Sec Form 4 Filing - MPM BIOVENTURES V, L.P. @ ARATANA THERAPEUTICS, INC. - 2014-03-10

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person MPM BIOVENTURES V, L.P. 2. Issuer Name and Ticker or Trading Symbol ARATANA THERAPEUTICS, INC. [ PETX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O MPM ASSET MANAGEMENT, 200 CLARENDON STREET, 54TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 03/10/2014 (Street) BOSTON, MA02116 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 03/10/2014 S 600,000 ( 1 ) D $ 20.02 2,751,048 I See Footnote ( 2 ) Common Stock 38,386 I By Luke Evnin Common Stock 22,767 I By James Paul Scopa Common Stock 17,937 I By Vaughn Kailian ( 3 ) Common Stock 37,117 I By MPM Capital LLC ( 4 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MPM BIOVENTURES V, L.P. C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X Scopa James Paul C/O MPM ASSET MANAGEMENT 601 GATEWAY BOULEVARD, SUITE 350 SOUTH SAN FRANCISCO, CA94080 X EVNIN LUKE C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X Foley Todd C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X GADICKE ANSBERT C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X KAILIAN VAUGHN M C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X MPM ASSET MANAGEMENT INVESTORS BV5 LLC C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X MPM BIOVENTURES V GP LLC C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X MPM BIOVENTURES V LLC C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON, MA02116 X Signatures By Ansbert Gadicke, member of MPM BioVentures V LLC, the managing member of MPMBioVentures V GP LLC, the general partner of MPM BioVentures V, L.P. /s/ Ansbert Gadicke 03/12/2014 Signature of Reporting Person Date /s/ James Paul Scopa 03/12/2014 Signature of Reporting Person Date /s/ Luke Evnin 03/12/2014 Signature of Reporting Person Date /s/ Todd Foley 03/12/2014 Signature of Reporting Person Date /s/ Ansbert Gadicke 03/12/2014 Signature of Reporting Person Date /s/ Vaughn Kailian 03/12/2014 Signature of Reporting Person Date By Ansbert Gadicke, member of MPM BioVentures V LLC, the manager of MPM Asset Management Investors BV5 LLC /s/ Ansbert Gadicke 03/12/2014 Signature of Reporting Person Date By Ansbert Gadicke, member of MPM BioVentures V LLC, the managing member of MPM BioVentures V GP LLC /s/ Ansbert Gadicke 03/12/2014 Signature of Reporting Person Date By Ansbert Gadicke, member of MPM BioVentures V LLC /s/ Ansbert Gadicke 03/12/2014 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares were sold as follows: 577,520 by MPM BioVentures V, L.P. ("BV V") and 22,480 by MPM Asset Management Investors BV5 LLC ("AM BV5"). MPM BioVentures V GP LLC and MPM BioVentures V LLC ("BV LLC") are the direct and indirect general partners of BV V and BV LLC is the manager of AM BV5. Ansbert Gadicke, Luke Evnin, Vaughn M. Kailian, James Paul Scopa and Todd Foley are the members of BV LLC. Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its respective pecuniary interest therein. ( 2 )The shares are held as follows: 2,647,974 by BV V and 103,074 by AM BV5. Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its respective pecuniary interest therein. ( 3 )Includes 2,627 shares held by The Vaughn and Patricia Kailian Revocable Trust u/a/dtd 12/18/1992, of which the Reporting Person is trustee. ( 4 )Medical Portfolio Management LLC ("MPM Medical") is the managing member of MPM Capital LLC, and Messrs. Evnin and Gadicke are members of MPM Medical. Messrs. Evnin and Gadicke disclaim beneficial ownership of the shares held by MPM Capital LLC except to the extent of their respective pecuniary interests therein.

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