13D Filing: Engaged Capital and Aratana Therapeutics Inc. (PETX)

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).

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

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.

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.

(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.

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.

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.

(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.

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.

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.

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.

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

SCHEDULE A

Directors and Officers of Engaged
Capital Flagship Fund, Ltd.

*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.

SCHEDULE B

Transactions in Securities of
the Issuer During the Past 60 Days

Engaged
Capital Flagship Master Fund, LP

Engaged
Capital, LLC

(Through
the Engaged Capital Account)