SC 13D

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO § 240.13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO

§ 240.13d-2(a)

(Amendment No.  )¹

Aratana Therapeutics, Inc.

(Name of Issuer)

Common Stock, $0.001 par value per share

(Title of Class of Securities)

03874P101

(CUSIP Number)

glenn w. welling

engaged capital, llc

610 Newport Center Drive, Suite 250

Newport Beach, California 92660

(949) 734-7900

STEVE WOLOSKY, ESQ.

OLSHAN FROME WOLOSKY LLP

1325 Avenue of the Americas

New York, New York 10019

(212) 451-2300

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

April 4, 2018

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box ¨.

Note:  Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits.  See § 240.13d-7 for other parties to whom copies are to be sent.

1              The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Engaged Capital Flagship Master Fund, LP
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
			WC
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			CAYMAN ISLANDS
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					2,189,101
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					2,189,101
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			2,189,101
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			4.8%
	14	TYPE OF REPORTING PERSON
			PN

2

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Engaged Capital Flagship Fund, LP
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
			OO
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			DELAWARE
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					2,189,101
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					2,189,101
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			2,189,101
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			4.8%
	14	TYPE OF REPORTING PERSON
			PN

3

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Engaged Capital Flagship Fund, Ltd.
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
			OO
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			CAYMAN ISLANDS
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					2,189,101
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					2,189,101
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			2,189,101
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			4.8%
	14	TYPE OF REPORTING PERSON
			CO

4

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Engaged Capital, LLC
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
			OO
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			DELAWARE
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					2,400,000
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					2,400,000
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			2,400,000
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			5.2%
	14	TYPE OF REPORTING PERSON
			OO

5

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Engaged Capital Holdings, LLC
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
			OO
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			DELAWARE
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					2,400,000
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					2,400,000
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			2,400,000
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			5.2%
	14	TYPE OF REPORTING PERSON
			OO

6

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Glenn W. Welling
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
			OO
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			USA
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					2,400,000
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					2,400,000
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			2,400,000
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			5.2%
	14	TYPE OF REPORTING PERSON
			IN

7

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Craig A. Barbarosh
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			USA
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					- 0 -
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					- 0 -
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			- 0 -
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			0%
	14	TYPE OF REPORTING PERSON
			IN

8

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Eric J. Ende
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			USA
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					- 0 -
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					- 0 -
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			- 0 -
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			0%
	14	TYPE OF REPORTING PERSON
			IN

9

CUSIP No. 03874P101

	1	NAME OF REPORTING PERSON
			Lowell W. Robinson
	2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP				(a) ☒
						(b) ☐
	3	SEC USE ONLY
	4	SOURCE OF FUNDS
	5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)				☐
	6	CITIZENSHIP OR PLACE OF ORGANIZATION
			USA
NUMBER OF			7	SOLE VOTING POWER
SHARES
BENEFICIALLY					- 0 -
OWNED BY			8	SHARED VOTING POWER
EACH
REPORTING					- 0 -
PERSON WITH			9	SOLE DISPOSITIVE POWER
					- 0 -
			10	SHARED DISPOSITIVE POWER
					- 0 -
	11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
			- 0 -
	12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
	13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
			0%
	14	TYPE OF REPORTING PERSON
			IN

10

CUSIP No. 03874P101

The following constitutes the Schedule 13D filed by the undersigned (the “Schedule 13D”).

Item 1. Security and Issuer.

This statement relates to the common stock, $0.001 par value per share (the “Shares”), of Aratana Therapeutics, Inc., a Delaware corporation (the “Issuer”). The address of the principal executive offices of the Issuer is 11400 Tomahawk Creek Parkway, Suite 340, Leawood, Kansas 66211.

Item 2. Identity and Background.

(a) This statement is filed by:

(i) Engaged Capital Flagship Master Fund, LP (“Engaged Capital Flagship Master”), a Cayman Islands exempted limited partnership, with respect to the Shares directly and beneficially owned by it;

(ii) Engaged Capital Flagship Fund, LP (“Engaged Capital Fund”), a Delaware limited partnership, as a feeder fund of Engaged Capital Flagship Master;

(iii) Engaged Capital Flagship Fund, Ltd. (“Engaged Capital Offshore”), a Cayman Islands exempted company, as a feeder fund of Engaged Capital Flagship Master;

(iv) Engaged Capital, LLC, a Delaware limited liability company (“Engaged Capital”), as the general partner and investment adviser of Engaged Capital Flagship Master and the investment adviser of a certain managed account (the “Engaged Capital Account”);

(v) Engaged Capital Holdings, LLC, a Delaware limited liability company (“Engaged Holdings”), as the managing member of Engaged Capital;

(vi) Glenn W. Welling, as the Founder and Chief Investment Officer (“CIO”) of Engaged Capital and the sole member of Engaged Holdings;

(vii) Craig A. Barbarosh;

(viii) Eric J. Ende; and

(ix) Lowell W. Robinson.

Each of the foregoing is referred to as a “Reporting Person” and collectively as the “Reporting Persons.” Each of the Reporting Persons is party to that certain Joint Filing and Solicitation Agreement, as further described in Item 6. Accordingly, the Reporting Persons are hereby filing a joint Schedule 13D.

(b)       The address of the principal office of each of Engaged Capital Flagship Master and Engaged Capital Offshore is c/o Conyers Trust Company (Cayman) Limited, Cricket Square, Hutchins Drive, P.O. Box 2681, Grand Cayman KY1-1111, Cayman Islands. The address of the principal office of each of Engaged Capital Fund, Engaged Capital, Engaged Holdings and Mr. Welling is 610 Newport Center Drive, Suite 250, Newport Beach, California 92660. The officers and directors of Engaged Capital Offshore and their principal occupations and business addresses are set forth on Schedule A and are incorporated by reference in this Item 2. The principal business address of Mr. Barbarosh is 100 Spectrum Center Drive, Suite 1050, Irvine, California 92618. The principal business address of Dr. Ende is 6231 PGA Blvd., Suite 104-168, Palm Beach Gardens, Florida 33418. The principal business address of Mr. Robinson is 470 West End Avenue, New York, New York 10024.

11

CUSIP No. 03874P101

(c)       The principal business of Engaged Capital Flagship Master is investing in securities. Each of Engaged Capital Fund and Engaged Capital Offshore is a private investment partnership that serves as a feeder fund of Engaged Capital Flagship Master. Engaged Capital is a registered investment advisor and serves as the investment adviser to each of Engaged Capital Flagship Master, Engaged Capital Fund, Engaged Capital Offshore and the Engaged Capital Account. Engaged Capital is also the general partner of each of Engaged Capital Flagship Master and Engaged Capital Fund. Engaged Holdings serves as the managing member of Engaged Capital. Mr. Welling is the Founder and CIO of Engaged Capital, the sole member of Engaged Holdings and a director of Engaged Capital Offshore. Mr. Barbarosh is a partner at the international law firm of Katten Muchin Rosenman LLP. Dr. Ende is President of Ende BioMedical Consulting Group, Inc., a firm focused on helping life sciences companies raise capital, identify licensing partners and optimize corporate structure as well as analyzing both private and public investment opportunities for clients within the life sciences industry. Mr. Robinson is an experienced executive and currently serves as a director of EVINE Live Inc. (f/k/a ShopHQ), a digital omnichannel home shopping network.

(d)       No Reporting Person, nor any person listed on Schedule A, annexed hereto, has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e)       No Reporting Person, nor any person listed on Schedule A, annexed hereto, has during the last five years, been party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f)       Engaged Capital Flagship Master and Engaged Capital Offshore are organized under the laws of the Cayman Islands. Engaged Capital Fund, Engaged Capital and Engaged Holdings are organized under the laws of the State of Delaware. Messrs. Welling, Barbarosh, Ende and Robinson are citizens of the United States of America. The citizenship of the persons listed on Schedule A is set forth therein.

Item 3. Source and Amount of Funds or Other Consideration.

The Shares purchased by Engaged Capital Flagship Master and held in the Engaged Capital Account were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business). The aggregate purchase price of the 2,189,101 Shares beneficially owned by Engaged Capital Flagship Master is approximately $10,952,990, including brokerage commissions. The aggregate purchase price of the 210,899 Shares held in the Engaged Capital Account is approximately $1,052,292, including brokerage commissions.

12

CUSIP No. 03874P101

Item 4. Purpose of Transaction.

The Reporting Persons purchased the Shares based on the Reporting Persons’ belief that the Shares, when purchased, were undervalued and represented an attractive investment opportunity. Depending upon overall market conditions, other investment opportunities available to the Reporting Persons, and the availability of Shares at prices that would make the purchase or sale of Shares desirable, the Reporting Persons may endeavor to increase or decrease their position in the Issuer through, among other things, the purchase or sale of Shares on the open market or in private transactions or otherwise, on such terms and at such times as the Reporting Persons may deem advisable.

Engaged Capital (together with its affiliates, “Engaged”) has engaged, and intends to continue to engage, in communications with the Issuer’s Board of Directors (the “Board”) and management team regarding means to create stockholder value.

On March 23, 2018, Engaged delivered a letter (the “Nomination Letter”) to the Issuer nominating Craig A. Barbarosh, Eric J. Ende and Lowell W. Robinson (the “Nominees”) for election to the Board at the 2018 annual meeting of stockholders (the “Annual Meeting”).

No Reporting Person has any present plan or proposal which would relate to or result in any of the matters set forth in subparagraphs (a) - (j) of Item 4 of Schedule 13D except as set forth herein or such as would occur upon or in connection with completion of, or following, any of the actions discussed herein. The Reporting Persons intend to review their investment in the Issuer on a continuing basis. Depending on various factors including, without limitation, the Issuer’s financial position and investment strategy, the price levels of the Shares, conditions in the securities markets and general economic and industry conditions, the Reporting Persons may in the future take such actions with respect to their investment in the Issuer as they deem appropriate including, without limitation, engaging in additional communications with management and the Board of the Issuer, engaging in discussions with stockholders of the Issuer and others about the Issuer and the Reporting Persons’ investment in the Issuer and Engaged’s nomination of the Nominees, making proposals to the Issuer concerning changes to the capital allocation strategy, capitalization, ownership structure, a sale of the Issuer, Board structure (including Board composition) or operations of the Issuer, purchasing additional Shares, selling some or all of their Shares, engaging in short selling of or any hedging or similar transaction with respect to the Shares, or changing their intention with respect to any and all matters referred to in Item 4.

Item 5. Interest in Securities of the Issuer.

(a)       The aggregate percentage of Shares reported owned by each person named herein is based upon 45,854,403 Shares outstanding as of March 9, 2018, which is the total number of Shares outstanding as reported in the Issuer’s annual report on Form 10-K filed with the Securities and Exchange Commission on March 14, 2018.

As of the close of business on April 4, 2018, Engaged Capital Flagship Master beneficially owned 2,189,101 Shares, constituting approximately 4.8% of the Shares outstanding. Each of Engaged Capital Fund and Engaged Capital Offshore, as feeder funds of Engaged Capital Flagship Master, may be deemed to beneficially own the 2,189,101 Shares owned by Engaged Capital Flagship Master, constituting approximately 4.8% of the Shares outstanding.

As of the close of business on April 4, 2018, 210,899 Shares were held in the Engaged Capital Account, constituting less than 1% of the Shares outstanding.

Engaged Capital, as the general partner and investment adviser of Engaged Capital Flagship Master and the investment adviser of the Engaged Capital Account, may be deemed to beneficially own the 2,400,000 Shares owned in the aggregate by Engaged Capital Flagship Master and held in the Engaged Capital Account, constituting approximately 5.2% of the Shares outstanding. Engaged Holdings, as the managing member of Engaged Capital, may be deemed to beneficially own the 2,400,000 Shares owned in the aggregate by Engaged Capital Flagship Master and held in the Engaged Capital Account, constituting approximately 5.2% of the Shares outstanding. Mr. Welling, as the Founder and CIO of Engaged Capital and sole member of Engaged Holdings, may be deemed to beneficially own the 2,400,000 Shares owned in the aggregate by Engaged Capital Flagship Master and held in the Engaged Capital Account, constituting approximately 5.2% of the Shares outstanding.

13

CUSIP No. 03874P101

As of the close of business on April 4, 2018, Messrs. Barbarosh, Ende and Robinson did not beneficially own any Shares, constituting 0% of the Shares outstanding.

Each Reporting Person, as a member of a “group” with the other Reporting Persons for the purposes of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), may be deemed the beneficial owner of the Shares directly owned by the other Reporting Persons.  The filing of this Schedule 13D shall not be deemed an admission that the Reporting Persons are, for purposes of Section 13(d) of the Exchange Act, the beneficial owners of any securities of the Issuer he or it does not directly own. Each of the Reporting Persons specifically disclaims beneficial ownership of the securities reported herein that he or it does not directly own.

(b)       By virtue of their respective positions with Engaged Capital Flagship Master, each of Engaged Capital Fund, Engaged Capital Offshore, Engaged Capital, Engaged Holdings and Mr. Welling may be deemed to have sole power to vote and dispose of the Shares reported owned by Engaged Capital Flagship Master.

By virtue of their respective positions with the Engaged Capital Account, each of Engaged Capital, Engaged Holdings and Mr. Welling may be deemed to have sole power to vote and dispose of the Shares held in the Engaged Capital Account.

(c)       Schedule B annexed hereto lists all transactions in securities of the Issuer by the Reporting Persons during the past 60 days. All of such transactions were effected in the open market.

(d)       No person other than the Reporting Persons is known to have the right to receive, or the power to direct the receipt of dividends from, or proceeds from the sale of, the Shares.

(e)       Not applicable.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

On April 4, 2017, the Reporting Persons entered into a Joint Filing and Solicitation Agreement pursuant to which, among other things, the parties agreed to (a) the joint filing on behalf of each of them of statements on Schedule 13D, and any amendments thereto, with respect to the securities of the Issuer and (b) solicit proxies for the election of the Nominees at the Annual Meeting. A copy of the Joint Filing and Solicitation Agreement is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Engaged Capital Flagship Master has entered into letter agreements pursuant to which it and its affiliates agreed to indemnify Messrs. Barbarosh, Ende and Robinson against claims arising from the solicitation of proxies from the Issuer’s stockholders in connection with the Annual Meeting and any related transactions. A form of the indemnification letter agreement is attached hereto as Exhibit 99.2 and is incorporated herein by reference.

14

CUSIP No. 03874P101

Other than as described herein, there are no contracts, arrangements, understandings or relationships among the Reporting Persons, or between the Reporting Persons and any other person, with respect to the securities of the Issuer.

Item 7. Material to be Filed as Exhibits.

99.1 Joint Filing and Solicitation Agreement, dated April 4, 2018.

99.2 Form of Indemnification Letter Agreement.

99.3 Powers of Attorney.

15

CUSIP No. 03874P101

SIGNATURES

After reasonable inquiry and to the best of his knowledge and belief, the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: April 5, 2018 

Engaged Capital Flagship Master Fund, LP
By:	Engaged Capital, LLC General Partner
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Founder and Chief Investment Officer

Engaged Capital Flagship Fund, LP
By:	Engaged Capital, LLC General Partner
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Founder and Chief Investment Officer

Engaged Capital Flagship Fund, Ltd.
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Director

Engaged Capital, LLC
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Founder and Chief Investment Officer

Engaged Capital Holdings, LLC
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Sole Member

/s/ Glenn W. Welling

Glenn W. Welling

Individually and as attorney-in-fact for Craig A. Barbarosh, Eric J. Ende and Lowell W. Robinson

16

CUSIP No. 03874P101

SCHEDULE A

Directors and Officers of Engaged Capital Flagship Fund, Ltd.

Name and Position	Principal Occupation	Principal Business Address	Citizenship
Glenn W. Welling Director*
Mark John Cook Director	Company Director	3rd Floor, Harbour Centre George Town, Grand Cayman Cayman Islands	Australia
Mark Victor Murray Director	Company Director	2F Landmark Square 64 Earth Close Seven Mile Beach Grand Cayman Cayman Islands	United Kingdom & British Overseas Territory Citizen (Cayman Islands)

*Mr. Welling is a Reporting Person and, as such, the information with respect to Mr. Welling called for by Item 2 of Schedule 13D is set forth therein.

CUSIP No. 03874P101

SCHEDULE B

Transactions in Securities of the Issuer During the Past 60 Days

Nature of the Transaction Securities Purchased/(Sold) Price Per Share($) Date of Purchase / Sale

Engaged Capital Flagship Master Fund, LP

Purchase of Common Stock	23,200	4.3692	04/02/2018
Purchase of Common Stock	6,688	4.5064	04/03/2018
Purchase of Common Stock	331,200	4.8726	04/04/2018

Engaged Capital, LLC

(Through the Engaged Capital Account)

Purchase of Common Stock	6,000	4.3692	04/02/2018
Purchase of Common Stock	1,731	4.5064	04/03/2018
Purchase of Common Stock	31,181	4.8726	04/04/2018

EX-99.1

Exhibit 99.1

JOINT FILING AND SOLICITATION AGREEMENT

WHEREAS, certain of the undersigned are stockholders, direct or beneficial, of Aratana Therapeutics, Inc., a Delaware corporation (the “Company”);

WHEREAS, Engaged Capital Flagship Master Fund, LP, Engaged Capital Flagship Fund, LP, Engaged Capital Flagship Fund, Ltd., Engaged Capital, LLC, Engaged Capital Holdings, LLC and Glenn W. Welling (together, “Engaged Capital”), Craig A. Barbarosh, Eric J. Ende and Lowell W. Robinson wish to form a group for the purpose of seeking representation on the Board of Directors of the Company (the “Board”) at the 2018 annual meeting of stockholders of the Company (including any other meeting of stockholders held in lieu thereof, and any adjournments, postponements, reschedulings or continuations thereof, the “2018 Annual Meeting”) and for the purpose of taking all other action necessary to achieve the foregoing.

NOW, IT IS AGREED, this 4^th day of April 2018 by the parties hereto:

1.       In accordance with Rule 13d-1(k)(1)(iii) under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), each of the undersigned (collectively, the “Group”) agrees to the joint filing on behalf of each of them of statements on Schedule 13D, and any amendments thereto, with respect to the securities of the Company. Each member of the Group shall be responsible for the accuracy and completeness of his/its own disclosure therein, and is not responsible for the accuracy and completeness of the information concerning the other members, unless such member knows or has reason to know that such information is inaccurate.

2.       So long as this agreement is in effect, each of the undersigned shall provide written notice to Olshan Frome Wolosky LLP (“Olshan”) of (i) any of their purchases or sales of securities of the Company or (ii) any securities of the Company over which they acquire or dispose of beneficial ownership. Notice shall be given no later than 24 hours after each such transaction. For purposes of this agreement, the term “beneficial ownership” shall have the meaning of such term set forth in Rule 13d-3 under the Exchange Act.

3.       Each of the undersigned agrees to form the Group for the purpose of (i) soliciting proxies for the election of the persons nominated by Engaged Capital to the Board at the 2018 Annual Meeting, (ii) taking such other actions as the parties deem advisable and (iii) taking all other action necessary or advisable to achieve the foregoing.

4.       Engaged Capital shall have the right to pre-approve all expenses incurred in connection with the Group’s activities and agrees to pay directly all such pre-approved expenses.

5.       Each of the undersigned agrees that any filing with the Securities and Exchange Commission, press release or stockholder communication proposed to be made or issued by the Group or any member of the Group in connection with the Group’s activities set forth in Section 3 shall be first approved by Engaged Capital, or its representatives, which approval shall not be unreasonably withheld.

6.       The relationship of the parties hereto shall be limited to carrying on the business of the Group in accordance with the terms of this agreement. Such relationship shall be construed and deemed to be for the sole and limited purpose of carrying on such business as described herein. Nothing herein shall be construed to authorize any party to act as an agent for any other party, or to create a joint venture or partnership, or to constitute an indemnification. Nothing herein shall restrict any party’s right to purchase or sell securities of the Company, as he/it deems appropriate, in his/its sole discretion, provided that all such purchases and sales are made in compliance with all applicable securities laws and the provisions of this agreement.

7.       This agreement may be executed in counterparts, each of which shall be deemed an original and all of which, taken together, shall constitute but one and the same instrument, which may be sufficiently evidenced by one counterpart.

8.       This agreement is governed by and will be construed in accordance with the laws of the State of New York. In the event of any dispute arising out of the provisions of this agreement or their investment in the Company, the parties hereto consent and submit to the exclusive jurisdiction of the United States District Court for the Southern District of New York located in the Borough of Manhattan or the courts of the State of New York located in the County of New York.

9.       Any party hereto may terminate his/its obligations under this agreement on 24 hours’ written notice to all other parties, with a copy by fax to Steve Wolosky at Olshan, Fax No. (212) 451-2222.

10.       Each party acknowledges that Olshan shall act as counsel for both the Group and Engaged Capital relating to their investment in the Company.

11.       Each of the undersigned parties hereby agrees that this agreement shall be filed as an exhibit to a Schedule 13D pursuant to Rule 13d-1(k)(1)(iii) under the Exchange Act.

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IN WITNESS WHEREOF, the parties hereto have caused this agreement to be executed as of the day and year first above written.

Engaged Capital Flagship Master Fund, LP
By:	Engaged Capital, LLC General Partner
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Founder and Chief Investment Officer

Engaged Capital Flagship Fund, LP
By:	Engaged Capital, LLC General Partner
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Founder and Chief Investment Officer

Engaged Capital Flagship Fund, Ltd.
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Director

Engaged Capital, LLC
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Founder and Chief Investment Officer

Engaged Capital Holdings, LLC
By:	/s/ Glenn W. Welling
	Name:	Glenn W. Welling
	Title:	Sole Member

/s/ Glenn W. Welling

Glenn W. Welling

Individually and as attorney-in-fact for Craig A. Barbarosh, Eric J. Ende and Lowell W. Robinson

EX-99.2

Exhibit 99.2

ENGAGED CAPITAL FLAGSHIP MASTER FUND, LP

c/o ENGAGED CAPITAL, LLC

610 Newport Center Drive, Suite 250

Newport Beach, California 92660

March __, 2018

Re: Aratana Therapeutics, Inc.

Dear ________:

Thank you for agreeing to serve as a nominee for election to the Board of Directors of Aratana Therapeutics, Inc. (the “Company”) in connection with the proxy solicitation that Engaged Capital Flagship Master Fund, LP and its affiliates (collectively, the “Engaged Capital Group”) is considering undertaking to nominate and elect directors at the Company’s 2018 annual meeting of stockholders, or any other meeting of stockholders held in lieu thereof, and any adjournments, postponements, reschedulings or continuations thereof (the “Engaged Capital Group Solicitation”). Your outstanding qualifications, we believe, will prove a valuable asset to the Company and all of its stockholders. This letter (this “Agreement”) will set forth the terms of our agreement.

The members of the Engaged Capital Group agree to jointly and severally indemnify and hold you harmless against any and all claims of any nature, whenever brought, arising from the Engaged Capital Group Solicitation and any related transactions, irrespective of the outcome; provided, however, that you will not be entitled to indemnification for claims arising from your gross negligence, willful misconduct, intentional and material violations of law, criminal actions or material breach of the terms of this Agreement; provided further, that upon your becoming a director of the Company, this indemnification shall not apply to any claims made against you in your capacity as a director of the Company. This indemnification will include any and all losses, liabilities, damages, demands, claims, suits, actions, judgments, or causes of action, assessments, costs and expenses, including, without limitation, interest, penalties, reasonable attorneys’ fees, and any and all reasonable costs and expenses incurred in investigating, preparing or defending against any litigation, commenced or threatened, any civil, criminal, administrative or arbitration action, or any claim whatsoever, and any and all amounts paid in settlement of any claim or litigation asserted against, resulting, imposed upon, or incurred or suffered by you, directly or indirectly, as a result of or arising from the Engaged Capital Group Solicitation and any related transactions (each, a “Loss”).

In the event of a claim against you pursuant to the prior paragraph or the occurrence of a Loss, you shall give the Engaged Capital Group prompt written notice of such claim or Loss (provided that failure to promptly notify the Engaged Capital Group shall not relieve us from any liability which we may have on account of this Agreement, except to the extent we shall have been materially prejudiced by such failure). Upon receipt of such written notice, the Engaged Capital Group will provide you with counsel to represent you. Such counsel shall be reasonably acceptable to you. In addition, you will be reimbursed promptly for all Losses suffered by you and as incurred as provided herein. The Engaged Capital Group may not enter into any settlement of loss or claim without your consent unless such settlement includes a release of you from any and all liability in respect of such claim.

You hereby agree to keep confidential and not disclose to any party, without the consent of the Engaged Capital Group, any confidential, proprietary or non-public information (collectively, “Information”) of the Engaged Capital Group, its affiliates or any members of any group formed by the Engaged Capital Group pursuant to Rule 13d-1(k)(1)(iii) under the Securities Exchange Act of 1934, as amended (“Schedule 13D Group”) which you have heretofore obtained or may obtain in connection with your service as a nominee hereunder. Notwithstanding the foregoing, Information shall not include any information that is publicly disclosed by the Engaged Capital Group, its affiliates or any members of any Schedule 13D Group or any information that you can demonstrate is now, or hereafter becomes, through no act or failure to act on your part, otherwise generally known to the public.

Notwithstanding the foregoing, if you are required by applicable law, rule, regulation or legal process to disclose any Information you may do so provided that you first promptly notify the Engaged Capital Group so that the Engaged Capital Group or any member thereof may seek a protective order or other appropriate remedy or, in the Engaged Capital Group’s sole discretion, waive compliance with the terms of this Agreement. In the event that no such protective order or other remedy is obtained or the Engaged Capital Group does not waive compliance with the terms of this Agreement, you may consult with counsel at the cost of the Engaged Capital Group and you may furnish only that portion of the Information which you are advised by counsel is legally required to be so disclosed and you will request that the party(ies) receiving such Information maintain it as confidential.

All Information, all copies thereof, and any studies, notes, records, analysis, compilations or other documents prepared by you containing such Information, shall be and remain the property of the Engaged Capital Group and, upon the request of a representative of the Engaged Capital Group, all such Information shall be returned or, at the Engaged Capital Group’s option, destroyed by you, with such destruction confirmed by you to the Engaged Capital Group in writing.

This Agreement shall be governed by the laws of the State of New York, without regard to the principles of the conflicts of laws thereof. 

* * *

If you agree to the foregoing terms, please sign below to indicate your acceptance.

Very truly yours,

ENGAGED CAPITAL FLAGSHIP MASTER FUND, LP
By:	Engaged Capital, LLC, its General Partner
By:
Name:	Glenn W. Welling
Title:	Founder and Chief Investment Officer

ACCEPTED AND AGREED:

__________________________

EX-99.3

Exhibit 99.3

POWER OF ATTORNEY

Know all by these presents, that the undersigned hereby constitutes and appoints Glenn W. Welling the undersigned’s true and lawful attorney-in-fact to take any and all action in connection with (i) the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of Aratana Therapeutics, Inc., a Delaware corporation (the “Company”), directly or indirectly beneficially owned by Engaged Capital Flagship Master Fund, LP or any of its affiliates (collectively, the “Group”), and (ii) any proxy solicitation of the Group to elect the Group’s slate of director nominees to the board of directors of the Company at the 2018 annual meeting of stockholders of the Company (the “Solicitation”). Such action shall include, but not be limited to:

1.executing for and on behalf of the undersigned any Schedule 13D, and amendments thereto, filed by the Group that are required to be filed under Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the rules thereunder in connection with the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of the Company or the Solicitation;

2.if applicable, executing for and on behalf of the undersigned all Forms 3, 4 and 5 required to be filed under Section 16(a) of the Exchange Act in connection with the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of the Company or the Solicitation;

3.executing for and on behalf of the undersigned all Joint Filing and Solicitation Agreements or similar documents pursuant to which the undersigned shall agree to be a member of the Group;

4.performing any and all acts for and on behalf of the undersigned that may be necessary or desirable to complete and execute any such document, complete and execute any amendment or amendments thereto, and timely file such form with the United States Securities and Exchange Commission and any stock exchange or similar authority; and

5.taking any other action of any type whatsoever in connection with the Solicitation, including entering into any settlement agreement, that in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by, the undersigned, it being understood that the documents executed by such attorney-in-fact on behalf of the undersigned pursuant to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve in such attorney-in-fact’s discretion.

The undersigned hereby grants to such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact’s substitutes, shall lawfully do or cause to be done by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorney-in-fact, in serving in such capacity at the request of the undersigned, is not assuming any of the undersigned's responsibilities to comply with Section 13(d), Section 16 or Section 14 of the Exchange Act.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer a member of the Group unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 20^th day of March 2018.

/s/ Craig A. Barbarosh

CRAIG A. BARBAROSH

POWER OF ATTORNEY

Know all by these presents, that the undersigned hereby constitutes and appoints Glenn W. Welling the undersigned’s true and lawful attorney-in-fact to take any and all action in connection with (i) the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of Aratana Therapeutics, Inc., a Delaware corporation (the “Company”), directly or indirectly beneficially owned by Engaged Capital Flagship Master Fund, LP or any of its affiliates (collectively, the “Group”), and (ii) any proxy solicitation of the Group to elect the Group’s slate of director nominees to the board of directors of the Company at the 2018 annual meeting of stockholders of the Company (the “Solicitation”). Such action shall include, but not be limited to:

1.executing for and on behalf of the undersigned any Schedule 13D, and amendments thereto, filed by the Group that are required to be filed under Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the rules thereunder in connection with the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of the Company or the Solicitation;

2.if applicable, executing for and on behalf of the undersigned all Forms 3, 4 and 5 required to be filed under Section 16(a) of the Exchange Act in connection with the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of the Company or the Solicitation;

3.executing for and on behalf of the undersigned all Joint Filing and Solicitation Agreements or similar documents pursuant to which the undersigned shall agree to be a member of the Group;

4.performing any and all acts for and on behalf of the undersigned that may be necessary or desirable to complete and execute any such document, complete and execute any amendment or amendments thereto, and timely file such form with the United States Securities and Exchange Commission and any stock exchange or similar authority; and

5.taking any other action of any type whatsoever in connection with the Solicitation, including entering into any settlement agreement, that in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by, the undersigned, it being understood that the documents executed by such attorney-in-fact on behalf of the undersigned pursuant to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve in such attorney-in-fact’s discretion.

The undersigned hereby grants to such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact’s substitutes, shall lawfully do or cause to be done by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorney-in-fact, in serving in such capacity at the request of the undersigned, is not assuming any of the undersigned's responsibilities to comply with Section 13(d), Section 16 or Section 14 of the Exchange Act.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer a member of the Group unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 20^th day of March 2018.

/s/ Eric J. Ende

ERIC J. ENDE

POWER OF ATTORNEY

Know all by these presents, that the undersigned hereby constitutes and appoints Glenn W. Welling the undersigned’s true and lawful attorney-in-fact to take any and all action in connection with (i) the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of Aratana Therapeutics, Inc., a Delaware corporation (the “Company”), directly or indirectly beneficially owned by Engaged Capital Flagship Master Fund, LP or any of its affiliates (collectively, the “Group”), and (ii) any proxy solicitation of the Group to elect the Group’s slate of director nominees to the board of directors of the Company at the 2018 annual meeting of stockholders of the Company (the “Solicitation”). Such action shall include, but not be limited to:

1.executing for and on behalf of the undersigned any Schedule 13D, and amendments thereto, filed by the Group that are required to be filed under Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the rules thereunder in connection with the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of the Company or the Solicitation;

2.if applicable, executing for and on behalf of the undersigned all Forms 3, 4 and 5 required to be filed under Section 16(a) of the Exchange Act in connection with the undersigned’s beneficial ownership of, or participation in a group with respect to, securities of the Company or the Solicitation;

3.executing for and on behalf of the undersigned all Joint Filing and Solicitation Agreements or similar documents pursuant to which the undersigned shall agree to be a member of the Group;

4.performing any and all acts for and on behalf of the undersigned that may be necessary or desirable to complete and execute any such document, complete and execute any amendment or amendments thereto, and timely file such form with the United States Securities and Exchange Commission and any stock exchange or similar authority; and

5.taking any other action of any type whatsoever in connection with the Solicitation, including entering into any settlement agreement, that in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by, the undersigned, it being understood that the documents executed by such attorney-in-fact on behalf of the undersigned pursuant to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve in such attorney-in-fact’s discretion.

The undersigned hereby grants to such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact’s substitutes, shall lawfully do or cause to be done by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorney-in-fact, in serving in such capacity at the request of the undersigned, is not assuming any of the undersigned's responsibilities to comply with Section 13(d), Section 16 or Section 14 of the Exchange Act.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer a member of the Group unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 20^th day of March 2018.

/s/ Lowell W. Robinson

LOWELL W. ROBINSON