I do not have the book by Mr. Cremo, so I will rely on you to present specific examples and run through how it was analyzed in the past and in the modern times by scientists. I have access to scientific papers, so I can look at the primary sources if they have been digitized.
It is not a categorical denial of older works. Its just that for older works, we have to very careful in separating wheat from the chaff, even from the same scientists. I would trust older conclusions if modern scientists have relooked at the sites and confirmed the older conclusions. I think much of the evidence Mr. Cremo is citing is based on poor fieldwork done at a time when good understanding of how to carefully preserve the note the provenance of the fossils was absent. Neither the field of geology nor the field of ecology was well developed (dating techniques were unknown, plate tectonics was unknown, nobody has even started studying ecology as a systematic science and had no idea how to connect the various fossils found in a site together, there was no basic understanding on how exactly do sedimentary rocks form and fault through plate deformations etc. etc.). The reason I do not trust early scientists is not that they had somehow less skill than people working today, they simply did not possess the tools that could help them get the correct interpretation of what they were uncovering. They got nice fossils, but their explanation of the context of the fossils (where, when, what, how, why) were almost always wrong. Paleontology, unlike physics and much like forensics, is a science that depends on other sciences a lot. Geology, minerology, ecology, climatology, planetary sciences, dating technology etc. While it is not absolutely dependent on them, it really needs these other sciences to get it right to get its own conclusions about fossils and ancient ecosystems right. And we know that half of these sciences were non-existent or were wrong about absolutely everything 60 years ago. I would say that since the time of Newton till about 1950-1960, the only true science was physics and everything else (like chemistry and biology) was more of science wannabes. With the explication of the quantum foundations of chemistry and the unification of organic and inorganic chemical principles, chemistry emerged as a pure science from about 1950 onwards making its sub-disciplines (mineralogy etc.) true quantitative sciences. With the coming of molecular genetics, bio-physics and bio-chemistry of cells, developmental biology and quantitative evolutionary and ecological biology as well as germ theory of disease, biology and its associated disciplines emerge as a coherent science only from 1980 onwards. Social sciences, psychology, economics are still science wannabes.
In case this seems arbitrary, let me explain how I make the distinction between pre-scientific and scientific phases.
In any field of science look at the fundamental unit of study and ask if the science has a quantitative model of that unit that tells you how, what, why, when of its past and future behavior.
In physics this unit has 4 interconnected entities:- space, time, matter, energy. The first quantitative model of these 4 comes from Newton and his work launches physics as a true science (even though Galileo and others who came before him did a lot of good work, the absence of this quantitative model makes their works before physics as a proper science).
In chemistry, this unit is the molecule. Even though descriptive features of chemical reactions had been investigated from 17th century onwards (Dalton, Lavoisier etc.) the quantitative model of molecules that explains how all molecules behave had to wait the periodic table, the explication of atoms by modern physics and rise of quantum mechanics that explains chemical change through changes in energy levels of electrons. All of this came together only after 1940.
In biology, the unit is the cell. The explication of the cell is very very recent and had to wait for advances in genetics, analysis of proteins, better microscopes that can look inside a cell in real time. It is only in the last 20 years that one can say that cells are becoming well enough understood to build quantitative models for it very basic functions.
