| FORM 4 | 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 or Section 30(h) of the Investment Company Act of 1940 | 
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| Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). | |||||||||||||||||
| Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10. | |||||||||||||||||
| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 | 2. Issuer Name and Ticker or Trading Symbol ARATANA THERAPEUTICS, INC. [ PETX ] | 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) 
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| 3. Date of Earliest Transaction
         (Month/Day/Year) 03/03/2014 | ||||||||||||||||||||||||||
| 4. If Amendment, Date of Original Filed
         (Month/Day/Year) | 6. Individual or Joint/Group Filing (Check Applicable Line) 
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| Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned | ||||||||||
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| 1. Title of Security (Instr. 3) | 2. Transaction Date (Month/Day/Year) | 2A. Deemed Execution Date, if any (Month/Day/Year) | 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 | 03/03/2014 | J(1) | 1,000,000(2) | D | $0.00 | 3,351,048 | I | See Footnote(3) | ||
| Common Stock | 03/03/2014 | J(1) | 20,876 | A | $0.00 | 26,713 | I | By Ansbert Gadicke | ||
| Common Stock | 03/03/2014 | J(1) | 20,876 | A | $0.00 | 38,386 | I | By Luke Evnin | ||
| Common Stock | 03/03/2014 | J(1) | 20,876 | A | $0.00 | 22,767 | I | By James Paul Scopa | ||
| Common Stock | 03/03/2014 | J(1) | 15,310 | A | $0.00 | 17,937 | I | By Vaughn Kailian(4) | ||
| Common Stock | 03/03/2014 | J(1) | 12,247 | A | $0.00 | 12,393 | I | By The Todd Foley Trust | ||
| Common Stock | 03/03/2014 | J(1) | 37,117 | A | $0.00 | 37,117 | I | By MPM Capital LLC(5) | ||
| Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities) | |||||||||||||||
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| 1. Title of Derivative Security (Instr. 3) | 2. Conversion or Exercise Price of Derivative Security | 3. Transaction Date (Month/Day/Year) | 3A. Deemed Execution Date, if any (Month/Day/Year) | 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 (Month/Day/Year) | 7. Title and Amount of Securities Underlying Derivative Security (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: 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 | ||||||||
| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
 | ||||||||||||||||||||||||
| 1. Name and Address of Reporting Person* 
 
 
 (Street) 
 
 Relationship of Reporting Person(s) to Issuer 
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| Explanation of Responses: | 
| 1. Pro-rata distribution of partnership interests. | 
| 2. The shares were distributed as follows: 962,533 by MPM BioVentures V, L.P. ("BV V") and 37,467 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. | 
| 3. The shares are held as follows: 3,225,494 by BV V and 125,554 by AM BV5. Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its respective pecuniary interest therein. | 
| 4. 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. | 
| 5. MPM Founders LLC ("MPM Founders") is the managing member of MPM Capital LLC, and Messrs. Evnin and Gadicke are members of MPM Founders. 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. | 
| Remarks: | 
| By Ansbert Gadicke, member of MPM BioVentures V LLC, the managing member of MPM BioVentures V GP LLC, the general partner of MPM BioVentures V, L.P. /s/ Ansbert Gadicke | 03/05/2014 | |
| /s/ James Paul Scopa | 03/05/2014 | |
| /s/ Luke Evnin | 03/05/2014 | |
| /s/ Todd Foley | 03/05/2014 | |
| /s/ Ansbert Gadicke | 03/05/2014 | |
| /s/ Vaughn Kailian | 03/05/2014 | |
| By Ansbert Gadicke, member of MPM BioVentures V LLC, the manager of MPM Asset Management Investors BV5 LLC /s/ Ansbert Gadicke | 03/05/2014 | |
| By Ansbert Gadicke, member of MPM BioVentures V LLC, the managing member of MPM BioVentures V GP LLC /s/ Ansbert Gadicke | 03/05/2014 | |
| By Ansbert Gadicke, member of MPM BioVentures V LLC /s/ Ansbert Gadicke | 03/05/2014 | |
| ** Signature of Reporting Person | Date | |
| Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. | ||
| * If the form is filed by more than one reporting person, see Instruction 4 (b)(v). | ||
| ** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a). | ||
| Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure. | ||
| Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number. | ||