ALA Booklist (Sun May 01 00:00:00 CDT 2016)

In the annals of class-petdom, few indeed could ever match aptly named Hamstersaurus Rex for loyalty and ferocity t to mention an insatiable appetite for snack food manufactured in the labs, whoops, no, "kitchens" of local megacorporation SmilesCorp. Transformed into a shark-toothed hybrid, thanks to an overdose of bodybuilding supplement, Hammie Rex joins forces with sixth-grade bully victim Sam Gibbs and repeatedly comes to the rescue in encounters with Kiefer "Beefer" Vanderkoff, menace of Horace Hotwater Middle School. With Sam's frequent cartoon drawings catching the comical high spots, events escalate from the odd swirly to a climactic Science Night catastrophe featuring both a battle royal between the redoubtable rodent and Beefer's boa, and the unveiling of SmilesCorp's latest development. The corporate satire is just byplay for the main event, though; by the end, the bully has been so humiliated that readers may feel a morsel of sympathy (just to keep things tidy, he transfers to another school), and Sam and his shirt-pocket buddy are triumphant.

Horn Book

After Sam dubs the classroom pet Hamstersaurus Rex, it eats a strange protein powder and mutates into a tiny dinosaur-hamster hybrid; Sam teams up with "Hammie" to stop a bully. In Squirrel Kong, they prove another mutant framed Hammie for attacking the school. Amusing, Big Natestyle black-and-white spot art can't salvage this forgettable new series, filled with lackluster characters and hackneyed cartoon antics.

Kirkus Reviews

Taking care of a pet can be time-consuming, but caring for a secret mutant hamster could take over your life.When a hamster mysteriously appears at the back of Mr. Copeland's sixth-grade classroom, Sam Gibbs, though he hasn't been the most popular student since the, ah, caricature-drawing incident, gets to name it: Hamstersaurus Rex (due to its tiny T-rex arms). Hammie escapes and later saves Sam from Kiefer "Beefer" Vanderkoff, Horace Hotwater Middle School's dimmest bully, by dropping a solar system made of pennies on Beefer's head. After gorging on SmilesCorp snacks and a different product called Dinoblast Powerpacker, Hammie mutates into a part-dinosaur, part-hamster eating machine with a fondness for Sam, who can't take Hammie home due to his mother's fur allergy. Can Sam keep Hammie a secret, save the rodent from Beefer's revenge, and feed the furry garbage disposal enough to quiet its rampages? O'Donnell kicks off a new series with an illustrated origin story sure to please fans of Betty G. Birney's Humphrey and Lincoln Peirce's Big Nate. High jinks are funny and gross without being too rude, and characters are developed just realistically enough to ensure readers will identify with Sam and his female best friend, Dylan. Miller's cartoons depict a largely white student body, including Sam, Beefer, and Dylan. A certain pleaser where furry fictions are well-loved. (Science fiction. 7-11)

School Library Journal (Thu Sep 01 00:00:00 CDT 2016)

Gr 3-6 Entering the extended family that includes Timmy Failure, Otis Dooda, and Greg Heffley, Sam Gibbs is a lovable, misunderstood outsider. Sam is down and out because of an ill-fated foray into caricature drawing that turns his classmates against him and leaves him ripe and ready for a magical sidekick. He finds one when the class hamster consumes a bit too much of their gym teacher's bodybuilding powder and transforms into a mutant creature with a voracious appetite and physical characteristics of a small but incredibly strong dinosaur. O'Donnell's comedy bona fides include writing for the TV show Billy on the Street and penning essays for McSweeney's and The New Yorker . As with most successful kid-centric comedy, he gets lots of mileage out of the communication breakdown between kids and adults, which enables Sam to hide his wild, snack food-wolfing pal much longer than he should be able to. O'Donnell's farcical stock characters (nicely complemented by Miller's cartoon-style illustrations), such as the teacher's pet and the secretly sad gym teacher, are another source of amusement. The more major characters, including Sam's disc golf-playing BFF Dylan and swirlie-loving bully, Beefer Vanderkoff, are only modestly fleshed outnot necessarily a bad thing, since O'Donnell is aiming for rapid-fire amusement in the form of briskly deployed gags. O'Donnell misses an opportunity by not giving Hamstersaurus Rex, the character, a voice of his own. That would have made Sam's alone time with the swiftly changing animal more satisfying (and potentially funnier). Still, adults and kids alike will find that O'Donnell's deadpan, mildly absurdist writing style will generate some satisfying laughs. VERDICT A funny, lighthearted option for fans of Tom Angleberger. Abigail Garnett, Brooklyn Public Library