Question: Code of the Clans is a field guide in a novel series written by a group of authors that collectively use what pseudonym? 

Context articles: Warriors (novel series)
Code of the Clans
Twilight (Hunter novel)
Cats of the Clans
A Field Guide to Australian Birds (Slater)
Secrets of the Clans
Battles of the Clans
Roger Conant (herpetologist)
The Spiderwick Chronicles
The Princeton Field Guide to Dinosaurs

Warriors is a series of novels published by HarperCollins; it is written by authors Kate Cary, Cherith Baldry, Tui Sutherland, with the plot developed by editor Victoria Holmes, who collectively use the pseudonym Erin Hunter.
 The series follows the adventures of four Clans of wild cats—ThunderClan, ShadowClan, WindClan, and RiverClan —in their forest and lake homes, who look up to StarClan, their warriors ancestors, and spirits in the stars, who guide the four clans.
 SkyClan, the long-forgotten fifth Clan of the forest, is later introduced in the stand-alone novel "Firestar's Quest".
 It receives additional focus in the novel "SkyClan's Destiny", the manga trilogy "SkyClan and the Stranger", and the 2013 novella "Cloudstar's Journey".
Code of the Clans is a field guide in the "Warriors" novel series.
 Code of the Clans is about the Warrior code and includes an ominous sign from StarClan that signaled the need to patrol borders, the unexpected help from a warrior ancestor that cemented the importance of elders, a secret coup that led to a deputy's new role, a medicine cat's pleas that stopped a spree of inner Clan bloodshed and many more stories.
Twilight is a children's fantasy novel in the "Warriors" novel series written by Erin Hunter, a pseudonym used by multiple authors.
 It is the fifth book in the series "" and continues the cat clans' adventures while seeking a new home.
 It was generally well received by critics.
Cats of the Clans is a field guide in the "Warriors" novel series.
 the novel itself consists of biographical sketches of the Clans and cats, in the form of stories told to three kittens who died and went to StarClan.
 The narrator is Rock, a mysterious blind cat.
 The book has sold more than 150,000 copies.
A Field Guide to Australian Birds is a two-volume bird field guide published by Rigby of Adelaide, South Australia, in its Rigby Field Guide series.
 The first volume (Volume One: Non-Passerines) was issued in 1970, with the second volume (Volume Two: Passerines) appearing in 1974.
 It was Australia’s first new national bird field guide since the 1931 publication of the first edition of Neville Cayley’s "What Bird is That?
".
 It was principally authored by Australian ornithologist, artist and photographer Peter Slater.
Secrets of the Clans is the first field guide in the "Warriors" novel series.
 It is a book containing several short stories, as well as general information, serving as a guide to the fictional world described in the other "Warriors" novels.
Battles of the Clans is the fourth field guide in the Warriors series.
 It was written by Erin Hunter and released on June 1, 2010.
Roger Conant (May 6, 1909 – December 19, 2003) was an American herpetologist, author, educator and conservationist.
 He was Director Emeritus of the Philadelphia Zoo and Adjunct Professor at the University of New Mexico.
 He wrote one of the first comprehensive field guides for North American reptiles in 1958 entitled: "Field Guide to Reptiles and Amphibians of the Eastern United States", in the Peterson Field Guide series.
The Spiderwick Chronicles is a series of children's books by Tony DiTerlizzi and Holly Black.
 They chronicle the adventures of the Grace children, twins Simon and Jared and their older sister Mallory, after they move into the Spiderwick Estate and discover a world of fairies that they never knew existed.The first book, "The Field Guide", was published in 2003 and then followed by "The Seeing Stone "(2003), "Lucinda's Secret "(2003), "The Ironwood Tree "(2004), and "The Wrath of Mulgarath "(2004).
 Several companion books have been published including "Arthur Spiderwick's Field Guide to the Fantastical World Around You "(2005), "Notebook for Fantastical Observations "(2005), and "Care and Feeding of Sprites" (2006).
 A second series, entitled "Beyond the Spiderwick Chronicles "includes "The Nixie's Song" (2007), "A Giant Problem" (2008), and "The Wyrm King ("2009).
 A feature film adaptation, also titled "The Spiderwick Chronicles", was produced by Nickelodeon Movies and premiered on February 14, 2008; an accompanying video game was released in early February 2008.
The Princeton Field Guide to Dinosaurs is a book on dinosaurs written by the paleontologist and artist Gregory S. Paul.
 It and was published by Princeton University Press in 2010.
 It has also been printed in a British edition titled "Dinosaurs: A Field Guide", produced by A & C Black.