Loading URDF file into gazebo

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I recently download a URDF file, the link is https://github.com/UMich-BipedLab/Cas... , I would like to simulate this model inside the gazebo and apply the PID control on the joints, so the first step I done is to using roslaunch on the URDF file to simulate the model on the gazebo, the launch file shown below:

<launch>

  <!-- these are the arguments you can pass this launch file, for example paused:=true -->
  <arg name="paused" default="false"/>
  <arg name="use_sim_time" default="true"/>
  <arg name="gui" default="true"/>
  <arg name="headless" default="false"/>
  <arg name="debug" default="false"/>

  <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find cassie_gazebo)/worlds/cassie.world"/>
    <arg name="debug" value="$(arg debug)" />
    <arg name="gui" value="$(arg gui)" />
    <arg name="paused" value="$(arg paused)"/>
    <arg name="use_sim_time" value="$(arg use_sim_time)"/>
    <arg name="headless" value="$(arg headless)"/>
  </include>

  <!-- Load the URDF into the ROS Parameter Server -->
<param name="cassie_description" textfile="$(find cassie_description)/urdf/cassie.urdf"/>

  <!-- Run a python script to the send a service call to gazebo_ros to spawn a URDF robot -->
<node name="mybot_spawn" pkg="gazebo_ros" type="spawn_model" output="screen"
args="-urdf -param cassie_description -model cassie" />


  <!-- ros_control rrbot launch file -->
  <!--include file="$(find rrbot_control)/launch/rrbot_control.launch" /-->

</launch>

The launching is successful, the model appear on the left control panel, however there is only one link which is pelvis appeared on the list, other links does not show on the list.

I also use the following command to verify if the launch file is wrong, this work perfectly fine for other model, and the same problem appear with the following command:

rosrun gazebo_ros spawn_model -file `rospack find cassie_description`/urdf/cassie.urdf -urdf -z 1 -model cassie

I would be really appreciated for anyone who could solve this problem.