X0206 3 2013-06-26 0 0001509190 ARATANA THERAPEUTICS, INC. PETX 0001379218 Vander Vort John C/O MPM ASSET MANAGEMENT 200 CLARENDON STREET, 54TH FLOOR BOSTON MA 02116 1 0 1 0 Common Stock 180505 I See Footnote Common Stock 24067 D Series A Preferred Stock Common Stock 2406739 I See Footnote Series B Preferred Stock Common Stock 802246 I See Footnote Series C Preferred Stock Common Stock 225631 I See Footnote Reflects a 1-for-1.662 reverse split effected May 22, 2013. The shares are held as follows: 173,755 by MPM BioVentures V, L.P. ("BV V") and 6,750 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. The Reporting Person is a member of BV LLC. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. Each share of Series A Preferred Stock, Series B Preferred Stock and Series C Preferred Stock is convertible into 0.6016847 of a share of Common Stock without payment of further consideration and will automatically convert into 0.6016847 of a share of Common Stock upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. The shares are held as follows: 2,316,738 by BV V and 90,001 by AM BV5. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. The shares are held as follows: 772,246 by BV V and 30,000 by AM BV5. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. The shares are held as follows: 217,194 by BV V and 8,437 by AM BV5. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. /s/ John Vander Vort 2013-06-26