Updated: May 21, 2010
Additions/Comments:

The Cretaceous–Tertiary extinction event, which occurred approximately 65.5 million years ago, is widely known as the K–T extinction event where K is the traditional abbreviation for the Cretaceous Period derived from the German name "Kreidezeit", and T is the abbreviation for the Tertiary Period (a period of time now covered by the Paleogene and Neogene periods). Whatever the name, this event saw the large-scale mass extinction of approximately half of all animal and plant species in a geologically short period of time. It famously ended the "Age of Reptiles" because many of the archosaurs, a group of reptiles including the birds, crocodiles, pterosaurs and most notably, the dinosaurs, suddenly vanished from the fossil record. There have been hundreds of theories as to its cause with the most notable being those of an impact event or events, catastrophic volcanic activity, falling sea level or a combination of events.

But what if the K-T extinction event had not occurred? How might dinosaurs and their allies have evolved? Below, in the best tradition of Dinosaur Central magpie-ing, we have cherry-picked the Internet and elsewhere for a collection of web and other material that explore this notion. These resources range from rational to the surrealistic; from the sober to the whimsical.

Non-fiction

Novels

Short fiction

Television

Other

Interlude 1: What is it with dinosaurs and the Wild West?

The Dinosauroid

Articles

A gallery of dinosauroids

Interlude 2: A checklist of dinosauroids and their kin in fiction

Interlude 3: "Dinosauroids" from filmed fiction

The New Dinosaurs: An Alternative Evolution
A book written by geologist and palaeontologist Dougal Dixon. While Dixon's earlier book After Man is set fifty million years in the future, The New Dinosaurs speculates on how the dinosaurs would have evolved over the last 65 million years had the Cretaceous-Tertiary extinction event not taken place.

The New Dinosaurs: An alternative evolution
Very naughtily the whole book is available online.

Wikipedia: The New Dinosaurs: An Alternative Evolution

New Dinosaurs
A review by Darren Naish on the Dinosaur Mailing List.

Speculations on Dixon’s New Dinosaurs: Classifying The New Dinosaurs for Spec World
An essay Darren Naish has written that attempts to combine Dougal Dixon's book The New Dinosaurs with the more recent web work "Spec World" (see below).

Come back Lank, (nearly) all is forgiven
An blog entry by Darren Naish examining the plausibility of the Lank, an evolved hypothetical pterosaur from Dixon's The New Dinosaurs.

The Speculative Dinosaur Project ("Spec World")
A large and comprehensive website that catalogues the life of an alternative Earth where the KT extinction did not occur.

The Bestiary: An Illustrated Guide to the Beasts of Skull Island
Part of the website created for Peter Jackson's 2005 version of King Kong. Select "The Bestiary" from Special Features to see a selection from the vast menagerie of animals created by the film makers.

Kong: King Of Skull Island
Joe DeVito (Author, Artist), Brad Strickland (Author)
In a way similar to Jackson's Kong, the dinosaurs of this lavishly illustrated novel have continued to evolve. These include the dromaeosaur "Slashers", the intelligent mega-theropod "Gaw" and a race of sentient dinosaurs, the Deathrunners.

Eden Trilogy
Harry Harrison
In a world where dinosaurs never went extinct, hunter-gatherer clans of humans live among the great beasts in North America, meanwhile, the Yilane, a race of intelligent, evolved mesosaurs, thrive in Africa an Europe. But when an oncoming ice age forces the cold-blooded Yilane to explore westward, they discover the humans and take a young boy named Kerrick back to Africa with them as their slave. The series chronicles the adventures of Kerrick who escapes his captors and comes to lead his people against the saurian threat from across the sea.

Wikipedia: West of Eden

Prehistoric Pulp: West of Eden

West of Eden: An Interview with Harry Harrison

Second Summer: The Turnback Time
Amelia Walsh and James Stambaugh
Planet Earth, reduced by global warming to an apocalyptic wilderness, finds its inhabitants decimated by a reawakened Mesozoic plague. Then, rising from millions of years of hibernation, a breed of reasoning dinosaurs, Troodons, enter what is left of a world devastated by the human species and plague.

Destroyermen Saga
Tayor Anderson
Anderson’s outstanding first novel combines alternate history and seafaring. Two U.S. four-stacker destroyers on the run from the Japanese in the spring of 1942 sail into a mysterious squall. The USS Walker emerges upon an alternate earth, where the dinosaurs were never wiped out. One savage sapient race, the Grik, has evolved from the raptors; another, from lemurs. The latter becomes the allies of the castaways in parallel time, and together they prepare to fight the Grik, solve some of the mysteries of this world, and find the missing second destroyer.

Titles in the series included: Into the Storm: Destroyermen, Book I, Crusade: Destroyermen and Maelstrom: Destroyermen, Book III.

Charon's Ark
Rick Gauger
To the teachers and students of Seattle’s Garfield High School, the trip was just a public relations lark – for helping a wealthy Pacific island open a science museum, they were to get a free trip around the world. It all seemed too easy. It was. As their chartered 747 crossed the Pacific, a huge spacecraft swooped down, cut off its wings, swallowed it up, and headed deep into outer space. Next stop: Charon, the moon of Pluto. They discover that Charon is a hollow sphere and was built by aliens as a nature preserve to save Earth’s dinosaurs.

The Rex series
Eric Garcia
In Eric Garcia's wild but winning first mystery, dinosaurs never did get wiped out--they evolved secretly and now make up about 5 percent of the world's population. There are dinosaur doctors, lawyers, even detectives like Rubio--although he's hit a low point in his own career because of the suspicious death of his beloved partner. This series comprises three titles: Anonymous Rex (1999), Casual Rex (2001) and Hot and Sweaty Rex (2004)

The People of the Pole
Charles Derennes
The North Pole Kingdom is a country under the Arctic, inhabited by civilized dinosaurs. It consists of a maze of underground tunnels with several exits onto the icy wastes. The dinosaur society is carefully organized and all members have specific occupations. The main job is to watch over huge machines that transform the North Pole’s electromagnetic energy into heat and light. The workers responsible for this task are accompanied by younger apprentices.  Should a worker neglect his duties, the apprentice takes over immediately and the worker is driven to the slaughterhouse. The dinosaurs dress in a sort of overall made out of sealskin. Their faces are like those of giant lizards and betray no emotions.

Fallen Cloud Saga
Kurt R.A. Giambastian
A series of four books, including The Year the Cloud Fell, The Spirit of Thunder, Shadow of the Storm, and From the Heart of the Storm chronicling an alternative world in which North American geography includes a large gulf where Texas should be, and some species of dinosaurs surviving to modern time.

The Homecoming
Barry B. Longyear
After 70 million star cycles, the Nitolans' star fleet returns to its beloved planet, only to find that its name is now Earth and its dominant race has evolved from what the dinosaur-like Nitolans knew as a kind of edible tree squirrel.

Dinosaur Wars
Thomas P. Hopp
Dinosaurs are not extinct. Wildlife biologist Chase Armstrong and rancher’s daughter Kit Daniels are swept into an epic struggle when a species of intelligent, human-sized dinosaur returns from outer space to reclaim its home world —our world! The invaders bring with them all the great beasts of the Cretaceous Era. A sequel, Dinosaur Wars: Counterattack followed.

"Dinosaur on a Bicycle"
Tim Sullivan
In an alternate universe where intelligent dinosaurs dominate the earth, a 19th-century dinosaur scientist sends his assistant back to the Cretaceous Era to visit their relatives. He meets up with a couple of time-traveling humans from another alternate universe and has some interesting adventures with the female after the man is eaten by a T-rex. They eventually discover a Nexus of Realities where they meet up with intelligent, time-traveling monkeys, raccoons, dogs, cats, lobsters, fish, cockroaches, rats, etc.

"Foster Mother"
Carol Emshwiller
A woman in an isolated mountain region raises an infant dinosauroid to be a weapon, but forms an emotional bond with it that leads her to question whether or not she'll be able to give up custody of her foster child. A short story found in Report to the Men's Club and Other Stories.

"Obsidian Harvest"
Rick Cook and Ernest Hogan
Set in a world where the Aztec Empire never fell and dinosaurs can still be found in South America. Published in Analog, April 2000.

"One Giant Step"
John E. Stith
In an alternate future, the super-intelligent descendants of the dinosaurs invent time travel. So they travel back in time 65 million years to meet their dinosaur ancestors. “That’s one small step for a reptile, one giant step for Reptilia.” But one of the three travelers, Ektor, has smuggled back some bombs, which he uses to wipe out all his own ancestors, because of all the suffering and mass extinction of other species the reptile overlords have caused. “Reptiles were not meant to rule the Earth… let some other species take over,” he announces before detonating. As result, insects develop intelligence and go back 65 million years.
Published: In Dinosaur Fantastic (eds. Mike Resnick and Martin H. Greenberg), DAW 1993 and SFBC 1994.

"Trembling Earth"
Allen Steele
A presidential candidate's visit to the dinosaur-inhabited Okafenokee wildlife refuge goes terribly wrong, and the details are revealed as the survivors explain their harrowing experience to a committee. Included in the anthology Dinosaurs II edited by Jack Dann and Gardner Dozois.

Dinosapien
A British/Canadian children's television program that focuses on what would happen if dinosaurs had continued to exist and evolve into more intelligent beings.

Dino-Rampage
The Dino-rampage series is a 3D animated series depicting the coexistence of dinosaurs with human beings in future time.

Dinosaur Planet: Broncosaurus Rex
Dinosaur Planet: Broncosaurus Rex is a science fiction world setting. The basic premise is that the Civil War did not end as we know it, but resulted in separate Federal and Confederate nations. This state continued into the space age. In the year 2202, an alien planet full of dinosaurs was discovered, opening new mysteries and establishing the world of Dinosaur Planet: Broncosaurus Rex.

And in a similar vein...

Interlude 1: What is it with dinosaurs and the Wild West?

Anthroposaurus Sapiens
The article argues the case that some dinosaurs may have got to be really brainy – to the point of hominid intelligence.

Dinos on the Moon
Report on a presentation by NASA scientist Chris McKay who suggests that we dig for dinosaur relics on the moon at a recent SETI conference.

DeviantArtist: Dinosauroids
DeviantART artists explore the dinosauroid: nemo-ramjet and povorot (Simon Roy)

A gallery

Dinosauroids revisited
A blog entry by Darren Naish examining the "dinosauroid" or humanoid dinosaur idea.

Forget K-T
Some visual musings by Simon Roy on speculative dinosaurs: what would have happened evolutionarily had the Cretaceous extinction not happened... or rather, that Chicxulub had never struck Mexico.

How intelligent dinosaurs conquered the world
Another blog entry by Darren Naish drawing attention to the smart theropods invented by John McLoughlin and Mike Magee.

Dinosauroid cave art discovered
Darren Naish's notion of what a "real" dinosauroid might look like has inspired blogger Nemo Ramjet to produce Avisapiens saurotheos, a post-Cretaceous big-brained maniraptoran. On a parallel Earth where theropod dinosaurs have followed a similar evolutionary path to hominids, this is the result.

Smartasaurus
An article in Cosmos magazine considering the question that if they hadn't been wiped out in a global catastrophe 65 million years ago, could dinosaurs have evolved intelligence?

Troodon sapiens?: Thoughts on the "Dinosauroid"
By Brian Switek, an ecology and evolution student at Rutgers University.

Dino Friday Repost: Dinosauroids!
At his Love in the Time of Chasmosaurs blogsite David Orr reflects on Dale Russell's dinosauroid thought experiment.

Interlude 3: "Dinosauroids" from filmed fiction