Thomas Holtz - University of Maryland (original) (raw)

Papers by Thomas Holtz

Paleoceanography, Apr 1, 1995

We reconstructed late Quaternary deep (3000-4100 m) and intermediate depth (1000-2500 m) paleocea... more We reconstructed late Quaternary deep (3000-4100 m) and intermediate depth (1000-2500 m) paleoceanographic history of the Eurasian Basin, Arctic Ocean from ostracode assemblages in cores from the Lomonosov Ridge, Gakkel Ridge, Yermak Plateau, Morris Jesup Rise, and Amundsen and Makarov Basin obtained during the 1991 Polarstem cruise. Modem assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant, relatively species-rich benthic ostracode assemblages, in part, reflecting the influence of high organic productivity and inflowing Atlantic water. In contrast, deep Arctic Eurasian basin assemblages have low abundance and low diversity and are dominated by Krithe and Cytheropteron reflecting faunal exchange with the Greenland Sea via the Fram Strait. Major faunal changes occurred in the Arctic during the last glacial/interglacial transition and the Holocene. Low-abundance, low-diversity assemblages from the Lomonosov and Gakkel Ridges in the Eurasian Basin from the last glacial period have modem analogs in cold, low-salinity, lownutrient Greenland Sea deep water; glacial assemblages from the deep Nansen and Amundsen Basins have modern analogs in the deep Canada Basin. During Termination 1 at intermediate depths, diversity and abundance increased coincident with increased biogenic sediment, reflecting increased organic productivity, reduced sea-ice, and enhanced inflowing North Atlantic water. During deglaciation deep Nanscn Basin assemblages were similar to those living today in the deep Greenland Sea, perhaps reflecting deepwater exchange via the Fram StraiL In the central Arctic, early Holocene faunas indicate weaker North Atlantic water inflow at middepths immediately following Termination 1, about 8500-7000 year B.P., followed by a period of strong Canada Basin water overflow across the Lomonosov Ridge into the Morris Jesup Rise area and central Arctic Ocean. Modem perennial sea-ice cover evolved over the last 4000-5000 years. Late Quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold, deepwater of Greenland Sea origin and warmer and middepth Atlantic water to the Eurasian Basin through the Fram Strait, and export of Arctic Ocean deepwater.

Acta Geologica Sinica-english Edition, Jun 1, 2017

The spinosaurids represent an enigmatic and highly unusual form of large tetanuran theropods that... more The spinosaurids represent an enigmatic and highly unusual form of large tetanuran theropods that were first identified in 1915. A recent flurry of discoveries and taxonomic revisions of this important and interesting clade had added greatly to our knowledge, however, spinosaur body fossils are generally rare and most species are known from only limited skeletal remains. Their unusual anatomical adaptations to the skull, limbs and axial column all differ from other large theropods and point to an unusual ecological niche and a lifestyle intimately linked to water.

T.Rex: Hunter or Scavenger?

Living Dinosaurs: The Evolutionary History of Modern Birds. Edited by Gareth Dyke and Gary Kaiser. Hoboken (New Jersey): Wiley-Blackwell. $129.95. xv + 422 p. + 8 pl.; ill.; index. ISBN: 978-0-4706-5666-2. 2011

The Quarterly Review of Biology, Dec 1, 2012

Table 2) Occurrence of ostracoda in surface sediments of the Arctic Ocean

Decision letter: Spinosaurus is not an aquatic dinosaur

Arctic Ostracodes Database- 2015

(Table 2) Occurrence of ostracoda in sediment core PS2200-5

Table 4) Absolute abundance of ostracoda in shallow Arctic coretop samples

27. Mesozoic Biogeography of Dinosauria

Canadian Journal of Earth Sciences, 2021

Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greate... more Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greater taxonomic diversity among larger (>50 kg) theropod taxa than communities of the Campano-Maastrichtian, particularly to those of eastern/central Asia and Laramidia. The large carnivore guilds in Asiamerican assemblages are monopolized by tyrannosaurids, with adult medium-sized (50–500 kg) predators rare or absent. In contrast, various clades of theropods are found to occupy these body sizes in earlier faunas, including early tyrannosauroids. Assemblages with “missing middle-sized” predators are not found to have correspondingly sparser diversity of potential prey species recorded in these same faunas. The “missing middle-sized” niches in the theropod guilds of Late Cretaceous Laramidia and Asia may have been assimilated by juvenile and subadults of tyrannosaurid species, functionally distinct from their adult ecomorphologies. It is speculated that if tyrannosaurids assimilated the ni...

PRISM 8 degrees X 10 degrees North Hemisphere paleoclimate reconstruction; digital data

Open-File Report, 1994

Cretaceous Research, 2019

In a recent paper, the contention that spinosaurine theropods were semi-aquatic was supported by ... more In a recent paper, the contention that spinosaurine theropods were semi-aquatic was supported by Arden et al., (2019) and they provided a hypothetical sequence of acquisition of traits that had evolved in line with this lifestyle. However, we find that the presented traits were either loosely defined and/or are clearly distinct from those traits seen in extant animals with adaptations to life in water. Some spinosaurs may have spent extensive time in water, but the data to support this is currently insufficient and other hypotheses for their behaviour also fit the available data.

PeerJ, 2019

SynopsisTyrannosaurid dinosaurs had large preserved leg muscle attachments and low rotational ine... more SynopsisTyrannosaurid dinosaurs had large preserved leg muscle attachments and low rotational inertia relative to their body mass, indicating that they could turn more quickly than other large theropods.MethodsTo compare turning capability in theropods, we regressed agility estimates against body mass, incorporating superellipse-based modeled mass, centers of mass, and rotational inertia (mass moment of inertia). Muscle force relative to body mass is a direct correlate of agility in humans, and torque gives potential angular acceleration. Agility scores therefore include rotational inertia values divided by proxies for (1) muscle force (ilium area and estimates of m. caudofemoralis longus cross-section), and (2) musculoskeletal torque. Phylogenetic ANCOVA (phylANCOVA) allow assessment of differences in agility between tyrannosaurids and non-tyrannosaurid theropods (accounting for both ontogeny and phylogeny). We applied conditional error probabilitiesa(p) to stringently test the nul...

Cretaceous Research, 2016

Dentary groove morphology does not distinguish 'Nanotyrannus' as a valid taxon of tyrannosauroid ... more Dentary groove morphology does not distinguish 'Nanotyrannus' as a valid taxon of tyrannosauroid dinosaur. Comment on: "Distribution of the dentary groove of theropod dinosaurs: implications for theropod phylogeny and the validity of the genus Nanotyrannus

The Complete T. Rex: How Stunning New Discoveries are Changing Our Understanding of the World's Most Famous Dinosaur.John R. Horner , Don Lessem

The Quarterly Review of Biology, 1995

Vertebrate Anatomy Morphology Palaeontology

Tyrannosaurid dinosaurs were ecologically unique vertebrates as the sole clade of large terrestri... more Tyrannosaurid dinosaurs were ecologically unique vertebrates as the sole clade of large terrestrial carnivores (adults >400 kg) in their continent-spanning habitats. Expanded ligaments between metatarsals, inferred by gross morphology of attachment correlates, have been hypothesized to have strengthened their specialized arctometatarsus. We tested the hypothesis of ligament presence with scanning electron microscopy and histological thin sections of putative attachment sites in a third metatarsal of the tyrannosaurid Gorgosaurus libratus, compared with a thin section from the unspecialized metatarsals of the early theropod Coelophysis bauri. In the Gorgosaurus metatarsal, Sharpey´s fibers and rough, pitted surface textures consistent with ligament coalescence occur at expansive distal regions and localized rugosities are ideally located for resisting torsional loading on the foot. Sparser Sharpey’s fibers occur at expected locations in other arctometatarsus-bearing coelurosaurs. ...

Jr. is a dinosaur paleontologist in the Department of Geology at the University of Maryland, Coll... more Jr. is a dinosaur paleontologist in the Department of Geology at the University of Maryland, College Park. He received his Ph. D. in geology and geophysics at Yale University. His primary research interests are the evolution and adaptations of theropod dinosaurs, especially the Tyrannosauridae (tyrant dinosaurs); the ecomorphology of predation; and the effect of plate tectonics on Mesozoic terrestrial vertebrate distributions. He is Director of the College Park Scholars Earth, Life & Time program, a two-year honors program for ...