nodose ornamentation with distinctive branching pore canals that open atop the nodes. Its two-layered microstructure consists of a mammillary layer and a continuous layer with rugged grain boundaries between calcite grains. Although the exact identity of the egg producer is unknown, the eggshell microstructure and small size is consistent with a small-bodied avian or non-avian theropod. The specific combination of small egg size, branching pores, two-layered microstructure, and dispersituberculate ornamentation preserved in this new ootaxon is unique among theropod eggs. This underscores that both eggshell and skeletal fossils of Cretaceous theropods can display a mosaic of tran...

Research paper thumbnail of Ichnology, Paleodepositional Environments and Paleohydrology of the Non-Marine Upper Cretaceous (Coniacian) Frontier Formation Deposits of the Western Centennial Mountains, Montana

GSA 2020 Connects Online, 2020

Research paper thumbnail of Insect Trace Fossils and Their Paleontological Importance in the Two Medicine Formation (Campanian), Choteau, Montana

GSA Annual Meeting in Phoenix, Arizona, USA - 2019, 2019

Research paper thumbnail of New occurrence of Neurankylus sp. (Testudines: Paracryptodiria: Baenidae) in the Upper Cretaceous Frontier Formation of south western Montana (USA)

Cretaceous Research, Apr 1, 2020

Research paper thumbnail of Autopod and track morphology elucidate on the putative producer in hadrosauriform ornithopods: a case study of manus tracks from the Frontier Formation (Coniacian), Montana

Historical Biology, Apr 5, 2023

Research paper thumbnail of Preservation of aragonite in Late Cretaceous (Campanian) turtle eggshell

Palaeogeography, Palaeoclimatology, Palaeoecology, 2022

Research paper thumbnail of Developmental strategies underlying gigantism and miniaturization in non-avialan theropod dinosaurs

Science

In amniotes, the predominant developmental strategy underlying body size evolution is thought to ... more In amniotes, the predominant developmental strategy underlying body size evolution is thought to be adjustments to the rate of growth rather than its duration. However, most theoretical and experimental studies supporting this axiom focus on pairwise comparisons and/or lack an explicit phylogenetic framework. We present the first large-scale phylogenetic comparative analysis examining developmental strategies underlying the evolution of body size, focusing on non-avialan theropod dinosaurs. We reconstruct ancestral states of growth rate and body mass in a taxonomically rich dataset, finding that contrary to expectations, changes in the rate and duration of growth played nearly equal roles in the evolution of the vast body size disparity present in non-avialan theropods—and perhaps that of amniotes in general.

Research paper thumbnail of Pelvic Coevolution with Egg Size and Shape in Modern Birds: Implication for Reproductive Biology of Extinct Dinosaurs

Geological Society of America Abstracts with Programs, 2017

Research paper thumbnail of Ichnology and sedimentology of the Coniacian non-marine Frontier Formation, western Centennial Mountains, southwestern Montana, USA

Research paper thumbnail of Photogrammetry of the Oryctodromeus cubicularis type locality burrow and the utility of preexisting, standard field photographs for three dimensional digital reconstruction

Research paper thumbnail of Dinosaur tracks from the Frontier Formation, Montana: preservation, distribution and palaeoecological significance for the middle Cretaceous terrestrial ecosystems of North America

Research paper thumbnail of Montana Climatic Changes Associated with the Cretaceous Claggett and Bearpaw Transgressions

ABSTRACT Two transgressions of the Cretaceous interior sea, the Claggett and Bearpaw, greatly red... more ABSTRACT Two transgressions of the Cretaceous interior sea, the Claggett and Bearpaw, greatly reduced the quantity of terrestrial habitats. Dinosaur lineages of the terrestrial Two Medicine and Judith River Formations of central Montana show evolutionary changes associated with at least the more extensive Bearpaw transgression. A lacustrine varve-like sequence assodated with a pulmonate-dominated gastropod fauna is reported from the uppermost Two Medidne Formation and together with abundant caliche horizons suggests sporadic or possibly seasonal precipitation. This together with a review of paleodimatic data and models as well as comparisons with geographically similar modern localities indicate that the more extensive Bearpaw transgression had a climatic impact which also qualitatively affected terrestrial ecosystems. This elimination of a wetter coastal region would have been an evolutionary barrier mainly for lower coastal plain dinosaurs.

Research paper thumbnail of Paleoenvironmental Implications of Invertebrate Fecal Pellets (Edaphichnium ISP.) at an Ichnofossil-Rich Dinosaur Nesting Locality, Upper Cretaceous Two Medicine Formation, Montana, Usa

PALAIOS, Sep 28, 2021

ABSTRACTThe terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the ... more ABSTRACTThe terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the Pleistocene and is characterized by tubular burrows with ellipsoidal fecal pellets, indicating substrate feeding by earthworms or other invertebrates. We describe 11 specimens attributable to Edaphichnium isp. from Egg Mountain, a terrestrial locality with a diverse fossil assemblage from the Upper Cretaceous Two Medicine Formation in Montana, USA, and assess their paleoenvironmental and paleoecological implications. These ichnofossils were recovered from a 1.5 meter stratigraphic succession comprised of calcareous siltstones and limestones with abundant fossil insect pupal cases, representing well-drained paleosols. Although burrows are not always present, three recurring arrangements of Edaphichnium isp. fecal pellets are identified: linearly arranged pellets, horizon-confined pellets, and pellets in clusters dispersed vertically and horizontally throughout the matrix. Two color patterns (light and dark pellets) are also distinguished. Pellets are fine-grained and have a consistently ellipsoidal shape (length:diameter of 1.57), with maximum lengths ranging from 1.9–6.7 mm (mean 4.1 mm) and maximum diameters ranging from 1.0–4.1 mm (mean 2.6 mm). Geochemical analyses indicate pellets are comprised of varying proportions of calcite, plagioclase, and quartz, and are enriched in phosphorus relative to the sedimentary host matrix. Possible trace makers include chafer or other coleopteran larvae, millipedes, and earthworms, suggesting a range of capable trace makers of Edaphichnium-like fecal pellets. Edaphichnium isp. at specific stratigraphic horizons suggests increased organic content in the subsurface, potentially connected to depositional hiatuses. Edaphichnium isp. adds a secondary component to the Celliforma ichnofacies known from Egg Mountain and surrounding strata, and to the array of nesting, feeding, and dwelling traces of wasps, beetles, other invertebrates, mammals, and dinosaurs from the locality.

Research paper thumbnail of Insect trace fossils elucidate depositional environments and sedimentation at a dinosaur nesting site from the Cretaceous (Campanian) Two Medicine Formation of Montana

Palaeogeography, Palaeoclimatology, Palaeoecology, Nov 1, 2019

Research paper thumbnail of Gut Contents from a Cretaceous Tyrannosaurid: Implications for Theropod Dinosaur Digestive Tracts

Journal of Paleontology, Mar 1, 2001

Research paper thumbnail of Paleoecological implications of two closely associated egg types from the Upper Cretaceous St. Mary River Formation, Montana

Cretaceous Research, Nov 1, 2017

Research paper thumbnail of A New Enantiornithine Bird From the Upper Cretaceous Two Medicine Formation of Montana

Journal of Vertebrate Paleontology, Mar 14, 1995

Research paper thumbnail of Preservation of aragonite in Late Cretaceous (Campanian) turtle eggshell

Zenodo (CERN European Organization for Nuclear Research), Nov 1, 2021

Research paper thumbnail of Nevadadromeus schmitti (gen. et sp. nov.), a New Basal Neornithischian with Affinities to the Thescelosaurinae, from the Upper Cretaceous (Cenomanian) Willow Tank Formation of Southern Nevada

Journal of the Arizona-Nevada Academy of Science

Research paper thumbnail of Microstructural description of the maniraptoran egg Protoceratopsidovum

Papers in Palaeontology

Since their discovery in the 1920s, some asymmetric, elongated dinosaur eggs from the Upper Creta... more Since their discovery in the 1920s, some asymmetric, elongated dinosaur eggs from the Upper Cretaceous of Mongolia have been interpreted as ceratopsian eggs. However, recent views support a maniraptoran affinity mainly based on macroscopic features. Technical advancements in palaeontology provide a novel approach to diagnose maniraptoran eggs, and the discovery of soft ceratopsian eggs makes the debate a timely issue worth revisiting. Here, we analysed Protoceratopsidovum eggshell from southern Mongolia with electron backscatter diffraction and the results were compared with East Asian and North American maniraptoran and ornithischian eggs. The microstructure and crystallography of Protoceratopsidovum confirms the maniraptoran hypothesis, given that it shows diagnostic features of the clade absent from ornithischian (e.g. hadrosaur) eggs. Additional characters, such as egg shape, ornamentation, egg pairing and clutch structure also support a maniraptoran affinity. Protoceratopsidovu...

Research paper thumbnail of Tiny, ornamented eggs and eggshell from the Upper Cretaceous of Utah represent a new ootaxon with theropod affinities

Scientific Reports, 2021

A new Cretaceous ootaxon (eggshell type) from the Kaiparowits Formation of Grand Staircase-Escala... more A new Cretaceous ootaxon (eggshell type) from the Kaiparowits Formation of Grand Staircase-Escalante National Monument is among a growing number of very small eggs described from the Mesozoic. Analyses of two partial eggs (~ 17.7 mm in diameter) and 29 eggshell fragments reveal that this new ootaxon exhibits nodose ornamentation with distinctive branching pore canals that open atop the nodes. Its two-layered microstructure consists of a mammillary layer and a continuous layer with rugged grain boundaries between calcite grains. Although the exact identity of the egg producer is unknown, the eggshell microstructure and small size is consistent with a small-bodied avian or non-avian theropod. The specific combination of small egg size, branching pores, two-layered microstructure, and dispersituberculate ornamentation preserved in this new ootaxon is unique among theropod eggs. This underscores that both eggshell and skeletal fossils of Cretaceous theropods can display a mosaic of tran...